Bolt Biotherapeutics (BOLT) 10-Q 9 Nov 21 2021 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2021	Nov. 02, 2021
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2021
Document Fiscal Year Focus	2021
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		37,284,650
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, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 23,649	$ 5,542
Short-term investments	189,244	17,296
Prepaid expenses and other current assets	9,595	2,523
Total current assets	222,488	25,361
Property and equipment, net	5,631	4,083
Operating lease right-of-use assets	25,216	12,267
Finance lease right-of-use assets	21	34
Restricted cash	1,565	1,565
Deferred offering costs		2,357
Long-term investments	77,639
Other assets	990	875
Total assets	333,550	46,542
Current liabilities:
Accounts payable	5,155	1,598
Accrued expenses and other current liabilities	10,922	6,663
Deferred revenue	5,207	1,502
Operating lease liabilities	2,411	1,501
Total current liabilities	23,695	11,264
Operating lease liabilities, net of current portion	22,519	9,376
Deferred revenue, non-current	12,206
Convertible preferred stock purchase right liability, non-current		25,224
Other long-term liabilities	217	329
Total liabilities	58,637	46,193
Commitments and contingencies (Note 7)
Convertible preferred stock, $0.00001 par value; 10,000,000 shares and 20,843,367 shares authorized at September 30, 2021 and December 31, 2020, respectively; zero and 15,232,275 shares issued and outstanding at September 30, 2021 and December 31, 2020, respectively.		105,296
Stockholders' equity (deficit):
Additional paid-in capital	454,784	3,452
Accumulated other comprehensive loss	(38)
Accumulated deficit	(179,833)	(108,399)
Total stockholders' equity (deficit):	274,913	(104,947)
Total liabilities, convertible preferred stock, and stockholders' equity (deficit)	$ 333,550	$ 46,542

CONDENSED BALANCE SHEETS (Una_2

CONDENSED BALANCE SHEETS (Unaudited) (Parenthetical) - $ / shares	Sep. 30, 2021	Dec. 31, 2020
Statement Of Financial Position [Abstract]
Convertible preferred stock, par value per share	$ 0.00001	$ 0.00001
Convertible preferred stock, shares authorized	10,000,000	20,843,367
Convertible preferred stock, shares issued	0	15,232,275
Convertible preferred stock, shares outstanding	0	15,232,275
Common stock, par value per share	$ 0.00001	$ 0.00001
Common stock, shares authorized	200,000,000	198,000,000
Common stock, shares, issued	37,248,072	2,130,139
Common stock, shares, outstanding	37,248,072	2,130,139

CONDENSED STATEMENTS OF OPERATI

CONDENSED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Income Statement [Abstract]
Collaboration revenue	$ 752		$ 752	$ 231
Operating expenses:
Research and development	19,337	$ 9,540	53,171	25,493
General and administrative	4,941	2,865	13,294	6,998
Total operating expense	24,278	12,405	66,465	32,491
Loss from operations	(23,526)	(12,405)	(65,713)	(32,260)
Other income (expense), net
Interest income, net	131	24	363	187
Change in fair value of preferred stock right liability		2,380	(6,084)	2,380
Total other income (expense), net	131	2,404	(5,721)	2,567
Net loss	(23,395)	(10,001)	(71,434)	(29,693)
Net unrealized gain (loss) on marketable securities	(15)	1	(38)	2
Comprehensive loss	$ (23,410)	$ (10,000)	$ (71,472)	$ (29,691)
Net loss per share, basic and diluted	$ (0.63)	$ (4.73)	$ (2.24)	$ (14.19)
Weighted-average shares outstanding, basic and diluted	37,206,793	2,112,499	31,824,180	2,092,977

CONDENSED STATEMENTS OF CONVERT

CONDENSED STATEMENTS OF CONVERTIBLE PREFERRED STOCK AND STOCKHOLDERS' EQUITY (DEFICIT) (Unaudited) - USD ($) $ in Thousands	Total	Convertible Preferred Stock	Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Loss	Accumulated Deficit
Beginning Balance at Dec. 31, 2019	$ (45,846)			$ 1,825		$ (47,671)
Beginning Balance, Shares at Dec. 31, 2019			1,921,642
Beginning Balance at Dec. 31, 2019		$ 77,505
Beginning Balance, Shares at Dec. 31, 2019		10,070,102
Issuance of Series C-1 convertible preferred stock, net of issuance costs of $285 and convertible preferred stock purchase right liability of $13,479		$ 27,791
Issuance of Series C-1 convertible preferred stock, net of issuance costs of $285 and convertible preferred stock purchase right liability of $13,479, Shares		5,162,173
Issuance of common stock upon exercise of stock options	80			80
Issuance of common stock upon exercise of stock options,Shares			84,751
Issuance of common stock upon exercise of common stock warrants	6			6
Issuance of common stock upon exercise of common stock warrants, Shares			89,420
Vesting of early exercised options and restricted stock awards	14			14
Stock-based compensation	851			851
Unrealized gain (loss) on available-for-sale investments	2				$ 2
Net loss	(29,693)					(29,693)
Ending Balance at Sep. 30, 2020	(74,586)			2,776	2	(77,364)
Ending Balance, Shares at Sep. 30, 2020		15,232,275
Ending Balance at Sep. 30, 2020		$ 105,296
Ending Balance, Shares at Sep. 30, 2020			2,095,813
Beginning Balance at Jun. 30, 2020	(65,041)			2,321	1	(67,363)
Beginning Balance, Shares at Jun. 30, 2020			1,939,343
Beginning Balance at Jun. 30, 2020		$ 105,356
Beginning Balance, Shares at Jun. 30, 2020		15,232,275
Adjustment to issuance cost for issuance of Series C-1 convertible preferred stock		$ (60)
Issuance of common stock upon exercise of stock options	41			41
Issuance of common stock upon exercise of stock options,Shares			67,050
Issuance of common stock upon exercise of common stock warrants	6			6
Issuance of common stock upon exercise of common stock warrants, Shares			89,420
Vesting of early exercised options and restricted stock awards	5			5
Stock-based compensation	403			403
Unrealized gain (loss) on available-for-sale investments	1				1
Net loss	(10,001)					(10,001)
Ending Balance at Sep. 30, 2020	(74,586)			2,776	2	(77,364)
Ending Balance, Shares at Sep. 30, 2020		15,232,275
Ending Balance at Sep. 30, 2020		$ 105,296
Ending Balance, Shares at Sep. 30, 2020			2,095,813
Beginning Balance at Dec. 31, 2020	(104,947)			3,452		(108,399)
Beginning Balance, Shares at Dec. 31, 2020			2,130,139
Beginning Balance at Dec. 31, 2020	$ 105,296	$ 105,296
Beginning Balance, Shares at Dec. 31, 2020	15,232,275	15,232,275
Issuance of Series C-2 convertible preferred stock, net of issuance cost of $42		$ 51,902
Issuance of Series C-2 convertible preferred stock, net of issuance cost of $42, Shares		5,611,059
Reclassification of convertible preferred stock purchase right liability to equity upon issuance of convertible C-2 preferred stock		$ 31,308
Conversion of convertible preferred stock to common stock	$ 188,506			188,506
Conversion of convertible preferred stock to common stock, Shares			20,843,334
Temporary equity, Conversion of convertible preferred stock to common stock		$ (188,506)
Temporary equity, Conversion of convertible preferred stock to common stock, Shares		(20,843,334)
Issuance of common stock upon initial public offering, net of issuance costs of $22,541	241,959			241,959
Issuance of common stock upon initial public offering, net of issuance costs of $22,541, Shares			13,225,000
Issuance of common stock upon exercise of stock options	337			337
Issuance of common stock upon exercise of stock options,Shares			116,266
Issuance of common stock upon exercise of common stock warrants, Shares			82,603
Issuance of common stock related to stock purchase agreement	13,638			13,638
Issuance of common stock related to stock purchase agreement, Shares			821,045
Issuance of common stock under employee stock purchase plan	420			420
Issuance of common stock under employee stock purchase plan, Shares			29,685
Vesting of early exercised options	114			114
Stock-based compensation	6,358			6,358
Unrealized gain (loss) on available-for-sale investments	(38)				(38)
Net loss	(71,434)					(71,434)
Ending Balance at Sep. 30, 2021	$ 274,913			454,784	(38)	(179,833)
Ending Balance, Shares at Sep. 30, 2021	0
Ending Balance, Shares at Sep. 30, 2021			37,248,072
Beginning Balance at Jun. 30, 2021	$ 295,896			452,357	(23)	(156,438)
Beginning Balance, Shares at Jun. 30, 2021			37,191,005
Issuance of common stock upon exercise of stock options	185			185
Issuance of common stock upon exercise of stock options,Shares			57,067
Vesting of early exercised options	16			16
Stock-based compensation	2,226			2,226
Unrealized gain (loss) on available-for-sale investments	(15)				(15)
Net loss	(23,395)					(23,395)
Ending Balance at Sep. 30, 2021	$ 274,913			$ 454,784	$ (38)	$ (179,833)
Ending Balance, Shares at Sep. 30, 2021	0
Ending Balance, Shares at Sep. 30, 2021			37,248,072

