Vir Biotechnology and Gilead will develop three dual-masked T-cell engagers for solid tumors under a deal worth up to $1.875 billion plus royalties.
Written By: Creola Gonsalves, MS Biotech
Reviewed By: Pharmacally Editorial Team
Vir Biotechnology has entered a collaboration and licensing agreement with Gilead Sciences to discover three dual-masked T-cell engager (TCE) candidates targeting selected solid tumor-associated antigens. The agreement combines Vir’s PRO-XTEN® masking technology and AI-enabled protein engineering platform with Gilead’s oncology development and commercialization capabilities, with potential payments to Vir reaching $1.875 billion, excluding royalties.
Collaboration Focuses on Expanding T-Cell Engagers in Solid Tumors
T-cell engagers redirect T cells toward cancer cells, bringing the immune system into direct contact with malignant cells to trigger tumor-cell killing. Although this approach has established clinical utility in hematologic malignancies, its application in solid tumors remains challenging because of on-target and off-tumor activity, systemic immune activation, and associated toxicities.
Under the agreement, Vir will discover, design, and optimize three dual-masked TCE development candidates against selected solid tumor-associated antigens. Gilead will hold an exclusive license to nominate candidates and advance them through subsequent development, manufacturing, and commercialization.
The collaboration represents Vir’s second partnership built around its universal PRO-XTEN masking technology, following its earlier agreement with Sanofi. The new arrangement expands the platform’s potential application in oncology through the discovery of three additional candidates.
PRO-XTEN Technology Seeks to Improve the Therapeutic Window
Vir’s PRO-XTEN platform originated at Amunix Pharmaceuticals, which Sanofi acquired in 2021. Vir subsequently licensed the PRO-XTEN platform and three clinical-stage T-cell engagers from Sanofi in 2024, adding the technology to its oncology development capabilities.
The platform uses protease-cleavable masks to keep TCEs inactive until they reach the tumor microenvironment. Tumor-associated proteases remove the masks, allowing the molecules to engage T cells and promote cancer-cell destruction.
In a conventional TCE, one binding domain recognizes CD3 on T cells, while another recognizes a tumor-associated antigen (TAA). Dual masking can restrict these binding interactions before tumor-selective activation, potentially reducing unwanted immune engagement in circulation. The precise masking architecture of the three newly announced candidates has not been disclosed.
By limiting activation outside the intended tumor environment, the approach could reduce systemic toxicity and improve the therapeutic index, which reflects the balance between effective and harmful drug exposure. The technology may also extend molecular half-life and support less frequent dosing, although these benefits remain to be demonstrated for the new candidates.
Vir will apply its proprietary dAIsY™ platform, which integrates data, artificial intelligence, protein structure, and antibody engineering, to optimize the candidates across multiple parameters. The objective is to identify molecules that combine potent antitumor activity with a wider therapeutic window across solid tumor targets.
Gilead Assumes Responsibility for Clinical Development
Vir will lead candidate discovery and optimization, while Gilead will take responsibility for downstream development, manufacturing, and commercialization. This structure allows Vir to leverage its discovery capabilities while relying on Gilead’s established oncology infrastructure to advance selected molecules toward clinical evaluation.
Vir President and CEO Marianne De Backer described the collaboration as an opportunity to generate differentiated candidates for difficult-to-treat solid tumors while advancing the company’s own clinical oncology portfolio. Gilead’s research leadership highlighted the combination of its oncology development expertise with Vir’s discovery platform.
No specific tumor indications, development timelines, clinical trial plans, or first-in-human milestones were disclosed in the announcement.
Agreement Includes Up to $1.875 Billion in Potential Payments
Vir will receive $90 million in upfront consideration, comprising $65 million in cash and a $25 million equity investment priced at a 30% premium. The company is also eligible for up to $45 million in near-term preclinical milestone payments.
Beyond these initial payments, the agreement provides for up to $1.74 billion in potential development, regulatory, and commercial milestones, as well as tiered royalties ranging from high single digits to low double digits on net sales.
Clinical Interpretation
The partnership reflects continued investment in approaches that address the safety limitations of T-cell engagers in solid tumors. PRO-XTEN’s protease-dependent activation could help separate tumor-directed activity from systemic exposure, but its clinical value will depend on whether masking remains stable in circulation and activates reliably within tumors. The agreement provides a route to test the platform across three candidates, although clinical benefit, safety, and the breadth of eligible tumor types remain unproven.
Reference
Vir Biotechnology Enters Multi-Program Collaboration and License Agreement with Gilead Sciences to Discover and Develop Novel PRO-XTEN® Dual-masked T-cell Engagers for Solid Tumors, Vir Biotechnology, 14 October 2026
About the Writer
Creola Gonsalves (Linkedin) is an M.S. Biotechnology postgraduate with a strong interest in clinical research, evidence interpretation, and healthcare writing, with a focus on translating life-science knowledge into meaningful real-world insights.
She is trained in Good Clinical Practice (GCP), clinical research principles, and critical interpretation of randomized clinical trials, with certifications from NIH and Stanford University.
Her research background in biotechnological applications and microbial research strengthens her ability to understand scientific evidence and develop clear, accurate, and research-driven healthcare content.