Bolt Biotherapeutics (BOLT) 10-Q 9 Nov 23 2023 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2023	Nov. 02, 2023
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2023
Document Fiscal Year Focus	2023
Document Fiscal Period Focus	Q3
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		37,965,870
Entity Shell Company	false
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	true
Title of 12(b) Security	Common Stock, $0.00001 par value
Trading Symbol	BOLT
Security Exchange Name	NASDAQ
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 Quarterly Report	true
Document Transition Report	false

CONDENSED BALANCE SHEETS (Unaud

CONDENSED BALANCE SHEETS (Unaudited) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Current assets:
Cash and cash equivalents	$ 9,160	$ 9,244
Short-term investments	110,564	159,644
Prepaid expenses and other current assets	5,742	3,858
Total current assets	125,466	172,746
Property and equipment, net	5,266	6,453
Operating lease right-of-use assets	19,878	22,072
Restricted cash	1,765	1,565
Long-term investments	21,638	23,943
Other assets	1,342	1,028
Total assets	175,355	227,807
Current liabilities:
Accounts payable	3,682	3,594
Accrued expenses and other current liabilities	10,451	15,140
Deferred revenue	1,938	1,993
Operating lease liabilities	2,680	2,391
Total current liabilities	18,751	23,118
Operating lease liabilities, net of current portion	18,177	20,220
Deferred revenue, non-current	10,125	12,921
Other long-term liabilities	43	42
Total liabilities	47,096	56,301
Commitments and contingencies (Note 7)
Stockholders' equity (deficit):
Preferred stock, $0.00001 par value, authorized shares 10,000,000 shares authorized at September 30, 2023 and December 31, 2022 zero; shares issued and outstanding at September 30, 2023 and December 31, 2022	0	0
Common stock, $0.00001 par value; 200,000,000 shares authorized at September 30, 2023 and December 31, 2022; 37,965,870 and 37,797,902 shares issued and outstanding at September 30, 2023 and December 31, 2022, respectively	1	0
Additional paid-in capital	474,814	467,513
Accumulated other comprehensive loss	(174)	(919)
Accumulated deficit	(346,382)	(295,088)
Total stockholders' equity (deficit):	128,259	171,506
Total liabilities and stockholders' equity	$ 175,355	$ 227,807

CONDENSED BALANCE SHEETS (Una_2

CONDENSED BALANCE SHEETS (Unaudited) (Parenthetical) - $ / shares	Sep. 30, 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	37,965,870	37,797,902
Common stock, shares, outstanding	37,965,870	37,797,902

CONDENSED STATEMENTS OF OPERATI

CONDENSED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Income Statement [Abstract]
Collaboration revenue	$ 2,528	$ 2,112	$ 5,787	$ 4,318
Operating expenses:
Research and development	14,951	18,973	45,220	56,278
General and administrative	5,760	5,485	16,997	17,321
Total operating expense	20,711	24,458	62,217	73,599
Loss from operations	(18,183)	(22,346)	(56,430)	(69,281)
Other income, net
Interest income, net	1,926	587	5,136	1,180
Total other income, net	1,926	587	5,136	1,180
Net loss	(16,257)	(21,759)	(51,294)	(68,101)
Net unrealized gain (loss) on marketable securities	55	94	745	(1,388)
Comprehensive loss	$ (16,202)	$ (21,665)	$ (50,549)	$ (69,489)
Net loss per share, basic	$ (0.43)	$ (0.58)	$ (1.36)	$ (1.83)
Net loss per share, diluted	$ (0.43)	$ (0.58)	$ (1.36)	$ (1.83)
Weighted-average shares outstanding, basic	37,868,480	37,454,340	37,768,308	37,293,121
Weighted-average shares outstanding, diluted	37,868,480	37,454,340	37,768,308	37,293,121

CONDENSED STATEMENTS OF PREFERR

CONDENSED STATEMENTS OF PREFERRED STOCK AND STOCKHOLDERS' EQUITY (DEFICIT) (Unaudited) - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive 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
Vesting of restricted stock units		65,301
Issuance of common stock under employee stock purchase plan	224		224
Issuance of common stock under employee stock purchase plan, Shares		136,711
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	7,453		7,453
Unrealized loss on available-for-sale investments	(1,388)			(1,388)
Net loss	(68,101)				(68,101)
Ending Balance at Sep. 30, 2022	188,446		465,246	(1,709)	(275,091)
Ending Balance, Shares at Sep. 30, 2022		37,660,893
Beginning Balance at Jun. 30, 2022	207,968		463,103	(1,803)	(253,332)
Beginning Balance, Shares at Jun. 30, 2022		37,641,459
Vesting of restricted stock units		19,434
Stock-based compensation	2,143		2,143
Unrealized loss on available-for-sale investments	94			94
Net loss	(21,759)				(21,759)
Ending Balance at Sep. 30, 2022	188,446		465,246	(1,709)	(275,091)
Ending Balance, Shares at Sep. 30, 2022		37,660,893
Beginning Balance at Dec. 31, 2022	171,506		467,513	(919)	(295,088)
Beginning Balance, Shares at Dec. 31, 2022		37,797,902
Vesting of restricted stock units		44,901
Issuance of common stock under employee stock purchase plan	141	$ 1	140
Issuance of common stock under employee stock purchase plan, Shares		118,566
Issuance of common stock upon exercise of stock options	6		6
Issuance of common stock upon exercise of stock options,Shares		4,501
Stock-based compensation	7,155		7,155
Unrealized loss on available-for-sale investments	745			745
Net loss	(51,294)				(51,294)
Ending Balance at Sep. 30, 2023	128,259	$ 1	474,814	(174)	(346,382)
Ending Balance, Shares at Sep. 30, 2023		37,965,870
Beginning Balance at Jun. 30, 2023	142,132	$ 1	472,485	(229)	(330,125)
Beginning Balance, Shares at Jun. 30, 2023		37,950,986
Vesting of restricted stock units		14,884
Stock-based compensation	2,329		2,329
Unrealized loss on available-for-sale investments	55			55
Net loss	(16,257)				(16,257)
Ending Balance at Sep. 30, 2023	$ 128,259	$ 1	$ 474,814	$ (174)	$ (346,382)
Ending Balance, Shares at Sep. 30, 2023		37,965,870

