Engineering and characterization of a novel fusion protein incorporating B7.2 and an anti-ErbB-2 single-chain antibody fragment for the activation ofjurkat T cells

The provision of the T-cell costimulatory molecule B7 to tumor cells can be an effective way to trigger a tumor-specific cytolytic T-cell response. On e way to provide B7 to tumor cells would be to couple an antitumor antibody directly to B7. Such a molecule should target tumors displaying antigen an d provide the costimulatory signal to T cells, resulting in the initiation of an antitumor T-cell response. To this end, a fusion protein was designed that incorporates a single-chain antibody fragment (scFv) to erbB-2 (Her2/ neu), an oncogene product overexpressed by 30% to 50% of breast carcinomas, and the ECD of B7-2 (CD86). This fusion protein, expressed and purified fr om Pichia pastoris, was shown to retain binding activity to both counter re ceptors, erbB-2 and CD28. The fusion protein was also shown to target erb-2 -positive tumor cells and to deliver a CD28-specific T-cell costimulatory s ignal. These results suggest that a fusion protein engineered to target tum or cells and signal T cells for activation may be an effective means of can cer immunotherapy. Further studies should be performed to characterize the fusion protein in erbB-2 tumor-bearing mice for in vivo tumor targeting, bi odistribution, and efficacy.