Current status of research on sperm antigens: potential applications as contraceptive vaccines.

Immunocontraception has been suggested as a solution to the need for alternative and reversible contraception. This article reviews the current status of research on sperm antigens and discusses their potential role in the development of a new contraceptive technology. A contraceptive vaccine is suggested by the observed association between infertility and antisperm antibodies in both male and female human subjects. Fertility suppression has been well documented in female laboratory animals immunized with sperm. The goal of current research efforts is to identify the responsible antigen(s) from extracts of sperm and testes. Development of a contraceptive vaccine requires a highly specific and immunogenic sperm antigen that is available in relatively large quantities and is amenable to chemical synthesis. Lactate dehydrogenase C4 (LDH-C4; LDH-X) appears to be the most viable sperm-specific antigen for vaccine development. Immunization with LDH-C4 does suppress fertility, and the complete biochemical characterization of this isoenzyme is underway. Research suggests that LDH-C4 immunization results in immunoglobulins that enter the female reproductive tract and prevent sperm from fertilizing the egg. Manipulation of the secretory immune system of the female reproductive tract could enhance the immunocontraceptive effect. For LDH-C4 to provide the basis for a practical immunological contraceptive, 2 major problems must be overcome: 1) a synthetic substitute for the natural product antigen must be identified, and 2) the contraceptive effect must be made more nearly complete. Despite these practical problems, prospects are good that a vaccine to prevent pregnancy will become available during the next decade.