XLO

Received FDA clearance of IND application for XTX501, a potential best-in-class bispecific PD-1 / masked IL-2 Advancing IND-enabling studies for potential first-in-class multi-specific, masked T cell engager programs targeting CLDN18.2 and PSMA+STEAP1; IND applications anticipated in the second half of 2027 Cash runway into the first quarter of 2028 expected to support key milestones across pipeline of next generation multi-specific I-O therapies WALTHAM, Mass., Aug. 12, 2026 (GLOBE NEWSWIRE) -- Xilio Therapeutics, Inc. (Nasdaq: XLO), a clinical-stage biotechnology company discovering and developing masked immuno-oncology therapies for people living with cancer, today announced pipeline progress and business updates and reported financial results for the second quarter ended June 30, 2026. “In the second quarter, we remained focused on disciplined execution across our pipeline as we continued to advance our next generation of masked immuno-oncology therapies toward the clinic. Today, we are excited to announce FDA clearance of our IND for XTX501, a bispecific PD-1 / masked IL-2 that we believe has the potential to become a foundational backbone therapy for solid tumors,” said René Russo, Pharm.D., president and chief executive officer of Xilio. “At the same time, we are advancing IND-enabling studies for our multi-specific, masked T cell engagers targeting CLDN18.2 and PSMA+STEAP1. Together, these programs highlight the potential to leverage our masking technology to unlock the next generation of sophisticated, multi-specific I-O therapies for people living with cancer.” Pipeline Progress and Business Updates XTX501: bispecific PD-1 / masked IL-2 XTX501 is a novel bispecific PD-1 / masked IL-2 that has the potential to be a foundational backbone therapy for solid tumors, including in combination with other agents. XTX501 is designed to selectively stimulate PD-1 positive, antigen-experienced T cells and enhance their function while overcoming IL-2 receptor-mediated clearance, peripheral activity and tolerability issues associated with non-masked IL-2 agents. Xilio received clearance from the U.S. Food and Drug Administration (FDA) for the company’s investigational new drug application (IND) to proceed to a Phase 1/2 clinical trial for XTX501. Xilio expects to initiate dosing in the Phase 1 portion of the trial in patients with metastatic non-small cell lung cancer (NSCLC) and select advanced solid tumors in the second half of 2026. Xilio plans to report initial Phase 1 data in patients with metastatic NSCLC in the second half of 2027. Masked T Cell Engager Programs Xilio is leveraging its proprietary, clinically-validated masking technology and modular T cell engager (TCE) architectures to advance two wholly-owned masked TCE programs, as well as an additional masked TCE program in collaboration with AbbVie Group Holdings Limited (AbbVie). The company’s masked TCEs are designed with a masked CD3 targeting domain and one or more tumor-associated antigen (TAA) binding domains as part of the core molecule design. In addition, the company’s modular architecture enables the incorporation of a co-stimulatory domain designed to further enhance potency and durability of T cell response, as well as the potential to mask the TAA binding domain(s) and/or mask the co-stimulatory signaling domain. Upon tumor-selective activation, Xilio’s TCE molecules are designed to release a potent, short half-life TCE in the tumor microenvironment. Xilio is advancing IND-enabling studies for a potential first-in-class masked TCE program targeting CLDN18.2 and a potential first-in-class multi-specific, masked TCE program targeting PSMA and STEAP1 with built-in co-stimulatory signaling. CLDN18.2 is a TAA expressed in gastrointestinal cancers (gastric, pancreatic and esophageal), and PSMA and STEAP1 are TAAs expressed in prostate cancer. Xilio plans to submit INDs for its CLDN18.2 and PSMA+STEAP1 programs in the second half of 2027. Efarindodekin alfa: masked IL-12 Xilio is evaluating efarindodekin alfa as a monotherapy in an ongoing Phase 2 clinical trial in patients with advanced solid tumors and expects to deliver an option data package to Gilead Sciences, Inc. (Gilead) in the first half of 2027. Recent Corporate Updates Xilio appointed Ben Harshbarger as its chief legal officer in June 2026. Ben has over 20 years of executive leadership and legal expertise within the biopharmaceutical industry. Read more here. Second Quarter 2026 Financial Results Cash Position: Cash and cash equivalents were $136.0 million as of June 30, 2026, compared to $137.5 million as of December 31, 2025. Collaboration and License Revenue: Collaboration and license revenue was $18.7 million for the quarter ended June 30, 2026, compared to $8.1 million for the quarter ended June 30, 2025. The increase was driven by an increase in collaboration and license revenue recognized under the collaboration and license agreements with AbbVie and Gilead. Research & Development (R&D) Expenses: R&D expenses were $14.6 million for the quarter ended June 30, 2026, compared to $15.3 million for the quarter ended June 30, 2025. The decrease was primarily driven by decreased clinical development activities related to vilastobart and decreased manufacturing activities for XTX501, partially offset by increased costs related to masked TCE programs and indirect research and development and increased personnel-related costs. General & Administrative (G&A) Expenses: G&A expenses were $7.6 million for the quarter ended June 30, 2026, compared to $7.1 million for the quarter ended June 30, 2025. The increase was primarily driven by an increase in personnel-related costs. Net Loss: Net loss was $6.4 million for the quarter ended June 30, 2026, compared to a net loss of $15.8 million for the quarter ended June 30, 2025. Cash Runway Based on its current operating plans, Xilio anticipates that its existing cash and cash equivalents will be sufficient to enable it to fund its operating expenses and capital expenditure requirements into the first quarter of 2028. This estimate excludes up to $36.2 million in additional gross proceeds in the second half of 2026 if all outstanding Series C warrants are exercised at their current exercise price and any potential additional milestone payments, option-related fees or other contingent payments under Xilio’s collaboration and license agreements with AbbVie and Gilead, including up to $31.0 million in near-term milestones and option extension fees that could be achieved under the AbbVie collaboration through the first half of 2027. About XTX501 and the Phase 1/2 Clinical Trial XTX501 is an investigational bispecific PD-1 / masked IL-2 designed to selectively stimulate PD-1 positive, antigen-experienced T cells and enhance their function while overcoming IL-2 receptor-mediated clearance, peripheral activity and tolerability issues associated with non-masked IL-2 agents. Xilio is evaluating the safety and tolerability of XTX501 as a monotherapy in patients with metastatic non-small cell lung cancer (NSCLC) and select advanced solid tumors in the Phase 1 portion of a first-in-human, multi-center, open-label Phase 1/2 clinical trial at multiple sites in the United States. Please refer to NCT07688577 on www.clinicaltrials.gov for additional details. About Xilio Therapeutics Xilio Therapeutics is a clinical-stage biotechnology company discovering and developing masked 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. Leveraging our clinically-validated masking technology and capabilities, Xilio is developing I-O therapies designed to selectively activate within the tumor microenvironment to achieve durable efficacy without the severe side effects associated with systemically active I-O agents. Learn more by visiting www.xiliotx.com and follow us on LinkedIn (Xilio Therapeutics, Inc.). 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, expectations, development timelines and anticipated milestones for Xilio’s programs; the timing of clinical development, data releases, regulatory submissions, delivery of option data packages or other program updates; the promise or potential success of Xilio’s programs, including the best-in-class potential of XTX501 and the potential for XTX501 to be a foundational backbone therapy for solid tumors and the first-in-class potential of Xilio’s masked TCE programs targeting CLDN18.2 and PSMA+STEAP1; the timing and receipt of future contingent payments under Xilio’s collaboration and license agreements with AbbVie and Gilead; the potential receipt of up to $36.2 million in additional gross proceeds in the second half of 2026 if all of the Series C warrants are exercised at their current exercise price; the sufficiency of, and the period in which Xilio expects to have, cash to fund its operations and capital expenditure requirements; and Xilio’s strategy, goals and anticipated financial performance (including anticipated cash runway), 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 related to general market conditions and geopolitical uncertainties; 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; initial, preliminary, interim or retrospective preclinical or clinical data or results may not be replicated in or 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 may not support further development of such product candidates; actions of regulatory agencies 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 need to obtain additional cash resources to advance its pipeline of masked I-O molecules; the impact of international trade policies on Xilio’s business, including U.S. and China trade policies; and Xilio’s ability to maintain its collaboration and license agreements with AbbVie and Gilead. 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. Investor Contact  Alex Lobo, Precision [email protected] Media Contact  Josie Butler, [email protected] (1)   On March 13, 2026, the company effected a 1-for-14 reverse stock split of its common stock. All share amounts and per share amounts in this press release have been adjusted retroactively to reflect the reverse stock split for the periods presented.(2)   Operating expenses include the following amounts of non-cash stock-based compensation expense: (3)   Weighted average common shares outstanding, basic and diluted, includes prefunded warrants to purchase common stock, as the prefunded warrants are exercisable at any time for nominal cash consideration.

