Abstract 274: Bavituximab modulates tumor microenvironment and activates CD8+ tumor infiltrating lymphocytes in a patient-derived 3D ex vivo system of lung cancer

Abstract

Abstract Bavituximab is a monoclonal antibody directed against the membrane phospholipid phosphatidylserine exposed on the outer leaflet of tumor and vascular endothelial cells of the tumor microenvironment. Bavituximab modulates the tumor microenvironment by blocking PS-mediated immune suppression and activating cytotoxic T lymphocyte anti-tumor responses. In this study, we tested the immunomodulatory effect of bavituximab using a proprietary 3D ex vivo tumor microsphere technology. Upon obtaining informed consent, fresh tumor tissue from lung cancer patients were collected at the time of surgical resection. Tissue was processed for characterization of the tumor microenvironment and potential immunosuppressive mechanisms such as expression of PD-1, CTLA4, LAG3, TIM3, BTLA, and Adenosine A2AR. 3D tumor microspheres were prepared and cells were treated ex vivo with f(ab)’2 version of bavituximab, bavituximab, docetaxel, and a combination of bavituximab and docetaxel for 36 hours within the 3D tumor microsphere simulating an intact tumor microenvironment made up of tumor infiltrating lymphocytes (TIL) and myeloid cells. At the end of the treatment, TILs were analyzed by flow cytometry for cell activation and changes in CD4, CD8 and Treg (CD25+/CD127-) subpopulations. A multiplex human cytokine assay was used to simultaneously analyze the differential secretion of cytokines, including human IFN-gamma in culture media as a surrogate of TIL activation. Preliminary results indicate the combination of bavituximab and docetaxel can induce TIL activation as demonstrated by a significant increase in IFN-gamma secretion when compared to tumors treated with control or either agent alone. Flow cytometry analysis revealed that this effect was associated with low PD-1 expression on CD8 cells, but did not correlate with other known immune-modulating receptors. This lung patient derived ex-vivo approach indicates that bavituximab in combination with docetaxel can elicit a tumor specific immune response in human adenocarcinoma of the lung. This effect involves, at least in part, activation of CD8+ TIL and increased inflammatory cytokine production by lymphoid and myeloid cells. In addition, we have observed low PD1 expression as a potential prognostic biomarker of positive response to bavituximab treatment. Citation Format: Soner Altiok, Melanie Mediavilla-Valera, Jenny Kreahling, David Noyes, Tiffany N. Razabdouski, Nikoletta L. Kallinteris, Joseph Shan, Scott Antonia. Bavituximab modulates tumor microenvironment and activates CD8+ tumor infiltrating lymphocytes in a patient-derived 3D ex vivo system of lung cancer. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 274. doi:10.1158/1538-7445.AM2015-274