0001558370-24-004530 | 10-K | XBRL Viewer

Income Taxes

12 Months Ended

Dec. 31, 2023

12. Income Taxes

The Company has not recorded a current or deferred tax provision for the years ended December 31, 2023 and 2022. The effective income tax rate differed from the amount computed by applying the federal statutory rate to the Company’s loss before income taxes as follows:


	Year Ended December 31,
	2023		2022
Tax effected at statutory rate	21.0	%	21.0	%
State taxes	6.5		5.2
Stock-based compensation	(1.4)		(0.6)
Non-deductible expenses	(0.8)		(0.9)
Federal research and development credits	3.5		2.8
Change in valuation allowance	(28.8)		(27.5)
Effective income tax rate	0.0	%	0.0	%

Deferred tax assets consist of the following as of December 31, 2023 and 2022:


	Year Ended December 31,
	2023		2022
Deferred tax assets:
Federal net operating loss carryforwards	$	43,953	$	37,277
State net operating loss carryforwards		11,433		9,267
Capitalized research and development expenditures		24,485		14,469
Research and development credit carryforwards		10,359		7,104
Lease liability		2,510		2,761
Accruals and reserves		210		241
Intangible assets		1,793		1,917
Stock-based compensation		1,213		1,374
Total deferred tax assets:		95,956		74,410
Valuation allowance		(92,978)		(71,003)
Subtotal		2,978		3,407
Deferred tax liabilities:
Property and equipment		(1,578)		(1,881)
Right of use asset		(1,400)		(1,526)
Total deferred tax liabilities		(2,978)		(3,407)
Net deferred tax assets	$	—	$	—

The Company has had no income tax expense due to operating losses incurred since inception. Deferred tax assets are reduced by a valuation allowance if, based on the weight of available positive and negative evidence, it is more likely than not that some portion or all of the deferred tax assets will not be realized. The Company has evaluated the positive and negative evidence bearing upon the realizability of its deferred tax assets. Based on this, the Company has provided a valuation allowance for the full amount of the net deferred tax assets as the realization of the deferred tax assets is not determined to be more likely than not. During the year ended December 31, 2023, the valuation allowance increased by $22.0 million primarily due to the Company’s book loss and capitalized research and development expenditures reported in the period and the generation of additional research and development credits.

As of December 31, 2023, the Company had $209.3 million and $180.9 million of federal and state operating loss carryforwards, respectively. Of the federal net operating loss carryovers, $204.5 million are not subject to expiration and the remaining federal and state net operating loss carryovers begin to expire in 2035. These loss carryforwards are available to reduce future federal taxable income, if any. As of December 31, 2023, the Company had federal and state research and development credit carryovers of $7.8 million and $3.1 million, which may be available to offset any future income tax and which will begin to expire in 2033. These loss and credit carryforwards are subject to review and possible adjustment by the appropriate taxing authorities.

Utilization of the Company’s net operating loss (“NOL”) carryforwards and research and development credit carryforwards may be subject to a substantial annual limitation due to ownership change limitations that have occurred previously or that could occur in the future in accordance with Section 382 of the Internal Revenue Code of 1986, as amended (“Section 382”) as well as similar state provisions. These ownership changes may limit the amount of NOL and research and development credit carryforwards that can be utilized annually to offset future taxable income and taxes, respectively. In general, an ownership change as defined by Section 382 results from transactions increasing the ownership of certain stockholders or public groups in the stock of a corporation by more than 50% over a three-year period. Since its formation, the Company has raised capital through the issuance of capital stock on several occasions. These financings could result in an “ownership change” as defined by Section 382. The Company has not yet completed a detailed study of its inception to date ownership change activity.

The Company follows the provisions of ASC 740-10, Accounting for Uncertainty in Income Taxes, which specifies how tax benefits for uncertain tax positions are to be recognized, measured, and recorded in financial statements; requires certain disclosures of uncertain tax matters; specifies how reserves for uncertain tax positions should be classified on the balance sheet; and provides transition and interim period guidance, among other provisions. As of December 31, 2023, and 2022, the Company has not recorded tax reserves associated with any unrecognized tax benefits. The Company’s policy is to recognize interest and penalties accrued on any uncertain tax positions as a component of income tax expense, if any, in its statements of income. As of December 31, 2023, and 2022, the Company had no reserves for uncertain tax positions. For the years ended December 31, 2023 and 2022, no estimated interest or penalties were recognized on uncertain tax positions. The Company has not recorded any interest or penalties on any unrecognized tax benefits since its inception.

The Company has not conducted a study of its research and development credit carryforwards. This study may result in an adjustment to research and development credit carryforwards; however, until a study is completed, and any adjustment is known, no amounts are being presented as an uncertain tax position. A full valuation allowance has been provided against the Company’s research and development credits and, if an adjustment is required, this adjustment would be offset by an adjustment to the valuation allowance. Thus, there would be no impact to the consolidated balance sheets or statements of operations and comprehensive loss if an adjustment were required.

The 2017 Tax Cuts and Jobs Act (“TCJA”) included a multitude of tax provisions, including several deferred changes that became effective for tax years ending after December 31, 2021. Included in the provisions was the TCJA’s amendment to Section 174 of the Internal Revenue Code of 1986, as amended (“Section 174”), which now requires U.S.-based and non-U.S-based research and experimental expenditures to be capitalized and amortized over a period of five or 15 years, respectively, for amounts paid in tax years starting after December 31, 2021. Prior to the TCJA amendment, Section 174 allowed taxpayers to either immediately deduct research and experimental expenditures in the year paid or incurred. The Company applied this required change in accounting method beginning in 2022.

The Company’s tax returns remain open to examination by the Internal Revenue Service and the Commonwealth of Massachusetts for the years ended December 31, 2020 to December 31, 2022. In addition, the Company’s tax carryover attributes such as net operating losses or credits from earlier periods are also subject to examination. The Company is currently not subject to any examinations by the Internal Revenue Service or any other tax authorities for any tax years.

- 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

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+ Details

Summary of Significant Accounting Policies - Segment Information (Details)	12 Months Ended
	Dec. 31, 2023 segment
Summary of Significant Accounting Policies
Number of operating segments	1

CONDENSED CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Current assets
Cash and cash equivalents	$ 44,704	$ 120,385
Prepaid expenses and other current assets	3,423	4,111
Total current assets	48,127	124,496
Restricted cash	1,587	1,562
Property and equipment, net	5,942	7,255
Operating lease right-of-use asset	5,125	5,585
Other non-current assets	145	267
Total assets	60,926	139,165
Current liabilities
Accounts payable	1,050	3,125
Accrued expenses	10,497	10,327
Operating lease liability, current portion	1,047	918
Note payable, current portion	3,315	6,667
Other current liabilities	48	82
Total current liabilities	15,957	21,119
Note payable, net of current portion		3,165
Operating lease liability, net of current portion	8,142	9,189
Other non-current liabilities		45
Total liabilities	24,099	33,518
Commitments and contingencies (Note 8)
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 December 31, 2023 and December 31, 2022; 27,613,263 shares issued and 27,607,646 shares outstanding at December 31, 2023; 27,471,607 shares issued and 27,425,447 shares outstanding at December 31, 2022	3	3
Additional paid-in capital	362,336	354,752
Accumulated deficit	(325,512)	(249,108)
Total stockholders' equity	36,827	105,647
Total liabilities and stockholders' equity	$ 60,926	$ 139,165

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Cash flows from operating activities:
Net loss	$ (76,404)	$ (88,222)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	1,900	1,847
Non-cash interest expense	157	223
Stock-based compensation expense	7,382	8,424
Loss on disposal of property and equipment	3	1
Changes in operating assets and liabilities:
Prepaid and other assets	688	344
Operating lease right-of-use asset	460	391
Accounts payable	(2,063)	485
Accrued expenses and other liabilities	175	1,585
Operating lease liability	(918)	(801)
Net cash used in operating activities	(68,620)	(75,723)
Cash flows from investing activities:
Purchases of property and equipment	(486)	(1,867)
Net cash used in investing activities	(486)	(1,867)
Cash flows from financing activities:
Repayments of debt principal	(6,667)
Payments of finance lease	(85)	(85)
Proceeds from issuance of common stock under employee stock purchase plan	194
Proceeds from exercise of stock options	8	16
Net cash used in financing activities	(6,550)	(69)
Decrease in cash, cash equivalents and restricted cash	(75,656)	(77,659)
Cash, cash equivalents and restricted cash, beginning of period	121,947	199,606
Cash, cash equivalents and restricted cash, end of period	46,291	121,947
Supplemental cash flow disclosure:
Cash paid for interest	573	555
Supplemental disclosure of non-cash activities:
Capital expenditures included in accounts payable or accrued expenses		19
Reconciliation to amounts within the consolidated balance sheets:
Cash and cash equivalents	44,704	120,385
Restricted cash	1,587	1,562
Cash, cash equivalents and restricted cash, end of period	$ 46,291	$ 121,947

Preferred Stock and Common Stock - Shares Reserved for Future Issuance (Details) - shares	Dec. 31, 2023	Dec. 31, 2022	Oct. 31, 2021
Shares for future issuance
Shares reserved for future issuance (in shares)	10,160,112	8,653,472
2020 Plan, 2021 Plan and 2022 Inducement Plan \| Employee Stock Option
Shares for future issuance
Shares reserved for future issuance (in shares)	9,456,237	8,084,121
2021 ESPP
Shares for future issuance
Shares reserved for future issuance (in shares)	701,244	566,720	292,031
Warrants
Shares for future issuance
Shares reserved for future issuance (in shares)	2,631	2,631

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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+ Details

401(k) Plan

12 Months Ended

Dec. 31, 2023

401(k) Plan

401(k) Plan

13. 401(k) Plan

The Company maintains a defined contribution savings plan for employees that is defined to qualify under Section 401(k) of the Internal Revenue Code, as amended, (the “401(k) Plan”) in which substantially all employees are eligible to participate. Under the 401(k) Plan, all employees who meet minimum age and service requirements may elect to defer a portion of their annual compensation on a pre-tax basis or post-tax basis, up to the maximum amount prescribed by statute. For each participating employee, the Company makes matching contributions equal to 100% of the first 3% of compensation contributed, plus 50% of the next 2% of compensation contributed, for a maximum of up to 4% of the employee’s eligible compensation. Matching contributions are fully vested at the time of contribution. The Company incurred expenses related to matching contributions on behalf of employees to the 401(k) Plan of $0.7 million and $0.3 million during the years ended December 31, 2023 and 2022, respectively.

