Enhancement of the efficacy of radiofrequency ablation by neoadjuvant oncolytic virus therapy via antitumor immunity and the booster effect of immune checkpoint inhibitors.

Abstract

253 Background: A third generation oncolytic herpes simplex virus type 1, G47Δ, destroys tumor cells selectively and induces antitumor immune responses. Radiofrequency ablation (RFA) is a standard local therapy for hepatocellular carcinoma (HCC). Here, we examined the efficacy of G47Δ used in combination with RFA and evaluated the antitumor immune responses. Methods: In A/J mice harboring bilateral poorly immunogenic Neuro2a subcutaneous tumors, tumors on one side were treated with intratumoral injections with G47Δ (2×106 pfu) on days 0, 2 and 4 followed by RFA treatment on day 6, which results in complete regression of the treated tumors. We further treated with an immune checkpoint inhibitor (ICI) in combination. Tumor infiltrating lymphocytes in contralateral tumors were analyzed with flow cytometric analysis. To examine the contribution of CD8+ T cells, CD8+ T cells were depleted by treatment with anti-CD8 monoclonal antibody. To mimic a remote recurrence, unilateral subcutaneous tumors were treated with G47Δ and RFA, and Neuro2a cells were implanted on the same day of RFA. In a separate experiment without rechallenge, antitumor immunity was evaluated using ELISpot assay on day 20. Results: The G47Δ+RFA treatment caused smaller volumes of contralateral tumors and increased infiltration of CD8+/CD45+ T cells within the tumor, compared with RFA or G47Δ monotherapy. Without CD8+ T cells, the antitumor effect on the contralateral tumors was completely abolished. When mice were rechallenged, those cured by G47Δ+RFA rejected the Neuro2a more frequently than those cured by RFA alone. ELISpot assay revealed that the number of Neuro2a reactive splenocytes was significantly greater in the G47Δ+RFA group than the RFA group. The G47Δ+RFA+anti-PD-L1 treatment caused smaller volumes of contralateral tumors compared with G47Δ+RFA treatment, whereas anti-PD-L1 alone showed no effect. Conclusions: Intratumoral administration of G47Δ prior to RFA would enhance systemic antitumor immunity that is further enhanced by ICI.