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

Immunocontraceptive potential of a GnRH receptor-based fusion recombinant protein

BACKGROUND

The management of stray dog population has been of utmost importance due to their overpopulation, increase in dog bites incidence, and rabies. Contraceptive vaccines, a non-surgical alternative to spaying and neutering are viewed as a valuable option for the management of dog population. In this study, the contraceptive potential of a recombinant fusion protein containing the three genes GnRH, GnRH receptor, and ZP3 was explored.

RESULTS

The gene fragment encoding GnRH, GnRHR, and ZP3 along with the antigenic epitopes of canine distemper virus and tetanus toxoid was assembled, synthesized, and cloned into pET28a expression vector. The resulting construct GVAC08 was successfully transformed into BL21DE3 strain of E. coli and confirmed by colony PCR. The recombinant GVAC08 protein was expressed and purified using Ni-NTA and was confirmed to be a 50-KDa protein by SDS PAGE and Western blot. Mice were immunized with the GVAC08 protein using Freund's complete adjuvant followed by a booster using Freund's incomplete adjuvant. This induced a high antibody titer against GnRH, GnRH receptor, and ZP3 which was determined by ELISA.

CONCLUSION

Mating studies showed that the GVAC08 recombinant protein was able to reduce the litter size in immunized mice showing improved efficacy. However, the vaccine candidate with further improvements will be a viable contraceptive vaccine.

The bioactivities of the central segment of Zp2 polypeptide

In order to understand the role of the protein zona pellucida 2 in fertilization, an antibody against a central segment of the zona pellucida 2 peptide, segment 190-505 (Z2eH), was prepared. The influence of the antibody on sperm-zona interaction was tested using the sperm-egg binding assay. The effect of the antibody on fertility was evaluated by passive immunization with anti-Z2eH antibody. Immunohistochemical assay showed that an antibody from rabbit reacted specifically with the natural zona pellucida on mouse ovarian sections. Immunofluorescence assay showed that the antibody bound specifically to the zonae pellucidae of the ovulated oocytes and 2-cell embryos after passive immunization. The antibody-treated oocytes bound capacitated sperm as control oocytes, passive immunization did not impede the action of sperm to fertilize the oocyte in vivo. These findings suggest that the central peptide of ZP2 (190-505) is immunogenic and contains zona pellucida-specific epitopes, however the central polypeptide might not be the crucial part from which to construct a functional domain to bind sperm.

Contraceptive efficacy of recombinant fusion protein comprising zona pellucida glycoprotein-3 fragment and gonadotropin releasing hormone

Contraceptive vaccines have been used for the management of wildlife population. In the present study, we have examined the contraceptive potential of Escherichia coli-expressed recombinant fusion protein comprising of 'promiscuous' T cell epitope of tetanus toxoid [TT; amino acid (aa) residues 830-844] followed by dilysine linker (KK), dog ZP3 fragment (aa residues 307-346), triglycine spacer (GGG), T cell epitope of bovine RNase (bRNase; aa residues 94-104), GnRH, T cell epitope of circumsporozoite protein of Plasmodium falciparum (CSP; aa residues 362-383), and GnRH. SDS-PAGE analysis of the purified refolded protein revealed a dominant ∼12 kDa band, which in Western blot reacted with mouse polyclonal antibodies against dog ZP3 fragment and mouse monoclonal antibodies against GnRH. Immunization of female FvB/J mice following two booster schedule with the above recombinant protein supplemented with alum led to high antibody titres against the immunogen as well as ZP3 and GnRH as determined by ELISA. The immune sera reacted with zona pellucida of mouse oocyte and also inhibited in-vitro fertilization. The qRT-PCR studies showed decrease in the ovarian GnRH receptor in mice immunized with the recombinant fusion protein. Mating studies revealed high contraceptive efficacy of the recombinant protein as in two independent experiments, 90% of the immunized female mice failed to conceive. Following one booster immunization schedule, 50% of the immunized female mice failed to conceive. However, in adjuvanted controls, all the female mice became pregnant. To conclude, the recombinant protein described herein has a good potential to be developed as candidate contraceptive vaccine.

Contraceptive vaccines based on the zona pellucida glycoproteins for dogs and other wildlife population management

Zona pellucida (ZP) glycoproteins, by virtue of their critical role in fertilization, have been proposed as candidate antigens for the development of contraceptive vaccines. In this review, the potential of a ZP-based contraceptive vaccine for the management of wildlife population, with special reference to street dogs, is discussed. Immunization of various animal species, including female dogs, with native porcine ZP led to inhibition of fertility, which was associated with the ovarian dysfunction. Immunization of female dogs with Escherichia coli-expressed recombinant dog ZP glycoprotein-3 (ZP3) either coupled to diphtheria toxoid or expressed as fusion protein with 'promiscuous' T non-B-cell epitope of tetanus toxoid also led to inhibition of fertility. To improve the contraceptive efficacy of ZP-based contraceptive vaccine, various groups are working on improving the immunogen, use of DNA vaccine as prime-boost strategy, and delivering the zona proteins/peptides presented on either virus-like particles or entrapped in microsphere. Host-specific live vectors such as ectromelia virus and cytomegalovirus have also been used to deliver mouse ZP3 in mice. Various studies show the enormous potential of the ZP-based vaccine for the management of wildlife population, where permanent sterilization may be desirable.