Pay vs Performance Disclosure - USD ($) $ in Thousands	12 Months Ended
Pay vs Performance Disclosure - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Pay vs Performance Disclosure
Net Income (Loss)	$ (76,404)	$ (88,222)

- Definition

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

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+ Details

Property and Equipment, Net

12 Months Ended

Dec. 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 December 31, 2023 and 2022:


	December 31,		December 31,
	2023		2022
Laboratory equipment	$	5,815	$	5,587
Computers and software		183		228
Furniture and fixtures		681		636
Leasehold improvements		5,124		5,124
Construction in process		—		98
Total property and equipment		11,803		11,673
Less: accumulated depreciation		(5,861)		(4,418)
Property and equipment, net	$	5,942	$	7,255

The Company incurred depreciation and amortization expense related to property and equipment of $1.8 million and $1.7 million for the years ended December 31, 2023 and 2022, respectively.

Stock-Based Compensation - Employee Stock Purchase Plan (Details) - shares		1 Months Ended	12 Months Ended
	Jan. 01, 2024	Oct. 31, 2021	Dec. 31, 2023	Dec. 31, 2022
Stock-Based Compensation
Common stock reserved for issuance (in shares)			10,160,112	8,653,472
2021 ESPP
Stock-Based Compensation
Common stock reserved for issuance (in shares)		292,031	701,244	566,720
Shares available for future issuance (in shares)			701,244
Shares issued under plan (in shares)			140,192	0
2021 ESPP \| Maximum
Stock-Based Compensation
Annual increase in number of shares reserved for issuance (as a percent)		1.00%
Annual increase in number of shares reserved and available for issuance (in shares)		584,062
2021 ESPP \| Subsequent events
Stock-Based Compensation
Additional common stock reserved under the plan (in shares)	276,132

Stock-Based Compensation - Restricted Stock (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended	12 Months Ended
	Jun. 30, 2020	Dec. 31, 2023	Dec. 31, 2022
Weighted Average Grant Date Fair Value
Stock-based compensation expense		$ 7,382	$ 8,424
Restricted stock
Equity Based Compensation
Outstanding unvested awards at beginning of period (in shares)		46,160
Vested (in shares)		(39,250)
Canceled/Forfeited (in shares)		(1,293)
Outstanding unvested awards at end of period (in shares)		5,617	46,160
Weighted Average Grant Date Fair Value
Outstanding unvested awards 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 unvested awards at end of period (in dollars per share)		$ 5.51	$ 5.51
Granted (in shares)	552,546
Stock-based compensation expense		$ 300	$ 400
Aggregate fair value of restricted stock awards that vested		100	$ 300
Restricted stock \| Maximum
Weighted Average Grant Date Fair Value
Unrecognized stock-based compensation expense		$ 100

Accrued Expenses (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Accrued Expenses
External research and development	$ 4,867	$ 3,178
Personnel related	4,690	5,413
Professional and consulting services	845	1,536
Other	95	200
Total accrued expenses	$ 10,497	$ 10,327

Preferred Stock and Common Stock (Tables)

12 Months Ended

Dec. 31, 2023

Preferred Stock and Common Stock

Schedule of Shares Reserved for Future Issuance


	December 31,	December 31,
	2023	2022
Stock options	9,456,237	8,084,121
Employee Stock Purchase Plan	701,244	566,720
Warrants	2,631	2,631
Total shares reserved for future issuance	10,160,112	8,653,472

Leases - Schedule of supplemental balance sheet information related to leases (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Operating Lease:
Operating lease right-of-use asset	$ 5,125	$ 5,585
Operating lease liability, current portion	1,047	918
Operating lease liability, net of current portion	8,142	9,189
Finance Lease:
Other non-current assets	$ 134	$ 219
Finance Lease, Right-of-Use Asset, Statement of Financial Position	Other non-current assets	Other non-current assets
Other current liabilities	$ 48	$ 82
Finance Lease, Liability, Current, Statement of Financial Position	Other current liabilities	Other current liabilities
Other liabilities, long-term		$ 45
Finance Lease, Liability, Noncurrent, Statement of Financial Position	Other non-current liabilities	Other non-current liabilities
Weighted-average remaining lease term (in years):
Operating lease	6 years 2 months 12 days	7 years 2 months 12 days
Finance lease	8 months 12 days	1 year 8 months 12 days
Weighted-average discount rate:
Operating lease	8.00%	8.00%
Finance lease	6.90%	6.90%

Accrued Expenses (Tables)

12 Months Ended

Dec. 31, 2023

Accrued Expenses

Summary of accrued expenses


	December 31,		December 31,
	2023		2022
External research and development	$	4,867	$	3,178
Personnel-related		4,690		5,413
Professional and consulting fees		845		1,536
Other		95		200
Total accrued expenses	$	10,497	$	10,327

Accrued Expenses

12 Months Ended

Dec. 31, 2023

Accrued Expenses

Accrued Expenses

4. Accrued Expenses

Accrued expenses consist of the following as of December 31, 2023 and 2022:


	December 31,		December 31,
	2023		2022
External research and development	$	4,867	$	3,178
Personnel-related		4,690		5,413
Professional and consulting fees		845		1,536
Other		95		200
Total accrued expenses	$	10,497	$	10,327

Collaboration Agreements and Intellectual Property Licenses - Intellectual Property Licenses (Details) $ in Thousands	1 Months Ended	12 Months Ended
	Aug. 31, 2016 USD ($) item shares	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)	Dec. 31, 2020 USD ($)	Sep. 30, 2016 USD ($)
Agreements
Research and development		$ 52,136	$ 59,201
License Agreement \| AskGene
Agreements
Upfront payments payable				$ 6,000
Research and development				6,000
License Agreement \| AskGene \| Maximum \| IL-2 products
Agreements
Regulatory milestone payments payable				$ 13,000
License Agreement \| City of Hope
Agreements
Number of shares of common stock issued \| shares	24,019
Number of licensed products or services \| item	3
Costs incurred related to payment of specified development milestones		0	0
License Agreement \| City of Hope \| Maximum
Agreements
Development and regulatory milestones payable per product or licensed service	$ 10,300
License Agreement \| WuXi Biologics
Agreements
Development and regulatory milestones payable per product or licensed service					$ 25,800
Costs incurred related to payment of specified development milestones		$ 0	$ 0

Stock-Based Compensation - Stock options, fair value assumptions (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Stock-Based Compensation
Fair value of options granted (in dollars per share)	$ 2.02	$ 5.58
Maximum
Stock-Based Compensation
Aggregate intrinsic value of options exercised (in dollars)	$ 0.1	$ 0.1
Employee Stock Option
Stock-Based Compensation
Risk-free interest rate, minimum (as a percent)	3.57%	1.47%
Risk-free interest rate, maximum (as a percent)	4.40%	4.22%
Expected dividend yield (as a percent)	0.00%	0.00%
Expected volatility, minimum (as percentage)	81.70%	80.80%
Expected volatility, maximum (as percentage)	87.30%	87.60%
Unrecognized stock-based compensation expense	$ 12.5
Weighted-average period for unrecognized compensation expense to be recognized	2 years
Employee Stock Option \| Minimum
Stock-Based Compensation
Expected term (in years)	5 years 6 months	5 years 3 months 18 days
Employee Stock Option \| Maximum
Stock-Based Compensation
Expected term (in years)	6 years 1 month 6 days	6 years 1 month 6 days

Preferred Stock and Common Stock - Authorized (Details) - $ / shares	Dec. 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

Stock-Based Compensation - Stock option activity (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Options Outstanding
Outstanding at beginning of period (in shares)	4,960,553
Granted (in shares)	3,738,555
Exercised (in shares)	(2,757)
Cancelled/forfeited (in shares)	(1,240,556)
Outstanding at end of period (in shares)	7,455,795	4,960,553
Exercisable at end of period (in shares)	3,103,732
Weighted Average Exercise Price
Outstanding at beginning of period (in dollars per share)	$ 5.52	$ 8.04
Granted (in dollars per share)	2.75
Exercised (in dollars per share)	2.82
Cancelled/forfeited (in dollars per share)	7.26
Outstanding at end of period (in dollars per share)	5.52	$ 8.04
Exercisable at end of period (in dollars per share)	$ 7.04
Weighted Average Remaining Contractual Term (In years)
Outstanding (in years)	8 years	8 years 7 months 6 days
Exercisable at end of period (in years)	6 years 7 months 6 days
Aggregate Intrinsic Value
Outstanding (in dollars)		$ 89

Property and Equipment, Net (Tables)

12 Months Ended

Dec. 31, 2023

Property and Equipment, Net

Summary of property and equipment, net


	December 31,		December 31,
	2023		2022
Laboratory equipment	$	5,815	$	5,587
Computers and software		183		228
Furniture and fixtures		681		636
Leasehold improvements		5,124		5,124
Construction in process		—		98
Total property and equipment		11,803		11,673
Less: accumulated depreciation		(5,861)		(4,418)
Property and equipment, net	$	5,942	$	7,255

