Xilio Therapeutics Files IND for XTX501 Bispecific Masked IL-2 Ahead of Phase 1 Initiation

Xilio Therapeutics is moving its bispecific PD-1 / masked IL-2 candidate XTX501 toward a mid-2026 IND submission, with Phase 1 initiation targeted for the second half of 2026, a timeline that puts CMC teams and clinical supply operations under near-term pressure to demonstrate manufacturing readiness for a molecule class that carries distinct masking-domain characterisation requirements.

XTX501 is engineered to selectively stimulate PD-1-positive, antigen-experienced T cells while suppressing the peripheral activity and tolerability liabilities associated with unmasked IL-2 agents. Preclinical data showed robust monotherapy activity, including in PD-1-insensitive tumour settings, with tumour-selective pharmacodynamics consistent with the intended mechanism. Initial Phase 1 data in patients with metastatic non-small cell lung cancer are expected in the second half of 2027, subject to FDA IND clearance.

For QA and regulatory leads, the masking architecture introduces characterisation complexity that standard bispecific CMC packages do not fully address. Demonstrating that the masking domain remains intact through formulation, fill-finish, and storage, and is selectively cleaved only in the tumour microenvironment, will require robust analytical method development and process validation strategies aligned with ICH Q10 quality system expectations before the IND package is complete.

Beyond XTX501, Xilio presented preclinical data for XTX601, a masked T cell engager targeting CLDN18.2, at the AACR annual meeting, and is advancing a multi-specific masked TCE targeting PSMA and STEAP1. The company's modular TCE architecture incorporates masked CD3 targeting domains, tumour-associated antigen binding domains, and optional co-stimulatory domains, each variable adding combinatorial complexity to process development and release testing protocols.

Xilio also reported achieving a development milestone under its AbbVie collaboration, extending its cash runway into early 2028. For manufacturing and supply chain planners, that funding horizon sets a defined window within which Phase 1 clinical supply for XTX501 must be qualified and released.

The IND submission timeline and the Phase 1 data readout in the second half of 2027 will serve as the first measurable checkpoints for whether Xilio's masking platform can be translated from preclinical promise into a reproducible, GMP-compliant clinical manufacturing process.

Source: Xilio Therapeutics, Inc. via GlobeNewswire, 12 May 2026.