0000950170-24-034692 | 10-K | XBRL Viewer

Income Taxes

12 Months Ended

Dec. 31, 2023

12. Income Taxes

The Company recorded a current state tax provision of zero related to state minimum taxes for each of the years ended December 31, 2023 and 2022, which is recorded in general and administrative expenses in the accompanying statement of operations and comprehensive loss.

A reconciliation of the Company’s effective tax rate and federal statutory tax rate is summarized as follows (in thousands):


	Years Ended December 31,
	2023			2022
Income tax benefit at statutory rates	$	(14,531	)	$	(18,501	)
Permanent items		35			5
Valuation allowance		14,957			16,920
Stock-based compensation		1,367			1,307
Research and development tax credits		(1,828	)		269
Provision for income taxes	$	—		$	—

Deferred income taxes reflect the net tax effects of loss and credit carryforwards and temporary differences between the carrying amounts of assets and liabilities for financial reporting purposes and the amounts used for income tax purposes. Significant components of our deferred tax assets for federal and state income taxes are as follows (in thousands):


	December 31,
	2023			2022
Deferred tax assets:
Net operating loss carryforward	$	47,331		$	42,564
Research tax credits		9,465			6,928
Capitalized research and development expenses		21,848			13,250
Lease liability		5,736			6,600
Stock-based compensation		2,645			1,953
Reserves and accruals		2,493			3,787
Intangible assets		145			168
Total deferred tax assets		89,663			75,250
Less valuation allowance		(83,680	)		(68,192	)
Net deferred tax assets		5,983			7,058
Deferred tax liabilities:
Right-of-use assets		(5,424	)		(6,443	)
Property and equipment		(461	)		(472	)
Prepaid assets		(98	)		(143	)
Total deferred tax assets		(5,983	)		(7,058	)
Net deferred tax assets	$	—		$	—

A valuation allowance is required to be established when it is more likely than not that all or a portion of a deferred tax asset will not be realized. Realization of deferred tax assets is dependent upon future earnings, the timing and amount of which are uncertain. A full review of all positive and negative evidence needs to be considered. The Company has established a full valuation allowance against the net deferred tax assets as of December 31, 2023 and 2022 due to historical losses and uncertainty surrounding the use of such assets. The valuation allowance increased by $15.5 million between December 31, 2023 and December 31, 2022 primarily due to the generation of operating losses.

As of December 31, 2023, the Company has net operating loss carryforwards for federal and state income tax purposes of $205.7 million and $278.5 million, respectively. The federal net operating loss carryforwards generated prior to 2018 and state net operating loss carryforwards, if not utilized, will expire beginning in 2035. Federal net operating losses aggregating $201.3 million are not subject to expiration.

The Company has research credit carryforwards for federal and state income tax purposes of approximately $9.4 million and $5.6 million, respectively, as of December 31, 2023. The federal credits begin to expire in 2038 and the state credits can be carried forward indefinitely.

Utilization of some of the federal and state net operating loss and credit carryforwards may be subject to annual limitations due to the change in ownership provisions of the Internal Revenue Code of 1986 and similar state provisions. The annual limitation may result in the expiration of net operating losses and credits before utilization. The Company has performed a Section 382 study as of September 30, 2023 and expects approximately $2.8 million of federal research and development tax credits and $51.0 million of California net operating losses to expire unused due to Section 382 limitations.

The Company files tax returns in the United States, California and various states. The Company is not currently under examination in any of these jurisdictions and all of the Company’s tax years remain effectively open to examination due to net operating loss carryforwards.

The Company recognizes a tax benefit from uncertain tax positions when it is more likely than not that the position will be sustained upon examination, including resolutions of any related appeals or litigation processes, based on the technical merits. Due to the existence of the full valuation allowance, future changes in unrecognized tax benefits will not impact the Company’s effective tax rate. The Company does not foresee material changes to its liability for uncertain tax benefits within the next 12 months.

The following table summarizes the activity in the Company’s gross unrecognized tax benefits (in thousands):


	Years Ended December 31,
	2023			2022
Balance at beginning of period	$	13,819		$	12,659
Decrease related to prior year positions		(375	)		(5,054	)
Increase related to current year positions		5,304			6,214
Balance at end of period	$	18,748		$	13,819

During the years ended December 31, 2023 and 2022, no interest or penalties were required to be recognized relating for unrecognized tax benefits. In the event the Company should need to recognize interest and penalties related to unrecognized income tax liabilities, this amount will be recorded as an accrued liability and an increase to income tax expense.

On June 29, 2020, California Governor Newsom signed to law the state’s budget package which included Assembly Bill 85 (AB 85). AB 85 contained two major tax changes: (1) it suspends the usage of net operating losses (NOLs) for certain taxpayers; and (2) it limits certain business tax credits for tax years 2020, 2021, and 2022. Senate Bill 113 (SB 113), which Gov. Newsom signed into law Feb. 9, 2022, contains important California tax law changes, including reinstatement of 2022 business tax credits and net operating loss (NOL) deductions limited by AB 85. The Company is in a taxable loss position in 2023 and 2022 and thus the bill has no impact on the financial statements.

- Definition

The entire disclosure for income taxes. Disclosures may include net deferred tax liability or asset recognized in an enterprise's statement of financial position, net change during the year in the total valuation allowance, approximate tax effect of each type of temporary difference and carryforward that gives rise to a significant portion of deferred tax liabilities and deferred tax assets, utilization of a tax carryback, and tax uncertainties information.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480990/946-20-50-13

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 235
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-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(h)(2))
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-URI https://asc.fasb.org//1943274/2147480678/235-10-S99-1

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-Name Accounting Standards Codification
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-URI https://asc.fasb.org//740/tableOfContent

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
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-Name Accounting Standards Codification
-Section 50
-Paragraph 14
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482685/740-10-50-14

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
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-Name Accounting Standards Codification
-Section 50
-Paragraph 21
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482685/740-10-50-21

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 270
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482526/740-270-50-1

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 17
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482685/740-10-50-17

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
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-Section S99
-Paragraph 1
-Subparagraph (SAB TOPIC 6.I.5.Q1)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479360/740-10-S99-1

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 2
-Subparagraph (SAB Topic 11.C)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479360/740-10-S99-2

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 30
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482603/740-30-50-2

+ Details

Fair Value Measurements and Fair Value of Financial Instruments - Schedule of Gross Unrealized Losses and Fair Value of Company's Available-for-Sale Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Debt Securities, Available-for-Sale, Unrealized Loss Position [Line Items]
Less Than 12 Months Estimated Fair Value	$ 71,178	$ 24,880
More Than 12 Months Estimated Fair Value	46,614	102,536
Total Estimated Fair Value	117,792	127,416
Less Than 12 Months Unrealized Losses	(12)	(65)
More Than 12 Months Unrealized Losses	(41)	(867)
Total Unrealized Losses	(53)	(932)
Asset Backed Securities
Debt Securities, Available-for-Sale, Unrealized Loss Position [Line Items]
Less Than 12 Months Estimated Fair Value	4,686	3,180
More Than 12 Months Estimated Fair Value	12,656	9,485
Total Estimated Fair Value	17,342	12,665
Less Than 12 Months Unrealized Losses		(5)
More Than 12 Months Unrealized Losses	(15)	(94)
Total Unrealized Losses	(15)	(99)
U.S. Treasury Securities
Debt Securities, Available-for-Sale, Unrealized Loss Position [Line Items]
Less Than 12 Months Estimated Fair Value	34,104	14,723
More Than 12 Months Estimated Fair Value	9,843	39,508
Total Estimated Fair Value	43,947	54,231
Less Than 12 Months Unrealized Losses		(28)
More Than 12 Months Unrealized Losses	(11)	(489)
Total Unrealized Losses	(11)	(517)
Other Government Agency Securities
Debt Securities, Available-for-Sale, Unrealized Loss Position [Line Items]
Less Than 12 Months Estimated Fair Value	2,477
More Than 12 Months Estimated Fair Value	10,879	4,980
Total Estimated Fair Value	13,356	4,980
Less Than 12 Months Unrealized Losses	(1)
More Than 12 Months Unrealized Losses	(14)	(29)
Total Unrealized Losses	(15)	(29)
Commercial Paper
Debt Securities, Available-for-Sale, Unrealized Loss Position [Line Items]
Less Than 12 Months Estimated Fair Value	20,345
Total Estimated Fair Value	20,345
Less Than 12 Months Unrealized Losses	(10)
Total Unrealized Losses	(10)
Corporate Debt Securities
Debt Securities, Available-for-Sale, Unrealized Loss Position [Line Items]
Less Than 12 Months Estimated Fair Value	9,566	6,977
More Than 12 Months Estimated Fair Value	13,236	48,563
Total Estimated Fair Value	22,802	55,540
Less Than 12 Months Unrealized Losses	(1)	(32)
More Than 12 Months Unrealized Losses	(1)	(255)
Total Unrealized Losses	$ (2)	$ (287)

BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Current assets:
Cash and cash equivalents	$ 10,810	$ 9,244
Short-term investments	91,379	159,644
Prepaid expenses and other current assets	3,519	3,858
Total current assets	105,708	172,746
Property and equipment, net	4,957	6,453
Operating lease right-of-use assets	19,120	22,072
Restricted cash	1,765	1,565
Long-term investments	26,413	23,943
Other assets	1,821	1,028
Total assets	159,784	227,807
Current liabilities:
Accounts payable	2,987	3,594
Accrued expenses and other current liabilities	12,486	15,140
Deferred revenue	2,201	1,993
Operating lease liabilities	2,782	2,391
Total current liabilities	20,456	23,118
Operating lease liabilities, net of current portion	17,437	20,220
Deferred revenue, non-current	9,107	12,921
Other long-term liabilities	43	42
Total liabilities	47,043	56,301
Commitments and contingencies (Note 7)
Stockholders' equity:
Preferred stock, $0.00001 par value, authorized shares - 10,000,000 shares authorized at December 31, 2023 and 2022; zero shares issued and outstanding at December 31, 2023 and 2022	0	0
Common stock, $0.00001 par value; 200,000,000 shares authorized at December 31, 2023 and 2022; 38,114,606 and 37,797,902 shares issued and outstanding at December 31, 2023 and 2022, respectively	1	0
Additional paid-in capital	476,988	467,513
Accumulated other comprehensive gain (loss)	37	(919)
Accumulated deficit	(364,285)	(295,088)
Total stockholders' equity	112,741	171,506
Total liabilities, convertible preferred stock, and stockholders' equity	$ 159,784	$ 227,807

STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
CASH FLOWS FROM OPERATING ACTIVITIES:
Net loss	$ (69,197)	$ (88,098)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	1,854	1,666
Stock-based compensation expense	9,223	9,576
Accretion of premium/discount on short-term investments	(4,493)	184
Non-cash lease expense	2,952	3,225
Changes in operating assets and liabilities:
Prepaid expenses and other assets	(454)	(903)
Accounts payable and accrued expenses	(3,413)	2,768
Operating lease liabilities	(2,392)	(2,596)
Deferred revenue	(3,606)	(2,162)
Other long-term liabilities	1	(164)
Net cash used in operating activities	(69,525)	(76,504)
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchase of property and equipment	(206)	(1,953)
Purchases of marketable securities	(164,988)	(180,704)
Maturities of marketable securities	236,232	240,519
Net cash provided by (used in) investing activities	71,038	57,862
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from issuance of common stock	253	503
Net cash provided by financing activities	253	503
NET INCREASE (DECREASE) IN CASH	1,766	(18,139)
Cash, cash equivalents and restricted cash at beginning of year	10,809	28,948
Cash, cash equivalents and restricted cash at end of period	12,575	10,809
Reconciliation of cash, cash equivalents and restricted cash:
Cash and cash equivalents	10,810	9,244
Restricted cash	1,765	1,565
Total cash, cash equivalents and restricted cash	12,575	10,809
Supplemental schedule of non-cash investing and financing activities:
Purchases of property and equipment included in accounts payable and accrued liabilities	152	8
Deferred offering costs in accounts payable and accrued liabilities	$ 102	102
Right of use assets obtained in exchange for operating lease obligations		$ 852

Stock-Based Compensation - Summary of Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Share-Based Payment Arrangement [Abstract]
Options Outstanding, Beginning balance	7,225,635
Options Outstanding, Granted	4,095,780
Options Outstanding, Exercised	(4,501)
Options Outstanding, Canceled/forfeited	(610,373)
Options Outstanding, Ending balance	10,706,541	7,225,635
Options Outstanding, Exercisable at December 31, 2023	6,189,313
Options Outstanding, Vested or expected to vest at December 31, 2023	10,706,541
Weighted-average Exercise Price, Beginning balance	$ 5.55
Weighted-average Exercise Price, Granted	1.46
Weighted-average Exercise Price, Exercised	1.39
Weighted-average Exercise Price, Canceled/forfeited	3.32
Weighted-average Exercise Price, Ending balance	4.12	$ 5.55
Weighted-average Exercise Price, Exercisable at December 31, 2023	4.82
Weighted-average Exercise Price, Vested or expected to vest at December 31, 2023	$ 4.12
Weighted-average Remaining Contractual Term (in years), Outstanding	7 years 8 months 12 days	8 years
Weighted-average Remaining Contractual Term (in years), Exercisable at December 31, 2023	7 years
Weighted-average Remaining Contractual Term (in years), Vested or expected to vest at December 31, 2023	7 years 8 months 12 days
Weighted-average Grant Date Fair Value, Granted	$ 1.11
Aggregate Intrinsic Value, Outstanding	$ 12
Aggregate Intrinsic Value, Vested or expected to vest at December 31, 2023	$ 12

Fair Value Measurements and Fair Value of Financial Instruments

12 Months Ended

Dec. 31, 2023

Fair Value Disclosures [Abstract]

Fair Value Measurements and Fair Value of Financial Instruments

3. Fair Value Measurements and Fair Value of Financial Instruments

The authoritative guidance on fair value measurements establishes a three-tier fair value hierarchy for disclosure of fair value measurements as follows:

Level 1—Quoted prices in active markets for identical assets or liabilities.

Level 2—Observable inputs other than Level 1 prices, such as quoted prices for similar assets or liabilities, quoted prices in markets that are not active or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities.

Level 3—Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities.

Assets and liabilities measured at fair value are classified in their entirety based on the lowest level of input that is significant to the fair value measurement. The Company’s assessment of the significance of a particular input to the fair value measurement in its entirety requires management to make judgments and consider factors specific to the asset or liability.

During the years ended December 31, 2023 and 2022, financial assets measured on a recurring basis consist of cash invested in money market accounts, short-term investments, and long-term investments. The fair value of short-term and long-term investments is based upon market prices quoted on the last day of the fiscal period or other observable market inputs. The Company obtains pricing information from its investment manager and generally determines the fair value of investment securities using standard observable inputs, including reported trades, broker/dealer quotes, bids and/or offers. Financial liabilities measured at fair value on a recurring basis include the convertible preferred stock purchase right liability described below.

