0001558370-22-008441 | 10-Q | XBRL Viewer

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Document and Entity Information - shares	3 Months Ended
Document and Entity Information - shares	Mar. 31, 2022	May 04, 2022
Document and Entity Information [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Mar. 31, 2022
Document Transition Report	false
Entity File Number	001-40925
Entity Registrant Name	Xilio Therapeutics, Inc.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	85-1623397
Entity Address, Address Line One	828 Winter Street
Entity Address, Address Line Two	Suite 300
Entity Address, City or Town	Waltham
Entity Address State Or Province	MA
Entity Address, Postal Zip Code	02451
City Area Code	617
Local Phone Number	430-4680
Title of 12(b) Security	Common stock, par value $0.0001 per share
Trading Symbol	XLO
Security Exchange Name	NASDAQ
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		27,471,607
Entity Central Index Key	0001840233
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2022
Document Fiscal Period Focus	Q1
Amendment Flag	false

CONDENSED CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Current assets
Cash and cash equivalents	$ 176,959	$ 198,053
Prepaid expenses and other current assets	4,128	4,464
Total current assets	181,087	202,517
Restricted cash	1,553	1,553
Property and equipment, net	7,468	7,620
Operating lease right-of-use asset	5,885	5,977
Other non-current assets	359	393
Total assets	196,352	218,060
Current liabilities
Accounts payable	2,324	3,144
Accrued expenses	7,323	8,751
Operating lease liability, current portion	829	801
Notes payable, current portion	1,667
Other current liabilities	82	82
Total current liabilities	12,225	12,778
Notes payable, net of current portion	8,012	9,628
Operating lease liability, net of current portion	9,894	10,107
Other liabilities, long-term	100	118
Total liabilities	30,231	32,631
Commitments and contingencies (Note 7)
Stockholders' equity
Preferred stock, $0.0001 par value; 5,000,000 shares authorized, no shares issued or outstanding at March 31, 2022 and December 31, 2021
Common stock, $0.0001 par value; 200,000,000 shares authorized at March 31, 2022 and December 31, 2021; 27,471,607 shares issued and 27,376,473 shares outstanding at March 31, 2022; 27,468,950 shares issued and 27,358,375 shares outstanding at December 31, 2021	3	3
Additional paid-in capital	348,357	346,312
Accumulated deficit	(182,239)	(160,886)
Total stockholders' equity (deficit)	166,121	185,429
Total liabilities and stockholders' equity	$ 196,352	$ 218,060

CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares	Mar. 31, 2022	Dec. 31, 2021
CONSOLIDATED BALANCE SHEETS
Preferred stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Preferred stock, shares authorized	5,000,000	5,000,000
Preferred stock, shares issued	0	0
Common stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Common stock, shares authorized	200,000,000	200,000,000
Common stock, shares issued	27,471,607	27,468,950
Common stock, shares outstanding	27,376,473	27,358,375

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Operating expenses
Research and development	$ 14,920	$ 11,621
General and administrative	6,304	4,899
Total operating expenses	21,224	16,520
Loss from operations	(21,224)	(16,520)
Other expense, net
Other expense, net	(129)	(147)
Total other expense, net	(129)	(147)
Net loss	(21,353)	(16,667)
Comprehensive loss	$ (21,353)	$ (16,667)
Net loss per share, basic (in dollars per share)	$ (0.78)	$ (23.53)
Net loss per share, diluted (in dollars per share)	$ (0.78)	$ (23.53)
Weighted average common shares outstanding, basic (in shares)	27,367,377	708,264
Weighted average common shares outstanding, diluted (in shares)	27,367,377	708,264

CONDENSED CONSOLIDATED STATEMENTS OF CONVERTIBLE PREFERRED STOCK $ in Thousands	3 Months Ended
	Mar. 31, 2021 USD ($) shares
Series A Convertible Preferred Stock
Temporary Equity
Beginning balance \| $	$ 7,309
Beginning balance (in shares) \| shares	7,500,000
Ending balance \| $	$ 7,309
Ending balance (in shares) \| shares	7,500,000
Series A-1 Convertible Preferred Stock
Temporary Equity
Beginning balance \| $	$ 20,740
Beginning balance (in shares) \| shares	19,565,216
Ending balance \| $	$ 20,740
Ending balance (in shares) \| shares	19,565,216
Series B Convertible Preferred Stock
Temporary Equity
Beginning balance \| $	$ 49,953
Beginning balance (in shares) \| shares	39,723,312
Issuance of preferred stock or units, net of issuance costs \| $	$ 50,200
Issuance of preferred stock or units (in shares) \| shares	39,723,312
Ending balance \| $	$ 100,153
Ending balance (in shares) \| shares	79,446,624
Series C Convertible Preferred Stock
Temporary Equity
Issuance of preferred stock or units, net of issuance costs \| $	$ 94,686
Issuance of preferred stock or units (in shares) \| shares	68,271,641
Ending balance \| $	$ 94,686
Ending balance (in shares) \| shares	68,271,641

- Definition

Carrying amount, attributable to parent, of an entity's issued and outstanding stock which is not included within permanent equity. Temporary equity is a security with redemption features that are outside the control of the issuer, is not classified as an asset or liability in conformity with GAAP, and is not mandatorily redeemable. Includes any type of security that is redeemable at a fixed or determinable price or on a fixed or determinable date or dates, is redeemable at the option of the holder, or has conditions for redemption which are not solely within the control of the issuer. Includes stock with a put option held by an ESOP and stock redeemable by a holder only in the event of a change in control of the issuer.

+ References + Details

CONDENSED CONSOLIDATED STATEMENTS OF CONVERTIBLE PREFERRED STOCK (Parenthetical) $ in Thousands	3 Months Ended
	Mar. 31, 2021 USD ($)
Series B Convertible Preferred Stock
Issuance costs	$ 50
Series C Convertible Preferred Stock
Issuance costs	$ 314

CONDENSED CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (DEFICIT) - USD ($) $ in Thousands	Common Stock	Additional Paid-In Capital	Accumulated Deficit	Total
Beginning balance at Dec. 31, 2020		$ 1,799	$ (85,086)	$ (83,287)
Beginning balance (in shares) at Dec. 31, 2020	689,929
Stockholders' Deficit
Vesting of restricted common stock (in shares)	27,989
Exercise of stock options		25		25
Exercise of stock options (in shares)	4,473
Equity-based compensation expense		794		794
Net loss			(16,667)	(16,667)
Ending balance at Mar. 31, 2021		2,618	(101,753)	(99,135)
Ending balance (in shares) at Mar. 31, 2021	722,391
Beginning balance at Dec. 31, 2021	$ 3	346,312	(160,886)	185,429
Beginning balance (in shares) at Dec. 31, 2021	27,358,375
Stockholders' Deficit
Vesting of restricted common stock (in shares)	15,441
Exercise of stock options		16		$ 16
Exercise of stock options (in shares)	2,657			2,657
Equity-based compensation expense		2,029		$ 2,029
Net loss			(21,353)	(21,353)
Ending balance at Mar. 31, 2022	$ 3	$ 348,357	$ (182,239)	$ 166,121
Ending balance (in shares) at Mar. 31, 2022	27,376,473

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

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- Definition

Total of all stockholders' equity (deficit) items, net of receivables from officers, directors, owners, and affiliates of the entity which are attributable to the parent. The amount of the economic entity's stockholders' equity attributable to the parent excludes the amount of stockholders' equity which is allocable to that ownership interest in subsidiary equity which is not attributable to the parent (noncontrolling interest, minority interest). This excludes temporary equity and is sometimes called permanent equity.

