The 2014 FDA approval of CD3 × CD19 biAb blinatumomab (Blincyto®) for the treatment of adults and children with refractory or relapsed pre-B cell acute lymphoblastic leukemia (pre-B-ALL) followed by its 2018 FDA approval for the treatment of adults and children with pre-B ALL in first or second complete remission with minimal residual disease, are milestones marking the therapeutic utility of T-cell engaging biAbs (3–5). The gene discussed is CD19; the disease is acute lymphoblastic leukemia.