Definition

A bispecific T-cell engager (BiTE) antibody composed of two single-chain variable fragments (scFv), one directed against the tumor-associated antigen (TAA) FLT3 tyrosine kinase receptor (Fms-like tyrosine kinase 3; FLT3; FLT-3; CD135; fetal liver kinase-2; FLK2), fused to one that is directed against the CD3 antigen found on T lymphocytes, with potential immunostimulating and antineoplastic activities. Upon administration of anti-FLT3/CD3 BiTE antibody AMG 427, this bispecific antibody binds to both CD3 on cytotoxic T lymphocytes (CTLs) and FLT3 found on FLT3-expressing tumor cells. This activates and redirects CTLs to FLT3-expressing tumor cells, which results in the CTL-mediated cell death of FLT3-expressing tumor cells. FLT3, a cytokine receptor belonging to the class III tyrosine kinase receptors, is overexpressed or mutated in most B-lineage and acute myeloid leukemias (AMLs).