On track for planned IND submission in mid-2026 and Phase 1 initiation in the second half of 2026 for XTX501, a potential best-in-class bispecific PD-1 / masked IL-2 Presented new preclinical data for XTX601, a potential first-in-class masked T cell engager targeting CLDN18.2, at the AACR annual meeting Advancing potential first-in-class multi-specific, masked T cell engager targeting PSMA and STEAP1 Achieved development milestone under AbbVie collaboration and extended cash runway into early 2028 WALTHAM, Mass., May 12, 2026 (GLOBE NEWSWIRE) -- Xilio Therapeutics, Inc. (Nasdaq: XLO), a clinical-stage biotechnology company discovering and developing masked immuno-oncology therapies for people living with cancer, today announced pipeline progress and business updates and reported financial results for the first quarter ended March 31, 2026. “We ended the first quarter of 2026 with strong momentum across our pipeline of highly differentiated I-O therapies leveraging our best-in-class masking technology,” said René Russo, Pharm.D., president and chief executive officer of Xilio. “XTX501 has the potential to be a foundational backbone therapy for combination regimens across a broad range of solid tumors, and we are on track to advance this program into the clinic this year. In addition, our recent data for our CLDN18.2 program presented at AACR further demonstrate the power of our masking technology to unlock the potential of T cell engagers. This progress, together with the recent achievement of another financial milestone under our AbbVie collaboration, highlights the productivity of our pipeline and underscores our ability to maximize the value of our clinically-validated masking technology.” Pipeline Progress and Business Updates XTX501: bispecific PD-1 / masked IL-2 XTX501 is a novel bispecific PD-1 / masked IL-2 that has the potential to be a foundational “backbone” therapy for combination treatment with other agents. XTX501 is designed to selectively stimulate PD-1 positive, antigen-experienced T cells and enhance their function while overcoming IL-2 receptor-mediated clearance, peripheral activity and tolerability issues associated with non-masked IL-2 agents. In preclinical studies, XTX501 demonstrated robust monotherapy activity (including in settings insensitive to PD-1 therapy) and tumor-selective pharmacodynamics consistent with its intended mechanism of action. Xilio is currently advancing XTX501 through investigational new drug (IND)-enabling studies and plans to submit an IND application in the middle of 2026. Xilio plans to initiate a Phase 1 trial for XTX501 in the second half of 2026 and report initial Phase 1 data in patients with metastatic non-small cell lung cancer in the second half of 2027, subject to clearance of the IND by the U.S. Food and Drug Administration. Masked T Cell Engager Programs Xilio is leveraging its proprietary, clinically-validated masking technology and modular T cell engager (TCE) architectures to advance two wholly-owned masked TCE programs, as well as an additional masked TCE program in collaboration with AbbVie Group Holdings Limited (AbbVie). Xilio’s masked TCEs include a masked CD3 targeting domain and one or more tumor-associated antigen (TAA) binding domains (which may be masked) as part of the core molecule design. Depending on the desired properties that Xilio is seeking to achieve for a particular molecule, Xilio’s modular architecture enables the ability to incorporate a co-stimulatory domain designed to further enhance potency and durability of T cell response, include multiple TAA binding domains and/or also mask the TAA binding domain(s) and/or co-stimulatory signaling domain. Upon tumor-selective activation, Xilio’s TCE molecules are designed to release a potent, short half-life TCE in the tumor microenvironment. Xilio is advancing XTX601, a potential first-in-class masked TCE targeting CLDN18.2, a TAA expressed in gastrointestinal cancers (gastric, pancreatic and esophageal). In parallel, Xilio is leveraging its modular design architecture to evaluate designs that incorporate masking of the CLDN18.2 binding domain and/or the addition of a co-stimulatory domain. Xilio initiated IND-enabling activities for its CLDN18.2 program in the first quarter of 2026. In April 2026, Xilio presented new preclinical data for XTX601 at the American Association for Cancer Research (AACR) Annual Meeting demonstrating protease-dependent, tumor-selective activation and potent anti-tumor activity in multiple preclinical models. In addition, XTX601 was well-tolerated in non-human primates with a favorable therapeutic index. For more information, read the press release here. Xilio is also advancing a potential first-in-class multi-specific, masked TCE program targeting PSMA and STEAP1 with built-in co-stimulatory signaling. PSMA and STEAP1 are expressed in most prostate cancer tumors, and targeting both TAAs with a single molecule has the potential to address tumor heterogeneity while minimizing the potential for resistance due to antigen escape. Xilio anticipates initiating IND-enabling activities for its PSMA+STEAP1 program in the second quarter of 2026. Xilio plans to submit IND applications for its CLDN18.2 and PSMA+STEAP1 programs in 2027. Efarindodekin alfa: masked IL-12 Xilio is evaluating efarindodekin alfa as a monotherapy in an ongoing Phase 2 clinical trial in patients with advanced solid tumors and expects to deliver an option data package to Gilead Sciences, Inc. (Gilead) in the first half of 2027. Recent Corporate Updates Xilio strengthened its board of directors with the appointment of Cheryl R. Blanchard, Ph.D., a renowned biopharmaceutical leader, in April 2026. Dr. Blanchard brings more than 30 years of leadership experience to Xilio, with deep scientific, operational and commercial leadership in life science companies. In the second quarter of 2026, Xilio achieved a $6.0 million development milestone related to the masked antibody-based immunotherapy program under the company’s collaboration, license and option agreement with AbbVie. First Quarter 2026 Financial Results Cash Position: Cash and cash equivalents were $150.3 million as of March 31, 2026, compared to $137.5 million as of December 31, 2025. The increase was primarily driven by $37.3 million in net proceeds from a follow-on offering in February 2026. Collaboration and License Revenue: Collaboration and license revenue was $12.6 million for the quarter ended March 31, 2026, compared to $2.9 million for the quarter ended March 31, 2025. The increase was primarily driven by an increase in collaboration and license revenue recognized under the collaboration and license agreements with AbbVie and Gilead. Research & Development (R&D) Expenses: R&D expenses were $19.8 million for the quarter ended March 31, 2026, compared to $8.3 million for the quarter ended March 31, 2025. The increase was primarily driven by manufacturing activities related to IND-enabling studies and preclinical development activities for XTX501, increased costs related to masked TCE programs and indirect research and development, increased clinical development activities related to efarindodekin alfa and increased personnel-related costs. General & Administrative (G&A) Expenses: G&A expenses were $6.9 million for the quarter ended March 31, 2026, compared to $8.5 million for the quarter ended March 31, 2025. The decrease was primarily driven by a decrease in professional and consulting fees, including legal fees and other professional costs and a decrease in personnel-related costs. Net Loss: Net loss was $9.5 million for the quarter ended March 31, 2026, compared to a net loss of $13.3 million for the quarter ended March 31, 2025. Cash Runway Based on its current operating plans, Xilio anticipates that its cash and cash equivalents as of March 31, 2026, together with the development milestone achieved under the AbbVie collaboration in the second quarter of 2026, will be sufficient to enable it to fund its operating expenses and capital expenditure requirements into early 2028. This estimate excludes any potential additional milestone payments, option-related fees or other contingent payments under Xilio’s collaboration and license agreements with AbbVie and Gilead and excludes up to $36.2 million in additional gross proceeds in the second half of 2026 if all outstanding Series C warrants are exercised at their current exercise price. Xilio has the potential to achieve up to $31.0 million in additional near-term milestones and option extension fees under the existing AbbVie collaboration through the first half of 2027. About Xilio Therapeutics Xilio Therapeutics is a clinical-stage biotechnology company discovering and developing masked 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. Leveraging our clinically-validated masking technology and capabilities, Xilio is developing I-O therapies designed to selectively activate within the tumor microenvironment to achieve durable efficacy without the severe side effects associated with systemically active I-O agents. Learn more by visiting www.xiliotx.com and follow us on LinkedIn (Xilio Therapeutics, Inc.). 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, expectations, development timelines and anticipated milestones for Xilio’s programs; the timing of clinical development, data releases, regulatory submissions, delivery of option data packages or other program updates; the promise or potential success of Xilio’s programs, including the best-in-class potential of XTX501 and the potential for XTX501 to be a foundational “backbone” therapy for combination treatment with other agents and the first-in-class potential of Xilio’s masked TCE programs targeting CLDN18.2 and PSMA+STEAP1; the timing and receipt of future contingent payments under Xilio’s collaboration and license agreements with AbbVie and Gilead; the potential receipt of up to $36.2 million in additional gross proceeds in the second half of 2026 if all of the Series C warrants are exercised at their current exercise price; the sufficiency of, and the period in which Xilio expects to have, cash to fund its operations and capital expenditure requirements; 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 related to general market conditions and geopolitical uncertainties; 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; initial, preliminary, interim or retrospective preclinical or clinical data or results may not be replicated in or 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 may not support further development of such product candidates; actions of regulatory agencies 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 need to obtain additional cash resources to advance its pipeline of masked I-O molecules; the impact of international trade policies on Xilio’s business, including U.S. and China trade policies; and Xilio’s ability to maintain its collaboration and license agreements with AbbVie and Gilead. 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 Annual Report on Form 10-K 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. Investor Contact  Alex Lobo, Precision [email protected] Media Contact  Josie Butler, [email protected] (1) On March 13, 2026, the company effected a 1-for-14 reverse stock split of its common stock. All share amounts and per share amounts in this press release have been adjusted retroactively to reflect the reverse stock split for the periods presented.(2) Operating expenses include the following amounts of non-cash stock-based compensation expense: (3) Weighted average common shares outstanding, basic and diluted, includes prefunded warrants to purchase common stock, as the prefunded warrants are exercisable at any time for nominal cash consideration.

