Strategies for designing an immunocontraceptive vaccine based on zona pellucida synthetic peptides and recombinant antigen

Abstract

Immunization of female bonnet monkeys (Macaca radiata) with pig zona pellucida glycoprotein ZP3 using adjuvants permissible for human use leads to infertility. Fifty per cent of the animals conceived after antibody titres declined. Animals that failed to regain their fertility did not show any obvious ovarian changes. As part of the attempt to design an effective immunocontraceptive vaccine based on synthetic peptides, the epitopes recognized by monoclonal antibodies (mAb) against pig ZP3 α and ZP3 β and possessing contraceptive efficacy in vitro were mapped. These studies identified an N-blocked decapeptide from the N-terminus corresponding to 23-32 amino acids of the precursor protein of pig ZP3 β. As an alternative approach to using synthetic peptides, DNA encoding bonnet monkey ZP3 was cloned and sequenced. The deduced primary amino acid sequence revealed an overall similarity of 93.9% with human ZP3. Bonnet monkey ZP3 corresponding to an internal 975 nucleotide fragment excluding the N-terminus signal sequence and the C-terminus transmembrane domain has been expressed in Escherichia coli. These results will assist in the design of an immunocontraceptive vaccine based on either synthetic peptides or recombinant glycoproteins or proteins corresponding to ZP. Previous studies have demonstrated the efficacy, in mice, of synthetic peptides derived from zona pellucida (ZP) glycoprotein in blocking fertility without ovarian dysfunction. This study used bonnet monkeys (closely related to humans in the primate evolutionary tree and less susceptible to summer amenorrhea than rhesus monkeys) to explore the design of an immunocontraceptive vaccine based on synthetic peptides, recombinant glycoproteins, or proteins corresponding to ZP. Immunization of female monkeys with pig ZP3 glycoprotein using adjuvants permissible for human use produced infertility. Although only half the animals conceived after antibody titres declined, monkeys that failed to conceive did not show any obvious ovarian changes. Mapping of the epitopes recognized by monoclonal antibodies against ZP3 α and β and possessing contraceptive efficacy in vitro identified an N-blocked decapeptide from the N-terminus corresponding to 23-32 amino acids of the precursor protein of pig ZP3 β. When DNA encoding bonnet monkey ZP3 was cloned and sequenced, the deduced primary amino acid sequence showed a 93.9% similarity with human ZP3. Bonnet monkey ZP3 corresponding to an internal 975 nucleotide fragment excluding the N-terminus signal sequence and the C-terminus transmembrane domain has been expressed in Escherichia coli.