Current status of veterinary vaccines

The major goals of veterinary vaccines are to improve the health and welfare of companion animals, increase production of livestock in a cost-effective manner, and prevent animal-to-human transmission from both domestic animals and wildlife. These diverse aims have led to different approaches to the development of veterinary vaccines from crude but effective whole-pathogen preparations to molecularly defined subunit vaccines, genetically engineered organisms or chimeras, vectored antigen formulations, and naked DNA injections. The final successful outcome of vaccine research and development is the generation of a product that will be available in the marketplace or that will be used in the field to achieve desired outcomes. As detailed in this review, successful veterinary vaccines have been produced against viral, bacterial, protozoal, and multicellular pathogens, which in many ways have led the field in the application and adaptation of novel technologies. These veterinary vaccines have had, and continue to have, a major impact not only on animal health and production but also on human health through increasing safe food supplies and preventing animal-to-human transmission of infectious diseases. The continued interaction between animals and human researchers and health professionals will be of major importance for adapting new technologies, providing animal models of disease, and confronting new and emerging infectious diseases.

Molecular cloning and assessment of the immunocontraceptive potential of the zona pellucida subunit 3 from Brandt's vole (Microtus brandti)

A full-length cDNA encoding Brandt's vole (Microtus brandti) zona pellucida glycoprotein subunit 3 (vZP3) was isolated using rapid amplification of cDNA ends-polymerase chain reaction (RACE-PCR). The cDNA contains an open reading frame of 1254 nucleotides encoding a polypeptide of 418 amino acid residues. The deduced amino acid sequence of vZP3 revealed high overall homology with hamster (82.1%), mouse (81.3%) and rat (80.6%). A synthetic vZP3 peptide corresponding to amino acid residues 328-343 was conjugated to keyhole limpet hemocyanin (KLH-vZP3(328-343)) and used to immunise female Brandt's voles in order to test the efficacy of this peptide as a contraceptive antigen. High IgG antibody levels to the vZP3(328-343) peptide were present in the sera of female voles immunised with KLH-vZP3(328-343) and these also cross-reacted to the zona pellucida in ovaries of Brandt's vole. The fertility of the KLH-vZP3(328-343) -immunised voles was reduced by 50% compared with controls without evidence of significant ovarian pathology.

Development of canine herpesvirus based antifertility vaccines for foxes using bacterial artificial chromosomes

Using bacterial artificial chromosome (BAC) technology, a canine herpesvirus (CHV)-based recombinant vaccine vector was produced for the development of an antifertility vaccine for foxes. Infectious viruses were recovered following transfection of canid cells with a BAC plasmid carrying the complete CHV genome. In vitro growth characteristics of BAC-derived viruses were similar to that of wildtype (wt)-CHV. Two recombinant antigens, fox zona pellucida protein subunit 3 (fZPC) and enhanced green fluorescent protein (EGFP) as control antigen, were inserted into thymidine kinase (TK) locus of the CHV genome and shown to be efficiently expressed in vitro. Inoculation of foxes with transgenic CHVs induced CHV specific antibodies, but was innocuous and failed to elicit transgene-specific antibody responses. Infectious virus or viral DNA was not detected in mucosal secretions or tissues of vaccinated foxes. The CHV-BAC system proved to be a quick and reliable method to manipulate the CHV genome. It will help to readily apply changes in the vector design in order to improve virus replication in vivo.