There were no transfers within the hierarchy during the years ended December 31, 2023 and 2022.

Marketable securities, all of which are classified as available-for-sale securities, consisted of the following at December 31, 2023 and 2022 (in thousands):


	December 31, 2023
	Amortized		Unrealized		Unrealized			Estimated
	Cost		Gains		Losses			Fair Value
Asset backed securities	$	17,347	$	10	$	(15	)	$	17,342
U.S. treasury securities		43,924		34		(11	)		43,947
Other government agency securities		13,371		—		(15	)		13,356
Commercial paper		20,351		4		(10	)		20,345
Corporate debt securities		22,763		41		(2	)		22,802
Total	$	117,756	$	89	$	(53	)	$	117,792


	December 31, 2022
	Amortized		Unrealized		Unrealized			Estimated
	Cost		Gains		Losses			Fair Value
Asset backed securities	$	12,754	$	11	$	(99	)	$	12,666
U.S. treasury securities		54,747		1		(517	)		54,231
Other government agency securities		5,009		—		(29	)		4,980
Commercial paper		56,170		—		—			56,170
Corporate debt securities		55,827		—		(287	)		55,540
Total	$	184,507	$	12	$	(932	)	$	183,587

As of December 31, 2023, the unrealized losses for available-for-sale investments were primarily due to changes in interest rates and not due to increased credit risks associated with specific securities. The contractual terms of those investments do not permit the issuer to settle the securities at a price less than the amortized cost bases of the investments. The Company does not currently intend to sell the investments and it is not more likely than not that the Company will be required to sell the investments before recovery of their amortized cost bases, which may be at the time of maturity. As of December 31, 2023, no allowance for credit losses was recorded and the Company did not recognize any impairment losses related to investments.

The tables below show the gross unrealized losses and fair value of the Company's available-for-sale securities with unrealized losses that are not deemed to have credit losses (in thousands), aggregated by investment category and length of time that individual securities have been in a continuous unrealized loss position at December 31, 2023 and 2022, respectively:


	December 31, 2023
	Less Than 12 Months					More Than 12 Months					Total
	Estimated		Unrealized			Estimated		Unrealized			Estimated		Unrealized
	Fair Value		Losses			Fair Value		Losses			Fair Value		Losses
Asset-backed securities	$	4,686	$	—		$	12,656	$	(15	)	$	17,342	$	(15	)
U.S. treasury securities		34,104		—			9,843		(11	)		43,947		(11	)
Other government agency securities		2,477		(1	)		10,879		(14	)		13,356		(15	)
Commercial paper		20,345		(10	)		—		—			20,345		(10	)
Corporate debt securities		9,566		(1	)		13,236		(1	)		22,802		(2	)
Total	$	71,178	$	(12	)	$	46,614	$	(41	)	$	117,792	$	(53	)


	December 31, 2022
	Less Than 12 Months					More Than 12 Months					Total
	Estimated		Unrealized			Estimated		Unrealized			Estimated		Unrealized
	Fair Value		Losses			Fair Value		Losses			Fair Value		Losses
Asset-backed securities	$	3,180	$	(5	)	$	9,485	$	(94	)	$	12,665	$	(99	)
U.S. treasury securities		14,723		(28	)		39,508		(489	)		54,231		(517	)
Other government agency securities		—		—			4,980		(29	)		4,980		(29	)
Corporate debt securities		6,977		(32	)		48,563		(255	)		55,540		(287	)
Total	$	24,880	$	(65	)	$	102,536	$	(867	)	$	127,416	$	(932	)

Accrued interest receivable on available-for-sale securities were $0.3 million and $0.5 million at December 31, 2023 and 2022, respectively, which are recorded in cash and cash equivalents line item on the Company's balance sheets. The Company has not written off any accrued interest receivables for the years ended December 31, 2023 and 2022.

At December 31, 2023 and 2022, the fair values of the Company’s assets and liabilities, which are measured at fair value on a recurring basis, were determined using the following inputs (in thousands):


	December 31, 2023
	Total		(Level 1)		(Level 2)		(Level 3)
Money market funds	$	8,641	$	8,641	$	—	$	—
Asset backed securities		17,342		—		17,342		—
U.S. treasury securities		43,947		33,001		10,946		—
Other government agency securities		13,356		—		13,356		—
Commercial paper		20,345		—		20,345		—
Corporate debt securities		22,802		—		22,802		—
Total	$	126,433	$	41,642	$	84,791	$	—


	December 31, 2022
	Total		(Level 1)		(Level 2)		(Level 3)
Money market funds	$	6,885	$	6,885	$	—	$	—
Asset backed securities		12,666		—		12,666		—
U.S. treasury securities		54,231		54,231		—		—
Other government agency securities		4,980		—		4,980		—
Commercial paper		56,170		—		56,170		—
Corporate debt securities		55,540		—		55,540		—
Total	$	190,472	$	61,116	$	129,356	$	—

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References + Details

Stock-Based Compensation - Summary of Restricted Stock Awards Activity (Details) - Restricted Stock Units - $ / shares	1 Months Ended	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2023
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
RSU Outstanding, Beginning balance		121,867
RSU Outstanding, Granted	336,000
RSU Outstanding, Vested		(58,034)
RSU Outstanding, Canceled/forfeited		(11,300)
RSU Outstanding, Ending balance		52,533
Weighted-average Grant Date Fair Value, Beginning balance		$ 4.51
Weighted-average Grant Date Fair Value, Granted	$ 4.51
Weighted-average Grant Date Fair Value, Vested		4.51
Weighted-average Grant Date Fair Value, Canceled/forfeited		4.51
Weighted-average Grant Date Fair Value, Ending balance		$ 4.51

Balance Sheet Components

12 Months Ended

Dec. 31, 2023

Balance Sheet Related Disclosures [Abstract]

Balance Sheet Components

5. Balance Sheet Components

Property and Equipment, net

Property and equipment, net, consist of the following (in thousands):


	December 31,
	2023			2022
Laboratory equipment	$	10,038		$	9,738
Office equipment		386			358
Leasehold improvements		285			272
Total property and equipment		10,709			10,368
Less accumulated depreciation and amortization		(5,752	)		(3,915	)
Total	$	4,957		$	6,453

Depreciation expense related to property and equipment was $1.9 million and $1.7 million for the years ended December 31, 2023 and 2022, respectively.

Prepaids and Other Current Assets and Other Non-current Assets

Prepaids and Other Current Assets and Other Non-current Assets, consist of the following (in thousands):


	December 31,
	2023		2022
Prepaids and other current assets:
Cloud computing arrangement implementation costs	$	178	$	—
Other prepaids and other current assets		3,341		3,858
Prepaids and other current assets		3,519		3,858
Other non-current assets
Cloud computing arrangement implementation costs - non-current		371		—
Other non-current assets		1,450		1,028
Other non-current assets		1,821		1,028

As of December 31, 2023 and 2022, cloud computing arrangement implementation costs consisted of deferred costs of $0.6 million and zero, respectively, and associated accumulated amortization of $30,000 and zero, respectively.

Accrued Expenses and Other Current Liabilities

Accrued expenses and other current liabilities consist of the following (in thousands):


	December 31,
	2023		2022
Accrued research and development	$	6,092	$	9,373
Accrued compensation		5,820		4,804
Accrued other		574		963
Total	$	12,486	$	15,140

Stock-Based Compensation - Additional Information (Details) - USD ($)		1 Months Ended			12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Jan. 31, 2021	Sep. 30, 2020	Dec. 31, 2023	Dec. 31, 2022	Jan. 01, 2023	Jan. 01, 2022
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock option agreement					The 2021 Plan authorized issuance of up to 8,075,000 shares of common stock and stock awards granted under the 2021 Plan vest at the rate specified in the stock option agreement and shall have terms no more than ten years from the date of grant. The terms and conditions governing the stock awards under the 2021 Plan are at the sole discretion of the board of directors.
Common stock reserved for issuance					11,971,397
Stock-based compensation expense					$ 9,223,000	$ 9,576,000
Intrinsic value of options exercised					2,000	45,000
Fair value of options vested					2,100,000	7,900,000
Unrecognized stock-based compensation related to unvested stock options					9,700,000
Performance and Service Based Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares issued				526,018
Vesting period				48 months
Stock-based compensation expense					$ 100,000	$ 300,000
Weighted-average grant date fair value of awards					$ 3.24
Employee Stock Option
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock reserved for issuance					10,706,541
Weighted-average period					1 year 9 months 18 days
Restricted Stock Units
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock reserved for issuance					52,533
Shares issued		336,000
Vesting period		3 years
Weighted-average grant date fair value of awards		$ 4.51
Unrecognized stock-based compensation expense relating to unvested restricted stock awards					$ 200,000
Weighted-average period					1 year
Aggregate intrinsic value					$ 59,000
Common Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Issuance of common stock under employee stock purchase plan, Shares					254,169	258,488
2021 Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock reserved for issuance					638,430		1,889,895	1,869,984
2021 Plan \| Common Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares authorized for issuance			8,075,000
Percentage equal to number of shares of common stock outstanding	5.00%
2021 Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Percentage equal to number of shares of common stock outstanding	1.00%
Common stock reserved for issuance					573,893		377,979
Purchase price of stock as percentage of fair market value			85.00%
2021 Employee Stock Purchase Plan \| Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock reserved for issuance	840,000					840,000
2021 Employee Stock Purchase Plan \| Common Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares authorized for issuance			420,000
Plan offering period			2 years
Issuance of common stock under employee stock purchase plan, Shares					254,169
2021 Employee Stock Purchase Plan \| Common Stock \| Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Percentage of eligible compensation for payroll deductions to purchase stock			15.00%

STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit
Beginning Balance at Dec. 31, 2021	$ 250,119		$ 457,430	$ (321)	$ (206,990)
Beginning Balance, Shares at Dec. 31, 2021		37,399,694
Issuance of common stock upon vesting of restricted stock units		80,533
Issuance of common stock under employee stock purchase plan	368		368
Issuance of common stock under employee stock purchase plan, Shares		258,488
Issuance of common stock upon exercise of stock options	135		135
Issuance of common stock upon exercise of stock options, Shares		59,187
Vesting of early exercised options	4		4
Stock-based compensation	9,576		9,576
Unrealized loss on available-for-sale investments	(598)			(598)
Net loss	(88,098)				(88,098)
Ending Balance at Dec. 31, 2022	171,506		467,513	(919)	(295,088)
Ending Balance, Shares at Dec. 31, 2022		37,797,902
Issuance of common stock upon vesting of restricted stock units		58,034
Issuance of common stock under employee stock purchase plan	247	$ 1	246
Issuance of common stock under employee stock purchase plan, Shares		254,169
Issuance of common stock upon exercise of stock options	$ 6		6
Issuance of common stock upon exercise of stock options, Shares	4,501	4,501
Stock-based compensation	$ 9,223		9,223
Unrealized loss on available-for-sale investments	956			956
Net loss	(69,197)				(69,197)
Ending Balance at Dec. 31, 2023	$ 112,741	$ 1	$ 476,988	$ 37	$ (364,285)
Ending Balance, Shares at Dec. 31, 2023		38,114,606

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2023

Income Tax Disclosure [Abstract]

Summary of Reconciliation of Effective Tax Rate and Federal Statutory Tax Rate

A reconciliation of the Company’s effective tax rate and federal statutory tax rate is summarized as follows (in thousands):


	Years Ended December 31,
	2023			2022
Income tax benefit at statutory rates	$	(14,531	)	$	(18,501	)
Permanent items		35			5
Valuation allowance		14,957			16,920
Stock-based compensation		1,367			1,307
Research and development tax credits		(1,828	)		269
Provision for income taxes	$	—		$	—

Summary of Significant Components of Deferred Tax Assets and Liabilities for Federal and State Income Taxes

Significant components of our deferred tax assets for federal and state income taxes are as follows (in thousands):


	December 31,
	2023			2022
Deferred tax assets:
Net operating loss carryforward	$	47,331		$	42,564
Research tax credits		9,465			6,928
Capitalized research and development expenses		21,848			13,250
Lease liability		5,736			6,600
Stock-based compensation		2,645			1,953
Reserves and accruals		2,493			3,787
Intangible assets		145			168
Total deferred tax assets		89,663			75,250
Less valuation allowance		(83,680	)		(68,192	)
Net deferred tax assets		5,983			7,058
Deferred tax liabilities:
Right-of-use assets		(5,424	)		(6,443	)
Property and equipment		(461	)		(472	)
Prepaid assets		(98	)		(143	)
Total deferred tax assets		(5,983	)		(7,058	)
Net deferred tax assets	$	—		$	—

Summary of Gross Unrecognized Tax Benefits

The following table summarizes the activity in the Company’s gross unrecognized tax benefits (in thousands):


	Years Ended December 31,
	2023			2022
Balance at beginning of period	$	13,819		$	12,659
Decrease related to prior year positions		(375	)		(5,054	)
Increase related to current year positions		5,304			6,214
Balance at end of period	$	18,748		$	13,819

Summary of Significant Accounting Policies

12 Months Ended

Dec. 31, 2023

Accounting Policies [Abstract]

Summary of Significant Accounting Policies

2. Summary of Significant Accounting Policies

Basis of Presentation

The Company’s financial statements have been prepared in accordance with U.S. generally accepted accounting principles (“U.S. GAAP”). Certain reclassifications on the statement of cash flows have been made to prior period amounts to conform to current period presentation.

Risks and Uncertainties

The Company is subject to a number of risks similar to other early-stage biopharmaceutical companies, including, but not limited to, changes in any of the following areas that the Company believes could have a material adverse effect on its future financial position or results of operations: risks related to the successful discovery and development of its product candidates, ability to raise additional capital, development of new technological innovations by its competitors, delay or inability to obtain chemical or biological intermediates from such suppliers required for the synthesis of the Company’s product candidates, protection of intellectual property rights, litigation or claims against the Company based on intellectual property rights, and regulatory clearance and market acceptance of the Company’s products.

Global economic and business activities continue to face widespread macroeconomic uncertainties, including pandemics, labor shortages, inflation and monetary supply shifts, and potential disruptions from major geopolitical conflicts. The Company continues to actively monitor the impact of these macroeconomic factors on its financial condition, liquidity, operations, and workforce. The extent of the impact of these factors on the Company’s operational and financial performance, including its ability to execute its business strategies and initiatives in the expected time frame, will depend on future developments, which are uncertain and cannot be predicted; however, any continued or renewed disruption resulting from these factors could negatively impact the Company’s business.

The Company relies on single source manufacturers and suppliers for the supply of its product candidates. Disruption from these manufacturers or suppliers would have a negative impact on the Company’s business, financial position, and results of operations.