Subsequent Events (Details) - Subsequent events $ / shares in Units, $ in Millions	Mar. 28, 2024 USD ($) $ / shares shares	Mar. 27, 2024 USD ($) employee $ / shares
Strategic Portfolio Reprioritization and Workforce Reduction
Reduction in headcount (number of employees) \| employee		15
Reduction in headcount (percent of employees)		21.00%
Initial Gilead Private Placement
License Agreement and Issuance of Commons Stock
Purchase price (in dollars per share) \| $ / shares	$ 1.97
Number of shares sold \| shares	6,860,223
Aggregate purchase price (in dollars) \| $	$ 13.5
March 2024 Private Placement
License Agreement and Issuance of Commons Stock
Purchase price (in dollars per share) \| $ / shares	$ 0.64
Number of shares sold \| shares	1,953,125
March 2024 Private Placement
Warrants issued (in shares) \| shares	15,627,441
Purchase price, warrant (in dollars per share) \| $ / shares	$ 0.6399
License Agreement \| Gilead Sciences, Inc.
License Agreement and Issuance of Commons Stock
Upfront payment to be received \| $		$ 43.5
Upfront cash payment to be received \| $		30.0
Amount of initial payment to be received related to equity investment \| $		$ 13.5
Purchase price (in dollars per share) \| $ / shares		$ 1.97

Description of Business and Liquidity and Going Concern

12 Months Ended

Dec. 31, 2023

Description of Business and Liquidity and Going Concern

Description of Business and Liquidity and Going Concern

1. Description of Business, Liquidity and Going Concern

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 Going Concern

Since its inception, the Company has devoted substantially all of its financial resources and efforts to research and development activities. As of December 31, 2023, the Company had an accumulated deficit of $325.5 million and has incurred significant operating losses, including net losses of $76.4 million and $88.2 million for the years ended December 31, 2023 and 2022, respectively. The Company expects its operating losses and negative operating cash flows to continue for the foreseeable future as it continues to advance its product candidates through clinical trials, maintains the infrastructure necessary to support these activities and continues to incur costs associated with operating as a public company. As of December 31, 2023, the Company had cash and cash equivalents of $44.7 million. The Company anticipates that its cash and cash equivalents as of December 31, 2023, together with (i) the $30.0 million upfront payment under the exclusive license agreement with Gilead Sciences, Inc. (“Gilead”), (ii) the approximately $13.5 million in proceeds from the initial private placement with Gilead, which closed on March 28, 2024, and (iii) the approximately $11.3 million in gross proceeds from the Company’s private placement, which is expected to close on April 2, 2024 (subject to customary closing conditions), and after giving effect to (a) one-time costs and anticipated future cost savings associated with the Company’s strategic portfolio reprioritization and workforce reduction announced in March 2024 and (b) the repayment in the first quarter of 2024 of the outstanding loan balance under the Company’s loan and security agreement with Pacific Western Bank (“PacWest”), will be sufficient to fund the Company’s operating expenses and capital expenditure requirements into the second quarter of 2025. For further information regarding these transactions and other subsequent events, please see Note 14, Subsequent Events. However, the Company has based this estimate on assumptions that may prove to be wrong, and the Company could exhaust its available capital resources sooner than it anticipates. In addition, since these amounts may not be sufficient to fund its operations for at least twelve months from the date of issuance of the consolidated financial statements, there is substantial doubt about the Company’s ability to continue as a going concern.

To continue to fund the operations of the Company, management has developed plans, which in the near term primarily consist of raising additional capital through one or more of the following: additional equity or debt financings; additional collaborations, partnerships or licensing transactions; or other sources. However, there can be no assurance that the Company will be able to complete any such transaction on acceptable terms or otherwise, and the Company may be unable to obtain sufficient additional capital. If the Company is not able to secure sufficient additional capital in the near term, the Company may in the future need to implement additional cost reduction strategies, which could include delaying, limiting, further reducing or eliminating both internal and external costs related to its operations and research and development programs.

The accompanying consolidated financial statements have been prepared on a going concern basis, which contemplates the realization of assets and satisfaction of liabilities in the ordinary course of business. The consolidated financial statements do not include any adjustments relating to the recoverability and classification of recorded asset amounts or the amounts and classification of liabilities that might result from the outcome of this uncertainty.

Leases - Future minimum lease payments under non-cancellable leases (Details) $ in Thousands	Dec. 31, 2023 USD ($)
Operating leases
2024	$ 1,733
2025	1,785
2026	1,839
2027	1,894
2028	1,951
Thereafter	2,516
Total future minimum lease payments	11,718
Present value adjustment	(2,529)
Present value of lease liabilities	$ 9,189
Operating Lease, Liability, Statement of Financial Position	Operating lease liability, current portion, Operating lease liability, net of current portion
Finance lease
2024	$ 49
Total future minimum lease payments	49
Present value adjustment	(1)
Present value of lease liabilities	$ 48
Finance Lease, Liability, Statement of Financial Position	Other current liabilities, Other non-current liabilities

Income Taxes - Effective income tax rate reconciliation (Details)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Effective income tax rate reconciliation
Tax effected at statutory rate	21.00%	21.00%
State taxes	6.50%	5.20%
Stock-based compensation	(1.40%)	(0.60%)
Non-deductible expenses	(0.80%)	(0.90%)
Federal research and development credits	3.50%	2.80%
Change in valuation allowance	(28.80%)	(27.50%)
Effective income tax rate	0.00%	0.00%

Net Loss Per Share (Details) - shares	12 Months Ended
Net Loss Per Share (Details) - shares	Dec. 31, 2023	Dec. 31, 2022
Net Loss Per Share
Total common stock equivalents	7,532,685	5,086,566
Restricted stock
Net Loss Per Share
Total common stock equivalents	5,617	46,160
Employee Stock Option
Net Loss Per Share
Total common stock equivalents	7,455,795	4,960,553
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	68,642	77,222

Loan and Security Agreement

12 Months Ended

Dec. 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, entered into a loan and security agreement (as amended and restated in May 2023, the “Loan Agreement”) with PacWest, with the Company as a guarantor. Under the Loan Agreement, in November 2019, Xilio Development borrowed $10.0 million under a term loan. Interest on amounts outstanding under the Loan Agreement accrued at a variable annual rate equal to the greater of (i) the prime rate plus 0.25% or (ii) 4.75%. As of December 31, 2023, the interest rate on the term loan was 8.75%. Xilio Development was required to make interest-only payments on any outstanding balances through December 31, 2022. Xilio Development commenced making equal monthly payments of principal plus interest in January 2023.

As of December 31, 2023, the Company and Xilio Development were in compliance with all covenants under the Loan Agreement. Xilio Development had the following future loan principal payments under the Loan Agreement at December 31, 2023:


	Minimum Loan
	Payments
2024	$	3,333
Total future principal payments		3,333
Less: unamortized discount		(18)
Total note payable	$	3,315

The Company recognized $0.7 million and $0.8 million of interest expense related to the Loan Agreement for the years ended December 31, 2023 and 2022, respectively, which is reflected in other income, net on the consolidated statements of operations and comprehensive loss.

In the first quarter of 2024, Xilio Development repaid all amounts outstanding under the Loan Agreement, and PacWest released all security interests in Xilio Development’s and its affiliates’ assets.

- 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://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Subparagraph (h)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1B

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

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 470
-Name Accounting Standards Codification
-Publisher FASB
-URI https://asc.fasb.org//470/tableOfContent

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1B

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Subparagraph (g)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1B

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Subparagraph (i)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1B

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1C
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1C

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
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-Name Accounting Standards Codification
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-Paragraph 1C
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-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1C

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1C
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1C

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
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-Name Accounting Standards Codification
-Section 50
-Paragraph 1E
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-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1E

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1I
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1I

Reference 12: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
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-Section 50
-Paragraph 1I
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1I

Reference 13: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1I
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1I

+ Details

Summary of Significant Accounting Policies - Stock-Based Compensation (Details)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Employee Stock Option
Stock-Based Compensation
Expected dividend yield (as a percent)	0.00%	0.00%

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

+ Details

Description of Business and Liquidity and Going Concern - Liquidity and Going Concern (Details) - USD ($) $ in Thousands				12 Months Ended
	Apr. 02, 2024	Mar. 28, 2024	Mar. 27, 2024	Dec. 31, 2023	Dec. 31, 2022
Agreements
Accumulated deficit				$ 325,512	$ 249,108
Net loss				76,404	88,222
Cash and cash equivalents				$ 44,704	$ 120,385
Substantial doubt about going concern within one year				true
Initial Gilead Private Placement \| Subsequent events
Agreements
Aggregate gross proceeds from private placement (in dollars)		$ 13,500
March 2024 Private Placement \| Forecast
Agreements
Aggregate gross proceeds from private placement (in dollars)	$ 11,300
License Agreement \| Gilead Sciences, Inc. \| Subsequent events
Agreements
Upfront cash payment to be received			$ 30,000

Preferred Stock and Common Stock - Voting, Dividends and Liquidation (Details) - Common Stock $ in Millions	12 Months Ended	26 Months Ended
	Dec. 31, 2023 Vote	Dec. 31, 2023 USD ($)
Preferred stock and Common stock
Number of votes for each share held \| Vote	1
Dividends declared \| $		$ 0.0

Summary of Significant Accounting Policies - Property and Equipment (Details)	Dec. 31, 2023
Computers and software
Property and Equipment
Estimated Useful Life	3 years
Laboratory equipment
Property and Equipment
Estimated Useful Life	5 years
Furniture & fixtures
Property and Equipment
Estimated Useful Life	5 years

Net Loss Per Share

12 Months Ended

Dec. 31, 2023

Net Loss Per Share

Net Loss Per Share

11. Net Loss Per Share

The following table sets forth the outstanding common stock equivalents, presented based on amounts outstanding at each period end, that were excluded from the calculation of diluted net loss per share for the periods indicated because including them would have been anti-dilutive.


