Xilio Therapeutics (XLO) 10-Q 9 May 23 2023 Q1 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2023	May 05, 2023
Document and Entity Information [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Mar. 31, 2023
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	857
Local Phone Number	524-2466
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		27,470,702
Entity Central Index Key	0001840233
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2023
Document Fiscal Period Focus	Q1
Amendment Flag	false

CONDENSED CONSOLIDATED BALANCE

CONDENSED CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022
Current assets
Cash and cash equivalents	$ 93,271	$ 120,385
Prepaid expenses and other current assets	3,705	4,111
Total current assets	96,976	124,496
Restricted cash	1,568	1,562
Property and equipment, net	7,252	7,255
Operating lease right-of-use asset	5,477	5,585
Other non-current assets	232	267
Total assets	111,505	139,165
Current liabilities
Accounts payable	2,013	3,125
Accrued expenses	6,483	10,327
Operating lease liability, current portion	949	918
Note payable, current portion	6,667	6,667
Other current liabilities	82	82
Total current liabilities	16,194	21,119
Note payable, net of current portion	1,548	3,165
Operating lease liability, net of current portion	8,945	9,189
Other non-current liabilities	26	45
Total liabilities	26,713	33,518
Commitments and contingencies (Note 6)
Stockholders' equity
Preferred stock, $0.0001 par value; 5,000,000 shares authorized, no shares issued or outstanding
Common stock, $0.0001 par value; 200,000,000 shares authorized at March 31, 2023 and December 31, 2022; 27,470,534 shares issued and 27,439,820 shares outstanding at March 31, 2023; 27,471,607 shares issued and 27,425,447 shares outstanding at December 31, 2022	3	3
Additional paid-in capital	356,543	354,752
Accumulated deficit	(271,754)	(249,108)
Total stockholders' equity	84,792	105,647
Total liabilities and stockholders' equity	$ 111,505	$ 139,165

CONDENSED CONSOLIDATED BALANC_2

CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares	Mar. 31, 2023	Dec. 31, 2022
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
Preferred stock, shares outstanding	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	27,470,534	27,471,607
Common stock, shares outstanding	27,439,820	27,425,447

CONDENSED CONSOLIDATED STATEMEN

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Operating expenses
Research and development	$ 16,131	$ 14,920
General and administrative	7,395	6,304
Total operating expenses	23,526	21,224
Loss from operations	(23,526)	(21,224)
Other income (expense), net
Other income (expense), net	880	(129)
Total other income (expense), net	880	(129)
Net loss	(22,646)	(21,353)
Comprehensive loss	$ (22,646)	$ (21,353)
Net loss per share, basic (in dollars per share)	$ (0.83)	$ (0.78)
Net loss per share, diluted (in dollars per share)	$ (0.83)	$ (0.78)
Weighted average common shares outstanding, basic (in shares)	27,433,252	27,367,377
Weighted average common shares outstanding, diluted (in shares)	27,433,252	27,367,377

CONDENSED CONSOLIDATED STATEM_2

CONDENSED CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Common Stock	Additional Paid-In Capital	Accumulated Deficit	Total
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
Stock-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
Beginning balance at Dec. 31, 2022	$ 3	354,752	(249,108)	$ 105,647
Beginning balance (in shares) at Dec. 31, 2022	27,425,447
Stockholders' Deficit
Vesting of restricted common stock (in shares)	14,217
Exercise of stock options (in shares)	156			156
Stock-based compensation expense		1,791		$ 1,791
Net loss			(22,646)	(22,646)
Ending balance at Mar. 31, 2023	$ 3	$ 356,543	$ (271,754)	$ 84,792
Ending balance (in shares) at Mar. 31, 2023	27,439,820

CONDENSED CONSOLIDATED STATEM_3

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Cash flows from operating activities:
Net loss	$ (22,646)	$ (21,353)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	499	440
Non-cash interest expense	31	53
Stock-based compensation expense	1,791	2,029
Changes in operating assets and liabilities:
Prepaid and other assets	406	336
Operating lease right-of-use asset	108	92
Accounts payable	(1,358)	(820)
Accrued expenses and other liabilities	(3,868)	(1,427)
Operating lease liability	(213)	(185)
Net cash used in operating activities	(25,250)	(20,835)
Cash flows from investing activities:
Purchases of property and equipment	(170)	(254)
Net cash used in investing activities	(170)	(254)
Cash flows from financing activities:
Repayments of debt principal	(1,667)
Payments of finance lease	(21)	(21)
Proceeds from exercise of stock options		16
Net cash used in financing activities	(1,688)	(5)
Decrease in cash, cash equivalents and restricted cash	(27,108)	(21,094)
Cash, cash equivalents and restricted cash, beginning of period	121,947	199,606
Cash, cash equivalents and restricted cash, end of period	94,839	178,512
Supplemental cash flow disclosure:
Cash paid for interest	209	119
Supplemental disclosure of non-cash activities:
Capital expenditures included in accounts payable or accrued expenses	310
Reconciliation to amounts within the consolidated balance sheets:
Cash and cash equivalents	93,271	176,959
Restricted cash	1,568	1,553
Cash, cash equivalents and restricted cash, end of period	$ 94,839	$ 178,512

