IL21 and acute myeloid leukemia: Though not yet tested specifically for AML, several strategies that have been shown to improve CAR T cell expansion and persistence include expression of IL-15 (101) or IL-18 transgene (102), addition of exogenous IL-7, IL-15, and/or IL-21 cytokines during CAR T cell ex vivo expansion (103, 104), and many others that are currently being developed to skew CAR T cell phenotype toward a stem cell/ central memory phenotype.