Studies have found that exosomes derived from CAR-T cells display the functions of reducing the toxicity induced by CAR-T cells and can cross the blood-brain barrier and blood-tumor barrier [63], as well as loss of programmed cell death 1 (PD1) protein, which means that recombinant PD-L1 treatment fails to weaken the antitumor effect [64]. This evidence concerns the gene PDCD1 and neoplasm.