Replimune's Oncolytic Virus Achieves 47.8% Three-Year Survival in Checkpoint-Resistant Melanoma as Company Lines Up Third FDA Submission
IGNYTE trial data show 83.5% of responders alive at three years; Replimune plans third BLA resubmission after two FDA rejections.
Overview
An engineered herpes simplex virus combined with a checkpoint inhibitor kept nearly half of patients with checkpoint-resistant advanced melanoma alive at three years — a result that Replimune’s chief medical officer called “rarely seen” in this historically treatment-resistant setting. The three-year landmark survival analysis from the IGNYTE phase 3 trial (NCT03767348) was presented in an oral session at the 2026 American Society of Clinical Oncology (ASCO) Annual Meeting on May 30, arriving one day after Replimune announced it had aligned with the FDA on a path toward a third Biologics License Application (BLA) resubmission.
What the Data Show
The IGNYTE trial enrolled 140 patients with advanced melanoma whose disease had progressed on prior anti-PD-1 therapy — a population with limited existing options once immunotherapy fails. Patients had a median age of 62 years, 67.9% were male, and 49.3% had stage IVM1b/c/d disease. Some 63.6% had BRAF wild-type status. Enrollment was stratified by tumor location: 104 patients had superficial-only lesions, 14 had deep or visceral disease combined with superficial lesions, and 22 had deep or visceral lesions only, according to CancerNetwork.
The combination of RP1 (vusolimogene oderparepvec) plus nivolumab produced a median overall survival of 32.9 months (95% CI, 25.8–46.0) across all 140 treated patients, as reported by Replimune. Annual OS rates reached 75.3% at one year, 61.5% at two years, and 47.8% at three years, per CancerNetwork.
Among patients who responded to the treatment, outcomes were strikingly better: 83.5% of responders were alive at three years, and their median OS had not been reached by the time of data cut, compared with 18.5 months for non-responders. The objective response rate was 33.6%, median duration of response was 24.8 months, and 44.8% of responders maintained their responses at three years, according to Replimune. Median progression-free survival was 3.6 months overall but reached 34.9 months among responders, per CancerNetwork.
The survival benefit held across clinically relevant subgroups, regardless of disease stage, PD-L1 expression status, prior anti-CTLA-4 therapy, or whether patients had primary or secondary anti-PD-1 resistance, according to Replimune.
The Drug and Its Mechanism
RP1, whose generic name is vusolimogene oderparepvec, is an engineered herpes simplex virus equipped with a fusogenic protein (GALV-GP R−) and GM-CSF. The design is intended to maximize tumor cell killing, enhance immunogenicity of tumor cell death, and activate a systemic anti-tumor immune response, according to Replimune. It is injected directly into tumors and combined with nivolumab, a systemic PD-1 checkpoint inhibitor.
Oncolytic viruses represent a distinct approach from standard immunotherapy: instead of simply releasing a brake on the immune system, they infect and kill cancer cells directly, releasing tumor antigens in the process and potentially generating an immune response against lesions the virus never directly reached — including deep or visceral tumors in patients who received only superficial injections.
Safety Profile
The combination demonstrated a manageable safety profile over the long-term follow-up period. Treatment-related adverse effects occurred in 88.7% of patients at any grade, with grade 3/4 events in 12.8%. The most common toxicities were chills, fatigue, and pyrexia — consistent with the flu-like profile expected from a viral-based therapy. No grade 5 events were reported and no new safety signals emerged over the observation period, per CancerNetwork.
Regulatory History and Path Forward
The IGNYTE data have accumulated against a difficult regulatory backdrop. Replimune first received a Complete Response Letter from the FDA in July 2025, with the agency finding that the phase 1/2 IGNYTE trial was an inadequate standalone investigation and citing patient population heterogeneity as preventing proper interpretation. The company resubmitted the BLA in October 2025, with the FDA assigning an April 10, 2026 PDUFA date under a Class 2 review timeline. The agency then issued a second Complete Response Letter in April 2026, again determining that the IGNYTE data were insufficient to demonstrate substantial evidence of RP1’s effectiveness, per CancerNetwork.
On May 29, 2026 — the day before the ASCO oral presentation — Replimune announced that it had reached alignment with the FDA on a path forward and planned to resubmit the BLA “in the coming days.” The FDA indicated it would treat the resubmission as an urgent matter and prioritize its review “in recognition of the significant unmet need for patients in the advanced melanoma community,” according to Replimune.
“We are grateful to the FDA leadership for their willingness to engage in a collaborative dialogue,” Replimune CEO Sushil Patel said, according to Replimune.
Significance for the Field
The IGNYTE three-year data offer a rare view of durable outcomes in a patient population that has historically fared poorly once first-line immunotherapy fails. The combination’s 47.8% three-year OS rate across all treated patients, and 83.5% among responders, stands out in a setting where options are typically limited.
“The overall survival analysis from IGNYTE shows that nearly half of all treated patients in the study were alive at three years, including 83.5% of responders to RP1 plus nivolumab. This represents a durable benefit that is rarely seen in anti-PD-1-failed melanoma, a setting with historically limited treatment options,” said Kostas Xynos, MD, PhD, MBA, Chief Medical Officer of Replimune, according to Replimune.
Presenter Michael K. Wong, MD, PhD, FRCPC, physician-in-chief at Roswell Park Comprehensive Cancer Center, summarized the findings: “RP1 plus nivolumab had a long-term clinical benefit, a consistent benefit across clinically relevant subgroups, and continues to demonstrate a favorable safety profile,” according to CancerNetwork.
What We Don’t Know
The FDA’s two prior rejections centered on the trial’s adequacy as a standalone investigation, with concerns about patient population heterogeneity — a statistical challenge when superficial-only and visceral disease patients are enrolled together. What additional data or analytical strategies Replimune will submit in its third resubmission to resolve those concerns has not been disclosed publicly. A new PDUFA date has not yet been announced as of the time of this report. The FDA’s prioritized review designation signals urgency, but the timeline for a final decision remains unclear.