Minimal residual disease is a serious problem in the therapy of many common malignancies including breast, lung, ovarian and gastrointestinal cancer. More effective therapies are required to target minimal residual disease and micrometastases. The applicant believes that combined recruitment and costimulation using antibody fusion proteins may act synergistically to amplify host response to tumors. The applicant will synthesize antibody fusion molecules with variable domains directed against tumor associated antigens, such as CEA or her2/neu, linked to sequences encoding the chemokine RANTES and/or to the extracellular domain of the B7.1 T-cell costimulatory ligand. RANTES, a C-C chemokine acts to recruit T-cells and other immune effector cells to sites of inflammation. B7.1, the ligand for the CD28 costimulatory receptor acts to deliver a second signal required for T-cell activation following engagement of the T-cell receptor (TCR). Fusion with RANTES is designed to increase transendothelial migration and recruitment of the immune effector cells, while fusion with B7.1 is expected to activate a specific host response to tumor from effector cell population. The applicant will construct and purify novel antibody fusion proteins specific for the tumor-associated antigens, her2/neu and CEA, linked to the chemokine RANTES and/or the extracellular domain of the B7.1 costimulatory ligand. Two promising fusions to RANTES and to B7.1 have already been constructed and are being actively characterized. He will evaluate the immunoreactivity, receptor binding properties and biological activity of fusion proteins in vitro. RANTES fusions will be studied for antigen binding, binding to cellular receptors, and for ability to elicit chemotaxis. B7.1 fusion proteins will be characterized for ability to bind to antigen, cognate cellular receptors (CTLA4 and CD28), and to deliver a co-stimulatory signal in vitro. He will characterize the properties of the recombinant fusion proteins in vivo and their effectiveness in causing tumor rejection. Localization of radiolabelled fusion proteins in vivo will be studied in SCID mice implanted with her2/neu or CEA expressing and non-expressing tumors. Tumor models that express the target antigens will be studied in immunologically competent syngeneic mice. Fusion proteins will be tested for efficacy in eliciting tumor rejection and a cytolytic T-cell response. Both CEA and her2/neu are expressed at low levels in certain normal tissues. Therefore, the applicant will model efficacy and potential toxicity of anti CEA fusion proteins in a transgenic CEA mouse. The use of antibody fusion proteins may overcome limitations of gene transfer and/or standard antibody therapy and represents a promising approach to the problem of minimal residual disease.