CONDENSED STATEMENTS OF CASH FL

CONDENSED STATEMENTS OF CASH FLOWS (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022
CASH FLOWS FROM OPERATING ACTIVITIES:
Net loss	$ (51,294)	$ (68,101)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	1,387	1,204
Stock-based compensation expense	7,155	7,453
Accretion (amortization) of premium/discount on marketable securities	(3,299)	655
Non-cash lease expense	2,194	2,520
Changes in operating assets and liabilities:
Prepaid expenses and other assets	(2,198)	(713)
Accounts payable and accrued expenses	(4,601)	2,481
Operating lease liabilities	(1,754)	(1,966)
Deferred revenue	(2,851)	(2,079)
Other long-term liabilities	1	(6)
Net cash used in operating activities	(55,260)	(58,552)
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchase of property and equipment	(200)	(1,769)
Purchases of marketable securities	(132,828)	(155,345)
Maturities of marketable securities	188,257	198,541
Net cash provided by investing activities	55,229	41,427
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from issuance of common stock	147	359
Net cash provided by financing activities	147	359
Net increase (decrease) in cash	116	(16,766)
Cash, cash equivalents and restricted cash at beginning of year	10,809	28,948
Cash, cash equivalents and restricted cash at end of period	10,925	12,182
Reconciliation of cash, cash equivalents and restricted cash:
Cash and cash equivalents	9,160	10,617
Restricted cash	1,765	1,565
Total cash, cash equivalents and restricted cash	10,925	12,182
Supplemental schedule of non-cash investing and financing activities:
Purchases of property and equipment included in accounts payable and accrued liabilities		182
Deferred offering costs in accounts payable and accrued liabilities	$ 102	102
Right of use assets obtained in exchange for operating lease obligations		$ 852

Description of the Business

Description of the Business	9 Months Ended
	Sep. 30, 2023
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Description of the Business	1. Description of the Business Bolt Biotherapeutics, Inc. (the “Company”) is a clinical-stage biopharmaceutical company developing novel immunotherapies for the treatment of cancer. The Company’s pipeline candidates are built on the Company’s deep expertise in myeloid biology and cancer drug development, uniting the targeting precision of antibodies with the power of the innate and adaptive immune system to reprogram the tumor microenvironment for a productive anti-cancer response.

Summary of Significant Accounti

Summary of Significant Accounting Policies	9 Months Ended
	Sep. 30, 2023
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Basis of Presentation The accompanying unaudited condensed financial statements as of September 30, 2023 and for the three and nine months ended September 30, 2023 and 2022 have been prepared in accordance with U.S. generally accepted accounting principles (“U.S. GAAP”) for interim financial information and pursuant to applicable rules and regulations of the SEC regarding interim financial reporting. Accordingly, they do not include all of the information and notes required by U.S. GAAP for complete financial statements. These unaudited condensed financial statements include only normal and recurring adjustments and certain immaterial reclassifications, which are normal in nature, that the Company believes are necessary to a fair statement of the Company’s financial position and the results of its operations and cash flows. The balance sheet as of December 31, 2022 was derived from the audited financial statements as of that date. These interim financial results are not necessarily indicative of results to be expected for the full year or any other period. These unaudited condensed financial statements and the notes accompanying them should be read in conjunction with the Company’s Annual Report on Form 10-K for the year ended December 31, 2022 . 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, recession risks 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 its inception and anticipates continuing to incur net losses for the foreseeable future. As of September 30, 2023 , the Company had cash and cash equivalents and marketable securities of $ 141.4 million and an accumulated deficit of $ 346.4 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 Quarterly Report on Form 10-Q. In the near term, the Company's primary uses of cash will be to fund the completion of key milestones for 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. 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 condensed 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. Concentrations of Credit Risk Financial instruments that potentially subject the Company to concentration of credit risk consist of cash, cash equivalents and marketable securities. As of September 30, 2023 and December 31, 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. 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. Recent Accounting Standards 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 unaudited condensed financial statements.

