Contraception.

The principle of vaccination for the purposes of fertility regulation is scientifically elegant and socially compelling. Factors such as economic production, convenience of use, relatively long-lasting but reversible protection, low failure rate and the avoidance of mechanical devices or exogenous hormones make this approach a potentially attractive option for family planning programmes in both developing and developed countries. The major efforts in research and development have involved the prospect of active immunization against specific antigens of sperm, oocyte, zygote and early embryo, and the pregnancy hormone human chorionic gonadotrophin (hCG). Several anti-hCG vaccines have entered clinical trials. They operate by preventing or interrupting pregnancy at the peri-implantation stage probably by neutralizing the luteotrophic effect of hCG. The most refined vaccine is one directed against the unique C-terminal peptide on the beta-subunit of hCG. This vaccine provokes antibodies that are specific for hCG and do not cross-react with human luteinizing hormone (hLH). Preclinical studies in baboons and data from a phase I human trial indicate that this method is free of side-effects and provides the promise of a duration of effectiveness of up to 12 months. Future research will optimize the anti-hCG approach, utilize new vaccine delivery systems and broaden the spectrum of target antigens of potential utility for contraceptive vaccines.