Zona pellucida-based contraceptive vaccines for human and animal utility

Contraceptive vaccines can be designed to inhibit (i) production of the gametes (sperm and oocyte), (ii) functions of gametes leading to block in fertilization, and (iii) the gamete outcome (pregnancy). The zona pellucida (ZP) glycoproteins have been proposed as candidates for developing contraceptive vaccines by virtue of their critical role in fertilization. Immunization of non-human primates with either native or recombinant ZP proteins leads to curtailment of fertility, which however is invariably associated with ovarian pathology. To avoid oophoritis, immunogens corresponding to mapped B cell epitopes of ZP proteins that are devoid of ‘oophoritogenic’ T cell epitopes have been proposed. However, ways to overcome the observed oophoritis associated with the ZP-based contraceptive vaccines are yet to be fully defined. This is essential if their use for control of human fertility is to be considered. Nonetheless, contraceptive vaccines based on ZP proteins have shown very promising results in controlling wildlife population such as wild horses, white-tailed deers, elephants, marsupials, grey seals and dogs, where long term infertility or even permanent sterility is desirable.