Fair Value Measurements and Fai

Fair Value Measurements and Fair Value of Financial Instruments	9 Months Ended
	Sep. 30, 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 no t 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 —U no bservable 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 three and nine months ended September 30, 2023, 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- 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. There were no transfers within the hierarchy during the three and nine months ended September 30, 2023 or 2022. Marketable securities, all of which are classified as available-for-sale securities, consisted of the following at September 30, 2023 and December 31, 2022 (in thousands): September 30, 2023 Amortized Unrealized Unrealized Estimated Cost Gains Losses Fair Value Asset-backed securities $ 17,555 $ — $ ( 59 ) $ 17,496 U.S. treasury securities 45,373 1 ( 39 ) 45,335 Other government agency securities 16,754 1 ( 60 ) 16,695 Commercial paper 32,000 — — 32,000 Corporate debt securities 20,696 1 ( 21 ) 20,676 Total $ 132,378 $ 3 $ ( 179 ) $ 132,202 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 September 30, 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 September 30, 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 September 30, 2023 and December 31, 2022, respectively: September 30, 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 $ 2,200 $ ( 3 ) $ 15,296 $ ( 56 ) $ 17,496 $ ( 59 ) U.S. treasury securities 39,477 ( 8 ) 5,858 ( 30 ) 45,335 ( 38 ) Other government agency securities 5,908 ( 2 ) 10,787 ( 59 ) 16,695 ( 61 ) Corporate debt securities 1,479 ( 3 ) 19,197 ( 18 ) 20,676 ( 21 ) Total $ 49,064 $ ( 16 ) $ 51,138 $ ( 163 ) $ 100,202 $ ( 179 ) 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 September 30, 2023 and December 31, 2022, respectively, which are recorded in cash and cash equivalents line item on the Company's condensed balance sheets. The Company has not written off any accrued interest receivables for the three and nine months ended September 30, 2023. As of September 30, 2023 and December 31, 2022, the fair values of the Company’s assets, which are measured at fair value on a recurring basis, were determined using the following inputs (in thousands): September 30, 2023 Total (Level 1) (Level 2) (Level 3) Money market funds $ 7,289 $ 7,289 $ — $ — Asset-backed securities 17,496 — 17,496 — U.S. treasury securities 45,335 45,335 — — Other government agency securities 16,695 — 16,695 — Commercial paper 32,000 — 32,000 — Corporate debt securities 20,676 — 20,676 — Total $ 139,491 $ 52,624 $ 86,867 $ — 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 $ —

License and Equity Agreement

License and Equity Agreement	9 Months Ended
	Sep. 30, 2023
License And Equity Agreement [Abstract]
License and Equity Agreement	4. License and Equity Agreement License and Equity Agreement with Related Party In May 2015, the Company entered into a license agreement (as amended, the “Stanford Agreement”), with The Board of Trustees of the Leland Stanford Junior University (“Stanford”). The Stanford Agreement provides the Company exclusive license to certain inventions. As consideration, the Company issued Stanford shares of its common stock and a limited right to purchase equity in future financing. Dr. Edgar G. Engleman, a founder and member of the board of directors of the Company, who is a professor at Stanford, was issued shares of common stock as part of the Company’s Series A financing in September 2016. Additionally, the Company is required by the Stanford Agreement to make milestone payments up to an aggregate of $ 0.4 million for the first licensed product that meets certain patent issuance, clinical and regulatory milestones, and an additional milestone payment of $ 0.2 million for each additional regulatory approval. The Company also agreed in the Stanford Agreement to pay Stanford tiered royalties on the Company’s and its sublicensees’ net sales of licensed products, if any, at low single-digit percentage rates, subject to certain reductions. Dr. Engleman is entitled to receive a share of any royalties that the Company pays to Stanford under the Stanford Agreement with respect to the covered intellectual property. No royalty payments have been made to date. Effective May 10, 2023, the Company terminated a separate license agreement with Stanford entered into in June 2018, after determining it was no longer necessary. The termination did not result in any payments due to Stanford.

Balance Sheet Components

Balance Sheet Components	9 Months Ended
	Sep. 30, 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): September 30, December 31, Laboratory equipment $ 9,905 $ 9,738 Office equipment 366 358 Leasehold improvements 286 272 Total property and equipment 10,557 10,368 Less accumulated depreciation and amortization ( 5,291 ) ( 3,915 ) Total $ 5,266 $ 6,453 Depreciation expense related to property and equipment was $ 0.5 million and $ 1.4 million for the three and nine months ended September 30, 2023 , respectively, and $ 0.4 million and $ 1.2 million for the same periods in 2022, respectively. Accrued Expenses and Other Current Liabilities Accrued expenses and other current liabilities consist of the following (in thousands): September 30, December 31, Accrued research and development $ 4,708 $ 9,373 Accrued compensation 4,894 4,804 Accrued other 849 963 Total $ 10,451 $ 15,140

Collaborations

Collaborations	9 Months Ended
	Sep. 30, 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 Industries, Inc. (“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. 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 September 30, 2023 and December 31, 2022 , contract liabilities totaling $ 1.5 million at each period-end were recorded in deferred revenue in long-term liabilities on the balance sheet due to the ongoing reevaluation of the research plan and the continued assessment of program development by both parties. The outcome of this reevaluation may impact the scope and timing of such services. The Toray Agreement includes both fixed and variable considerations. 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 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 A/S (“Genmab”). Together, the companies will evaluate Genmab antibodies and bispecific antibody engineering technologies in combination with the Company’s Boltbody 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 has 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 $ 26.1 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 September 30, 2023 , receivables of $ 0.3 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 September 30, 2023 , contract liabilities totaling $ 7.2 million were recorded in deferred revenue with $ 1.2 million in current liabilities and $ 6.0 million in non-current liabilities on the balance sheet based on the forecasted periods of performance. The following table presents changes in the Company contract liability (in thousands): Balance at December 31, 2022 $ 8,498 Addition—amount billed for research and development services 1,308 Revenue recognized ( 2,607 ) Balance at September 30, 2023 $ 7,199 The Company recorded $ 0.8 million and $ 2.6 million in revenue earned during the three and nine months ended September 30, 2023 , respectively, and $ 1.4 million and $ 3.0 million for the same periods in 2022, respectively, 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 was 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, has 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 Biologics, Inc. (“Innovent”). Under the Innovent Agreement, the companies will leverage Innovent’s proprietary therapeutic antibody portfolio and antibody discovery capability against Claudin 18.2 and other undisclosed oncology targets in combination with the Company’s Boltbody 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 has determined that the Innovent Agreement is a contract with a customer and should be accounted for under ASC 606. 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 $ 7.7 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. During the third quarter of 2023, the Company revised its estimates and decreased variable consideration by $ 6.7 million. The change had an immaterial impact on our contract liability and the revenue recognized during the period. As of September 30, 2023 , receivables of $ 2.5 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 September 30, 2023 , contract liabilities totaling $ 3.4 million were recorded in deferred revenue with $ 0.8 million in current liabilities and $ 2.6 million in non-current liabilities on the balance sheet based on the forecasted periods of performance. The following table presents changes in the Company contract liability (in thousands): Balance at December 31, 2022 $ 4,957 Addition—amount billed for research and development services 1,586 Revenue recognized ( 3,180 ) Balance at September 30, 2023 $ 3,363 The Company recorded $ 1.7 million and $ 3.2 million in revenue earned during the three and nine months ended September 30, 2023 , respectively, and $ 0.7 million and $ 1.3 million for the same periods in 2022, respectively, 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 was 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 payments, $ 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, has 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 BDC-1001 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, BDC-1001, 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 BDC-1001, 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 BDC-1001 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 BDC-1001 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, BDC-1001, 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 BDC-1001, 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.