	Year Ended
	December 31,
	2023	2022
Unvested restricted common stock	5,617	46,160
Outstanding stock options	7,455,795	4,960,553
Warrants	2,631	2,631
Unvested employee stock purchase plan shares	68,642	77,222
Total common stock equivalents	7,532,685	5,086,566

Income Taxes - Operating loss carryforwards (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Income Taxes
Tax expense	$ 0	$ 0
Increase in valuation allowance	22,000
Federal
Income Taxes
Operating loss carryforwards	209,300
Operating loss carryovers not subject to expiration	204,500
State
Income Taxes
Operating loss carryforwards	$ 180,900

- Definition

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

+ References + Details

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)	64,415
Exercise of stock options		16		16
Exercise of stock options (in shares)	2,657
Stock-based compensation expense		8,424		8,424
Net Income (Loss)			(88,222)	(88,222)
Ending balance at Dec. 31, 2022	$ 3	354,752	(249,108)	105,647
Ending balance (in shares) at Dec. 31, 2022	27,425,447
Stockholders' Deficit
Issuance of common stock under employee stock purchase plan		194		194
Issuance of common stock under employee stock purchase plan (in shares)	140,192
Vesting of restricted common stock (in shares)	39,250
Exercise of stock options		8		$ 8
Exercise of stock options (in shares)	2,757			2,757
Stock-based compensation expense		7,382		$ 7,382
Net Income (Loss)			(76,404)	(76,404)
Ending balance at Dec. 31, 2023	$ 3	$ 362,336	$ (325,512)	$ 36,827
Ending balance (in shares) at Dec. 31, 2023	27,607,646

Income Taxes - Deferred tax assets (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Deferred tax assets:
Federal net operating loss carryforwards	$ 43,953	$ 37,277
State net operating loss carryforwards	11,433	9,267
Capitalized research and development expenditures	24,485	14,469
Research and development credit carryforwards	10,359	7,104
Lease liability	2,510	2,761
Accruals and reserves	210	241
Intangible assets	1,793	1,917
Stock-based compensation	1,213	1,374
Total deferred tax assets:	95,956	74,410
Valuation allowance	(92,978)	(71,003)
Subtotal	2,978	3,407
Deferred tax liabilities:
Property and equipment	(1,578)	(1,881)
Right of use asset	(1,400)	(1,526)
Total deferred tax liabilities	(2,978)	(3,407)
Total net deferred tax assets

Lease - Components of lease expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Leases
Operating lease cost	$ 1,225	$ 1,225
Variable lease cost	982	959
Total lease costs	2,207	2,184
Finance lease cost
Amortization of right of use asset	$ 85	$ 85
Finance Lease, Right-of-Use Asset, Statement of Financial Position	Other non-current assets	Other non-current assets
Interest on lease liability	$ 6	$ 12

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2023

Income Taxes

Schedule of effective income tax rate differs from federal statutory rate


	Year Ended December 31,
	2023		2022
Tax effected at statutory rate	21.0	%	21.0	%
State taxes	6.5		5.2
Stock-based compensation	(1.4)		(0.6)
Non-deductible expenses	(0.8)		(0.9)
Federal research and development credits	3.5		2.8
Change in valuation allowance	(28.8)		(27.5)
Effective income tax rate	0.0	%	0.0	%

Schedule of deferred tax assets


	Year Ended December 31,
	2023		2022
Deferred tax assets:
Federal net operating loss carryforwards	$	43,953	$	37,277
State net operating loss carryforwards		11,433		9,267
Capitalized research and development expenditures		24,485		14,469
Research and development credit carryforwards		10,359		7,104
Lease liability		2,510		2,761
Accruals and reserves		210		241
Intangible assets		1,793		1,917
Stock-based compensation		1,213		1,374
Total deferred tax assets:		95,956		74,410
Valuation allowance		(92,978)		(71,003)
Subtotal		2,978		3,407
Deferred tax liabilities:
Property and equipment		(1,578)		(1,881)
Right of use asset		(1,400)		(1,526)
Total deferred tax liabilities		(2,978)		(3,407)
Net deferred tax assets	$	—	$	—

Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2023

Stock-Based Compensation

Schedule of stock-based compensation expense


	Year Ended December 31,
	2023		2022
Research and development expense	$	2,189	$	2,427
General and administrative expense		5,193		5,997
Total stock-based compensation expense	$	7,382	$	8,424

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	8.6	$	89
Granted	3,738,555	$	2.75
Exercised	(2,757)	$	2.82
Cancelled/forfeited	(1,240,556)	$	7.26
Outstanding as of December 31, 2023	7,455,795	$	5.52	8.0	$	-
Exercisable as of December 31, 2023	3,103,732	$	7.04	6.6	$	-

(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.

Schedule of assumptions used in determining fair value of options granted


	Year Ended December 31,
	2023			2022
Risk-free interest rate		3.57 - 4.40	%		1.47 – 4.22	%
Expected dividend yield		0	%		0	%
Expected term (in years)		5.5 - 6.1			5.3 – 6.1
Expected volatility		81.7 - 87.3	%		80.8 – 87.6	%

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	(39,250)	$	5.51
Canceled/Forfeited	(1,293)	$	5.51
Unvested as of December 31, 2023	5,617	$	5.51

Summary of Significant Accounting Policies

12 Months Ended

Dec. 31, 2023

Summary of Significant Accounting Policies

Summary of Significant Accounting Policies

2. Summary of Significant Accounting Policies

Basis of Presentation

These 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 U.S. Securities and Exchange Commission (the “SEC”). 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 December 31, 2026, or such earlier time that it is no longer an emerging growth company.

Principles of Consolidation

The accompanying consolidated financial statements include the accounts of the Company and its wholly owned subsidiaries: Xilio Development, Inc. (“Xilio Development”), a Delaware corporation, and Xilio Securities Corporation, a Massachusetts corporation. All intercompany accounts and transactions have been eliminated in consolidation.

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 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 consolidated financial statements include, but are not limited to, estimates related to accrued expenses, the valuation of stock-based compensation, including stock options and restricted common stock, useful life of long-lived assets and income taxes. Actual results could differ from those estimates.

Segment Information

The Company has one operating segment. Operating segments are defined as components of an enterprise about which separate discrete information is available for evaluation by the chief operating decision maker in deciding how to allocate resources and assess performance. The Company’s chief operating decision-maker is its chief executive officer. The Company and its chief operating decision-maker view the Company’s operations and manage its business as a single operating segment. All of the Company’s long-lived assets are held in the United States.

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. Restricted cash 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 consolidated balance sheets.

Concentrations of Credit Risk and Significant Suppliers

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 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.

The Company is dependent on a third-party manufacturer to supply material and manufacturing process development services for its product candidates and related research and development activities. These research and development programs and activities could be adversely affected by a significant interruption in the supply of such products and services which could have a material adverse effect on the Company’s business, financial position and results of operations.

Fair Value Measurements

Certain assets and liabilities are carried at fair value under GAAP. Fair value is defined as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. Valuation techniques used to measure fair value must maximize the use of observable inputs and minimize the use of unobservable inputs. Financial assets and liabilities carried at fair value are to be classified and disclosed in one of the following three levels of the fair value hierarchy, of which the first two are considered observable and the last is considered unobservable:

●

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

●

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

●

Level 3—Unobservable inputs that are supported by little or no market activity and that are significant to determining the fair value of the assets or liabilities, including pricing models, discounted cash flow methodologies and similar techniques.

To the extent the valuation is based on models or inputs that are less observable or unobservable in the market, the determination of fair value requires more judgment. Accordingly, the degree of judgment exercised by the Company in determining fair value is greatest for instruments categorized in Level 3. A financial instrument’s level within the fair value hierarchy is based on the lowest level of any input that is significant to the fair value measurement.

The carrying values of the Company’s cash, prepaid expenses, accounts payable and accrued expenses approximate their fair value due to their short-term nature. The carrying value of the Company’s outstanding debt as of December 31, 2023 and 2022 approximates fair value based on the variable interest rate for the borrowings as well as the short duration of the term of the note.

Property and Equipment

Property and equipment is stated at cost, net of accumulated depreciation and amortization. Depreciation and amortization are calculated using the straight-line method over the estimated useful lives of the assets, which are as follows:


		Estimated Useful Life
Computers and software		3 years
Laboratory equipment		5 years
Furniture and fixtures		5 years
Leasehold improvements		Shorter of the useful life or the remaining term of the lease

Upon retirement or sale, the cost of assets disposed of and the related accumulated depreciation and amortization are removed from the accounts and any resulting gain or loss is included in loss from operations. Expenditures for repairs and maintenance that do not improve or extend the lives of the respective assets are charged to expense as incurred, while costs of major additions and betterments are capitalized.

Impairment of Long-Lived Assets

The Company periodically evaluates its long-lived assets, which consist of property and equipment, and any leased assets, for impairment whenever events or changes in circumstances indicate that a potential impairment may have occurred. If such events or changes in circumstances arise, the Company compares the carrying amount of the long-lived assets to the estimated future undiscounted cash flows expected to be generated by the long-lived assets. If the estimated aggregate undiscounted cash flows are less than the carrying amount of the long-lived assets, an impairment charge, calculated as the amount by which the carrying amount of the assets exceeds the estimated fair value of the assets, is recorded. The estimated fair value of the long-lived assets is determined based on the estimated discounted cash flows expected to be generated from the long-lived assets. The Company did not recognize impairment charges during the years ended December 31, 2023 and 2022, respectively.

