CD19 and acute lymphoblastic leukemia: Both the triplebody 19-3-19 and the BiTE 19-3 bound to primary human T cells isolated from ex vivo expanded mononuclear cells (Fig. 3A; left), as well as to CD19-positive Nalm-6 cells (a pre-B ALL-derived cell line; Fig. 3A, right), but it did not bind to antigen-negative HEK 293F cells (data not shown).