Astellas has agreed a US$1.7bn global prostate cancer deal with Vir Biotechnology to develop a masked T-cell engager designed to harness the immune system against the disease.
The collaboration centres on VIR-5500, a PSMAxCD3 bispecific drug known as a T-cell engager, or TCE. TCEs activate immune cells called T cells and direct them to attack cancer cells.
Unlike radioligand therapies, which deliver radioactive material to tumours, TCEs aim to recruit the body’s own defences.
VIR-5500 targets PSMA, a protein found on prostate cancer cells, and uses what Vir calls PRO-XTEN dual-masking technology.
This is designed to keep the drug inactive until it is unmasked within the tumour, which the company says may limit side effects elsewhere in the body.
Vir says only about 30 per cent of patients with metastatic castration-resistant prostate cancer, an advanced form of the disease that no longer responds to hormone-blocking treatment, survive for five years after diagnosis.
Marianne De Backer, chief executive of Vir, said: “The field is moving very, very fast.
“And we believe that we could accelerate the programme by working together with someone who has a really strong track record in the space.”
Updated phase 1 data presented at the 2026 ASCO Genitourinary Cancers Symposium showed that 82 per cent of heavily pretreated patients receiving the highest evaluated doses achieved a 50 per cent or greater reduction in PSA levels, a marker of disease activity. Among patients with measurable tumours, 45 per cent recorded an objective response.
Cytokine release syndrome, an immune overreaction commonly associated with TCEs, was observed in 50 per cent of the 58 patients treated and was described by Vir as generally restricted to mild events.
The company said preventative steroids were not required and no drugs were used to manage severe CRS.
Under the agreement, Astellas will provide US$335m in upfront and near-term payments, including US$240m in cash, US$75m through an equity investment and a US$20m near-term milestone.
Vir is eligible for up to US$1.37bn in additional development, regulatory and sales milestones, along with tiered double-digit royalties on sales outside the US.
Development costs will be shared 60–40, with Vir holding an option to co-promote the drug in the US, while Astellas will be responsible for commercialisation elsewhere.
For Astellas, the deal may strengthen its position in prostate cancer as Xtandi, its partnered drug with Pfizer, begins to lose patent protection in several territories this year.
Vir licensed the underlying technology from Sanofi in 2024, meaning some proceeds from the agreement will be shared with the French pharmaceutical company.
Competition in the field remains strong. Novartis already markets its radioligand therapy Pluvicto, while Janux Therapeutics has a masked TCE that is currently ahead of VIR-5500 in development.
Amgen and Johnson & Johnson are also developing TCE candidates for prostate cancer.
Vir plans to move VIR-5500 into phase 3 trials in 2027 and to begin testing the drug in earlier-stage disease in the second quarter of 2026.
Johann de Bono, the phase 1 trial’s principal investigator and a prostate cancer expert at the Institute of Cancer Research in the UK, said: “It is remarkable to see these early signs of profound anti-tumour activity in heavily pretreated mCRPC patients, and the favourable tolerability with minimal CRS to date means VIR-5500 could play a role in treating earlier disease.”
Anthony Jarkowski, primary focus lead of immuno-oncology at Astellas, added: “What really stood out to us is how they’re balanced, efficacy and toxicity.”