Leases

The Company determines if an arrangement is or contains a lease at inception. Operating leases are included in right-of-use lease assets (“ROU assets”) and in both the current portion of lease liabilities and long-term lease liabilities on the Company’s consolidated balance sheets. Lease expense for operating leases is recognized on a straight-line basis over the lease term as an operating expense in the consolidated statements of operations and comprehensive loss. Assets subject to finance leases are included in other non-current assets and the related lease obligation is included in other current liabilities and other long-term liabilities on the Company’s consolidated balance sheets. Lease expense for finance leases is recognized as depreciation expense and interest expense in the consolidated statements of operations and comprehensive loss using the effective interest method. The Company has elected the short-term lease recognition exemption for short-term leases, which allows the Company not to recognize lease liabilities and ROU assets on the consolidated balance sheets for leases with an original term of twelve months or less.

ROU assets represent the Company’s right to use an underlying asset for the lease term, and lease liabilities represent the Company’s obligation to make lease payments arising from the lease. Operating lease liabilities and their corresponding ROU assets are initially recorded based on the present value of lease payments over the expected remaining lease term. When determining the lease term, the Company includes options to extend or terminate the lease when it is reasonably certain that the option will be exercised. Certain adjustments to the ROU asset may be required for items such as incentives received. The interest rate implicit in lease contracts is typically not readily determinable. As a result, the Company utilizes its incremental borrowing rate to discount lease payments. The incremental borrowing rate reflects the fixed rate at which the Company could borrow, on a collateralized basis, the amount of the lease payments in the same currency, for a similar term, in a similar economic environment. Prospectively, the Company will adjust the ROU assets for straight-line rent

expense or any incentives received and remeasure the lease liability at the net present value using the same incremental borrowing rate that was in effect as of the lease commencement or transition date.

The Company has lease agreements with lease and non-lease components, which are accounted for as a combined element.

Research and Development Costs and Accruals

Research and development expenses are expensed as incurred and consist of costs incurred in performing research and development activities, including compensation related expenses for research and development personnel, preclinical and clinical activities including cost of supply and manufacturing process development activities, overhead expenses including facilities expenses, materials and supplies, amounts paid to consultants and outside service providers, and depreciation of equipment. Upfront payments made for the licensing of technology are expensed as research and development expenses in the period in which they are incurred. In general, contingent payments are recognized when it becomes probable the payment will be required. Any contingent payments that qualify as a derivative liability are recognized at fair value on the Company’s consolidated balance sheets. Nonrefundable advance payments for goods or services to be received in the future for use in research and development activities are recorded as prepaid expenses. The prepaid amounts are expensed as the related goods are delivered or the services are performed.

The Company records accruals for estimated ongoing research and development costs, including costs associated with contracts with third-party contract research organizations and contract manufacturing organizations. When evaluating the adequacy of the accrued liabilities, the Company analyzes progress of the preclinical studies or clinical trials, including the phase or completion of events, invoices received and contracted costs. Significant judgments and estimates are made in determining the accrued balances at the end of any reporting period. Actual results could differ from the Company’s estimates. The Company’s historical accrual estimates have not been materially different from the actual costs.

Collaboration Agreements

The Company analyzes its collaboration agreements to assess whether such arrangements involve joint operating activities performed by parties that are both active participants in the activities and exposed to significant risks and rewards dependent on the commercial success of such activities and therefore within the scope of ASC 808, Collaborative Arrangements (“ASC 808”). For arrangements within the scope of ASC 808 that contain multiple elements, the Company first determines which elements of the collaboration are deemed to be within the scope of ASC 808 and which elements of the collaboration are more reflective of a vendor-customer relationship and therefore within the scope of ASC 606, Revenue from Contracts with Customers (“ASC 606”). For elements of collaboration arrangements that are accounted for pursuant to ASC 808, an appropriate recognition method is determined and applied consistently, either by analogy to authoritative accounting literature or by applying a reasonable and rational policy election. For collaboration agreements where the Company is reimbursed for a portion of its research and development expenses or participates in the cost-sharing of such research and development expenses, such reimbursements and cost-sharing arrangements are reflected as a reduction of research and development expenses in the Company’s consolidated statements of operations and comprehensive loss, as the Company does not consider performing research and development services for reimbursement to be a part of its ongoing major or central operations.

Patent Costs

All patent-related costs incurred in connection with filing and prosecuting patent applications are expensed as incurred due to the uncertainty about the recovery of the expenditure. Amounts incurred are classified as general and administrative expenses in the accompanying consolidated statements of operations and comprehensive loss.

Stock-Based Compensation

The Company issues stock-based awards to employees, directors and non-employees, generally in the form of stock options. The Company measures employee stock-based compensation based on the grant date fair value of the stock-based awards and recognizes stock-based compensation expense on a straight-line basis over the requisite service period of the awards, which is generally the vesting period of the respective award, in accordance with ASC 718, Compensation—Stock

Compensation (“ASC 718”). ASC 718 requires all stock-based payments to employees, which includes grants of employee stock awards, to be recognized in the consolidated statements of operations and comprehensive loss based on their grant date fair values.

There are significant judgments and estimates inherent in the determination of the fair value of the common securities. The Company considers the fair value of common stock to be equal to its current share price. The Company estimates the fair value of stock options using the Black-Scholes option pricing model, which uses as inputs the estimated fair value of common stock, and certain management estimates, including the expected stock price volatility, the expected term of the award, the risk-free rate, and expected dividends. Expected volatility is calculated based on reported volatility data for a representative group of publicly traded companies for which historical information is available. The Company selects companies with comparable characteristics with historical share price information that approximates the expected term of the stock-based awards. The Company computes the historical volatility data using the daily closing prices for the selected companies’ shares during the equivalent period that approximates the calculated expected term of the stock options. The Company will continue to apply this method until a sufficient amount of historical information regarding the volatility of its stock price becomes available. The risk-free interest rate is based on the U.S. Treasury yield curve in effect at the time of grant commensurate with the expected term assumption. The Company uses the simplified method as prescribed by the SEC Staff Accounting Bulletin No. 107, Share-Based Payment, under which the expected term is presumed to be the midpoint between the vesting date and the end of the contractual term. The Company utilizes this method due to lack of historical exercise data and the plain nature of its stock-based awards. The expected dividend yield is assumed to be zero as the Company has no current plans to pay any dividends on common stock. The Company recognizes forfeitures as they occur.

The Company classifies stock-based compensation expense in its consolidated statements of operations and comprehensive loss consistent with the classification of the award recipient’s salary and related costs or the award recipient’s service payments, as applicable.

Comprehensive Loss

Comprehensive loss is the change in equity of a business enterprise during a period from transactions and other events and circumstances from non-owner sources. Comprehensive loss includes net loss and the change in accumulated other comprehensive loss for the period. The Company did not have any items of comprehensive income or loss other than net loss for the years ended December 31, 2023 and 2022.

Net Loss Per Share

The Company calculates basic net loss per share attributable to common stockholders by dividing the net loss attributable to common stockholders by the weighted average number of common shares outstanding for the period, which excludes shares of restricted common stock that are not vested. Diluted net loss per share is calculated by dividing net loss by the weighted average number of shares of common stock outstanding, as applicable, after giving consideration to the dilutive effect of stock options, restricted common stock and warrants that are outstanding during the period. The Company has generated a net loss in all periods presented, so the basic and diluted net loss per share are the same, as the inclusion of the potentially dilutive securities would be anti-dilutive.

Income Taxes

Income taxes for Xilio Therapeutics, Inc. are recorded in accordance with ASC Topic 740, Income Taxes, which provides for deferred taxes using an asset and liability approach. Under this method, deferred income tax assets and liabilities are recognized based on future income tax consequences attributable to differences between the financial statement carrying amount of existing assets and liabilities, and their respective income tax basis. Deferred income tax assets and liabilities are measured using enacted income tax rates expected to apply to taxable income in the years in which those temporary differences are expected to be recovered or settled. The effect of changes in income tax rates on deferred income tax assets and liabilities is recognized as income or expense in the period that includes the enactment date and subject to a valuation allowance which is established for any income tax benefits of which future realization is not more likely than not.

The Company provides reserves for potential payments of tax to various tax authorities related to uncertain tax positions. The tax benefits recorded are based on a determination of whether and how much of a tax benefit taken by the Company in its tax filings or positions is “more likely than not” to be realized following resolution of any uncertainty related to the tax benefit, assuming that the matter in question will be raised by the tax authorities. At December 31, 2023 and 2022, the Company had not identified any significant uncertain tax positions.

Recent Accounting Pronouncements Not Yet Adopted

In November 2023, the FASB issued Accounting Standards Update No. 2023-07, Segment Reporting (Topic 280): Improvements to Reportable Segment Disclosures (“ASU 2023-07”), which is intended to improve reportable segment disclosure requirements, primarily through enhanced disclosures about significant segment expenses that are regularly provided to the chief operating decision maker. The guidance is effective for fiscal years beginning after December 15, 2023 and interim periods within fiscal years beginning after December 15, 2024. Early adoption is permitted. The guidance is to be applied retrospectively to all prior periods presented in the financial statements. Upon transition, the segment expense categories and amounts disclosed in the prior periods should be based on the significant segment expense categories identified and disclosed in the period of adoption. The Company is currently evaluating the potential impact of adopting this new guidance on its consolidated financial statements and related disclosures.

