Contraceptive vaccines (CV) may provide viable and valuable alternatives to the presently available methods of
contraception. The molecules that are being explored for CV development either target gamete production [
luteinizing hormone-releasing hormone (
LHRH)/
GnRH, FSH], gamete function [sperm
antigens and oocyte zona pellucida (ZP)], and gamete outcome (HCG). CV targeting gamete production have shown varied degrees of efficacy; however, they either affect sex
steroids causing impotency and/or show only a partial rather than a complete effect in inhibiting gametogenesis. However,
vaccines based on
LHRH/
GnRH are being developed by several
pharmaceutical companies as substitutes for
castration of domestic pets, farm and wild animals, and for therapeutic anticancer purposes such as in
prostatic hypertrophy and
carcinoma. These
vaccines may also find applications in clinical situations that require the inhibition of increased secretions of sex
steroids, such as in
uterine fibroids,
polycystic ovary syndrome,
endometriosis and
precocious puberty. CV targeting molecules involved in gamete function such as sperm
antigens and
ZP proteins are exciting choices. Sperm constitute the most promising and exciting target for CV. Several sperm-specific
antigens have been delineated in several laboratories and are being actively explored for CV development. Studies are focused on delineating appropriate sperm-specific
epitopes, and increasing the immunogenicity (specifically in the local genital tract) and efficacy on the
vaccines. Anti-sperm antibody (ASA)-mediated immunoinfertility provides a naturally occurring model to indicate how a
vaccine might work in humans.
Vaccines based on
ZP proteins are quite efficacious in producing
contraceptive effects, but may induce
oophoritis, affecting sex
steroids. They are being successfully tested to control
feral populations of dogs, deer, horses and elephants, and populations of several species of zoo animals. The current research for human applicability is focused on delineating
infertility-related
epitopes (B-cell epitopes) from
oophoritis-inducing
epitopes (T-cell epitopes).
Vaccines targeting gamete outcome primarily focus on the HCG molecule. The HCG
vaccine is the first
vaccine to undergo Phase I and II clinical trials in humans. Both efficacy and lack of immunopathology have been reasonably well demonstrated for this
vaccine. At the present time, studies are focused on increasing the immunogenicity and efficacy of the
birth control vaccine, and examining its clinical applications in various HCG-producing
cancers. The present article will focus on the current status of the anti-sperm, anti-ZP, anti-
LHRH/
GnRH and anti-HCG
vaccines.