RP1 combined with nivolumab provided deep and durable systemic responses in patients with anti-PD-1-failed melanoma, including those with poor prognostic factors. The safety profile was favorable, with mostly grade 1/2 adverse events. (Funded by Replimune, Inc.; IGNYTE ClinicalTrials.gov, NCT03767348; EudraCT number, 2016-004548-12).