In December 2023, the FASB issued Accounting Standards Update No. 2023-09, Income Taxes (Topic 740): Improvements to Income Tax Disclosures (“ASU 2023-09”), which modifies the rules on income tax disclosures to require entities to disclose (1) specific categories in the rate reconciliation, (2) the income or loss from continuing operations before income tax expense or benefit (separated between domestic and foreign) and (3) income tax expense or benefit from continuing operations (separated by federal, state and foreign). ASU 2023-09 also requires entities to disclose their income tax payments to international, federal, state and local jurisdictions, among other changes. The guidance is effective for annual periods beginning after December 15, 2024. Early adoption is permitted for annual financial statements that have not yet been issued or made available for issuance. ASU 2023-09 should be applied on a prospective basis, but retrospective application is permitted. This Company is currently evaluating the potential impact of adopting this new guidance on its consolidated financial statements and related disclosures.

Income Taxes - Tax credit carryforwards (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Tax Credit Carryforward
Reserves for uncertain tax positions	$ 0	$ 0
Estimated interest or penalties recognized	0	$ 0
Federal \| Research and development credit carryovers
Tax Credit Carryforward
Credit carryovers	7,800
State \| Research and development credit carryovers
Tax Credit Carryforward
Credit carryovers	$ 3,100

Net Loss Per Share (Tables)

12 Months Ended

Dec. 31, 2023

Net Loss Per Share

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


	Year Ended
	December 31,
	2023	2022
Unvested restricted common stock	5,617	46,160
Outstanding stock options	7,455,795	4,960,553
Warrants	2,631	2,631
Unvested employee stock purchase plan shares	68,642	77,222
Total common stock equivalents	7,532,685	5,086,566

Summary of Significant Accounting Policies (Policies)

12 Months Ended

Dec. 31, 2023

Summary of Significant Accounting Policies

Basis of Presentation

Principles of Consolidation

Use of Estimates

Segment Information

Cash Equivalents and Restricted Cash

Concentrations of Credit Risk and Significant Suppliers

Fair Value Measurements

●

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

●

Property and Equipment


		Estimated Useful Life
Computers and software		3 years
Laboratory equipment		5 years
Furniture and fixtures		5 years
Leasehold improvements		Shorter of the useful life or the remaining term of the lease

Impairment of Long-Lived Assets

Leases

The Company has lease agreements with lease and non-lease components, which are accounted for as a combined element.

Research and Development Costs and Accruals

Collaboration Agreements

Patent Costs

Stock-Based Compensation

Comprehensive Loss

Net Loss Per Share

Income Taxes

Recent Accounting Pronouncements Not Yet Adopted

Subsequent Events

12 Months Ended

Dec. 31, 2023

Subsequent Events.

Subsequent Events

14. Subsequent Events

License Agreement and Issuance of Common Stock

On March 27, 2024, Xilio Development entered into an exclusive license agreement with Gilead Sciences, Inc. (“Gilead”), pursuant to which it granted Gilead an exclusive global license to develop and commercialize XTX301, the Company’s tumor-activated IL-12 product candidate, and specified other molecules directed to IL-12.

Under the license agreement, the Company is eligible to receive approximately $43.5 million in upfront payments, including a cash payment of $30.0 million and an initial equity investment by Gilead of approximately $13.5 million in the Company’s common stock at a purchase price of $1.97 per share.

In connection with the execution of the license agreement, on March 27, 2024, the Company entered into a stock purchase agreement with Gilead pursuant to which the Company agreed to initially issue and sell 6,860,223 of its shares of common stock to Gilead in a private placement at a purchase price of $1.97 per share for an aggregate purchase price of approximately $13.5 million.

The initial Gilead private placement closed on March 28, 2024, and the $30.0 million upfront cash payment is payable by Gilead within a specified time period promptly following signing of the license agreement.

March 2024 Private Placement

On March 28, 2024, the Company entered into a securities purchase agreement with certain existing accredited investors pursuant to which the Company agreed to sell and issue to the investors in a private placement an aggregate of 1,953,125 shares of the Company’s common stock at a purchase price of $0.64 per share, and to certain investors in lieu of shares of the Company’s common stock, prefunded warrants to purchase up to an aggregate of 15,627,441 shares of the Company’s common stock at a purchase price of $0.6399 per prefunded warrant. The private placement is anticipated to close on April 2, 2024, subject to customary closing conditions.

Strategic Portfolio Reprioritization and Workforce Reduction

On March 27, 2024, the board of directors of the Company approved a strategic portfolio reprioritization and restructuring. As part of the strategic portfolio reprioritization and restructuring, the Company plans to undertake efforts to further reduce its expenses and streamline its operations, including a reduction in headcount of 15 employees, representing approximately 21% of the Company’s workforce immediately prior to the workforce reduction.

Document and Entity Information - USD ($) $ in Millions	12 Months Ended
Document and Entity Information - USD ($) $ in Millions	Dec. 31, 2023	Mar. 28, 2024	Jun. 30, 2023
Document and Entity Information [Abstract]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 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 Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
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
ICFR Auditor Attestation Flag	false
Document Financial Statement Error Correction	false
Entity Shell Company	false
Entity Public Float			$ 67.7
Entity Common Stock, Shares Outstanding		34,473,486
Auditor Firm ID	42
Auditor Name	Ernst & Young LLP
Auditor Location	Boston, Massachusetts
Entity Central Index Key	0001840233
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2023
Document Fiscal Period Focus	FY
Amendment Flag	false

Collaboration Agreements and Intellectual Property Licenses - Collaboration Agreements (Details) $ in Millions	12 Months Ended
	Dec. 31, 2023 USD ($)
Clinical Supply Agreement \| F. Hoffmann-La Roche Ltd.
Agreements
Reduction in research and development expenses	$ 2.0

CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares	Dec. 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	27,613,263	27,471,607
Common stock, shares outstanding	27,607,646	27,425,447

Leases - Schedule of supplemental cash flow information related to leases (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Cash paid for amounts included in the measurement of lease liabilities:
Operating cash flows from operating leases	$ 1,683	$ 1,634
Financing cash flows from finance leases	$ 85	$ 85

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Operating expenses
Research and development	$ 52,136	$ 59,201
General and administrative	26,997	29,948
Total operating expenses	79,133	89,149
Loss from operations	(79,133)	(89,149)
Other income, net
Other income, net	2,729	927
Total other income, net	2,729	927
Net loss	(76,404)	(88,222)
Comprehensive loss	$ (76,404)	$ (88,222)
Net loss per share, basic (in dollars per share)	$ (2.78)	$ (3.22)
Net loss per share, diluted (in dollars per share)	$ (2.78)	$ (3.22)
Weighted average common shares outstanding, basic (in shares)	27,496,107	27,392,087
Weighted average common shares outstanding, diluted (in shares)	27,496,107	27,392,087

Stock-Based Compensation - 2022 Inducement Plan (Details) - shares	Dec. 31, 2023	Dec. 31, 2022
Stock-Based Compensation
Common stock reserved for issuance (in shares)	10,160,112	8,653,472
2022 Inducement Plan
Stock-Based Compensation
Common stock reserved for issuance (in shares)		275,000
Shares available for future issuance (in shares)	220,000

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

+ Details

Collaboration Agreements and Intellectual Property Licenses

12 Months Ended

Dec. 31, 2023

Collaboration Agreements and Intellectual Property Licenses

Collaboration Agreements and Intellectual Property Licenses

6. Collaboration Agreements and Intellectual Property Licenses

Clinical Trial Collaboration with F. Hoffmann-La Roche

In July 2023, the Company and F. Hoffmann-La Roche Ltd. (“Roche”) entered into a clinical trial collaboration (the “Roche Clinical Collaboration”) pursuant to a clinical supply agreement to evaluate XTX101 in combination with atezolizumab (Tecentriq®) in a Phase 1/2 clinical trial consisting of a Phase 1 dose escalation cohort assessing the combination in patients with advanced solid tumors and a planned Phase 2 clinical trial assessing the combination in patients with microsatellite stable colorectal cancer.

Under the clinical supply agreement, the Company is eligible to receive specified cost-sharing payments from Roche, and each company will supply its respective anti-cancer agent to support the Phase 1/2 clinical trial. The Company is responsible for conducting the Phase 1/2 clinical trial and retains global development and commercialization rights to XTX101.

The Company concluded that the cost-sharing payments from the Roche Clinical Collaboration are not in the scope of ASC 606 because the Company does not consider performing research and development services for reimbursement to be part of its ongoing major or central operations. Therefore, the Company applied a reasonable, rational, and consistently applied accounting policy election to record the cost-sharing payments from the Roche Clinical Collaboration as a reduction of research and development expenses in the consolidated statements of operations and comprehensive loss for the period in which a study development event is achieved. During the year ended December 31, 2023, the Company recognized a reduction of research and development expenses of $2.0 million.

Cross-License Agreement with AskGene

In December 2020, Xilio Development entered into a cross-license agreement with AskGene Pharma, Inc. (“AskGene”) pursuant to which AskGene granted Xilio Development certain exclusive licenses for AskGene patent rights related to non-antigen binding IL-2 products in the field of oncology and certain co-exclusive licenses for AskGene patent rights related to antigen binding IL-2 products in all fields. Under the agreement, AskGene retains rights to the AskGene patent rights in Singapore, Thailand, Malaysia, Vietnam, the People’s Republic of China, Taiwan, Macau, Hong Kong, Korea and India (the “AskGene territory”) and granted licenses to Xilio Development for the AskGene patent rights worldwide, excluding the AskGene territory (the “Xilio Development territory”).

Under the agreement, Xilio Development paid AskGene an upfront payment of $6.0 million, and for any licensed IL-2 product, Xilio Development is obligated to pay AskGene up to $13.0 million in the aggregate upon the achievement of specified regulatory milestones. In addition, subject to specified conditions, for any IL-2 licensed product, Xilio Development is obligated to pay AskGene percentage royalties in the mid-single digits on aggregate annual net sales of IL-2 licensed products in the Xilio Development territory during the applicable royalty term.

During the term of the agreement, AskGene has agreed not to exploit any non-antigen binding IL-2 product comprised of specified masking technology in the field of oncology in the Xilio Development territory.