Description of Business and Liq

Description of Business and Liquidity and Capital Resources	3 Months Ended
	Mar. 31, 2023
Description of Business and Liquidity and Capital Resources
Description of Business and Liquidity and Capital Resources	1. Description of Business and Liquidity and Capital Resources Description of Business Xilio Therapeutics, Inc. (“Xilio” or the “Company”) is a clinical-stage biotechnology company dedicated to discovering and developing tumor-activated immuno-oncology (“I-O”) therapies with the goal of significantly improving outcomes for people living with cancer without the systemic side effects of current I-O treatments. The Company was incorporated in Delaware in June 2020, and its headquarters are located in Waltham, Massachusetts. Liquidity and Capital Resources Since its 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, 2023, the Company had cash and cash equivalents of $93.3 million. The Company believes that its existing cash and cash equivalents will be sufficient to enable the Company to fund its operating expenses and capital expenditure requirements into the end of the second quarter of 2024, which is 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 preferred units and convertible preferred stock, a debt financing and its initial public offering (“IPO”), completed in the fourth quarter of 2021, in which the Company received net proceeds of $116.4 million. 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 Accounti

Summary of Significant Accounting Policies	3 Months Ended
	Mar. 31, 2023
Summary of Significant Accounting Policies
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Basis of Presentation The Company’s unaudited interim condensed consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States (“U.S. GAAP”). Any reference in these notes to applicable guidance is meant to refer to the authoritative U.S. GAAP as found in the Accounting Standards Codification (“ASC”) and Accounting Standards Updates (“ASUs”) of the Financial Accounting Standards Board (“FASB”). Certain information and footnote disclosures normally included in financial statements prepared in accordance with U.S. GAAP have been condensed or omitted from this report, as is permitted by such rules and regulations. Accordingly, these financial statements should be read in conjunction with the audited financial statements as of and for the year ended December 31, 2022 and notes thereto, included in the Company’s Annual Report on Form 10-K filed with the U.S. Securities and Exchange Commission (“SEC”) on March 2, 2023. The unaudited interim condensed consolidated financial statements have been prepared on the same basis as the audited financial statements. In the opinion of the Company’s management, the accompanying unaudited interim condensed consolidated financial statements contain all adjustments which are necessary to present fairly the Company’s financial position as of March 31, 2023 and the results of its operations and cash flows for the three months ended March 31, 2023 and March 31, 2022. Such adjustments are of a normal and recurring nature. The results for the three months ended March 31, 2023 are not necessarily indicative of the results for the year ending December 31, 2023 or for any future period. Principles of Consolidation The accompanying condensed consolidated financial statements include the accounts of the Company and its wholly owned subsidiaries: Xilio Development, Inc., a Delaware corporation and Xilio Securities Corporation, a Massachusetts security corporation. 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, 2022. 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, 2022. Concentrations of Credit Risk Financial instruments that potentially expose the Company to concentrations of credit risk consist primarily of cash and cash equivalents. The Company holds all cash and cash equivalents at accredited financial institutions. Bank accounts in the United States are generally insured by the Federal Deposit Insurance Corporation (“FDIC”) up to $250,000. Substantially all of the Company’s cash and cash equivalents are FDIC insured, including funds held through an insured cash sweep program. The Company has not experienced any losses in its cash and cash equivalents and does not believe that it is subject to unusual credit risk beyond the normal credit risk associated with commercial banking relationships. ​

Property and Equipment, Net

Property and Equipment, Net	3 Months Ended
	Mar. 31, 2023
Property and Equipment, Net
Property and Equipment, Net	3. Property and Equipment, Net Property and equipment, net consists of the following as of March 31, 2023 and December 31, 2022: ​ ​ ​ ​ ​ ​ ​ ​ ​ March 31, December 31, ​ ​ 2023 ​ 2022 Laboratory equipment ​ $ 6,101 ​ $ 5,587 Computers and software ​ 228 ​ 228 Furniture and fixtures ​ 681 ​ 636 Leasehold improvements ​ 5,124 ​ 5,124 Construction in process ​ — ​ 98 Total property and equipment ​ ​ 12,134 ​ ​ 11,673 Less: accumulated depreciation ​ (4,882) ​ (4,418) Property and equipment, net ​ $ 7,252 ​ $ 7,255 ​ The Company incurred depreciation and amortization expense related to property and equipment of $0.5 million and $0.4 million for the three months ended March 31, 2023 and 2022, respectively.

