Fusion proteins of B7.1 and a carcinoembryonic antigen (CEA)-specific antibody fragment opsonize CEA-expressing tumor cells and coactivate T-cell immunity

Genetic engineering can be used to generate antigen-specific molecules for improved tumor immunotherapy, We have constructed genes coding for fusion p roteins consisting of a high-affinity antibody single-chain antibody fragme nt (scFv) specific for the human carcinoembryonic antigen (CEA) and the cos timulation domain of the murine B7.1 molecule (mB7.1) linked to the antibod y moiety by an lgG3 peptide linker. The hybrid genes were constructed in 2 orientations, one with the scFv located N-terminal to mB7.1 and one vice ve rsa, Soluble proteins were expressed by CHO cells, purified using anti-idio type-affinity chromatography and characterized by tumor-cell binding and co stimulation activity. When tumor cells expressing CEA on the cell membrane were opsonized with the CEA-specific costimulators, both fusion proteins sp ecifically stimulated murine T-cell preparations to proliferate in a simila r manner. Our data suggest that "costimulation coating" of tumor cells may be a suitable approach for activation of a sustained cellular antitumor res ponse. It also provides the opportunity to increase tumor immunogenicity us ing easily generated soluble fusion proteins that advantageously link biolo gical functions of both the humoral and the cellular arm of the specific im mune system. (C) 2001 Wiley-Liss, Inc.