Analysis of an epitope sequence recognized by a monoclonal antibody MAb-5H4 against a porcine zona pellucida glycoprotein (pZP4) that blocks fertilization

Minimal motif mapping of a known epitope on human zona pellucida protein-4 using a peptide biosynthesis strategy

An important step in the development of a human zona pellucida (huZP) peptide vaccine is to define the minimal amino acid motif for a mapped B cell epitope peptide within huZP4. Identification of this minimal motif is necessary to remove an overlapping T cell epitope that induces a pathogenic T cell response. Here we describe motif (PLTLEL(314-319)) mapping of an 18mer B cell epitope peptide(308-325) on huZP4 protein (previously known as huZP1/ZPB protein), achieved using a set of 22 biosynthetic 8mer peptides fused with truncated glutathione S-transferase (GST) or truncated streptavidin protein, and detected using rabbit anti-porcine zona pellucida (pZP) IgG. The immunogenicity of the B cell epitope peptide was evaluated in rabbits using expressed B cell epitope peptide fused with truncated streptavidin as the antigen. This construct elicited high titer antibody to the 18mer B cell epitope peptide, with reactivity to native human ZP, the biosynthetic 18mer peptide and the 18mer peptide GST fusion protein.

Mapping of B cell epitopes on the zona pellucida 2 protein of a marsupial, the brushtail possum (Trichosurus vulpecula)

Immunocontraceptive vaccines against zona pellucida (ZP) proteins are being developed for brushtail possum (Trichosurus vulpecula) management in New Zealand. Mapping of B cell epitopes on the ZP2 protein of possums was undertaken in this study to define the antigenic regions that may be crucial to sperm-egg binding. The amino acid sequence of the full-length possum ZP2 protein (712 amino acids) was used to synthesize a complete set of 71 (15-mer) biotinylated peptides with an offset of five amino acids. The peptides were used in a modified enzyme-linked immunosorbent assay (ELISA) to identify continuous epitopes recognized by antibodies in the sera of possums immunized with recombinant possum ZP2 (rZP2) constructs. Seventeen continuous epitopes were located on possum ZP2 protein. Comparisons of the peptide binding pattern of antibodies in individual sera with the fertility status of the same immunized possums revealed three significant infertility-relevant peptide epitopes (amino acids 111-125, 301-315, and 431-445). One of these (amino acids 431-445) bound to possum spermatozoa from the caudal epididymis. The implications of these findings for developing immunocontraceptive vaccines for possum control are discussed.

In search of the active PZP epitope in white-tailed deer immunocontraception

Native porcine zona pellucida (PZP) has been shown to be highly effective as an immunocontraceptive in white-tailed deer. However, the immunogenicity of PZP extracted from pig ovaries may vary from lot to lot and the extract has the potential of containing either viral or pathogenic material. Determination of the immunocontraceptive epitopes of PZP would allow portions of the molecule to be synthesized or inserted into a recombinant system for production of a consistent and safe vaccine. In this study, epitopes of PZP were selected and tested by in vitro binding, immunogenicity in rabbits, immunogenicity and immunocontraception in deer. Sera from PZP immunocontracepted deer were tested on ELISA plates containing immobilized peptides from ZP1 and ZP3alpha. Peptides with which sera from infertile deer reacted (six peptides from ZP1 and six peptides from ZP3alpha) were selected, synthesized and tested for immunogenicity in rabbits. Deer were then immunized with combinations of peptides from either the ZP1 or ZP3alpha groups. ZP3alpha peptides induced high immune titers against native PZP, but did not induce infertility in the deer. Although ZP1 peptides induced lower titers, deer immunized with two ZP1 peptides exhibited multiple estrus events and infertility, typical of that for deer immunized with native PZP vaccine. Competitive inhibition assays using the ZP1 peptides demonstrated that the peptide comprising pins 10-16 was most effective in blocking binding by the serum antibody of native PZP immunized deer. This peptide was used to immunocontracept deer, resulting in a significant reduction in fawning for 1 year.

Prospect for immunocontraception using the NH2-terminal recombinant peptide of human zona pellucida protein (hZPA)

PROBLEM

The zona pellucida is a feasible candidate for contraceptive vaccine. Our previous study showed that a human zona pellucida (ZPA) recombinant protein produced antiserum that inhibited human in vitro fertilization in rabbits. The objective of this study is to examine whether the human recombinant protein produce fertilization-blocking antiserum in a non-human primate.

