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$(R)$ ) 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. 
 

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November 13, 2025 07:30 ET (12:30 GMT)