Immunization with HCV synthetic peptides conjugated to the P64k protein elicited strong antibody response in mice

Two synthetic peptides comprising aa regions in the NS4 protein (aa 1689-1735) and the hypervariable region I (HVR I, aa 384-414) in the HCV E2 protein were conjugated to the P64k protein, a previously demonstrated carrier protein. These peptides were also conjugated to the Co.120 protein, a truncated HCV core variant, to evaluate for the first time its ability as a carrier for B cell epitopes. Five micrograms of free peptides or conjugates, without an adjuvant, were administered subcutaneously to mice to evaluate the immune response of anti-HCV peptides. After four doses at weeks 0, 3, 6 and 10, only the animals vaccinated with the conjugates had a positive antibody response against HCV peptides. Mice immunized with the conjugated P64k elicited the strongest antibody response against both NS4 and HVR I peptides (p<0.01). Particularly, the mean antibody titers against the HVR I peptide reached 1: 39 000 in mice immunized with the conjugated P64k. Unfortunately, anti-HVR I antibodies elicited by both, Co.120 and P64k conjugates only recognized the homologous HVR I sequence. Our results indicate that conjugation to carrier proteins could be a feasible strategy to induce a strong antibody response against the HVR I that is potentially able to neutralize the homologous isolate of HCV.