Background: Patients (pts) with melanoma who progress on anti–PD-1 therapy (anti–PD-1–failed) have limited treatment options. RP1 is an HSV-1–based oncolytic immunotherapy expressing human GM-CSF and a fusogenic protein (GALV-GP-R−). Here, we present data from the first 75 pts enrolled into the registration-directed (R-D) cohort in anti–PD-1–failed melanoma (target enrollment N = 125) from the phase 1/2 IGNYTE study (NCT03767348). Methods: Pts must have locally advanced or metastatic cutaneous melanoma with ≥1 measurable and injectable tumor (≥1 cm) and confirmed progressive disease (PD) on 2 assessments ≥28 days apart while on ≥8 consecutive weeks of anti–PD-1 ± anti–CTLA-4 therapy, with anti–PD-1 being the last treatment received. Pts on prior adjuvant anti–PD-1 therapy must have had PD confirmed by biopsy while on adjuvant therapy. RP1 is initially given intratumorally at 10⁶ PFU/mL and then every 2 weeks (Q2W) at 10⁷ PFU/mL for ≤8 total cycles (≤10 mL/dose) combined with nivolumab (nivo; cycles 2–8, 240 mg IV); pts then receive nivo alone (240 mg Q2W or 480 mg Q4W IV) for ≤2 years, with the option to reinitiate RP1 if specified criteria are met. Results: A total of 91 pts are included in this analysis (initial melanoma cohort, 16 pts; R-D cohort, 75 pts; data cut: Dec 30, 2022). The overall objective response rate (ORR) was 37.4% (initial cohort, 37.5%; R-D cohort, 37.3%) and 18.7% of pts achieved complete response (CR; Table). The response rates seen were also encouraging when evaluated by prior anti–PD-1 therapy setting and disease stage (Table). Responses were seen in uninjected lesions in most responding patients, including in pts with bulky and visceral disease. The majority of responses were observed in pts with PD-L1–negative tumors at baseline (17 of 52 pts with PD-L1–negative tumors responded, compared to 15 of 26 pts with PD-L1–positive tumors, and 2 of 13 pts for whom PD-L1 status was unknown). 85.3% of responses were ongoing 3.7–36.6 months from initiating therapy. Most treatment-related adverse events (TRAEs) were Grade 1–2 with the most common (>20%) being fatigue, chills, pyrexia, and nausea. Conclusions: The initial data from this expanded cohort show that RP1 + nivo provides durable and clinically meaningful antitumor activity in pts with anti–PD-1–failed melanoma. Responses were observed in both injected and uninjected lesions, including visceral lesions. The combination continues to be well tolerated, with mostly on-target TRAEs. Additional and updated data will be presented. Clinical trial information: NCT03767348.

^aInvestigator-assessed responses.