Mode-of Action

TACSYN specifically binds to human fms-like tyrosine kinase 3 (FLT3), which is a cell surface receptor expressed at high levels on leukemic blast cells and to CD3, a T-cell receptor exclusively expressed on T-cells. Based on SYNIMMUNE’s proprietary bispecific antibody platform, the tumour antigen specific antibody domain and the T-cell recruiting antibody domain are linked by an attenuated CH2 domain, which contains modifications to prevent Fc receptor binding of the molecule. TACSYN binds to FLT3 expressed on leukemic blast cells and at the same time to CD3 expressed on T-cells. The cross-linkage of the receptors on the T-cell leads to T-cell activation and consequently, during the immediate response, to direct killing of tumor cells by T-cells and during the delayed response to T-cell proliferation and thereby to an enlarged pool of T-effector cells. In addition, activated T-cells secrete pro-inflammatory cytokines, which recruit other immune cells. Both mechanisms boost the inflammatory anti-tumor response and strongly contribute to the killing of tumor cells.


TACSYN is indicated for the therapy of acute myeloid leukemia (AML) and acute lymphoblastic leukemia (ALL) in patients displaying a persistence of disease after chemotherapy or relapse after stem cell transplantation (SCT), i.e. a stage of existing disease with a relatively high and growing number of tumour cells (as opposed to the indication for FLYSYN for acute myeloid leukemia at minimum residual disease stage).

Approximately 20,000 and 6,500 new cases of acute myeloid leukemia (AML) and acute lymphoblastic leukemia respectively occur annually in the United States. In Europe there are about 27,000 annual cases of acute myeloid leukemia and about 9,000 annual cases of acute lymphoblastic leukemia. While acute myeloid leukemia occurs mainly in elderly patients and the mean age of diagnosis is approximately 70 years, 75% of acute lymphoblastic leukemia cases occur in young children. The average five year survival rate is 26% and 70% for acute myeloid leukemia and for acute lymphoblastic leukemia, respectively. Consequently there is a high medical need for effective treatments of these diseases.


Development Stage

SYNIMMUNE has completed the preclinical characterization of TACSYN and has demonstrated high target specificity, no aggregate formation, no off-target activation and specific lysis of FLT3 expressing tumor cells. In addition, SYNIMMUNE has developed a GMP manufacturing process for TACSYN.


TACSYN is subject by granted patents in Europe and by internationally pending patent applications.