Liquidity

The Company has incurred net losses and negative cash flows from operations since our inception and anticipates to continue to incur net losses for the foreseeable future. As of December 31, 2023, the Company had cash and cash equivalents and marketable securities of $128.6 million and an accumulated deficit of $364.3 million. Based upon the Company's current operating plans, the Company believes that its existing cash, cash equivalents and marketable securities will be sufficient to fund its operations for at least the next 12 months following the issuance date of this Annual Report on Form 10-K. The Company will need to raise additional capital to continue the advancement of its programs. In the near term, the Company's primary uses of cash will be to fund the completion of key milestones for trastuzumab imbotolimod, formerly known as BDC-1001, and BDC-3042 and to fund its operations, including research and development activities and employee salaries. This includes significant costs relating to clinical trials and manufacture of the Company's product candidates. The Company's uses of cash in the long term will be similar as the Company advances its research and development activities and pays employee salaries. Most pharmaceutical products require larger clinical trials as development progresses, and the Company expects its funding requirements to grow with the advancement of its programs. The Company's long-term funding requirements will depend on many factors, which are uncertain but include its portfolio prioritization decisions and the success of its collaborations. In turn, the Company's ability to raise additional capital through equity or partnering will depend on the general economic environment in which it operates and its ability to achieve key milestones.

Use of Estimates

The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets, liabilities, and the disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of expenses during the reporting period. On an ongoing basis, the Company evaluates its estimates and assumptions, including those related to revenue recognition, stock-based compensation and accrued liabilities. Management bases its estimates on historical experience and on various other assumptions that are believed to be reasonable under the circumstances, the results of which form the basis for making judgments about the carrying values of assets and liabilities that are not readily apparent from other sources. Actual results may differ materially from those estimates.

Concentrations of Credit Risk

Financial instruments that potentially subject the Company to concentration of credit risk consist of cash, cash equivalents and marketable securities. At December 31, 2023 and 2022, most of the Company’s funds were invested with a registered investment manager and custodied at one financial institution, with operating cash kept at a separate financial institution, and account balances may at times exceed federally insured limits. Management believes that the Company is not subject to unusual or significant credit risk beyond the normal credit risk associated with commercial banking relationships.

Cash and Cash Equivalents

The Company considers all highly liquid investments purchased with an original maturity of three months or less to be cash equivalents. As of December 31, 2023 and 2022, cash and cash equivalents consisted primarily of bank deposits and money market funds which were unrestricted as to withdrawal or use.

Allowance for Credit Losses

For available-for-sale securities in an unrealized loss position, the Company first assesses whether it intends to sell, or if it is more likely than not that the Company will be required to sell, the security before recovery of its amortized cost basis. If either of the criteria regarding intent or requirement to sell is met, the security’s amortized cost basis is written down to fair value through earnings. For available-for-sale securities that do not meet the aforementioned criteria, the Company evaluates whether the decline in fair value has resulted from credit losses or other factors. In making this assessment, the Company considers the severity of the impairment, any changes in interest rates, market conditions, changes to the underlying credit ratings and forecasted recovery, among other factors. The credit-related portion of unrealized losses, and any subsequent improvements, are recorded in interest income through an allowance account. Any impairment that has not been recorded through an allowance for credit losses is included in other comprehensive income (loss) on the statements of operations and comprehensive loss.

The Company elected the practical expedient to exclude the applicable accrued interest from both the fair value and amortized costs basis of its available-for-sale securities for purposes of identifying and measuring an impairment. Accrued interest receivable on available-for-sale securities is recorded within cash and cash equivalents on the Company's balance sheets. The Company's accounting policy is to not measure an allowance for credit loss for accrued interest receivable and to write-off any uncollectible accrued interest receivable as a reversal of interest income in a timely manner, which the Company considers to be in the period in which it determines the accrued interest will not be collected by the Company

Marketable Securities

The Company classifies its marketable securities as available-for-sale and records such assets at estimated fair value in the balance sheets, with unrealized gains and non-credit related losses that are determined to be temporary, if any, reported as a component of other comprehensive income (loss) within the statements of operations and comprehensive loss and as a separate component of stockholders’ equity. The Company classifies marketable securities with remaining maturities greater than three months but less than one year as short-term investments, and those with remaining maturities greater than one year are classified as long-term investments. The Company invests its excess cash balances primarily in corporate debt securities. Realized gains and losses are calculated on the specific identification method and recorded as interest income and were immaterial for all periods presented.

Restricted Cash

As of December 31, 2023 and 2022, the Company had $1.8 million and $1.6 million, respectively, of long-term restricted cash deposited with a financial institution. The restricted cash is held in separate bank accounts to support letter of credit agreements related to the Company’s facility leases which expire in 2025 and 2031 (see Note 7) and corporate credit card program in 2023.

Property and Equipment

Property and equipment are stated at cost, net of accumulated depreciation and amortization. Depreciation and amortization begin at the time the asset is placed in service. Depreciation and amortization are computed using the straight-line method over the estimated useful lives of the assets of five years. Leasehold improvements are amortized over the shorter of the lease term or the estimated useful lives of the assets. Maintenance and repairs are expensed as incurred. Upon sale or retirement of assets, the cost and accumulated depreciation and amortization are removed from the balance sheet and any resulting gain or loss is reflected in the statement of operations and comprehensive loss in the period realized.

Cloud Computing Arrangements

The Company incurs costs to implement cloud computing arrangements hosted by third party vendors. Costs incurred to implement cloud computing service arrangements are capitalized when incurred during the application development phase, and recognized as prepaid and other assets and other non-current assets on the balance sheet. Implementation costs are subsequently amortized over the expected term of the related cloud service. The carrying value of cloud computing implementation costs are tested for impairment when an event or circumstance indicates that the asset might be impaired. Changes in cloud computing arrangement implementation costs are classified within operating activities in the statements of cash flows.

Impairment of Long-Lived Assets

The Company reviews long-lived assets, primarily comprised of property and equipment, for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable. Recoverability is measured by comparison of the carrying amount to the estimated undiscounted future cash flows, which the assets or asset groups are expected to generate. If such assets are considered to be impaired, the impairment to be recognized at the amount by which the carrying amount of the assets or asset groups exceeds the estimated fair value of the assets or asset groups. There have been no such impairments of long-lived assets during the periods presented.

Revenue Recognition

Under Accounting Standard Codification Topic 606, Revenue from Contract with Customers (“ASC 606”), the Company recognizes revenue when its customer obtains control of promised goods or services, in an amount that reflects the consideration which the Company expects to receive in exchange for those goods or services. To determine revenue recognition for arrangements that the Company determines are within the scope of ASC 606, the following steps are performed: (i) identification of a contract to provide goods or services to a customer; (ii) determination of whether the promised goods or services are performance obligations including whether they are distinct in the context of the contract; (iii) measurement of the transaction price, including the constraint on variable consideration, if any; (iv) where a contract contains multiple performance obligations, the Company must allocate the transaction price to the performance obligations based on estimated selling prices; and (v) recognition of revenue when (or as) each performance obligation is satisfied.

The Company only applies the five-step model to contracts when it is probable that the Company will collect the consideration it is entitled to in exchange for the goods or services it transfers to the customer.

At contract inception, once the contract is determined to be within the scope of ASC 606, the Company assesses the goods or services promised within each contract and determines those that are performance obligations and assesses whether each promised good or service is distinct. The Company then recognizes as revenue the amount of the transaction price that is allocated to the respective performance obligation when (or as) the performance obligation is satisfied.

As part of the accounting for these arrangements, the Company develops assumptions that require judgment to determine the stand-alone selling price for each performance obligation identified in the contract. The Company uses key assumptions to determine the stand-alone selling price, which may include development timelines, reimbursement rates for personnel costs, discount rates, and probabilities of technical and regulatory success. The Company evaluates each performance obligation and determines if it is satisfied over time. In addition, variable consideration must be evaluated to determine if it is constrained and, therefore, excluded from the transaction price.

If the license to the Company’s intellectual property is determined to be distinct from the other performance obligations identified in the arrangement, the Company recognizes revenues allocated to the license when the license is transferred to the customer and the customer is able to use and benefit from the license. For licenses that are bundled with other promised goods or services, the Company utilizes judgment to assess the nature of the combined performance obligation to determine whether the combined performance obligation is satisfied over time or at a point in time and, if over time, the appropriate method of measuring progress for purposes of recognizing revenue. The Company evaluates the measure of progress each reporting period and, if necessary, adjusts the measure of performance and related revenue recognition. Any change made to estimated progress towards completion of a performance obligation due to changes in the estimated activities required to complete the performance obligation and, therefore, revenue recognized will be recorded as a change in estimate.

The Company receives payments from its collaborators based on billing schedules established in each contract. Upfront payments and other payments may require deferral of revenue recognition to a future period until the Company performs its obligation under its collaboration arrangements. Amounts are recorded as accounts receivable when the Company’s right to consideration is unconditional. The Company does not assess whether a contract has a significant financing component if the expectation at contract inception is such that the payment by the customer is akin to a deposit for research and development services.

To date, all of the Company’s revenue has been derived from its development agreement with Toray Industries, Inc. (“Toray”), Genmab A/S (“Genmab”), and Innovent Biologics, Inc. (“Innovent”), as described in Note 6.

Research and Development Expenses

Research and development costs are charged to expense as incurred. Research and development expenses include certain payroll and personnel expenses, laboratory supplies, consulting costs, external contract research and development expenses, and allocated overhead, including rent, equipment depreciation and utilities. Advance payments for goods or services for future research and development activities are deferred and expensed as the goods are delivered or the related services are performed.

The Company estimates preclinical studies and clinical trial expenses based on the services performed pursuant to contracts with research institutions and clinical research organizations that conduct and manage preclinical studies and trials on the Company’s behalf. In accruing service fees, the Company estimates the time period over which services will be performed and the level of effort to be expended in each period. These estimates are based on communications with the third-party service providers and the Company’s estimates of accrued expenses and on information available at each balance sheet date. If the actual timing of the performance of services or the level of effort varies from the estimate, the Company will adjust the accrual accordingly.

Fair Value Measurements

Fair value is defined as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. As such, fair value is a market-based measurement that should be determined based on assumptions that market participants would use in pricing an asset or liability. Cash and cash equivalents, restricted cash, marketable debt securities, accounts payable, accrued expenses and other current liabilities are reported at their respective fair values in our balance sheets. The carrying amount of the remaining financial instruments approximate fair value due to their short-term nature. Refer to Note 3 for the methodologies and assumptions used in valuing financial instruments.

Leases

The Company determines whether an arrangement is a lease at inception. Specifically, it considers whether it controls the underlying asset and has the right to obtain substantially all the economic benefits or outputs from the asset. If the contractual arrangement contains a lease, the Company then determines the classification of the lease, operating or finance, using the classification criteria described in Accounting Standard Codification Topic 842, Leases (“ASC 842”). The Company has elected not to separate lease components from non-lease components, such as common area maintenance charges, and instead accounts for the lease and non-lease components as a single component.

At the commencement date of a lease, the Company recognizes lease liabilities which represent its obligation to make lease payments, and right-of-use assets (“ROU assets”) which represent its right to use the underlying asset during the lease term. The lease liability is measured at the present value of lease payments over the lease term. As the Company’s leases typically do not provide an implicit rate, the Company uses an incremental borrowing rate based on the information available at the lease commencement date. The ROU asset is measured at cost, which includes the initial measurement of the lease liability and initial direct costs incurred by the Company and excludes lease incentives. ROU assets are recorded in operating lease ROU assets and lease liabilities are recorded in operating lease liabilities, current and noncurrent in the balance sheets.

Lease terms may include options to extend or terminate the lease when it is reasonably certain that the Company will exercise that option. Operating lease expense is recognized on a straight-line basis over the lease term. The Company does not recognize lease liabilities and ROU assets for short-term leases with terms of twelve months or less.

Stock-Based Compensation Expense

The Company accounts for stock-based compensation by measuring and recognizing compensation expense for all share-based payments made to employees and non-employees based on estimated grant-date fair values. For stock-based payments with service conditions only, the Company uses the straight-line method to allocate compensation cost to reporting periods over each award’s requisite service period, which is generally the vesting period. For stock-based payments with both performance and service conditions, the Company recognizes expense based on the fair value of the performance awards over the estimated service period (under the graded vesting method) to the extent the achievement of the related performance criteria is estimated to be probable. The grant date fair value is utilized for restricted stock awards and the fair value of each stock option grant is estimated on the date of grant using the Black-Scholes model. The Black-Scholes model requires the input of subjective assumptions, including expected volatility, expected dividend yield, expected term, risk-free interest rate, and the estimated fair value of the underlying common stock on the date of grant. The Company accounts for forfeitures as they occur.

Income Taxes

The Company accounts for income taxes using the asset and liability method. Under this method, deferred tax assets and liabilities are determined based on differences between financial reporting and tax reporting bases of assets and liabilities and are measured using enacted tax rates and laws that are expected to be in effect when the differences are expected to reverse. Changes in deferred tax assets and liabilities are recorded in the provision for income taxes.

Realization of deferred tax assets is dependent upon future earnings, the timing and amount of which are uncertain. A valuation allowance is provided against deferred tax assets unless it is more likely than not that they will be realized.

The Company utilizes a two-step approach to recognize and measure uncertain tax positions. The first step is to evaluate the tax position for recognition by determining if the weight of available evidence indicates that it is more likely than not that the position will be sustained upon tax authority examination, including resolution of related appeals or litigation processes, if any. The second step is to measure the tax benefit as the largest amount that is more than 50% likely of being realized upon ultimate settlement. The Company’s policy is to recognize interest and penalties related to the underpayment of income taxes as a component of income tax expense or benefit. To date, there have been no interest or penalties charged in relation to the unrecognized tax benefits.

Net Loss Per Share

Basic net loss per share is calculated by dividing the net loss by the weighted-average number of shares of common stock outstanding during the period, without consideration for potentially dilutive securities. Diluted net loss per share is computed by dividing the net loss by the weighted-average number of common stock and potentially dilutive securities outstanding for the period. For purposes of the diluted net loss per share calculation, convertible preferred stock, stock options, common stock subject to repurchase related to unvested restricted stock awards and early exercise of stock options are considered potentially dilutive securities. Basic and diluted net loss per share is presented in conformity with the two-class method required for participating securities as the convertible preferred stock is considered a participating security because it participates in dividends with common stock. The Company also considers the shares issued upon the early exercise of stock options subject to repurchase to be participating securities because holders of such shares have non-forfeitable dividend rights in the event a dividend is paid on common stock. The holders of all series of convertible preferred stock and the holders of early exercised shares subject to repurchase do not have a contractual obligation to share in the Company’s losses. As such, the net loss was attributed entirely to common stockholders. Because the Company has reported a net loss for all periods presented, diluted net loss per share is the same as basic net loss per share for all periods presented as potentially dilutive securities were anti-dilutive.

Comprehensive Loss

Comprehensive loss includes all changes in equity (net assets) during a period from non-owner sources, including unrealized gains and losses on marketable securities. The Company incurred a net unrealized gain on marketable securities of $1.0 million and a net unrealized loss $0.6 million during the years ended December 31, 2023 and 2022, respectively.

