The development of genetically modified CAR-T cells targeting CD19, an antigen that is frequently over-expressed in various B-cell malignancies, is changing the therapeutic landscape in pediatric and adult patients with relapsed/refractory (r/r) B-cell acute lymphoblastic leukemia (B-ALL) and subtypes of non-Hodgkin Lymphoma (NHL). The gene discussed is CD19; the disease is acute lymphoblastic leukemia.