Vaccines for immunological control of fertility

Single neonatal estrogen implant sterilizes female animals by decreasing hypothalamic KISS1 expression

Reproductive sterilization by surgical gonadectomy is strongly advocated to help manage animal populations, especially domesticated pets, and to prevent reproductive behaviors and diseases. This study explored the use of a single-injection method to induce sterility in female animals as an alternative to surgical ovariohysterectomy. The idea was based on our recent finding that repetitive daily injection of estrogen into neonatal rats disrupted hypothalamic expression of Kisspeptin (KISS1), the neuropeptide that triggers and regulates pulsatile secretion of GnRH. Neonatal female rats were dosed with estradiol benzoate (EB) either by daily injections for 11 days or by subcutaneous implantation of an EB-containing silicone capsule designed to release EB over 2-3 weeks. Rats treated by either method did not exhibit estrous cyclicity, were anovulatory, and became infertile. The EB-treated rats had fewer hypothalamic Kisspeptin neurons, but the GnRH-LH axis remained responsive to Kisspeptin stimulation. Because it would be desirable to use a biodegradable carrier that is also easier to handle, an injectable EB carrier was developed from PLGA microspheres to provide pharmacokinetics comparable to the EB-containing silicone capsule. A single neonatal injection of EB-microspheres at an equivalent dosage resulted in sterility in the female rat. In neonatal female Beagle dogs, implantation of an EB-containing silicone capsule also reduced ovarian follicle development and significantly inhibited KISS1 expression in the hypothalamus. None of the treatments produced any concerning health effects, other than infertility. Therefore, further development of this technology for sterilization in domestic female animals, such as dogs and cats is worthy of investigation.

Researching immunocontraceptive vaccines with mares (Equus caballus) as both a target and model for African elephant (Loxodonta africana) cows: A review

A sequence of studies is reviewed that reported the domestic horse (Equus caballus) mare as an appropriate and accessible research platform for recording clinical and laboratory data post-immunisation with anti- GnRH and -zona pellucida (ZP) immunocontraceptive vaccines. Experience with a native porcine ZP (pZP) vaccine in African elephant (Loxodonta africana) cows highlighted needs for improving vaccine formulations and more clearly defining associated ovarian effects and safety profiles. Initially, the efficacy, reversibility and safety of the GnRH vaccine Improvac^® in mares was demonstrated using reproductive tract ultrasonography and concurrently measuring serum antibody titres and progesterone concentrations. Results informed the study design and minimally invasive monitoring of post-treatment ovarian steroid responses of this vaccine in free-ranging African elephant cows. A subsequent sequence of studies reported reversible contraceptive and immunological efficacy in pony mares immunised with pZP formulated with Freund's adjuvants. By comparison, mares treated with a recombinant ZP3 and ZP4 (reZP) vaccine showed disappointing responses. Unexpectedly, most pZP-treated mares showed ovarian inactivity. In attempting to understand this response, results showed the involvement of cytotoxic (CD8+) T-cells negatively correlated to serum ovarian steroid and anti-Müllerian hormone (AMH) levels. Of concern was the prevalence of injection-site lesions ascribable to Freund's adjuvants. Following this, mares treated with both pZP and a novel reZP vaccine formulated with non-Freund's adjuvants showed comparable immunological responses and ovarian inactivity, notably without adverse treatment reactions. In addition, measuring AMH showed promise for monitoring ovarian function in anti-ZP-treated animals.

Non-surgical sterilisation methods may offer a sustainable solution to feral horse (Equus caballus) overpopulation

Feral horses are a significant pest species in many parts of the world, contributing to land erosion, weed dispersal and the loss of native flora and fauna. There is an urgent need to modify feral horse management strategies to achieve public acceptance and long-term population control. One way to achieve this is by using non-surgical methods of sterilisation, which are suitable in the context of this mobile and long-lived species. In this review we consider the benefits of implementing novel mechanisms designed to elicit a state of permanent sterility (including redox cycling to generate oxidative stress in the gonad, random peptide phage display to target non-renewable germ cells and the generation of autoantibodies against proteins essential for conception via covalent modification) compared with that of traditional immunocontraceptive approaches. The need for a better understanding of mare folliculogenesis and conception factors, including maternal recognition of pregnancy, is also reviewed because they hold considerable potential in providing a non-surgical mechanism for sterilisation. In conclusion, the authors contend that non-surgical measures that are single shot and irreversible may provide a sustainable and effective strategy for feral horse control.

Production of tag-free recombinant fusion protein encompassing promiscuous T cell epitope of tetanus toxoid and dog zona pellucida glycoprotein-3 for contraceptive vaccine development

Affinity tags can interfere in various physicochemical properties and immunogenicity of the recombinant proteins. In the present study, tag-free recombinant fusion protein encompassing promiscuous T cell epitope of tetanus toxoid [TT; amino acid (aa) residues 830-844] followed by dilysine linker and dog zona pellucida glycoprotein-3 (ZP3; aa residues 23-348) (TT-KK-ZP3) was expressed in Escherichia coli. The recombinant protein, expressed as inclusion bodies (IBs), was purified by isolation of IBs, processed to remove host cell proteins, followed by solubilization and refolding. A specific 39 kDa protein including ZP3 was identified by SDS-PAGE. CD spectra showed the presence of α-helices and β-sheets, and fluorescent spectroscopy revealed emission maxima of 265 A.U. at 339 nm for refolded protein and showed red shift in the presence of 6 M guanidine hydrochloride. Immunization of inbred FvB/J female mice with purified recombinant TT-KK-ZP3 (25 μg/animal) led to generation of high antibody titers against the recombinant protein. The antibodies reacted specifically with ZP matrix surrounding mouse oocytes. Immunized mice showed significant reduction in fertility as compared to the control group. The studies described herein provide a simple method to produce and purify tag-free recombinant protein for the development of a contraceptive vaccine.

Mapping of minimal motifs of B-cell epitopes on human zona pellucida glycoprotein-3

The human zona pellucida glycoprotein-3 (hZP3) by virtue of its critical role during fertilization has been proposed as a promising candidate antigen to develop a contraceptive vaccine. In this direction, it is imperative to map minimal motifs of the B cell epitopes (BCEs) so as to avoid ZP-specific oophoritogenic T cell epitopes (TCEs) in the ZP3-based immunogens. In this study, based on known results of mapping marmoset and bonnet monkey ZP3 (mstZP3 and bmZP3), two predictable epitopes^{23–30  and  301–320} on hZP3 were first confirmed and five minimal motifs within four epitopes on hZP3 were defined using serum to recombinant hZP3a^22–176 or hZP3b^177–348 as well as a biosynthetic peptide strategy. These defined minimal motifs were QPLWLL^23–28 for hZP3^23–30, MQVTDD^103–108 for hZP3^93–110, EENW^178–181 for hZP3^172–190, as well as SNSWF^306–310 and EGP^313–315 for hZP3^301–320, respectively. Furthermore, the antigenicity of two peptides for hZP3^172–187 and hZP3^301–315 and specificity of the antibody response to these peptides were also evaluated, which produced high-titer antibodies in immunized animals that were capable of reacting to ZP on human oocytes, r-hZP3b^177–348 protein, as well as r-hZP3^172–190, r-hZP3^303–310, and r-hZP3^313–320 epitope peptides fused with truncated GST188 protein.

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.