Segment Reporting

The Company has one operating segment. Operating segments are identified as components of an enterprise about which separate discrete financial information is available for evaluation by the chief operating decision-maker, which is the Company's Chief Executive Officer, in making decisions regarding resource allocation and assessing performance.

Recent Accounting Standards

From time to time, new accounting standards are issued by the Financial Accounting Standards Board (the “FASB”), or other standard setting bodies and adopted by the Company as of the specified effective date. Unless otherwise discussed, the impact of recently issued standards that are not yet effective will not have a material impact on the Company’s financial position or results of operations upon adoption.

Recently Adopted Accounting Pronouncements

In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments- Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments, and subsequent amendments to the initial guidance under ASU 2018-19, ASU 2019-04, ASU 2019-05, ASU 2020-03, and ASU 2020-02. The standard changes how entities will measure credit losses for most financial assets and certain other instruments that are not measured at fair value through net income. Financial assets measured at amortized cost will be presented at the net amount expected to be collected by using an allowance for credit losses. The Company adopted ASU 2016-13 as of January 1, 2023. The adoption of ASU 2016-13 did not have a material impact on the Company's financial position or results of operations.

In December 2023, the FASB issued ASU 2023-09, Income Taxes (Topic 740): Improvements to Income Tax Disclosures (“ASU 2023-09”). ASU 2023-09 requires enhanced annual disclosures regarding the rate reconciliation and income taxes paid information. ASU 2023-09 is effective for annual periods beginning after December 15, 2024 and may be adopted on a prospective or retrospective basis. Early adoption is permitted. The Company is evaluating the impact of this guidance on its financial statements and related disclosures.

Summary of Significant Accounting Policies - Additional Information (Details)	12 Months Ended
	Dec. 31, 2023 USD ($) Segment	Dec. 31, 2022 USD ($)
Summary Of Significant Accounting Policies [Line Items]
Cash and cash equivalents and marketable securities	$ 128,600,000
Accumulated deficit	(364,285,000)	$ (295,088,000)
Restricted cash	$ 1,765,000	1,565,000
Estimated useful life	5 years
Impairments of long-lived assets	$ 0	0
Unrecognized tax benefits, interest or penalties	0	0
Net unrealized gain (loss) on marketable securities	$ 956,000	$ (598,000)
Number of operating segment \| Segment	1
Accounting Standards Update [Extensible Enumeration]	us-gaap:AccountingStandardsUpdate201613Member
Change in accounting principle, accounting standards update, adopted	true
Change in accounting principle, accounting standards update, adopted date	Jan. 01, 2023
Change in accounting principle, accounting standards update, immaterial effect	true

Fair Value Measurements and Fair Value of Financial Instruments (Tables)

12 Months Ended

Dec. 31, 2023

Fair Value Disclosures [Abstract]

Schedule of Marketable Securities Classified as Available-for-sale Securities

Marketable securities, all of which are classified as available-for-sale securities, consisted of the following at December 31, 2023 and 2022 (in thousands):


	December 31, 2023
	Amortized		Unrealized		Unrealized			Estimated
	Cost		Gains		Losses			Fair Value
Asset backed securities	$	17,347	$	10	$	(15	)	$	17,342
U.S. treasury securities		43,924		34		(11	)		43,947
Other government agency securities		13,371		—		(15	)		13,356
Commercial paper		20,351		4		(10	)		20,345
Corporate debt securities		22,763		41		(2	)		22,802
Total	$	117,756	$	89	$	(53	)	$	117,792


	December 31, 2022
	Amortized		Unrealized		Unrealized			Estimated
	Cost		Gains		Losses			Fair Value
Asset backed securities	$	12,754	$	11	$	(99	)	$	12,666
U.S. treasury securities		54,747		1		(517	)		54,231
Other government agency securities		5,009		—		(29	)		4,980
Commercial paper		56,170		—		—			56,170
Corporate debt securities		55,827		—		(287	)		55,540
Total	$	184,507	$	12	$	(932	)	$	183,587

Schedule of Gross Unrealized Losses and Fair Value of Company's Available-for-Sale Securities


	December 31, 2023
	Less Than 12 Months					More Than 12 Months					Total
	Estimated		Unrealized			Estimated		Unrealized			Estimated		Unrealized
	Fair Value		Losses			Fair Value		Losses			Fair Value		Losses
Asset-backed securities	$	4,686	$	—		$	12,656	$	(15	)	$	17,342	$	(15	)
U.S. treasury securities		34,104		—			9,843		(11	)		43,947		(11	)
Other government agency securities		2,477		(1	)		10,879		(14	)		13,356		(15	)
Commercial paper		20,345		(10	)		—		—			20,345		(10	)
Corporate debt securities		9,566		(1	)		13,236		(1	)		22,802		(2	)
Total	$	71,178	$	(12	)	$	46,614	$	(41	)	$	117,792	$	(53	)


	December 31, 2022
	Less Than 12 Months					More Than 12 Months					Total
	Estimated		Unrealized			Estimated		Unrealized			Estimated		Unrealized
	Fair Value		Losses			Fair Value		Losses			Fair Value		Losses
Asset-backed securities	$	3,180	$	(5	)	$	9,485	$	(94	)	$	12,665	$	(99	)
U.S. treasury securities		14,723		(28	)		39,508		(489	)		54,231		(517	)
Other government agency securities		—		—			4,980		(29	)		4,980		(29	)
Corporate debt securities		6,977		(32	)		48,563		(255	)		55,540		(287	)
Total	$	24,880	$	(65	)	$	102,536	$	(867	)	$	127,416	$	(932	)

Schedule of Fair Values of Assets and Liabilities Measured at Fair Value on Recurring Basis


	December 31, 2023
	Total		(Level 1)		(Level 2)		(Level 3)
Money market funds	$	8,641	$	8,641	$	—	$	—
Asset backed securities		17,342		—		17,342		—
U.S. treasury securities		43,947		33,001		10,946		—
Other government agency securities		13,356		—		13,356		—
Commercial paper		20,345		—		20,345		—
Corporate debt securities		22,802		—		22,802		—
Total	$	126,433	$	41,642	$	84,791	$	—


	December 31, 2022
	Total		(Level 1)		(Level 2)		(Level 3)
Money market funds	$	6,885	$	6,885	$	—	$	—
Asset backed securities		12,666		—		12,666		—
U.S. treasury securities		54,231		54,231		—		—
Other government agency securities		4,980		—		4,980		—
Commercial paper		56,170		—		56,170		—
Corporate debt securities		55,540		—		55,540		—
Total	$	190,472	$	61,116	$	129,356	$	—

