Vaccines for Control of Fertility

Abstract

Major developments in birth control vaccines are on the horizon. The human chorionic gonadotropin (hCG) vaccine has entered phase II clinical trials after successful completion of phase I studies at 5 centers in India and 4 centers abroad. It is the most advanced vaccine of its type in the world. The trials are being conducted on women of proven fertility who are sexually active. The available results indicate the efficiency of the vaccine to prevent pregnancy in women at or above titres of 50 ng/ml. A vaccine inducing antibodies against gonadotropin releasing hormone (GnRH) has been approved in India for trials in postpartum women, to determine whether immunization can help prolong lactational amenorrhea. The GnRH vaccine is also in clinical trial in prostate cancer patients at 2 centers in India and in Austria and the Dominican Republic. The follicle stimulating hormone (FSH) vaccine is about to enter phase I clinical trial after completing experimental and toxicological studies. A vaccine against FSH has been developed for human males employing ovine FSH (oFSH) as an immunogen. oFSH adsorbed on alum induces antibodies reactive with human FSH in bonnet monkeys. Immunization leads to oligospermia with resultant impairment of fertilization potential. No reduction in testosterone levels has been reported. Research is in progress to identify antigens on spermatozoa, which could serve as vaccine candidates. PH-20, a protein located on the inner acrosomal membrane of capacitated sperms, has been reported to have 100% contraceptive efficacy in both sexes of guinea pigs in active immunization studies. cDNA probes of PH-20 cross-react with genomic DNAs of mouse, rat, hamster, and human. The sperm antigen, lactate dehydrogenase C4 (LDH-C4), is a glycolytic enzyme. Active immunization with LDH-C4 suppressed fertility in mice, rabbits, and baboons. SP-10, which is a testis-specific human sperm protein, is also a promising candidate.