Evaluation of the Contraceptive Potential of Recombinant Human ZP3 and Human ZP3 Peptides in a Primate Model: Their Safety and Efficacy

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Abstract
PROBLEM: The unique recognition events that result in the avid binding of mammalian spermatozoa to the surface of the zona pellucida (ZP) are being exploited in the development of contraceptive vaccines. In this study, the safety and efficacy of a vaccination strategy based on the induction of active immunity against purified, glycosylated, recombinant human ZP3 (rhZP3) has been evaluated in a primate model, Callithrix jacchus. METHOD OF STUDY: Long‐term infertility was established after immunization with rhZP3 and the resulting immune sera reacted with rhZP3 on an enzyme‐linked immunosorbent assay (ELISA) and immunolocalized exclusively to the outer surface of native ZP on marmoset ovarian sections. However, this contraceptive effect was inevitably associated with the eventual appearance of an ovarian pathology characterized by a depletion of primordial follicles. In an attempt to circumvent this side effect, human ZP3 (hZP3) was epitope mapped and four continuous, immunodominant B‐cell epitopes (hZP345–64, hZP393–110, hZP3172–190 and hZP3341–360) were evaluated for contraceptive efficacy in vivo. Using peptide‐tetanus toxoid (TT) conjugates to enhance immunogenicity, antipeptide antibodies were raised against these immunogens, which also cross‐reacted with rhZP3 on ELISA. In addition, antibodies against hZP345–64 and hZP3172–190 recognized native ZP on marmoset ovarian sections when a microwave technique was used to enhance epitope presentation. RESULTS: No ovarian pathology was observed after the long‐term administration of these peptide immunogens, and fertility was suppressed when compared with TT controls but could not be correlated to the antibody titer. CONCLUSION: Clearly, further research is required to identify optimal B‐cell epitopes that will reliably induce infertility, free from any ovarian pathology.