Local Delivery of OncoVEXmGM-CSF Generates Systemic Antitumor Immune Responses Enhanced by Cytotoxic T-Lymphocyte-Associated Protein Blockade

Purpose: Talimogene laherparepvec, a new oncolytic immunotherapy, has been recently approved for the treatment of melanoma. Using a murine version of the virus, we characterized local and systemic antitumor immune responses driving efficacy in murine syngeneic models.Experimental Design: The activity of talimogene laherparepvec was characterized against melanoma cell lines using an in vitro viability assay. Efficacy of OncoVEX^mGM-CSF (talimogene laherparepvec with the mouse granulocyte-macrophage colony-stimulating factor transgene) alone or in combination with checkpoint blockade was characterized in A20 and CT-26 contralateral murine tumor models. CD8⁺ depletion, adoptive T-cell transfers, and Enzyme-Linked ImmunoSpot assays were used to study the mechanism of action (MOA) of systemic immune responses.Results: Treatment with OncoVEX^mGM-CSF cured all injected A20 tumors and half of contralateral tumors. Viral presence was limited to injected tumors and was not responsible for systemic efficacy. A significant increase in T cells (CD3⁺/CD8⁺) was observed in injected and contralateral tumors at 168 hours. Ex vivo analyses showed these cytotoxic T lymphocytes were tumor-specific. Increased neutrophils, monocytes, and chemokines were observed in injected tumors only. Importantly, depletion of CD8⁺ T cells abolished all systemic efficacy and significantly decreased local efficacy. In addition, immune cell transfer from OncoVEX^mGM-CSF-cured mice significantly protected from tumor challenge. Finally, combination of OncoVEX^mGM-CSF and checkpoint blockade resulted in increased tumor-specific CD8⁺ anti-AH1 T cells and systemic efficacy.Conclusions: The data support a dual MOA for OncoVEX^mGM-CSF that involves direct oncolysis of injected tumors and activation of a CD8⁺-dependent systemic response that clears injected and contralateral tumors when combined with checkpoint inhibition. Clin Cancer Res; 23(20); 6190-202. ©2017 AACR.

Abstract 4038: Developmentof a murine tumor immunophenotyping platform to support drug discovery anddevelopment in immuno-oncology

Recent clinical data highlights the importance of immune cell localization, phenotype, and gene signature as it correlates to a productive anti-tumor response. Preclinically, multiple syngeneic mouse models have been used to study the effects of immunomodulation and define anti-tumor responses to transplanted “self” tumors. However, while the literature describes distinct aspects of many of these models, there is no comprehensive dataset comparing and contrasting their tumor-immune microenvironments across models. These data are critical for better understanding the role that various immune populations play in the anti-tumor response and interpreting observed changes in tumor clearance following treatment with immunomodulatory agents. We have therefore established a platform that 1) quantitates the types of immune cells within murine tumor models, and 2) describes the location of these cells within the tumor. In parallel to the immunophenotyping efforts we have benchmarked tumor models based on their response to antibodies against T cell checkpoint pathways.

We sought to use this immunophenotyping platform to identify specific immune modulation that occurs in syngeneic tumors post depletion of macrophages via CSF1R blockade. Tumor-associated macrophages (TAMs) are believed to help promote tumor survival through suppression of the adaptive immune response and the secretion of growth factors that promote tumor growth and angiogenesis. Therefore depletion of TAMs should lead to T-cell recruitment and bolster the antitumor T-cell response. Here we show that treatment of CT-26 and RENCA syngeneic tumors with a CSF1R antagonist leads to depletion of MHCII+ and F4/80+ expressing cells. Future experiments will seek to understand if CSF1R blockade improves the response to T-cell checkpoint immunotherapies. In summary, the development of a murine tumor immunophenotyping platform has allowed insight and evaluation of immune cells in the tumor microenvironment that can ultimately be leveraged to understand the synergistic effects of immunotherapeutics.

Citation Format: Brian Belmontes, Stephanie Matyas, Sarah O’Brien, Hong Tan, Kenneth Ganley, Kimberly Merriam, Jim Rottman, Jackson Egen, Pedro Beltran, Gordon Moody. Developmentof a murine tumor immunophenotyping platform to support drug discovery anddevelopment in immuno-oncology. [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 4038.

The costimulatory molecule ICOS plays an important role in the immunopathogenesis of EAE

The inducible costimulatory molecule (ICOS) is expressed on activated T cells and participates in a variety of important immunoregulatory functions. After the induction of experimental allergic encephalomyelitis in SJL mice with proteolipid protein (PLP), brain ICOS mRNA and protein were up-regulated on infiltrating CD3+ T cells before disease onset. ICOS blockade during the efferent immune response (9-20 days after immunization) abrogated disease, but blockade during antigen priming (1-10 days after immunization) exacerbated disease. Upon culture with PLP and compared with immunized controls, splenocytes produced either decreased interferon-gamma (IFN-gamma, in efferent blockade) or excessive IFN-gamma (in priming blockade). PLP-specific immunoglobulin G1 was decreased in animals treated with anti-ICOS during antigen priming, but not in other groups.