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+ Details

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Cash flows from operating activities:
Net loss	$ (21,353)	$ (16,667)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	440	350
Non-cash interest expense	53	38
Equity-based compensation expense	2,029	794
Change in fair value of warrant and derivative liabilities		15
Changes in operating assets and liabilities:
Prepaid and other assets	336	153
Operating lease right-of-use asset	92	78
Accounts payable	(820)	(2,838)
Accrued expenses and other liabilities	(1,427)	(4,627)
Operating lease liability	(185)	(30)
Net cash used in operating activities	(20,835)	(22,734)
Cash flows from investing activities:
Purchases of property and equipment	(254)	(170)
Net cash used in investing activities	(254)	(170)
Cash flows from financing activities:
Payments of finance lease	(21)	(21)
Proceeds from issuance of convertible preferred stock, net of issuance costs		144,886
Proceeds from exercise of stock options	16	25
Net cash (used in) provided by financing activities	(5)	144,890
(Decrease) increase in cash, cash equivalents and restricted cash	(21,094)	121,986
Cash, cash equivalents and restricted cash, beginning of period	199,606	20,789
Cash, cash equivalents and restricted cash, end of period	178,512	142,775
Supplemental cash flow disclosure:
Cash paid for interest	$ 119	125
Supplemental disclosure of non-cash activities:
Capital expenditures included in accounts payable or accrued expenses		249
Deferred offering costs included in accounts payable or accrued expenses		$ 201

Description of Business, Initial Public Offering and Liquidity and Capital Resources

3 Months Ended

Mar. 31, 2022

Description of Business, Initial Public Offering and Liquidity and Capital Resources

Description of Business, Initial Public Offering and Liquidity and Capital Resources

1. Description of Business, Initial Public Offering and Liquidity and Capital Resources

Description of Business

Xilio Therapeutics, Inc. (“Xilio” or the “Company”), incorporated in Delaware in June 2020, is a clinical-stage biotechnology company focused on harnessing the immune system to achieve deep and durable clinical responses to improve the lives of patients with cancer. The Company’s headquarters are based in Waltham, Massachusetts.

Initial Public Offering

On October 26, 2021, the Company completed its initial public offering (“IPO”) of common stock, in which it issued and sold an aggregate of 7,353,000 shares at a public offering price of $16.00 per share. On November 1, 2021, the Company issued and sold an additional 766,106 shares of common stock at a public offering price of $16.00 per share pursuant to the partial exercise by the underwriters of their option to purchase additional shares. The Company received aggregate gross proceeds of $129.9 million or aggregate net proceeds of $116.4 million from its IPO, including the partial exercise of the underwriters’ option, after deducting underwriting discounts and commissions and offering expenses payable by the Company.

In connection with the IPO, the Company effected a 1-for-9.5 reverse stock split of the Company’s issued and outstanding shares of common stock. The reverse stock split was effective on October 15, 2021. Accordingly, all share and per share amounts of common stock for all periods presented in these condensed consolidated financial statements and related notes have been retroactively adjusted to give effect to the reverse stock split. Upon the closing of the IPO, all shares of the Company’s then outstanding preferred stock automatically converted into an aggregate of 18,398,248 shares of common stock (see Note 8).

Liquidity and Capital Resources

Since inception, the Company has devoted substantially all of its financial resources and efforts to research and development activities.

The Company is subject to risks and uncertainties common to early-stage companies in the biotechnology industry, including but not limited to, risks associated with the successful research, development and manufacturing of product candidates, and, if approved, any products, obtaining regulatory approvals for product candidates, and, if approved, commercialization of any products, protection and enforcement of intellectual property and proprietary technology, development by third parties of potentially competitive products or product candidates, compliance with governmental regulations, and the ability to secure additional capital to fund operations. Programs currently under development will require significant additional research and development efforts, including preclinical and clinical testing and manufacturing process development and will need to obtain regulatory approval prior to commercialization. These efforts require significant amounts of additional capital, adequate personnel and infrastructure and extensive compliance-reporting capabilities. Even if the Company’s product development efforts are successful, it is uncertain when, if ever, the Company will realize revenue from product sales.

As of March 31, 2022, the Company had cash and cash equivalents of $177.0 million. The Company expects that its cash and cash equivalents will be sufficient to meet its projected operating requirements and capital expenditures for at least twelve months from the date of issuance of these condensed consolidated financial statements. The Company expects to continue to generate negative cash flows from operations and net losses for the foreseeable future and will need additional capital in the future to support its continuing operations and growth strategy as it continues to invest significantly in research and development of its product candidates, including preclinical and clinical testing and manufacturing process

development. To date, the Company has primarily funded its operations with proceeds from the sale of convertible preferred units and convertible preferred stock, a debt financing and the IPO. Management’s conclusion with respect to its ability to fund operations is based on estimates that are subject to risks and uncertainties that may prove to be incorrect. If actual results differ from management’s estimates, the Company may be required to seek additional capital sooner or curtail planned activities to reduce operating expenses, which may have an adverse impact on the Company’s ability to achieve its business objectives.

Summary of Significant Accounting Policies

3 Months Ended

Mar. 31, 2022

Summary of Significant Accounting Policies

Summary of Significant Accounting Policies

2. Summary of Significant Accounting Policies

Basis of Presentation

These condensed consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States (“GAAP”) and pursuant to the rules and regulations of the United States Securities and Exchange Commission, (the “SEC”). Certain information and footnote disclosures normally included in the financial statements prepared in accordance with GAAP have been condensed or omitted pursuant to such rules and regulations. These condensed consolidated financial statements should be read in conjunction with the Company’s audited consolidated financial statements and the notes thereto included in the Company’s Annual Report on Form 10-K for the fiscal year ended December 31, 2021. Any reference in these notes to applicable guidance is meant to refer to the authoritative GAAP as found in the Accounting Standards Codification (“ASC”) and Accounting Standards Updates (“ASUs”) of the Financial Accounting Standards Board (“FASB”).

In April 2012, the Jumpstart Our Business Startups Act of 2012 (the “JOBS Act”) was enacted. Section 107(b) of the JOBS Act provides that an emerging growth company can take advantage of an extended transition period for complying with new or revised accounting standards. Thus, an emerging growth company can delay the adoption of certain accounting standards until those standards would otherwise apply to private companies. The Company has elected not to “opt out” of such extended transition period, which means that when a standard is issued or revised and it has different application dates for public or private companies, the Company can adopt the new or revised standard at the time private companies adopt the new or revised standard and may do so until such time that the Company either (1) irrevocably elects to “opt out” of such extended transition period or (2) no longer qualifies as an emerging growth company. The Company may take advantage of these exemptions up until the last day of the fiscal year following the fifth anniversary of its initial public offering or such earlier time that it is no longer an emerging growth company.

