Design of EpCAM-specific costimulatory single-chain constructs. The single-chain constructs consist of: B7-1, B7-2, LFA-3, the extracellular parts of human B7-1, B7-2 and LFA-3 respectively, each comprising two Ig-like domains. ICAM-1, the extracellular part of human ICAM-1 comprising five Ig-like domains. Anti-EpCAM scFv (4-7), the EpCAM-specific scFv antibody fragment 4-7 comprising the Ig heavy and light chain variable regions VH and VL respectively connected by a 15 amino acid glycine-serine linker (G₄S₁)₃. His₆, 6 histidine residues at the C-terminus of anti-EpCAM scFv (4-7). G₄S1, 5 amino acid glycine-serine linker connecting B7-1, B7-2, LFA-3 or ICAM-1 with anti-EpCAM scFv (4-7).