Effect of dendritic cells (DC) transduced with chimeric antigen receptor (CAR) on CAR T-cell cytotoxicity.

Abstract

144 Background: T cells interacting DC could be superior in T cell cytotoxicity. CD141+/Cleg9a+ intra-tumoral DC play a critical role in tumor cytotoxicity. Therefore, combining intra-tumoral DC in CAR T cell would safely increase localized CAR T cell cytotoxicity. We hypothesized that bioengineered DC compartment could be an excellent source for enhanced CAR T cell cytotoxicity. Methods: DC precursors and T cells of PBMC were transduced with a CAR (pCCL-anti-CD33-4-1BB-CD3z-T2A-GFP; CAR-DC or CAR T). For comparison, additional DC were transduced with 4-1BB cDNA (pCCL-4-1BB-T2A-GFP; 4-1BB-DC) or mock control (pCCL-eGFP). In addition to lentivirus transduction, differentiation of DC in vitro employed Flt3L/GM-CSF/IL-4. Transduced CAR T and CAR-DC were sorted by GFP expression at day 5. After further 10 days of culture, cells were harvested and analyzed for phenotype. An acute myeloid leukemia (AML) cell line (Kasumi-1) was treated with CAR T +/- CAR-DC, 4-1BB-DC, or mock control for functional assays. Results: Frequencies of cells expressing CD141+/Cleg9a+ were higher in 4-1BB-DC vs. control DC (33% vs. 1.5%). After mixing CAR T and CAR-DC (5X105) with Kasumi-1 (1X105) for 6 hours, CAR T/CAR-DC showed 100% Kasumi-1 cell cytotoxicity compared to 70% of CAR T by trypan blue. CAR T/CAR-DC also demonstrated higher Annexin V positive Kasumi-1 cells compared with CAR-T (91% vs. 52%). CAR T with or without CAR-DC were also assessed with multiplex immunoassays. CAR T cells mixed with CAR-DC induced higher level of IFN-gamma (10,316 vs. 6,186 pg/ml), IL-2 (68,840 vs. 64,708 pg/ml), and TNFalpha (1,361 vs. 905 pg/ml) (Kasumi-1 cells mixed with CAR-T cells of 10 E/T ratio) than CAR T cells. CAR-DC produced significantly higher IL-12 cytokine production (1,352 vs. 161 pg/ml) than CAR T cells in response to CD33 but independent to T cells, confirmed by comparing IL-12 production with CAR T/4-1BB-DC. Conclusions: These data show that in vitro differentiation of DC bearing 4-1BB increases CD141+/Cleg9a+ DC population and that interaction with CAR-DC to CAR T cells enhances anti-AML cytotoxicity. Our finding may implicate the development of CAR-DC therapy combined to CAR T cells to increase the efficiency of cancer immunotherapy.