Xilio Begins Phase 2 Dosing Of Tumor-Activated IL-12 Therapy XTX301, Secures $17.5M Gilead Milestone

Xilio Therapeutics, Inc., announced the initiation of patient dosing in the Phase 2 portion of its ongoing Phase 1/2 clinical trial evaluating efarindodekin alfa (XTX301), a tumour-activated IL-12, as a monotherapy for certain advanced solid tumours. This milestone also triggered a $17.5 million payment from Gilead Sciences, Inc., under their 2024 license agreement covering XTX301 and Xilio’s broader tumour-activated IL-12 program.

“We are pleased to announce the initiation of the Phase 2 clinical trial for efarindodekin alfa (XTX301), a tumor-activated IL-12, in patients with advanced solid tumors. The achievement of this important milestone highlights the promising Phase 1 data demonstrated for efarindodekin alfa to date, including two partial responses in late-line patients with advanced solid tumors and a generally well-tolerated safety profile. These data also provide further clinical validation for our proprietary masking technology and approach, which we believe is best-in-class and has potential across a wide range of therapies and modalities,” said René Russo, Pharm.D., president and chief executive officer of Xilio. 

XTX301 is designed to selectively activate IL-12 within tumors, aiming to enhance anti-tumor immunity and convert “cold” tumors into inflamed or “hot” tumors. In the Phase 1 trial, XTX301 was generally well tolerated up to the recommended Phase 2 dose, with most treatment-related side effects reported as Grade 1 or 2. Encouraging clinical activity was observed, including two partial tumour responses (one confirmed and one unconfirmed) and sustained interferon gamma signaling without tachyphylaxis across treatment cycles.

“We are encouraged by the totality of data observed to date for efarindodekin alfa (XTX301) as a monotherapy in patients with advanced solid tumors, and we are excited for the potential that IL-12 has to treat a broad range of tumor types. We look forward to advancing the efarindodekin alfa (XTX301) program in the Phase 2 trial in partnership with Xilio,” said Bernard Fine, vice president, oncology early development at Gilead. 

Based on these Phase 1 findings, Xilio has moved forward with Phase 2 dosing and expects to further evaluate XTX301’s efficacy in advanced solid tumors. Enrollment in Phase 1A monotherapy dose escalation has been completed, while patient recruitment continues in the Phase 1B expansion. Financially, Xilio reported $121.6 million in cash and equivalents as of June 30, 2025, and expects the Gilead milestone payment in Q4 2025. Together, these resources are anticipated to fund operations into the first quarter of 2027.