New Cancer Drugs · global
After Two FDA Rejections, Replimune’s Melanoma Virus Therapy Faces Public Review
The FDA will convene experts to reassess the combination of RP1 and nivolumab; the meeting concerns not only a new cancer drug, but also whether a single-arm trial and intratumoral injections can adequately demonstrate systemic efficacy.
A Massachusetts biotechnology company that sharply reduced its workforce following regulatory setbacks is approaching a pivotal moment for its survival. The U.S. Food and Drug Administration (FDA) has scheduled a public advisory committee meeting for July 30 to review Replimune’s biologics license application, BLA 125827. The candidate therapy, vusolimogene oderparepvec, also known as RP1, is intended for use in combination with the immune checkpoint inhibitor nivolumab to treat adults with advanced melanoma whose disease has progressed after anti-PD-1 therapy.
RP1 is an engineered herpes simplex virus designed to be injected directly into tumors, destroying cancer cells and releasing tumor antigens to trigger an immune response. The virus also carries a fusion protein and GM-CSF to enhance tumor cell death and immune activation. The rationale for combining it with nivolumab is to turn the immune stimulation generated by local injections into a systemic attack on other lesions.
The dispute is not over whether responses have been observed, but whether the existing trial can demonstrate that those responses were truly attributable to RP1. Results from the IGNYTE trial released by Replimune showed that patients whose disease progressed after anti-PD-1 treatment achieved an objective response rate of 34% with the combination therapy, with a median duration of response of 24.8 months. However, this represents the company’s characterization of the data, and the FDA previously concluded that the study did not provide adequate and well-controlled evidence of efficacy.
The FDA’s publicly released second complete response letter further stated that, among some patients classified as responders, all target lesions had been injected with RP1, making it difficult for reviewers to determine whether efficacy was limited to local effects or extended to uninjected lesions. The document also noted that response assessment methods and determinations of disease progression may have been confounded by factors including reinjection, meaning RP1’s systemic antitumor activity has not yet been clearly characterized.
The application received complete response letters twice, in July 2025 and April 2026, meaning the FDA determined that the available data were insufficient for approval at those times. After the second setback, Replimune began a major downsizing. Related Massachusetts filings and media reports indicate that more than 200 employees were laid off, affecting its Woburn headquarters and Framingham manufacturing facility. The company subsequently resubmitted its data and said the FDA had accepted the submission as a Class 1 response, with a decision targeted by August 2.
The July 30 expert meeting will bring this scientific and regulatory debate into a public forum. The committee’s recommendation is not binding, and the FDA may still reach a different decision. Until the full meeting background documents are released, it will also be impossible for outside observers to know whether the review issues have materially changed. Whatever the outcome, the case could become an important precedent for intratumoral virus therapies: local tumor shrinkage may be striking, but approval still requires evidence that efficacy can be reliably attributed to the new therapy and that it provides patients with an interpretable overall clinical benefit.