Stability is an important factor for developing epitope-driven vaccines. In previous study [46], the peptide 121-145 of PPE68 (Rv3873) which was a major antigenic protein encoded by Mycobacteriun tuberculosis-specific genomic region of difference 1 was identified by antigen-specific T-cell lines from HLA-heteregeneous subjects, and conserved in all sequenced strains/species of M. tuberculosis and M. tuberculosis complex, and several other pathogenic mycobacterial species; the peptide aa 121–145 was thought to be exploited as a peptide-based vaccine candidate against tuberculosis and other mycobacterial diseases. Therefore, we analyzed the conservation of KU55933 in the 11 CD8+ CTL epitopes using the Wu–Kabat variability index. All three epitopes from gp51 showed significantly higher variability than epitopes from gp30 and Tax. In particular, gp51N11 which induced responses in four all experimental calves, had the highest Wu–Kabat variability value. The epitope gp51N12 showed a similar pattern as gp51N11, in that it induced cytotoxic activity on autologous BLV-infected cells and had a high Wu–Kabat variability value. These data indicate that gp51N11 and gp51N12 are more variable at amino acid positions 141 and 155, respectively. The gp51 mediates binding of virions to cell surface receptors [42], and induces the expression of specific antibodies in infected animals [1]. Variability within the gp51N11 and gp51N12 epitopes allow for efficient modification of host immune responses. Although many vaccine trials have been undertaken [43], an effective vaccine has yet not been developed against BLV maybe because vaccine strategies have focused on the Env protein gp51. In contrast to gp51, epitopes derived from gp30 and Tax are less polymorphic. These results provide useful information for BLV vaccines development.
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