Contraceptive vaccines

Abstract

The basic principle of a contraceptive (or anti-fertility) vaccine is to use the body's own immune defence mechanisms to provide protection against an unplanned pregnancy. Factors such as: economic production, convenience of use, relatively long-lasting but reversible action, 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, ovum, zygote and early embryo, and the pregnancy hormone hCG. Several anti-hCG vaccines have entered clinical trials and show promising results. These vaccines operate by preventing or interrupting pregnancy at the peri-implantation stage probably by neutralizing the luteotrophic action 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 hLH. Future research efforts aim to optimize the anti hCG approach, utilize new vaccine delivery systems, and broaden the spectrum of target antigens of potential utility for contraceptive vaccines.

PIP: Immunological contraception has numerous potential advantages over currently available methods of family planning: choice of several sites of action in the reproductive process, including in the male; freedom from menstrual, systemic, metabolic, or endocrine sequelae; lack of interference with sexual response or activity; ease of administration, enabling distribution by paramedical personnel; sustained and defined duration of action; high intrinsic efficacy; reduced user failure; and economical production. On the other hand, diverse groups have expressed concerns about the potential for abuse by health authorities. At present, potentially feasible approaches to contraceptive vaccine development involve target antigens in the gametes, zygote, blastocyst, and early developing placenta. Recent advances in molecular genetics and hybridoma technology have provided impetus to anti-sperm and anti-ovum vaccine development. Moreover, several promising human chorionic gonadotropin (hCG) vaccines have entered clinical trials. These vaccines prevent or interrupt pregnancy at the pre-implantation stage, probably by neutralizing the luteotrophic action of hCG. Future research will attempt to optimize the anti-hCG approach, utilize new vaccine development systems, and broaden the spectrum of target antigens.