IMMUNOGENICITY OF ZONA-PELLUCIDA VACCINES

Development of zona pellucida (ZP) based contraceptive vaccines raises a number of complications that challenge current immunological capabi lities. Our research examines two aspects of these immunological probl ems. First, recent studies demonstrate that one bacterially expressed rabbit ZP recombinant vaccine (rec55) induces autoantibodies in primat es that prevent sperm-ZP binding and induction of the acrosome reactio n in the homologous ZP in vitro. Immunization with rec55 does not indu ce ovarian pathology, and the duration of antibody titres indicates th at this vaccine would have reversible effects on fertility. However, t he immunogenicity of the rec55 protein produced in the pEX bacterial e xpression vector is low. We have therefore expressed the cDNA encoding rec55 using the pGEX vector for the following reasons: (i) the pGEX e xpressed recombinant proteins are soluble in aqueous solution; (ii) af finity purification of recombinant proteins on glutathione Sepharose c olumns is more effective for obtaining larger quantities of purified p rotein; and () the availability of protease cleavage sites between the ZP in and glutathione S transferase fusion proteins should eliminate the possibility of carrier-mediated suppression of immune responses. T hese improvements in protein production and purification yield immunog en which is more malleable to immunological studies. Second, while it is clear that ZP recombinant vaccines can eliminate the problem of ova rian pathology, it is important to understand how such pathology resul ts from immunization with native ZP proteins and certain recombinant Z P proteins. To this end, we have initiated immunization studies in bab oons comparing rabbit ZP and pig ZP immunogens in Titremax adjuvant. U nilateral ovariectomies at different time points after immunization (1 .5, 2, 4 and 6 months) will allow studies on the time course of pathol ogy within the ovary. Comparison of these results with ongoing rabbit ZP immunizations will help elucidate the differences in immunogenicity of ZP proteins isolated from the two species.