CD19 and precursor B-cell acute lymphoblastic leukemia: CD19 CAR-T, arguably the most successful CAR-T cell therapy to date in the clinic, involves genetically engineering autologous T cells ex vivo to express CARs against a B-lineage antigen CD19, which is expressed on tumor cells such as diffuse large B-cell lymphoma (DLBCL) and B-cell precursor acute lymphocytic leukemia (B-ALL) [3–5].