Commitment and Contingencies

Commitment and Contingencies	9 Months Ended
	Sep. 30, 2023
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	7. Commitments and Contingencies Leases On August 7, 2020, the Company executed a non-cancellable lease agreement for 71,646 square feet of space (the “Chesapeake Master Lease”) 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 $ 0.2 million and $ 0.6 million for the three and nine months ended September 30, 2023 , respectively, and $ 0.2 million and $ 0.7 million for the same periods in 2022, respectively. At September 30, 2023 and December 31, 2022, finance right-of-use leases were used to finance capital equipment such as printers or ozone generators, and are immaterial. The weighted-average remaining lease term and discount rate related to the Company’s lease liabilities as of September 30, 2023 were 6.9 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. The components of lease expense were as follows (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2023 2022 2023 2022 Total operating lease cost $ 1,120 $ 1,051 $ 3,360 $ 3,226 Supplemental cash flow information related to leases was as follows (in thousands): Nine Months Ended September 30, 2023 2022 Operating cash flows from operating leases $ 3,524 $ 3,413 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 September 30, 2023 (in thousands): Operating Leases Sublease Income 2023 $ 1,201 $ 177 2024 4,886 540 2025 4,340 — 2026 3,484 — 2027 3,602 — Thereafter 13,238 — Total minimum lease payments/sublease income 30,751 717 Less imputed interest ( 9,894 ) — Total $ 20,857 $ 717 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 September 30, 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 September 30, 2023, the Company did not have any material indemnification claims that were probable or reasonably possible and, consequently, had 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.

Common Stock

Common Stock	9 Months Ended
	Sep. 30, 2023
Equity [Abstract]
Common Stock	8. Common Stock Shelf Registration and At-The-Market Equity Offering On March 30, 2022, the Company filed a shelf registration statement on Form S-3 (the "Registration Statement"). Pursuant to the Registration Statement, the Company may offer and sell securities having an aggregate public offering price of up to $ 250.0 million. In connection with the filing of the Registration Statement, the Company also entered into a sales agreement with Cowen and Company, LLC ("Cowen"), as sales agent or principal, pursuant to which the Company may issue and sell shares of its common stock for an aggregate offering price of up to $ 75.0 million under an at-the-market (the “ATM”) offering program. Pursuant to the ATM, the Company will pay Cowen a commission rate equal to 3.0 % of the gross proceeds from the sale of any shares of common stock. The Company is not obligated to make any sales of shares of its common stock under the ATM. As of September 30, 2023 , no shares of the Company's common stock have been sold under this ATM.

Stock-Based Compensation

Stock-Based Compensation	9 Months Ended
	Sep. 30, 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 it became effective upon the execution of the underwriting agreement for the Company’s IPO. In addition, the number of shares of common stock reserved for issuance under the 2021 Plan automatically increases on the first day of January of each calendar year that commences after the 2021 Plan became 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 on January 1, 2023. 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 it became effective upon the execution of the underwriting agreement for the Company’s IPO. The 2021 ESPP 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 six-month purchase periods within the two-year offering period. In addition, the number of shares of common stock reserved for issuance under the 2021 ESPP automatically increases on January 1 of each calendar year that commences after the ESPP became 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 2021 ESPP was increased by 377,979 shares on January 1, 2023. 118,566 shares were issued under the ESPP during the nine months ended September 30, 2023 , and 136,711 shares were issued under the ESPP during the same period in 2022. 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 expense related to the Performance Awards of approximately $ 33,000 and $ 0.1 million for the three and nine months ended September 30, 2023 , respectively and $ 0.1 million and $ 0.2 million for the same periods in 2022, respectively. The weighted-average grant date fair value of the Performance Awards was $ 3.24 per share. Restricted Stock Units 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 units 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 unit represents the right to receive one share of the Company's common stock when and if the applicable vesting conditions are satisfied. 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): Three Months Ended September 30, Nine Months Ended September 30, 2023 2022 2023 2022 Research and development $ 969 $ 834 $ 2,900 $ 3,223 General and administrative 1,360 1,309 4,255 4,230 Total $ 2,329 $ 2,143 $ 7,155 $ 7,453