Accrued Expenses

Accrued Expenses	3 Months Ended
	Mar. 31, 2023
Accrued Expenses
Accrued Expenses	4. Accrued Expenses Accrued expenses consist of the following as of March 31, 2023 and December 31, 2022: ​ ​ ​ ​ ​ ​ ​ ​ ​ March 31, December 31, ​ ​ 2023 ​ 2022 External research and development ​ $ 3,640 ​ $ 3,178 Personnel-related ​ 1,745 ​ 5,413 Professional and consulting fees ​ 829 ​ 1,536 Other ​ ​ 269 ​ ​ 200 Total accrued expenses ​ $ 6,483 ​ $ 10,327 ​

Loan and Security Agreement

Loan and Security Agreement	3 Months Ended
	Mar. 31, 2023
Loan and Security Agreement
Loan and Security Agreement	5. Loan and Security Agreement ​ In November 2019, the Company’s wholly owned subsidiary, Xilio Development, Inc. (“Borrower”), entered into a loan and security agreement (as amended and restated in May 2023, the “Loan Agreement”) with Pacific Western Bank (“PacWest”), with the Company as a guarantor. Under the Loan Agreement, in November 2019, the Borrower borrowed $10.0 million under a term loan. 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 of March 31, 2023, the interest rate on the term loan was 8.25%. The Borrower was required to make interest-only payments on any outstanding balances through December 31, 2022. The Borrower commenced making equal monthly payments of principal plus interest in January 2023, and it will be required to make such payments until the term loan matures on June 30, 2024. ​ 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 Borrower granted PacWest a first priority security interest on substantially all of the Borrower’s assets, excluding 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, 2023, the Company and Borrower were in compliance with all covenants under the Loan Agreement. ​ The Borrower has the following minimum aggregate future loan principal payments under the Loan Agreement as of March 31, 2023: ​ ​ ​ ​ ​ ​ Minimum Loan ​ ​ Payments 2023 (remaining nine months) ​ $ 5,000 2024 ​ 3,333 Total future principal payments ​ 8,333 Less: unamortized discount ​ (118) Total note payable ​ $ 8,215 ​ The Company recognized $0.2 million of interest expense related to the Loan Agreement for each of the three months ended March 31, 2023 and 2022, which is reflected in other income (expense), net on the condensed consolidated statements of operations and comprehensive loss.

Commitments and Contingencies

Commitments and Contingencies	3 Months Ended
	Mar. 31, 2023
Commitments and Contingencies
Commitments and Contingencies	6. Commitments and Contingencies The Company has an operating lease for its headquarters and a finance lease for certain lab equipment. In August 2019, the Company entered into a facility lease agreement with a landlord providing funding for tenant improvements and occupancy of approximately 27,830 square feet of office and laboratory space (the “premises”) 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 an additional term 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, 2023 and December 31, 2022, the Company had a letter of credit for the benefit of its landlord in the amount of $1.6 million, collateralized by a money market account, which is recorded as restricted cash on the condensed consolidated balance sheets.

Preferred Stock and Common Stoc

Preferred Stock and Common Stock	3 Months Ended
	Mar. 31, 2023
Preferred Stock and Common Stock
Preferred Stock and Common Stock	7. Preferred Stock and Common Stock Undesignated Preferred Stock As of March 31, 2023 and December 31, 2022, 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. As of March 31, 2023 and December 31, 2022, there were no shares of preferred stock issued or outstanding. Common Stock As of March 31, 2023 and December 31, 2022, the Company is authorized to issue up to 200,000,000 shares of common stock, $0.0001 par value per share under its certificate of incorporation, as amended. Shares Reserved for Future Issuance As of March 31, 2023 and December 31, 2022, the Company had reserved shares of common stock for future issuance under the 2020 Stock Incentive Plan (as amended, the “2020 Plan”), the 2021 Stock Incentive Plan (the “2021 Plan”), the 2022 Inducement Stock Incentive Plan (the “2022 Inducement Plan”) and the 2021 Employee Stock Purchase Plan (the “2021 ESPP”) as follows: ​ ​ ​ ​ ​ ​ ​ ​ March 31, ​ December 31, ​ ​ 2023 ​ 2022 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 Plan and 2020 Plan 6,087,600 4,960,553 Shares of common stock reserved for future awards under the 2021 Plan 3,096,174 2,848,568 Shares of common stock reserved for future awards under the 2022 Inducement Plan ​ 275,000 ​ 275,000 Shares of common stock reserved for purchase under the 2021 ESPP ​ 841,436 ​ 566,720 Total shares reserved for future issuance 10,302,841 8,653,472 ​

