Astellas and Vir Biotechnology struck a global co‑development and co‑commercialization deal for VIR‑5500, a PRO‑XTEN masked T‑cell engager targeting PSMA in prostate cancer. The agreement could generate up to $1.7 billion for Vir and builds on Vir’s pivot into oncology using the PRO‑XTEN platform, which masks T‑cell engagers to reduce off‑tumor toxicity until activation in the tumor microenvironment. VIR‑5500 is a Phase I candidate and sits alongside other PRO‑XTEN‑derived TCEs in Vir’s oncology portfolio. The deal gives Astellas an oncology asset that leverages masked TCE technology and provides Vir with development scale and commercial footprint, including potential combinations with checkpoint inhibitors. Analysts called the pact validation for Vir’s oncology strategy and the broader masked‑TCE approach as companies seek safer, more selective T‑cell engager modalities.