Principles of Consolidation

The accompanying condensed consolidated financial statements include the accounts of the Company and its wholly owned subsidiaries: Xilio Therapeutics LLC, Xilio Concerto LLC, Xilio Development, Inc. and Xilio Securities Corporation, which is a Massachusetts subsidiary created to buy, sell and hold securities. All intercompany accounts and transactions have been eliminated in consolidation.

Significant Accounting Policies

The significant accounting policies used in preparation of the unaudited condensed consolidated financial statements are described in Note 2, “Summary of Significant Accounting Policies” of the audited consolidated financial statements included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2021. There have been no material changes to the significant accounting policies previously disclosed in the Company’s Annual Report on Form 10-K for the year ended December 31, 2021.

Unaudited Interim Condensed Consolidated Financial Information

The accompanying condensed consolidated balance sheet as of March 31, 2022, the condensed consolidated statements of operations and comprehensive loss for the three months ended March 31, 2022 and 2021, the statements of cash flows for the three months ended March 31, 2022 and 2021 and the condensed consolidated statements of convertible preferred stock and stockholders’ equity (deficit) for the three months ended March 31, 2022 and 2021 are unaudited. The financial data and other information contained in the notes thereto as of and for the three months ended March 31, 2022 and 2021

are also unaudited. The condensed consolidated balance sheet data as of December 31, 2021 was derived from the Company’s audited consolidated financial statements included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2021.

The unaudited interim condensed consolidated financial statements have been prepared on the same basis as the audited annual consolidated financial statements, and in the opinion of management, reflect all adjustments, which include only normal recurring adjustments necessary for the fair presentation of the Company’s financial position as of March 31, 2022, the results of its operations for the three months ended March 31, 2022 and 2021 and cash flows for the three months ended March 31, 2022 and 2021. These unaudited condensed consolidated financial statements should be read in conjunction with the audited consolidated financial statements as of and for the year ended December 31, 2021, and the notes thereto, included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2021.

The results for the three months ended March 31, 2022 are not necessarily indicative of results to be expected for the year ended December 31, 2022, or any other interim periods, or any future year or period.

Use of Estimates

The preparation of financial statements in accordance with GAAP requires management to make estimates and judgments that may affect the reported amounts of assets and liabilities and related disclosures of contingent assets and liabilities at the date of the financial statements and the related reporting of expenses during the reporting period. Management considers many factors in selecting appropriate financial accounting policies and controls, and in developing the estimates and assumptions that are used in the preparation of these condensed consolidated financial statements. Factors that may affect estimates include expected business and operational changes, sensitivity and volatility associated with the assumptions used in developing estimates, and whether historical trends are expected to be representative of future trends. The estimation process often may yield a range of potentially reasonable estimates of the ultimate future outcomes and management must select an amount that falls within that range of reasonable estimates. Significant estimates of accounting reflected in these condensed consolidated financial statements include, but are not limited to, estimates related to accrued expenses, the valuation of equity-based compensation, including stock options and restricted common stock, the useful life of long-lived assets and income taxes. Actual results could differ from those estimates.

Cash, Cash Equivalents and Restricted Cash

The Company considers all short-term, highly liquid investments with original maturities of 90 days or less at acquisition date to be cash equivalents. Cash equivalents, which consist of money market accounts, are stated at fair value. Restricted cash primarily represents a letter of credit issued to the landlord of the Company’s facility lease and is reflected in non-current assets on the accompanying condensed consolidated balance sheets. Cash, cash equivalents and restricted cash consists of the following:


	March 31,		March 31,
	2022		2021
Cash and cash equivalents	$	176,959	$	141,222
Restricted cash		1,553		1,553
Total cash, cash equivalents and restricted cash as shown on the consolidated statement of cash flows	$	178,512	$	142,775

Recently Adopted Accounting Pronouncements

In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments—Credit Losses (Topic 326)—Measurement of Credit Losses on Financial Instruments, as amended (“ASU 2016-13”). The provisions of ASU 2016-13 modify the impairment model to utilize an expected loss methodology in place of the previously used incurred loss methodology and require a consideration of a broader range of reasonable and supportable information to inform credit loss estimates. The Company adopted ASU 2016-13 as of January 1, 2022, and the adoption did not have a material effect on its condensed consolidated financial statements and related disclosures.

In August 2020, the FASB issued ASU No. 2020-06, Debt—Debt with Conversion and Other Options (Subtopic 470-20) and Derivatives and Hedging Contracts in Entity’s Own Equity (Subtopic 815-40) (“ASU 2020-06”), which reduces the number of accounting models for convertible debt instruments and convertible preferred stock as well as amends the derivatives scope exception for contracts in an entity’s own equity. The Company adopted ASU 2020-06 as of January 1, 2022, and the adoption did not have a material effect on its condensed consolidated financial statements and related disclosures.

Fair Value Measurements

3 Months Ended

Mar. 31, 2022

Fair Value Measurements

Fair Value Measurements

3. Fair Value Measurements

The Company measures the following financial assets at fair value on a recurring basis. The fair value of these assets was determined as follows:


			Quoted
			Prices in
			Active		Significant
			Markets for		Other		Significant
			Identical		Observable		Unobservable
	March 31,		Assets		Inputs		Inputs
	2022		Level 1		Level 2		Level 3
Financial assets:
Cash equivalents—money market funds	$	934	$	934	$	—	$	—
Total financial assets	$	934	$	934	$	—	$	—


			Quoted
			Prices in
			Active		Significant
			Markets for		Other		Significant
			Identical		Observable		Unobservable
		December 31,	Assets		Inputs		Inputs
	2021		Level 1		Level 2		Level 3
Financial assets:
Cash equivalents—money market funds	$	8,534	$	8,534	$	—	$	—
Total financial assets	$	8,534	$	8,534	$	—	$	—

During the three months ended March 31, 2022 and March 31, 2021, the Company did not hold any investments and there were no transfers between Level 1, Level 2, and Level 3.

- Definition

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

+ References + Details

Property and Equipment, Net

3 Months Ended

Mar. 31, 2022

Property and Equipment, Net

Property and Equipment, Net

4. Property and Equipment, Net

Property and equipment, net consists of the following as of March 31, 2022 and December 31, 2021:


	March 31,		December 31,
	2022		2021
Laboratory equipment	$	4,369	$	3,805
Computers and software		228		228
Furniture and fixtures		636		636
Leasehold improvements		5,124		5,124
Construction in process		229		539
Total property and equipment	$	10,586	$	10,332
Less accumulated depreciation		(3,118)		(2,712)
Property and equipment, net	$	7,468	$	7,620

The Company incurred depreciation and amortization expense related to property and equipment, net of $0.4 million for each of the three months ended March 31, 2022 and 2021, respectively.