In addition, Xilio Development granted a non-exclusive, royalty-free, non-transferable, worldwide license to AskGene for specified Xilio patent rights related to non-antigen binding IL-2 products in the field of immunology and for specified Xilio patent rights related to antigen binding IL-2 products in all fields. Subject to the terms of the agreement and during the time period specified, Xilio Development also granted AskGene an option to obtain a license in the AskGene territory to develop and commercialize IL-2 licensed products. If AskGene exercises its option to develop and commercialize IL-2 licensed products in the AskGene territory, then the parties will negotiate and enter into a license agreement for AskGene’s exclusive development and commercialization of such products in the AskGene territory, and AskGene would be obligated to pay Xilio Development percentage royalties in the mid-single digits on aggregate annual net sales of such licensed products in the AskGene territory.

The Company accounted for the agreement as an asset acquisition, as the Company only acquired licenses to specified patents from AskGene (an input) and no additional processes or outputs as a part of the agreement. The $6.0 million upfront payment was recorded as research and development expense in the consolidated statement of operations and comprehensive loss during the year ended December 31, 2020, as the acquired licenses were determined to have no alternative future use and the technological feasibility of the intellectual property has not yet been reached. Any additional payments that are contingent upon achievement of development and regulatory milestones or upon sales of licensed products will not be recognized until it becomes probable that the Company will be required to make such payments.

Amended and Restated Exclusive License Agreement with City of Hope

In August 2016, Xilio Development entered into an amended and restated exclusive license agreement with City of Hope pursuant to which City of Hope granted Xilio Development an exclusive worldwide license to specified patent rights related to the Company’s anti-CTLA-4 monoclonal antibody program.

Under the agreement, the Company issued 24,019 shares of common stock to City of Hope. For the first three licensed products or licensed services to achieve specified development and regulatory milestones, Xilio Development is obligated to pay City of Hope up to $10.3 million in the aggregate per licensed product or licensed service. In addition, subject to

specified conditions, Xilio Development is obligated to pay City of Hope tiered royalties in the low single digits on aggregate annual net sales of licensed products or licensed services on a country-by-country basis until the expiration of the last-to-expire patent or patent application licensed from City of Hope covering the applicable licensed product or licensed service in such country. Xilio Development is also obligated to pay City of Hope a portion of any consideration Xilio Development receives for the grant of sublicenses under the agreement ranging from a low double digit to mid-twenties percentage of such consideration, subject to specified conditions under that agreement at the time that Xilio Development grants any such sublicense.

The Company incurred no costs related to the payment of specified development milestones under the agreement during the years ended December 31, 2023 and 2022. Any additional payments that are contingent upon achievement of development and regulatory milestones or upon sales of licensed products will not be recognized until it becomes probable that the Company will be required to make such payments.

CTLA-4 Monoclonal Antibody License Agreement with WuXi Biologics

In September 2016, the Company entered into a license agreement with WuXi Biologics (Hong Kong) Limited (“WuXi Biologics”), as amended in December 2017, pursuant to which WuXi Biologics granted the Company an exclusive worldwide license to specified monoclonal antibodies and patent rights and know-how controlled by WuXi Biologics, including certain patent rights related to the Company’s anti-CTLA-4 monoclonal antibody program.

For each product that exploits the rights licensed under the agreement, the Company is obligated to pay WuXi Biologics up to approximately $25.8 million in the aggregate for specified development and regulatory milestones. In addition, subject to specified conditions, the Company is obligated to pay WuXi Biologics tiered royalties in the low to mid-single digits on aggregate annual worldwide net sales of licensed products during the applicable royalty term.

The Company incurred no costs related to the payment of specified development milestones under the agreement during the years ended December 31, 2023 and 2022. Any additional payments that are contingent upon the achievement of development and regulatory milestones or sales of licensed products will not be recognized until it becomes probable that the Company will be required to make such payments.

Stock-Based Compensation - Stock-based compensation expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Stock-Based Compensation
Total stock-based compensation expense	$ 7,382	$ 8,424
Research and development expense
Stock-Based Compensation
Total stock-based compensation expense	2,189	2,427
General and administrative expense
Stock-Based Compensation
Total stock-based compensation expense	$ 5,193	$ 5,997

Stock-Based Compensation

12 Months Ended

Dec. 31, 2023

Stock-Based Compensation

Stock-Based Compensation

10. Stock-Based Compensation

Equity Incentive Plans

2020 Stock Incentive Plan

Under the 2020 Stock Incentive Plan (as amended, 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 September 2021, the Company’s board of directors and stockholders adopted the 2021 Stock Incentive Plan (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 Company initially reserved 6,579,016 shares of common stock under the 2021 Plan. The 2021 Plan provides that the number of shares reserved and available for issuance under the 2021 Plan will be cumulatively increased on January 1 of each calendar year by 5% of the number of shares of common stock outstanding on such date or such lesser amount determined by the Company’s board of directors. On January 1, 2024, the number of shares reserved for issuance under the 2021 Plan automatically increased by 1,380,663 shares. As of December 31, 2023, there were 1,780,442 shares available for future grant under the 2021 Plan.

2022 Inducement Plan

In 2022, the Company’s board of directors adopted the 2022 Inducement Stock Incentive Plan pursuant to Nasdaq Rule 5635(c)(4) (the “2022 Inducement Plan”). 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. As of December 31, 2023, there were 220,000 shares available for future grant under the 2022 Inducement Plan.

2021 Employee Stock Purchase Plan

In 2021, the Company’s board of directors and stockholders adopted the 2021 Employee Stock Purchase Plan (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. 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 1% of the number of shares of the Company’s common stock outstanding on such date or such lesser amount determined by the Company’s board of directors (up to a maximum increase of 584,062 shares of common stock per year). On January 1, 2024, the number of shares reserved for issuance under the 2021 ESPP was increased by 276,132 shares. The Company issued 140,192 shares under the 2021 ESPP during the year ended December 31, 2023 and no shares under the 2021 ESPP during the year ended December 31, 2022. As of December 31, 2023, there were 701,244 shares available for future issuance under the 2021 ESPP.

Total Stock-Based Compensation Expense

During the years ended December 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 consolidated statements of operations and comprehensive loss:


	Year Ended December 31,
	2023		2022
Research and development expense	$	2,189	$	2,427
General and administrative expense		5,193		5,997
Total stock-based compensation expense	$	7,382	$	8,424

Stock Options

A summary of stock option activity under the Company’s Stock Incentive Plans 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	8.6	$	89
Granted	3,738,555	$	2.75
Exercised	(2,757)	$	2.82
Cancelled/forfeited	(1,240,556)	$	7.26
Outstanding as of December 31, 2023	7,455,795	$	5.52	8.0	$	-
Exercisable as of December 31, 2023	3,103,732	$	7.04	6.6	$	-

(1)

Using the Black-Scholes option pricing model, the weighted average fair value of options granted to employees and directors during the years ended December 31, 2023 and 2022 was $2.02 per share and $5.58 per share, respectively. The Company satisfies stock option exercises with newly issued shares of common stock. The aggregate intrinsic value of stock options exercised during each of the years ended December 31, 2023 and 2022 was less than $0.1 million.

The following assumptions were used in determining the fair value of options granted to employees during the years ended December 31, 2023 and 2022:


	Year Ended December 31,
	2023			2022
Risk-free interest rate		3.57 - 4.40	%		1.47 – 4.22	%
Expected dividend yield		0	%		0	%
Expected term (in years)		5.5 - 6.1			5.3 – 6.1
Expected volatility		81.7 - 87.3	%		80.8 – 87.6	%

As of December 31, 2023, the Company had unrecognized stock-based compensation expense of $12.5 million related to stock options issued to employees and directors, which is expected to be recognized over a weighted average period of 2.0 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	(39,250)	$	5.51
Canceled/Forfeited	(1,293)	$	5.51
Unvested as of December 31, 2023	5,617	$	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. The Company recorded stock-based compensation expense for restricted stock granted to employees, directors and non-employees of $0.3 million and $0.4 million for the years ended December 31, 2023 and 2022. During the years ended December 31, 2023 and 2022, the aggregate fair value of the restricted stock awards that vested was $0.1 million and $0.3 million, respectively. As of December 31, 2023, total unrecognized compensation cost related to unvested restricted stock awards was less than $0.1 million, which is expected to be recognized during the first quarter of 2024.