Net Loss Per Share

Net Loss Per Share	9 Months Ended
	Sep. 30, 2023
Earnings Per Share [Abstract]
Net Loss Per Share	10. Net Loss Per Share The following table sets forth the computation of the Company’s basic and diluted net loss per share attributable to common stockholders, which excludes shares which are legally outstanding, but subject to repurchase by the Company (in thousands, except share and per share amounts): Three Months Ended September 30, Nine Months Ended September 30, 2023 2022 2023 2022 Numerator: Net loss $ ( 16,257 ) $ ( 21,759 ) $ ( 51,294 ) $ ( 68,101 ) Denominator: Weighted average common shares outstanding 37,954,383 37,645,895 37,869,602 37,533,016 Weighted average common stock outstanding subject to repurchase related to unvested early exercised stock options and restricted stock awards ( 85,903 ) ( 191,555 ) ( 101,294 ) ( 239,895 ) Weighted average common shares outstanding - basic and 37,868,480 37,454,340 37,768,308 37,293,121 Net loss per share attributable to common stockholders, basic $ ( 0.43 ) $ ( 0.58 ) $ ( 1.36 ) $ ( 1.83 ) Potentially dilutive shares to be issued under the ESPP as of September 30, 2023 and 2022 were not included in the calculation of dilutive net loss per share because they would be anti-dilutive and were immaterial. In addition, potential dilutive securities not included in the calculation of diluted net loss per share because to do so would be anti-dilutive are as follows (in common stock equivalent shares): As of September 30, 2023 2022 Common stock options issued and outstanding 10,904,136 7,262,069 Common stock outstanding subject to repurchase related to 74,416 156,899 Total 10,978,552 7,418,968

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2023
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying unaudited condensed financial statements as of September 30, 2023 and for the three and nine months ended September 30, 2023 and 2022 have been prepared in accordance with U.S. generally accepted accounting principles (“U.S. GAAP”) for interim financial information and pursuant to applicable rules and regulations of the SEC regarding interim financial reporting. Accordingly, they do not include all of the information and notes required by U.S. GAAP for complete financial statements. These unaudited condensed financial statements include only normal and recurring adjustments and certain immaterial reclassifications, which are normal in nature, that the Company believes are necessary to a fair statement of the Company’s financial position and the results of its operations and cash flows. The balance sheet as of December 31, 2022 was derived from the audited financial statements as of that date. These interim financial results are not necessarily indicative of results to be expected for the full year or any other period. These unaudited condensed financial statements and the notes accompanying them should be read in conjunction with the Company’s Annual Report on Form 10-K for the year ended December 31, 2022 .
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, recession risks 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 its inception and anticipates continuing to incur net losses for the foreseeable future. As of September 30, 2023 , the Company had cash and cash equivalents and marketable securities of $ 141.4 million and an accumulated deficit of $ 346.4 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 Quarterly Report on Form 10-Q. In the near term, the Company's primary uses of cash will be to fund the completion of key milestones for 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.
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 condensed 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.
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. As of September 30, 2023 and December 31, 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.
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.
Recent Accounting Standards	Recent Accounting Standards 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 unaudited condensed financial statements.

Fair Value Measurements and F_2

Fair Value Measurements and Fair Value of Financial Instruments (Tables)	9 Months Ended
	Sep. 30, 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 September 30, 2023 and December 31, 2022 (in thousands): September 30, 2023 Amortized Unrealized Unrealized Estimated Cost Gains Losses Fair Value Asset-backed securities $ 17,555 $ — $ ( 59 ) $ 17,496 U.S. treasury securities 45,373 1 ( 39 ) 45,335 Other government agency securities 16,754 1 ( 60 ) 16,695 Commercial paper 32,000 — — 32,000 Corporate debt securities 20,696 1 ( 21 ) 20,676 Total $ 132,378 $ 3 $ ( 179 ) $ 132,202 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	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 September 30, 2023 and December 31, 2022, respectively: September 30, 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 $ 2,200 $ ( 3 ) $ 15,296 $ ( 56 ) $ 17,496 $ ( 59 ) U.S. treasury securities 39,477 ( 8 ) 5,858 ( 30 ) 45,335 ( 38 ) Other government agency securities 5,908 ( 2 ) 10,787 ( 59 ) 16,695 ( 61 ) Corporate debt securities 1,479 ( 3 ) 19,197 ( 18 ) 20,676 ( 21 ) Total $ 49,064 $ ( 16 ) $ 51,138 $ ( 163 ) $ 100,202 $ ( 179 ) 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	As of September 30, 2023 and December 31, 2022, the fair values of the Company’s assets, which are measured at fair value on a recurring basis, were determined using the following inputs (in thousands): September 30, 2023 Total (Level 1) (Level 2) (Level 3) Money market funds $ 7,289 $ 7,289 $ — $ — Asset-backed securities 17,496 — 17,496 — U.S. treasury securities 45,335 45,335 — — Other government agency securities 16,695 — 16,695 — Commercial paper 32,000 — 32,000 — Corporate debt securities 20,676 — 20,676 — Total $ 139,491 $ 52,624 $ 86,867 $ — 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 $ —

Balance Sheet Components (Table

Balance Sheet Components (Tables)	9 Months Ended
	Sep. 30, 2023
Balance Sheet Related Disclosures [Abstract]
Property and Equipment, Net	Property and equipment, net, consist of the following (in thousands): September 30, December 31, Laboratory equipment $ 9,905 $ 9,738 Office equipment 366 358 Leasehold improvements 286 272 Total property and equipment 10,557 10,368 Less accumulated depreciation and amortization ( 5,291 ) ( 3,915 ) Total $ 5,266 $ 6,453
Accrued Expenses and Other Current Liabilities	Accrued expenses and other current liabilities consist of the following (in thousands): September 30, December 31, Accrued research and development $ 4,708 $ 9,373 Accrued compensation 4,894 4,804 Accrued other 849 963 Total $ 10,451 $ 15,140

Collaborations (Tables)

Collaborations (Tables)	9 Months Ended
	Sep. 30, 2023
Genmab Agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Schedule of Changes in Contract Liability	The following table presents changes in the Company contract liability (in thousands): Balance at December 31, 2022 $ 8,498 Addition—amount billed for research and development services 1,308 Revenue recognized ( 2,607 ) Balance at September 30, 2023 $ 7,199
Innovent Agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Schedule of Changes in Contract Liability	The following table presents changes in the Company contract liability (in thousands): Balance at December 31, 2022 $ 4,957 Addition—amount billed for research and development services 1,586 Revenue recognized ( 3,180 ) Balance at September 30, 2023 $ 3,363

