T cells transduced with a CD19-directed chimeric antigen receptor (CAR) have become standard of care (SOC) for patients with B-lineage acute lymphoblastic leukemia (ALL), large B-cell lymphoma (LBCL), and mantle cell lymphoma (MCL), and have dramatically impacted treatment algorithms in these entities in recent years (1–4). This evidence concerns the gene CD19 and mantle cell lymphoma.