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. 
 

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