Updated results from the skin cancer cohorts from an ongoing phase 1/2 multicohort study of RP1, an enhanced potency oncolytic HSV, combined with nivolumab (IGNYTE).

9553 Background: RP1 is an enhanced potency oncolytic version of HSV1 that expresses human GM-CSF and the fusogenic protein GALV-GP R-. IGNYTE is a multicohort phase 1/2 study that evaluates the safety and efficacy of RP1 in combination with nivo (NCT03767348) in a range of tumor types. Preliminary data demonstrated a durable anti-tumor activity and tolerability for RP1+nivo. Here, we present updated results from the initial and melanoma (mel) and anti-PD1 naïve non-melanoma skin cancer (NMSC) cohorts with RP1+nivo. Methods: RP1 is administered via intratumoral injection Q2W, up to 10 mL/visit, first alone at a dose of 10 6 PFU/mL and then starting with the 2 nd dose at 10 7 PFU/mL in combination with nivo (240 mg IV Q2W for 4 months (mos) then 480 mg IV Q4W up to 2 yrs) for up to 8 doses, with the option to re-initiate RP-1. Eligible patients (pts) must have at least one measurable & injectable tumor of ≥ 1 cm, ECOG 0-1, and no prior oncolytic therapy. For mel, both anti-PD1 naïve and failed pts were eligible, for NMSC pts who were anti-PD1 naïve. Results: As of data extraction on January 31, 2022, 13/36 pts with mel (36.1%) and 19/31 pts with NMSC (61.3%) had a best response of PR or CR. For mel this was 5/8 (62.5%), 6/16 (37.5%), 0/6 and 2/6 (33.3%) for pts with anti-PD1 naïve cutaneous, anti-PD1/anti-PD1+anti-CTLA-4 failed cutaneous, uveal and mucosal mel respectively. For the anti-PD1 naïve NMSC this included 11/17 (64.7%), 1/4 (25%), 3/4 (75%) and 4/6 (66.6%) patients with CSCC, BCC, MCC and angiosarcoma respectively, including 8/17 (47.1%) being CR for CSCC. Current immature median DOR was 13.27 mos (current range 3.67-16.93 mos) for mel, and 7.32 mos (current range 1.88-23.11mos) for anti-PD1 naïve NMSC. Any grade TEAE ( > 25%) in all cohorts combined were fatigue, nausea, pyrexia, chills, diarrhoea, pruritus, and influenza-like illness. TEAE ≥grade 3 ( > 5%) were disease progression and fatigue. No deaths related to RP1 was observed, with one death related to nivo (myocarditis). Biomarker data from paired biopsies indicated robust T cell infiltration and an increase in tumor inflammation gene signature post-treatment. Clinical responses observed were independent of baseline tumor PD-L1 expression status. Conclusions: RP1 in combination with nivo provides a durable anti-tumor activity in pts with skin cancers, including anti-PD1 failed and anti-PD1/anti-CTLA-4 failed mel. The combination continued to be generally well tolerated with no new safety signals identified. Based on this data, enrollment into both a registration-directed cohort of pts who have anti-PD1 failed cutaneous mel (n = 125) and a cohort of pts with anti-PD1 failed NMSC (n = 30) is ongoing. Up-to-date data from this ongoing trial will be reported at the conference. A randomized Ph2 trial of RP1+cemiplimab vs. cemiplimab alone in anti-PD1 naïve NMSC is also underway (NCT04050436). Clinical trial information: NCT03767348.