IL21 and plasma cell myeloma: A previous study utilizing cord blood-derived CAR-NK and CAR-T cells in the setting of multiple myeloma and non-Hodgkin lymphoma reported the added benefits of CAR-NK cells in attenuating CAR-T cell exhaustion and promoting early activation of CAR-T cells.47 We hypothesized that CD4+ CAR-T cells would provide cytokines, such as IL-2 and IL-21 for improving CAR-NK cell survival and persistence.