Whilst the use of anti-CD19 CAR T cells to treat refractory CD19+ B-ALL has been incredibly effective, with up to 90% of pediatric patients achieving complete responses, CAR T cells have thus far been less efficacious in the context of solid tumors with a complete response rate of only 4.1% in a meta-analysis of solid tumor trials63,64. This evidence concerns the gene CD19 and acute lymphoblastic leukemia.