CONDENSED STATEMENTS OF CONVE_2

CONDENSED STATEMENTS OF CONVERTIBLE PREFERRED STOCK AND STOCKHOLDERS' EQUITY (DEFICIT) (Unaudited) (Parenthetical) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Common Stock
Stock issuance cost	$ 22,541
Convertible Preferred Stock
Stock issuance cost	$ 42
Purchase right liability		$ 13,479
Series C-1 Convertible Preferred Stock
Stock issuance cost		$ 285

CONDENSED STATEMENTS OF CASH FL

CONDENSED STATEMENTS OF CASH FLOWS (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
CASH FLOWS FROM OPERATING ACTIVITIES:
Net loss	$ (71,434)	$ (29,693)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	832	390
Stock-based compensation expense	6,358	851
Accretion of premium/discount on marketable securities	1,871	(23)
Unrealized gain (loss) on marketable securities, net	(38)	2
Change in fair value of convertible preferred stock purchase rights liabilities	6,084	(2,380)
Non-cash lease expense	1,935	1,352
Changes in operating assets and liabilities:
Prepaid expenses and other assets	(7,187)	(1,544)
Accounts payable and accrued expenses	7,225	(221)
Operating lease liabilities	(831)	(3,251)
Deferred revenue	15,911	(69)
Other long-term liabilities	2	168
Net cash used in operating activities	(39,272)	(34,418)
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchase of property and equipment	(1,776)	(2,364)
Purchases of marketable securities	(283,688)	(33,229)
Maturities of marketable securities	32,230	13,297
Net cash used in investing activities	(253,234)	(22,296)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from issuance of preferred stock, net of issuance cost	51,902	41,270
Proceeds from initial public offering, net of issuance cost	244,316
Proceeds from issuance of common stock related to stock purchase agreement	13,638
Proceeds from issuance of common stock	757	216
Payment of deferred offering costs		(824)
Net cash provided by financing activities	310,613	40,662
Net increase (decrease) in cash	18,107	(16,052)
Cash, cash equivalents and restricted cash at beginning of year	7,107	35,410
Cash, cash equivalents and restricted cash at end of period	25,214	19,358
Reconciliation of cash, cash equivalents and restricted cash:
Cash and cash equivalents	23,649	17,793
Restricted cash	1,565	1,565
Total cash, cash equivalents and restricted cash	25,214	19,358
Supplemental schedule of non-cash investing and financing activities:
Vesting of early exercised options	114	20
Purchases of property and equipment included in accounts payable and accrued liabilities	591	859
Deferred offering costs in accounts payable and accrued liabilities		1,456
Right of use assets obtained in exchange for operating lease obligations	$ 14,884	$ 4,081

Description of the Business

Description of the Business	9 Months Ended
	Sep. 30, 2021
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 biotechnology company pioneering a new class of immuno-oncology agents that combine the targeting precision of antibodies with the power of both the innate and adaptive immune systems. Initial Public Offering and Related Transactions On February 9, 2021, the Company completed its initial public offering (“IPO”) pursuant to a registration statement on Form S-1 (File No. 333-252136) that was declared effective by the Securities and Exchange Commission (the “SEC”) on February 4, 2021 and sold an aggregate of 13,225,000 shares of its common stock, including the full exercise of the underwriters’ option to purchase 1,725,000 shares, at a price per share of $20.00. Proceeds from the IPO, net of underwriting discounts, commissions and offering costs, were approximately $242.0 million. In addition, each of the following occurred on February 4, 2021, in connection with the completion of the Company’s IPO: • the conversion of all outstanding shares of convertible preferred stock into 20,843,334 shares of the Company’s common stock; and • the amendment and restatement of the Company’s certificate of incorporation, authorizing 200,000,000 shares of common stock and 10,000,000 shares of undesignated preferred stock.

Summary of Significant Accounti

Summary of Significant Accounting Policies	9 Months Ended
	Sep. 30, 2021
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, 2021 and for the three and nine months ended September 30, 2021 and 2020 have been prepared in accordance with U.S. generally accepted accounting principles (“U.S. GAAP”) Reverse Stock Split On January 26, 2021, the Company amended and restated its amended and restated certificate of incorporation to effect a 1-for-7 reverse stock split of the Company’s outstanding common stock and convertible preferred stock. The par value and authorized shares of the common stock were not adjusted as a result of the reverse stock split. All issued and outstanding common stock, options to purchase common stock, early exercised options and per share amounts contained in the financial statements have been retroactively adjusted to give effect to the reverse stock split for all periods presented. Other 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 and delay or inability to obtain chemical or biological intermediates from such suppliers required for the synthesis of the Company’s product candidates, including due to the impact of the current COVID-19 pandemic, protection of intellectual property rights, litigation or claims against the Company based on intellectual property rights, regulatory clearance and market acceptance of the Company’s products. The current COVID-19 pandemic, which is impacting worldwide economic activity, poses the risk that the Company or its employees, contractors, suppliers , and other partners may be prevented from conducting business activities for an indefinite period, including due to shutdowns that may be requested or mandated by governmental authorities. The extent to which the COVID-19 pandemic will impact the Company’s business will depend on future developments that are highly uncertain and cannot be predicted at this time. The preparation of financial statements in conformity with generally accepted accounting principles requires management to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. The extent to which the COVID-19 pandemic may directly or indirectly impact the Company’s financial statements is highly uncertain and subject to change. Management considered the potential impact of the COVID-19 pandemic on its estimates and assumptions and there was not a material impact to the Company’s con densed financial statements as of and for the three and nine months ended September 30 , 2021; however, actual results could differ from those estimates and there may be changes to management’s estimates in future periods. 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. 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 and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. On an ongoing basis, the Company evaluates its estimates and assumptions, including those related to revenue recognition, the valuation of common stock, stock-based compensation, convertible preferred stock purchase right liabilities 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. Deferred Offering Costs The Company capitalized certain legal, accounting, and other third-party fees that were directly related to the Company’s IPO. After the completion of the IPO in February 2021, the total deferred offering costs of $4.0 million were offset against the proceeds from the IPO and reclassified to additional paid-in capital in the accompanying the balance sheets. At December 31, 2020, deferred offering costs totaling $2.4 million were included as non-current assets in the accompanying balance sheet. 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, 2021 and December 31, 2020, most of the Company’s funds were invested with a registered investment manager and custodied at one financial institution, with working capital kept at a separate financial institution, and account balances may at times exceed federally insured limits. Management believes that the Company is not exposed to significant credit risk due to the financial strength of the depository institutions where the funds are held. Cash and Cash Equivalents The Company considers all highly liquid investments purchased with an original maturity of three months or less to be cash equivalents. As of September 30, 2021 and December 31, 2020, cash and cash equivalents consisted primarily of bank deposits and money market funds, which were unrestricted as to withdrawal or use. 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 losses that are determined to be temporary, if any, excess cash balances primarily in corporate debt securities with strong credit ratings. Realized gains and losses are calculated on the specific identification method and recorded as interest income and were immaterial for all periods presented. Restricted Cash As of September 30, 2021 and December 31, 2020, the Company had $1.6 million of long-term restricted cash deposited with a financial institution. The restricted cash is held in separate bank accounts to support letter of credit agreements related to the Company’s facility leases that expire in 2025 and 2031 (see Note 7). Fair Value Measurements Fair value is defined as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. As such, fair value is a market-based measurement that should be determined based on assumptions that market participants would use in pricing an asset or liability. Cash and cash equivalents, restricted cash, marketable debt securities, accounts payable, accrued expenses and other current liabilities are reported at their respective fair values in our condensed balance sheets. The carrying amount of the remaining financial instruments approximate fair value due to their short-term nature. Refer to Note 3 for the methodologies and assumptions used in valuing financial instruments. 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 From time to time, new accounting standards are issued by the Financial Accounting Standards Board (the “FASB”), or other standard setting bodies and adopted by the Company as of the specified effective date. There have been no new accounting pronouncements issued nor adopted during the three and nine months ended September 30, 2021 that are of significance to the Company’s financial position or results of operations.

