A half-life extended (HLE), human bispecific T-cell engager (BiTE) antibody composed of two single-chain variable fragments (scFv), one directed against the tumor-associated antigen (TAA) human mucin 17 (MUC17), and one directed against human CD3, a T-cell surface antigen found on T-lymphocytes, with potential antineoplastic activity. Upon administration, anti-MUC17/CD3 BiTE antibody AMG 199 binds to both CD3 on T-cells and MUC17 expressed on tumor cells. This results in the cross-linking of T-cells and tumor cells, and induces a potent cytotoxic T-lymphocyte (CTL) response against MUC17-expressing tumor cells. MUC17, a member of the mucin family of glycoproteins, is overexpressed in a variety of tumor cells of epithelial origin and plays a key role in tumor cell dissemination.