XTX501, a potential best-in-class bispecific PD-1 / masked IL-2, on track for planned IND submission in mid-2026 and Phase 1 initiation in the second half of 2026 Advancing potential first-in-class multi-specific, masked T cell engager targeting PSMA and STEAP1 Plan to present new preclinical data at AACR for potential first-in-class masked T cell engager program targeting CLDN18.2 Extended cash runway through the end of 2027 WALTHAM, Mass., March 23, 2026 (GLOBE NEWSWIRE) -- Xilio Therapeutics, Inc. (Nasdaq: XLO), a clinical-stage biotechnology company discovering and developing masked immuno-oncology therapies for people living with cancer, today announced pipeline progress and business updates and reported financial results for the fourth quarter and full year ended December 31, 2025. “As we enter 2026, we are well-positioned to leverage our clinically validated masking technology to continue advancing our next generation of multi-specific I-O therapies toward the clinic,” said René Russo, Pharm.D., president and chief executive officer of Xilio. “We are encouraged by the progress the field has recently made with masked T cell engagers for prostate cancer, and we are excited to be advancing a potential first-in-class multi-specific masked T cell engager targeting both PSMA and STEAP1 with built-in co-stimulatory signaling designed to enhance potency and durability of response. We believe that targeting both PSMA and STEAP1, which are the most prevalent tumor-associated antigens expressed in prostate cancer, will minimize resistance due to antigen escape. In addition, this quarter we continued to make strong progress advancing XTX501, our potential best-in-class bispecific PD-1 / masked IL-2, toward a planned IND submission mid-year.” Pipeline Progress and Business Updates XTX501: bispecific PD-1 / masked IL-2 XTX501 is a novel bispecific PD-1 / masked IL-2 designed to selectively stimulate PD-1 positive, antigen-experienced T cells and enhance their function. XTX501 incorporates masking and is designed to overcome IL-2 receptor-mediated clearance, peripheral activity and tolerability issues associated with non-masked IL-2 agents. In preclinical studies, XTX501 demonstrated robust monotherapy activity (including in settings insensitive to PD-1 therapy) and tumor-selective pharmacodynamics consistent with its intended mechanism of action. Xilio is currently advancing XTX501 through investigational new drug (IND)-enabling studies and plans to submit an IND application for XTX501 in the middle of 2026. Xilio plans to initiate a Phase 1 trial for XTX501 in the second half of 2026 and report initial Phase 1 data in the second half of 2027, subject to clearance of the IND by the U.S. Food and Drug Administration. Xilio plans to initially evaluate XTX501 in patients with metastatic non-small cell lung cancer before expanding development to other solid tumor types, including tumors that are insensitive to PD-1 therapy. The company believes XTX501 also has the potential to be a foundational “backbone” therapy for combination treatment with other agents. Masked T Cell Engager Programs Xilio is leveraging its proprietary, clinically-validated masking technology to advance two wholly-owned programs for masked T cell engagers, as well as an additional program in collaboration with AbbVie Group Holdings Limited (AbbVie). Xilio’s masked T cell engagers include molecules with one or more tumor-associated antigen (TAA) binding domains and a CD3 targeting domain, which are designed to release a potent, short half-life T cell engager upon tumor-selective activation (ATACR format), and molecules that include a co-stimulatory domain designed to further enhance potency and durability of the T cell response (SEECR format). Depending on the desired properties that Xilio is seeking to achieve for a particular molecule and TAA(s), Xilio’s modular architecture for its masked T cell engagers enables optionality to: include multiple TAA binding domains; add a co-stimulatory domain; and/or mask the CD3 targeting domain, TAA binding domain(s) and/or the co-stimulatory signaling domain. Xilio is advancing a wholly-owned masked T cell engager program targeting CLDN18.2 (ATACR format). Xilio’s modular design architecture for T cell engagers also enables flexibility to evaluate designs that incorporate masking of the CLDN18.2 binding domain and/or add a co-stimulatory domain (SEECR format) in parallel with advancing the current molecule design. CLDN18.2 is expressed in gastrointestinal cancers (including gastric, pancreatic and esophageal) and lung cancer. Xilio plans to present new preclinical data for its CLDN18.2 program in a poster presentation at the American Association for Cancer Research (AACR) Annual Meeting taking place from April 17-22, 2026 (abstract number: 1619). Xilio is advancing a wholly-owned multi-specific, masked T cell engager program targeting PSMA and STEAP1 with built-in co-stimulatory signaling (SEECR format). Xilio anticipates nominating a development candidate in the second quarter of 2026. PSMA and STEAP1 are expressed in most prostate cancer tumors, and targeting both of these TAAs has the potential to address tumor heterogeneity while minimizing the potential for resistance due to antigen escape. Xilio plans to advance these masked T cell engager programs into IND-enabling studies and submit IND applications for each of these programs in 2027. Efarindodekin alfa: masked IL-12 Xilio is evaluating efarindodekin alfa as a monotherapy in an ongoing Phase 2 clinical trial in patients with advanced solid tumors and expects to deliver an option data package to Gilead Sciences, Inc. (Gilead) in the first half of 2027. Recent Corporate Updates In January 2026, Xilio announced the appointment of Sara Bonstein as chair of the board of directors. In January 2026, Xilio announced the receipt of $35.8 million in gross proceeds from the exercise of Series B warrants, before deducting underwriting discounts and commissions and any offering expenses, including the full exercise of Series B warrants held by Coastlands Capital, Frazier Life Sciences and Gilead. The Series B warrants were issued in connection with a follow-on offering in June 2025. In January 2026, Xilio announced the achievement of a development milestone related to the masked antibody-based immunotherapy program under the company’s collaboration, license and option agreement with AbbVie. In February 2026, Xilio closed a follow-on offering of prefunded warrants for $40.0 million in gross proceeds, before deducting underwriting discounts and commissions and any offering expenses. The offering was led by existing investor Coastlands Capital and included participation from OrbiMed, Perceptive Advisors and Gilead, as well as other new and existing institutional investors. Year-End and Fourth Quarter 2025 Financial Results Cash Position: Cash and cash equivalents were $137.5 million as of December 31, 2025, compared to $55.3 million as of December 31, 2024. In the fourth quarter of 2025, Xilio received $35.8 million in gross proceeds from Series B warrant exercises and a $17.5 million development milestone payment under its license agreement with Gilead. Collaboration and License Revenue: Collaboration and license revenue was $13.7 million for the quarter ended December 31, 2025, compared to $1.7 million for the quarter ended December 31, 2024. Collaboration and license revenue was $43.8 million for the year ended December 31, 2025, compared to $6.3 million for the year ended December 31, 2024. The year-over-year increase was primarily driven by collaboration and license revenue recognized under the collaboration, license and option agreement and stock purchase agreement that Xilio entered into in February 2025 with AbbVie and an increase in collaboration and license revenue recognized under the license agreement with Gilead due to the achievement of a $17.5 million development milestone during the third quarter of 2025. Research & Development (R&D) Expenses: R&D expenses were $18.1 million for the quarter ended December 31, 2025, compared to $8.8 million for the quarter ended December 31, 2024. R&D expenses were $56.0 million for the year ended December 31, 2025, compared to $41.2 million for the year ended December 31, 2024. The year-over-year increase was primarily driven by manufacturing activities related to IND-enabling studies and preclinical development activities for XTX501, increased clinical development activities related to efarindodekin alfa, increased costs related to masked T cell engager programs and indirect research and development and increased personnel-related costs, which were partially offset by a decrease in costs related to vilastobart and XTX202. General & Administrative (G&A) Expenses: G&A expenses were $7.4 million for the quarter ended December 31, 2025, compared to $6.5 million for the quarter ended December 31, 2024. G&A expenses were $29.7 million for the year ended December 31, 2025, compared to $24.8 million for the year ended December 31, 2024. The year-over-year increase was primarily driven by an increase in professional and consulting fees, including legal fees and other professional costs, and an increase in personnel-related costs, which were partially offset by a decrease in costs related to directors’ and officers’ liability insurance. Net Income (Loss): Net income was $10.4 million for the quarter ended December 31, 2025, compared to a net loss of $13.1 million for the quarter ended December 31, 2024. Net loss was $35.0 million for the year ended December 31, 2025, compared to $58.2 million for the year ended December 31, 2024. The year-over-year decrease in net loss was primarily driven by increased collaboration and license revenue for the year ended December 31, 2025. Cash Runway Based on its current operating plans, Xilio anticipates that its existing cash and cash equivalents will be sufficient to enable it to fund its operating expenses and capital expenditure requirements through the end of 2027. This estimate excludes any potential future milestone payments, option-related fees or other contingent payments under Xilio’s collaboration and partnership agreements with AbbVie and Gilead and excludes up to $36.2 million in additional gross proceeds in the second half of 2026 if all outstanding Series C warrants are exercised at their current exercise price. About Xilio Therapeutics Xilio Therapeutics is a clinical-stage biotechnology company discovering and developing masked 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. Leveraging our clinically-validated masking technology and capabilities, Xilio is developing I-O therapies designed to selectively activate within the tumor microenvironment to achieve durable efficacy without the severe side effects associated with systemically active I-O agents. Learn more by visiting www.xiliotx.com and follow us on LinkedIn (Xilio Therapeutics, Inc.). 