Fair Value Measurements and Fai

Fair Value Measurements and Fair Value of Financial Instruments	9 Months Ended
	Sep. 30, 2021
Fair Value Disclosures [Abstract]
Fair Value Measurements and Fair Value of Financial Instruments	3. Fair Value Measurements and Fair Value of Financial Instruments The authoritative guidance on fair value measurements establishes a three-tier fair value hierarchy for disclosure of fair value measurements as follows: Level 1 —Quoted prices in active markets for identical assets or liabilities. Level 2 —Observable inputs other than Level 1 prices, such as quoted prices for similar assets or liabilities, quoted prices in markets that are not active or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities. Level 3 —Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities. Assets and liabilities measured at fair value are classified in their entirety based on the lowest level of input that is significant to the fair value measurement. The Company’s assessment of the significance of a particular input to the fair value measurement in its entirety requires management to make judgments and consider factors specific to the asset or liability. During the three and nine months ended September 30, 2021 , financial assets measured on a recurring basis consist of cash invested in money market accounts , short-term investments , and long-term investments . The fair value of short-term and long-term investments is based upon market prices quoted on the last day of the fiscal period or other observable market inputs. The Company obtains pricing information from its investment manager and generally determines the fair value of investment securities using standard observable inputs, including reported trades, broker/dealer quotes, bids and/or offers. Financial liabilities measured at fair value on a recurring basis include the convertible preferred stock purchase rights liabilities described below. There were no Marketable securities, all of which are classified as available-for-sale securities, consisted of the following at September 30, 2021 and December 31, 2020 (in thousands): September 30, 2021 Amortized Unrealized Unrealized Estimated Cost Gains Losses Fair Value Asset-backed securities $ 30,490 $ 3 $ (8 ) $ 30,485 U.S. treasury securities 39,983 2 (13 ) 39,972 Other government agency securities 5,083 — (4 ) 5,079 Commercial paper 95,943 — — 95,943 Corporate debt securities 95,422 6 (24 ) 95,404 Total $ 266,921 $ 11 $ (49 ) $ 266,883 December 31, 2020 Amortized Unrealized Unrealized Estimated Cost Gains Losses Fair Value Asset-backed securities $ 2,639 $ — $ — $ 2,639 U.S. treasury securities 1,300 — — 1,300 Commercial paper 6,795 — — 6,795 Corporate debt securities 6,562 1 (1 ) 6,562 Total $ 17,296 $ 1 $ (1 ) $ 17,296 At September 30, 2021 and December 31, 2020, the fair values of the Company’s assets and liabilities, which are measured at fair value on a recurring basis, were determined using the following inputs (in thousands): September 30, 2021 Total (Level 1) (Level 2) (Level 3) Money market funds $ 20,102 $ 20,102 $ — $ — Asset-backed securities 30,485 — 30,485 — U.S. treasury securities 39,972 — 39,972 — Other government agency securities 5,079 — 5,079 — Commercial paper 95,943 — 95,943 — Corporate debt securities 95,404 — 95,404 — Total $ 286,985 $ 20,102 $ 266,883 $ — December 31, 2020 Total (Level 1) (Level 2) (Level 3) Money market funds $ 3,921 $ 3,921 $ — $ — Asset-backed securities 2,640 — 2,640 — U.S. treasury securities 1,300 1,300 — — Commercial paper 6,795 — 6,795 — Corporate debt securities 6,561 — 6,561 — Total $ 21,217 $ 5,221 $ 15,996 $ — Liabilities: Preferred stock purchase rights liability $ 25,224 $ — $ — $ 25,224 Level 3 liabilities that are measured at fair value on a recurring basis consist of the convertible preferred stock purchase right liabilities. The following table provides a summary of changes in the estimated fair value of the financial instruments using significant Level 3 inputs (in thousands): Series C Convertible Preferred Stock Purchase Right Liability Balance at December 31, 2020 $ 25,224 Change in fair value 6,084 Reclassification to equity (31,308 ) Balance at September 30, 2021 $ — The fair value of the convertible preferred stock purchase right liabilities is estimated using an income-based approach incorporating probability considerations for different scenarios. The main assumptions include the probability and timing of the tranche closing, and the estimated value of the Company’s equity at that time. In January 2021, the Company issued the additional shares of Series C-2 convertible preferred stock and accordingly, this contractual obligation was settled, and the preferred stock purchase right liability was remeasured to its fair value and reclassified to permanent equity. The fair value of the convertible preferred stock purchase right liability immediately prior to settlement was increased to $31.3 million as a result of the estimated probability of the occurrence of the second closing of Series C convertible preferred stock increasing to 80%, timing related to the occurrence of the second closing decreasing to 0.06 years and the increase in the future expected value of the Series C preferred shares to $16.25 per share.

License and Equity Agreement

License and Equity Agreement	9 Months Ended
	Sep. 30, 2021
License And Equity Agreement [Abstract]
License and Equity Agreement	4. License and Equity Agreement License and Equity Agreement with Related Party In May 2015 and June 2018, the Company entered into license agreements (the “Stanford Agreement”), as amended, with The Board of Trustees of the Leland Stanford Junior University (“Stanford”). The Stanford Agreement provides the Company exclusive licenses 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.

