Astellas and Vir Biotechnology struck a global co‑development and licensing pact to advance VIR‑5500, a PRO‑XTEN dual‑masked CD3 T‑cell engager targeting PSMA for prostate cancer. The deal provides Vir with substantial near‑term cash and equity and up to $1.37 billion in milestone and sales‑based payments, signaling Astellas’ commitment to oncology bispecifics. Under the agreement, Astellas assumes global development and commercialization responsibilities while Vir retains upside through milestones and royalties. The PRO‑XTEN masking approach is designed to limit systemic T‑cell activation and improve the therapeutic index for potent CD3 engager modalities. The alliance underscores big pharma’s appetite for next‑generation T‑cell engager platforms that can deliver targeted cytotoxicity with improved safety, and it reinforces a trend where oncology pivots attract large strategic investments from established players.