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The following synthetic peptides were made as immunogens for development of a zona-based contraceptive vaccine: P1, KQPFWLLQGGASRAETSVQPVLVE [amino acids (aa) 23-45 with an additional K at the N-terminus]; P2, FSEEKLVFSLRLMEENC (aa 164-179 with an additional C at the C-terminus and T170 replaced by V); and P3, CSFSKSSNSWFPVEGPADICQCC (aa 300-322). The aa are numbered on the basis of bonnet monkey ZP3 precursor protein. Antibodies against an additional peptide P4, KGDCGTPSHSRRQPHVVSQWSRSA (aa 324-347), significantly inhibits human sperm-oocyte binding. In addition, antibodies against cocktail of peptide-diphtheria toxoid conjugates also significantly inhibit the binding of spermatozoa to zona pellucida in a hemizona assay. These results will further help in the design of an immunocontraceptive vaccine based upon synthetic peptides corresponding to ZP3.

Zona pellucida (ZP) glycoproteins have been proposed as candidate antigens for immunocontraception. Studies on this potential use can be facilitated by the availability of recombinant proteins. A cDNA lambda gt11 library was constructed using poly(A)+ mRNA isolated from bonnet monkey (Macaca radiata) ovaries and was screened for bonnet monkey ZP1 using a 404-basepair (bp) human ZP1 fragment (nucleotides 818-1221) as probe. Bonnet monkey ZP1 cDNA comprises 1617 nucleotides and encodes a polypeptide of 539 amino acid residues that share 92.0% identity with human ZP1. The major difference between bonnet monkey ZP1 and human ZP1 is the deletion of a 28-amino acid domain (amino acid residues 100-127 corresponding to human ZP1). An internal fragment (1317 bp) of bonnet monkey ZP1, excluding the N-terminus signal sequence and the C-terminus transmembrane-like domain, was amplified by polymerase chain reaction. The amplified Sac I and Kpn I restricted fragment was cloned in a frame downstream of the T5 promoter under the lac operator control for expression in the pQE-30 vector. Recombinant ZP1 (r-ZP1) was expressed as a polyhistidine fusion protein in Escherichia coli strains SG13009[pREP4] and ompT and Ion protease-deficient BL21 (plysS). SDS-PAGE analysis and immunoblotting with a murine monoclonal antibody, MA-410 (raised against porcine ZP3alpha--a homologue of bonnet monkey ZP1--and cross-reactive with bonnet monkey zona pellucida), revealed major bands of 51 and 40 kDa besides truncated fragments. Optimum expression of r-ZP1 was observed at 0.5 mM isopropyl beta-D-thiogalactopyranoside (IPTG). Immunization of male rabbits with r-ZP1 purified on nickel-nitrilotriacetic acid (NTA) resin under denaturing conditions and of female rabbits with r-ZP1 conjugated with diphtheria toxoid-generated antibodies reactive with r-ZP1 in ELISA. Moreover, immune sera, when tested by indirect immunofluorescence on bonnet monkey ovarian sections, showed positive fluorescence with zona pellucida. The information on the sequence of bonnet monkey ZP1 and the availability of the recombinant protein will help toward better understanding and evaluation of the contraceptive potential of homologous immunization in a nonhuman primate model.