Stock-Based Compensation

Stock-Based Compensation	3 Months Ended
	Mar. 31, 2023
Stock-Based Compensation
Stock-Based Compensation	8. Stock-Based Compensation Equity Incentive Plans 2020 Stock Incentive Plan In 2020, the Company adopted 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. 2021 Stock Incentive Plan In 2021, the Company’s board of directors and stockholders adopted the 2021 Plan, which became effective immediately prior to the IPO in October 2021. Upon effectiveness of the 2021 Plan, the Company ceased granting awards under the 2020 Plan. 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 2021 Plan 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 the Company 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. On January 1, 2023, the number of shares reserved for issuance under the 2021 Plan automatically increased by 1,373,580 shares. As of March 31, 2023, there were 3,096,174 shares available for future issuance under the 2021 Plan. 2022 Inducement Plan In 2022, the Company’s board of directors adopted the 2022 Inducement Plan pursuant to Nasdaq Rule 5635(c)(4). In accordance with Rule 5635(c)(4), stock-based incentive awards under the 2022 Inducement Plan may only be made to a newly hired employee who has not previously been a member of the Company’s board of directors, or an employee who is being rehired following a bona fide period of non-employment by the Company as a material inducement to the employee’s entering into employment with the Company. An aggregate of 275,000 shares of the Company’s common stock has been reserved for issuance under the 2022 Inducement Plan. The exercise price of stock options granted under the 2022 Inducement Plan will not be less than the fair market value of a share of the Company’s common stock on the grant date. Other terms of awards, including vesting requirements, are determined by the Company’s board of directors and are subject to the provisions of the 2022 Inducement Plan. As of March 31, 2023, no shares have been granted under the 2022 Inducement Plan. 2021 Employee Stock Purchase Plan In 2021, the Company’s board of directors and stockholders adopted the 2021 ESPP, which became effective immediately prior to the IPO in October 2021. The Company initially reserved 292,031 shares of common stock for issuance under the 2021 ESPP. In addition, the 2021 ESPP provides that the number of shares of common stock reserved for issuance under the 2021 ESPP will be cumulatively increased on January 1 of each calendar year 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. On January 1, 2023, the number of shares reserved for issuance under the 2021 ESPP was increased by 274,716 shares. The first offering period under the 2021 ESPP commenced on December 1, 2022 and ends May 31, 2023. As of March 31, 2023, no shares have been issued under the 2021 ESPP. As of March 31, 2023, there were 841,436 shares available for future issuance under the 2021 ESPP. Stock-Based Compensation Expense During the three months ended March 31, 2023 and 2022, 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, ​ ​ 2023 2022 Research and development expense ​ $ 573 ​ $ 596 ​ General and administrative expense ​ 1,218 ​ 1,433 ​ Total stock-based compensation expense ​ $ 1,791 ​ $ 2,029 ​ ​ Stock Options A summary of stock option activity under the Company’s 2020 Plan, 2021 Plan and 2022 Inducement Plan is as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted ​ ​ ​ ​ ​ ​ ​ ​ ​ Average ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Remaining ​ Aggregate ​ ​ ​ ​ Weighted ​ Contractual ​ Intrinsic ​ ​ Number of ​ Average ​ Term ​ Value (1) ​ Stock Options Exercise Price (In years) (In thousands) Outstanding as of December 31, 2022 4,960,553 $ 8.04 8.59 ​ $ 89 Granted 1,530,505 ​ $ 2.69 ​ Exercised (156) ​ $ 2.69 ​ Cancelled/forfeited (403,302) ​ $ 7.36 ​ Outstanding as of March 31, 2023 6,087,600 ​ $ 6.74 8.45 ​ $ 962 Exercisable as of March 31, 2023 2,060,294 ​ $ 7.82 7.43 ​ $ 47 ​ (1) The aggregate intrinsic value of stock options is calculated as the difference between the exercise price of the stock options and the fair value of the Company’s common stock for those stock options that had exercise prices lower than the fair value of the Company’s common stock as of the end of the period. ​ 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, 2023 and 2022 was $1.95 and $8.83, respectively. The following assumptions were used in determining the fair value of options granted during the three months ended March 31, 2023 and 2022: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended March 31, ​ ​ ​ 2023 ​ 2022 ​ Risk-free interest rate ​ ​ 3.97 – 3.98 % ​ 1.47 – 1.89 % Expected dividend yield ​ ​ 0 % ​ 0 % Expected term (in years) ​ ​ 6.02 – 6.08 ​ ​ 6.00 – 6.08 ​ Expected volatility ​ ​ 82.35 % ​ 80.75 – 80.92 % ​ As of March 31, 2023, the Company had unrecognized stock-based compensation expense of $16.1 million related to stock options issued to employees and directors, which is expected to be recognized over a weighted-average period of 2.75 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, 2022 ​ 46,160 ​ $ 5.51 Vested ​ (14,217) ​ $ 5.51 Canceled/Forfeited (1,229) $ 5.51 Unvested as of March 31, 2023 30,714 $ 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, 2023 and 2022, the aggregate fair value of the restricted stock awards that vested was less than $0.1 million and $0.2 million, respectively. As of March 31, 2023, total unrecognized stock-based compensation expense related to unvested restricted stock awards was $0.2 million, which is expected to be recognized over a weighted-average period of 0.80 years.

