Replimune gives cancer immunotherapy a third try after FDA leadership shakeup

Replimune Resubmits RP1 BLA for Melanoma After FDA Leadership Changes

Replimune is resubmitting its biologics license application (BLA) for its melanoma therapy, RP1, in combination with Bristol Myers Squibb’s PD-1 blocker Opdivo. This marks the company's third attempt to gain approval for advanced melanoma patients who have progressed after prior PD-1 treatment, following two previous rejections in July 2025 and April 2026. The resubmission comes amid significant changes in FDA leadership, including the departures of former Commissioner Marty Makary and CBER director Vinay Prasad, who were in their posts during the prior denials. The FDA has indicated it will treat Replimune’s resubmission as an "urgent matter" and prioritize its review.

• Replimune is making a third attempt to gain FDA approval for its melanoma therapy, RP1, following two prior rejections in July 2025 and April 2026. This resubmission is strategically timed after a series of high-level departures at the FDA, including former Commissioner Marty Makary and CBER director Vinay Prasad, who were associated with the previous denials. The company's CEO cited "collaborative dialogue" with the FDA as a factor in finding a path forward.
• The biologics license application (BLA) for RP1 is for advanced melanoma patients who have experienced disease progression after prior PD-1 treatment. RP1 is proposed for use in combination with Bristol Myers Squibb’s PD-1 blocker, Opdivo. This specific patient population and combination therapy define the target market and treatment approach Replimune is pursuing for its oncolytic immunotherapy.
• The FDA has committed to treating Replimune’s resubmission as an "urgent matter" and prioritizing its review, signaling a potentially more favorable environment. The previous rejections, which led to complete response letters, occurred in July 2025 and April 2026. The first rejection was reportedly influenced by former FDA oncology leader Richard Pazdur, while the second occurred under Prasad and Makary's leadership.

Safety and Tolerability of RP1 + Opdivo in Advanced Melanoma

The combination of RP1 (vusolimogene oderparepvec) and nivolumab demonstrated a favorable safety profile in a 2025 study of 140 patients with anti-PD-1-failed advanced melanoma. Treatment-related adverse events were predominantly mild to moderate, with 77.1% of patients experiencing grade 1/2 events, while only 9.3% had grade 3 events and 3.6% had grade 4 events. Notably, no grade 5 (fatal) treatment-related adverse events were observed in this patient population.

The study enrolled patients with particularly challenging disease characteristics, including 48.6% with stage IVM1b/c/d disease, 65.7% with primary anti-PD-1 resistance, 56.4% who were PD-L1 negative, and 46.4% who had received prior anti-PD-1 and anti-CTLA-4 therapy. Despite these poor prognostic factors, the safety profile remained manageable with the intratumoral administration of RP1 (≤8 doses, ≤10 mL/dose with additional doses allowed) combined with up to 2 years of nivolumab treatment.

The tolerability data supported the therapeutic benefit observed in this heavily pretreated population, with the combination achieving a confirmed objective response rate of 32.9% and a median duration of response of 33.7 months. The safety profile enabled delivery of deep and durable systemic responses in patients who had failed prior anti-PD-1 therapy, suggesting that the combination's risk-benefit profile supports its use in this challenging clinical setting.

Addressing Unmet Needs in Advanced Melanoma After PD-1 Progression

Despite significant therapeutic advances in advanced melanoma, substantial challenges persist that limit optimal patient outcomes. Treatment resistance remains a major hurdle, with most patients eventually developing progressive disease despite targeted therapies and immune checkpoint inhibitors. The complex interplay of resistance mechanisms, heterogeneous treatment responses, and significant toxicities continues to create barriers to achieving durable clinical benefit.

• Treatment resistance and limited durability — Most patients develop progressive disease despite targeted therapies and immune checkpoint inhibitors, with current targeted therapies suffering from limited efficacy due to reactivation of MAPK, PI3K-AKT, and Hippo pathways

• Suboptimal response rates and survival outcomes — PD-1/PD-L1 and CTLA-4 inhibitors demonstrate low response rates in many patients, and treatment options have historically been constrained by modest response rates and failure to consistently improve overall survival

• Treatment-related toxicities and tolerability concerns — Immune-related adverse events and specific toxicities associated with newer agents like ipilimumab, vemurafenib, dabrafenib, and trametinib present management challenges, though most are mild to moderate in severity

• Drug delivery and pharmacokinetic limitations — Conventional therapies suffer from poor anti-cancer efficacy due to premature drug degradation, severe adverse effects from systemic exposure, and insufficient drug concentration at tumor sites

• Diagnostic and biomarker challenges — Current melanoma diagnosis involves painful sampling techniques, limited imaging capabilities, and insufficient understanding of genetic markers, leading to potential misdiagnosis, delayed diagnosis, and lack of reliable predictive biomarkers for treatment selection

• Limited efficacy in metastatic disease — Advanced melanoma patients face poor prognosis with limited benefit from surgical resection and conventional therapies due to widespread metastasis, while novel approaches like CAR-T cell therapy show less success compared to hematologic malignancies

• Healthcare system limitations — Current melanoma care faces challenges including late diagnosis and staging, false positives, lack of standardization in treatment approaches, high treatment costs, and persistent issues with disease recurrence

The Competitive Landscape for Advanced Melanoma Post-PD-1

Several oncolytic viruses are being investigated in combination with checkpoint inhibitors for advanced melanoma and other malignancies, utilizing similar mechanisms of action to RP1 and Opdivo. The most clinically advanced is talimogene laherparepvec (T-VEC), which has demonstrated promising efficacy in combination studies with both ipilimumab and pembrolizumab.

Oncolytic Immunotherapy's Next Frontier: RP1 in Refractory Melanoma

The journey of oncolytic viruses in cancer therapy has been one of persistent innovation, and Replimune's latest resubmission for RP1 in combination with Opdivo marks a pivotal moment. For patients battling advanced melanoma who have progressed after initial PD-1 blockade, treatment options are severely limited, representing a critical unmet need. The clinical data from the IGNYTE study for RP1 plus nivolumab offers a beacon of hope, demonstrating a confirmed objective response rate of nearly 33% and a remarkable median duration of response exceeding 33 months. These are not just numbers; they represent meaningful, durable systemic responses, even in patients with challenging prognostic factors like primary anti-PD-1 resistance or prior anti-CTLA-4 exposure. The ability of RP1, an HSV-1-based oncolytic immunotherapy, to induce broad immune activation, including increased CD8+ T-cell infiltration and PD-L1 expression, suggests it can effectively 're-sensitize' tumors to checkpoint inhibition, turning immunologically 'cold' tumors 'hot.'

However, this is Replimune's third attempt at approval, following two previous rejections. This history underscores the rigorous scrutiny applied to novel therapies, particularly in a disease area where the treatment paradigm has already been revolutionized by multiple immunotherapies. While the FDA's designation of the resubmission as an 'urgent matter' and recent leadership changes might signal a more favorable environment, the bar for approval remains high. The competitive landscape of advanced melanoma is fierce, with numerous approved and investigational agents. RP1's success will hinge on its ability to consistently deliver durable benefits in this difficult-to-treat, refractory population, differentiating itself from existing and emerging therapies. Ultimately, a positive outcome would not only provide a much-needed lifeline for patients but also solidify the role of oncolytic viruses as a powerful, synergistic component in the evolving arsenal of cancer immunotherapies.