A synthetic gonadotropin-releasing hormone (GnRH) vaccine for control of fertility and hormone dependent diseases without any adjuvant

Active immunization against self-peptides have gained widespread acceptance inspite of their low immunogenicity. Recent applications involving multiple copies of self-peptides in linear alignment and conjugation with carrier proteins appear to increase the immune response against self-peptides. As with most vaccines, however, immunogens require supplementation with adjuvants to elicit an optimum immune response. In the present study, we prepared a double-chain miniprotein with each chain containing three linear repeats of the self-peptide gonadotropin-releasing hormone (GnRH3), the hinge region of human IgG1 (hinge), and a T-helper epitope from the measles virus protein (MVP). The GnRH3-hinge-MVP miniprotein was conjugated to purified recombinant heat shock protein 65 (Hsp65) of Mycobacterium bovis and used to immunize rats primed with subcutaneous injections of Bacillus Calmette-Guerin (BCG) in the absence of adjuvants. The GnRH3-hinge-MVP-Hsp65 stimulated the production of specific anti-GnRH antibodies in the absence of adjuvants and the antibody titer was comparable to that produced in rats immunized with the dimeric miniprotein in the presence of Freund's adjuvant. Moreover, immunization with the adjuvant-free GnRH3-hinge-MVP-Hsp65 induced degeneration of the reproductive organs in both male and female rats unlike those immunized in the absence of Hsp65 or in control animals inoculated with the vehicle only. Histological examination of the affected organs showed atrophy of the seminiferous tubules with dimished spermatogenesis in the testes of male rats. In female rats, the uteri were much smaller in size and the ovaries exhibited reduced follicular development. These findings demonstrated that GnRH3-hinge-MVP-Hsp65 mounted a strong immune response in the absence of conventional adjuvants, and could prove useful in control of fertility and the treatment of conditions/diseases where GnRH ablation is required.