Structure of constructs. (A) The EpCAM-specific heterodimeric B7-1 construct consists of: B7-1, the extracellular part of human B7-1 comprising two Ig-like domains. Hinge (-o-), the upper hinge region of human IgG3. Ckappa, constant region domain of human Ig kappa light chain. CH1, the first constant region domain of the human IgG1 heavy chain comprising at its C-terminus (i) the cysteine residue that forms the interchain disulfide bond (-S-S-) with the C-terminal cysteine of Ckappa, followed by (ii) six histidine residues (His₆). Anti-EpCAM scFv (M79), scFv fragment of EpCAM-specific monoclonal antibody M79, comprising the variable regions of the corresponding Ig light and heavy chains, denoted VL and VH respectively, connected by a 15-amino acid glycine-serine linker (G₄S)₃. (B) Bispecific single-chain antibody (bscAb) EpCAM x CD3 (without a Flag tag) providing T cells with the TCR signal through simultaneous binding of its anti-CD3 scFv arm (to the CD3 component of their TCR complex) and of its anti-EpCAM scFv arm derived from monoclonal antibody M79 (to EpCAM-positive cells). VL and VH, the variable regions of the anti-EpCAM or anti-CD3 Ig light and heavy chains respectively. His₆, C-terminal tag consisting of 6 histidine residues.