CD19-directed chimeric antigen receptor T cell (CD19CART) immunotherapy induced initial remissions in 80–90% of patients with multiply-relapsed/refractory B-ALL treated on institutional phase 1 trials [22–24], leading to FDA approval of the CD19CART tisagenlecleucel for children and AYAs in second or greater relapse of B-ALL. Here, CD19 is linked to precursor B-cell acute lymphoblastic leukemia.