Balance Sheet Components

Balance Sheet Components	9 Months Ended
	Sep. 30, 2021
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, 2021 December 31, 2020 Laboratory equipment $ 7,236 $ 5,253 Leasehold improvements 132 — Office equipment 321 69 Total property and equipment 7,689 5,322 Less accumulated depreciation and amortization (2,058 ) (1,239 ) Total $ 5,631 $ 4,083 Depreciation expense related to property and equipment was $0.3 million and $0.8 million for the three and nine months ended September 30, 2021, respectively, and $0.2 million and $0.4 million for the same periods in 2020, respectively. Accrued Expenses and Other Current Liabilities Accrued expenses and other current liabilities consist of the following (in thousands): September 30, 2021 December 31, 2020 Accrued research and development $ 6,140 $ 3,199 Accrued compensation 3,945 2,885 Accrued other 837 579 Total $ 10,922 $ 6,663

Collaborations

Collaborations	9 Months Ended
	Sep. 30, 2021
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 Development 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 Development Agreement is a contract with a customer and should be accounted for under ASC 606. In conjunction with the Toray Development 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 Development agreement and included in the total consideration for collaboration revenue. In February 2021, in connection with the Company’s IPO, all outstanding shares of Series T convertible preferred stock were converted into shares of the Company’s common stock. In the Toray Development 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, which is estimated to take place by the second half of 2022. The research plan is currently being reevaluated by both parties and the outcome of this reevaluation may impact the scope and timing of such services. As of September 30, 2021 and December 31, 2020, contract liabilities totaling $1.5 million at each period-end were recorded in deferred revenue in current liabilities on the balance sheet. The Toray Development Agreement includes optional additional items which will be accounted for as contract modifications when development advances past certain milestones and the parties both exercise their opt-in rights. Oncology Research and Development Collaboration with Genmab A/S In May 2021, the Company entered into a License and Collaboration Agreement (the “Genmab Agreement”) with Genmab A/S (“Genmab”). Together, the companies will evaluate Genmab antibodies and bispecific antibody engineering technologies in combination with the Company’s ISAC technology platform, with the goal of discovering and developing next-generation bispecific ISACs for the treatment of cancer. Under this research collaboration, the companies will evaluate multiple bispecific ISAC concepts to identify up to three clinical candidates for development. Genmab will fund the research, along with the preclinical and clinical development of these candidates through initial clinical proof of concept. Under the Genmab Agreement, the Company received an upfront payment of $10.0 million. The Company determined that the Genmab Agreement is a contract with a customer and should be accounted for under ASC 606. In conjunction with the Genmab Agreement, the Company entered into a stock purchase agreement (the “Genmab SPA”) for the issuance of 821,045 shares of the Company’s common stock to Genmab for a total purchase price of $15.0 million. These contracts have been evaluated together and the consideration in excess of the fair value of the common stock of $1.4 million has been allocated to the Genmab Agreement and included in the total consideration for collaboration revenue. In the Genmab Agreement, the Company has identified one bundled performance obligation that includes the license rights, research and development services and services associated with participation on a joint research committee. The transaction price includes the $10.0 million upfront payment, the $1.4 million allocated from the Genmab SPA, and $7.9 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, 2021, receivable s 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, 2021 , contract liabilities totaling $ million were recorded in deferred revenue with $ 2.9 million in current liabilities and $ 8.0 million in non-current liabilities on the balance sheet. The Company recorded $ 0.8 million in revenue earned during the three and nine months ended September 30, 2021 , based on services performed under the Genmab Agreement during the se period s . 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 and the parties exercise their respective program opt in rights . With respect to each candidate for which a party has exercised its program opt in rights , the other party is eligible to receive potential development and sales-based milestone payments for exclusively developed and commercialized candidate 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 $ 285.0 million per therapeutic candidate exclusively developed and commercialized by Genmab, along with tiered royalties . 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”). Together, the companies will leverage Innovent’s proprietary therapeutic antibody portfolio and antibody discovery capability against undisclosed oncology targets in combination with the Company’s advanced ISAC technology and myeloid biology expertise to create up to three new candidates for cancer treatments. Innovent will fund the initial research, along with the preclinical and clinical development of these candidates through initial clinical proof of concept. Under the Innovent Agreement, the Company will receive an upfront payment of $5.0 million. The Company determined that the Innovent Agreement is a contract with a customer and should be accounted for under ASC 606. In conjunction with the Innovent Agreement, the Company entered into a stock purchase agreement with Innovent (the “Innovent SPA”) which contains both a put option and call option allowing Innovent and the Company to respectively initiate a market value purchase and sale of the Company’s common stock, for an aggregate investment of up to $10.0 million by Innovent, subject to certain share price limitations. The Innovent Agreement and Innovent SPA have been evaluated together and since the options may be exercised at market value by either party, no consideration from the Innovent SPA has been allocated to the Innovent Agreement and included in the total consideration for collaboration revenue. As of September 30, 2021, both options remain fully outstanding and expire in May 2022. In the Innovent Agreement, the Company has identified one bundled performance obligation that includes the license rights, research and development services and services associated with participation on a joint research committee. The transaction price includes the $5.0 million upfront payment and up to $7.5 million of estimated variable consideration related to compensation for research and development services at the agreed upon full-time employee rate. Collaboration revenue is recognized over time proportionate to the costs that the Company has incurred to perform the services using an input method as a measure of progress towards satisfying the performance obligation, which is based on project hours. Amounts are billed based on estimated variable consideration in the quarter ahead of performance and are trued up on the subsequent quarter’s invoice following the work performed. The cumulative effect of revisions to estimated hours to complete the Company’s performance obligation will be recorded in the period in which changes are identified and amounts can be reasonably estimated. As of September 30, 2021, receivable for the upfront payment of $5 million was recorded as part of the prepaid expenses and other current assets line item on the balance sheet. The upfront payment of $5 million was subsequently received in October 2021. 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, 2021, contract liabilities totaling $5.0 million were recorded in deferred revenue with $0.8 million in current liabilities and $4.2 million in non-current liabilities on the balance sheet. There was no revenue earned during the three and nine months ended September 30, 2021, 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-transferrable, 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 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 , which will belong solely to . 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 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. As of

Commitment and Contingencies

Commitment and Contingencies	9 Months Ended
	Sep. 30, 2021
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	7. Commitments and Contingencies Leases The Company has operating leases for its corporate office, laboratory and vivarium space in Redwood City, California. eight-year 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 will expire on July 31, 2022. The second sublease agreement, to sublease 10,500 square feet, commenced in June 2021 and will expire on July 31, 2023. Rent for both subleases are subject to scheduled annual increases and the subtenants are responsible for certain operating expenses and taxes throughout the term under the sublease agreements. The subtenants have no option to extend the sublease term. Sublease income under the two sublease agreements for the three and nine months ended September 30, 2021, was approximately $0.2 million and $0.5 million, respectively. At September 30, 2021 and December 31, 2020, finance right-of-use leases are used to finance capital equipment such as printers or ozone generators and it is immaterial. The weighted-average remaining lease term and discount rate related to the Company’s lease liabilities as of September 30, 2021 were 8.2 years and 10.9%, 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, 2020 were 6.3 years and 9.5%, 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, 2021 2020 2021 2020 Total operating lease cost $ 1,229 $ 724 $ 2,721 $ 1,919 Supplemental cash flow information related to leases was as follows (in thousands): Nine Months Ended September 30, 2021 2020 Operating cash flows from operating leases $ 1,884 $ 3,639 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, 2021 (in thousands): Operating Leases Sublease Income 2021 $ 1,228 $ 323 2022 4,994 1,048 2023 4,612 403 2024 4,772 — 2025 4,227 — Thereafter 19,709 — Total minimum lease payments/sublease income 39,542 1,774 Less imputed interest (14,612 ) — Total $ 24,930 $ 1,774 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 cancelable by the Company upon delivering the appropriate prior written notice. At September 30, 2021, 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, 2021, the Company did not have any material indemnification claims that were probable or reasonably possible and consequently had not recorded related liabilities. 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.

