CD38 and plasma cell myeloma: Daratumumab is a human IgGκ monoclonal antibody targeting CD38 with a direct on-tumor [1, 2, 3, 4] and immunomodulatory [5, 6, 7] mechanism of action, demonstrating greater cytotoxicity toward multiple myeloma (MM) cells ex vivo compared with analogs of other CD38 antibodies [8].