The collaboration aims to accelerate development of a masked T-cell engager for advanced disease.

February 24, 2026

Targeting Advanced Prostate Cancer

Advanced prostate cancer moves quickly. Once the disease progresses to a metastatic, castration-resistant stage, treatment options narrow and long-term survival rates remain low. Astellas Pharma and Vir Biotechnology are moving to accelerate development of a new investigational therapy aimed at addressing that challenge.

The companies have entered into a global collaboration to co-develop and commercialize VIR-5500, a T-cell engager designed to target prostate-specific membrane antigen, or PSMA. The therapy is currently in Phase 1 trials for patients with advanced metastatic prostate cancer.

How VIR-5500 Is Designed to Work

VIR-5500 is engineered with a focused objective: activate the immune system at the tumor site while limiting unintended effects elsewhere in the body.

The therapy combines:

• A bispecific antibody that binds to PSMA on tumor cells and CD3 on T cells
• Vir’s PRO-XTEN masking technology, designed to keep the therapy inactive until it reaches the tumor microenvironment

By remaining masked in circulation and activating within the tumor environment, the approach is intended to improve the therapeutic window while maintaining anti-tumor activity.

Financial and Development Structure

The collaboration outlines a clear division of responsibilities and economics.

Vir will receive $335 million in upfront and near-term payments, including cash, an equity investment priced at a premium, and a milestone payment. The company is also eligible for up to $1.37 billion in additional development, regulatory, and sales milestones.

Development costs will be shared:

• Astellas will cover 60 percent
• Vir will cover 40 percent

Vir will continue overseeing the ongoing Phase 1 study before development leadership transitions to Astellas.

Commercialization Plans

In the United States, the companies will split profits and losses evenly, and Vir retains the option to co-promote the therapy.

Outside the U.S., Astellas will lead commercialization efforts and will pay tiered double-digit royalties on net sales.

Strategic Implications

For Astellas, the agreement builds on a prostate cancer portfolio that has already reached more than 1.5 million patients worldwide.

For Vir, the partnership advances the clinical development of its PRO-XTEN platform in oncology and positions VIR-5500 for broader global development.

The transaction remains subject to customary closing conditions, including regulatory clearance.