Analysis of recombinant mouse zona pellucida protein 2 (ZP2) constructs for immunocontraception

In this study we have examined the potential of recombinant mouse zona pellucida glycoprotein 2 (ZP2) as a target for immunocontraception. Immunogenicity studies and fertility trials were performed in outbred Swiss-Webster mice using four ZP2 constructs: Val(35)-Gly(200) (ZP2(V35-G200)), Val(35)-Leu(331) (ZP2(V35-L331)), Pro(325)-Ala(637) (ZP2(P325-A637)), and Val(35)-Ala(637) (ZP2(V35-A637)). A significant antibody response occurred to three of the four immunogens, however antibodies capable of recognizing native ZP occurred only after immunization with ZP2(V35-A637) and ZP2(P325-A637). Only immunization with ZP2(V35-A637) correlated with a reduction in fertility. Examination of the physiological basis for infertility revealed that: (1) passive transfer of ZP2 antiserum induced infertility in non-immune mice; (2) ovaries of infertile mice appeared histologically normal; (3) infertile mice produced normal numbers of eggs and (4) ZP of ovulated eggs from infertile mice demonstrated a significant reduction in the number of sperm bound compared to eggs from adjuvant controls. Infertility can be caused entirely by ZP2 antibodies without the incidence of significant ovarian pathology. This study also demonstrated that immunization with the bioactive (sperm binding) region of ZP2, recombinant ZP2(V35-G200), did not result in a significant immune response that recognized native ZP or inhibited fertility. Consequently we designed a ZP2-sperm antigen construct, replacing the C-terminal region of ZP2 with Sp17. This construct proved to be immunogenic and reduce fertility while directing the immune response to the Val(35)-Gly(200) region of ZP2.