After two rejections, Replimune (Nasdaq:REPL) is back at the FDA’s door with RP1 and this time, the data and a mobilized patient community may finally tip the scales. In late July, the agency’s Oncologic Drugs Advisory Committee (ODAC) will weigh vusolimogene oderparepvec, Replimune’s oncolytic immunotherapy, in combination with nivolumab for advanced melanoma that has progressed on anti-PD-1 therapy. A decision is due by August 2, 2026. Third FDA reviews are rare; third reviews that reach a public advisory vote are rarer still. That the agency moved quickly to reconsider a program it twice declined and chose to adjudicate it in the open signals that the central question is genuinely unsettled, and genuinely worth settling.
Two letters, one unresolved question
Replimune’s regulatory road has been unusually rough. Both prior rejections turned on the same scientific pivot: whether a single-arm trial can show that RP1 adds benefit on top of nivolumab what regulators call “contribution of effect.”
- July 2025 (first CRL): The FDA judged the Phase 1/2 IGNYTE trial not adequate and well-controlled, citing heterogeneity in the patient population and unresolved questions about the confirmatory trial’s design. Notably, no safety issues were raised.
- April 2026 (second CRL): The agency again found the evidence insufficient to establish effectiveness. Replimune disclosed that a new review team had replaced the original reviewers and declined to meet during the cycle; a former senior reviewer publicly noted that the clinical team had considered the contribution-of-effect data adequate before leadership overruled them.
The second letter landed hard. Replimune announced layoffs and a pullback of U.S. manufacturing, warning that without timely accelerated approval the program was not viable. CEO Sushil Patel said a treatment patients urgently needed would not reach them
Not because the medicine failed. Because the system did
Sushil Patel/LinkedIn
Then, after what the company described as productive discussions, the FDA reversed course and accepted a third resubmission in June, this time promising an advisory committee and an expedited clock.
What the IGNYTE data actually show
The clinical rationale is why this program refuses to fade. Roughly half of advanced-melanoma patients never respond to, or eventually progress on, checkpoint blockade and once anti-PD-1 therapy fails, options thin out fast. RP1 is engineered to attack that gap on two fronts: a modified herpes simplex virus, armed with a fusogenic glycoprotein and GM-CSF, that lyses tumor cells directly while priming a systemic anti-tumor immune response.
In the registration-directed IGNYTE cohort (n=140) of post-PD-1 patients, updated results presented at ASCO 2026 showed:
- Objective response rate: 33.6%, including complete responses in roughly 15% of patients
- Median duration of response: 24.8 months
- Median overall survival: 32.9 months; 3-year OS of 47.8% overall and 83.5% among responders
- Durability: 44.8% of responders remained in response at three years; median PFS of 30.6 months in responders versus 4.4 months on their prior PD-1 regimen
- Safety: no new signals; tolerability consistent across the program
Responses this deep and durable, in a setting with few alternatives, are hard to dismiss. The honest caveat is the one the FDA keeps pressing: a single-arm study cannot cleanly separate RP1’s contribution from nivolumab’s. That is a legitimate scientific question not a verdict on the drug.
A community that wants the option
Something else has shifted: the melanoma community has made itself heard. After the FDA’s second rejection, Sam Guild, president of AIM at Melanoma, said
This is not the outcome the melanoma community had hoped for
Sam Guild/AIM at Melanoma
while emphasizing that progress in cancer research is rarely linear. AIM reported receiving messages from hundreds of patients and families, many of whom said they had been waiting for RP1 because they were running out of treatment options.
That concern soon became a coordinated advocacy campaign. AIM at Melanoma, the Melanoma Research Alliance, the Melanoma Research Foundation and other patient organizations jointly asked the FDA to reconsider its decision and consider making RP1 available while the remaining regulatory questions were addressed.
The FDA subsequently responded to the coalition’s letter and acknowledged the patient and caregiver accounts submitted with it. Reflecting on that response, the Melanoma Research Alliance said it affirmed that “the voices of patients, families, advocates, researchers, and clinicians are being heard,” and reiterated its commitment to expanding treatment options for people with advanced melanoma.
When the FDA accepted the latest resubmission, the Melanoma Research Foundation said the accelerated reconsideration “underscores immense hope” for patients with anti-PD-1-refractory metastatic melanoma who have not benefited from other approved treatments or clinical trials.
In announcing the third acceptance, Replimune credited support from the broader melanoma community. That support now extends well beyond the company and its investigators. It includes independent patient organizations arguing that people who have exhausted available options should have access to a generally well-tolerated therapy associated with durable responses while definitive evidence is generated.
That evidence is already being pursued in the global, randomized Phase 3 IGNYTE-3 trial, which is enrolling roughly 400 patients and is intended to provide the controlled data needed to resolve RP1’s contribution of effect. The accelerated-approval pathway was built for precisely this kind of trade-off: earlier access in a serious disease with substantial unmet need, paired with a binding obligation to confirm the benefit.
What a third CRL would mean
A third rejection is a real possibility, and its weight would extend beyond one company. For patients, it would likely foreclose perhaps for good a therapy that has produced multi-year remissions in a lethal disease. For Replimune, management has said the program’s viability hinges on this decision. And for the field, it would sharpen a hard, unresolved debate: how should regulators evaluate oncolytic and combination immunotherapies when randomized data aren’t yet mature, and where should the bar for “contribution of effect” sit? However ODAC votes, that conversation will shape how the next generation of these therapies is designed and reviewed. A “no” would be a loss but also a lesson the field cannot get by avoiding.
Why late July matters
The most persuasive case for RP1 isn’t a stock chart or a press release; it’s a cohort of patients still alive and in response years after exhausting standard options. That is the evidence ODAC will actually weigh, alongside the FDA’s fair question about proof. Both deserve a serious hearing. If the panel and the agency conclude the benefit is real and the confirmatory plan is sound, RP1 could become a meaningful new option in post-PD-1 melanoma and a template for how oncolytic immunotherapy earns its place.
Watch this space. Follow the ODAC discussion in late July and the FDA’s decision by August 2. Whichever way it lands, it will shape post-PD-1 melanoma care and the regulatory playbook for oncolytic immunotherapy for years to come.
Read more biotech insights on OncoDaily Biotech.
Written by: Semiramida Nina Markosyan, Editor, OncoDaily Canada