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, expectations, development timelines and anticipated milestones for Xilio’s programs; the timing of clinical development, data releases, regulatory submissions, delivery of option data packages or other program updates; the promise or potential success of Xilio’s programs, including the first-in-class potential of Xilio’s masked T cell engager targeting PSMA and STEAP1, the best-in-class potential of XTX501 and the potential for XTX501 to be a foundational “backbone” therapy for combination treatment with other agents; the timing and receipt of future contingent payments under Xilio’s collaboration and license agreements with AbbVie and Gilead; the potential receipt of up to $36.2 million in additional gross proceeds in the second half of 2026 if all of the Series C warrants are exercised at their current exercise price; the sufficiency of, and the period in which Xilio expects to have, cash to fund its operations and capital expenditure requirements; 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 related to general market conditions and geopolitical uncertainties; 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; initial, preliminary, interim or retrospective preclinical or clinical data or results may not be replicated in or 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 may not support further development of such product candidates; actions of regulatory agencies 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 need to obtain additional cash resources to advance its pipeline of masked I-O molecules; the impact of international trade policies on Xilio’s business, including U.S. and China trade policies; and Xilio’s ability to maintain its collaboration or partnership agreements with AbbVie, Gilead and Roche. 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. Investor Contact Alex Lobo, Precision AQ [email protected] Media Contact Josie Butler, 1AB [email protected]

Reported late-breaking Phase 2 data at SITC for vilastobart demonstrating a 40% ORR in heavily pretreated patients with MSS mCRC without liver metastases and high plasma tumor mutational burden Presented Phase 1 data at SITC for efarindodekin alfa showing promising monotherapy anti-tumor activity and generally well-tolerated safety profile in patients with advanced solid tumors Announced new preclinical data at SITC for masked T cell engager programs supporting best-in-class potential and showing efficient masking, potent anti-tumor activity and broad therapeutic index Anticipate cash runway into the first quarter of 2027 WALTHAM, Mass., Nov. 13, 2025 (GLOBE NEWSWIRE) -- 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, 2025. “As we advance our robust pipeline of innovative masked immunotherapies, we continue to provide additional validation of our proprietary masking technology and ability to deliver differentiated molecules across a wide range of targets and design formats,” said René Russo, Pharm.D., president and chief executive officer of Xilio. “At SITC, we presented compelling data across our clinical and preclinical programs, including data supporting the best-in-class potential of our masked T cell engager programs to meaningfully widen the therapeutic window relative to non-masked T cell engagers as well as our unique ability to incorporate co-stimulation to substantially improve the durability of T cell response.” Dr. Russo added, “For our clinical-stage programs, we continue to be encouraged by the promising data for both vilastobart and efarindodekin alfa, which have each shown differentiated clinical efficacy and safety for patients with high unmet need. In particular, new data for vilastobart leveraging plasma TMB as a predictive biomarker showed a 40% response rate in patients with MSS mCRC without liver metastases, supporting the significant opportunity for vilastobart as a combination therapy. As we look ahead to 2026, we are focused on execution across our clinical programs, while rapidly advancing XTX501, our bispecific PD-1/IL-2, toward a planned IND submission in mid 2026 and our masked T cell engager programs into IND-enabling studies.” Pipeline and Business Updates Vilastobart: tumor-activated, Fc-enhanced anti-CTLA-4 Vilastobart is currently being evaluated in combination with atezolizumab (Tecentriq®) in Phase 1C combination dose escalation in patients with advanced solid tumors and in a Phase 2 clinical trial in patients with microsatellite stable (MSS) metastatic colorectal cancer (mCRC). In November 2025, Xilio announced new late-breaking data from its ongoing Phase 2 clinical trial at the Society for Immunotherapy of Cancer (SITC) 40th Annual Meeting. These data demonstrated a 40% objective response rate (ORR) in heavily pre-treated, plasma tumor mutational burden (TMB) high patients (≥10 mutations/Mb) with MSS mCRC without liver metastases and showed a statistically significant correlation (p=0.05) between plasma TMB status and response. Approximately 55% of patients with MSS mCRC are estimated to have high plasma TMB, representing a meaningful patient population with high unmet need. For more information, read the press release here, and watch a replay of the webcast with leading colorectal cancer experts here. In November 2025, Xilio announced additional new Phase 2 data presented at SITC, which demonstrated the potential for circulating tumor DNA (ctDNA) as an early predictive biomarker for response to treatment with vilastobart in combination with atezolizumab in patients with MSS mCRC. For more information, read the press release here. Based on the promising clinical activity and safety profile demonstrated by vilastobart as a combination therapy, including in patients who had high plasma TMB, Xilio is actively seeking a partner to develop vilastobart in combination with PD-(L)1 or PD1-VEGF in MSS CRC and other tumor types. Efarindodekin Alfa: tumor-activated IL-12 Xilio is evaluating efarindodekin alfa as a monotherapy in an ongoing Phase 1/2 clinical trial in patients with advanced solid tumors. In November 2025, Xilio presented Phase 1 monotherapy dose escalation data for efarindodekin alfa at SITC demonstrating promising monotherapy anti-tumor activity in patients with advanced solid tumors as well as a generally well-tolerated safety profile at doses over 100-fold greater than the maximum tolerated dose of recombinant human IL-12. For more information, read the press release here. In September 2025, Xilio announced the selection of an initial recommended phase 2 dose (RP2D) and schedule for efarindodekin alfa and initiated patient dosing in the Phase 2 portion of the clinical trial. In connection with the initiation of Phase 2, Xilio achieved a development milestone of $17.5 million under its license agreement with Gilead Sciences, Inc. (Gilead). For more information, read the press release here. Xilio has completed enrollment in the Phase 1A monotherapy dose escalation and Phase 1B monotherapy dose expansion portions of the ongoing Phase 1/2 clinical trial, and evaluation of those patients is ongoing. XTX501: bispecific PD-1 / masked IL-2 XTX501 is a novel, bispecific PD-1 / masked IL-2 designed to selectively stimulate PD-1 positive, antigen-experienced T cells and enhance their function. XTX501 incorporates masking designed to overcome IL-2 receptor-mediated clearance and peripheral activity. In preclinical studies, XTX501 demonstrated robust monotherapy activity (including in settings insensitive to PD-1) and tumor-selective pharmacodynamics consistent with its intended mechanism of action. XTX501 is currently advancing through investigational new drug (IND)-enabling studies, and Xilio plans to submit an IND application for XTX501 in the middle of 2026. Masked T Cell Engager Programs Xilio is leveraging its proprietary, clinically validated tumor-activation platform to advance multiple preclinical programs for masked T cell engagers, including wholly owned programs targeting tumor-associated antigens for PSMA (prostate cancer), CLDN18.2 (gastric, pancreatic, esophageal and lung cancers) and STEAP1 (prostate, colorectal and lung cancers), as well as an additional program in collaboration with AbbVie Group Holdings Limited (AbbVie). Xilio’s masked T cell engager programs include bispecific molecules