CTLA4 and plasma cell myeloma: Additionally, myeloma cell line MOPC315.BM-derived EVs promoted myeloma cell escape and progression by modulating the lymphoid-like cell phenotype, in which CD4+ T cells exhibited pro-tumorigenic features, increasing the expression of immune checkpoint PD-1 and CTLA-4 while decreasing the expression of CD27, and facilitating the generation of an immunosuppressive environment (18).