Convertible Preferred Stock

Convertible Preferred Stock	9 Months Ended
	Sep. 30, 2021
Equity [Abstract]
Convertible Preferred Stock	8. Convertible Preferred Stock Issuance of Series C-1 and Series C-2 Convertible Preferred Stock In June 2020, the Company entered into a preferred stock purchase agreement (the “Series C Agreement”) with existing and new investors to raise up to $93.5 million in two separate tranches. The first tranche closed in June 2020 and the Company raised $41.3 million, net of issuance costs of $0.2 million, and issued 5,162,173 shares of Series C-1 convertible preferred stock at $8.05 per share. In addition, the investors agreed to buy and the Company agreed to sell up to 5,611,065 shares of Series C-2 convertible preferred stock at a price per share of $9.2575, for potential additional gross proceeds of $51.9 million, upon the achievement of certain milestones as defined in the agreement. The commitment made by the investors to invest in the second tranche of the Series C Agreement was considered a separate freestanding financial instrument and was recorded as a Convertible Preferred Stock Purchase Right Liability in the amount of $13.5 million upon the issuance of the first tranche of the Series C-1 convertible preferred stock in June 2020. The commitment was accounted for at fair value during the period it was outstanding with changes in fair value recorded as other income (expense) in the statement of operations and comprehensive loss. During the nine months ended September 30, 2021, changes in fair value of this liability totaling $ 6.1 million have been recorded in other income (expense) in the statement of operations and comprehensive loss. In January 2021, the Company issued the additional 5,611,059 shares of Series C-2 convertible preferred stock for net proceeds of $ 51.9 million and accordingly, this contractual obligation was settled and the preferred stock purchase right liability was remeasured to its fair value and reclassified to permanent equity. In February 2021, all outstanding shares of convertible preferred stock were converted into the Company’s common stock in connection with the IPO.

Common Stock

Common Stock	9 Months Ended
	Sep. 30, 2021
Equity [Abstract]
Common Stock	9. COMMON STOCK Common Stock Warrants In July 2018, the Company issued 249,218 warrants to purchase common stock to the Series B investors in the first tranche. The warrants were deemed to be freestanding instruments indexed to the Company’s common stock and met the requirements for equity classification. The warrants had an expiration date of July 26, 2028 and were exercisable at the option of the warrant holder for $0.07 per share. In February 2021, all outstanding warrants were exercised to purchase 82,603 shares of the Company’s common stock in connection with the IPO.

Stock-Based Compensation

Stock-Based Compensation	9 Months Ended
	Sep. 30, 2021
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock-Based Compensation	10. STOCK-BASED COMPENSATION Approval of 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, 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 840,000 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 the six-month purchase periods within the two-year 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 $0.1 million and $0.7 million for the three and nine months ended September 30, 2021, respectively. The weighted-average grant date fair value of the Performance Awards was $3.24 per share. 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, 2021 2020 2021 2020 Research and development $ 1,231 $ 222 $ 3,328 $ 420 General and administrative 995 181 3,030 431 Total $ 2,226 $ 403 $ 6,358 $ 851 Early Exercise Liability Some of the options granted under the 2015 Plan may be exercised prior to the time that the options have vested, provided that such shares remain subject to repurchase until such time as they have vested. The right to repurchase these shares lapses over the vesting periods, which are generally four years. As of September 30, 2021 and December 31, 2020, there were 4,966 and 47,180, respectively, unvested shares representing an early exercise liability of approximately $ and $0.1 million , respectively . The unvested shares purchased by the employees are not deemed, for accounting purposes, to be outstanding.

Net Loss Per Share

Net Loss Per Share	9 Months Ended
	Sep. 30, 2021
Earnings Per Share [Abstract]
Net Loss Per Share	11. 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, 2021 2020 2021 2020 Numerator: Net loss $ (23,395 ) $ (10,001 ) $ (71,434 ) $ (29,693 ) Denominator: Weighted average common shares outstanding 37,214,513 1,982,788 31,837,227 1,951,427 Weighted average common stock outstanding subject to repurchase related to unvested early exercised stock options and restricted stock awards (7,720 ) (33,211 ) (24,847 ) (27,365 ) Weighted average warrants to purchase common stock — 162,922 11,800 168,915 Weighted average common shares outstanding - basic and diluted 37,206,793 2,112,499 31,824,180 2,092,977 Net loss per share attributable to common stockholders, basic and diluted $ (0.63 ) $ (4.73 ) $ (2.24 ) $ (14.19 ) Potentially 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): Three and Nine Months Ended 2021 2020 Convertible preferred stock — 15,232,275 Common stock options issued and outstanding 5,197,275 3,764,659 Common stock outstanding subject to repurchase related to unvested early exercised stock options and restricted stock awards 4,966 58,247 Total 5,202,241 19,055,181 The ESPP did not exist in 2020, and the potentially dilutive shares to be issued under the ESPP as of September 30, 2021 were not included in the calculation of dilutive net loss per share because they would be anti-dilutive and were immaterial.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2021
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying unaudited condensed financial statements as of September 30, 2021 and for the three and nine months ended September 30, 2021 and 2020 have been prepared in accordance with U.S. generally accepted accounting principles (“U.S. GAAP”)
Reverse Stock Split	Reverse Stock Split On January 26, 2021, the Company amended and restated its amended and restated certificate of incorporation to effect a 1-for-7 reverse stock split of the Company’s outstanding common stock and convertible preferred stock. The par value and authorized shares of the common stock were not adjusted as a result of the reverse stock split. All issued and outstanding common stock, options to purchase common stock, early exercised options and per share amounts contained in the financial statements have been retroactively adjusted to give effect to the reverse stock split for all periods presented.
Other Risks and Uncertainties	Other 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 and delay or inability to obtain chemical or biological intermediates from such suppliers required for the synthesis of the Company’s product candidates, including due to the impact of the current COVID-19 pandemic, protection of intellectual property rights, litigation or claims against the Company based on intellectual property rights, regulatory clearance and market acceptance of the Company’s products. The current COVID-19 pandemic, which is impacting worldwide economic activity, poses the risk that the Company or its employees, contractors, suppliers , and other partners may be prevented from conducting business activities for an indefinite period, including due to shutdowns that may be requested or mandated by governmental authorities. The extent to which the COVID-19 pandemic will impact the Company’s business will depend on future developments that are highly uncertain and cannot be predicted at this time. The preparation of financial statements in conformity with generally accepted accounting principles requires management to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. The extent to which the COVID-19 pandemic may directly or indirectly impact the Company’s financial statements is highly uncertain and subject to change. Management considered the potential impact of the COVID-19 pandemic on its estimates and assumptions and there was not a material impact to the Company’s con densed financial statements as of and for the three and nine months ended September 30 , 2021; however, actual results could differ from those estimates and there may be changes to management’s estimates in future periods. 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.
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 and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. On an ongoing basis, the Company evaluates its estimates and assumptions, including those related to revenue recognition, the valuation of common stock, stock-based compensation, convertible preferred stock purchase right liabilities 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.
Deferred Offering Costs	Deferred Offering Costs The Company capitalized certain legal, accounting, and other third-party fees that were directly related to the Company’s IPO. After the completion of the IPO in February 2021, the total deferred offering costs of $4.0 million were offset against the proceeds from the IPO and reclassified to additional paid-in capital in the accompanying the balance sheets. At December 31, 2020, deferred offering costs totaling $2.4 million were included as non-current assets in the accompanying balance sheet.
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, 2021 and December 31, 2020, most of the Company’s funds were invested with a registered investment manager and custodied at one financial institution, with working capital kept at a separate financial institution, and account balances may at times exceed federally insured limits. Management believes that the Company is not exposed to significant credit risk due to the financial strength of the depository institutions where the funds are held.
Cash and Cash Equivalents	Cash and Cash Equivalents The Company considers all highly liquid investments purchased with an original maturity of three months or less to be cash equivalents. As of September 30, 2021 and December 31, 2020, cash and cash equivalents consisted primarily of bank deposits and money market funds, which were unrestricted as to withdrawal or use.
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 losses that are determined to be temporary, if any, excess cash balances primarily in corporate debt securities with strong credit ratings. Realized gains and losses are calculated on the specific identification method and recorded as interest income and were immaterial for all periods presented.
Restricted Cash	Restricted Cash As of September 30, 2021 and December 31, 2020, the Company had $1.6 million of long-term restricted cash deposited with a financial institution. The restricted cash is held in separate bank accounts to support letter of credit agreements related to the Company’s facility leases that expire in 2025 and 2031 (see Note 7).
Fair Value Measurements	Fair Value Measurements Fair value is defined as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. As such, fair value is a market-based measurement that should be determined based on assumptions that market participants would use in pricing an asset or liability. Cash and cash equivalents, restricted cash, marketable debt securities, accounts payable, accrued expenses and other current liabilities are reported at their respective fair values in our condensed balance sheets. The carrying amount of the remaining financial instruments approximate fair value due to their short-term nature. Refer to Note 3 for the methodologies and assumptions used in valuing financial instruments.
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 From time to time, new accounting standards are issued by the Financial Accounting Standards Board (the “FASB”), or other standard setting bodies and adopted by the Company as of the specified effective date. There have been no new accounting pronouncements issued nor adopted during the three and nine months ended September 30, 2021 that are of significance to the Company’s financial position or results of operations.

