Vir Biotechnology Doses First Patient in Early Trial of Cancer Therapy

The novel dual-masked T-cell engager aims to improve safety and efficacy in treating aggressive solid tumors.

July 25, 2025

Vir Advances New Cancer Therapy with First Human Dose

Vir Biotechnology has officially kicked off its Phase 1 clinical trial for VIR-5525, a new therapy designed to target hard-to-treat cancers. The first patient has been dosed, putting the company one step closer to offering a potentially safer and more effective treatment for tumors that express EGFR, a well-established cancer target.

This isn’t Vir’s first foray into dual-masked T-cell engagers. VIR-5525 is the third candidate to reach clinical trials using the company’s PRO-XTEN™ masking technology—an approach designed to activate the drug only in the tumor microenvironment. By keeping the drug inactive until it reaches its target, Vir aims to reduce off-target toxicity while maintaining a strong therapeutic effect.

The Phase 1 study is open-label and non-randomized, evaluating VIR-5525 both on its own and alongside pembrolizumab. The focus is on several high-need cancer types:

• Non-small cell lung cancer (NSCLC)


• Colorectal cancer (CRC)


• Head and neck squamous cell carcinoma (HNSCC)


• Cutaneous squamous cell carcinoma (cSCC)

Strategic Milestone and Pipeline Expansion

There’s more riding on this milestone than just clinical progress. Dosing the first patient also unlocks a $75 million payment from Sanofi under a 2024 licensing deal. The funds, held as restricted cash since the agreement closed, will be booked as a research and development expense in Q3 2025.

Meanwhile, Vir continues to move forward with two other dual-masked programs—VIR-5818 for HER2-expressing tumors and VIR-5500 for PSMA-positive prostate cancer. Early results, shared earlier this year, showed encouraging signals in patients who had already exhausted other options.

Building for the Long Term

Looking ahead, Vir is building out its pipeline with a suite of preclinical candidates. These programs combine the PRO-XTEN™ platform with antibody designs discovered through the company’s internal discovery engine and AI system, dAIsY™. Each one targets solid tumors where current treatment options come up short.

The aim is clear: improve tolerability without compromising efficacy, and give clinicians new tools for a tough-to-treat set of diseases.