The US FDA's Cellular, Tissue, and Gene Therapies Advisory Committee issued a briefing document ahead of a July 30 meeting to publicly deliberate on Replimune's (Nasdaq: REPL) Biologic License Application (BLA) for vusolimogene oderparepvec (RP1) in combination with nivolumab in unresectable advanced cutaneous melanoma post anti-PD-1 treatment. The meeting follows two Complete Response Letters and a pattern of resubmissions that the FDA describes as providing minimal new data. The briefing document presents a skeptical review across all three efficacy pillars it examined, and the single voting question posed to the committee — whether the IGNYTE trial results are evaluable and clinically meaningful — signals that FDA reviewers have already reached a clear preliminary view of the application.
The Massachusetts-based Replimune submitted its initial BLA in November 2024, received a first CRL in July 2025, resubmitted in October 2025, received a second CRL in April 2026, and filed again on June 2, 2026. Each resubmission has drawn the same characterization from FDA reviewers: essentially the same data package with insufficient new evidence to address the identified deficiencies.
The proposed indication covers adult patients with unresectable advanced cutaneous melanoma who experienced disease progression on a PD-1-blocking antibody-based therapy — a population with genuine unmet need. At least 50% of patients treated with frontline anti-PD-1-based therapy experience disease progression within one year, and the FDA briefing document acknowledges that treatment options with proven clinical benefit in this setting are limited.
Vusolimogene oderparepvec is a genetically modified herpes simplex virus type 1 engineered with deletions of the neurovirulence factor ICP34.5 and the antigen presentation inhibitor ICP47, and insertions encoding a fusogenic glycoprotein (GALV-GP-R-) intended to enhance viral tumor spread and human GM-CSF to activate dendritic cells and monocytes. The proposed mechanism is a combination of direct oncolytic tumor killing and systemic immune activation — the latter being central to the regulatory dispute.
The primary efficacy data derive from IGNYTE (Study RPL-001-16), a single-arm, multicenter Phase I/II study. In the 140-patient anti-PD-1 refractory cutaneous melanoma cohort, Replimune reported an ORR of 33.6% (95% CI: 25.8%–42.0%) with a median duration of response of 24.8 months. FDA's own analysis tells a different story. When responders who had all target lesions injected with RP1 — or who had no target lesions at baseline — are excluded to more closely align with RECIST v1.1 principles, the agency's primary efficacy analysis yields an ORR of 15.7% (95% CI: 10.1%–22.8%) with a median duration of response of 14.1 months. Over 53% of Replimune-reported responders lacked non-injected target lesions, meaning there was no measurable basis to assess whether any systemic antitumor activity had occurred.
FDA identifies four further sources of response assessment unreliability: 14 reported responders received study treatment after investigator-determined progressive disease, potentially inflating both ORR and duration of response; 115 invasive procedures were performed on tumor lesions among the 47 Applicant-reported responders, with at least seven complete responses appearing to have been reclassified following biopsies or resections; 13 responders had at least one non-evaluable IRC timepoint, including one patient with three consecutive missing assessments spanning more than eight months before a partial response designation; and the Independent Review Committee itself was established retrospectively via a protocol amendment after enrollment had begun, with the Applicant providing clinical data including pathology results to the reviewers.
The second major deficiency is the inability to determine whether RP1 contributes anything to the observed effect beyond nivolumab alone. IGNYTE had no concurrent control arm, and FDA communicated as early as March 2021 that the single-arm design would not isolate the contribution of each combination component. Historical control comparisons are complicated by substantial heterogeneity in the IGNYTE population: 43.6% had received prior anti-PD-1 plus anti-CTLA-4 combination therapy, 25.7% had prior anti-PD-1 only in the adjuvant setting, 40% had received more than one line of anti-PD-1 therapy, and 29.2% had Stage III disease. Published retrospective data on immune checkpoint inhibitor rechallenge show widely variable response rates that cannot serve as a reliable benchmark. FDA also cites the CERPASS trial — a randomized Phase II study of RP1 plus cemiplimab versus cemiplimab alone in advanced cutaneous squamous cell carcinoma — which did not demonstrate a statistically significant ORR improvement for the combination, providing less support for the proposed RP1-checkpoint inhibitor synergy.