Net Loss Per Share

Net Loss Per Share	3 Months Ended
	Mar. 31, 2023
Net Loss Per Share
Net Loss Per Share	9. 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, ​ ​ ​ 2023 ​ 2022 ​ Unvested restricted common stock 30,714 95,134 Outstanding stock options 6,087,600 4,948,376 Warrants 2,631 2,631 Unvested employee stock purchase plan shares ​ 68,884 ​ — ​ Total common stock equivalents 6,189,829 5,046,141 ​

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	3 Months Ended
	Mar. 31, 2023
Summary of Significant Accounting Policies
Basis of Presentation	Basis of Presentation The Company’s unaudited interim condensed consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States (“U.S. GAAP”). Any reference in these notes to applicable guidance is meant to refer to the authoritative U.S. GAAP as found in the Accounting Standards Codification (“ASC”) and Accounting Standards Updates (“ASUs”) of the Financial Accounting Standards Board (“FASB”). Certain information and footnote disclosures normally included in financial statements prepared in accordance with U.S. GAAP have been condensed or omitted from this report, as is permitted by such rules and regulations. Accordingly, these financial statements should be read in conjunction with the audited financial statements as of and for the year ended December 31, 2022 and notes thereto, included in the Company’s Annual Report on Form 10-K filed with the U.S. Securities and Exchange Commission (“SEC”) on March 2, 2023. The unaudited interim condensed consolidated financial statements have been prepared on the same basis as the audited financial statements. In the opinion of the Company’s management, the accompanying unaudited interim condensed consolidated financial statements contain all adjustments which are necessary to present fairly the Company’s financial position as of March 31, 2023 and the results of its operations and cash flows for the three months ended March 31, 2023 and March 31, 2022. Such adjustments are of a normal and recurring nature. The results for the three months ended March 31, 2023 are not necessarily indicative of the results for the year ending December 31, 2023 or for any future period.
Principles of Consolidation	Principles of Consolidation The accompanying condensed consolidated financial statements include the accounts of the Company and its wholly owned subsidiaries: Xilio Development, Inc., a Delaware corporation and Xilio Securities Corporation, a Massachusetts security corporation. All intercompany accounts and transactions have been eliminated in consolidation.
Concentrations of Credit Risk	Concentrations of Credit Risk Financial instruments that potentially expose the Company to concentrations of credit risk consist primarily of cash and cash equivalents. The Company holds all cash and cash equivalents at accredited financial institutions. Bank accounts in the United States are generally insured by the Federal Deposit Insurance Corporation (“FDIC”) up to $250,000. Substantially all of the Company’s cash and cash equivalents are FDIC insured, including funds held through an insured cash sweep program. The Company has not experienced any losses in its cash and cash equivalents and does not believe that it is subject to unusual credit risk beyond the normal credit risk associated with commercial banking relationships.

Property and Equipment, Net (Ta

Property and Equipment, Net (Tables)	3 Months Ended
	Mar. 31, 2023
Property and Equipment, Net
Summary of property and equipment, net	​ ​ ​ ​ ​ ​ ​ ​ ​ March 31, December 31, ​ ​ 2023 ​ 2022 Laboratory equipment ​ $ 6,101 ​ $ 5,587 Computers and software ​ 228 ​ 228 Furniture and fixtures ​ 681 ​ 636 Leasehold improvements ​ 5,124 ​ 5,124 Construction in process ​ — ​ 98 Total property and equipment ​ ​ 12,134 ​ ​ 11,673 Less: accumulated depreciation ​ (4,882) ​ (4,418) Property and equipment, net ​ $ 7,252 ​ $ 7,255 ​

Accrued Expenses (Tables)