Fair Value Measurements and F_2

Fair Value Measurements and Fair Value of Financial Instruments (Tables)	9 Months Ended
	Sep. 30, 2021
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, 2021 and December 31, 2020 (in thousands): September 30, 2021 Amortized Unrealized Unrealized Estimated Cost Gains Losses Fair Value Asset-backed securities $ 30,490 $ 3 $ (8 ) $ 30,485 U.S. treasury securities 39,983 2 (13 ) 39,972 Other government agency securities 5,083 — (4 ) 5,079 Commercial paper 95,943 — — 95,943 Corporate debt securities 95,422 6 (24 ) 95,404 Total $ 266,921 $ 11 $ (49 ) $ 266,883 December 31, 2020 Amortized Unrealized Unrealized Estimated Cost Gains Losses Fair Value Asset-backed securities $ 2,639 $ — $ — $ 2,639 U.S. treasury securities 1,300 — — 1,300 Commercial paper 6,795 — — 6,795 Corporate debt securities 6,562 1 (1 ) 6,562 Total $ 17,296 $ 1 $ (1 ) $ 17,296
Schedule of Fair Values of Assets and Liabilities Measured at Fair Value on Recurring Basis	At September 30, 2021 and December 31, 2020, the fair values of the Company’s assets and liabilities, which are measured at fair value on a recurring basis, were determined using the following inputs (in thousands): September 30, 2021 Total (Level 1) (Level 2) (Level 3) Money market funds $ 20,102 $ 20,102 $ — $ — Asset-backed securities 30,485 — 30,485 — U.S. treasury securities 39,972 — 39,972 — Other government agency securities 5,079 — 5,079 — Commercial paper 95,943 — 95,943 — Corporate debt securities 95,404 — 95,404 — Total $ 286,985 $ 20,102 $ 266,883 $ — December 31, 2020 Total (Level 1) (Level 2) (Level 3) Money market funds $ 3,921 $ 3,921 $ — $ — Asset-backed securities 2,640 — 2,640 — U.S. treasury securities 1,300 1,300 — — Commercial paper 6,795 — 6,795 — Corporate debt securities 6,561 — 6,561 — Total $ 21,217 $ 5,221 $ 15,996 $ — Liabilities: Preferred stock purchase rights liability $ 25,224 $ — $ — $ 25,224
Schedule of Changes in Estimated Fair Value of Financial Instruments	The following table provides a summary of changes in the estimated fair value of the financial instruments using significant Level 3 inputs (in thousands): Series C Convertible Preferred Stock Purchase Right Liability Balance at December 31, 2020 $ 25,224 Change in fair value 6,084 Reclassification to equity (31,308 ) Balance at September 30, 2021 $ —

Balance Sheet Components (Table

Balance Sheet Components (Tables)	9 Months Ended
	Sep. 30, 2021
Balance Sheet Related Disclosures [Abstract]
Property and Equipment, Net	Property and equipment, net, consist of the following (in thousands): September 30, 2021 December 31, 2020 Laboratory equipment $ 7,236 $ 5,253 Leasehold improvements 132 — Office equipment 321 69 Total property and equipment 7,689 5,322 Less accumulated depreciation and amortization (2,058 ) (1,239 ) Total $ 5,631 $ 4,083
Accrued Expenses and Other Current Liabilities	Accrued expenses and other current liabilities consist of the following (in thousands): September 30, 2021 December 31, 2020 Accrued research and development $ 6,140 $ 3,199 Accrued compensation 3,945 2,885 Accrued other 837 579 Total $ 10,922 $ 6,663

Commitment and Contingencies (T

Commitment and Contingencies (Tables)	9 Months Ended
	Sep. 30, 2021
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, 2021 2020 2021 2020 Total operating lease cost $ 1,229 $ 724 $ 2,721 $ 1,919
Supplemental Cash Flow Information Related to Leases	Supplemental cash flow information related to leases was as follows (in thousands): Nine Months Ended September 30, 2021 2020 Operating cash flows from operating leases $ 1,884 $ 3,639
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, 2021 (in thousands): Operating Leases Sublease Income 2021 $ 1,228 $ 323 2022 4,994 1,048 2023 4,612 403 2024 4,772 — 2025 4,227 — Thereafter 19,709 — Total minimum lease payments/sublease income 39,542 1,774 Less imputed interest (14,612 ) — Total $ 24,930 $ 1,774

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	9 Months Ended
	Sep. 30, 2021
Disclosure Of Compensation Related Costs Sharebased Payments [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, 2021 2020 2021 2020 Research and development $ 1,231 $ 222 $ 3,328 $ 420 General and administrative 995 181 3,030 431 Total $ 2,226 $ 403 $ 6,358 $ 851

Net Loss Per Share (Tables)

Net Loss Per Share (Tables)	9 Months Ended
	Sep. 30, 2021
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, 2021 2020 2021 2020 Numerator: Net loss $ (23,395 ) $ (10,001 ) $ (71,434 ) $ (29,693 ) Denominator: Weighted average common shares outstanding 37,214,513 1,982,788 31,837,227 1,951,427 Weighted average common stock outstanding subject to repurchase related to unvested early exercised stock options and restricted stock awards (7,720 ) (33,211 ) (24,847 ) (27,365 ) Weighted average warrants to purchase common stock — 162,922 11,800 168,915 Weighted average common shares outstanding - basic and diluted 37,206,793 2,112,499 31,824,180 2,092,977 Net loss per share attributable to common stockholders, basic and diluted $ (0.63 ) $ (4.73 ) $ (2.24 ) $ (14.19 )
Potentially Dilutive Securities not Included in the Calculation of Diluted Net Loss per Share	Potentially 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): Three and Nine Months Ended 2021 2020 Convertible preferred stock — 15,232,275 Common stock options issued and outstanding 5,197,275 3,764,659 Common stock outstanding subject to repurchase related to unvested early exercised stock options and restricted stock awards 4,966 58,247 Total 5,202,241 19,055,181

