Astellas Pharma and Vir Biotechnology struck a global co‑development and co‑commercialization pact around Vir’s PRO‑XTEN masked T‑cell engager program, centered on the prostate cancer candidate VIR‑5500. Under the agreement Vir will receive upfront and near‑term payments and is eligible for development, regulatory and commercial milestones that could total up to $1.7 billion, plus royalties. VIR‑5500 is a dual‑masked CD3 T‑cell engager designed to remain inert until it reaches the tumor microenvironment, aiming to reduce off‑target toxicity while engaging T cells against PSMA‑expressing prostate tumors. Vir will share a portion of proceeds from the Astellas collaboration with Sanofi, reflecting prior licensing and platform deals that underpin the PRO‑XTEN approach. The deal pairs Astellas’ development and commercialization scale with Vir’s masked TCE technology, and comes alongside early clinical signals and commentary from analysts that the alliance validates Vir’s oncology pivot. Marianne De Backer (Vir CEO) framed the platform as modular and broadly applicable across solid tumor targets.