The use of immunosome technology for vaccines against rabies and other viral diseases

Abstract

Subunit viral vaccines present several advantages. They are free of nucleic acids (of viral and/or cellular origin) and proteins of cellular and/or serum origin; they contain only the relevant antigen. For rabies virus, the antigen which induces the virus-neutralizing antibody (VNAb) is the glycoprotein (GP), which is anchored, in form of spikes, to the viral membrane. The GP may be extracted from the virion but, after solubilization and purification, it appears to be poorly immunogenic. In order to restore its immunogenicity, GP molecules are anchored to preformed liposomes (unilamellar phospholipid vesicles) to mimic their native structure and environment. The subunit vaccine obtained by this technique is called an "immunosome" (IMS). Rabies immunosomes exhibit structural and immunological properties very similar to those of the viral particle. The rabies glycoprotein molecules, anchored to the lipid bilayer of the liposome, correctly expose the immunodominant epitope involved in VNAb induction and induce a strong specific humoral immune response. They also induce a specific cellular immune response. As a result IMS have a highly protective activity when tested with either pre- or post-exposure potency tests. Immunosome technology may be applied to other purified membrane proteins or amphiphilic peptides to restore their immunogenicity.