Comparison of Immunogenicity of HCV CD8-epitopes as a Single Epitope, Mixture of Epitopes and Polytope Peptide

Objective: Animal studies show that vaccination with epitope-based peptides results in protective immunity. However, immunodominance should be regarded as a major challenge in this area. Considering the advantages of epitopic-vaccines against hepatitis C virus (HCV) infection, herein, we compared the occurrence of immunodominance following mice immunization with three different HCV epitopic-peptide formulations.
Methods: We synthesized four CD8+ epitopic-peptides (C1,E6,N,E4) that were derived from HCV-antigens. A polytope-peptide (C1E6NE4) spanning fusion of epitopes was designed based on immunoinformatics analyses for optimum proteasomal cleavage. BALB/c mice received three subcutaneous injections that contained 10 µg of peptide (minimal epitopes, or mixture of four epitopes or long-polytope) formulated with CpG (50 µg) and Montanide-ISA720 (70%) adjuvants in the tail-base at three-week intervals. Considering the H2-Dd (BALB/c)-restriction of C1 and E4-epitopes, three weeks after the last injection splenocytes from vaccinated animals were subjected to IFNγ/IL4 ELISpot assays in the presence of C1 and E4-peptides.
Results: All vaccinated animals promoted Th1-oriented responses as evidenced by detection of IFNγ-secreting cells and a low-level of IL4 secretion. Mice injected with minimal CTL-epitopes provoked stronger responses, however, due to the higher affinity of E4-epitope for H2-Dd, frequency of E4-specific cells was considerably higher than C1-specific ones, showing some level of immunodominance. Interestingly, animals vaccinated with polytope-peptide developed high-quality balanced responses against both C1and E4-epitopes, however at a lower intensity.
Conclusion: These results supported the superiority of polytope-peptides over minimal epitopes, yet emphasized the key role of polytope design and optimization to avoid epitope dominancy.