Summary of Significant Accounting Policies (Policies)	12 Months Ended
Summary of Significant Accounting Policies (Policies)	Dec. 31, 2023
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The Company’s financial statements have been prepared in accordance with U.S. generally accepted accounting principles (“U.S. GAAP”). Certain reclassifications on the statement of cash flows have been made to prior period amounts to conform to current period presentation.
Risks and Uncertainties	Risks and Uncertainties The Company is subject to a number of risks similar to other early-stage biopharmaceutical companies, including, but not limited to, changes in any of the following areas that the Company believes could have a material adverse effect on its future financial position or results of operations: risks related to the successful discovery and development of its product candidates, ability to raise additional capital, development of new technological innovations by its competitors, delay or inability to obtain chemical or biological intermediates from such suppliers required for the synthesis of the Company’s product candidates, protection of intellectual property rights, litigation or claims against the Company based on intellectual property rights, and regulatory clearance and market acceptance of the Company’s products. Global economic and business activities continue to face widespread macroeconomic uncertainties, including pandemics, labor shortages, inflation and monetary supply shifts, and potential disruptions from major geopolitical conflicts. The Company continues to actively monitor the impact of these macroeconomic factors on its financial condition, liquidity, operations, and workforce. The extent of the impact of these factors on the Company’s operational and financial performance, including its ability to execute its business strategies and initiatives in the expected time frame, will depend on future developments, which are uncertain and cannot be predicted; however, any continued or renewed disruption resulting from these factors could negatively impact the Company’s business. The Company relies on single source manufacturers and suppliers for the supply of its product candidates. Disruption from these manufacturers or suppliers would have a negative impact on the Company’s business, financial position, and results of operations.
Liquidity	Liquidity The Company has incurred net losses and negative cash flows from operations since our inception and anticipates to continue to incur net losses for the foreseeable future. As of December 31, 2023, the Company had cash and cash equivalents and marketable securities of $128.6 million and an accumulated deficit of $364.3 million. Based upon the Company's current operating plans, the Company believes that its existing cash, cash equivalents and marketable securities will be sufficient to fund its operations for at least the next 12 months following the issuance date of this Annual Report on Form 10-K. The Company will need to raise additional capital to continue the advancement of its programs. In the near term, the Company's primary uses of cash will be to fund the completion of key milestones for trastuzumab imbotolimod, formerly known as BDC-1001, and BDC-3042 and to fund its operations, including research and development activities and employee salaries. This includes significant costs relating to clinical trials and manufacture of the Company's product candidates. The Company's uses of cash in the long term will be similar as the Company advances its research and development activities and pays employee salaries. Most pharmaceutical products require larger clinical trials as development progresses, and the Company expects its funding requirements to grow with the advancement of its programs. The Company's long-term funding requirements will depend on many factors, which are uncertain but include its portfolio prioritization decisions and the success of its collaborations. In turn, the Company's ability to raise additional capital through equity or partnering will depend on the general economic environment in which it operates and its ability to achieve key milestones.
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets, liabilities, and the disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of expenses during the reporting period. On an ongoing basis, the Company evaluates its estimates and assumptions, including those related to revenue recognition, stock-based compensation and accrued liabilities. Management bases its estimates on historical experience and on various other assumptions that are believed to be reasonable under the circumstances, the results of which form the basis for making judgments about the carrying values of assets and liabilities that are not readily apparent from other sources. Actual results may differ materially from those estimates.
Concentrations of Credit Risk	Concentrations of Credit Risk Financial instruments that potentially subject the Company to concentration of credit risk consist of cash, cash equivalents and marketable securities. At December 31, 2023 and 2022, most of the Company’s funds were invested with a registered investment manager and custodied at one financial institution, with operating cash kept at a separate financial institution, and account balances may at times exceed federally insured limits. Management believes that the Company is not subject to unusual or significant credit risk beyond the normal credit risk associated with commercial banking relationships.
Cash and Cash Equivalents	Cash and Cash Equivalents The Company considers all highly liquid investments purchased with an original maturity of three months or less to be cash equivalents. As of December 31, 2023 and 2022, cash and cash equivalents consisted primarily of bank deposits and money market funds which were unrestricted as to withdrawal or use.
Allowance for Credit Losses	Allowance for Credit Losses For available-for-sale securities in an unrealized loss position, the Company first assesses whether it intends to sell, or if it is more likely than not that the Company will be required to sell, the security before recovery of its amortized cost basis. If either of the criteria regarding intent or requirement to sell is met, the security’s amortized cost basis is written down to fair value through earnings. For available-for-sale securities that do not meet the aforementioned criteria, the Company evaluates whether the decline in fair value has resulted from credit losses or other factors. In making this assessment, the Company considers the severity of the impairment, any changes in interest rates, market conditions, changes to the underlying credit ratings and forecasted recovery, among other factors. The credit-related portion of unrealized losses, and any subsequent improvements, are recorded in interest income through an allowance account. Any impairment that has not been recorded through an allowance for credit losses is included in other comprehensive income (loss) on the statements of operations and comprehensive loss. The Company elected the practical expedient to exclude the applicable accrued interest from both the fair value and amortized costs basis of its available-for-sale securities for purposes of identifying and measuring an impairment. Accrued interest receivable on available-for-sale securities is recorded within cash and cash equivalents on the Company's balance sheets. The Company's accounting policy is to not measure an allowance for credit loss for accrued interest receivable and to write-off any uncollectible accrued interest receivable as a reversal of interest income in a timely manner, which the Company considers to be in the period in which it determines the accrued interest will not be collected by the Company
Marketable Securities	Marketable Securities The Company classifies its marketable securities as available-for-sale and records such assets at estimated fair value in the balance sheets, with unrealized gains and non-credit related losses that are determined to be temporary, if any, reported as a component of other comprehensive income (loss) within the statements of operations and comprehensive loss and as a separate component of stockholders’ equity. The Company classifies marketable securities with remaining maturities greater than three months but less than one year as short-term investments, and those with remaining maturities greater than one year are classified as long-term investments. The Company invests its excess cash balances primarily in corporate debt securities. Realized gains and losses are calculated on the specific identification method and recorded as interest income and were immaterial for all periods presented.
Restricted Cash	Restricted Cash As of December 31, 2023 and 2022, the Company had $1.8 million and $1.6 million, respectively, of long-term restricted cash deposited with a financial institution. The restricted cash is held in separate bank accounts to support letter of credit agreements related to the Company’s facility leases which expire in 2025 and 2031 (see Note 7) and corporate credit card program in 2023.
Property and Equipment	Property and Equipment Property and equipment are stated at cost, net of accumulated depreciation and amortization. Depreciation and amortization begin at the time the asset is placed in service. Depreciation and amortization are computed using the straight-line method over the estimated useful lives of the assets of five years. Leasehold improvements are amortized over the shorter of the lease term or the estimated useful lives of the assets. Maintenance and repairs are expensed as incurred. Upon sale or retirement of assets, the cost and accumulated depreciation and amortization are removed from the balance sheet and any resulting gain or loss is reflected in the statement of operations and comprehensive loss in the period realized.
Cloud Computing Arrangements	Cloud Computing Arrangements The Company incurs costs to implement cloud computing arrangements hosted by third party vendors. Costs incurred to implement cloud computing service arrangements are capitalized when incurred during the application development phase, and recognized as prepaid and other assets and other non-current assets on the balance sheet. Implementation costs are subsequently amortized over the expected term of the related cloud service. The carrying value of cloud computing implementation costs are tested for impairment when an event or circumstance indicates that the asset might be impaired. Changes in cloud computing arrangement implementation costs are classified within operating activities in the statements of cash flows.
Impairment of Long-lived Assets	Impairment of Long-Lived Assets The Company reviews long-lived assets, primarily comprised of property and equipment, for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable. Recoverability is measured by comparison of the carrying amount to the estimated undiscounted future cash flows, which the assets or asset groups are expected to generate. If such assets are considered to be impaired, the impairment to be recognized at the amount by which the carrying amount of the assets or asset groups exceeds the estimated fair value of the assets or asset groups. There have been no such impairments of long-lived assets during the periods presented.
Revenue Recognition	Revenue Recognition Under Accounting Standard Codification Topic 606, Revenue from Contract with Customers (“ASC 606”), the Company recognizes revenue when its customer obtains control of promised goods or services, in an amount that reflects the consideration which the Company expects to receive in exchange for those goods or services. To determine revenue recognition for arrangements that the Company determines are within the scope of ASC 606, the following steps are performed: (i) identification of a contract to provide goods or services to a customer; (ii) determination of whether the promised goods or services are performance obligations including whether they are distinct in the context of the contract; (iii) measurement of the transaction price, including the constraint on variable consideration, if any; (iv) where a contract contains multiple performance obligations, the Company must allocate the transaction price to the performance obligations based on estimated selling prices; and (v) recognition of revenue when (or as) each performance obligation is satisfied. The Company only applies the five-step model to contracts when it is probable that the Company will collect the consideration it is entitled to in exchange for the goods or services it transfers to the customer. At contract inception, once the contract is determined to be within the scope of ASC 606, the Company assesses the goods or services promised within each contract and determines those that are performance obligations and assesses whether each promised good or service is distinct. The Company then recognizes as revenue the amount of the transaction price that is allocated to the respective performance obligation when (or as) the performance obligation is satisfied. As part of the accounting for these arrangements, the Company develops assumptions that require judgment to determine the stand-alone selling price for each performance obligation identified in the contract. The Company uses key assumptions to determine the stand-alone selling price, which may include development timelines, reimbursement rates for personnel costs, discount rates, and probabilities of technical and regulatory success. The Company evaluates each performance obligation and determines if it is satisfied over time. In addition, variable consideration must be evaluated to determine if it is constrained and, therefore, excluded from the transaction price. If the license to the Company’s intellectual property is determined to be distinct from the other performance obligations identified in the arrangement, the Company recognizes revenues allocated to the license when the license is transferred to the customer and the customer is able to use and benefit from the license. For licenses that are bundled with other promised goods or services, the Company utilizes judgment to assess the nature of the combined performance obligation to determine whether the combined performance obligation is satisfied over time or at a point in time and, if over time, the appropriate method of measuring progress for purposes of recognizing revenue. The Company evaluates the measure of progress each reporting period and, if necessary, adjusts the measure of performance and related revenue recognition. Any change made to estimated progress towards completion of a performance obligation due to changes in the estimated activities required to complete the performance obligation and, therefore, revenue recognized will be recorded as a change in estimate. The Company receives payments from its collaborators based on billing schedules established in each contract. Upfront payments and other payments may require deferral of revenue recognition to a future period until the Company performs its obligation under its collaboration arrangements. Amounts are recorded as accounts receivable when the Company’s right to consideration is unconditional. The Company does not assess whether a contract has a significant financing component if the expectation at contract inception is such that the payment by the customer is akin to a deposit for research and development services. To date, all of the Company’s revenue has been derived from its development agreement with Toray Industries, Inc. (“Toray”), Genmab A/S (“Genmab”), and Innovent Biologics, Inc. (“Innovent”), as described in Note 6.
Research and Development Expenses	Research and Development Expenses Research and development costs are charged to expense as incurred. Research and development expenses include certain payroll and personnel expenses, laboratory supplies, consulting costs, external contract research and development expenses, and allocated overhead, including rent, equipment depreciation and utilities. Advance payments for goods or services for future research and development activities are deferred and expensed as the goods are delivered or the related services are performed. The Company estimates preclinical studies and clinical trial expenses based on the services performed pursuant to contracts with research institutions and clinical research organizations that conduct and manage preclinical studies and trials on the Company’s behalf. In accruing service fees, the Company estimates the time period over which services will be performed and the level of effort to be expended in each period. These estimates are based on communications with the third-party service providers and the Company’s estimates of accrued expenses and on information available at each balance sheet date. If the actual timing of the performance of services or the level of effort varies from the estimate, the Company will adjust the accrual accordingly.
Fair Value Measurements	Fair Value Measurements Fair value is defined as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. As such, fair value is a market-based measurement that should be determined based on assumptions that market participants would use in pricing an asset or liability. Cash and cash equivalents, restricted cash, marketable debt securities, accounts payable, accrued expenses and other current liabilities are reported at their respective fair values in our balance sheets. The carrying amount of the remaining financial instruments approximate fair value due to their short-term nature. Refer to Note 3 for the methodologies and assumptions used in valuing financial instruments.
Leases	Leases The Company determines whether an arrangement is a lease at inception. Specifically, it considers whether it controls the underlying asset and has the right to obtain substantially all the economic benefits or outputs from the asset. If the contractual arrangement contains a lease, the Company then determines the classification of the lease, operating or finance, using the classification criteria described in Accounting Standard Codification Topic 842, Leases (“ASC 842”). The Company has elected not to separate lease components from non-lease components, such as common area maintenance charges, and instead accounts for the lease and non-lease components as a single component. At the commencement date of a lease, the Company recognizes lease liabilities which represent its obligation to make lease payments, and right-of-use assets (“ROU assets”) which represent its right to use the underlying asset during the lease term. The lease liability is measured at the present value of lease payments over the lease term. As the Company’s leases typically do not provide an implicit rate, the Company uses an incremental borrowing rate based on the information available at the lease commencement date. The ROU asset is measured at cost, which includes the initial measurement of the lease liability and initial direct costs incurred by the Company and excludes lease incentives. ROU assets are recorded in operating lease ROU assets and lease liabilities are recorded in operating lease liabilities, current and noncurrent in the balance sheets. Lease terms may include options to extend or terminate the lease when it is reasonably certain that the Company will exercise that option. Operating lease expense is recognized on a straight-line basis over the lease term. The Company does not recognize lease liabilities and ROU assets for short-term leases with terms of twelve months or less.
Stock-Based Compensation Expense	Stock-Based Compensation Expense The Company accounts for stock-based compensation by measuring and recognizing compensation expense for all share-based payments made to employees and non-employees based on estimated grant-date fair values. For stock-based payments with service conditions only, the Company uses the straight-line method to allocate compensation cost to reporting periods over each award’s requisite service period, which is generally the vesting period. For stock-based payments with both performance and service conditions, the Company recognizes expense based on the fair value of the performance awards over the estimated service period (under the graded vesting method) to the extent the achievement of the related performance criteria is estimated to be probable. The grant date fair value is utilized for restricted stock awards and the fair value of each stock option grant is estimated on the date of grant using the Black-Scholes model. The Black-Scholes model requires the input of subjective assumptions, including expected volatility, expected dividend yield, expected term, risk-free interest rate, and the estimated fair value of the underlying common stock on the date of grant. The Company accounts for forfeitures as they occur.
Income Taxes	Income Taxes The Company accounts for income taxes using the asset and liability method. Under this method, deferred tax assets and liabilities are determined based on differences between financial reporting and tax reporting bases of assets and liabilities and are measured using enacted tax rates and laws that are expected to be in effect when the differences are expected to reverse. Changes in deferred tax assets and liabilities are recorded in the provision for income taxes. Realization of deferred tax assets is dependent upon future earnings, the timing and amount of which are uncertain. A valuation allowance is provided against deferred tax assets unless it is more likely than not that they will be realized. The Company utilizes a two-step approach to recognize and measure uncertain tax positions. The first step is to evaluate the tax position for recognition by determining if the weight of available evidence indicates that it is more likely than not that the position will be sustained upon tax authority examination, including resolution of related appeals or litigation processes, if any. The second step is to measure the tax benefit as the largest amount that is more than 50% likely of being realized upon ultimate settlement. The Company’s policy is to recognize interest and penalties related to the underpayment of income taxes as a component of income tax expense or benefit. To date, there have been no interest or penalties charged in relation to the unrecognized tax benefits.
Net Loss Per Share	Net Loss Per Share Basic net loss per share is calculated by dividing the net loss by the weighted-average number of shares of common stock outstanding during the period, without consideration for potentially dilutive securities. Diluted net loss per share is computed by dividing the net loss by the weighted-average number of common stock and potentially dilutive securities outstanding for the period. For purposes of the diluted net loss per share calculation, convertible preferred stock, stock options, common stock subject to repurchase related to unvested restricted stock awards and early exercise of stock options are considered potentially dilutive securities. Basic and diluted net loss per share is presented in conformity with the two-class method required for participating securities as the convertible preferred stock is considered a participating security because it participates in dividends with common stock. The Company also considers the shares issued upon the early exercise of stock options subject to repurchase to be participating securities because holders of such shares have non-forfeitable dividend rights in the event a dividend is paid on common stock. The holders of all series of convertible preferred stock and the holders of early exercised shares subject to repurchase do not have a contractual obligation to share in the Company’s losses. As such, the net loss was attributed entirely to common stockholders. Because the Company has reported a net loss for all periods presented, diluted net loss per share is the same as basic net loss per share for all periods presented as potentially dilutive securities were anti-dilutive.
Comprehensive Loss	Comprehensive Loss Comprehensive loss includes all changes in equity (net assets) during a period from non-owner sources, including unrealized gains and losses on marketable securities. The Company incurred a net unrealized gain on marketable securities of $1.0 million and a net unrealized loss $0.6 million during the years ended December 31, 2023 and 2022, respectively.
Segment Reporting	Segment Reporting The Company has one operating segment. Operating segments are identified as components of an enterprise about which separate discrete financial information is available for evaluation by the chief operating decision-maker, which is the Company's Chief Executive Officer, in making decisions regarding resource allocation and assessing performance.
Recent Accounting Standards and Recently Adopted Accounting Pronouncements	Recent Accounting Standards From time to time, new accounting standards are issued by the Financial Accounting Standards Board (the “FASB”), or other standard setting bodies and adopted by the Company as of the specified effective date. Unless otherwise discussed, the impact of recently issued standards that are not yet effective will not have a material impact on the Company’s financial position or results of operations upon adoption. Recently Adopted Accounting Pronouncements In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments- Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments, and subsequent amendments to the initial guidance under ASU 2018-19, ASU 2019-04, ASU 2019-05, ASU 2020-03, and ASU 2020-02. The standard changes how entities will measure credit losses for most financial assets and certain other instruments that are not measured at fair value through net income. Financial assets measured at amortized cost will be presented at the net amount expected to be collected by using an allowance for credit losses. The Company adopted ASU 2016-13 as of January 1, 2023. The adoption of ASU 2016-13 did not have a material impact on the Company's financial position or results of operations. In December 2023, the FASB issued ASU 2023-09, Income Taxes (Topic 740): Improvements to Income Tax Disclosures (“ASU 2023-09”). ASU 2023-09 requires enhanced annual disclosures regarding the rate reconciliation and income taxes paid information. ASU 2023-09 is effective for annual periods beginning after December 15, 2024 and may be adopted on a prospective or retrospective basis. Early adoption is permitted. The Company is evaluating the impact of this guidance on its financial statements and related disclosures.

Document and Entity Information - USD ($) $ in Millions	12 Months Ended
Document and Entity Information - USD ($) $ in Millions	Dec. 31, 2023	Mar. 14, 2024	Jun. 30, 2023
Cover [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2023
Document Fiscal Year Focus	2023
Document Fiscal Period Focus	FY
Entity Registrant Name	Bolt Biotherapeutics, Inc.
Entity Central Index Key	0001641281
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Common Stock, Shares Outstanding		38,127,740
Entity Shell Company	false
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	true
ICFR Auditor Attestation Flag	false
Document Financial Statement Error Correction [Flag]	false
Entity Public Float			$ 32.1
Title of 12(b) Security	Common Stock, $0.00001 par value
Trading Symbol	BOLT
Security Exchange Name	NASDAQ
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity File Number	001-39988
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	47-2804636
Entity Address, Address Line One	900 Chesapeake
Entity Address, Address Line Two	Drive
Entity Address, City or Town	Redwood City
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	94063
City Area Code	650
Local Phone Number	665-9295
Document Annual Report	true
Document Transition Report	false
Auditor Firm ID	238
Auditor Name	PricewaterhouseCoopers LLP
Auditor Location	San Jose, California
Documents Incorporated by Reference	DOCUMENTS INCORPORATED BY REFERENCE Designated portions of the Proxy Statement relating to registrant’s 2024 Annual Meeting of Stockholders, which will be filed with the Securities and Exchange Commission within 120 days after the end of fiscal year 2023, are incorporated by reference into Part III of this Annual Report.

Collaborations - Additional Information (Details) - USD ($)	1 Months Ended			12 Months Ended
	Aug. 31, 2021	May 31, 2021	Mar. 31, 2019	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Contract liability				$ 3,100,000
Collaboration revenue				7,876,000	$ 5,729,000
Toray Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Contract liability				1,500,000	1,500,000
Variable consideration related to reimbursements for research and development services			$ 1,800,000
Contract liability, current				500,000	500,000
Contract liability, non-current				1,000,000	1,000,000
Revenue				0	0
Genmab Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Contract liability				6,664,000	8,498,000	$ 10,574,000
Upfront payment received		$ 10,000,000
Allocated from stock purchase agreement		1,400,000
Variable consideration related to reimbursements for research and development services		31,000,000
Contract liability, current				1,000,000
Contract liability, non-current				5,700,000
Collaboration revenue				3,700,000	4,200,000
Potential future sale milestone payments		$ 160,000,000
Genmab Agreement \| Prepaid Expenses and Other Current Assets
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Research and development services receivables				600,000
Genmab Agreement \| Common Stock
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Common stock sold		821,045
Consideration in excess of fair value		$ 1,400,000
Purchase price under Stock Purchase Agreement		15,000,000
Genmab Agreement \| Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Potential future sale milestone payments		$ 125,000,000
Innovent Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Contract liability				3,142,000	4,957,000	$ 5,000,000
Upfront payment received	$ 5,000,000
Allocated from stock purchase agreement	0
Contract liability, current				600,000
Contract liability, non-current				2,500,000
Collaboration revenue				$ 4,100,000	$ 1,500,000
Potential future development milestone payments	111,500,000
Potential future sale milestone payments	297,500,000
Stock purchase agreement expiration term				May 25, 2022
Innovent Agreement \| Prepaid Expenses and Other Current Assets
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Research and development services receivables				$ 700,000
Innovent Agreement \| Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Variable consideration related to reimbursements for research and development services	8,000,000
Potential license option exercise fee	28,500,000
Innovent Agreement \| Maximum \| Common Stock
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Aggregate investment under stock purchase agreement	$ 10,000,000
Series T Convertible Preferred Stock \| Toray Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Common stock sold			717,514
Consideration in excess of fair value			$ 1,500,000
Allocated from stock purchase agreement			$ 1,500,000

STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Income Statement [Abstract]
Collaboration revenue	$ 7,876	$ 5,729
Operating expenses:
Research and development	61,542	73,123
General and administrative	22,530	22,927
Total operating expense	84,072	96,050
Loss from operations	(76,196)	(90,321)
Other income, net
Interest income	6,999	2,223
Total other income, net	6,999	2,223
Net loss	(69,197)	(88,098)
Net unrealized gain (loss) on marketable securities	956	(598)
Comprehensive loss	$ (68,241)	$ (88,696)
Net loss per share, basic	$ (1.83)	$ (2.36)
Net loss per share, diluted	$ (1.83)	$ (2.36)
Weighted-average shares outstanding, basic	37,811,984	37,358,425
Weighted-average shares outstanding, diluted	37,811,984	37,358,425

Collaborations

12 Months Ended

Dec. 31, 2023

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Collaborations

6. Collaborations

Joint Development and License Agreement with Toray Industries, Inc.

