Generation of cytotoxicity against hepatitis delta virus genotypes and quasispecies by epitope modification

Quasispecies are likely responsible for virus escape from host immune surveillance. The aim of this study was to enhance the immune response against varied sequences within the HDV quasispecies in an attempt to control chronic delta hepatitis.

The HLA-A2 restricted peptides spanning aa 43-51 of HDAg and three variant peptides bearing single amino acid substitutions were synthesized. Their immunogenicity and capacity to induce effective CTL responses were studied in HHD-2 mice.

Native HDV epitope produced limited cytotoxic immune response. Two modified HDV peptides (HDV 43-51 1Y; tyrosine substitution in positive 1, and 43-51 3A; alanine substitution in position 3) could enhance not only the binding affinity with HLA-A2.1 molecules but also the immunogenicity. Ex vivo interferon-gamma ELISPOT and CTL assays revealed that the two modified epitopes-induced CTLs had a higher functional avidity and produced stronger cytotoxicity to lyse constitutively HDAg-expressing Hep-G2 cells. Interestingly, the spectrums of the T cell receptor (TCR) cross-reactivity are broadened and response to multiple HDV variants by the enhanced epitopes immunization.

The modified HDV peptides can enhance the immunogenicity and the induced CTLs can cross-react with multiple HDV variants. Combination with the two enhanced epitopes might be a potential immunotherapeutic agent to control HDV quasispecies in HLA-A2 chronic hepatitis D patients.