Recent advances in contraceptive vaccine development: a mini-review

Contraceptive vaccines (CV) may provide viable and valuable alternatives to the presently available methods of contraception. The molecules that are being explored for CV development either target gamete production [luteinizing hormone-releasing hormone (LHRH)/GnRH, FSH], gamete function [sperm antigens and oocyte zona pellucida (ZP)], and gamete outcome (HCG). CV targeting gamete production have shown varied degrees of efficacy; however, they either affect sex steroids causing impotency and/or show only a partial rather than a complete effect in inhibiting gametogenesis. However, vaccines based on LHRH/GnRH are being developed by several pharmaceutical companies as substitutes for castration of domestic pets, farm and wild animals, and for therapeutic anticancer purposes such as in prostatic hypertrophy and carcinoma. These vaccines may also find applications in clinical situations that require the inhibition of increased secretions of sex steroids, such as in uterine fibroids, polycystic ovary syndrome, endometriosis and precocious puberty. CV targeting molecules involved in gamete function such as sperm antigens and ZP proteins are exciting choices. Sperm constitute the most promising and exciting target for CV. Several sperm-specific antigens have been delineated in several laboratories and are being actively explored for CV development. Studies are focused on delineating appropriate sperm-specific epitopes, and increasing the immunogenicity (specifically in the local genital tract) and efficacy on the vaccines. Anti-sperm antibody (ASA)-mediated immunoinfertility provides a naturally occurring model to indicate how a vaccine might work in humans. Vaccines based on ZP proteins are quite efficacious in producing contraceptive effects, but may induce oophoritis, affecting sex steroids. They are being successfully tested to control feral populations of dogs, deer, horses and elephants, and populations of several species of zoo animals. The current research for human applicability is focused on delineating infertility-related epitopes (B-cell epitopes) from oophoritis-inducing epitopes (T-cell epitopes). Vaccines targeting gamete outcome primarily focus on the HCG molecule. The HCG vaccine is the first vaccine to undergo Phase I and II clinical trials in humans. Both efficacy and lack of immunopathology have been reasonably well demonstrated for this vaccine. At the present time, studies are focused on increasing the immunogenicity and efficacy of the birth control vaccine, and examining its clinical applications in various HCG-producing cancers. The present article will focus on the current status of the anti-sperm, anti-ZP, anti-LHRH/GnRH and anti-HCG vaccines.

Experimental inoculation of European red foxes with recombinant vaccinia virus expressing zona pellucida C proteins

The antifertility potential of zona pellucida proteins was tested in European red foxes by immunizing females with recombinant vaccinia viruses that express zona pellucida subunit C proteins. The fox zona pellucida C (fZPC) protein was newly identified and isolated as a cDNA clone from fox ovary RNA. Eighteen European foxes were inoculated with the recombinant vaccinia viruses or with wildtype vaccinia virus (wtVV) and their clinical, virological and immune responses evaluated. Following intradermal inoculation with wtVV or recombinant vaccinia virus expressing fox zona pellucida C (rVV-fZPC), or after peroral administration with recombinant vaccinia virus expressing the porcine zona pellucida C protein (rVV-pZPC) clinical signs of disease were not observed. Five out of six foxes developed antibodies to wtVV proteins. However, none of 12 foxes (six inoculated intradermally with rVV-fZPC, six perorally with rVV-pZPC) reacted in immunoblots with the transgenic fZPC or pZPC, respectively. Infectious wtVV, rVV-fZPC or rVV-pZPC was not isolated from mucosal secretions of any of the foxes whereas viral DNA was present in oral swabs of 3/18 foxes as determined by PCR. Hematological parameters remained mostly unchanged. Histopathological changes were not observed in the ovaries of rVV-fZPC or wtVV inoculated foxes. The data indicate that inoculation of foxes with cell culture infectious wtVV, rVV-fZPC or rVV-pZPC did not result in production of infectious progeny virus in vivo. For this reason transgene expression may have been insufficient to induce adequate immune responses against the transgenic proteins.

EFFECTS OF PORCINE ZONA PELLUCIDA IMMUNOCONTRACEPTIVES IN ZOO FELIDS

Methods of contraception are necessary for management of zoo felids; however, the most commonly used contraceptive (melengestrol acetate implant) is associated with serious adverse reactions with long-term use. Porcine zona pellucida (pZP) vaccines are promising as contraceptives, but their safety in zoo felids has not been tested. pZP vaccine was administered to 27 female felids representing 10 species, including African lion (Panthera leo), Asian leopard (P. pardus), jaguar (P. onca), tiger (P. tigris), snow leopard (P. uncia), cougar (Felis concolor), Siberian lynx (F. lynx), Canada lynx (F. canadensis), serval (F. serval), and bobcat (F. rufus), in 15 facilities. Over 6 wk, each animal received three i.m. injections of 65 microg pZP with Freund's complete adjuvant (FCA), Freund's incomplete adjuvant, or carbopol as the adjuvant. Behavioral signs of estrus were seen in 14 of the vaccinated felids. An unacceptably high incidence of adverse reactions was seen including injection site swelling, lameness, limb swelling, or abscessation (or all) in five felids after injection with FCA as the initial adjuvant. Adverse behavioral signs, including increased irritability and aggression, were seen in four felids. Six of the felids were assayed for antibodies against pZP during the 12 mo after vaccination; all showed antibody production. Antibody levels appeared to peak 1-4 mo after vaccination began, although elevated antibody levels persisted in two animals for > 12 mo after the first injection. All vaccinated felids were ovariohysterectomized 3-13 mo after vaccination. Folliculogenesis was present in all treated animals, and there was no histopathologic evidence of inflammatory damage to ovaries. Contraceptive efficacy was not specifically evaluated in this study; however, two of the three felids housed with an intact male became pregnant during the study, one of which gave birth to healthy cubs.