Accrued Expenses (Tables)	3 Months Ended
	Mar. 31, 2023
Accrued Expenses
Summary of accrued expenses	​ ​ ​ ​ ​ ​ ​ ​ ​ March 31, December 31, ​ ​ 2023 ​ 2022 External research and development ​ $ 3,640 ​ $ 3,178 Personnel-related ​ 1,745 ​ 5,413 Professional and consulting fees ​ 829 ​ 1,536 Other ​ ​ 269 ​ ​ 200 Total accrued expenses ​ $ 6,483 ​ $ 10,327

Loan and Security Agreement (Ta

Loan and Security Agreement (Tables)	3 Months Ended
	Mar. 31, 2023
Loan and Security Agreement
Schedule of minimum aggregate future loan principal payments	​ ​ ​ ​ ​ ​ Minimum Loan ​ ​ Payments 2023 (remaining nine months) ​ $ 5,000 2024 ​ 3,333 Total future principal payments ​ 8,333 Less: unamortized discount ​ (118) Total note payable ​ $ 8,215 ​

Preferred Stock and Common St_2

Preferred Stock and Common Stock (Tables)	3 Months Ended
	Mar. 31, 2023
Preferred Stock and Common Stock
Schedule of Shares Reserved for Future Issuance	​ ​ ​ ​ ​ ​ ​ ​ March 31, ​ December 31, ​ ​ 2023 ​ 2022 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 Plan and 2020 Plan 6,087,600 4,960,553 Shares of common stock reserved for future awards under the 2021 Plan 3,096,174 2,848,568 Shares of common stock reserved for future awards under the 2022 Inducement Plan ​ 275,000 ​ 275,000 Shares of common stock reserved for purchase under the 2021 ESPP ​ 841,436 ​ 566,720 Total shares reserved for future issuance 10,302,841 8,653,472

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	3 Months Ended
	Mar. 31, 2023
Stock-Based Compensation
Schedule of stock-based compensation expense	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended March 31, ​ ​ 2023 2022 Research and development expense ​ $ 573 ​ $ 596 ​ General and administrative expense ​ 1,218 ​ 1,433 ​ Total stock-based compensation expense ​ $ 1,791 ​ $ 2,029 ​ ​
Summary of stock option activity	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted ​ ​ ​ ​ ​ ​ ​ ​ ​ Average ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Remaining ​ Aggregate ​ ​ ​ ​ Weighted ​ Contractual ​ Intrinsic ​ ​ Number of ​ Average ​ Term ​ Value (1) ​ Stock Options Exercise Price (In years) (In thousands) Outstanding as of December 31, 2022 4,960,553 $ 8.04 8.59 ​ $ 89 Granted 1,530,505 ​ $ 2.69 ​ Exercised (156) ​ $ 2.69 ​ Cancelled/forfeited (403,302) ​ $ 7.36 ​ Outstanding as of March 31, 2023 6,087,600 ​ $ 6.74 8.45 ​ $ 962 Exercisable as of March 31, 2023 2,060,294 ​ $ 7.82 7.43 ​ $ 47 ​
Schedule of assumptions used in determining fair value of options granted	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended March 31, ​ ​ ​ 2023 ​ 2022 ​ Risk-free interest rate ​ ​ 3.97 – 3.98 % ​ 1.47 – 1.89 % Expected dividend yield ​ ​ 0 % ​ 0 % Expected term (in years) ​ ​ 6.02 – 6.08 ​ ​ 6.00 – 6.08 ​ Expected volatility ​ ​ 82.35 % ​ 80.75 – 80.92 % ​
Summary of restricted stock activity	​ ​ ​ ​ ​ ​ ​ ​ Number Weighted ​ ​ of Shares ​ Average ​ ​ of Restricted ​ Grant Date ​ Stock Fair Value Unvested as of December 31, 2022 ​ 46,160 ​ $ 5.51 Vested ​ (14,217) ​ $ 5.51 Canceled/Forfeited (1,229) $ 5.51 Unvested as of March 31, 2023 30,714 $ 5.51 ​

Net Loss Per Share (Tables)

Net Loss Per Share (Tables)	3 Months Ended
	Mar. 31, 2023
Net Loss Per Share
Schedule of antidilutive securities excluded from computation of diluted net loss per share	​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ ​ March 31, ​ ​ ​ 2023 ​ 2022 ​ Unvested restricted common stock 30,714 95,134 Outstanding stock options 6,087,600 4,948,376 Warrants 2,631 2,631 Unvested employee stock purchase plan shares ​ 68,884 ​ — ​ Total common stock equivalents 6,189,829 5,046,141

Description of Business and L_2

Description of Business and Liquidity and Capital Resources - Liquidity and Capital Resources (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Dec. 31, 2022	Mar. 31, 2022
Description of Business and Liquidity and Capital Resources
Cash and cash equivalents	$ 93,271	$ 120,385	$ 176,959
Substantial doubt about going concern within one year	false

