Xilio Therapeutics Unveils Promising Preclinical Data for Masked T Cell Engager XTX601

New findings at AACR Annual Meeting highlight potential for wide therapeutic index and favorable tolerability profile

Apr. 17, 2026 at 9:34pm

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A minimalist neon outline of a human T cell receptor in vibrant shades of blue and purple, representing the targeted activation of the T cell engager within the tumor microenvironment.Xilio's masked T cell engager technology aims to selectively activate within the tumor, avoiding the systemic toxicity that has limited this approach in solid cancers.San Diego Today

Xilio Therapeutics, a clinical-stage biotech company, presented new preclinical data for its masked T cell engager XTX601 at the AACR Annual Meeting. The data showed XTX601 demonstrated protease-dependent activation and potent anti-tumor activity across multiple CLDN18.2-expressing tumor models, while being well-tolerated in non-human primates with no evidence of cytokine release syndrome.

Why it matters

T cell engagers have faced challenges in solid tumors due to the inability to achieve meaningful anti-tumor activity without severe systemic toxicities. Xilio's masking technology aims to address this by selectively activating the T cell engager within the tumor microenvironment, potentially unlocking the full potential of this therapeutic approach.

The details

XTX601 incorporates Xilio's clinically-validated masking technology and advanced tumor-activated cell engager (ATACR) format, which consists of a T cell engager with a masked CD3 targeting domain. This design is intended to minimize systemic T cell engagement in healthy tissue and overcome the toxicity issues that have limited non-masked T cell engagers targeting CLDN18.2. XTX601 also includes a conditional half-life modulation element to further limit peripheral exposure.

  • The AACR Annual Meeting took place from April 17–22, 2026 in San Diego, California.
  • Xilio plans to advance its masked T cell engager program targeting CLDN18.2 into IND-enabling studies and submit an IND application in 2027.

The players

Xilio Therapeutics

A clinical-stage biotechnology company discovering and developing masked immuno-oncology therapies with the goal of improving outcomes for cancer patients without severe side effects.

Uli Bialucha, Ph.D.

Chief scientific officer of Xilio Therapeutics.

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What they’re saying

“The data to be presented at AACR underscore the significant potential of our clinically-validated masking technology to address the central challenge that has limited the advancement of T cell engagers in solid tumors – namely, the inability to achieve meaningful anti-tumor activity without inducing severe systemic toxicities.”

— Uli Bialucha, Chief Scientific Officer, Xilio Therapeutics

What’s next

Xilio plans to advance its masked T cell engager program targeting CLDN18.2 into investigational new drug (IND)-enabling studies and submit an IND application for this program in 2027.

The takeaway

Xilio's masking technology shows promise in addressing the key challenge of achieving meaningful anti-tumor activity with T cell engagers without severe systemic toxicities, potentially unlocking the full potential of this therapeutic approach in solid tumors.