Overcoming leukemia heterogeneity by combining T cell engaging bispecific antibodies.

BACKGROUND: Leukemia represents about 5% of all human cancers. Despite advances in therapeutics, a substantial number of patients succumb to the disease. Several subtypes of leukemia are inherently more resistant to treatment despite intensive chemotherapy or targeted therapy. METHODS: Here we describe the generation of T cell engaging (CD3) bispecific antibodies (BsAbs) built on humanized IgG frameworks using the IgG(L)-scFv format against two targets expressed on acute lymphoblastic leukemia (ALL) and on acute myeloid leukemia (AML). RESULTS: Each BsAb mediated potent anti-leukemia effect against ALL (CD19) and AML (CD33) in vitro and in xenograft models. Importantly, the CD19-specific BsAb (BC250) was effective against hematogenous spread preventing metastases to liver and kidney in mice bearing ALL and Burkitt's lymphoma xenografts. BC250 was more potent than the The Food and Drug Administration (FDA)-approved BsAb blinatumomab against ALL xenografts in vivo as measured by tumor bioluminescence and mouse survival. Furthermore, the combination of the CD19 and CD33 BsAbs in two xenograft models of mixed phenotype acute leukemia (biphenotypic and bilineal leukemia) was far superior than monotherapy with either of the BsAbs alone. CONCLUSIONS: Selective combinations of these leukemia-specific BsAb offer the potential to overcome tumor heterogeneity or clonal escape in the modern era of antibody-based T cell-driven immunotherapy.