Abstract 3680: Cancer-killing viruses combined with tumor-targeting immune checkpoint modulation elicits anin situvaccination effect and expansion of tumor-specific T cells responsible for efficacious systemic anti-cancer activity

Oncolytic viruses are cancer-selective and disrupt immunosuppression within the tumor, but they show suboptimal efficacy in patients. Immune checkpoint modulation is efficacious in a variety of cancers but is associated with nonspecific T-cell activation and a limited effect in tumors with a nonimmunogenic microenvironment. We hypothesized that combining these two strategies likely resulted in both efficacious and specific cancer therapy. Therefore, we constructed oncolytic adenovirus Delta-24-RGDOX expressing the immune co-stimulator OX40L and tested its activity in orthotopic GL261-C57BL/6 glioma and B16-C57BL/6 melanoma mouse models. Compared to its predecessor Delta-24-RGD, Delta-24-RGDOX was more effective to induce inflammatory activation within the tumors, enhanced the capability of the tumor cells to directly activate cancer-specific T cells and the proliferation of the cell population through OX40L expression on the cell surface, resulting in specific anti-tumor immunity. To track the expansion and migration of tumor-specific T cells during virotherapy, we first injected OVA-specific CD8+ T cells from OT-I/Luc transgenic mice in the first tumor derived from B16-OVA cells, followed by Delta-24-RGDOX injection in the same tumor. Monitoring the T cells with bioluminescent imaging revealed that the viral injection greatly augmented the T cell population than the PBS treatment within the tumor, and promoted the T cell migration to distant B16-OVA tumor but not to B16 tumor, suggesting local viral treatment enhanced the expansion of tumor-specific T cells and the migration of these cells to a distant tumor with the same tumor antigen. Consistently, flow cytometry analysis with OVA-tetramer staining showed that virus treatment greatly increased the frequency of OVA-specific CD8+ T cells in the local and distant tumors, peripheral blood and spleen (from high to low frequency). 70-80% cells of this cell population were CD44+ CD62L+ that are markers for central memory T cells. Hence, this new virus was efficacious to inhibit the virus-injected tumor and distant tumor, prolong the survival of the treated mice and induce immune memory specific to the virus-injected tumor type. Importantly, intratumoral injection of Delta-24-RGDOX and an anti-PD-L1 antibody synergized to reject gliomas and significantly increased survival in mice. Our data demonstrate that combining an oncolytic virus with tumor-targeting immune checkpoint modulation elicits potent in situ cancer vaccination and skews the injected tumor microenvironment from tumorigenic to immunogenic, resulting in a local expansion of the tumor-specific T cells. Moreover, this local effect is capable to extend to distant tumors, achieving specific and long-lasting systemic therapeutic efficacy. Citation Format: Hong Jiang, Andrew Dong, Yisel Rivera-Molina, Karen Clise-Dwyer, Xuejun Fan, Francisco W. Martinez, Teresa Nguyen, Verlene Henry, Caroline Carrillo, Candelaria Gomez-Manzano, Juan Fueyo. Cancer-killing viruses combined with tumor-targeting immune checkpoint modulation elicits an in situ vaccination effect and expansion of tumor-specific T cells responsible for efficacious systemic anti-cancer activity [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 3680. doi:10.1158/1538-7445.AM2017-3680