Xilio Therapeutics Announces Pipeline and Business Updates and Third Quarter 2023 Financial Results Demonstrated initial clinical validation of tumor-selective activation technology for both XTX101, a tumor-activated, Fc

Xilio Therapeutics Announces Pipeline and Business Updates and Third Quarter 2023 Financial Results

Demonstrated initial clinical validation of tumor-selective activation technology for both XTX101, a tumor-activated, Fc-enhanced anti-CTLA-4, and XTX202, a tumor-activated, beta-gamma IL-2

On track to activate trial sites for XTX101 dose escalation in combination with atezolizumab under clinical collaboration with Roche in the fourth quarter of 2023

Reported initial Phase 1/2 data for XTX202, including a 50% disease control rate at higher doses ( 2.8 mg/kg), and plans to evaluate XTX202 as monotherapy at 4.0 mg/kg in ongoing Phase 2 trial in patients with melanoma and renal cell carcinoma

Anticipate reporting preliminary Phase 1 safety data for XTX301, a tumor-activated, engineered IL-12, in the fourth quarter of 2023

WALTHAM, Mass., November 9, 2023 - Xilio Therapeutics, Inc. (Nasdaq: XLO), a clinical-stage biotechnology company discovering and developing tumor-activated immuno-oncology therapies for people living with cancer, today announced pipeline progress and business updates and reported financial results for the third quarter ended September 30, 2023.

"Colorectal cancer is the third largest solid tumor cancer in terms of number of patients diagnosed annually and the second leading cause of cancer-related deaths globally," said Ren Russo, Pharm.D., president and chief executive officer of Xilio. "Rates of MSS colorectal cancer are rising in younger people, particularly in men under 50 years old, and patients often present with advanced Stage 4 disease along with liver metastases. Despite these alarming trends, there are few treatment options and no approved immunotherapies for these patients today. We believe the unique tumor-selective mechanism of XTX101 combined with atezolizumab has the potential to treat MSS colorectal cancer, and we are focused on initiating the co-funded collaboration with Roche to study this combination in patients. We are also encouraged by the recent Phase 1/2 data reported at SITC for XTX202 demonstrating a 50% disease control rate at higher doses ( 2.8 mg/kg), including patients with cold tumors, and a generally well-tolerated safety profile across all dose levels. We look forward to evaluating the 4 mg/kg dose for XTX202 in Phase 2 for patients with melanoma and renal cell carcinoma."

Pipeline and Business Updates

XTX101: tumor-activated, Fc-enhanced anti-CTLA-4

XTX101 is an investigational tumor-activated, Fc-enhanced, high affinity binding anti-CTLA-4 designed to block CTLA-4 and deplete regulatory T cells when activated (unmasked) in the tumor microenvironment (TME). XTX101 is currently being evaluated at the recommended Phase 2 dose and schedule of 150 mg once every six weeks in monotherapy dose expansion of an ongoing Phase 1 clinical trial in patients with advanced solid tumors.

In addition, subject to obtaining sufficient additional capital, Xilio plans to:

XTX202: tumor-activated, engineered, beta-gamma biased IL-2

XTX202 is an investigational tumor-activated, engineered, beta-gamma biased IL-2 molecule designed to potently stimulate CD8+ effector T cells and natural killer (NK) cells without concomitant stimulation of regulatory T cells when activated (unmasked) in the TME. XTX202 is currently being evaluated in an ongoing Phase 1/2 clinical trial in patients with advanced solid tumors.

XTX301: tumor-activated, engineered IL-12

XTX301 is an investigational tumor-activated, engineered IL-12 molecule designed to potently stimulate anti-tumor immunity and reprogram the TME of poorly immunogenic "cold" tumors towards an inflamed or "hot" state.

Corporate Highlights

Upcoming Presentations

Xilio will present a poster for XTX101 with updated preliminary Phase 1 data and outlining the planned Phase 2 trial design at the European Society for Medical Oncology (ESMO) Immuno-Oncology Annual Congress on December 6-8, 2023.

Title: Phase 1/2 study of XTX101, a masked, tumor-activated Fc-enhanced anti-CTLA-4 in patients with advanced solid tumors

Presentation Date and Time: Thursday, December 7, 2023, from 12:00 to 1:00 p.m. CET

Abstract number: 490

Third Quarter 2023 Financial Results

Xilio continues to anticipate that its existing cash and cash equivalents will be sufficient to fund its operating expenses and capital expenditure requirements into the end of the second quarter of 2024.

About XTX101 (anti-CTLA-4) and the Phase 1 Monotherapy and Phase 1/2 Combination Clinical Trials

XTX101 is an investigational tumor-activated, Fc-enhanced, high affinity binding anti-CTLA-4 monoclonal antibody designed to block CTLA-4 and deplete regulatory T cells when activated (unmasked) in the tumor microenvironment (TME). The Phase 1 clinical trial is a first-in-human, multi-center, open-label trial designed to evaluate the safety and tolerability of XTX101 for the treatment of adult patients with advanced solid tumors. Xilio has completed monotherapy dose escalation (Part 1A) and is currently enrolling patients at the recommended Phase 2 dose and schedule of 150 mg once every six weeks in monotherapy dose expansion (Part 1B). Please refer to NCT04896697 on www.clinicaltrials.gov for additional details.