Commitment and Contingencies (T

Commitment and Contingencies (Tables)	9 Months Ended
	Sep. 30, 2023
Commitments and Contingencies Disclosure [Abstract]
Components of Lease Expense	The components of lease expense were as follows (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2023 2022 2023 2022 Total operating lease cost $ 1,120 $ 1,051 $ 3,360 $ 3,226
Supplemental Cash Flow Information Related to Leases	Supplemental cash flow information related to leases was as follows (in thousands): Nine Months Ended September 30, 2023 2022 Operating cash flows from operating leases $ 3,524 $ 3,413
Schedule by Year for Future Maturities of Operating Lease Liabilities and Sublease Income to be Received	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 September 30, 2023 (in thousands): Operating Leases Sublease Income 2023 $ 1,201 $ 177 2024 4,886 540 2025 4,340 — 2026 3,484 — 2027 3,602 — Thereafter 13,238 — Total minimum lease payments/sublease income 30,751 717 Less imputed interest ( 9,894 ) — Total $ 20,857 $ 717

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	9 Months Ended
	Sep. 30, 2023
Share-Based Payment Arrangement [Abstract]
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): Three Months Ended September 30, Nine Months Ended September 30, 2023 2022 2023 2022 Research and development $ 969 $ 834 $ 2,900 $ 3,223 General and administrative 1,360 1,309 4,255 4,230 Total $ 2,329 $ 2,143 $ 7,155 $ 7,453

Net Loss Per Share (Tables)

Net Loss Per Share (Tables)	9 Months Ended
	Sep. 30, 2023
Earnings Per Share [Abstract]
Computation of Basic and Diluted Net Loss per Share Attributable to Common Stockholders, which excludes Shares Legally Outstanding	The following table sets forth the computation of the Company’s basic and diluted net loss per share attributable to common stockholders, which excludes shares which are legally outstanding, but subject to repurchase by the Company (in thousands, except share and per share amounts): Three Months Ended September 30, Nine Months Ended September 30, 2023 2022 2023 2022 Numerator: Net loss $ ( 16,257 ) $ ( 21,759 ) $ ( 51,294 ) $ ( 68,101 ) Denominator: Weighted average common shares outstanding 37,954,383 37,645,895 37,869,602 37,533,016 Weighted average common stock outstanding subject to repurchase related to unvested early exercised stock options and restricted stock awards ( 85,903 ) ( 191,555 ) ( 101,294 ) ( 239,895 ) Weighted average common shares outstanding - basic and 37,868,480 37,454,340 37,768,308 37,293,121 Net loss per share attributable to common stockholders, basic $ ( 0.43 ) $ ( 0.58 ) $ ( 1.36 ) $ ( 1.83 )
Potentially Dilutive Securities not Included in the Calculation of Diluted Net Loss per Share	In addition, potential dilutive securities not included in the calculation of diluted net loss per share because to do so would be anti-dilutive are as follows (in common stock equivalent shares): As of September 30, 2023 2022 Common stock options issued and outstanding 10,904,136 7,262,069 Common stock outstanding subject to repurchase related to 74,416 156,899 Total 10,978,552 7,418,968

Summary of Significant Accoun_3

Summary of Significant Accounting Policies - Additional Information (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Accounting Policies [Abstract]
Cash and cash equivalents and marketable securities	$ 141,400
Accumulated deficit	$ (346,382)	$ (295,088)

Fair Value Measurements and F_3

Fair Value Measurements and Fair Value of Financial Instruments - Additional Information (Details) - USD ($)	9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022
Fair Value Disclosures [Abstract]
Fair value, asset, transfers into level 3	$ 0	$ 0
Fair value, asset, transfers out of level 3	0	0
Fair value, liability, transfers into level 3	0	0
Fair value, liability, transfers out of level 3	0	$ 0
Allowance for credit losses	0
Accrued interest receivable on available-for-sale securities	$ 300,000		$ 500,000

Fair Value Measurements and F_4

Fair Value Measurements and Fair Value of Financial Instruments - Schedule of Marketable Securities Classified as Available-for-sale Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	$ 132,378	$ 184,507
Unrealized Gains	3	12
Unrealized Losses	(179)	(932)
Estimated Fair Value	132,202	183,587
Asset Backed Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	17,555	12,754
Unrealized Gains		11
Unrealized Losses	(59)	(99)
Estimated Fair Value	17,496	12,666
U.S. Treasury Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	45,373	54,747
Unrealized Gains	1	1
Unrealized Losses	(39)	(517)
Estimated Fair Value	45,335	54,231
Other Government Agency Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	16,754	5,009
Unrealized Gains	1
Unrealized Losses	(60)	(29)
Estimated Fair Value	16,695	4,980
Commercial Paper
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	32,000	56,170
Estimated Fair Value	32,000	56,170
Corporate Debt Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	20,696	55,827
Unrealized Gains	1
Unrealized Losses	(21)	(287)
Estimated Fair Value	$ 20,676	$ 55,540

