Tumor-derived extracellular vesicles (EVs) are active contributors in
metastasis and immunosuppression in tumor microenvironment. At least some of the EVs carry
tumor surface molecules such as
tumor-associated
antigens (TAAs) and/or checkpoint inhibitors, and potentially could interact with T cells or CAR T cells. Upon contact with T cells, EVs could alter their phenotype and functions by triggering signaling through TCR or CAR reprogramming them to escape immune response. We hypothesize that EVs that possess TAA on the surface will probably interact with CAR T cells which can recognize and bind corresponding TAA. This interaction between EVs and CAR T cells may change the outcome of CAR T-based
cancer immunotherapy since it should affect CAR T cells. Also, EVs could serve as adjuvants and antigenic components of antitumor
vaccines. Herein, we isolated EVs from B cell precursor
leukemia cell line (
pre-B ALL) Nalm-6 and demonstrated that recognition and binding of CD19+EVs with CD19-CAR T cells strongly depends on the presence of
CD19 antigen. CD19+EVs induce secretion of pro-inflammatory
cytokines (IL-2 and IFN-y) and upregulated transcription of activation-related genes (IFNG, IFNGR1, FASLG,
IL2) in CD19-CAR T cells.
Tumor necrosis factor receptor superfamily (TNFRSF4 and TNFRSF9) and T-cell exhaustion markers (CTLA4, LAG3, TIM3 and PDCD1LG2) were also upregulated in CD19-CAR T cells after incubation with CD19+EVs. Long-term cultivation of CD19+ or PD-L1+EVs with CD19-CAR T cells led to increased terminal differentiation and functional exhaustion according to elevated expression of PD-1, TIGIT, CD57. In summary, our results suggest that chronic exposure of CD19-CAR T cells to CD19+EVs mediates activation and systemic exhaustion in
antigen-specific manner, and this negative effect is accompanied by the impaired cytotoxic activity in vitro.