Effect of bavituximab in combination with nivolumab on tumor immune response in a 3D ex vivo system of lung cancer patients.

e23091 Background: Bavituximab is a chimeric monoclonal antibody that targets the membrane phospholipid phosphatidylserine (PS) exposed on endothelial cells and cancer cells in solid tumors. Our previous studies showed that bavituximab enhances the activation of CD8+ TILs that correlates with increased cytokine production by lymphoid and myeloid cells in lung cancer with low PD-L1 expression suggesting that the interruption of the PD-1/PD-L1 axis by nivolumab may enhance the bavituximab effect in tumors. Methods: Fresh tumor tissues obtained from consented patients with NSCLC at the time of surgical resection were utilized in a 3D ex vivo tumor miscrosphere assay, where 3D tumor microspheres were treated with bavituximab or nivolumab alone or in combination at 10 mg/ml for 36 hours. At the end of the treatment, a multiplex human cytokine assay was used to simultaneously analyze the differential secretion of cytokines, including human IFNg, in culture media as a surrogate of TIL activation. In addition, a gene expression analysis using a NanoString platform containing probes to quantitate 770 immune function genes. Results: Preliminary results indicate the combination treatment with bavituximab and nivolumab led to increased expression of genes involved in M1 polarization of tumor associated macrophages in a subpopulation of lung tumors that closely correlated with release of cytokines such as MIP1b (CCL4) which is a chemoattractant for natural killer cells, monocytes and a variety of other cells involved in tumor immune response. Conclusions: This lung patient derived ex-vivo approach indicates that bavituximab in combination with nivolumab may enhance immune response. This response likely involves M1 polarization of tumor associated macrophages and suggests potential clinical implications in the treatment of lung cancer.