Dual-targeting triplebody 33-3-19 mediates selective lysis of biphenotypic CD19+ CD33+ leukemia cells

// Claudia C. Roskopf 1 , Todd A. Braciak 1 , Nadja C. Fenn 2 , Sebastian Kobold 3 , Georg H. Fey 4 , Karl-Peter Hopfner 2 , Fuat S. Oduncu 1 1 Klinikum der Universitat Munchen, Medizinische Klinik und Poliklinik IV, Hematology/Oncology, Munich, Germany 2 Ludwig-Maximilians-Universitat Munchen, Department of Biochemistry and Gene Center, Munich, Germany 3 Center for Integrated Protein Science (CIPSM) and Klinikum der Universitat Munchen, Medizinische Klinik und Poliklinik IV, Division of Clinical Pharmacology, Munich, Germany 4 Friedrich-Alexander-University Erlangen-Nuremberg, Department of Biology, Erlangen, Germany Correspondence to: Claudia C. Roskopf, e-mail: Claudia.Roskopf@med.uni-muenchen.de Keywords: leukemia, mixed phenotype acute leukemia (MPAL), immunotherapy, dual-targeting triplebody, selectivity Received: November 11, 2015      Accepted: February 23, 2016      Published: March 10, 2016 ABSTRACT Simultaneous targeting of multiple tumor-associated antigens (TAAs) in cancer immunotherapy is presumed to enhance tumor cell selectivity and to reduce immune escape. The combination of B lymphoid marker CD19 and myeloid marker CD33 is exclusively present on biphenotypic B/myeloid leukemia cells. Triplebody 33-3-19 binds specifically to both of these TAAs and activates T cells as immune effectors. Thereby it induces specific lysis of established myeloid (MOLM13, THP-1) and B-lymphoid cell lines (BV173, SEM, Raji, ARH77) as well as of primary patient cells. EC 50 values range from 3 pM to 2.4 nM. In accordance with our hypothesis, 33-3-19 is able to induce preferential lysis of double- rather than single-positive leukemia cells in a target cell mixture: CD19/CD33 double-positive BV173 cells were eliminated to a significantly greater extent than CD19 single-positive SEM cells (36.6% vs. 20.9% in 3 hours, p = 0.0048) in the presence of both cell lines. In contrast, equivalent elimination efficiencies were observed for both cell lines, when control triplebody 19-3-19 or a mixture of the bispecific single chain variable fragments 19-3 and 33-3 were used. This result highlights the potential of dual-targeting agents for efficient and selective immune-intervention in leukemia patients.