Accrued Expenses

3 Months Ended

Mar. 31, 2022

Accrued Expenses

Accrued Expenses

5. Accrued Expenses

Accrued expenses consist of the following as of March 31, 2022 and December 31, 2021:


	March 31,		December 31,
	2022		2021
External research and development	$	4,987	$	2,794
Personnel-related		1,483		5,145
Professional and consulting fees		659		491
Other		194		321
Total accrued expenses	$	7,323	$	8,751

Loan and Security Agreement

3 Months Ended

Mar. 31, 2022

Loan and Security Agreement

Loan and Security Agreement

6. Loan and Security Agreement

Initial Loan Agreement

In November 2019, the Company entered into a loan and security agreement with Pacific Western Bank (“PacWest”), as amended by a first amendment, dated March 12, 2021, and a second amendment, dated May 10, 2021 (the “Initial Loan Agreement”). Pursuant to the Initial Loan Agreement, the Company borrowed $10.0 million under a term loan. Interest on the outstanding initial loan balance accrued at a variable annual rate equal to the greater of (i) the prime rate, as defined in the Initial Loan Agreement, plus 0.25% or (ii) 5.00%. The Company was required to make interest only payments on the loan on a monthly basis through May 21, 2021. Subsequent to the interest-only period, the Company was required to make equal monthly payments of principal plus interest until the scheduled loan maturity on November 21, 2023. In addition, under the Initial Loan Agreement, the Company was obligated to pay a one-time $0.5 million fee to PacWest upon the occurrence of specified liquidation events, including an initial public offering. The fee represented a derivative instrument that the Company bifurcated from the debt arrangement and carried at fair value with any changes in such fair value recorded to other income (expense), net in the Company’s consolidated statements of operations and comprehensive loss. Upon the closing of the loan, the fair value of the debt derivative liability was $0.4 million that, together with certain legal and other fees incurred by the Company and associated with the Initial Loan Agreement, was recognized as a debt discount and reflected as a reduction in the carrying value of the debt. The debt discount has been accreted and recognized as additional interest expense over the term of the Initial Loan Agreement using the effective interest method.

Amended Loan Agreement

On September 17, 2021, the Company entered into a third amendment (the “Third Amendment”) to the Initial Loan Agreement (as amended, and together with the Initial Loan Agreement, the “Loan Agreement”), pursuant to which the Company borrowed $10.0 million under a new term loan and used the proceeds of such new term loan to repay the outstanding balance on the prior term loan. In addition, as a result of the amendment, prior to December 31, 2022, the Company has the ability to request one or more additional term loans in an aggregate principal amount of $10.0 million. Interest on amounts outstanding under the Loan Agreement accrue at a variable annual rate equal to the greater of (i) the prime rate plus 0.25% or (ii) 4.75%. As a result of the Third Amendment, the Company is required to make interest-only payments on any outstanding balances through December 31, 2022. Subsequent to the interest-only period, the Company will be required to make equal monthly payments of principal plus interest until the loan matures on June 30, 2024. In addition, as a result of the Third Amendment, the one-time fee the Company was obligated to pay to PacWest upon the occurrence of specified liquidation events, including an initial public offering, was increased from $0.5 million to an amount between $0.8 million and $1.0 million, depending on the timing and occurrence of specified events, including the closing of the IPO. The Company paid the one-time fee of $0.8 million to PacWest in October 2021 upon the closing of the IPO. As a result of the Third Amendment, the Company is also obligated to pay PacWest a fee of 1.0% of the aggregate principal amounts then outstanding if any term loans are repaid prior to September 17, 2022, which is approximately one year from the date of the Third Amendment. Using the net present value method, the Company concluded the amendment should be accounted for as a debt modification as the present value of the remaining cash flows of the amended term loan are not substantially different from the present value of the remaining cash flows of the initial term loan.

The Loan Agreement contains customary representations, warranties and covenants and also includes customary terms covering events of default, including payment defaults, breaches of covenants, a change of control provision and occurrence of a material adverse effect. As security for its obligations under the Loan Agreement, the Company granted PacWest a first priority security interest on substantially all of the Company’s assets (other than intellectual property), subject to certain exceptions.

The Company has determined that the risk of subjective acceleration under the material adverse effect clause is not probable and therefore has classified the long-term portion of the outstanding principal in non-current liabilities. Upon the occurrence and continuation of an event of default, a default interest rate of an additional 5% per annum may be applied to the outstanding loan balance, and the administrative agent, collateral agent, and lender may declare all outstanding obligations immediately due and payable and exercise all of their rights and remedies as set forth in the Loan Agreement and under applicable law. As of March 31, 2022, the Company was in compliance with all covenants under the Loan Agreement.

The Company has the following minimum aggregate future loan payments under the Loan Agreement at March 31, 2022:


	Minimum Loan
	Payments
2022	$	—
2023		6,667
2024		3,333
Total future principal payments		10,000
Less: unamortized discount		(321)
Total notes payable	$	9,679

The Company recognized $0.2 million of interest expense related to the Loan Agreement during each of the three months ended March 31, 2022 and 2021, respectively, which is reflected in other expense, net on the consolidated statements of operations and comprehensive loss.

- Definition

The entire disclosure for information about short-term and long-term debt arrangements, which includes amounts of borrowings under each line of credit, note payable, commercial paper issue, bonds indenture, debenture issue, own-share lending arrangements and any other contractual agreement to repay funds, and about the underlying arrangements, rationale for a classification as long-term, including repayment terms, interest rates, collateral provided, restrictions on use of assets and activities, whether or not in compliance with debt covenants, and other matters important to users of the financial statements, such as the effects of refinancing and noncompliance with debt covenants.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-URI http://asc.fasb.org/topic&trid=2208564

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 1B
-Subparagraph (h)
-URI http://asc.fasb.org/extlink&oid=123466505&loc=SL123495323-112611

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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-Section 50
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Reference 4: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
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-Paragraph 1I
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Reference 5: http://www.xbrl.org/2003/role/disclosureRef
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-Section 50
-Paragraph 1I
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=123466505&loc=SL123495371-112611

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(c))
-URI http://asc.fasb.org/extlink&oid=120395691&loc=d3e23780-122690

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 1B
-Subparagraph (g)
-URI http://asc.fasb.org/extlink&oid=123466505&loc=SL123495323-112611

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
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-URI http://asc.fasb.org/extlink&oid=123466505&loc=SL123495334-112611

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 20
-Section 50
-Paragraph 1C
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=123466505&loc=SL123495334-112611

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
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Reference 11: http://www.xbrl.org/2003/role/disclosureRef
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-Paragraph 1B
-URI http://asc.fasb.org/extlink&oid=123466505&loc=SL123495323-112611

Reference 12: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
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-URI http://asc.fasb.org/extlink&oid=123466505&loc=SL123495371-112611

Reference 13: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
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-Section 50
-Paragraph 1B
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-URI http://asc.fasb.org/extlink&oid=123466505&loc=SL123495323-112611

+ Details

Commitments and Contingencies

3 Months Ended

Mar. 31, 2022

Commitments and Contingencies

Commitments and Contingencies

7. Commitments and Contingencies

Leases

The Company has an operating lease for its facility and a finance lease for certain lab equipment. In August 2019, the Company entered into a lease agreement with a landlord providing funding for tenant improvements and occupancy of approximately 27,830 square feet of office and laboratory space at 828 Winter Street, Waltham, Massachusetts. The initial term of the lease expires in March 2030, unless terminated earlier in accordance with the terms of the lease. The Company has an option to extend the lease for a period of five years at then-market rates. The Company is obligated to pay its portion of real estate taxes and costs related to the premises, including costs of operations, maintenance, repair, replacement, and management of the leased premises, which it began paying simultaneous with the rent commencement date in March 2020. As of March 31, 2022, the Company has a letter of credit for the benefit of its landlord in the amount of $1.6 million, collateralized by a money market fund, which is classified as restricted cash on the condensed consolidated balance sheets.

