A highly specific antibody response after protein prime-peptide boost immunization with Eppin/B-cell epitope in mice

Eppin seems to be a promising target for developing immunocontraceptives for males. In an attempt to develop a safer vaccine, the immune response should be specifically directed according to its fertility inhibition mechanism. The mechanism of Eppin as an immunocontraceptive agent is now assumed to be the inhibitory effect of Eppin-specific antibody on sperm motility. Hence, to make Eppin a successful immunocontraceptive, avid and specific antibody responses have to be elicited. We had employed the inoculation modality of protein prime-peptide boost with rhEppin and epitope-based peptide, which has previously showed a satisfying result of fertility inhibition with minimal adverse effects. We here further explored the immunological features and efficiency of a protein prime-peptide boost strategy. The results of the present study showed that all the animals injected with rhEppin followed by epitope-based peptide boost, elicited enhanced specific anti-Eppin antibodies. The IgG subclasses of the antibodies generated by this regimen were primarily of IgG2b and IgG1 isotypes, and more importantly, the IgA level of epidydimis lavage was much higher, which correlated well with the results of cytokine profiles in spleen cell cultures. Furthermore, the results of peptide competition assays demonstrated that rhEppin alone prime-boost vaccination lead to a broader B-cell response while protein prime-epitope-peptide boosts directed the immune response mainly against the epitope. The results indicate that this immunization strategy may be advantageous in eliciting a highly specific humoral immune response.