Description of the Business - A

Description of the Business - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands	Feb. 09, 2021	Feb. 04, 2021	Sep. 30, 2021	Dec. 31, 2020
Subsidiary Sale Of Stock [Line Items]
Proceeds from stock sold, net of underwriting discounts, commissions and offering costs			$ 244,316
Common stock, shares authorized		200,000,000	200,000,000	198,000,000
Preferred stock, shares authorized		10,000,000
Common Stock
Subsidiary Sale Of Stock [Line Items]
Aggregate stock sold			13,225,000
Outstanding shares of convertible preferred stock converted into common stock		20,843,334	20,843,334
IPO | Common Stock
Subsidiary Sale Of Stock [Line Items]
Aggregate stock sold	13,225,000
Sale of stock, price per share	$ 20
Proceeds from stock sold, net of underwriting discounts, commissions and offering costs	$ 242,000
Underwriters' Option | Common Stock
Subsidiary Sale Of Stock [Line Items]
Aggregate stock sold	1,725,000

Summary of Significant Accoun_3

Summary of Significant Accounting Policies - Additional Information (Details) $ in Thousands	Jan. 26, 2021	Sep. 30, 2021USD ($)	Feb. 28, 2021USD ($)	Dec. 31, 2020USD ($)
Summary Of Significant Accounting Policies [Line Items]
Deferred offering costs noncurrent				$ 2,400
Deferred offering costs to offset against proceeds from IPO			$ 4,000
Restricted cash		$ 1,565		$ 1,565
Common Stock and Convertible Preferred Stock
Summary Of Significant Accounting Policies [Line Items]
Reverse stock split		1-for-7
Reverse stock split ratio	0.142857

Fair Value Measurements and F_3

Fair Value Measurements and Fair Value of Financial Instruments - Additional Information (Details) - USD ($)	1 Months Ended	3 Months Ended		9 Months Ended
	Jan. 31, 2021	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair value, assets, level 1 to level 2 transfers		$ 0	$ 0	$ 0	$ 0
Fair value, assets, level 2 to level 1 transfers		0	0	0	0
Fair value, liabilities, level 1 to level 2 transfers		0	0	0	0
Fair value, liabilities, level 2 to level 1 transfers		0	0	0	0
Fair value, asset, transfers into level 3		0	0	0	$ 0
Fair value, asset, transfers out of level 3		0	0	0
Fair value, liability, transfers into level 3		0	0	0
Fair value, liability, transfers out of level 3		$ 0	$ 0	$ 0
Series C-2 Convertible Preferred Stock
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair value of convertible preferred stock purchase right liability	$ 31,300,000
Percentage of increase in convertible preferred stock	80.00%
Period of timing related to occurrence	21 days
Increase in future expected value of share	$ 16.25

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, 2021	Dec. 31, 2020
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	$ 266,921	$ 17,296
Unrealized Gains	11	1
Unrealized Losses	(49)	(1)
Estimated Fair Value	266,883	17,296
Asset Backed Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	30,490	2,639
Unrealized Gains	3
Unrealized Losses	(8)
Estimated Fair Value	30,485	2,639
U.S. Treasury Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	39,983	1,300
Unrealized Gains	2
Unrealized Losses	(13)
Estimated Fair Value	39,972	1,300
Other Government Agency Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	5,083
Unrealized Losses	(4)
Estimated Fair Value	5,079
Commercial Paper
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	95,943	6,795
Estimated Fair Value	95,943	6,795
Corporate Debt Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	95,422	6,562
Unrealized Gains	6	1
Unrealized Losses	(24)	(1)
Estimated Fair Value	$ 95,404	$ 6,562

Fair Value Measurements and F_5

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, 2021	Dec. 31, 2020
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total asset	$ 286,985	$ 21,217
Liabilities:
Preferred stock purchase rights liability		25,224
Money Market Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total asset	20,102	3,921
Asset Backed Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total asset	30,485	2,640
U.S. Treasury Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total asset	39,972	1,300
Other Government Agency Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total asset	5,079
Commercial Paper
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total asset	95,943	6,795
Corporate Debt Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total asset	95,404	6,561
Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total asset	20,102	5,221
Level 1 | Money Market Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total asset	20,102	3,921
Level 1 | U.S. Treasury Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total asset		1,300
Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total asset	266,883	15,996
Level 2 | Asset Backed Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total asset	30,485	2,640
Level 2 | U.S. Treasury Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total asset	39,972
Level 2 | Other Government Agency Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total asset	5,079
Level 2 | Commercial Paper
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total asset	95,943	6,795
Level 2 | Corporate Debt Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total asset	$ 95,404	6,561
Level 3
Liabilities:
Preferred stock purchase rights liability		$ 25,224

Fair Value Measurements and F_6

Fair Value Measurements and Fair Value of Financial Instruments - Schedule of Changes in Estimated Fair Value of Financial Instruments (Details) - Recurring Basis $ in Thousands	9 Months Ended
	Sep. 30, 2021USD ($)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Balance at December 31, 2020	$ 25,224
Change in fair value	6,084
Reclassification to equity	$ (31,308)

License and Equity Agreement -

License and Equity Agreement - Additional Information (Details) - Stanford Agreement	77 Months Ended
	Sep. 30, 2021USD ($)
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, 2021	Dec. 31, 2020
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 7,689	$ 5,322
Less accumulated depreciation and amortization	(2,058)	(1,239)
Total	5,631	4,083
Equipment
Property Plant And Equipment [Line Items]
Property and equipment, gross	7,236	5,253
Leasehold Improvements
Property Plant And Equipment [Line Items]
Property and equipment, gross	132
Office Equipment
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 321	$ 69

Balance Sheet Components - Addi

Balance Sheet Components - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Balance Sheet Related Disclosures [Abstract]
Depreciation expense	$ 0.3	$ 0.2	$ 0.8	$ 0.4

Balance Sheet Components - Accr

Balance Sheet Components - Accrued Expenses and Other Current Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Balance Sheet Related Disclosures [Abstract]
Accrued research and development	$ 6,140	$ 3,199
Accrued compensation	3,945	2,885
Accrued other	837	579
Total	$ 10,922	$ 6,663

Collaborations - Additional Inf

Collaborations - Additional Information (Details) - USD ($)	1 Months Ended				3 Months Ended	9 Months Ended
	Oct. 31, 2021	Aug. 31, 2021	May 31, 2021	Mar. 31, 2019	Sep. 30, 2021	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Consideration in excess of fair value						$ 241,959,000
Collaboration revenue					$ 752,000	$ 752,000	$ 231,000
Common Stock
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Issuance of shares						13,225,000
Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Potential future milestone payments						$ 2,000,000
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					10,900,000	10,900,000
Upfront payment received			$ 10,000,000
Contract liability, current					2,900,000	2,900,000
Contract liability, non-current					8,000,000	8,000,000
Allocated from stock purchase agreement			1,400,000
Variable consideration related to reimbursements for research and development services			$ 7,900,000
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]
Issuance of shares			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 milestone payments			$ 285,000,000
Innovent Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Contract liability					5,000,000	5,000,000
Contract liability, current					800,000	800,000
Contract liability, non-current					4,200,000	4,200,000
Collaboration revenue					0	0
Allocated from stock purchase agreement		$ 0
Upfront payment receivable		5,000,000			$ 5,000,000	$ 5,000,000
Potential license option exercise fee and development and sales-based milestone payments receivable		437,500,000
Stock purchase agreement expiration date						2022-05
Innovent Agreement | Subsequent Event
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront payment received	$ 5,000,000
Innovent Agreement | Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Variable consideration related to reimbursements for research and development services		7,500,000
Innovent Agreement | Maximum | Common Stock
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Aggregate investment under stock purchase agreement		$ 10,000,000
Series T Convertible Preferred Stock | Toray Development Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Issuance of shares				717,514
Consideration in excess of fair value				$ 1,500,000

