Clustering of rare peptide segments in the HCV immunome.

Our previous research and a comprehensive meta-analysis of data from the literature on epitope mapping has revealed that the B cell epitope repertoire is allocated to rare peptide motifs, i.e., antigenic peptide sequences endowed with a low level of similarity to the host proteome. From a clinical point of view, low-similarity peptides able to evoke an immune response appear to be of special interest for the rational design of vaccines for poorly treatable diseases such as hepatitis-C virus (HCV) infection. Indeed, low similarity peptides would guarantee the highest specificity and lowest cross-reactivity, i.e., effectiveness without adverse side-effects. In this study, aimed at gaining further information for the development of effective anti-HCV peptide-based vaccines, the HCV epitopes recognized by human antibodies and currently catalogued in the Immune Epitope Data Base (IEDB) were examined for pentamer sequence similarities to the human proteome. We report that the analyzed HCV determinants are characterized by the presence of fragment absent from (or scarcely represented in) human proteins. These data confirm the low-similarity hypothesis, according to which a low-similarity to the host proteome defines the nonself character of microbial antigens and modulates peptide immunogenicity. Moreover, this study indicates a concrete and safe immunotherapeutic approach which might be used in a universal anti-HCV vaccine.