On May 12, 2026 Xilio Therapeutics, Inc. (Nasdaq: XLO), a clinical-stage biotechnology company discovering and developing masked immuno-oncology therapies for people living with cancer, reported pipeline progress and business updates and reported financial results for the first quarter ended March 31, 2026.

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"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 (Free AACR Whitepaper) 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.

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Xilio is currently advancing XTX501 through investigational new drug (IND)-enabling studies and plans to submit an IND application in the middle of 2026.
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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.

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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.
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In April 2026, Xilio presented new preclinical data for XTX601 at the American Association for Cancer Research (AACR) (Free AACR Whitepaper) 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.
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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.
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Xilio plans to submit IND applications for its CLDN18.2 and PSMA+STEAP1 programs in 2027.

Efarindodekin alfa: masked IL-12

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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
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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.
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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

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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.
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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.
Exhibit 99.1

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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.
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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.
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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.

(Press release, Xilio Therapeutics, MAY 12, 2026, View Source [SID1234665562])