Income Taxes - Provision (Details) - USD ($) $ in Thousands	12 Months Ended
Income Taxes - Provision (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Income Taxes
Tax expense	$ 0	$ 0

- Definition

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

+ References + Details

401(k) Plan (Details) - USD ($) $ in Millions	12 Months Ended
401(k) Plan (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
401(k) Plan
Matching contributions expense (in dollars)	$ 0.7	$ 0.3
Maximum
401(k) Plan
Percentage of employees' gross pay for which the employer contributes a matching contribution	4.00%
First 3% of compensation contributed
401(k) Plan
Percentage employer matches of employee's percentage contribution	100.00%
Percentage of employees' gross pay for which the employer contributes a matching contribution	3.00%
Next 2% of compensation contributed
401(k) Plan
Percentage employer matches of employee's percentage contribution	50.00%
Percentage of employees' gross pay for which the employer contributes a matching contribution	2.00%

Leases (Tables)

12 Months Ended

Dec. 31, 2023

Leases

Schedule of components of lease expense


	Year Ended
	December 31,
	2023		2022
Operating lease cost	$	1,225	$	1,225
Variable lease cost		982		959
Total lease costs	$	2,207	$	2,184
Finance lease cost:
Amortization of right-of-use asset	$	85	$	85
Interest on lease liability		6		12

Schedule of supplemental balance sheet information related to leases


	Year Ended
	December 31,
	2023			2022
Operating Lease:
Operating lease right-of-use asset	$	5,125		$	5,585
Operating lease liability, current portion	$	1,047		$	918
Operating lease liability, net of current portion	$	8,142		$	9,189
Finance Lease:
Other non-current assets	$	134		$	219
Other current liabilities		48			82
Other liabilities, long-term		—			45
Weighted-average remaining lease term (in years):
Operating lease		6.2			7.2
Finance lease		0.7			1.7
Weighted-average discount rate:
Operating lease		8.0	%		8.0	%
Finance lease		6.9	%		6.9	%

Schedule of supplemental cash flow information related to leases


		Year Ended
		December 31,
		2023		2022
Cash paid for amounts included in the measurement of lease liabilities:
Operating cash flows from operating leases	$	1,683	$	1,634
Financing cash flows from finance leases		85		85

Schedule of Future Lease Payments Under Operating Leases


	Operating Lease		Finance Lease
2024	$	1,733	$	49
2025		1,785		—
2026		1,839		—
2027		1,894		—
2028		1,951		—
Thereafter		2,516		—
Total future minimum lease payments		11,718		49
Present value adjustment		(2,529)		(1)
Present value of lease liabilities	$	9,189	$	48

Schedule of Future Lease Payments Under financing Leases


	Operating Lease		Finance Lease
2024	$	1,733	$	49
2025		1,785		—
2026		1,839		—
2027		1,894		—
2028		1,951		—
Thereafter		2,516		—
Total future minimum lease payments		11,718		49
Present value adjustment		(2,529)		(1)
Present value of lease liabilities	$	9,189	$	48

Loan and Security Agreement - Description (Details) - Loan Agreement - USD ($) $ in Millions	1 Months Ended
	Nov. 30, 2019	Dec. 31, 2023
Loan and security agreement
Borrowed amount	$ 10.0
Interest rate at end of period (as a percent)		8.75%
Minimum
Loan and security agreement
Stated interest rate	4.75%
Prime rate
Loan and security agreement
Basis spread (as percent)	0.25%

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

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+ Details

Leases

12 Months Ended

Dec. 31, 2023

Leases

Leases

7. Leases

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 a right to a five-year option to extend 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 December 31, 2023 and 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 account, which is recorded as restricted cash on the consolidated balance sheets.

The components of lease expense were as follows:


	Year Ended
	December 31,
	2023		2022
Operating lease cost	$	1,225	$	1,225
Variable lease cost		982		959
Total lease costs	$	2,207	$	2,184
Finance lease cost:
Amortization of right-of-use asset	$	85	$	85
Interest on lease liability		6		12

Supplemental balance sheet information related to the leases was as follows (in thousands, except for remaining lease term and discount rates):


	Year Ended
	December 31,
	2023			2022
Operating Lease:
Operating lease right-of-use asset	$	5,125		$	5,585
Operating lease liability, current portion	$	1,047		$	918
Operating lease liability, net of current portion	$	8,142		$	9,189
Finance Lease:
Other non-current assets	$	134		$	219
Other current liabilities		48			82
Other liabilities, long-term		—			45
Weighted-average remaining lease term (in years):
Operating lease		6.2			7.2
Finance lease		0.7			1.7
Weighted-average discount rate:
Operating lease		8.0	%		8.0	%
Finance lease		6.9	%		6.9	%

Supplemental cash flow information related to leases was as follows:


		Year Ended
		December 31,
		2023		2022
Cash paid for amounts included in the measurement of lease liabilities:
Operating cash flows from operating leases	$	1,683	$	1,634
Financing cash flows from finance leases		85		85

Future minimum lease payments under non-cancellable leases as of December 31, 2023 are as follows:


	Operating Lease		Finance Lease
2024	$	1,733	$	49
2025		1,785		—
2026		1,839		—
2027		1,894		—
2028		1,951		—
Thereafter		2,516		—
Total future minimum lease payments		11,718		49
Present value adjustment		(2,529)		(1)
Present value of lease liabilities	$	9,189	$	48

Commitments and Contingencies

12 Months Ended

Dec. 31, 2023

Commitments and Contingencies

Commitments and Contingencies

8. Commitments and Contingencies

Indemnification Agreements

In the ordinary course of business, the Company enters into agreements that may include indemnification provisions. Pursuant to such agreements, the Company may indemnify, hold harmless and defend an indemnified party for losses suffered or incurred by the indemnified party. Some of the provisions will limit losses to those arising from third-party actions. In some cases, the indemnification will continue after the termination of the agreement. The maximum potential amount of future payments the Company could be required to make under these provisions is not determinable. The Company has never incurred material costs to defend lawsuits or settle claims related to these indemnification provisions. The Company has also entered into indemnification agreements with its directors that may require the Company to indemnify its directors against liabilities that may arise by reason of their status or service as directors to the fullest extent permitted by Delaware corporate law. The Company currently has directors’ and officers’ liability insurance.

To date, the Company has not incurred any material costs as a result of such indemnifications. The Company is not aware of any claims under indemnification arrangements, and it has not accrued any liabilities related to such obligations in its consolidated financial statements as of December 31, 2023 or 2022.

Legal Proceedings

The Company is not currently a party to any material legal proceedings.

Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2023

Summary of Significant Accounting Policies

Schedule of estimated useful lives of assets


		Estimated Useful Life
Computers and software		3 years
Laboratory equipment		5 years
Furniture and fixtures		5 years
Leasehold improvements		Shorter of the useful life or the remaining term of the lease

Stock-Based Compensation - Stock Incentive Plan (Details) - shares		1 Months Ended
	Jan. 01, 2024	Oct. 31, 2021	Dec. 31, 2023	Dec. 31, 2022
Stock-Based Compensation
Common stock reserved for issuance (in shares)			10,160,112	8,653,472
2021 Plan
Stock-Based Compensation
Common stock reserved for issuance (in shares)		6,579,016
Shares available for future issuance (in shares)			1,780,442
2021 Plan \| Subsequent events
Stock-Based Compensation
Additional common stock reserved under the plan (in shares)	1,380,663
2021 Plan \| Maximum
Stock-Based Compensation
Annual increase in number of shares reserved for issuance (as a percent)		5.00%

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

+ Details

Insider Trading Arrangements	3 Months Ended
Insider Trading Arrangements	Dec. 31, 2023
Trading Arrangements, by Individual
Rule 10b5-1 Arrangement Adopted	false
Non-Rule 10b5-1 Arrangement Adopted	false
Rule 10b5-1 Arrangement Terminated	false
Non-Rule 10b5-1 Arrangement Terminated	false

Loan and Security Agreement (Tables)

12 Months Ended

Dec. 31, 2023

Loan and Security Agreement

Schedule of minimum aggregate future loan principal payments


	Minimum Loan
	Payments
2024	$	3,333
Total future principal payments		3,333
Less: unamortized discount		(18)
Total note payable	$	3,315

Leases - Lease information (Details) $ in Millions	1 Months Ended
Leases - Lease information (Details) $ in Millions	Aug. 31, 2019 ft²	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)
Leases
Area leased (in square feet) \| ft²	27,830
Option to extend	true
Term of option to extend	5 years
Restricted cash
Leases
Letter of credit for the benefit of landlord \| $		$ 1.6	$ 1.6

Property and Equipment, Net (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Property and Equipment
Property and equipment	$ 11,803	$ 11,673
Less accumulated depreciation	(5,861)	(4,418)
Property and equipment, net	5,942	7,255
Depreciation	1,800	1,700
Laboratory equipment
Property and Equipment
Property and equipment	5,815	5,587
Computers and software
Property and Equipment
Property and equipment	183	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

Loan and Security Agreement - Maturities (Details) - Loan Agreement - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Minimum aggregate future loan payments
2024	$ 3,333
Total future principal payments	3,333
Less: unamortized discount	(18)
Total notes payable	3,315
Interest expense	$ 700	$ 800

- Definition

Amount, after deduction of unamortized premium (discount) and debt issuance cost, of long-term debt. Excludes lease obligation.

+ References + Details

Preferred Stock and Common Stock

12 Months Ended

Dec. 31, 2023

Preferred Stock and Common Stock

Preferred Stock and Common Stock

9. Preferred Stock and Common Stock

Undesignated Preferred Stock

As of December 31, 2023 and 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 December 31, 2023 and 2022, there were no shares of preferred stock issued or outstanding.

Common Stock

As of December 31, 2023 and 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.

The voting, dividend and liquidation rights of the holders of shares of common stock are subject to and qualified by the rights, powers and preferences of the holders of shares of the Company’s undesignated preferred stock, if and when such shares are issued. The rights, preferences and privileges of the Company’s common stock are as follows:

Voting

The holders of shares of common stock are entitled to one vote for each share of common stock held at any meeting of stockholders and at the time of any written action in lieu of a meeting of stockholders.

Dividends

The holders of shares of common stock are entitled to receive dividends, if and when declared by the Company’s board of directors. No dividends have been declared by the Company’s board of directors or paid by the Company to the holders of common stock since the issuance of the common stock.

Liquidation

Upon the dissolution, liquidation or winding up of the Company, whether voluntary or involuntary, holders of the common stock will be entitled to receive, pro rata based on the number of shares held by each such holder, all assets of the Company

available for distribution to its stockholders, subject to any preferential or other rights of any then outstanding preferred stock.

Shares Reserved for Future Issuance

The Company has reserved for future issuances the following shares of common stock as of December 31, 2023 and 2022:


	December 31,	December 31,
	2023	2022
Stock options	9,456,237	8,084,121
Employee Stock Purchase Plan	701,244	566,720
Warrants	2,631	2,631
Total shares reserved for future issuance	10,160,112	8,653,472

- Definition

The entire disclosure for equity.

+ References

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+ Details