The TcEs were engineered using knob-into-hole (30) technology, incorporating single-chain variable (scFv) and single-chain antigen-binding fragments (scFab) to enable monovalent binding to the membrane proximal domain IV of human Her2 (31) on tumor cells, based on trastuzumab, and the C-terminal peptide (32) of human CD3ε on T cells. Here, CD3E is linked to neoplasm.