Fc-fusion proteins as adjuvants and therapeutic reagents

• Main Author: Mekhaiel, David
• Published: University of Nottingham 2014
• Subjects: 616.079
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.662197

Fc-fusions proteins are a growing class of bio-therapeutics, widely used in the clinic as well as off label applications. In this work, the ability of the Fc region of IgG to act as an immunological adjuvant when fused to antigen was investigated. Fc-fusions were constructed, produced and purified, wherein the malarial antigen, MSP119, was fused to the Fc region of either mouse IgG2a or human IgG1. These monomeric Fc-fusion proteins were found to bind to Fc gamma receptors (FcyRs) in a similar fashion to the antibodies they were derived from. Immunisation of mice with these fusions resulted in the production of MSP119-specific antibodies, predominantly murine IgGl, with lower levels of IgG2a and IgG2b. However, these MSP119-specific antibodies had no influence on the course of a subsequent malarial challenge. In order to improve the immunogenicity of these monomeric Fc-fusion proteins, critical residues from IgM (a polymeric class of antibody) were introduced in an attempt to polymerise these fusions. The modifications described here, resulted in the formation of dimeric and barrel shaped hexameric IgGl based fusions, whilst failing to induce polymerisation of the mlgG2a based fusion proteins. In immunisation studies, these hexameric Fc-fusions were found to be less immunogenic than their monomeric counterparts, and again, failed to protect from challenge. Analysis of hexameric Fc-fusion binding to FcyRs revealed that the inclusion of the fusion partner, MSP119, significantly reduced the ability of the fusions to bind FcyRs. The ability of the hexameric Fc scaffold alone to act as a replacement for intravenous immunoglobulins (IVIG) in the treatment of immune thrombocytopenia (ITP) was also investigated. At the dose used in this work, under 2% of the commonly used dose of IVIG, the hexameric IgGl scaffold offered no amelioration of experimental ITP in mice. This work described here forms the foundation for the future use of stable well defined barrel shaped hexameric Fc-fusions, both as a platform for use in vaccination, and as a therapeutic reagent.