Engineering of N-glycosylation of hepatitis C virus envelope protein E2 enhances T cell responses for DNA immunization.

N-linked oligosaccharides are known to be important in modulating immunogenicity of some viral proteins. However, the roles of N-glycans of hepatitis C virus (HCV) E2 envelope glycoprotein in specific cellular immune responses remain elusive. Previous studies showed that the epitopes aa481-500 and aa551-570 of E2 might be important for immunoreactivity and that the binding site of E2 for hCD81 is located at aa480-493 and aa544-551 within the E2 protein. Here, we made plasmids containing genes encoding either wild type or mutant E2 proteins in which N-glycosylation sites (N560NT and N576ST) close to these important regions were mutated separately or in combination. The immunogenicities of wild type E2 and three mutated E2 proteins were analyzed in BALB/c mice using DNA vaccination. The E2-M2 mutant (at N576ST) significantly enhanced (compared to control) E2-specific CTL activity (P<0.05), expression of IFN-gamma (P<0.05) and suppression of tumor growth (P<0.05). Also, high IgG2a/IgG1 ratios were elicited in a Th1-type response. These results indicate that engineering of the N-glycosylation site N576ST of HCV E2 protein enhances specific cellular immune responses, providing insights into the development of E2-based DNA vaccines with enhanced immunogenicity.