In addition, Xilio plans to evaluate the safety, tolerability and efficacy of XTX101 in combination with atezolizumab (Tecentriq ) in the Phase 1/2 clinical trial. The Phase 1 portion is designed to assess the safety and tolerability of XTX101 in combination with atezolizumab in dose escalation in patients with advanced solid tumors. The planned Phase 2 portion is designed to evaluate the safety and efficacy of the combination in patients with microsatellite stable colorectal cancer (MSS CRC).

About XTX202 (IL-2) and the Phase 1/2 Clinical Trials

XTX202 is an investigational tumor-activated beta-gamma biased, engineered IL-2 molecule designed to potently stimulate CD8+ effector T cells and natural killer (NK) cells without concomitant stimulation of regulatory T cells when activated (unmasked) in the tumor microenvironment (TME). The Phase 1 clinical trial for XTX202 is a first-in-human, multi-center, open-label trial designed to evaluate the safety and tolerability of XTX202 as a monotherapy in patients with advanced solid tumors. The Phase 2 clinical trial for XTX202 is a multi-center, open-label trial designed to evaluate the safety and efficacy of XTX202 as a monotherapy in patients with unresectable or metastatic melanoma and metastatic renal cell carcinoma who have progressed on standard-of-care treatment. Please refer to NCT05052268 on www.clinicaltrials.gov for additional details.

About XTX301 (IL-12) and the Phase 1 Clinical Trial

XTX301 is an investigational tumor-activated, engineered IL-12 molecule designed to potently stimulate anti-tumor immunity and reprogram the tumor microenvironment (TME) of poorly immunogenic "cold" tumors towards an inflamed or "hot" state. The Phase 1 clinical trial for XTX301 is a first-in-human, multi-center, open-label trial designed to evaluate the safety and tolerability of XTX301 as a monotherapy in patients with advanced solid tumors. Please refer to NCT05684965 on www.clinicaltrials.gov for additional details.

About Xilio Therapeutics

Cautionary Note Regarding Forward-Looking Statements

This press release contains forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995, as amended, including, without limitation, statements regarding plans to activate clinical trial sites for the Phase 1 dose escalation portion of the clinical trial evaluating XTX101 in combination with atezolizumab; plans to report preliminary Phase 1 safety data for XTX301; additional plans and anticipated milestones for XTX101, XTX202 and XTX301, subject to obtaining sufficient additional capital; the potential benefits of any of Xilio's current or future product candidates in treating patients as a monotherapy or combination therapy; the period in which Xilio expects to have cash to fund its operations; and Xilio's strategy, goals and anticipated financial performance, milestones, business plans and focus. The words "aim," "may," "will," "could," "would," "should," "expect," "plan," "anticipate," "intend," "believe," "estimate," "predict," "project," "potential," "continue," "seek," "target" and similar expressions are intended to identify forward-looking statements, although not all forward-looking statements contain these identifying words. Any forward-looking statements in this press release are based on management's current expectations and beliefs and are subject to a number of important risks, uncertainties and other factors that may cause actual events or results to differ materially from those expressed or implied by any forward-looking statements contained in this press release, including, without limitation, risks and uncertainties related to ongoing and planned research and development activities, including initiating, conducting or completing preclinical studies and clinical trials and the timing and results of such preclinical studies or clinical trials; the delay of any current or planned preclinical studies or clinical trials or the development of Xilio's current or future product candidates; Xilio's ability to obtain and maintain sufficient preclinical and clinical supply of current or future product candidates; Xilio's advancement of multiple early-stage programs; interim or preliminary preclinical or clinical data or results, which may not be predictive of future preclinical or clinical data or results; Xilio's ability to successfully demonstrate the safety and efficacy of its product candidates and gain approval of its product candidates on a timely basis, if at all; results from preclinical studies or clinical trials for Xilio's product candidates, which may not support further development of such product candidates; actions of regulatory agencies, which may affect the initiation, timing and progress of current or future clinical trials; Xilio's ability to obtain, maintain and enforce patent and other intellectual property protection for current or future product candidates; Xilio's ability to obtain and maintain sufficient cash resources to fund its operations until and beyond the end of the second quarter of 2024; the impact of international trade policies on Xilio's business, including U.S. and China trade policies; and Xilio's ability to maintain its clinical trial collaboration with Roche to develop XTX101 in combination with atezolizumab. These and other risks and uncertainties are described in greater detail in the sections entitled "Risk Factor Summary" and "Risk Factors" in Xilio's filings with the U.S. Securities and Exchange Commission (SEC), including Xilio's most recent Quarterly Report on Form 10-Q and any other filings that Xilio has made or may make with the SEC in the future. Any forward-looking statements contained in this press release represent Xilio's views only as of the date hereof and should not be relied upon as representing its views as of any subsequent date. Except as required by law, Xilio explicitly disclaims any obligation to update any forward-looking statements.

This press release contains hyperlinks to information that is not deemed to be incorporated by reference in this press release.

TECENTRIQ is a registered trademark of Genentech USA, Inc., a member of the Roche Group.

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