designed using its advanced tumor-activated cell engager (ATACR) format, which consists of a T cell engager with a masked CD3 targeting domain, and tri-specific molecules designed using its selective effector-enhanced cell engager (SEECR) format. The SEECR format builds upon the ATACR format by adding co-stimulatory signaling designed to further enhance potency and durability of T cell activation. In November 2025, Xilio presented new preclinical data at SITC highlighting the potential for the company’s masking technology to significantly expand the therapeutic window for T cell engagers and overcome the challenges associated with current, systemically active non-masked T cell engagers. Xilio’s masked T cell engager molecules demonstrated potent anti-tumor activity with evidence of reduced systemic toxicity in murine models, supporting its broad applicability and potential best-in-class profile across a diverse range of targets, and the incorporation of co-stimulatory signaling in Xilio’s proprietary SEECR format enhanced durability of anti-tumor activity compared with T cell engager molecules that lacked co-stimulation. For more information, read the press release here. In the third quarter of 2025, Xilio nominated a development candidate for its PSMA program (ATACR format). Xilio anticipates nominating development candidates for its CLDN18.2 program (ATACR format) in the fourth quarter of 2025 and for its STEAP1 program (SEECR format) in the first half of 2026. Xilio anticipates advancing at least two of these programs into IND-enabling studies and submitting IND applications for those programs in 2027. Third Quarter 2025 Financial Results Cash Position: Cash and cash equivalents were $103.8 million as of September 30, 2025, compared to $55.3 million as of December 31, 2024. The increase was primarily driven by $52.0 million in total upfront payments under the collaboration, license and option agreement and stock purchase agreement entered into in February 2025 with AbbVie and $47.0 million in net proceeds received from Xilio’s June 2025 follow-on public offering, partially offset by cash used for operating activities. In the fourth quarter of 2025, Xilio received the $17.5 million development milestone payment under its license agreement with Gilead. Collaboration and License Revenue: Collaboration and license revenue was $19.1 million for the quarter ended September 30, 2025, compared to $2.3 million for the quarter ended September 30, 2024. Collaboration and license revenue for the quarter ended September 30, 2025 consisted of revenue recognized in connection with Xilio’s collaborations with AbbVie and Gilead, and collaboration and license revenue for the quarter ended September 30, 2024 consisted of revenue recognized in connection with Xilio’s collaboration with Gilead. Research & Development (R&D) Expenses: R&D expenses were $14.3 million for the quarter ended September 30, 2025, compared to $10.8 million for the quarter ended September 30, 2024. The increase was primarily driven by increased clinical development activities related to efarindodekin alfa, manufacturing activities related to IND-enabling studies and preclinical development activities for XTX501, increased costs related to early-stage programs and indirect research and development and increased personnel-related costs. General & Administrative (G&A) Expenses: G&A expenses were $6.7 million for the quarter ended September 30, 2025, compared to $6.3 million for the quarter ended September 30, 2024. The increase was primarily driven by an increase in professional and consulting fees, including legal fees and other professional costs, which were partially offset by a decrease in costs related to directors’ and officers’ liability insurance. Net Loss: Net loss was $16.3 million for the quarter ended September 30, 2025, compared to $14.0 million for the quarter ended September 30, 2024. Financial Guidance Based on its current operating plans, Xilio anticipates that its cash and cash equivalents as of September 30, 2025, together with the $17.5 million development milestone received under its license agreement with Gilead, will be sufficient to enable it to fund its operating expenses and capital expenditure requirements into the first quarter of 2027. About Vilastobart Vilastobart 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 in the tumor microenvironment (TME). In 2023, Xilio entered into a co-funded clinical trial collaboration with Roche to evaluate vilastobart in combination with atezolizumab (Tecentriq®) in a multi-center, open-label Phase 1/2 clinical trial. Xilio is currently evaluating the safety of the combination in Phase 1C dose escalation in patients with advanced solid tumors and the efficacy and safety of the combination in Phase 2 in patients with microsatellite stable (MSS) metastatic colorectal cancer (mCRC) with and without liver metastases. Please refer to NCT04896697 on www.clinicaltrials.gov for additional details. About Efarindodekin Alfa Efarindodekin alfa (XTX301) is an investigational tumor-activated IL-12 designed to potently stimulate anti-tumor immunity and reprogram the tumor microenvironment (TME) of poorly immunogenic “cold” tumors towards an inflamed or “hot” state. Xilio is currently evaluating the safety and tolerability of efarindodekin alfa as a monotherapy in patients with advanced solid tumors in the Phase 1 portion of a first-in-human, multi-center, open-label Phase 1/2 clinical trial and the safety and efficacy of efarindodekin alfa as a monotherapy in the Phase 2 portion in patients with advanced solid tumors. The Phase 2 portion of the trial is anticipated to enroll approximately 40 patients in specific tumor types at multiple sites in the United States. Please refer to NCT05684965 on www.clinicaltrials.gov for additional details. In March 2024, Xilio entered into an exclusive global license agreement with Gilead to develop and commercialize efarindodekin alfa and specified other molecules directed to IL-12.Xilio is responsible for conducting clinical development for efarindodekin alfa through the initial Phase 2 portion of the ongoing Phase 1/2 clinical trial. Following the delivery by Xilio of a specified clinical data package for efarindodekin alfa related to the Phase 1/2 clinical trial, Gilead can elect to transition responsibilities for the development and commercialization of efarindodekin alfa to Gilead, subject to the terms of the license agreement and payment by Gilead of a $75.0 million transition fee. If Gilead exercises its option for efarindodekin alfa, Xilio will be eligible to receive up to $500.0 million in specified development, regulatory and sales-based milestones and will be eligible to receive tiered royalties ranging from high single digits to mid-teens on annual global net product sales. About Xilio Therapeutics Xilio Therapeutics is a clinical-stage biotechnology company discovering and developing tumor-activated, or masked, 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 is leveraging its proprietary platform to advance a pipeline of novel, tumor-activated I-O molecules that are designed to optimize the therapeutic index by localizing anti-tumor activity within the tumor microenvironment. Learn more by visiting www.xiliotx.com and follow us on LinkedIn (Xilio Therapeutics, Inc.). 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, expectations, development timelines and anticipated milestones for Xilio’s programs; the timing of data releases or program updates; the potential of Xilio’s programs or platform; the ultimate safety and efficacy of Xilio’s current or future products as a monotherapy or combination therapy in any indication; the potential for plasma-based TMB as a predictive biomarker for response in patients with MSS mCRC; the receipt of future contingent payments under Xilio’s collaboration agreements with AbbVie or Gilead; the ability to partner the vilastobart program; the sufficiency of, and the period in which Xilio expects to have, cash to fund its operations, capital expenditure requirements, and development plans and milestones; 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 related to general market conditions and geopolitical uncertainties; 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 ability to advance multiple early stage masked T cell engager programs; initial, preliminary, interim or retrospective preclinical or clinical data or results may not be replicated in or 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 may not support further development of such product candidates; actions of regulatory agencies 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 need to obtain additional cash resources to advance its pipeline of tumor-activated I-O molecules; the impact of international trade policies on Xilio’s business, including U.S. and China trade policies; and Xilio’s ability to maintain its collaboration or partnership agreements with AbbVie, Gilead and Roche. 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. Investor Contact Alex Lobo, Precision AQ [email protected] Media Contact Josie Butler, 1AB [email protected] (1) Operating expenses include the following amounts of non-cash stock-based compensation expense: (2) Weighted average common shares outstanding, basic and diluted, includes prefunded warrants to purchase common stock issued in connection with (i) the company’s private placements with certain existing investors and Gilead in 2024 and (ii) the company’s June 2025 follow-on public offering, as the prefunded warrants are exercisable at any time for nominal cash consideration.

