Abstract 258: Talilmogene laherparepvec increases the anti-tumor efficacy of the anti-PD-1 immune checkpoint blockade

Talimogene laherparepvec is an investigational oncolytic immunotherapy based on a modified herpes simplex virus type-1 (HSV-1) designed to selectively replicate in tumors and to initiate a systemic immune response to target cancer cells that have metastasized. Intralesional administration of talimogene laherparepvec is intended to result in oncolysis within injected tumors. Iterative viral replication of virus within permissive tumor tissue results in lytic cell destruction and local release of progeny virus and tumor derived antigens. GM-CSF, a product of the viral transgene, is also produced locally such that it can recruit and stimulate antigen presenting cells which, in addition to relevant tumor-derived antigens, are required for the initiation of a systemic antitumor immune response. Recently, in a retrospective analysis of a Phase III melanoma trial investigators found that about two-thirds of the lesions injected with talimogene laherparepvec shrank 50% or more. And the same effect was seen in about a third of all uninjected tumors in the skin and lymph nodes and about a sixth of uninjected visceral lesions providing an indication that the treatment is triggering the desired immune system effect. Ongoing clinical trials are investigating T-VEC in combination with the immune checkpoint inhibiting antibodies ipilimumab and pembrolizumab in advanced melanoma. We sought to determine if the combination of intratumoral injection of talimogene laherparepvec and the systemic delivery of the checkpoint anti-PD1 antibody could increase the anti-tumor efficacy in a preclinical syngeneic contralateral tumor model. Using established MC-38 colon carcinoma tumors in C57Bl/6 mice, we delivered three intratumoral injections three days apart of the talimogene laherparepvec surrogate OncoVEXmuGM-CSF and twice weekly systemic injections of an antagonistic anti-PD-1 antibody. Either OncoVEXmuGM-CSF or anti-PD-1 alone induced modest tumor growth inhibition/tumor regressions of contralateral tumors. In combination, the OncoVEXmuGM-CSF injected tumor displayed 8/10 complete regressions and the distant tumors had 2/10 complete regressions. Peripheral blood was analyzed at 4 days and 10 days post the initial OncoVEXmuGM-CSF and anti-PD-1 antibody injections. OncoVEXmuGM-CSF increased the percent of PD-L1+ CD4 and CD8 T cells and the combination increased the percent of activated CD8+ T cells. Our findings demonstrate that localized therapy with talimogene laherparepvec augments the systemic anti-tumor immune response seen with anti-PD-1 therapy, providing a strong rationale for continued investigation of such combinations in the clinic. Citation Format: Julia Piasecki, Tiep le, Rafael Ponce, Courtney Beers. Talilmogene laherparepvec increases the anti-tumor efficacy of the anti-PD-1 immune checkpoint blockade. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 258. doi:10.1158/1538-7445.AM2015-258