Mimotopes of the hepatitis C virus hypervariable region 1, but not the natural sequences, induce cross-reactive antibody response by genetic immunization

The hypervariable region 1 (HVR1) of the putative envelope protein E2 of he patitis C virus (HCV) contains a principal neutralization epitope, and anti -HVR1 antibodies have been shown to possess protective activity in ex vivo neutralization experiments. However, the high rate of variability of this a ntigenic fragment may play a major role in the mechanism of escape from hos t immune response and might represent a major obstacle to developing an HCV vaccine. Thus, even if direct experimental evidence of the neutralizing po tential of anti-HVR1 antibodies by active immunization is still missing, th e generation of a vaccine candidate with a cross-reactive potential would b e highly desirable. To overcome the problem of HVR1 variability, we have en gineered cross-reactive HVR1 peptide mimics (mimotopes) at the N terminus o f the E2 ectodomain in plasmid vectors suitable for genetic immunization. H igh levels of secreted and biologically active mimotope/E2 chimeras were ob tained by transient transfection of these plasmids in cultured cells. All p lasmids elicited anti-HVR1 antibodies in mice and rabbits with some of them leading to a cross-reacting response against many HVR1 variants from natur al isolates. Epitope mapping revealed a pattern of reactivity similar to th at induced by HCV infection, In contrast, plasmids encoding naturally occur ring HVR1 sequences displayed either on full-length E2 in the context of th e whole HCV structural region, or on a soluble, secreted E2 ectodomain, did not induce a cross-reacting anti-HVR1 response.