Announced updated Phase 2 data at ASCO for vilastobart, a tumor-activated, Fc-enhanced, anti-CTLA-4, demonstrating deep and durable responses and a meaningfully differentiated safety and tolerability profile for an anti-CTLA-4 combination therapy On track with plans to nominate first development candidates for wholly owned masked T cell engager programs in second half of 2025 $121.6 million in cash and cash equivalents as of June 30, 2025, with anticipated cash runway through end of third quarter of 2026 WALTHAM, Mass., Aug. 14, 2025 (GLOBE NEWSWIRE) -- 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 second quarter ended June 30, 2025. “During the second quarter, we continued to make strong progress across our pipeline of novel tumor-activated immuno-oncology therapies, and with our recent financing, we believe that we are well-positioned to execute on our strategic goals,” said René Russo, Pharm.D., president and chief executive officer of Xilio. “We believe our masked T cell engager molecules have the potential to be best-in-class, and we anticipate nominating our first development candidates for our wholly owned programs later this year. In addition, we are very encouraged by the clinical progress for XTX301, our tumor-activated IL-12 advancing in partnership with Gilead, and we look forward to providing a program update in the near-term. We also recently reported updated Phase 2 combination data for vilastobart at ASCO and believe these data not only highlight the significant opportunity for vilastobart across a range of I-O combinations and tumor types, but also provide further clinical validation for our proprietary masking technology and approach.” Pipeline and Business Updates Vilastobart: tumor-activated, Fc-enhanced, high affinity binding anti-CTLA-4 Vilastobart 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 in the tumor microenvironment (TME). Vilastobart is currently being evaluated in combination with atezolizumab (Tecentriq®) in Phase 1C combination dose escalation in patients with advanced solid tumors and in a Phase 2 clinical trial in patients with metastatic microsatellite stable (MSS) colorectal cancer (CRC). In May 2025, Xilio announced promising updated Phase 2 data for vilastobart in combination with atezolizumab in patients with metastatic MSS CRC at the American Society of Clinical Oncology (ASCO) Annual Meeting. These data demonstrated a preliminary 26% objective response rate in heavily pre-treated metastatic MSS CRC patients without liver metastases, including deep and durable responses accompanied by substantial decreases in tumor biomarkers and improvements in clinical symptoms, as well as a differentiated and well-tolerated safety profile with a low incidence of colitis and other immune-related adverse events, which have historically limited the potential for anti-CTLA-4 therapies. For more information, read the press release here. Xilio anticipates reporting additional data from the Phase 2 trial in the first half of 2026. Based on the encouraging clinical data to date, Xilio believes vilastobart has the potential to be an I-O combination agent of choice and be combined with a range of existing and next-generation agents. Xilio continues to engage strategic partners on potential opportunities to accelerate and expand further development for vilastobart. XTX301: tumor-activated IL-12 XTX301 is an investigational tumor-activated IL-12 designed to potently stimulate anti-tumor immunity and reprogram the TME of poorly immunogenic “cold” tumors towards an inflamed or “hot” state. In March 2024, Xilio entered into an exclusive license agreement with Gilead Sciences, Inc. (Gilead) related to Xilio’s tumor-activated IL-12 program, including XTX301. Xilio is evaluating XTX301 as a monotherapy in an ongoing Phase 1 clinical trial in patients with advanced solid tumors. Xilio recently completed enrollment in Phase 1A monotherapy dose escalation and evaluation of those patients is ongoing. In addition, Xilio continues to enroll patients in Phase 1B monotherapy dose expansion of the ongoing Phase 1 clinical trial of XTX301. XTX501: masked PD-1/IL-2 bispecific XTX501 is a novel, tumor-activated bispecific PD-1/IL-2 designed to selectively stimulate PD-1 positive, antigen-experienced T cells and enhance their function. XTX501 incorporates masking designed to overcome IL-2 receptor-mediated clearance and peripheral activity. In preclinical studies, XTX501 demonstrated robust monotherapy activity (including in settings insensitive to PD-1) and tumor-selective pharmacodynamics consistent with its intended mechanism of action. Xilio is continuing to advance XTX501 in investigational new drug (IND)-enabling studies and plans to submit an IND application for XTX501 in the middle of 2026. Masked T Cell Engager Programs Xilio is leveraging its proprietary, clinically validated tumor-activation platform to advance multiple preclinical programs for masked T cell engagers, including wholly owned programs targeting the tumor-associated antigens for PSMA, CLDN18.2 and STEAP1 and an additional program in collaboration with AbbVie. Xilio’s masked T cell engager programs include bispecific molecules designed using its advanced tumor-activated cell engager (ATACR) format, which consists of a T cell engager with a masked CD3 targeting domain, and tri-specific molecules designed using its selective effector-enhanced cell engager (SEECR) format. The SEECR format builds upon the ATACR format by adding co-stimulatory signaling designed to further enhance potency and T cell activation. Xilio anticipates nominating development candidates for its PSMA program (ATACR format), CLDN18.2 program (ATACR format) and STEAP1 program (SEECR format) in the third quarter of 2025, fourth quarter of 2025 and first half of 2026, respectively. Xilio anticipates advancing at least two of these programs into initial IND-enabling studies and submitting IND applications for those programs in 2027. Corporate Updates In June 2025, Xilio closed a follow-on public offering of prefunded warrants and accompanying common stock warrants and received initial gross proceeds of approximately $50.0 million before deducting underwriting discounts and commissions and offering expenses. In connection with the offering, Xilio issued Series B and Series C common stock warrants and will receive up to $100.0 million of additional gross proceeds by the second half of 2026 if all of those warrants are exercised in cash at their initial exercise price of $0.75 per warrant. The financing was co-led by new investors Coastlands Capital and Frazier Life Sciences and included participation from Gilead Sciences, Inc., Logos Capital, Samsara BioCapital and other new and existing institutional investors. For more information, read the press release here. In June 2025, Xilio announced the appointment of Akintunde (Tunde) Bello, Ph.D., to the company’s board of directors. For more information, read the press release here. Second Quarter 2025 Financial Results Cash Position: Cash and cash equivalents were $121.6 million as of June 30, 2025, compared to $55.3 million as of December 31, 2024. In the second quarter of 2025, Xilio received $47.0 million in net proceeds from its June 2025 follow-on public offering after deducting underwriting discounts and commissions and offering expenses payable by the company. Collaboration and License Revenue: Collaboration and license revenue was $8.1 million for the quarter ended June 30, 2025, compared to $2.4 million for the quarter ended June 30, 2024. Collaboration and license revenue for the quarter ended June 30, 2025 consisted of revenue recognized in connection with Xilio’s collaborations with AbbVie and Gilead, and collaboration and license revenue for the quarter ended June 30, 2024 consisted of revenue recognized in connection with Xilio’s collaboration with Gilead. Research & Development (R&D) Expenses: R&D expenses were $15.3 million for the quarter ended June 30, 2025, compared to $11.2 million for the quarter ended June 30, 2024. The increase was primarily driven by increased clinical development activities related to vilastobart, increased costs related to early-stage programs and indirect research and development and increased personnel-related costs, which were partially offset by decreased costs related to clinical development activities for XTX202, a tumor-activated IL-2, as a result of discontinuing further investment in that program. For the quarter ended June 30, 2025, R&D expenses also included manufacturing activities related to IND-enabling studies and preclinical development activities for XTX501, which were not separately tracked for the quarter ended June 30, 2024 as the company had not yet begun performing IND-enabling studies. For the quarter ended June 30, 2024, R&D expenses also included a $1.0 million development milestone under the CTLA-4 