Fair Value Measurements and F_5

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	Sep. 30, 2023	Dec. 31, 2022
Debt Securities, Available-for-Sale, Unrealized Loss Position [Line Items]
Less Than 12 Months Estimated Fair Value	$ 49,064	$ 24,880
More Than 12 Months Estimated Fair Value	51,138	102,536
Total Estimated Fair Value	100,202	127,416
Less Than 12 Months Unrealized Losses	(16)	(65)
More Than 12 Months Unrealized Losses	(163)	(867)
Total Unrealized Losses	(179)	(932)
Asset Backed Securities
Debt Securities, Available-for-Sale, Unrealized Loss Position [Line Items]
Less Than 12 Months Estimated Fair Value	2,200	3,180
More Than 12 Months Estimated Fair Value	15,296	9,485
Total Estimated Fair Value	17,496	12,665
Less Than 12 Months Unrealized Losses	(3)	(5)
More Than 12 Months Unrealized Losses	(56)	(94)
Total Unrealized Losses	(59)	(99)
U.S. Treasury Securities
Debt Securities, Available-for-Sale, Unrealized Loss Position [Line Items]
Less Than 12 Months Estimated Fair Value	39,477	14,723
More Than 12 Months Estimated Fair Value	5,858	39,508
Total Estimated Fair Value	45,335	54,231
Less Than 12 Months Unrealized Losses	(8)	(28)
More Than 12 Months Unrealized Losses	(30)	(489)
Total Unrealized Losses	(38)	(517)
Other Government Agency Securities
Debt Securities, Available-for-Sale, Unrealized Loss Position [Line Items]
Less Than 12 Months Estimated Fair Value	5,908
More Than 12 Months Estimated Fair Value	10,787	4,980
Total Estimated Fair Value	16,695	4,980
Less Than 12 Months Unrealized Losses	(2)
More Than 12 Months Unrealized Losses	(59)	(29)
Total Unrealized Losses	(61)	(29)
Corporate Debt Securities
Debt Securities, Available-for-Sale, Unrealized Loss Position [Line Items]
Less Than 12 Months Estimated Fair Value	1,479	6,977
More Than 12 Months Estimated Fair Value	19,197	48,563
Total Estimated Fair Value	20,676	55,540
Less Than 12 Months Unrealized Losses	(3)	(32)
More Than 12 Months Unrealized Losses	(18)	(255)
Total Unrealized Losses	$ (21)	$ (287)

Fair Value Measurements and F_6

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	Sep. 30, 2023	Dec. 31, 2022
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total asset	$ 139,491	$ 190,472
Money Market Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total asset	7,289	6,885
Asset Backed Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total asset	17,496	12,666
U.S. Treasury Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total asset	45,335	54,231
Other Government Agency Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total asset	16,695	4,980
Commercial Paper
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total asset	32,000	56,170
Corporate Debt Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total asset	20,676	55,540
Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total asset	52,624	61,116
Level 1 | Money Market Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total asset	7,289	6,885
Level 1 | U.S. Treasury Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total asset	45,335	54,231
Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total asset	86,867	129,356
Level 2 | Asset Backed Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total asset	17,496	12,666
Level 2 | Other Government Agency Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total asset	16,695	4,980
Level 2 | Commercial Paper
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total asset	32,000	56,170
Level 2 | Corporate Debt Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total asset	$ 20,676	$ 55,540

License and Equity Agreement -

License and Equity Agreement - Additional Information (Details) - Stanford Agreement	9 Months Ended
	Sep. 30, 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

Balance Sheet Components - Prop

Balance Sheet Components - Property and Equipment, Net (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 10,557	$ 10,368
Less accumulated depreciation and amortization	(5,291)	(3,915)
Total	5,266	6,453
Laboratory Equipment
Property Plant And Equipment [Line Items]
Property and equipment, gross	9,905	9,738
Office Equipment
Property Plant And Equipment [Line Items]
Property and equipment, gross	366	358
Leasehold Improvements
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 286	$ 272

Balance Sheet Components - Addi

Balance Sheet Components - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Balance Sheet Related Disclosures [Abstract]
Depreciation expense	$ 0.5	$ 0.4	$ 1.4	$ 1.2

Balance Sheet Components - Accr

Balance Sheet Components - Accrued Expenses and Other Current Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Balance Sheet Related Disclosures [Abstract]
Accrued research and development	$ 4,708	$ 9,373
Accrued compensation	4,894	4,804
Accrued other	849	963
Total	$ 10,451	$ 15,140

Collaborations - Additional Inf

Collaborations - Additional Information (Details) - USD ($)	1 Months Ended			3 Months Ended		9 Months Ended
	Aug. 31, 2021	May 31, 2021	Mar. 31, 2019	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Contract liability				$ 3,400,000		$ 3,400,000
Collaboration revenue				2,528,000	$ 2,112,000	5,787,000	$ 4,318,000
Toray Development Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Contract liability				1,500,000		1,500,000		$ 1,500,000
Genmab Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Contract liability				7,199,000		7,199,000		8,498,000
Upfront payment received		$ 10,000,000
Contract liability, current				1,200,000		1,200,000
Contract liability, non-current				6,000,000		6,000,000
Collaboration revenue				800,000	1,400,000	2,600,000	3,000,000
Allocated from stock purchase agreement		1,400,000
Variable consideration related to reimbursements for research and development services		26,100,000
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						300,000
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				3,363,000		3,363,000		$ 4,957,000
Upfront payment received	$ 5,000,000
Contract liability, current				800,000		800,000
Contract liability, non-current				2,600,000		2,600,000
Collaboration revenue				1,700,000	$ 700,000	3,200,000	$ 1,300,000
Decreased variable consideration				$ 6,700,000
Potential future development milestone payments	111,500,000
Potential future sale milestone payments	297,500,000
Innovent Agreement | Prepaid Expenses and Other Current Assets
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Research and development services receivables						$ 2,500,000
Innovent Agreement | Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Variable consideration related to reimbursements for research and development services	7,700,000
Potential license option exercise fee	$ 28,500,000
Series T Convertible Preferred Stock | Toray Development Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Common stock sold			717,514
Consideration in excess of fair value			$ 1,500,000