Preferred Stock and Common Stock

3 Months Ended

Mar. 31, 2022

Preferred Stock and Common Stock

Preferred Stock and Common Stock

8. Preferred Stock and Common Stock

Undesignated Preferred Stock

As of March 31, 2022 and December 31, 2021, the Company’s certificate of incorporation, as amended, authorized the Company to issue up to 5,000,000 shares of undesignated preferred stock at $0.0001 par value per share.

Convertible Preferred Stock

Upon the closing of the IPO in October 2021, all shares of the Company’s then outstanding preferred stock automatically converted into an aggregate of 18,398,248 shares of common stock.

Common Stock

As of March 31, 2022 and December 31, 2021, the Company’s certificate of incorporation, as amended, authorized the Company to issue up to 200,000,000 shares of common stock, $0.0001 par value per share.

Shares Reserved for Future Issuance

As of March 31, 2022 and December 31, 2021, the Company had reserved shares of common stock for future issuance, including under the Company’s 2020 Stock Incentive Plan (as amended, the “2020 Plan”), 2021 Stock Incentive Plan (the “2021 Plan”) and 2021 Employee Stock Purchase Plan (the “2021 ESPP”) as follows:


	March 31,	December 31,
	2022	2021
Shares of common stock reserved for exercise of a warrant	2,631	2,631
Shares of common stock reserved for exercise of outstanding stock options under the 2021 and 2020 Stock Incentive Plans	4,948,376	4,088,456
Shares of common stock reserved for future awards under the 2021 Stock Incentive Plan	2,860,745	2,349,875
Shares of common stock reserved for purchase under the 2021 Employee Stock Purchase Plan	566,720	292,031
Total shares reserved for future issuance	8,378,472	6,732,993

Equity-Based Compensation

3 Months Ended

Mar. 31, 2022

Equity-Based Compensation

Equity-Based Compensation

9. Equity-Based Compensation

Equity Incentive Plans

2020 Stock Incentive Plan

In July 2020, the Company’s stockholders approved the 2020 Plan. Under the 2020 Plan, the Company was authorized to issue shares of common stock to the Company’s employees, officers, directors, consultants, and advisors in the form of options, restricted stock awards or other stock-based awards. Upon the effectiveness of the 2021 Plan in October 2021, the Company ceased granting awards under the 2020 Plan.

2021 Stock Incentive Plan

In September 2021, the Company’s board of directors adopted the 2021 Plan, which was approved by the Company’s stockholders and became effective immediately prior to the effectiveness of the Company’s registration statement on Form S-1, as amended (File No. 333-259973), which was declared effective by the SEC on October 21, 2021 (the “Registration Statement”). The 2021 Plan provides for the grant of incentive stock options, nonstatutory stock options, stock appreciation rights, restricted stock awards, restricted stock units, and other stock-based awards. The number of shares of the Company’s common stock initially reserved for issuance under the 2021 Plan was the sum of (1) 2,654,828; plus (2) the number of shares (up to 3,967,038 shares) as is equal to the sum of (x) the number of shares of the Company’s common

stock reserved for issuance under the 2020 Plan that remained available for grant under the 2020 Plan immediately prior to the effectiveness of the Registration Statement and (y) the number of shares of the Company’s common stock subject to outstanding awards whether granted under the 2020 Plan or outside of the 2020 Plan which awards expire, terminate or are otherwise surrendered, canceled, forfeited or repurchased by us at their original issuance price pursuant to a contractual repurchase right and that, prior to the effectiveness of the 2021 Plan, would have become available for issuance under the 2020 Plan; plus (3) an annual increase, to be added on the first day of each fiscal year, beginning with the fiscal year, commencing on January 1, 2022 and continuing until, and including, January 1, 2031, equal to the lesser of (i) 5% of the number of shares of the Company’s common stock outstanding on the first day of such fiscal year and (ii) the number of shares of common stock determined by the Company’s board of directors (the “Evergreen Provision”). Effective January 1, 2022, the number of shares reserved for issuance under the 2021 Plan increased by 1,373,447 shares in accordance with the Evergreen Provision.

As of March 31, 2022, there were 2,860,745 shares available for future issuance under the 2021 Plan.

2021 Employee Stock Purchase Plan

In September 2021, the Company’s board of directors adopted the 2021 ESPP, which was approved by the stockholders and became effective on October 21, 2021, immediately prior to the effectiveness of the Registration Statement. The Company initially reserved 292,031 shares of the Company’s common stock for future issuance under the 2021 ESPP. The number of shares of common stock reserved for issuance under the 2021 ESPP will automatically increase on each January 1, beginning on January 1, 2022 and ending on January 1, 2031, by the lesser of (i) 584,062 shares of common stock, (ii) 1% of the number of shares of the Company’s common stock outstanding on such date, and (iii) a number of shares of common stock as determined by the Company’s board of directors (the “ESPP Evergreen Provision”). Effective January 1, 2022, the number of shares reserved for issuance under the 2021 ESPP increased by 274,689 shares in accordance with the ESPP Evergreen Provision. As of March 31, 2022, no offering periods have commenced under the 2021 ESPP.

Equity-Based Compensation Expense

During the three months ended March 31, 2022 and 2021, the Company recorded compensation expense related to stock options and restricted common stock for employees and non-employees, which was allocated as follows in the condensed consolidated statements of operations and comprehensive loss:


	Three Months Ended March 31,
	2022		2021
Research and development expense	$	596	$	135
General and administrative expense		1,433		659
Total equity-based compensation expense	$	2,029	$	794

Stock Options

A summary of stock option activity under the 2021 Plan is as follows:


				Weighted
				Average
				Remaining	Aggregate
		Weighted		Contractual	Intrinsic
	Number of	Average		Term	Value
	Stock Options	Exercise Price		(In years)	(In thousands)
Outstanding as of December 31, 2021	4,088,456	$	8.59	9.13	$	30,291
Granted	874,830	$	12.67
Exercised	(2,657)	$	5.89
Cancelled/forfeited	(12,253)	$	13.71
Outstanding as of March 31, 2022	4,948,376	$	9.30	9.07	$	2,832
Exercisable as of March 31, 2022	1,064,255	$	7.09	8.27	$	1,115
Vested and expected to vest as of March 31, 2022	4,948,376	$	9.30	9.07	$	2,832

Using the Black-Scholes option pricing model, the weighted average fair value of options granted to employees and directors during the three months ended March 31, 2022 and 2021 was $8.83 and $4.32, respectively. The following assumptions were used in determining the fair value of options granted to employees the three months ended March 31, 2022 and 2021:


	Three Months Ended March 31,
	2022			2021
Risk-free interest rate		1.47 – 1.89	%		0.63 – 1.15	%
Expected dividend yield		0	%		0	%
Expected term (in years)		6.00 – 6.08			5.52 – 10.00
Expected volatility		80.75 – 80.92	%		84.61 – 85.26	%

The achievement of the performance conditions underlying outstanding performance-based awards was not probable as of March 31, 2022; therefore, no compensation expense was recorded for these awards. As of March 31, 2022, total unrecognized compensation costs related to performance-based awards was less than $0.1 million. As of March 31, 2022, total unrecognized compensation cost related to unvested stock options, excluding performance-based awards, was approximately $25.4 million, which is expected to be recognized over a weighted-average period of 3.04 years.