monoclonal antibody license agreement with WuXi Biologics (Hong Kong) Limited for which there was no comparable cost for the quarter ended June 30, 2025. General & Administrative (G&A) Expenses: G&A expenses were $7.1 million for the quarter ended June 30, 2025, compared to $5.8 million for the quarter ended June 30, 2024. The increase was primarily driven by an increase in professional and consulting fees, including legal fees and other professional costs, and an increase in personnel-related costs, which were partially offset by a decrease in costs related to directors’ and officers’ liability insurance. Net Loss: Net loss was $15.8 million for the quarter ended June 30, 2025, compared to $13.9 million for the quarter ended June 30, 2024. Financial Guidance Based on its current operating plans, Xilio anticipates that its cash and cash equivalents as of June 30, 2025 will be sufficient to enable it to fund its operating expenses and capital expenditure requirements through the end of the third quarter of 2026. About Vilastobart Vilastobart 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 in the tumor microenvironment (TME). In 2023, Xilio entered into a co-funded clinical trial collaboration with Roche to evaluate vilastobart in combination with atezolizumab (Tecentriq®) in a multi-center, open-label Phase 1/2 clinical trial. Xilio is currently evaluating the safety and tolerability of the combination in Phase 1C dose escalation in patients with advanced solid tumors and the safety and efficacy of the combination in Phase 2 in patients with metastatic microsatellite stable colorectal cancer with and without liver metastases. Please refer to NCT04896697 on www.clinicaltrials.gov for additional details. About XTX301 XTX301 is an investigational tumor-activated IL-12 designed to potently stimulate anti-tumor immunity and reprogram the tumor microenvironment (TME) of poorly immunogenic “cold” tumors towards an inflamed or “hot” state. In March 2024, Xilio entered into an exclusive license agreement with Gilead Sciences, Inc. for Xilio’s tumor-activated IL-12 program, including XTX301. Xilio is evaluating the safety and tolerability of XTX301 as a monotherapy in patients with advanced solid tumors in the Phase 1 portion of a first-in-human, multi-center, open-label Phase 1/2 clinical trial. Please refer to NCT05684965 on www.clinicaltrials.gov for additional details. About Xilio Therapeutics Xilio Therapeutics is a clinical-stage biotechnology company discovering and developing tumor-activated, or masked, 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 is leveraging its proprietary platform to advance a pipeline of novel, tumor-activated I-O molecules that are designed to optimize the therapeutic index by localizing anti-tumor activity within the tumor microenvironment. Learn more by visiting www.xiliotx.com and follow us on LinkedIn (Xilio Therapeutics, Inc.). 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, expectations, development timelines and anticipated milestones for Xilio’s programs; the timing of data releases or program updates; the timing and potential receipt of cash proceeds upon the exercise of common stock warrants issued in connection with the June 2025 follow-on public offering; the receipt of future contingent payments under Xilio’s collaboration or partnership agreements with AbbVie or Gilead; the ability to partner vilastobart and expand and accelerate further development; the potential benefits of any of Xilio’s current or future product candidates in any indication; the sufficiency of, and the period in which Xilio expects to have, cash to fund its operations, capital expenditure requirements, and development plans and milestones; 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 related to general market conditions and geopolitical uncertainties; 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 ability to advance multiple early stage masked T cell engager programs; initial, preliminary or interim preclinical or clinical data or results may not be replicated in or 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 may not support further development of such product candidates; actions of regulatory agencies 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 need to obtain additional cash resources to advance its pipeline of tumor-activated I-O molecules; the impact of international trade policies on Xilio’s business, including U.S. and China trade policies; and Xilio’s ability to maintain its collaboration or partnership agreements with AbbVie, Gilead and Roche. 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. Investor Contact [email protected] Media Contact Dan Budwick 1AB [email protected]

Updated Phase 2 data to be presented at ASCO for vilastobart, a tumor-activated, Fc-enhanced, anti-CTLA-4, in combination with atezolizumab in patients with metastatic microsatellite stable colorectal cancer (MSS CRC) Advancing multiple masked T cell engager programs utilizing Xilio’s novel ATACR and SEECR formats, with first development candidates anticipated in second half of 2025 WALTHAM, Mass., May 08, 2025 (GLOBE NEWSWIRE) -- 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 first quarter ended March 31, 2025. “In the first quarter, we presented encouraging initial Phase 2 data for vilastobart, our tumor-activated anti-CTLA-4, in combination with atezolizumab in patients with late-line MSS CRC. These data included a preliminary 27% objective response rate in late-line MSS CRC patients without liver metastases accompanied by a differentiated safety profile with a low incidence of colitis and other immune-related adverse events, which are common dose-limiting adverse events for other CTLA-4 agents,” said René Russo, Pharm.D., president and chief executive officer of Xilio. “MSS CRC is an immunologically cold tumor type that is very difficult to treat and increasing in incidence, particularly in younger people for whom no immunotherapy treatment options are currently available. We look forward to reporting updated Phase 2 data at the upcoming ASCO meeting, including additional response assessments and further follow-up on the previously reported data. This quarter was also marked by strong execution across our pipeline, as we continue to advance XTX301, our tumor-activated IL-12, in monotherapy dose escalation in partnership with Gilead, and multiple novel masked T cell engager programs internally and as part of our recently announced collaboration with AbbVie.” Pipeline and Business Updates Vilastobart: tumor-activated, Fc-enhanced, high affinity binding anti-CTLA-4 Vilastobart 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 in the tumor microenvironment (TME). Vilastobart is currently being evaluated in combination with atezolizumab (Tecentriq®) in Phase 1C combination dose escalation in patients with advanced solid tumors and in a Phase 2 clinical trial in patients with MSS CRC. In January 2025, Xilio announced encouraging initial Phase 2 data for vilastobart in combination with atezolizumab in patients with MSS CRC. As of a data cutoff date of January 13, 2025, the combination of vilastobart at 100 mg once every six weeks (Q6W) in combination with atezolizumab at 1200 mg once every three weeks (Q3W) demonstrated a preliminary 27% objective response rate in patients without liver metastases accompanied by a generally well-tolerated safety profile. Patients experienced a low incidence of colitis and other immune-related adverse events, which have historically limited the potential for anti-CTLA-4 therapies. For more information, read the press release here. Based on the promising initial Phase 2 data for vilastobart, Xilio is seeking opportunities to partner the vilastobart program to accelerate and expand further development. Xilio plans to report updated data from the ongoing Phase 2 clinical trial in patients with metastatic MSS CRC, including additional response assessments and further follow-up on the previously reported data, at the 2025 American Society of Clinical Oncology (ASCO) Annual Meeting being held in Chicago from May 30 to June 3, 2025. Title: Vilastobart (XTX101), a tumor-activated, Fc-enhanced anti-CTLA-4 monoclonal antibody, in combination with atezolizumab in patients with MSS CRC Abstract ID: 3553 Poster Session: Gastrointestinal Cancer – Colorectal and Anal Poster Board: 222 Session Date and Time: Saturday, May 31, from 9:00 a.m. to 12:00 p.m. CDT XTX301: tumor-activated IL-12 XTX301 is an investigational tumor-activated IL-12 designed to potently stimulate anti-tumor immunity and reprogram the TME of poorly immunogenic “cold” tumors towards an inflamed or “hot” state. In March 2024, Xilio entered into an exclusive license agreement with Gilead Sciences, Inc. (Gilead) related to Xilio’s tumor-activated IL-12 program, including XTX301. A maximum tolerated dose has not yet been established, and