Description of Business and L_3

Description of Business and Liquidity and Capital Resources - IPO (Details) $ in Millions	3 Months Ended
	Sep. 30, 2021 USD ($)
IPO
Sale of stock
Net proceeds received	$ 116.4

Property and Equipment, Net (De

Property and Equipment, Net (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022	Dec. 31, 2022
Property and Equipment
Property and equipment	$ 12,134		$ 11,673
Less accumulated depreciation	(4,882)		(4,418)
Property and equipment, net	7,252		7,255
Depreciation	500	$ 400
Laboratory equipment
Property and Equipment
Property and equipment	6,101		5,587
Computers and software
Property and Equipment
Property and equipment	228		228
Furniture & fixtures
Property and Equipment
Property and equipment	681		636
Leasehold improvements
Property and Equipment
Property and equipment	$ 5,124		5,124
Construction in process
Property and Equipment
Property and equipment			$ 98

Accrued Expenses (Details)

Accrued Expenses (Details) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022
Accrued Expenses
External research and development	$ 3,640	$ 3,178
Personnel related	1,745	5,413
Professional and consulting services	829	1,536
Other	269	200
Total accrued expenses	$ 6,483	$ 10,327

Loan and Security Agreement - D

Loan and Security Agreement - Description (Details) - Loan Agreement - USD ($) $ in Millions	1 Months Ended
	Nov. 30, 2019	Mar. 31, 2023
Loan and security agreement
Borrowed amount	$ 10
Interest rate at end of period (as a percent)		8.25%
Additional interest rate upon event of default (as a percent)	5%
Minimum
Loan and security agreement
Stated interest rate	4.75%
Prime rate
Loan and security agreement
Basis spread (as percent)	0.25%

Loan and Security Agreement - M

Loan and Security Agreement - Maturities (Details) - Loan Agreement - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Minimum aggregate future loan payments
2023 (remaining nine months)	$ 5,000
2024	3,333
Total future principal payments	8,333
Less: unamortized discount	(118)
Total notes payable	8,215
Interest expense	$ 200	$ 200

Commitments and Contingencies (

Commitments and Contingencies (Details) $ in Millions	1 Months Ended
	Aug. 31, 2019 ft²	Mar. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)
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	$ 1.6

Preferred Stock and Common St_3

Preferred Stock and Common Stock - Authorized (Details) - $ / shares	Mar. 31, 2023	Dec. 31, 2022
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
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, shares authorized	200,000,000	200,000,000
Common stock, par value (in dollars per share)	$ 0.0001	$ 0.0001

Preferred Stock and Common St_4

Preferred Stock and Common Stock - Shares Reserved for Future Issuance (Details) - shares	Mar. 31, 2023	Dec. 31, 2022
Shares for future issuance
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 Plans	6,087,600	4,960,553
Total shares reserved for future issuance	10,302,841	8,653,472
2021 Plan and 2020 Plan
Shares for future issuance
Shares of common stock reserved for exercise of outstanding stock options under the Plans	6,087,600	4,960,553
2021 Plan
Shares for future issuance
Shares of common stock reserved for future awards or purchase under the Plans	3,096,174	2,848,568
2022 Inducement Plan
Shares for future issuance
Shares of common stock reserved for future awards or purchase under the Plans	275,000	275,000
Total shares reserved for future issuance		275,000
2021 ESPP
Shares for future issuance
Shares of common stock reserved for future awards or purchase under the Plans	841,436	566,720

Stock-Based Compensation - Stoc

Stock-Based Compensation - Stock Incentive Plans (Details) - shares		1 Months Ended
	Jan. 01, 2023	Oct. 31, 2021	Mar. 31, 2023	Dec. 31, 2022
Stock-Based Compensation
Common stock reserved for issuance (in shares)			10,302,841	8,653,472
2021 Plan
Stock-Based Compensation
Additional common stock reserved under the plan (in shares)	1,373,580
Available for future issuance (in shares)			3,096,174	2,848,568
2021 Plan | Minimum
Stock-Based Compensation
Common stock reserved for issuance (in shares)		2,654,828
2021 Plan | Maximum
Stock-Based Compensation
Additional common stock to be reserved for issuance (in shares)		3,967,038
Annual increase in number of shares reserved for issuance (as a percent)		5%

Stock-Based Compensation - 2022

Stock-Based Compensation - 2022 Inducement Plan (Details) - shares	3 Months Ended
	Mar. 31, 2023	Dec. 31, 2022
Stock-Based Compensation
Common stock reserved for issuance (in shares)	10,302,841	8,653,472
Stock options granted during the period (in shares)	1,530,505
2022 Inducement Plan
Stock-Based Compensation
Common stock reserved for issuance (in shares)		275,000
Stock options granted during the period (in shares)	0

