SillaJen, Inc. has submitted CSR to the US FDA on 6 February 2024 for REN026, a phase 1b/2a dose escalation and safety/efficacy evaluation study of Pexa-Vec in combination with cemiplimab in patients with metastatic or unresectable renal cell carcinoma (RCC). The study demonstrated an acceptable safety profile and encouraging efficacy of the combination therapy of Pexa-VEC, an engineered oncolytic vaccinia virus, and Libtayo (cemiplimab), anti-PD-1 monoclonal antibody developed by Regeneron Pharmaceuticals Inc. In 2017, SillaJen began a collaboration agreement with Regeneron for the clinical study of Pexa-Vec in combination with cemiplimab in patients with RCC. Following the U.S. FDA IND approval in November 2017, SillaJen initiated the trial and 95 patients were enrolled from total of 21 clinical sites in the U.S., South Korea, and Australia.

The study ended in February 2023. The study was conducted in four study arms (A to D) to assess the safety and efficacy of the Pexa-Vec in combination with cemiplimab. In Arm C, consisting of patients naïve to Immune checkpoint inhibitors (ICIs), Pexa-Vec in combination with cemiplimab showed the overall response rate (ORR) of 23.3% and the median overall survival (OS) of 25.13 months.

Both ORR and OS were the highest compared to other study arms. In Arm D, patients with prior ICI treatment demonstrated ORR of 17.9 %, the second highest of the four arms. In particular, Arm D included 22 out of 28 patients (78.57%) with the three or more prior systemic regimens in metastatic setting and 5 patients (17.86%) with two prior treatments. Given the typically lower response rates in patients with more prior extensive treatments, the results are considered highly encouraging.