Expression of noncovalent hepatitis C virus envelope E1-E2 complexes is not required for the induction of antibodies with neutralizing properties following DNA immunization

Interactive glycoproteins present on the surface of viral particles represe nt the main target of neutralizing antibodies. The ability of DNA vaccinati on to induce antibodies directed at such structures was investigated by usi ng eight different expression plasmids engineered either to favor or to pre vent interaction between the hepatitis C virus (HCV) envelope glycoproteins E1 and E2. Independently of the injection route (intramuscular or intraepi dermal), plasmids expressing antigens capable of forming heterodimers presu med to be the prebudding form of the HCV envelope protein complex: failed t o induce any significant, stable antibodies following injection in mice. In sharp contrast, high titers of antibodies directed at both conformational and linear determinants were induced by using plasmids expressing severely truncated antigens that have lost the ability to form native complexes. In addition, only a truncated form of E2 induced antibodies reacting against t he hypervariable region 1 of E2 (specifically with the C-terminal part of i t) known to contain a neutralization site. When injected intraepidermally i nto small primates, the truncated E2-encoding plasmid induced antibodies ab le to neutralize in vitro the binding of a purified E2 protein onto suscept ible cells. Because such antibodies have been associated with viral clearan ce in both humans and chimpanzees, these findings may have important implic ations for the development of protective immunity against HCV.