Collaborations - Schedule of Ch

Collaborations - Schedule of Changes in Contract Liability (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2023 USD ($)
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Ending Balance	$ 3,400
Genmab Agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Beginning Balance	8,498
Addition - amount billed for research and development services	1,308
Revenue recognized	(2,607)
Ending Balance	7,199
Innovent Agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Beginning Balance	4,957
Addition - amount billed for research and development services	1,586
Revenue recognized	(3,180)
Ending Balance	$ 3,363

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Details)		1 Months Ended		3 Months Ended		9 Months Ended
	Aug. 07, 2020 USD ($) ft²	Aug. 31, 2022 ft²	Jun. 30, 2021 ft²	Sep. 30, 2023 USD ($)	Sep. 30, 2022 USD ($)	Sep. 30, 2023 USD ($) ft²	Sep. 30, 2022 USD ($)	Dec. 31, 2022
Commitments And Contingencies [Line Items]
Sublease income | $						$ 717,000
Weighted-average remaining lease term				6 years 10 months 24 days		6 years 10 months 24 days		7 years 4 months 24 days
Weighted-average discount rate				11.10%		11.10%		11%
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	71,646
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	10,000
Operating lease, area of property, additional space remaining			35,690
Sublease, area of property leased	10,000	11,655
Sublease expiration date	Aug. 31, 2022					Jul. 31, 2023
Increase decrease in operating lease sublease area of property leased		13,743
Sublease, area of property expected to be leased						10,500
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 | $				$ 200,000	$ 200,000	$ 600,000	$ 700,000
Chesapeake Master Lease | Maximum
Commitments And Contingencies [Line Items]
Sublease expiration date		Sep. 30, 2024

Commitments and Contingencies_2

Commitments and Contingencies - Components of Lease Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Commitments and Contingencies Disclosure [Abstract]
Total operating lease cost	$ 1,120	$ 1,051	$ 3,360	$ 3,226

Commitments and Contingencies_3

Commitments and Contingencies - Supplemental Cash Flow Information Related to Leases (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022
Commitments and Contingencies Disclosure [Abstract]
Operating cash flows from operating leases	$ 3,524	$ 3,413

Commitments and Contingencies_4

Commitments and Contingencies - Schedule by Year for Future Maturities of Operating Lease Liabilities and Sublease Income to be Received (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2023 USD ($)
Operating Leases
Operating Leases, 2023	$ 1,201
Operating Leases, 2024	4,886
Operating Leases, 2025	4,340
Operating Leases, 2026	3,484
Operating Leases, 2027	3,602
Operating Leases, Thereafter	13,238
Operating Leases, Total minimum lease payments	30,751
Less imputed interest	(9,894)
Operating lease liabilities	20,857
Sublease Income
Sublease Income, 2023	177
Sublease Income, 2024	540
Total Sublease Income	717
Sublease Income, Total	$ 717

Common Stock - Additional Infor

Common Stock - Additional Information (Details) - Shelf Registration and At-The-Market Equity Offering - USD ($) $ in Millions		9 Months Ended
	Mar. 30, 2022	Sep. 30, 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
Cowen and Company, LLC ("Cowen") | Common Stock
Class Of Warrant Or Right [Line Items]
Percentage of gross proceeds from sale of common stock	3%
Cowen and Company, LLC ("Cowen") | Maximum | Common Stock
Class Of Warrant Or Right [Line Items]
Aggregate offering price	$ 75

Stock-Based Compensation - Addi

Stock-Based Compensation - Additional Information (Details) - USD ($)		1 Months Ended			3 Months Ended		9 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Jan. 31, 2021	Sep. 30, 2020	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Jan. 01, 2023
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense							$ 7,155,000	$ 7,453,000
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					$ 33,000	$ 100,000	$ 100,000	$ 200,000
Weighted-average grant date fair value of awards							$ 3.24
Restricted Stock Units
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares issued		336,000
Vesting period		3 years
Weighted-average grant date fair value of awards		$ 4.51
Common Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Issuance of common stock under employee stock purchase plan, Shares							118,566	136,711
2021 Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock reserved for issuance									1,889,895
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%
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%
Common stock reserved for issuance					840,000		840,000		377,979
Purchase price of stock as percentage of fair market value			85%
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							118,566	136,711
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%

Stock-Based Compensation - Summ

Stock-Based Compensation - Summary of Components of Stock-Based Compensation Expense Recognized (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 2,329	$ 2,143	$ 7,155	$ 7,453
Research and Development
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	969	834	2,900	3,223
General and Administrative
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 1,360	$ 1,309	$ 4,255	$ 4,230

Net Loss Per Share - Computatio

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	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Numerator:
Net loss	$ (16,257)	$ (21,759)	$ (51,294)	$ (68,101)
Denominator:
Weighted average common shares outstanding	37,954,383	37,645,895	37,869,602	37,533,016
Weighted average common stock outstanding subject to repurchase related to unvested early exercised stock options and restricted stock awards	(85,903)	(191,555)	(101,294)	(239,895)
Weighted average common shares outstanding - basic	37,868,480	37,454,340	37,768,308	37,293,121
Weighted average common shares outstanding - diluted	37,868,480	37,454,340	37,768,308	37,293,121
Net loss per share attributable to common stockholders, basic	$ (0.43)	$ (0.58)	$ (1.36)	$ (1.83)
Net loss per share attributable to common stockholders, diluted	$ (0.43)	$ (0.58)	$ (1.36)	$ (1.83)

Net Loss Per Share - Potentiall

Net Loss Per Share - Potentially Dilutive Securities not Included in the Calculation of Diluted Net Loss per Share (Details) - shares	9 Months Ended
	Sep. 30, 2023	Sep. 30, 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	10,978,552	7,418,968
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	10,904,136	7,262,069
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	74,416	156,899