Restricted Stock

A summary of the Company’s restricted stock activity and related information is as follows:


	Number	Weighted
	of Shares	Average
	of Restricted	Grant Date
	Stock	Fair Value
Unvested as of December 31, 2021	110,575	$	5.51
Vested	(15,441)	$	5.51
Canceled/Forfeited	—	$	—
Unvested as of March 31, 2022	95,134	$	5.51

In June 2020, the Company granted 552,546 shares of common stock underlying restricted stock awards, and the Company has not subsequently granted any additional restricted stock awards. During the three months ended March 31, 2022, the aggregate fair value of the restricted stock awards that vested was $0.2 million. As of March 31, 2022, total unrecognized compensation cost related to unvested restricted stock awards was approximately $0.6 million, which is expected to be recognized over a weighted-average period of 1.57 years.

Income Taxes

3 Months Ended

Mar. 31, 2022

Income Taxes

Income Taxes

10. Income Taxes

The Company did not record a provision or benefit for income taxes during the three months ended March 31, 2022 and 2021. The Company continues to maintain a full valuation allowance against all of its deferred tax assets.

The Company has evaluated the positive and negative evidence involving its ability to realize its deferred tax assets and has considered its history of cumulative net losses incurred since inception and its lack of any commercially ready products. The Company has concluded that it is more likely than not that it will not realize the benefits of its deferred tax assets. The Company reevaluates the positive and negative evidence at each reporting period.

- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 21
-URI http://asc.fasb.org/extlink&oid=121826272&loc=d3e32857-109319

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SAB Topic 11.C)
-URI http://asc.fasb.org/extlink&oid=122134291&loc=d3e330215-122817

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 17
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121826272&loc=d3e32809-109319

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SAB TOPIC 6.I.5.Q1)
-URI http://asc.fasb.org/extlink&oid=122134291&loc=d3e330036-122817

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 14
-URI http://asc.fasb.org/extlink&oid=121826272&loc=d3e32705-109319

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 270
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6424409&loc=d3e44925-109338

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-URI http://asc.fasb.org/topic&trid=2144680

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 30
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=6424122&loc=d3e41874-109331

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(h)(2))
-URI http://asc.fasb.org/extlink&oid=120395691&loc=d3e23780-122690

+ Details

Net Loss Per Share

3 Months Ended

Mar. 31, 2022

Net Loss Per Share

Net Loss Per Share

11. Net Loss Per Share

The following table sets forth the outstanding shares of common stock equivalents, presented based on amounts outstanding at each period end, that were excluded from the calculation of diluted net loss per share attributable to common stockholders during each period because including them would have been anti-dilutive:


	Three Months Ended
	March 31,
	2022	2021
Convertible preferred stock	—	18,398,248
Unvested restricted common stock	95,134	251,599
Outstanding stock options	4,948,376	2,775,671
Warrants	2,631	2,631
Total common stock equivalents	5,046,141	21,428,149

Summary of Significant Accounting Policies (Policies)

3 Months Ended

Mar. 31, 2022

Summary of Significant Accounting Policies

Basis of Presentation

Principles of Consolidation

Unaudited Interim Condensed Consolidated Financial Information

Use of Estimates

Cash Equivalents and Restricted Cash

Cash, Cash Equivalents and Restricted Cash


	March 31,		March 31,
	2022		2021
Cash and cash equivalents	$	176,959	$	141,222
Restricted cash		1,553		1,553
Total cash, cash equivalents and restricted cash as shown on the consolidated statement of cash flows	$	178,512	$	142,775

Recently Adopted Accounting Pronouncements

Summary of Significant Accounting Policies (Tables)

3 Months Ended

Mar. 31, 2022

Summary of Significant Accounting Policies

Schedule of cash, cash equivalents and restricted cash


	March 31,		March 31,
	2022		2021
Cash and cash equivalents	$	176,959	$	141,222
Restricted cash		1,553		1,553
Total cash, cash equivalents and restricted cash as shown on the consolidated statement of cash flows	$	178,512	$	142,775

Fair Value Measurements (Tables)

3 Months Ended

Mar. 31, 2022

Fair Value Measurements

Schedule of financial assets at fair value on a recurring basis


			Quoted
			Prices in
			Active		Significant
			Markets for		Other		Significant
			Identical		Observable		Unobservable
	March 31,		Assets		Inputs		Inputs
	2022		Level 1		Level 2		Level 3
Financial assets:
Cash equivalents—money market funds	$	934	$	934	$	—	$	—
Total financial assets	$	934	$	934	$	—	$	—


			Quoted
			Prices in
			Active		Significant
			Markets for		Other		Significant
			Identical		Observable		Unobservable
		December 31,	Assets		Inputs		Inputs
	2021		Level 1		Level 2		Level 3
Financial assets:
Cash equivalents—money market funds	$	8,534	$	8,534	$	—	$	—
Total financial assets	$	8,534	$	8,534	$	—	$	—

Property and Equipment, Net (Tables)

3 Months Ended

Mar. 31, 2022

Property and Equipment, Net

Summary of property and equipment, net


	March 31,		December 31,
	2022		2021
Laboratory equipment	$	4,369	$	3,805
Computers and software		228		228
Furniture and fixtures		636		636
Leasehold improvements		5,124		5,124
Construction in process		229		539
Total property and equipment	$	10,586	$	10,332
Less accumulated depreciation		(3,118)		(2,712)
Property and equipment, net	$	7,468	$	7,620

Accrued Expenses (Tables)

3 Months Ended

Mar. 31, 2022

Accrued Expenses

Summary of accrued expenses


	March 31,		December 31,
	2022		2021
External research and development	$	4,987	$	2,794
Personnel-related		1,483		5,145
Professional and consulting fees		659		491
Other		194		321
Total accrued expenses	$	7,323	$	8,751

Loan and Security Agreement (Tables)

3 Months Ended

Mar. 31, 2022

Loan and Security Agreement

Schedule of minimum aggregate future loan payments

The Company has the following minimum aggregate future loan payments under the Loan Agreement at March 31, 2022:


	Minimum Loan
	Payments
2022	$	—
2023		6,667
2024		3,333
Total future principal payments		10,000
Less: unamortized discount		(321)
Total notes payable	$	9,679

Preferred Stock and Common Stock (Tables)

3 Months Ended

Mar. 31, 2022

Preferred Stock and Common Stock

Schedule of Shares Reserved for Future Issuance


	March 31,	December 31,
	2022	2021
Shares of common stock reserved for exercise of a warrant	2,631	2,631
Shares of common stock reserved for exercise of outstanding stock options under the 2021 and 2020 Stock Incentive Plans	4,948,376	4,088,456
Shares of common stock reserved for future awards under the 2021 Stock Incentive Plan	2,860,745	2,349,875
Shares of common stock reserved for purchase under the 2021 Employee Stock Purchase Plan	566,720	292,031
Total shares reserved for future issuance	8,378,472	6,732,993

Equity-Based Compensation (Tables)

3 Months Ended

Mar. 31, 2022

Equity-Based Compensation

Schedule of recorded compensation expense related to incentive units, stock options, and restricted common stock


	Three Months Ended March 31,
	2022		2021
Research and development expense	$	596	$	135
General and administrative expense		1,433		659
Total equity-based compensation expense	$	2,029	$	794

