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.