METHOD OF STUDY

The amino terminal regions consisting of pig (198 amino acids) and human (206 amino acids) zona pellucida proteins were prepared by Escherichia coli to produce antisera in bonnet monkeys (Macaca radiata). Antibody production was assessed by immunofluorescent staining and enzyme-linked immunosorbent assay (ELISA). Fertilization-blocking test was carried out using human oocytes that had failed in intracytoplasmic sperm injection (ICSI) treatment under patient's informed consent.

RESULTS

Both antisera against pig and human recombinant proteins recognized native human zona pellucida by immunofluorescent staining. However, anti-recombinant human ZPA reacted to native pig zona protein more strongly than pig zona pellucida by ELISA. When human oocytes were treated with antisera before insemination, anti-human ZPA antiserum inhibited human sperm binding to human zona pellucida, but anti-pig ZPA antiserum did not.

CONCLUSIONS

Bonnet monkey produced fertilization-blocking antibody by immunization with human recombinant ZPA. The homologous or highly similar sequence is effective for developing a contraceptive vaccine when using recombinant peptides.

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.

Contraceptive potential of synthetic peptides of zona pellucida protein (ZPA)

Previously, we produced a fertilization-blocking monoclonal antibody (MAb-5H4) to find a candidate peptide for a contraceptive vaccine. MAb-5H4 recognized a linear amino acid sequence of ZPA (No. 50-67) in pigs, humans and rabbits. In the present study, 18mer peptides corresponding to the sequence were conjugated with diphtheria toxoid as a carrier protein before immunization in rabbits. All three antisera recognized human zona pellucida on testing by immunofluorescent staining method. The two produced against human and rabbit peptides effectively inhibited human sperm binding to the zona pellucida, but the antiserum against the pig peptide did not. The former two peptides include an identical sequence (LDPEKLTL) of the minimum binding motif for MAb-5H4, but the latter peptide includes one amino acid replacement (K to N) in the sequence. It is thus concluded that a synthetic peptide including the sequence of LDPEKLTL could be a feasible candidate for developing a contraceptive vaccine for humans.

Expression of recombinant human zona pellucida protein 2 and its binding capacity to spermatozoa

The human zona pellucida (ZP) is composed of three major glycoproteins: ZP1, ZP2, and ZP3. The aim of this study was to clarify the role of ZP2 by focusing on the polypeptide structure. We produced in Escherichia coli a recombinant human ZP2 protein (rec-hZP2) corresponding to amino acid sequence 1-206 of the mature protein. The final yield of rec-hZP2 protein was 80 microg/ml Luria Broth medium. After 2-h incubation of human spermatozoa with rec-hZP2 in vitro, an immunofluorescent study indicated that rec-hZP2 bound only to acrosome-reacted spermatozoa. The binding site migrated from the acrosome to the midpiece of the spermatozoa. Rabbit and mouse antisera produced against rec-hZP2 stained native human ZP in the immunofluorescent study, and significantly blocked human sperm binding and penetration into human ZP as compared to control values. The N-terminal polypeptide portion of human ZP2 was shown to contain a binding site for acrosome-reacted spermatozoa and to play an important role in secondary sperm binding and penetration into the ZP.

Expression of a recombinant porcine zona pellucida glycoprotein ZP1 in mammalian cells

Porcine zona pellucida glycoprotein (pZP1) is a good candidate for a contraceptive vaccine. For the purpose of producing glycosylated pZP1, several types of recombinant pZP1 proteins were produced in mammalian cell lines. In the first experiment, a minigene encoding pZP1 (681 amino acids) was designed for insertion into an expression vector and then transfected to three cell lines (293T, CHO-K1, and LLC-PK1). The resulting recombinant proteins were highly glycosylated and were localized in the cytoplasm. To produce a secretory type of recombinant pZP1, in the second experiment, a cDNA coding for pZP1 excluding a putative transmembrane region and a smaller cDNA coding for 1-198 amino acid residues of pZP1 were designed to produce fusion proteins with the human IgG1 heavy chain. The resultant recombinant proteins were secreted into the supernatant from both transfected cell cultures. Recombinant secretory proteins are useful because of their simple affinity purification.