In March 2019, the Company entered into a Joint Development and License Agreement (the “Toray Agreement”) with Toray to jointly develop and commercialize a Boltbody immune-stimulating antibody conjugate (“ISAC”) containing Toray’s proprietary antibody to treat cancer. The Company determined that the Toray Agreement is a contract with a customer and should be accounted for under ASC 606. In conjunction with the Toray Agreement, the Company entered into a Series T Convertible Preferred Stock Purchase Agreement (the “Series T Agreement”) for the issuance of 717,514 shares of Series T convertible preferred stock to Toray. These contracts have been evaluated together and the consideration in excess of the fair value of the Series T convertible preferred stock of $1.5 million has been allocated to the Toray Agreement and included in the total consideration for collaboration revenue. In February 2021, in connection with the Company’s initial public offering (“IPO”), all outstanding shares of Series T convertible preferred stock were converted into shares of the Company’s common stock.

In the Toray Agreement, the Company has identified one bundled performance obligation which includes the license rights, research and development services and services associated with participation on a joint steering committee. The transaction price includes the $1.5 million allocated from the Series T convertible preferred stock and $1.8 million of estimated variable consideration related to compensation for research and development services at the agreed upon full-time employee rate and third-party costs. Collaboration revenue is recognized over time proportionate to the costs that the Company has incurred to perform the services using an input method as a measure of progress towards satisfying the performance obligation, which is based on project hours. Amounts are billed based on estimated variable consideration in the quarter ahead of performance and are trued up on the subsequent quarter’s invoice following the work performed. The cumulative effect of revisions to estimated hours to complete the Company’s performance obligation will be recorded in the period in which changes are identified and amounts can be reasonably estimated. Deferred revenue allocated to the unsatisfied performance obligation is recorded as a contract liability on the balance sheet and will be recognized over time as the services are performed. As of December 31, 2023, and 2022, contract liability totaling $1.5 million at each period-end were recorded in deferred revenue with $0.5 million in current liabilities and $1.0 million in non-current liabilities on the balance sheet based on the forecasted periods of performance.

The Company recorded zero revenue during the years ended December 31, 2023 and 2022. The Toray Agreement includes both fixed and variable consideration. Under the Toray Agreement, the Company will be compensated for early-stage development and manufacturing activities based on agreed full-time equivalent rates and actual out of pocket costs incurred through the completion of the first Phase 1 clinical trial for the lead product candidate and Toray is entitled to reimbursement for 50% of such development costs from the Company’s share of revenues collected from the sale or licensing of collaboration products. Although the legal term of the agreement is until collaboration products are no longer sold in the territories covered under the agreement, the parties have present enforceable rights and obligations through the end of the first Phase 1 clinical trial, after which both parties can opt out of continued development under the agreement. As such, the accounting term of the Toray Agreement was considered to terminate upon completion of the first Phase 1 clinical trial. After the conclusion of the first Phase 1 clinical trial, the parties will share equally all costs of development activities necessary for obtaining regulatory approval of collaboration products in the indications in the territories covered under the agreement, unless either party elects to opt out of its co-funding obligations or reduce them by half, which election can be on a region-by-region basis or for the territories covered under the agreement as a whole. Such optional additional items which will be accounted for as contract modifications when development advances past certain milestones and the parties both exercise their opt-in rights.

Oncology Research and Development Collaboration with Genmab A/S

In May 2021, the Company entered into a License and Collaboration Agreement (the “Genmab Agreement”) with Genmab. Together, the companies will evaluate Genmab antibodies and bispecific antibody engineering technologies in combination with the Company’s ISAC technology platform, with the goal of discovering and developing next-generation bispecific ISACs for the treatment of cancer. Under this research collaboration, the companies will evaluate multiple bispecific ISAC concepts to identify up to three clinical candidates for development. Genmab will fund the research, along with the preclinical and clinical development of these candidates through initial clinical proof of concept. Under the Genmab Agreement, the Company received an upfront payment of $10.0 million. The Company determined that the Genmab Agreement is a contract with a customer and should be accounted for under ASC 606. In conjunction with the Genmab Agreement, the Company entered into a stock purchase agreement (the “Genmab SPA”) for the issuance of 821,045 shares of the Company’s common stock to Genmab for a total purchase price of $15.0 million. These contracts have been evaluated together and the consideration in excess of the fair value of the common stock of $1.4 million has been allocated to the Genmab Agreement and included in the total consideration for collaboration revenue.

In the Genmab Agreement, the Company has identified one bundled performance obligation that includes the license rights, research and development services and services associated with participation on a joint research committee. The transaction price includes the $10.0 million upfront payment, the $1.4 million allocated from the Genmab SPA, and $31.0 million of estimated variable consideration related to compensation for research and development services at the agreed upon full-time employee rate and third-party costs. Collaboration revenue is recognized over time proportionate to the costs that the Company has incurred to perform the services using an input method as a measure of progress towards satisfying the performance obligation, which is based on project hours. Compensation for the research and development services are billed in the quarter based on actual hours incurred to satisfy the performance obligation. The cumulative effect of revisions to estimated hours to complete the Company’s performance obligation will be recorded in the period in which changes are identified and amounts can be reasonably estimated. As of December 31, 2023, receivables of $0.6 million related to research and development services performed under the Genmab Agreement were recorded as part of the prepaid expenses and other current assets line item on the balance sheet. Deferred revenue allocated to the unsatisfied performance obligation is recorded as a contract liability on the balance sheet and will be recognized over time as the services are performed. As of December 31, 2023, contract liabilities totaling $6.7 million were recorded in deferred revenue with $1.0 million in current liabilities and $5.7 million in non-current liabilities on the balance sheet based on the forecasted periods of performance.

The following table presents changes in the Company’s contract liability (in thousands):


Balance at December 31, 2021	$	10,574
Addition—amount billed for research and development services		2,166
Revenue recognized		(4,242	)
Balance at December 31, 2022		8,498
Addition—amount billed for research and development services		1,896
Revenue recognized		(3,730	)
Balance at December 31, 2023	$	6,664

The Company recorded $3.7 million and $4.2 million in revenue earned during the years ended December 31, 2023 and 2022, based on services performed under the Genmab Agreement during the period. Under the Genmab Agreement, the Company will be compensated for research and development services at the agreed upon full-time employee rate and third-party costs through initial clinical proof of concept of the therapeutic candidates, which also represents the period of time both parties have enforceable rights and obligations. As such, the accounting term of the Genmab Agreement is considered to terminate upon completion of the initial clinical proof of concept of the therapeutic candidates, after which both parties can exercise their respective program opt-in rights. The Genmab Agreement includes optional additional items which will be accounted for as contract modifications after initial clinical proof of concept of the therapeutic candidates. With respect to each candidate for which a party has exercised its program opt-in rights and has exclusive global rights, the other party is eligible to receive potential development and sales-based milestone payments and tiered royalties, subject to certain customary reductions, the amount of all such considerations will vary based on the market potential of the applicable territory for which such party has exercised its program opt-in rights. Under the Genmab Agreement, the Company is eligible to receive total potential milestone payments of up to $125.0 million in development milestones and $160.0 million in sale milestones per therapeutic candidate exclusively developed and commercialized by Genmab, along with tiered royalties at rates from a single digit to mid-teens percentage based on net sales of each therapeutic candidate. However, given the current phase of development of therapeutic candidates under the Genmab Agreement, the Company cannot estimate the probability or timing of achieving these milestones, and, therefore, have excluded all milestone and royalty payments from the transaction prices of the agreement.

Oncology Research and Development Collaboration with Innovent Biologics, Inc.

In August 2021, the Company entered into a License and Collaboration Agreement (the “Innovent Agreement”) with Innovent. Together, the companies will leverage Innovent’s proprietary therapeutic antibody portfolio and antibody discovery capability against undisclosed oncology targets in combination with the Company’s advanced ISAC technology and myeloid biology expertise to create up to three new candidates for cancer treatments. Innovent will fund the initial research, along with the preclinical and clinical development of these candidates through initial clinical proof of concept. Under the Innovent Agreement, the Company received an upfront payment of $5.0 million. The Company determined that the Innovent Agreement is a contract with a customer and should be accounted for under ASC 606. In conjunction with the Innovent Agreement, the Company entered into a stock purchase agreement with Innovent (the “Innovent SPA”) which contains both a put option and call option allowing Innovent and the Company to respectively initiate a market value purchase and sale of the Company’s common stock, for an aggregate investment of up to $10.0 million by Innovent, subject to certain share price limitations. The Innovent Agreement and Innovent SPA have been evaluated together and since the options may be exercised at market value by either party, no consideration from the Innovent SPA has been allocated to the Innovent Agreement and included in the total consideration for collaboration revenue. Both options expired unexercised on May 25, 2022.

In the Innovent Agreement, the Company has identified one bundled performance obligation that includes the license rights, research and development services and services associated with participation on a joint research committee. The transaction price includes the $5.0 million upfront payment and up to $8.0 million of estimated variable consideration related to compensation for research and development services at the agreed upon full-time employee rate and third-party costs. Collaboration revenue is recognized over time proportionate to the costs that the Company has incurred to perform the services using an input method as a measure of progress towards satisfying the performance obligation, which is based on project hours. Amounts are billed based on estimated variable consideration in the quarter ahead of performance and are trued up on the subsequent quarter’s invoice following the work performed. The cumulative effect of revisions to estimated hours to complete the Company’s performance obligation will be recorded in the period in which changes are identified and amounts can be reasonably estimated. As of December 31, 2023, receivables of $0.7 million related to research and development services performed under the Innovent Agreement were recorded as part of the prepaid expenses and other current assets line item on the balance sheet. Deferred revenue allocated to the unsatisfied performance obligation is recorded as a contract liability on the balance sheet and will be recognized over time as the services are performed. As of December 31, 2023, contract liabilities totaling $3.1 million were recorded in deferred revenue with $0.6 million in current liabilities and $2.5 million in non-current liabilities on the balance sheet based on the forecasted periods of performance.

The following table presents changes in the Company’s contract liability (in thousands):


Balance at December 31, 2021	$	5,000
Addition—amount billed for research and development services		1,444
Revenue recognized		(1,487	)
Balance at December 31, 2022		4,957
Addition—amount billed for research and development services		2,330
Revenue recognized		(4,145	)
Balance at December 31, 2023	$	3,142

The Company recorded $4.1 million and $1.5 million in revenue earned during the years ended December 31, 2023 and 2022, based on services performed under the Innovent Agreement during the period. Under the Innovent Agreement, the Company will be compensated for research and development services at the agreed upon full-time employee rate and third-party costs through initial clinical proof of concept of the therapeutic candidates, which also represents the period of time both parties have enforceable rights and obligations. As such, the accounting term of the Innovent Agreement is considered to terminate upon completion of the initial clinical proof of concept of the therapeutic candidates, after which both parties can exercise their respective license rights. The Innovent Agreement includes license options exercisable by each party to exclusively develop, manufacture and commercialize each candidate in a specific territory, which will be accounted for as contract modifications after the initial clinical proof of concept of the therapeutic candidates and the parties have exercised their respective license options with respect to each candidate. With respect to each candidate for which a party has exercised its license option, the other party is eligible to receive a license option exercise fee, potential development and sales-based milestone payments and tiered royalties, subject to certain customary reductions, the amount of all such considerations will vary based on the market potential of the applicable territory for which such party has exercised its license option. Under the Innovent Agreement, the Company is eligible to receive up to $28.5 million in potential license option exercise fee, $111.5 million in development milestone payment, $297.5 million in sales-based milestone payments, and tiered royalties at rates from a mid-single digit to low-teens percentage based on net sales, subject to certain customary reductions, for therapeutic candidates exclusively developed and commercialized by Innovent in specific territories. However, given the current phase of development of therapeutic candidates under the Innovent Agreement, the Company cannot estimate the probability or timing of achieving these milestones, and, therefore, have excluded all license option exercise fee, milestone and royalty payments from the transaction prices of the agreement.

Oncology Clinical Trial Collaboration and Supply Agreement with Bristol-Myers Squibb

In September 2021, the Company entered into a clinical collaboration and supply agreement with Bristol-Myers Squibb Company (“BMS”) to study trastuzumab imbotolimod in combination with BMS’s PD-1 checkpoint inhibitor nivolumab, for the treatment of HER2-expressing solid tumors (the “BMS Agreement”). Under the BMS Agreement, BMS granted the Company a non-exclusive, non-transferable, royalty-free license (with a right to sublicense) under its intellectual property to use nivolumab in a clinical trial for a combination therapy of nivolumab and the Company’s proprietary compound, trastuzumab imbotolimod, and has agreed to supply nivolumab at no cost to the Company and the Company will sponsor, fund and conduct the initial Phase 1/2 clinical trial in accordance with an agreed-upon protocol. Both parties will own the study data produced in the clinical trial, other than study data related solely to nivolumab, which will belong solely to BMS, or study data related solely to trastuzumab imbotolimod, which will belong solely to the Company. The parties may conduct additional clinical trials on the combined therapy which may be sponsored and funded by one party, or jointly funded. Given the terms of the BMS Agreement, the Company has concluded that it is not within the scope of ASC 808 or ASC 606. Any relevant costs arising from the clinical trial will be expensed as incurred and recorded in research and development expenses. The Company initiated the clinical trial for the combination therapy of nivolumab and trastuzumab imbotolimod in the fourth quarter of 2021.

Clinical Supply Agreement with F. Hoffmann-La Roche Ltd

In September 2022, the Company entered into a clinical supply agreement with Roche to study trastuzumab imbotolimod in combination with Roche’s pertuzumab (Perjeta®), a compound approved for the treatment of HER2-positive breast cancer (the "Roche Agreement"). Under the Roche Agreement, Roche granted the Company a non-exclusive, non-sublicenseable, royalty-free license under its intellectual property to use pertuzumab in a clinical trial for a combination therapy of pertuzumab and the Company's proprietary compound, trastuzumab imbotolimod, and has agreed to supply pertuzumab at no cost to the Company. The Company will sponsor, fund and conduct the initial Phase 2 clinical trial in accordance with an agreed-upon protocol. Both parties will own the study data produced in the clinical trial, other than study data related solely to pertuzumab, which will belong solely to Roche, or study data related solely to trastuzumab imbotolimod, which will belong solely to the Company. The parties may conduct additional clinical trials on the combined therapy which may be sponsored and funded by one party, or jointly funded. Given the terms of the Roche Agreement, the Company has concluded that it is not within the scope of ASC 808 or ASC 606. Any relevant costs arising from the clinical trial will be expensed as incurred and recorded in research and development expenses.

