Review: Sperm Proteins Being Studied for Use in a Contraceptive Vaccine

Abstract

In this review article seven basic characteristics necessary in the development of a contraceptive vaccine from sperm protein immunogen are listed and briefly commented on. Which sperm protein (or proteins) to consider as an antigenic candidate depends on several key aspects. The protein must be: specific only to sperm; expressed in other mammalian sperm such as monkeys for laboratory testing; located on or very near the sperm surface; and highly immunogenic. Sperm proteins which have received some testing attention include lactate dehydrogenase C-4 SP-10 acrosin FA-1 AH-20 and PH-20. The article then reviews each of these proteins. Antibodies to lactate dehydrogenase C-4 (LDH C-4) a cytoplasmic enzyme when tested in animals were found to reduce fertility by inhibiting sperm penetration through the cervical mucus. The acrosomal SP-10 protein was originally designated as the primary vaccine candidate; however the exact action mechanism is unknown. Further studies of SP-10 in baboons are underway. Another acrosomal protein is acrosin and it too has showed immunogenic properties. Though acrosin is known to have a definite function during fertilization immunizations with purified acrosin in female sheep and rabbits had no effect on their fertility. One critically important requirement any vaccine candidate must have is that it is a surface protein from the sperm. FA-1 AH-20 and PH-20 are all sperm surface proteins with AH-20 and PH-20 being specifically plasma membrane proteins and sperm specific. AH-20 has no known role in fertility and its testing demonstrated no effect on male or female guinea pig fertility. It was studied for its strong immunogenic properties. PH-20 has a known function in fertilization. When tested on female guinea pigs 100% infertility was achieved. Research testing with PH-20 should now be focused on primates. Research focused on developing a vaccine should be continued.