Gilead Taps Vir Biotechnology's PRO-XTEN Tech for Solid Tumors

Vir Biotechnology announced October 14, 2026, a collaboration and license agreement with Gilead Sciences to discover and develop up to 3 novel PRO-XTEN dual-masked T-cell engager (TCE) candidates targeting selected solid tumor antigens.¹ Vir Biotechnology will be responsible for discovery, design, and optimization of the candidates, while Gilead will hold an exclusive license to nominate and advance them, taking over subsequent development, manufacturing, and commercialization.¹

Vir Biotechnology is eligible to receive up to $135 million in total upfront and near-term preclinical milestone payments, consisting of $90 million upfront ($65 million in cash and a $25 million equity investment at a 30% premium) and up to $45 million in near-term preclinical milestones, plus up to $1.74 billion in further development, regulatory, and commercial milestones and tiered high-single-digit to low-double-digit royalties on net sales.¹

"We believe TCEs have a powerful role to play in the future of immunotherapy to treat cancer,” said Marianne De Backer, PhD, MSc, MBA, president and CEO of Vir Biotechnology, in a company press release.¹ “This collaboration with Gilead provides an opportunity to generate multiple differentiated candidates aimed at difficult-to-address solid tumors and to expand the potential impact of our science, while also advancing our own clinical oncology portfolio."

What does Gilead bring to this collaboration?

Gilead pairs its oncology development and commercialization expertise with Vir Biotechnology's TCE discovery and artificial intelligence (AI)-enabled protein engineering capabilities, including Vir Biotechnology's proprietary dAIsY (data AI structure and antibodY) platform for multiparameter optimization of candidate molecules.¹

"We look forward to combining Gilead's established and growing oncology capabilities, including our extensive development expertise and focus on next-generation immunotherapies, with Vir Biotechnology's innovative discovery capabilities," said Flavius Martin, MD, executive vice president of research at Gilead Sciences, in the release.¹ "Together with Vir Biotechnology, we seek to bring meaningful innovative therapeutics to patients."

Why does masking matter for TCEs in solid tumors?

TCEs direct T-cells to kill cancer cells and have become an important treatment option for blood cancers, but extending their therapeutic reach to solid tumors has been limited by toxicity, including on-target, off-tumor effects against healthy tissue that shares a targeted antigen, along with challenges in overcoming immune-excluded cold tumors.¹^,² Vir Biotechnology's PRO-XTEN technology is designed to extend a TCE's half-life and keep it inactive until it reaches the tumor microenvironment, at which tumor-specific proteases cleave off the mask and activate the molecule. According to Vir Biotechnology, this mechanism can limit toxicity, widen the therapeutic index, and potentially allow less frequent dosing.¹ This protease-activated masking approach, sometimes called a prodrug or probody strategy, is one of several design approaches researchers are using across the field to try to confine bispecific antibody activity to the tumor microenvironment.³

What clinical evidence supports the PRO-XTEN platform?

This is Vir Biotechnology's second collaboration built on PRO-XTEN. In its first, Astellas is co-developing VIR-5500, a prostate-specific membrane antigen-targeted PRO-XTEN dual-masked TCE for metastatic prostate cancer, under a deal that closed in April 2026.⁴ Updated phase 1 data reported in February 2026 showed a 45% objective response rate and an 82% PSA50 decline among efficacy-evaluable, heavily pretreated patients, with no dose-limiting toxicities and cytokine release syndrome, mostly low-grade, in half of patients.⁵

What are the limitations?

Today's agreement covers discovery-stage candidates with no disclosed clinical data, and Vir Biotechnology has not named the specific solid tumor antigens being targeted.¹ The $1.74 billion milestone figure is a contingent maximum tied to development, regulatory, and commercial success, not a guaranteed sum.¹ VIR-5500's phase 1 results, used here as evidence for the PRO-XTEN platform, come from a single, open-label, non-randomized trial in a different indication and antigen, and may not predict how the new candidates will perform.⁵

References

1. Vir Biotechnology. 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. Press release. Published October 14, 2026. Accessed October 14, 2026. https://investors.vir.bio/news/news-details/2026/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/default.aspx
2. Gerber WK, Xie Y, Patel SA. Expanding the therapeutic reach of chimeric antigen receptor T-cells and bispecific T-cell engagers across solid tumors. JCO Precis Oncol. 2025;9:e2400753. doi:10.1200/PO-24-00753
3. Ai Z, Wang B, Song Y, Cheng P, Liu X, Sun P. Prodrug-based bispecific antibodies for cancer therapy: advances and future directions. Front Immunol. 2025;16:1523693. doi:10.3389/fimmu.2025.1523693
4. Vir Biotechnology. Vir Biotechnology announces closing of global strategic collaboration with Astellas for the treatment of prostate cancer. Press release. Published April 16, 2026. Accessed October 14, 2026. https://investors.vir.bio/news/news-details/2026/Vir-Biotechnology-Announces-Closing-of-Global-Strategic-Collaboration-with-Astellas-for-the-Treatment-of-Prostate-Cancer/default.aspx
5. Vir Biotechnology. Vir Biotechnology reports positive updated phase 1 results for PSMA-targeting PRO-XTEN dual-masked T-cell engager VIR-5500 in patients with metastatic prostate cancer. Press release. Published February 23, 2026. Accessed October 14, 2026. https://www.businesswire.com/news/home/20260223892941/en/Vir-Biotechnology-Reports-Positive-Updated-Phase-1-Results-for-PSMA-targeting-PRO-XTEN%C2%AE-Dual-masked-T-Cell-Engager-VIR-5500-in-Patients-with-Metastatic-Prostate-Cancer