Net Loss Per Share - Computation of Basic and Diluted Net Loss per Share Attributable to Common Stockholders, which excludes Shares Legally Outstanding (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Numerator:
Net loss	$ (69,197)	$ (88,098)
Denominator:
Weighted average common shares outstanding	37,904,318	37,574,757
Common stock outstanding subject to repurchase related to unvested early exercised stock options and restricted stock awards	(92,334)	(216,332)
Weighted average common shares outstanding - basic	37,811,984	37,358,425
Weighted average common shares outstanding - diluted	37,811,984	37,358,425
Net loss per share attributable to common stockholders, basic	$ (1.83)	$ (2.36)
Net loss per share attributable to common stockholders, diluted	$ (1.83)	$ (2.36)

- Definition

The amount of net income (loss) for the period per each share of common stock or unit outstanding during the reporting period.

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+ Details

Income Taxes - Summary of Significant Components of Deferred Tax Assets and Liabilities for Federal and State Income Taxes (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Deferred tax assets:
Net operating loss carryforward	$ 47,331	$ 42,564
Research tax credits	9,465	6,928
Capitalized research and development expenses	21,848	13,250
Lease liability	5,736	6,600
Stock-based compensation	2,645	1,953
Reserves and accruals	2,493	3,787
Intangible assets	145	168
Total deferred tax assets	89,663	75,250
Less valuation allowance	(83,680)	(68,192)
Net deferred tax assets	5,983	7,058
Deferred tax liabilities:
Right-of-use assets	(5,424)	(6,443)
Property and equipment	(461)	(472)
Prepaid assets	(98)	(143)
Total deferred tax assets	(5,983)	(7,058)
Net deferred tax assets	$ 0	$ 0

Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2023

Share-Based Payment Arrangement [Abstract]

Summary of Stock Option Activity

The following table summarizes the stock option activity during the year ended December 31, 2023:


	Options Outstanding			Weighted-average Exercise Price		Weighted-average Remaining Contractual Term (in years)		Weighted-average Grant Date Fair Value		Aggregate Intrinsic Value (in thousands)
Outstanding at December 31, 2022		7,225,635		$	5.55		8.0			$	—
Granted		4,095,780		$	1.46			$	1.11
Exercised		(4,501	)	$	1.39
Canceled/forfeited		(610,373	)	$	3.32
Outstanding at December 31, 2023		10,706,541		$	4.12		7.7			$	12
Exercisable at December 31, 2023		6,189,313		$	4.82		7.0			$	—
Vested or expected to vest at December 31, 2023		10,706,541		$	4.12		7.7			$	12

Summary of Fair Value of Option Grant Estimated Using Black-Scholes Option-Pricing Model

The fair value of each option grant was estimated on the date of grant using the Black-Scholes option-pricing model with the following assumptions:


	Years Ended December 31,
	2023				2022
Expected volatility		92-94		%	88-93		%
Risk-free interest rate		3.5-4.9		%	1.7-4.3		%
Expected option life (in years)		5.2-6.1			5.0-6.1
Expected dividend yield			0.0	%		0.0	%
Fair value per share of common stock		$0.77-$1.47			$0.98-$2.75

Summary of Components of Stock-Based Compensation Expense Recognized

The following table summarizes the components of stock-based compensation expense recognized in the Company’s statement of operations and comprehensive loss (in thousands):


	Years Ended December 31,
	2023		2022
Research and development	$	3,702	$	4,109
General and administrative		5,521		5,467
Total	$	9,223	$	9,576

Summary of Restricted Stock Awards Activity

The following table summarizes the activity of the restricted stock awards during the year ended December 31, 2023:


	RSU Outstanding			Weighted-average Grant Date Fair Value
Outstanding at December 31, 2022		121,867		$	4.51
Granted		—
Vested		(58,034	)	$	4.51
Canceled/forfeited		(11,300	)	$	4.51
Outstanding at December 31, 2023		52,533		$	4.51

Commitment and Contingencies

12 Months Ended

Dec. 31, 2023

Commitments and Contingencies Disclosure [Abstract]

Commitments and Contingencies

7. Commitments and Contingencies

Leases

The Company has operating leases for its corporate office, laboratory and vivarium space in Redwood City, California. On August 7, 2020, the Company executed a non-cancellable lease agreement for 71,646 square feet of space (the “Chesapeake Master Lease”), which consist of 25,956 square feet under an existing lease and 45,690 square feet of additional space, for its corporate office, laboratory and vivarium space in Redwood City, California. The Chesapeake Master Lease has an initial term of ten years from the commencement date, with an option to extend the lease for an additional eight-year term. The Chesapeake Master Lease contains rent escalation, and the Company is also responsible for certain operating expenses and taxes throughout the lease term. In addition, the Company is entitled to up to $4.8 million of tenant improvement allowance, which was paid directly by the landlord to various vendors. Upon execution of the non-cancellable lease agreement, the Company took control of 10,000 square feet of space, which was subleased as further described below. The remaining 35,690 square feet of additional office, laboratory and vivarium space commenced in June 2021.

In connection with the execution of the Chesapeake Master Lease, the Company entered into two operating lease agreements to sublease portions of the premises to two unrelated third parties. The first sublease agreement, to sublease 10,000 square feet, commenced in August 2020 and expired on August 31, 2022. The second sublease agreement, to sublease 10,500 square feet, commenced in June 2021 and expired on July 31, 2023. In August 2022, the second sublease agreement was amended to expand the subleased premises to 11,655 square feet in the first year and further increase to 13,743 square feet in the second year. In addition, the expiration date of the second sublease was also amended to the expiration date of the Chesapeake Master Lease. The subtenant has an early termination option with the early termination date no earlier than September 30, 2024, and no option to extend the sublease term. Rent for the second sublease is subject to scheduled annual increases and the subtenant is responsible for certain operating expenses and taxes throughout the term under the sublease agreement. Sublease income under the two sublease agreements was approximately $0.8 million for each of the years ended December 31, 2023 and 2022.

At December 31, 2023 and 2022, we have no leases accounted for as finance right-of-use lease.

The weighted-average remaining lease term and discount rate related to the Company’s lease liabilities as of December 31, 2023 were 6.7 years and 11.1%, respectively, for the operating leases. The weighted-average remaining lease term and discount rate related to the Company’s lease liabilities as of December 31, 2022 were 7.4 years and 11.0%, respectively, for the operating leases. The Company lease discount rates are based on estimates of its incremental borrowing rate, as the discount rates implicit in the Company’s leases cannot be readily determined. As the Company does not have any outstanding debt, the Company estimates the incremental borrowing rate based on its estimated credit rating and available market information.

Cash required as security for our operation leases is secured by a letter of credit on behalf of the lessor in the amount of approximately $1.6 million and is recorded as restricted cash on the balance sheet as of December 31, 2023 and 2022.

The components of lease expense were as follows (in thousands):


	Years Ended December 31,
	2023		2022
Total operating lease cost	$	4,480	$	4,346

Supplemental cash flow information related to cash paid for amounts included in the measurement of lease liabilities was as follows (in thousands):


	Years Ended December 31,
	2023		2022
Operating cash flows from operating leases	$	4,726	$	4,660

The following is a schedule by year for future maturities of the Company’s operating lease liabilities and sublease income to be received as of December 31, 2023 (in thousands):



	Operating Leases			Sublease Income
2024	$	4,886		$	540
2025		4,340			—
2026		3,484			—
2027		3,602			—
2028		3,724			—
Thereafter		9,514			—
Total lease payments		29,550			540
Less interest		(9,331	)		—
Total	$	20,219			540

Supply Agreement

The Company has entered into a supply agreement with a contract manufacturer pursuant to which the Company may be required to pay milestone payments upon the achievement of specified regulatory milestones. The agreement is cancellable by the Company upon delivering the appropriate prior written notice. At December 31, 2023, potential future milestone payments under this agreement were up to $2.0 million.

Guarantees and Indemnifications

In the normal course of business, the Company enters into agreements that contain a variety of representations and provide for general indemnification. The Company’s exposure under these agreements is unknown because it involves claims that may be made against the Company in the future. To date, the Company has not paid any claims or been required to defend any action related to its indemnification obligations. As of December 31, 2023, the Company does not have any material indemnification claims that were probable or reasonably possible and consequently has not recorded related liabilities.

Other Commitments

The Company enters into agreements in the normal course of business, including with contract research organizations for clinical trials, contract manufacturing organizations for certain manufacturing services, and vendors for preclinical studies and other services and products for operating purposes, which are generally cancelable upon written notice.

Legal Proceedings

The Company is subject to claims and assessments from time to time in the ordinary course of business but is not aware of any such matters, individually or in the aggregate, that will have a material adverse effect on the Company’s financial position, results of operations or cash flows.

Balance Sheet Components (Tables)

12 Months Ended

Dec. 31, 2023

Balance Sheet Related Disclosures [Abstract]

Property and Equipment, Net

Property and equipment, net, consist of the following (in thousands):


	December 31,
	2023			2022
Laboratory equipment	$	10,038		$	9,738
Office equipment		386			358
Leasehold improvements		285			272
Total property and equipment		10,709			10,368
Less accumulated depreciation and amortization		(5,752	)		(3,915	)
Total	$	4,957		$	6,453

Prepaids and Other Current Assets and Other Non-current Assets

Prepaids and Other Current Assets and Other Non-current Assets, consist of the following (in thousands):


	December 31,
	2023		2022
Prepaids and other current assets:
Cloud computing arrangement implementation costs	$	178	$	—
Other prepaids and other current assets		3,341		3,858
Prepaids and other current assets		3,519		3,858
Other non-current assets
Cloud computing arrangement implementation costs - non-current		371		—
Other non-current assets		1,450		1,028
Other non-current assets		1,821		1,028

Accrued Expenses and Other Current Liabilities

Accrued expenses and other current liabilities consist of the following (in thousands):


	December 31,
	2023		2022
Accrued research and development	$	6,092	$	9,373
Accrued compensation		5,820		4,804
Accrued other		574		963
Total	$	12,486	$	15,140

Stock-Based Compensation - Summary of Fair Value of Option Grant Estimated Using Black-Scholes Option-Pricing Model (Details) - $ / shares	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected volatility, Minimum	92.00%	88.00%
Expected volatility, Maximum	94.00%	93.00%
Risk-free interest rate, Minimum	3.50%	1.70%
Risk-free interest rate, Maximum	4.90%	4.30%
Expected dividend yield	0.00%	0.00%
Minimum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected option life (in years)	5 years 2 months 12 days	5 years
Fair value per share of common stock	$ 0.77	$ 0.98
Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected option life (in years)	6 years 1 month 6 days	6 years 1 month 6 days
Fair value per share of common stock	$ 1.47	$ 2.75

Commitments and Contingencies - Additional Information (Details)		1 Months Ended		12 Months Ended
	Aug. 07, 2020 USD ($) ft²	Aug. 31, 2022 ft²	Jun. 30, 2021 ft²	Dec. 31, 2023 USD ($) ft²	Dec. 31, 2022 USD ($)
Commitments And Contingencies [Line Items]
Operating lease right-of-use assets \| $				$ 19,120,000	$ 22,072,000
Operating lease liabilities \| $				20,219,000
Sublease income \| $				$ 540,000
Weighted-average remaining lease term				6 years 8 months 12 days	7 years 4 months 24 days
Weighted-average discount rate				11.10%	11.00%
Cash collateral of operation leases recorded as restricted cash \| $				$ 1,765,000	$ 1,565,000
Maximum
Commitments And Contingencies [Line Items]
Potential future milestone payments \| $				$ 2,000,000
Chesapeake Master Lease
Commitments And Contingencies [Line Items]
Operating lease, area of property available \| ft²	71,646
Operating lease, area of property, extension space available \| ft²	25,956
Operating lease, area of property, additional space available \| ft²	45,690
Operating lease, initial term of contract	10 years
Operating lease, option to extend	true
Operating lease, extended additional term	8 years
Tenant improvement allowance \| $	$ 4,800,000
Operating lease, area of property subleased \| ft²	10,000
Operating lease, area of property, additional space remaining \| ft²			35,690
Sublease, area of property leased \| ft²	10,000	11,655
Sublease expiration date	Aug. 31, 2022			Jul. 31, 2023
Sublease, area of property expected to be leased \| ft²				10,500
Increase decrease in operating lease sublease area of property leased \| ft²		13,743
Operating sublease, option to extend, description				The subtenant has an early termination option with the early termination date no earlier than September 30, 2024, and no option to extend the sublease term
Operating sublease, option to extend		false
Sublease income \| $				$ 800,000	800,000
Cash collateral of operation leases recorded as restricted cash \| $				$ 1,600,000	$ 1,600,000
Chesapeake Master Lease \| Maximum
Commitments And Contingencies [Line Items]
Sublease expiration date		Sep. 30, 2024

Stock-Based Compensation

12 Months Ended

Dec. 31, 2023

Share-Based Payment Arrangement [Abstract]

Stock-Based Compensation

9. STOCK-BASED COMPENSATION

2021 Equity Incentive Plan and 2021 Employee Stock Purchase Plan

In January 2021, the Company’s board of directors adopted the 2021 Equity Incentive Plan (the “2021 Plan”) and the Company’s stockholders approved the 2021 Plan. The 2021 Plan authorized issuance of up to 8,075,000 shares of common stock and stock awards granted under the 2021 Plan vest at the rate specified in the stock option agreement and shall have terms no more than ten years from the date of grant. The terms and conditions governing the stock awards under the 2021 Plan are at the sole discretion of the board of directors. In addition, the number of shares of common stock reserved for issuance under the 2021 Plan will automatically increase on the first day of January 1 of each calendar year that commences after the 2021 Plan becomes effective and continuing through and including January 1, 2031, in an amount equal to 5% of the total number of shares of the Company’s common stock outstanding on December 31, or a lesser number of shares determined by the Company's board of directors or compensation committee. As a result, common stock reserved for issuance under the 2021 Plan was increased by 1,889,895 shares and 1,869,984 shares on January 1, 2023 and 2022, respectively.

In addition, in January 2021, the Company’s board of directors and stockholders adopted the 2021 Employee Stock Purchase Plan (the “ESPP”). The ESPP authorized issuance of up to 420,000 shares of common stock and permits participants to purchase common stock through payroll deductions of up to 15% of their eligible compensation. Employees purchase shares of common stock at a price per share equal to 85% of the lower of the fair market value at the start or end of the six-month purchase periods within the two-year offering period. In addition, the number of shares of common stock reserved for issuance under the ESPP will automatically increase on January 1 of each calendar year that commences after the ESPP becomes effective and continuing through and including January 1, 2031, by the lesser of (1) 1% of the total number of shares of the Company's common stock outstanding on December 31 of the preceding calendar year, (2) 840,000 shares, and (3) a number of shares determined by the Company's board of directors. As a result, common stock reserved for issuance under the ESPP was increased by 377,979 shares on January 1, 2023. During the year ended December 31, 2023, 254,169 shares were issued under the ESPP.