Summary of stock option activity


				Weighted
				Average
				Remaining	Aggregate
		Weighted		Contractual	Intrinsic
	Number of	Average		Term	Value
	Stock Options	Exercise Price		(In years)	(In thousands)
Outstanding as of December 31, 2021	4,088,456	$	8.59	9.13	$	30,291
Granted	874,830	$	12.67
Exercised	(2,657)	$	5.89
Cancelled/forfeited	(12,253)	$	13.71
Outstanding as of March 31, 2022	4,948,376	$	9.30	9.07	$	2,832
Exercisable as of March 31, 2022	1,064,255	$	7.09	8.27	$	1,115
Vested and expected to vest as of March 31, 2022	4,948,376	$	9.30	9.07	$	2,832

Schedule of assumptions used in determining the fair value of options granted to employees


	Three Months Ended March 31,
	2022			2021
Risk-free interest rate		1.47 – 1.89	%		0.63 – 1.15	%
Expected dividend yield		0	%		0	%
Expected term (in years)		6.00 – 6.08			5.52 – 10.00
Expected volatility		80.75 – 80.92	%		84.61 – 85.26	%

Schedule of company's restricted stock activity


	Number	Weighted
	of Shares	Average
	of Restricted	Grant Date
	Stock	Fair Value
Unvested as of December 31, 2021	110,575	$	5.51
Vested	(15,441)	$	5.51
Canceled/Forfeited	—	$	—
Unvested as of March 31, 2022	95,134	$	5.51

Net Loss Per Share (Tables)

3 Months Ended

Mar. 31, 2022

Net Loss Per Share

Schedule of antidilutive securities excluded from computation of diluted net loss per share


	Three Months Ended
	March 31,
	2022	2021
Convertible preferred stock	—	18,398,248
Unvested restricted common stock	95,134	251,599
Outstanding stock options	4,948,376	2,775,671
Warrants	2,631	2,631
Total common stock equivalents	5,046,141	21,428,149

Description of Business, Initial Public Offering and Liquidity and Capital Resources - IPO (Details) $ / shares in Units, $ in Millions					1 Months Ended
	Nov. 01, 2021 USD ($) $ / shares	Nov. 01, 2021 $ / shares shares	Oct. 26, 2021 $ / shares shares	Oct. 15, 2021	Oct. 31, 2021 shares
Sale of stock
Reverse stock split				0.1053
Common Stock
Sale of stock
Conversion of convertible preferred stock into common stock upon initial public offering (in shares)					18,398,248
IPO
Sale of stock
Gross proceeds received \| $	$ 129.9
Net proceeds received \| $	$ 116.4
IPO, Excluding Over-Allotment Option
Sale of stock
Number of shares issued and sold			7,353,000
Offering price (in dollar per share) \| $ / shares			$ 16.00
Over-Allotment Option
Sale of stock
Number of shares issued and sold		766,106
Offering price (in dollar per share) \| $ / shares	$ 16.00	$ 16.00

Description of Business, Initial Public Offering and Liquidity and Capital Resources - Liquidity and Capital Resources (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Dec. 31, 2021	Mar. 31, 2021
Description of Business, Initial Public Offering and Liquidity and Capital Resources
Cash and cash equivalents	$ 176,959	$ 198,053	$ 141,222
Substantial doubt about going concern within one year	false

Summary of Significant Accounting Policies - Cash Equivalents and Restricted Cash (Details) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021	Mar. 31, 2021	Dec. 31, 2020
Summary of Significant Accounting Policies
Cash and cash equivalents	$ 176,959	$ 198,053	$ 141,222
Restricted cash	1,553		1,553
Total cash, cash equivalents and restricted cash as shown on the consolidated statement of cash flows	$ 178,512	$ 199,606	$ 142,775	$ 20,789

Fair Value Measurements - Financial assets at fair value on a recurring basis (Details) - Recurring basis - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Financial assets:
Total financial assets	$ 934	$ 8,534
Cash equivalents-money market funds
Financial assets:
Total financial assets	934	8,534
Level 1
Financial assets:
Total financial assets	934	8,534
Level 1 \| Cash equivalents-money market funds
Financial assets:
Total financial assets	$ 934	$ 8,534

Fair Value Measurements - Transfers between levels (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2022	Dec. 31, 2021
Fair Value Measurements
Transfer of Level 1 to level 2	$ 0	$ 0
Transfer of Level 2 to level 1	0	0
Transfer into level 3	0	0
Transfer out level 3	$ 0	$ 0

Property and Equipment, Net (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021	Dec. 31, 2021
Property and Equipment
Property and equipment	$ 10,586		$ 10,332
Less accumulated depreciation	(3,118)		(2,712)
Property and equipment, net	7,468		7,620
Depreciation	400	$ 400
Laboratory equipment
Property and Equipment
Property and equipment	4,369		3,805
Computers and software
Property and Equipment
Property and equipment	228		228
Furniture & fixtures
Property and Equipment
Property and equipment	636		636
Leasehold improvements
Property and Equipment
Property and equipment	5,124		5,124
Construction in process
Property and Equipment
Property and equipment	$ 229		$ 539

Accrued Expenses (Details) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Accrued Expenses
External research and development	$ 4,987	$ 2,794
Personnel related	1,483	5,145
Professional and consulting services	659	491
Other	194	321
Total accrued expenses	$ 7,323	$ 8,751

Loan and Security Agreement - Description (Details) - Loan Agreement and Amended Loan Agreement - USD ($) $ in Millions		1 Months Ended
	Sep. 17, 2021	Oct. 31, 2021	Nov. 30, 2019	Sep. 16, 2021
Loan and security agreement
Borrowed amount	$ 10.0		$ 10.0
Additional borrowing capacity	$ 10.0
Fee payable upon occurrence of liquidation events, including initial public offering			$ 0.5	$ 0.5
Fee paid upon closing of IPO		$ 0.8
Fee payable (as percent)	1.00%
Additional interest rate upon event of default (as a percent)	5.00%
Minimum
Loan and security agreement
Stated interest rate	4.75%		5.00%
Fee payable upon occurrence of liquidation events, including initial public offering	$ 0.8
Maximum
Loan and security agreement
Fee payable upon occurrence of liquidation events, including initial public offering	$ 1.0
Debt derivative liability
Loan and security agreement
Derivative liability			$ 0.4
Prime rate
Loan and security agreement
Basis spread (as percent)	0.25%		0.25%

Loan and Security Agreement - Maturities (Details) - Loan Agreement and Amended Loan Agreement - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Minimum aggregate future loan payments
2023	$ 6,667
2024	3,333
Total future principal payments	10,000
Less: unamortized discount	(321)
Total notes payable	9,679
Interest expense	$ 200	$ 200

- Definition

Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ References + Details

Commitments and Contingencies - Lease information (Details) $ in Millions	1 Months Ended
	Aug. 31, 2019 ft²	Mar. 31, 2022 USD ($)
Commitments and Contingencies
Area leased (in square feet) \| ft²	27,830
Option to extend	true
Term of option to extend	5 years
Letter of credit for the benefit of landlord \| $		$ 1.6

