Abstract
One major area in pharmaceutical development in the coming decade will center on antibody-engineering technology and large-scale manufacturing of recombinant proteins. The leading products include humanized antibodies and immunoglobulin Fc fusion proteins designed to specifically target crucial etiologic or virulent factors for treating patients with a variety of diseases, e.g. cancer, autoimmune diseases, bacterial and viral infection, allergy, cardiovascular diseases, etc. For example, Rituxan, a chimeric antibody for treating B-lymphoma, binds to CD20 molecules on B cells leading to apoptosis and cell lysis mediated by antibody-dependent cell cytotoxicity and complement-dependent cytotoxicity. Another drug is Enbrel, used for treating rhumatoid arthritis, is a fusion protein of Fc and the extracellular portion of TNF receptor, capable of neutralizing TNF. The rationale for linking Fc fragment of IgG with therapeutic proteins or peptides to form fusion proteins are based on the following potential advantages: Fc fragments provide the dimeric conformation that sometimes enhances the stability of linked partners; improving the pharmacokinetic properties of the therapeutic partners in vivo; Fc may bind to Fc receptors and elicit immune mechanisms; amenable to large-scale manufacturing. In this thesis, we are experimenting in mouse models a novel rational-drug-design concept in designing a new version of therapeutic vaccine. Several surface proteins unique to mouse B cells, to which immune response was to be specifically induced, were fused with human IgG1.Fc fragment. In addition to the potential benefits mentioned above, the Fc fragment was used to provide T helper cell-reactive peptides in order to lift the immune tolerance towards self-antigen. We have selected two B cell-specific proteins, CD20, a component of a calcium-channel, and Igb, a part of the B cell antigen receptor complex, for the present studies. CD20 is responsible for regulating B-cell proliferation and Igb is involved in signal transduction coming through the receptor. We fused the extracellular segments of mouse CD20 and Igb to human Fc fragment of immunoglobulin g1 or g4 and used them to immunize BALB/c mice. In those immunized mice, auto-reactive antibodies were induced and the proportions of B cells among lymphocytes in the peripheral blood declined 20-40%. The weakened B-cell activity was reflected in the observation that in those immunized mice the immune response towards a bystander irrelevant antigen chicken ovalbumin was significantly reduced. In conclusion, the results of the present studies have shown in mouse models that specific autoreactivity against self-antigens on B cells can be elicited by immunizing with components of self proteins linked to Fc fragment of IgG. The results warrant further studies to the new approach of developing therapeutic vaccines for the treatment of B-cell-related diseases.