Xilio continues to enroll patients in Phase 1A monotherapy dose escalation and Phase 1B monotherapy dose expansion of the ongoing Phase 1 clinical trial of XTX301. XTX501: masked PD-1/IL-2 bispecific XTX501 is a novel, tumor-activated bispecific PD-1/IL-2 designed to selectively stimulate PD-1 positive, antigen-experienced T cells and enhance their function. XTX501 incorporates masking designed to overcome IL-2 receptor-mediated clearance and peripheral activity. In preclinical studies, XTX501 demonstrated robust monotherapy activity (including in settings insensitive to PD-1) and tumor-selective pharmacodynamics consistent with its intended mechanism of action. Xilio is currently advancing XTX501 in investigational new drug (IND) enabling studies and plans to submit an IND application for XTX501 in the middle of 2026. Masked T Cell Engager Programs Xilio is leveraging its proprietary, clinically validated tumor-activation platform to advance multiple preclinical programs for masked T cell engagers, including wholly owned programs targeting the tumor-associated antigens for PSMA, CLDN18.2 and STEAP1 and an additional program in collaboration with AbbVie. Xilio’s masked T cell engager programs include bispecific molecules designed using its advanced tumor-activated cell engager (ATACR) format, which consists of a T cell engager with a masked CD3 targeting domain, and tri-specific molecules designed using its selective effector-enhanced cell engager (SEECR) format. The SEECR format builds upon the ATACR format by adding co-stimulatory signaling designed to further enhance potency and T cell activation. Xilio anticipates nominating a development candidate for its PSMA program in the ATACR format in the third quarter of 2025 and submitting an IND application in the first quarter of 2027. PSMA has demonstrated potential as a T cell engager target for prostate cancer. Xilio anticipates nominating a development candidate for its CLDN18.2 program in the ATACR format in the fourth quarter of 2025 and submitting an IND application in the second quarter of 2027. CLDN18.2 has broad potential as a T cell engager target for gastric, pancreatic, esophageal and lung cancers. Xilio anticipates nominating a development candidate for its STEAP1 program in the SEECR format in the first half of 2026 and submitting an IND application in the second half of 2027. STEAP1 has broad potential as a T cell engager target for prostate, colorectal and lung cancers. Corporate Updates In the first quarter of 2025, Xilio announced a collaboration, license and option agreement with AbbVie leveraging Xilio’s proprietary tumor-activation technology and platform to discover and develop novel tumor-activated immunotherapies, including masked T cell engagers, and received $52.0 million in total upfront payments from AbbVie. Under the agreement, Xilio is also eligible to receive up to approximately $2.1 billion in total contingent payments for option-related fees and milestones plus tiered royalties. For more information, read the joint press release here. First Quarter 2025 Financial Results Cash Position: Cash and cash equivalents were $89.1 million as of March 31, 2025, compared to $55.3 million as of December 31, 2024. In the first quarter of 2025, Xilio received $52.0 million in total upfront payments in connection with the collaboration agreement with AbbVie. Collaboration and License Revenue: Collaboration and license revenue was $2.9 million for the quarter ended March 31, 2025, which consisted of $2.9 million of total revenue recognized in connection with the collaborations with AbbVie and Gilead. No collaboration and license revenue was recognized for the quarter ended March 31, 2024. Research & Development (R&D) Expenses: R&D expenses were $8.3 million for the quarter ended March 31, 2025, compared to $10.4 million for the quarter ended March 31, 2024. The decrease was primarily driven by decreased clinical development activities for XTX202, a masked IL-2, as a result of discontinuing further investment in XTX202, decreased personnel-related costs due to lower headcount and decreased manufacturing costs for XTX301, partially offset by increased spending related to early stage programs and indirect research and development, increased clinical development activities for vilastobart and manufacturing activities for XTX501 in connection with IND-enabling studies. General & Administrative (G&A) Expenses: G&A expenses were $8.5 million for the quarter ended March 31, 2025, compared to $6.1 million for the quarter ended March 31, 2024. The increase was primarily driven by an increase in legal fees and personnel-related costs, partially offset by a decrease in costs related to directors’ and officers’ liability insurance. Net Loss: Net loss was $13.3 million for the quarter ended March 31, 2025, compared to $17.2 million for the quarter ended March 31, 2024. Financial Guidance Based on its current operating plans, Xilio anticipates that its cash and cash equivalents as of March 31, 2025 will be sufficient to enable it to fund its operating expenses and capital expenditure requirements into the first quarter of 2026. About Vilastobart and the Phase 1/2 Combination Clinical Trial Vilastobart 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 in the tumor microenvironment (TME). In 2023, Xilio entered into a co-funded clinical trial collaboration with Roche to evaluate vilastobart in combination with atezolizumab (Tecentriq®) in a multi-center, open-label Phase 1/2 clinical trial. Xilio is currently evaluating the safety of the combination in Phase 1C dose escalation in patients with advanced solid tumors and the safety and efficacy of the combination in Phase 2 in patients with metastatic microsatellite stable colorectal cancer with and without liver metastases. Please refer to NCT04896697 on www.clinicaltrials.gov for additional details. About XTX301 and the Phase 1 Clinical Trial XTX301 is an investigational masked IL-12 designed to potently stimulate anti-tumor immunity and reprogram the tumor microenvironment (TME) of poorly immunogenic “cold” tumors towards an inflamed or “hot” state. In March 2024, Xilio entered into an exclusive license agreement with Gilead Sciences, Inc. for Xilio’s tumor-activated IL-12 program, including XTX301. Xilio is currently evaluating the safety and tolerability of XTX301 as a monotherapy in patients with advanced solid tumors in a first-in-human, multi-center, open-label Phase 1 clinical trial. Please refer to NCT05684965 on www.clinicaltrials.gov for additional details. About Xilio Therapeutics Xilio Therapeutics is a clinical-stage biotechnology company discovering and developing tumor-activated, or masked, 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 is leveraging its proprietary platform to advance a pipeline of novel, tumor-activated I-O molecules that are designed to optimize the therapeutic index by localizing anti-tumor activity within the tumor microenvironment. Learn more by visiting www.xiliotx.com and follow us on LinkedIn (Xilio Therapeutics, Inc.). 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, expectations, development timelines and anticipated milestones for Xilio’s programs; the timing of data releases; the receipt of future contingent payments under Xilio’s collaboration or partnership agreements with AbbVie and Gilead; the ability to partner vilastobart and expand and accelerate further development; the potential benefits of any of Xilio’s current or future product candidates in any indication; the sufficiency of, and the period in which Xilio expects to have, cash to fund its operations, capital expenditure requirements, and development plans and milestones; 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 related to general market conditions and geopolitical uncertainties; 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 ability to advance multiple early stage masked T cell engager programs; initial, preliminary or interim preclinical or clinical data or results may not be replicated in or 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 may not support further development of such product candidates; actions of regulatory agencies 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 need to obtain additional cash resources to fund its operations beyond the first quarter of 2026, including to advance its pipeline of tumor-activated I-O molecules; the impact of international trade policies on Xilio’s business, including U.S. and China trade policies; and Xilio’s ability to maintain its collaboration or partnership agreements with AbbVie, Gilead and Roche. 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 Annual Report on Form 10-K 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. Investor and Media Contact Scott Young Vice President, Investor Relations and Corporate Communications [email protected]