Abstract 567: In vivo intra-tumoral electroporation of Gp96-Ig/Fc-OX40L stimulates CD8+ T cell cross-priming to tumor specific neoantigens
Authors: de Silva Suresh , Fromm George , Haque Jamil , Campbell Jean S. , Pierce Robert H. , Schreiber Taylor H. 
Published: July 2016

Abstract
Cancer immunotherapy relies on presentation of shared- and neo- antigens from a patient's tumor cells for recognition and clearance by the immune system. However, the tumor microenvironment deploys multiple strategies to evade immune recognition and often remains non-immunogenic, which is one of the challenges that need to be addressed when designing new therapies. Among the strategies to increase a tumor's immunogenicity is their genetic manipulation in situ via expression of molecular chaperones, T cell costimulators and/or pro-inflammatory genes using DNA/RNA vectors packaged in oncolytic viruses, lipid based components or through electroporation. In vivo electroporation-mediated gene transfer of IL-12 triggers tumor regression and systemic anti-tumor immune responses in experimental mouse models and in patients, demonstrating the feasibility of this intratumoral (IT) gene-transfer technology. We set out to test whether intratumoral electroporation of Gp96-Ig/Fc-OX40L, a re-engineered molecular chaperone, designed to export and deliver MHC I-associated antigens to APCs in context of OX40L expression, would generate a robust anti-neoantigen CD8+ T cell response. Gp96-Ig/Fc-OX40L is a re-engineered molecular chaperone, designed to export and deliver MHC I-associated antigens to APCs in context of OX40L expression. To assess antigen-specific CD8+ expansion, mice were adoptively transferred with OT-I cells after B16.F10-ovalbumin cells were injected to generate primary and contralateral melanotic tumors. Contralateral tumors were monitored to assess whether a systemic CD8+ T cell response could be elicited following primary tumor electroporation. IT electroporation of DNA expressing Gp96-Ig/Fc-OX40L in the primary tumor triggered a significant expansion of antigen-specific OT-I cells, which was absent in control mice. Remarkably, increases in antigen-specific OT-I cells correlated with regression of both the treated primary and untreated contralateral tumors. We further validated our findings in a CT26 mouse colorectal cancer tumor model, in which the expression of Gp96-Ig/Fc-OX40L from electroporated DNA stimulated an expansion of antigen-specific CD8+ T cells and again led to regression of both the treated primary and untreated contralateral tumor. Our findings demonstrate that in situ manipulation of intratumoral cells to express Gp96-Ig/Fc-OX40L stimulates potent antigen-specific cross priming to tumor specific neoantigens that culminates in robust systemic anti-tumor response. These findings provide exciting proof-of-principal and warrant further investigation into the direct delivery of molecular chaperones such as Gp96-Ig/Fc-OX40L and/or pro-inflammatory molecules for elevating the immunogenicity of tumors for a potent anti-tumor CD8+ T cell response.
Citation Format: Suresh de Silva, George Fromm, Jamil Haque, Jean S. Campbell, Robert H. Pierce, Taylor H. Schreiber. In vivo intra-tumoral electroporation of Gp96-Ig/Fc-OX40L stimulates CD8+ T cell cross-priming to tumor specific neoantigens. [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 567.