Potent Synergy between Combination of Chimeric Antigen Receptor (CAR) Therapy Targeting CD19 in Conjunction with Dendritic Cell (DC)/Tumor Fusion Vaccine in Hematological Malignancies.

Introduction CAR T cells have demonstrated unique potency for tumor cytoreduction and durable response in hematological malignancies. However, disease relapse remains a concern due to the emergence of antigen negative variants, tolerization of CAR T cell populations and lack of T cell persistence. We postulated that vaccination with a personalized cancer vaccine, that we developed, in which patient derived tumor cells are fused with autologous dendritic cells would enhance CAR T cell efficacy through the expansion of T cell clonal populations and the vaccine mediated enhancement of T cell activation and persistence. In the present study, we examined the potential synergy between CAR T cells targeting CD19 and syngeneic DC/tumor fusions. Methods/Results CD19 CAR T cells and DC/tumor fusions were studied in the context of a murine A20 lymphoma model, and their combination effectively lysed A20 cells in a CTL assay in a higher percentage than CAR T cells alone (20% vs 34%). Moreover, we examined the interaction of vaccine and CAR T cells ex vivo using the IncuCyte S3 Live-Cell Analysis System which allows for live cell visualization of lysis of A20 cells over time. We studied the impact of combining vaccine educated and CAR T cells as well as an individual T cell population that underwent sequential vaccine mediated stimulation followed by transduction with the CD19 CAR. Even in this assay, coculture with either combined vaccine educated and CAR T cells or sequentially vaccine educated, and transduced T cells demonstrated the highest levels of cytotoxicity that was maintained over time. Enhanced lysis by combined vaccine stimulation and CAR T cells was similarly demonstrated in another tumor cell line, 5TGM1, a multiple myeloma cell line transduced to express CD19. On the contrary wild type 5TGM1 cells were recognized by the DC/tumor fusion stimulated cells in contrast to CAR T cells alone (40% vs. 8%). Finally, we examined the capacity of vaccine educated T cells in conjunction with CAR T cells to target A20 cells in an immunocompetent murine model. Mice were challenged with 1 × 106 A20 Mcherry-Luc and after lymphoma engraftment animals were treated with 3 × 106 T cells consisting of CAR T cells, vaccine educated T cells or the combination. Serial bioluminescence imaging demonstrated greatest reduction in tumor burden using combined CAR T and vaccine educated T cells with 4/5 animals still disease free at day 13 after tumor challenge. Conclusions Combined therapy with T cells stimulated by DC/tumor fusions and CAR T cells exhibited potent lysis of murine lymphoma and myeloma cells compared to CAR T cells or vaccine educated T cells alone in in vitro and immunocompetent murine models. These findings suggest potent synergy between these modalities that may overcome recognized pathways of resistance including the broadening of the tumor specific response and vaccine mediated activation of CAR T cell populations.