Performance and Service-Based Stock Options

In September 2020, the compensation committee of the Company’s board of directors granted 526,018 options to employees that would commence vesting upon the closing of the Series C-2 financing and generally vest monthly over 48 months (the “Performance Awards”). The Company recognizes expense based on the fair value of the Performance Awards over the estimated service period (under the graded vesting method) to the extent the achievement of the related performance criteria is estimated to be probable. The Company determined that the financing milestone was achieved during January 2021. Accordingly, the Company recognized stock-based compensation expenses related to the Performance Awards of approximately $0.1 million and $0.3 million for the years ended December 31, 2023 and 2022, respectively. The weighted-average grant date fair value of the Performance Awards was $3.24 per share.

The following table summarizes the stock option activity during the year ended December 31, 2023:


	Options Outstanding			Weighted-average Exercise Price		Weighted-average Remaining Contractual Term (in years)		Weighted-average Grant Date Fair Value		Aggregate Intrinsic Value (in thousands)
Outstanding at December 31, 2022		7,225,635		$	5.55		8.0			$	—
Granted		4,095,780		$	1.46			$	1.11
Exercised		(4,501	)	$	1.39
Canceled/forfeited		(610,373	)	$	3.32
Outstanding at December 31, 2023		10,706,541		$	4.12		7.7			$	12
Exercisable at December 31, 2023		6,189,313		$	4.82		7.0			$	—
Vested or expected to vest at December 31, 2023		10,706,541		$	4.12		7.7			$	12

The intrinsic value of options exercised was $2,000 and $45,000 during the year ended December 31, 2023 and 2022, respectively. The fair value of options vested was $2.1 million and $7.9 million during the years ended December 31, 2023 and 2022, respectively. As of December 31, 2023, there was approximately $9.7 million of unrecognized stock-based compensation related to unvested stock options, which the Company expects to recognize over a weighted-average period of 1.8 years.

The fair value of each option grant was estimated on the date of grant using the Black-Scholes option-pricing model with the following assumptions:


	Years Ended December 31,
	2023				2022
Expected volatility		92-94		%	88-93		%
Risk-free interest rate		3.5-4.9		%	1.7-4.3		%
Expected option life (in years)		5.2-6.1			5.0-6.1
Expected dividend yield			0.0	%		0.0	%
Fair value per share of common stock		$0.77-$1.47			$0.98-$2.75

Expected Term–The expected term of options granted represents the period of time that the options are expected to be outstanding. Due to the lack of historical exercise history, the expected term of the Company’s employee stock options has been determined utilizing the simplified method for awards that qualify as plain-vanilla options, which use the midpoint between the vesting date and the expiration date of each option.

Expected Volatility–The estimated volatility was based on the historical volatility of the common stock of a group of publicly traded companies deemed comparable to the Company.

Risk-Free Interest Rate–The risk-free interest rate is the implied yield in effect at the time of the option grant based on U.S. Treasury securities with contract maturities equal to the expected term of the Company’s stock options.

Dividend Rate–The Company has not paid any cash dividends on common stock since inception and does not anticipate paying any dividends in the foreseeable future. Consequently, an expected dividend yield of zero was used.

Fair Value of Common Stock–Determining the best estimated fair value of the Company’s common stock required significant judgment and management considered several factors, including the Company’s stage of development, equity market conditions affecting comparable public companies, significant milestones and progress of research and development efforts.

Stock-Based Compensation Expense

The following table summarizes the components of stock-based compensation expense recognized in the Company’s statement of operations and comprehensive loss (in thousands):


	Years Ended December 31,
	2023		2022
Research and development	$	3,702	$	4,109
General and administrative		5,521		5,467
Total	$	9,223	$	9,576

Restricted Stock Awards

In December 2021, the Company issued 336,000 restricted stock units under the 2021 Plan at a grant date fair value of $4.51 per share. These restricted stock awards vest in equal quarterly installments over three years, subject to the employee's continued employment with, or services to, the Company on each vesting date. Each restricted stock award represents the right to receive one share of the Company's common stock when and if the applicable vesting conditions are satisfied.

The following table summarizes the activity of the restricted stock awards during the year ended December 31, 2023:


	RSU Outstanding			Weighted-average Grant Date Fair Value
Outstanding at December 31, 2022		121,867		$	4.51
Granted		—
Vested		(58,034	)	$	4.51
Canceled/forfeited		(11,300	)	$	4.51
Outstanding at December 31, 2023		52,533		$	4.51

As of December 31, 2023, total unrecognized stock-based compensation expense relating to unvested restricted stock awards was $0.2 million and the weighted-average remaining vesting period was 1.0 years.

The aggregate intrinsic value of restricted stock award is calculated as the closing price per share of the Company’s common stock on the last trading day of the fiscal period, multiplied by the number of restricted stock awards expected to vest as of December 31, 2023. As of December 31, 2023, the aggregate intrinsic value of restricted stock awards was $59,000.

Subsequent Events	12 Months Ended
Subsequent Events	Dec. 31, 2023
Subsequent Events [Abstract]
Subsequent Events	13. Subsequent Events The Company signed an Amended and Restated Collaboration Agreement with Innovent in March 2024 (the “Amended Innovent Agreement”). Under the Amended Innovent Agreement, the Company receives worldwide rights to two ISAC programs and will be assuming all future development costs for the two ISAC programs. Innovent will manufacture the first cGMP batch of antibody and make a one-time payment to the Company of $4.7 million. Innovent is eligible to receive sales milestones payments and royalties on global net sales

Income Taxes - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Operating Loss Carryforwards [Line Items]
Current state tax provision related to state minimum taxes	$ 0	$ 0
Increase in valuation allowance	15,500,000	15,500,000
Unrecognized tax benefits, interest or penalties	0	$ 0
Federal
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	$ 205,700,000
Net operating loss carryforwards expiration year	2035
Net operating losses not subject to expiration	$ 201,300,000
Federal \| Research and Development
Operating Loss Carryforwards [Line Items]
Tax credit carryforwards			$ 2,800,000
Federal \| Research Credit Carryforwards
Operating Loss Carryforwards [Line Items]
Tax credit carryforwards	$ 9,400,000
Tax credit carryforwards expiration year	2038
State
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	$ 278,500,000
Net operating loss carryforwards expiration year	2035
State \| California
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards			$ 51,000,000
State \| Research Credit Carryforwards
Operating Loss Carryforwards [Line Items]
Tax credit carryforwards	$ 5,600,000
Tax credit carryforward expiration	indefinitely

401(K) Savings Plan - Additional Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Defined Contribution Plan Disclosure [Line Items]
Contributions made to savings plan	$ 0.6	$ 0.5
Maximum
Defined Contribution Plan Disclosure [Line Items]
Percentage of matching contributions made for eligible employees	3.00%

Net Loss Per Share - Potentially Dilutive Securities not Included in the Calculation of Diluted Net Loss per Share (Details) - shares	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potentially dilutive securities not included in the calculation of diluted net loss per share	10,759,074	7,347,502
Common Stock Options Issued and Outstanding
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potentially dilutive securities not included in the calculation of diluted net loss per share	10,706,541	7,225,635
Common Stock Outstanding Subject to Repurchase Related to Unvested Early Exercised Stock Options and Restricted Stock Awards
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potentially dilutive securities not included in the calculation of diluted net loss per share	52,533	121,867

Common Stock - Additional Information (Details) - Shelf Registration and At-The-Market Equity Offering - USD ($) $ in Millions		12 Months Ended
	Mar. 30, 2022	Dec. 31, 2023
Common Stock
Class Of Warrant Or Right [Line Items]
Common stock sold		0
Maximum
Class Of Warrant Or Right [Line Items]
Aggregate offering price	$ 250.0
Cowen and Company, LLC ("Cowen") \| Common Stock
Class Of Warrant Or Right [Line Items]
Percentage of gross proceeds from sale of common stock	3.00%
Cowen and Company, LLC ("Cowen") \| Maximum \| Common Stock
Class Of Warrant Or Right [Line Items]
Aggregate offering price	$ 75.0

Collaborations - Schedule of Changes in Contract Liability (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Ending Balance	$ 3,100
Genmab Agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Beginning Balance	8,498	$ 10,574
Addition - amount billed for research and development services	1,896	2,166
Revenue recognized	(3,730)	(4,242)
Ending Balance	6,664	8,498
Innovent Agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Beginning Balance	4,957	5,000
Addition - amount billed for research and development services	2,330	1,444
Revenue recognized	(4,145)	(1,487)
Ending Balance	$ 3,142	$ 4,957

Common Stock - Schedule of Common Stock Reserved for Future Issuance (Details) - shares	Dec. 31, 2023	Jan. 01, 2023	Jan. 01, 2022
Class Of Stock [Line Items]
Common stock reserved for issuance	11,971,397
Common Stock Options Issued and Outstanding
Class Of Stock [Line Items]
Common stock reserved for issuance	10,706,541
Common Stock Restricted Stock Awards Issued and Outstanding
Class Of Stock [Line Items]
Common stock reserved for issuance	52,533
Common Stock Available for Future Issuance under 2021 Plan
Class Of Stock [Line Items]
Common stock reserved for issuance	638,430	1,889,895	1,869,984
Common Stock Available for Future Issuance under ESPP
Class Of Stock [Line Items]
Common stock reserved for issuance	573,893	377,979

License and Equity Agreement - Additional Information (Details) - Stanford Agreement	12 Months Ended
	Dec. 31, 2023 USD ($)
License And Equity Agreement [Line Items]
Additional milestone payment	$ 200,000
Royalty payments	0
Maximum
License And Equity Agreement [Line Items]
Aggregate millstone payments	$ 400,000

Fair Value Measurements and Fair Value of Financial Instruments - Schedule of Marketable Securities Classified as Available-for-sale Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	$ 117,756	$ 184,507
Unrealized Gains	89	12
Unrealized Losses	(53)	(932)
Estimated Fair Value	117,792	183,587
Asset Backed Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	17,347	12,754
Unrealized Gains	10	11
Unrealized Losses	(15)	(99)
Estimated Fair Value	17,342	12,666
U.S. Treasury Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	43,924	54,747
Unrealized Gains	34	1
Unrealized Losses	(11)	(517)
Estimated Fair Value	43,947	54,231
Other Government Agency Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	13,371	5,009
Unrealized Losses	(15)	(29)
Estimated Fair Value	13,356	4,980
Commercial Paper
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	20,351	56,170
Unrealized Gains	4
Unrealized Losses	(10)
Estimated Fair Value	20,345	56,170
Corporate Debt Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	22,763	55,827
Unrealized Gains	41
Unrealized Losses	(2)	(287)
Estimated Fair Value	$ 22,802	$ 55,540

Fair Value Measurements and Fair Value of Financial Instruments - Schedule of Fair Values of Assets and Liabilities Measured at Fair Value on Recurring Basis (Details) - Recurring Basis - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total asset	$ 126,433	$ 190,472
Money Market Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total asset	8,641	6,885
Asset Backed Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total asset	17,342	12,666
U.S. Treasury Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total asset	43,947	54,231
Other Government Agency Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total asset	13,356	4,980
Commercial Paper
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total asset	20,345	56,170
Corporate Debt Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total asset	22,802	55,540
Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total asset	41,642	61,116
Level 1 \| Money Market Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total asset	8,641	6,885
Level 1 \| U.S. Treasury Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total asset	33,001	54,231
Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total asset	84,791	129,356
Level 2 \| Asset Backed Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total asset	17,342	12,666
Level 2 \| U.S. Treasury Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total asset	10,946
Level 2 \| Other Government Agency Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total asset	13,356	4,980
Level 2 \| Commercial Paper
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total asset	20,345	56,170
Level 2 \| Corporate Debt Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total asset	$ 22,802	$ 55,540

401(K) Savings Plan	12 Months Ended
401(K) Savings Plan	Dec. 31, 2023
Retirement Benefits [Abstract]
401(K) Savings Plan	11. 401(K) Savings Plan The Company established a defined-contribution savings plan under Section 401(k) of the Internal Revenue Code of 1986, as amended. The 401(k) Plan covers all employees who meet defined minimum age and service requirements and allows participants to defer a portion of their annual compensation on a pretax basis. Beginning in 2021, the Company makes matching contributions of up to 3% of the eligible employees’ compensation to the 401(k) plan. During the years ended December 31, 2023 and 2022, the Company made contributions to the 401(k) plan of $0.6 million and $0.5 million, respectively.

Subsequent Events - Additional Information (Details) $ in Millions	1 Months Ended
	Mar. 21, 2024 USD ($)
Subsequent Event \| Amended and Restated Collaboration Innovent Agreement
Subsequent Event [Line Items]
One-time payment receivable	$ 4.7

BALANCE SHEETS (Parenthetical) - $ / shares	Dec. 31, 2023	Dec. 31, 2022
Statement of Financial Position [Abstract]
Preferred Stock, Par or Stated Value Per Share	$ 0.00001	$ 0.00001
Preferred Stock, Shares Authorized	10,000,000	10,000,000
Preferred Stock, Shares Issued	0	0
Preferred Stock, Shares Outstanding	0	0
Common Stock, Par or Stated Value Per Share	$ 0.00001	$ 0.00001
Common stock, shares authorized	200,000,000	200,000,000
Common stock, shares, issued	38,114,606	37,797,902
Common stock, shares, outstanding	38,114,606	37,797,902

Commitments and Contingencies - Schedule by Year for Future Maturities of Operating Lease Liabilities and Sublease Income to be Received (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2023 USD ($)
Operating Leases
Operating Leases, 2024	$ 4,886
Operating Leases, 2025	4,340
Operating Leases, 2026	3,484
Operating Leases, 2027	3,602
Operating Leases, 2028	3,724
Operating Leases, Thereafter	9,514
Operating Leases, Total minimum lease payments	29,550
Less imputed interest	(9,331)
Operating lease liabilities	20,219
Sublease Income
Sublease Income, 2024	540
Total Sublease Income	540
Sublease Income, Total	$ 540

Stock-Based Compensation - Summary of Components of Stock-Based Compensation Expense Recognized (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 9,223	$ 9,576
Research and Development
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	3,702	4,109
General and Administrative
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 5,521	$ 5,467

Balance Sheet Components - Prepaids and Other Current Assets and Other Non-current Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Prepaids and other current assets:
Cloud computing arrangement implementation costs	$ 178
Other prepaids and other current assets	3,341	$ 3,858
Prepaids and other current assets	3,519	3,858
Other non-current assets
Cloud computing arrangement implementation costs - non-current	371
Other non-current assets	1,450	1,028
Other non-current assets	$ 1,821	$ 1,028

Balance Sheet Components - Property and Equipment, Net (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 10,709	$ 10,368
Less accumulated depreciation and amortization	(5,752)	(3,915)
Total	4,957	6,453
Laboratory Equipment
Property Plant And Equipment [Line Items]
Property and equipment, gross	10,038	9,738
Office Equipment
Property Plant And Equipment [Line Items]
Property and equipment, gross	386	358
Leasehold Improvements
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 285	$ 272

Balance Sheet Components - Accrued Expenses and Other Current Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Balance Sheet Related Disclosures [Abstract]
Accrued research and development	$ 6,092	$ 9,373
Accrued compensation	5,820	4,804
Accrued other	574	963
Total	$ 12,486	$ 15,140