Zona pellucida: current status as a candidate antigen for contraceptive vaccine development.

The porcine zona pellucida represents a unique immunocontraceptive target antigen. Initial active immunization studies using crude or partially purified zona components as immunogens resulted in adverse, nonreversible effects on ovarian folliculogenesis, but more recent findings in nonhuman primates indicate that such effects are not as severe and are reversible. Consequently, current efforts are directed toward identifying a zona immunogen that elicits contraceptive antibodies that produce no adverse effects on the ovary. Other studies are in progress to determine optimal injection/immunization format, proper immunogen dosage, and appropriate adjuvant for use in the zona-antizona immunocontraceptive system. Recent data have been very encouraging and emphasize the contraceptive efficacy of this approach to reproduction control.