CTLA4 and neoplasm: Studies have found that exosomes derived from tumors carry immunosuppressive proteins, including PD-1, CTLA-4, FasL, TRAIL, CD39, and CD73, which induce apoptosis and depletion of T lymphocytes to achieve tumor immune escape (Whiteside, 2013; Ukrainskaya et al., 2019; Benecke et al., 2021).