CD22 and leukemia: The relapses observed in these two patients, who previously achieved MRD-negative CR, were therefore not due to antigen escape but may be imputed to be, at least in part, to the result of the abrogated persistence of the infused CD19/CD22 CAR T cells, which suggests a loss of efficacy CD19/CD22 CAR T cell-mediated surveillance of leukemia.