Four Decades of Immunotherapy Dead Ends End With This Injection

A team from Mass General Brigham and Dana-Farber Cancer Institute has published results in Cell showing that a single injection of an oncolytic herpes simplex virus can recruit immune cells into glioblastoma tumors and extend survival in a Phase 1 trial — offering a rare bright spot in a cancer that has resisted immunotherapy for decades.

The study, published February 11, enrolled 41 patients with recurrent glioblastoma, the most common and aggressive primary brain tumor. Patients received a single injection of the engineered virus directly into their tumor. Researchers then analyzed tumor samples to track immune cell behavior. They found that the treatment induced sustained infiltration of cytotoxic T cells — the cancer-fighting immune cells — and that patients whose T cells positioned themselves closer to dying tumor cells lived longer after treatment.

The virus itself is a modified herpes simplex virus engineered by E. Antonio Chiocca, MD, PhD, executive director of the Center for Tumors of the Nervous System at Mass General Brigham Cancer Institute. The modification ensures the virus replicates only inside glioblastoma cells, sparing healthy brain tissue. Once inside a tumor cell, it kills the cell and produces copies that spread to neighboring cancer cells.

The critical finding is not just that the virus kills tumor cells directly — it converts a cold tumor into a warm one. Glioblastoma has historically been impervious to checkpoint inhibitors and other immunotherapies that have transformed care for melanoma and lung cancer, precisely because the tumors are densely immunosuppressive and lack T cell infiltration. This therapy appears to break that suppression.

The survival comparison is more cautious than headlines suggest. The trial was single-arm with no randomized control group; researchers compared outcomes to historically reported survival for recurrent glioblastoma. The treatment showed the strongest benefit in patients who already had antibodies against herpes simplex virus — a finding that raises questions about whether prior viral exposure could serve as a predictor of response.

Limitations are significant. Phase 1 trials are designed to test safety, not efficacy. Forty-one patients is a small cohort. The historical comparison means the survival benefit, while intriguing, needs confirmation in a randomized setting. Standard of care for glioblastoma — maximal surgical resection followed by radiation and temozolomide chemotherapy — has not meaningfully changed in 20 years. Any claim of a paradigm shift is premature.

Still, the mechanistic data are compelling. The researchers demonstrated that T cells not only infiltrated tumors but remained active and cytotoxic over time. That durability is what has been missing in glioblastoma immunotherapy attempts.

Co-senior author Kai Wucherpfennig, MD, PhD, chair of the Department of Cancer Immunology and Virology at Dana-Farber, framed the result carefully: "Findings from our clinical trial and our mechanistic study show that is now feasible to bring these critical immune cells into glioblastoma." Feasible is the operative word — Phase 2 and randomized trials are the obvious next step.

The paper is Meylan M et al. "Persistent T cell activation and cytotoxicity against glioblastoma following single oncolytic virus treatment in a clinical trial," Cell DOI: 10.1016/j.cell.2025.12.055. The clinical trial is registered at ClinicalTrials.gov (NCT03152318).