Preferred Stock and Common Stock - Authorized (Details) - $ / shares	1 Months Ended
	Oct. 31, 2021	Mar. 31, 2022	Dec. 31, 2021
Preferred stock and Common stock
Preferred stock, shares authorized		5,000,000	5,000,000
Preferred stock, par value (in dollars per share)		$ 0.0001	$ 0.0001
Common stock, shares authorized		200,000,000	200,000,000
Common stock, par value (in dollars per share)		$ 0.0001	$ 0.0001
Common Stock
Preferred stock and Common stock
Conversion of convertible preferred stock into common stock upon initial public offering (in shares)	18,398,248

Preferred Stock and Common Stock - Shares Reserved for Future Issuance (Details) - shares	Mar. 31, 2022	Dec. 31, 2021
Preferred Stock and Common Stock
Shares of common stock reserved for exercise of a warrant	2,631	2,631
Shares of common stock reserved for exercise of outstanding stock options under the 2021 and 2020 Stock Incentive Plans	4,948,376	4,088,456
Shares of common stock reserved for future awards under the 2021 Stock Incentive Plan	2,860,745	2,349,875
Shares of common stock reserved for purchase under the 2021 Employee Stock Purchase Plan	566,720	292,031
Total shares reserved for future issuance	8,378,472	6,732,993

Equity-Based Compensation - Equity Incentive Plans (Details) - shares	Oct. 21, 2021	Mar. 31, 2022	Jan. 01, 2022	Dec. 31, 2021
Equity-Based Compensation
Common stock reserved for issuance (in shares)		8,378,472		6,732,993
2021 Stock Incentive Plan
Equity-Based Compensation
Additional common stock reserved for issuance (in shares)			1,373,447
Available for future issuance (in shares)		2,860,745
2021 Stock Incentive Plan \| Minimum
Equity-Based Compensation
Common stock reserved for issuance (in shares)	2,654,828
2021 Stock Incentive Plan \| Maximum
Equity-Based Compensation
Common stock reserved for issuance (in shares)	3,967,038
Annual increase in number of shares reserved for issuance (as a percent)	5.00%

Equity-Based Compensation - Employee Stock Purchase Plan (Details) - shares	Jan. 01, 2022	Oct. 21, 2021	Mar. 31, 2022	Dec. 31, 2021
Equity-Based Compensation
Common stock reserved for issuance (in shares)			8,378,472	6,732,993
Employee Stock Purchase Plan
Equity-Based Compensation
Common stock reserved for issuance (in shares)		292,031
Additional common stock issuable under the plan	274,689
Employee Stock Purchase Plan \| Maximum
Equity-Based Compensation
Annual increase in number of shares reserved and available for issuance (in shares)		584,062
Annual increase in number of shares reserved for issuance (as a percent)		1.00%

Equity-Based Compensation - Equity-based compensation expense (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Equity-Based Compensation
Total compensation expense	$ 2,029	$ 794
Research and development expense
Equity-Based Compensation
Total compensation expense	596	135
General and administrative expense
Equity-Based Compensation
Total compensation expense	$ 1,433	$ 659

Equity-Based Compensation - Stock option activity (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2022	Dec. 31, 2021
Options Outstanding
Outstanding at beginning of period (in shares)	4,088,456
Granted (in shares)	874,830
Exercised (in shares)	(2,657)
Cancelled/forfeited (in shares)	(12,253)
Outstanding at end of period (in shares)	4,948,376	4,088,456
Exercisable at end of period (in shares)	1,064,255
Vested and expected to vest at end of period (in shares)	4,948,376
Weighted Average Exercise Price
Outstanding (in dollars per share)	$ 9.30	$ 8.59
Granted (in dollars per share)	12.67
Exercised (in dollars per share)	5.89
Cancelled/forfeited (in dollars per share)	13.71
Exercisable at end of period (in dollars per share)	7.09
Vested and expected to vest at end of period (in dollars per share)	$ 9.30
Weighted Average Remaining Contractual Term (In years)
Outstanding (in years)	9 years 25 days	9 years 1 month 17 days
Exercisable at end of period (in years)	8 years 3 months 7 days
Vested and expected to vest at end of period (in years)	9 years 25 days
Aggregate Intrinsic Value
Outstanding (in dollars)	$ 2,832	$ 30,291
Exercisable (in dollars)	1,115
Vested and expected to vest (in dollars)	$ 2,832

Equity-Based Compensation - Stock options, fair value assumptions (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Equity-Based Compensation
Fair value of options granted (in dollars per share)	$ 8.83	$ 4.32
Stock options granted during the period (in shares)	874,830
Equity-based compensation expense	$ 2,029	$ 794
Stock options
Equity-Based Compensation
Risk-free interest rate, minimum (as a percent)	1.47%	0.63%
Risk-free interest rate, maximum (as a percent)	1.89%	1.15%
Expected dividend yield (as a percent)	0.00%	0.00%
Expected volatility, minimum (as percentage)	80.75%	84.61%
Expected volatility, maximum (as percentage)	80.92%	85.26%
Stock options \| Minimum
Equity-Based Compensation
Expected term (in years)	6 years	5 years 6 months 7 days
Stock options \| Maximum
Equity-Based Compensation
Expected term (in years)	6 years 29 days	10 years
Stock options, excluding performance-based awards
Equity-Based Compensation
Total unrecognized compensation cost	$ 25,400
Weighted-average period for unrecognized compensation cost to be recognized	3 years 14 days
Stock options, vesting based on performance
Equity-Based Compensation
Equity-based compensation expense	$ 0
Stock options, vesting based on performance \| Maximum
Equity-Based Compensation
Total unrecognized compensation cost	$ 100

Equity-Based Compensation - Restricted Stock (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2022	Mar. 31, 2021	Jun. 30, 2020
Weighted Average Grant Date Fair Value
Equity-based compensation expense	$ 2,029	$ 794
Restricted Stock
Equity Based Compensation
Outstanding at beginning of period (in shares)	110,575
Vested (in shares)	(15,441)
Outstanding at end of period (in shares)	95,134
Weighted Average Grant Date Fair Value
Outstanding at beginning of period (in dollars per share)	$ 5.51
Vested (in dollars per share)	5.51
Outstanding at end of period (in dollars per share)	$ 5.51
Granted (in shares)			552,546
Aggregate fair value of restricted stock awards that vested	$ 200
Total unrecognized compensation cost of unvested restricted stock awards	$ 600
Weighted-average period for unrecognized compensation cost to be recognized	1 year 6 months 25 days

Income Taxes - Provision (Details) - USD ($) $ in Thousands	3 Months Ended
Income Taxes - Provision (Details) - USD ($) $ in Thousands	Mar. 31, 2022	Mar. 31, 2021
Income Taxes
Provision or benefit for income taxes	$ 0	$ 0

- Definition

Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

+ References + Details

Net Loss Per Share (Details) - shares	3 Months Ended
Net Loss Per Share (Details) - shares	Mar. 31, 2022	Mar. 31, 2021
Net Loss Per Share
Total common stock equivalents	5,046,141	21,428,149
Convertible preferred stock
Net Loss Per Share
Total common stock equivalents		18,398,248
Restricted Stock
Net Loss Per Share
Total common stock equivalents	95,134	251,599
Stock options
Net Loss Per Share
Total common stock equivalents	4,948,376	2,775,671
Warrants
Net Loss Per Share
Total common stock equivalents	2,631	2,631