In our experimental model, CD19 downregulation on Raji leukemia in the presence of CD19 CAR constructs 19A and 19B was rapid, with a significant loss of detected CD19 expression occurring after just an overnight co-culture with CAR T. The loss of CD19 expression was restored completely within 4 days after the CAR T cells were removed from culture. The gene discussed is CD19; the disease is leukemia.