Abstract 5617: Combined intratumoral electroporation and allogeneic vaccination of Gp96-Ig/Fc-OX40L stimulates CD8 T cell cross-priming to tumor specific neoantigens and enhanced anti-tumor response
Authors: Silva Suresh de , Fromm George , Mukhopadhyay Anandaroop , Campbell Jean , Pierce Robert , Schreiber Taylor 
Published: July 2017

Abstract
Growing clinical evidence has unequivocally proven that combination approaches are leading the way in increasing the overall response rates in cancer immunotherapy (IT), compared to single agent therapies. Most cancer ITs have a higher likelihood of succeeding if the targeted tumor has a preexisting state of inflammation elicited by the combined presentation of shared- and neo-antigens from tumor cells. Certain cancers have been deemed to be non-immunogenic due to tumor intrinsic strategies that evade immune recognition. Thus, novel combination treatment modalities are needed to convert non-immunogenic, ‘cold’ tumors into inflamed ‘hot’ tumors that are amenable to IT. Gp96-Ig/Fc-OX40L is a re-engineered molecular chaperone, designed to export and deliver MHC I-associated antigens to APCs in context of the immune costimulator, OX40L. Allogeneic cancer vaccine cell lines designed to co-secrete Gp96-Ig and Fc-OX40L, generate antigen-specific CD4+/CD8+ anti-tumor responses in both highly immunogenic (CT26) and less immunogenic (B16) mouse tumors (Fromm et al., Cancer Immunol Res, 2016). Such a strategy allows for Gp96-Ig-mediated chaperoning of antigens from the allogeneic vaccine cell line (shared antigens), which could benefit further from increased presentation of tumor-derived peptides (neo-antigens) that are only accessible if Gp96-Ig/Fc-OX40L is expressed from within the tumor. To achieve this, we have employed an in vivo electroporation-based strategy (EP) to deliver Gp96-Ig/Fc-OX40L expressing DNA to tumor cells in situ. Herein we set out to test whether a combination approach of intratumoral EP of Gp96-Ig/Fc-OX40L DNA and vaccination with allogeneic cells co-secreting the same effector molecules would lead to enhanced CD4+/CD8+ T cell cross-priming to tumor neo-antigens and superior anti-tumor activity over the individual monotherapies in a non-immunogenic B16 tumor model. To assess antigen-specific CD8+ T cell expansion, mice were adoptively transferred with OT-I cells after B16-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 vaccination and primary tumor EP. The combination approach lead to a significant synergistic expansion of OT-I cells in tumors and in the peripheral blood compared to the individual monotherapies. A synergistic increase in SIINFEKL-positive CD8+ TIL cells was also observed in treated tumors, which was associated with superior anti-tumor response in both the EP-treated primary and untreated contralateral tumors. These findings suggest that a combination approach of allogeneic vaccination and in situ tumor EP of Gp96-Ig/Fc-OX40L may have significant benefit in eliciting a potent immune response in less-immunogenic tumors.
Citation Format: Suresh de Silva, George Fromm, Anandaroop Mukhopadhyay, Jean Campbell, Robert Pierce, Taylor Schreiber. Combined intratumoral electroporation and allogeneic vaccination of Gp96-Ig/Fc-OX40L stimulates CD8 T cell cross-priming to tumor specific neoantigens and enhanced anti-tumor response [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5617. doi:10.1158/1538-7445.AM2017-5617