CD38 and plasma cell myeloma: The reasons for low levels of CD38 expression by myeloma cells during treatment with daratumumab may be antibody-mediated “capping” of the daratumumab–CD38 complex on the plasma membrane followed by exocytosis or endocytosis and degradation of the antigen–antibody complex or due to rapid elimination of myeloma cells expressing high levels of CD38, or as recently shown due to “trogocytosis”, a process where phagocytes nipple fragments of the plasma membrane carrying antigen–antibody complexes (16).