Abstract 2346: Intratumoral administration of OncoVEXmGM-CSFresults in local innate immune alterations and induces systemic anti-tumor effects in syngeneic mouse tumor models

Talimogene laherparepvec, is a modified oncolytic herpes simplex virus type-1 (HSV-1) designed to selectively replicate in tumors and to initiate a systemic immune response to target cancer cells. Intralesional administration of talimogene laherparepvec is intended to result in oncolysis within injected tumors, with lytic cell destruction promoting the local release of progeny virus and tumor derived antigens. GM-CSF, a product of the viral transgene, is also produced locally and is designed to recruit and stimulate antigen presenting cells to further enhance systemic antitumor immune response. While available evidence suggests that talimogene laherparepvec can induce effects in distant tumors via an immune-mediated effect, additional mechanistic evidence is being sought to help better understand the putative systemic effect. For preclinical mechanism of action studies we employed OncoVEX mGM-CSF , an HSV-1 virus modified in the same manner as talimogene laherparepvec except that murine GM-CSF is expressed. We utilized this virus to further dissect the underlying innate and adaptive immunity following viral administration in syngeneic tumor models. Intratumoral administration of OncoVEX mGM-CSF into established murine tumors induced regressions in the injected lesion but also resulted in significant anti-tumor effects in contralateral (uninjected) lesions. We have previously demonstrated by immunohistochemistry that the systemic effects observed in the contralateral lesions are not driven by systemic spread of the virus, but instead correlate with the infiltration of CD3+ T cell populations. Here we report the full phenotypic characterization of immune infiltrates by flow cytometry in both the injected and contralateral lesions. In a time-course fashion, this characterization revealed the initial infiltration of the injected tumor by innate effector cells and a concomitant induction of a potent type I interferon response. This in turn drives the local release of proinflammatory cytokines and chemokines, resulting in the recruitment of adaptive immune subsets to the injected tumor and enhancing systemic anti-tumor reactivity. Additionally, both the primary oncolytic replication of the virus and the activation of type I interferon pathway are directly correlated with STING activity. In conclusion, in vitro and in vivo observations suggest that intratumoral injection of OncoVEX mGM-CSF activates multiple immune-mediated mechanisms of action leading to T-cell activation and induction of anti-tumor immunity in mice. Citation Format: Keegan Cooke, Karen Fitzgerald, Becky Yang, Juan Estrada, Brian Belmontes, Pedro Beltran, Achim K. Moesta. Intratumoral administration of OncoVEX mGM-CSF results in local innate immune alterations and induces systemic anti-tumor effects in syngeneic mouse tumor models. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2346.