What Pharma Developers Can Learn From RP1's Rejection

On April 10, 2026, Replimune Group received a complete response letter (CRL) from the FDA, blocking the approval of RP1 (vusolimogene oderparepvec) in combination with nivolumab for advanced melanoma.1 The rejection comes as RP1 was previously awarded breakthrough therapy designation. In the Ignyte trial, patients with confirmed progression on an anti-PD-1-based regimen who received RP1 plus nivolumab had a 34% response rate with a median duration of 24.8 months, alongside a favorable safety profile. The FDA's own earlier assessment claimed that preliminary evidence showed substantial improvement over available therapies, but these reflections would change under a different team within the FDA.

Replimune CEO Sushil Patel stated in a press release,1 "It is deeply disappointing that the FDA has not exercised regulatory flexibility to meet patients' needs given the data supporting strong efficacy and the favorable safety profile. Approximately 8,500 Americans with advanced melanoma die every year. The country's foremost melanoma specialists stood behind the RP1 data. Patients and caregivers pleaded for urgency. All of it was met with inconsistent communication and a fragmented and slow-moving regulatory process which clearly puts U.S. innovation at risk."

What Went Wrong in the Approval Process?

Replimune reports that during the resubmission review, an entirely new review team was appointed, one that had no prior interaction with the program.1 A senior member of the original team stated publicly that the BLA clinical team felt the applicant had provided adequate evidence to support the contribution of effect of RP1 plus nivolumab. There was reportedly a disagreement between that initial team and the leadership at the FDA. That internal disagreement, surfacing only after the rejection, reflects a dynamic that development teams rarely have visibility into during the review process itself.

The continuity problem extended to technical positions as well.1 The company stated that the new team's conclusions in the rejection letter appear to contradict positions the agency expressed at a September 2025 Type A meeting. At that earlier meeting, the agency had not raised further concerns about patient population heterogeneity in the Ignyte trial following expert testimony and had acknowledged that randomizing patients to an anti-PD-1 only arm in a confirmatory study was not feasible. The agency also suggested a descriptive analysis from the confirmatory trial, Ignyte-3, to support the contribution of components. Replimune acted on this proposal and submitted it for feedback, but no response came before the agency accepted the resubmission.

Another contentious issue arose regarding the methodology for tumor assessment.1 The company had assessed responses using RECIST 1.1 without modifications, as the agency had requested, and submitted detailed analyses showing no material difference in response rates between injected and non-injected lesions, as well as a comprehensive review of whether biopsies and surgical interventions affected tumor response.

Standard meetings, which were initiated in 2021, were conducted before the original submission to align on trial design, patient population, and the requirements for the application package.1 While the agency preferred a randomized controlled trial, March 2021 meeting minutes reflected an openness to a single-arm trial if the data were sufficiently compelling. At a subsequent pre-submission meeting, the agency stated it did not object to a biologics license application built primarily on data from 140 patients in the Ignyte trial who had progressed on prior anti-PD-1 based therapy. The company then committed to a resource-intensive global Phase III confirmatory trial as a condition of accelerated approval, an investment that now carries no return. Patel confirmed that jobs were eliminated over the rejection of RP1, as it was not a viable product without that accelerated approval.

Is This Rejection Part of a Broader Pattern?

The procedural frustrations Replimune described are not unique.2 In January 2026, Pierre Fabre Pharmaceuticals received a rejection letter for tabelecleucel, a therapy targeting a rare post-transplant disease in which patients have no approved treatment options and a life expectancy often measured in weeks to months. The company had resubmitted its application following what it described as clear alignment with the agency on resubmission criteria with the prior rejection citing a single manufacturing deficiency and raising no safety or efficacy concerns. The agency then reversed course entirely, declaring the previously accepted single-arm trial no longer adequate and requesting a new study. Pierre Fabre, stated in a press release,2 "This represents a significant and unexpected change in position, and one that is contrary to extensive dialogue with the Agency over more than five years." These two rejection letters with near-identical narratives, years of agency alignment followed by an unexplained reversal, suggest a systemic problem that individual program strategy cannot reliably anticipate or prevent.

References

1. Replimune Group, Inc. Replimune receives complete response letter from FDA for RP1 biologics license application for the treatment of advanced melanoma. Replimune Group, Inc.; April 10, 2026. https://ir.replimune.com/news-releases/news-release-details/replimune-receives-complete-response-letter-fda-rp1-biologics-0
2. Pierre Fabre Pharmaceuticals, Inc. Pierre Fabre Pharmaceuticals statement regarding receipt of complete response letter for tabelecleucel biologics license application from the U.S. Food and Drug Administration. News release. January 12, 2026. https://www.prnewswire.com/news-releases/pierre-fabre-pharmaceuticals-statement-regarding-receipt-of-complete-response-letter-for-tabelecleucel-biologics-license-application-from-the-us-food-and-drug-administration-302658114.html