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Details)	Aug. 07, 2020USD ($)ft²	Jun. 30, 2021ft²	Sep. 30, 2021USD ($)	Sep. 30, 2021USD ($)ft²	Dec. 31, 2020USD ($)
Commitments And Contingencies [Line Items]
Operating lease right-of-use assets			$ 25,216,000	$ 25,216,000	$ 12,267,000
Operating lease liabilities			$ 24,930,000	24,930,000
Sublease income				$ 1,774,000
Weighted-average remaining lease term			8 years 2 months 12 days	8 years 2 months 12 days	6 years 3 months 18 days
Weighted-average discount rate			10.90%	10.90%	9.50%
Maximum
Commitments And Contingencies [Line Items]
Potential future milestone payments				$ 2,000,000
Chesapeake Master Lease
Commitments And Contingencies [Line Items]
Operating lease, area of property available | ft²	71,646
Operating lease, area of property, additional space available | ft²	45,690			45,690
Operating lease, area of property, extension space available | ft²	25,956	25,956
Operating lease, initial term of contract	10 years
Operating lease, option to extend	true
Operating lease, extended additional term	8 years
Tenant improvement allowance	$ 4,800,000
Operating lease, area of property subleased | ft²	10,000
Operating lease, area of property, additional space remaining | ft²		35,690
Operating lease right-of-use assets			$ 18,300,000	$ 18,300,000
Operating lease liabilities			19,000,000	$ 19,000,000
Sublease, area of property leased | ft²	10,000
Sublease expiration date	Jul. 31, 2022			Jul. 31, 2023
Sublease, area of property expected to be leased | ft²				10,500
Operating sublease, option to extend, description				The subtenants have no option to extend the sublease term.
Operating sublease, option to extend	false
Sublease income			$ 200,000	$ 500,000

Commitments and Contingencies_2

Commitments and Contingencies - Components of Lease Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Commitments And Contingencies Disclosure [Abstract]
Total operating lease cost	$ 1,229	$ 724	$ 2,721	$ 1,919

Commitments and Contingencies_3

Commitments and Contingencies - Supplemental Cash Flow Information Related to Leases (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Commitments And Contingencies Disclosure [Abstract]
Operating cash flows from operating leases	$ 1,884	$ 3,639

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, 2021USD ($)
Operating Leases
Operating Leases, 2021	$ 1,228
Operating Leases, 2022	4,994
Operating Leases, 2023	4,612
Operating Leases, 2024	4,772
Operating Leases, 2025	4,227
Operating Leases, Thereafter	19,709
Operating Leases, Total minimum lease payments	39,542
Less imputed interest	(14,612)
Operating lease liabilities	24,930
Sublease Income
Sublease Income, 2021	323
Sublease Income, 2022	1,048
Sublease Income, 2023	403
Total Sublease Income	1,774
Sublease Income, Total	$ 1,774

Convertible Preferred Stock - A

Convertible Preferred Stock - Additional Information (Details)	1 Months Ended		9 Months Ended
	Jan. 31, 2021USD ($)shares	Jun. 30, 2020USD ($)Tranche$ / sharesshares	Sep. 30, 2021USD ($)shares	Sep. 30, 2020USD ($)	Dec. 31, 2020USD ($)shares
Class Of Stock [Line Items]
Convertible preferred stock value					$ 105,296,000
Convertible preferred stock, shares issued | shares			0		15,232,275
Proceeds from issuance of preferred stock, net of issuance cost			$ 51,902,000	$ 41,270,000
Series C-2 Convertible Preferred Stock
Class Of Stock [Line Items]
Fair value of convertible preferred stock purchase right liability	$ 31,300,000
Series C Agreement
Class Of Stock [Line Items]
Convertible preferred stock, authorized amount		$ 93,500,000
Number of tranches | Tranche		2
First Tranche Series C Agreement
Class Of Stock [Line Items]
Convertible preferred stock value		$ 41,300,000
Net of issuance costs		$ 200,000
First Tranche Series C Agreement | Series C-1 Convertible Preferred Stock
Class Of Stock [Line Items]
Convertible preferred stock, shares issued | shares		5,162,173
Stock issued, price per share | $ / shares		$ 8.05
First Tranche Series C Agreement | Series C-2 Convertible Preferred Stock
Class Of Stock [Line Items]
Convertible preferred stock, shares issuable | shares		5,611,065
Stock price per share | $ / shares		$ 9.2575
Potential gross proceeds from issuance		$ 51,900,000
Second Tranche Series C Agreement
Class Of Stock [Line Items]
Changes in fair value of this liability			$ 6,100,000
Second Tranche Series C Agreement | Series C-1 Convertible Preferred Stock
Class Of Stock [Line Items]
Fair value of convertible preferred stock purchase right liability		$ 13,500,000
Second Tranche Series C Agreement | Series C-2 Convertible Preferred Stock
Class Of Stock [Line Items]
Convertible preferred stock, shares issued | shares	5,611,059
Proceeds from issuance of preferred stock, net of issuance cost	$ 51,900,000

Common Stock - Additional Infor

Common Stock - Additional Information (Details) - USD ($)	1 Months Ended
	Jul. 31, 2018	Feb. 28, 2021
Class Of Warrant Or Right [Line Items]
Warrants issued to purchase common stock	$ 249,218
Warrants expiration date	Jul. 26, 2028
Warrant exercise price	$ 0.07
Common Stock
Class Of Warrant Or Right [Line Items]
Number of common stock purchased upon exercise of warrants		82,603

Stock-Based Compensation - Addi

Stock-Based Compensation - Additional Information (Details) - USD ($)	1 Months Ended		3 Months Ended	9 Months Ended
	Jan. 31, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense				$ 6,358,000	$ 851,000
Performance and Service Based Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares granted		526,018
Vesting period		48 months
Stock-based compensation expense			$ 100,000	$ 700,000
Weighted-average grant date fair value of awards		$ 3.24
Common Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Issuance of common stock under employee stock purchase plan, Shares				29,685
2021 Plan | Common Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares authorized for issuance	8,075,000
2021 Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Purchase price of stock as percentage of fair market value	85.00%
2021 Employee Stock Purchase Plan | Common Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares authorized for issuance	840,000
Plan offering period	2 years
Issuance of common stock under employee stock purchase plan, Shares			29,685	29,685
2021 Employee Stock Purchase Plan | Common Stock | Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Percentage of eligible compensation for payroll deductions to purchase stock	15.00%
2015 Plan | Employee Stock Option
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unvested shares			4,966	4,966		47,180
Repurchase right vesting period				4 years
Early exercise liability			$ 13,000	$ 13,000		$ 100,000

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, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 2,226	$ 403	$ 6,358	$ 851
Research and Development
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	1,231	222	3,328	420
General and Administrative
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 995	$ 181	$ 3,030	$ 431

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, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Numerator:
Net loss	$ (23,395)	$ (10,001)	$ (71,434)	$ (29,693)
Denominator:
Weighted average common shares outstanding	37,214,513	1,982,788	31,837,227	1,951,427
Weighted average common stock outstanding subject to repurchase related to unvested early exercised stock options and restricted stock awards	(7,720)	(33,211)	(24,847)	(27,365)
Weighted average warrants to purchase common stock		162,922	11,800	168,915
Weighted average common shares outstanding - basic and diluted	37,206,793	2,112,499	31,824,180	2,092,977
Net loss per share attributable to common stockholders, basic and diluted	$ (0.63)	$ (4.73)	$ (2.24)	$ (14.19)

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	3 Months Ended	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
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	5,202,241	19,055,181
Convertible Preferred Stock
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		15,232,275
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	5,197,275	3,764,659
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	4,966	58,247