Stock-Based Compensation - Empl

Stock-Based Compensation - Employee Stock Purchase Plan (Details) - shares		1 Months Ended	3 Months Ended
	Jan. 01, 2023	Oct. 31, 2021	Mar. 31, 2023	Dec. 31, 2022
Stock-Based Compensation
Common stock reserved for issuance (in shares)			10,302,841	8,653,472
Employee stock purchase plan
Stock-Based Compensation
Common stock reserved for issuance (in shares)		292,031
Additional common stock reserved under the plan (in shares)	274,716
Shares issued under plan (in shares)			0
Available for future issuance (in shares)			841,436
Employee stock purchase plan | Maximum
Stock-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%

Stock-Based Compensation - St_2

Stock-Based Compensation - Stock-based compensation expense (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Stock-Based Compensation
Total compensation expense	$ 1,791	$ 2,029
Research and development expense
Stock-Based Compensation
Total compensation expense	573	596
General and administrative expense
Stock-Based Compensation
Total compensation expense	$ 1,218	$ 1,433

Stock-Based Compensation - St_3

Stock-Based Compensation - Stock option activity (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2023	Dec. 31, 2022
Options Outstanding
Outstanding at beginning of period (in shares)	4,960,553
Granted (in shares)	1,530,505
Exercised (in shares)	(156)
Cancelled/forfeited (in shares)	(403,302)
Outstanding at end of period (in shares)	6,087,600	4,960,553
Exercisable at end of period (in shares)	2,060,294
Weighted Average Exercise Price
Outstanding (in dollars per share)	$ 6.74	$ 8.04
Granted (in dollars per share)	2.69
Exercised (in dollars per share)	2.69
Cancelled/forfeited (in dollars per share)	7.36
Exercisable at end of period (in dollars per share)	$ 7.82
Weighted Average Remaining Contractual Term (In years)
Outstanding (in years)	8 years 5 months 12 days	8 years 7 months 2 days
Exercisable at end of period (in years)	7 years 5 months 4 days
Aggregate Intrinsic Value
Outstanding (in dollars)	$ 962	$ 89
Exercisable (in dollars)	$ 47

Stock-Based Compensation - St_4

Stock-Based Compensation - Stock options, fair value assumptions (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Stock-Based Compensation
Fair value of options granted (in dollars per share)	$ 1.95	$ 8.83
Stock options
Stock-Based Compensation
Risk-free interest rate, minimum (as a percent)	3.97%	1.47%
Risk-free interest rate, maximum (as a percent)	3.98%	1.89%
Expected dividend yield (as a percent)	0%	0%
Expected volatility (as a percent)	82.35%
Expected volatility, minimum (as percentage)		80.75%
Expected volatility, maximum (as percentage)		80.92%
Unrecognized stock-based compensation expense	$ 16.1
Weighted-average period for unrecognized compensation expense to be recognized	2 years 9 months
Stock options | Minimum
Stock-Based Compensation
Expected term (in years)	6 years 7 days	6 years
Stock options | Maximum
Stock-Based Compensation
Expected term (in years)	6 years 29 days	6 years 29 days

Stock-Based Compensation - Rest

Stock-Based Compensation - Restricted Stock (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended	3 Months Ended
	Jun. 30, 2020	Mar. 31, 2023	Mar. 31, 2022
Weighted Average Grant Date Fair Value
Stock-based compensation expense		$ 1,791	$ 2,029
Restricted stock
Equity Based Compensation
Outstanding at beginning of period (in shares)		46,160
Vested (in shares)		(14,217)
Canceled/Forfeited (in shares)		(1,229)
Outstanding at end of period (in shares)		30,714
Weighted Average Grant Date Fair Value
Outstanding at beginning of period (in dollars per share)		$ 5.51
Vested (in dollars per share)		5.51
Cancelled/forfeited (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 stock-based compensation expense		$ 200
Weighted-average period for unrecognized compensation expense to be recognized		9 months 18 days
Restricted stock | Maximum
Weighted Average Grant Date Fair Value
Aggregate fair value of restricted stock awards that vested		$ 100

Net Loss Per Share (Details)

Net Loss Per Share (Details) - shares	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Net Loss Per Share
Total common stock equivalents	6,189,829	5,046,141
Restricted stock
Net Loss Per Share
Total common stock equivalents	30,714	95,134
Stock options
Net Loss Per Share
Total common stock equivalents	6,087,600	4,948,376
Warrants
Net Loss Per Share
Total common stock equivalents	2,631	2,631
Employee stock purchase plan
Net Loss Per Share
Total common stock equivalents	68,884