Evaluation of infertility efficacy of the E. coli expressed STF2-GnRH vaccine in male cats

Male animal sterilization: history, current practices, and potential methods for replacing castration

Sterilization and castration have been synonyms for thousands of years. Making an animal sterile meant to render them incapable of producing offspring. Castration or the physical removal of the testes was discovered to be the most simple but reliable method for managing reproduction and sexual behavior in the male. Today, there continues to be global utilization of castration in domestic animals. More than six hundred million pigs are castrated every year, and surgical removal of testes in dogs and cats is a routine practice in veterinary medicine. However, modern biological research has extended the meaning of sterilization to include methods that spare testis removal and involve a variety of options, from chemical castration and immunocastration to various methods of vasectomy. This review begins with the history of sterilization, showing a direct link between its practice in man and animals. Then, it traces the evolution of concepts for inducing sterility, where research has overlapped with basic studies of reproductive hormones and the discovery of testicular toxicants, some of which serve as sterilizing agents in rodent pests. Finally, the most recent efforts to use the immune system and gene editing to block hormonal stimulation of testis function are discussed. As we respond to the crisis of animal overpopulation and strive for better animal welfare, these novel methods provide optimism for replacing surgical castration in some species.

Induction of immunocontraceptive effects in both male and female mice immunized with GnRH vaccine

Background

Gonadotropin‐releasing hormone (GnRH) plays a pivotal role in regulating the reproductive endocrine system.

Objective

An immunocontraception vaccine aimed at inhibiting the functions of GnRH is tested as a potential tool for controlling animal populations.

Methods

We developed a recombinant immunocontraceptive vaccine composed of GnRH‐I and GnRH‐II (GnRH I+II), which was conjugated with Salmonella typhimurium flagellin. Forty‐eight BALB/c mice aged 4 weeks were divided into four groups (each group had n = 12): non‐vaccinated male (NVM), non‐vaccinated female (NVF), vaccinated male (VM), and vaccinated female (VF). Mice in the vaccinated groups were vaccinated twice by intramuscular injection at 0 and 2 weeks with 300 μg of the recombinant GnRH protein complex per mouse. Mice in the non‐vaccinated groups were injected with saline and served as the unimmunized controls. Twenty‐four pairs of male and female mice were mated for 10–12 weeks after initial immunization in four groups: 6 NVF × 6 NVM, 6 VF × 6 NVM, 6 NVF × 6 VM, and 6 VF × 6 VM. Results: An increase (p < 0.001) in antibody titers in VM and VF mice was observed. The testosterone levels and the number of spermatocytes were lower (p < 0.001) in VM mice than those in the control mice. The progesterone levels and the number of corpora lutea were lower (p < 0.001) than those in the control mice. Mating results in both VM and VF mice confirmed a 60% reduction in pregnancy rates and offspring numbers.

Conclusions

The recombinant GnRH vaccine can be used for birth control in both male and female animals.

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.

Application of a high-quality, high-volume trap-neuter-return model of community cats in Seoul, Korea

Background

This study was performed to determine the characteristics of community cats that were admitted to trap–neuter–return(TNR) programs and the feasibility of the high-quality, high-volume spay/neuter (HQHVSN) model in Seoul, Korea.

Methods

TNR programs were performed eight times from 2017 to 2018, and a total of 375 community cats from the pilot areas were admitted. The pilot areas were selected regions wherein caregivers voluntarily participated in our TNR program. Each cat was anesthetized, assessed for health status, sterilized, vaccinated against feline viral rhinotracheitis, calicivirus and panleukopenia (FVR-CP), and rabies, and treated with insecticide after surgery. The time from anesthesia to recovery was evaluated to verify the efficiency of surgical time of the program. The TNR program at a local animal hospital and the program in this study were compared to assess the veterinary treatment administered and the cost for each cat.

Results

A total of 375 cats were underwent TNR in this study, including 192 (51.2%) intact females, 180 (48%) intact males, and three (0.8%) sterilized cats. Following surgery, 372 cats (99.2%) were returned to their original locations. Three cats (0.8%) died postoperatively. On average, 21.9% of the cats were pregnant during the TNRs, and the highest percentage of cats (63.9%) were pregnant in March. All cats presented to the TNR program were considered healthy enough to be part of the program after examination. For neutering one animal at a time, similar to conventional TNR ($140), it took 53 ± 16 mins for females and 30 ± 9 mins for males from anesthesia to recovery. In contrast, the standardized procedure can neuter multiple cats simultaneously, similar to the conveyor system, at an estimated rate of 6.8 mins per cat ($45 per female cat, $30 per male cat).

Conclusions

The TNR strategy in Seoul should be implemented by establishing dedicated clinics to concentrate on HQHVSN surgeries of cats. Through this pilot study, we were able to demonstrate that it is possible to effectively apply HQHVSN clinics in Korea. Future studies that perform intensive sterilization in targeted areas are necessary to confirm the efficacy of the TNR strategy.

Immunogenicity and contraceptive efficacy of recombinant fusion protein encompassing Sp17 spermatozoa-specific protein and GnRH: Relevance of adjuvants and microparticles based delivery to minimize number of injections

PROBLEM

Requirement of multiple injections of contraceptive vaccines to achieve infertility is one of the important impediments for their application. In the present study, attempts have been made to reduce the number of injections of contraceptive vaccine.

METHOD OF STUDY

Fusion protein encompassing C-terminus fragment of sperm protein Sp17 (aa residues 76-126) and two copies of gonadotropin-releasing hormone along with T-cell epitopes and dilysine linkers (abbreviated as Sp17_C -GnRH₂ ) was expressed in Escherichia coli. Its immunogenicity and contraceptive efficacy have been evaluated in female FVB/J mice using different adjuvants and delivery platforms.

RESULTS

Immunization of female mice with recombinant Sp17_C -GnRH₂ (25 μg/injection/mouse) emulsified with squalene-arlacel A following two injections schedule led to failure of 88.8% immunized animals to conceive, which was not significantly different from mice immunized with same protein along with alum following three injections schedule. To make single-dose vaccine, poly d,l-lactic acid-based microparticles (PLA-MPs) entrapping Sp17_C -GnRH₂ were prepared. Immunization of female mice with a combination of soluble Sp17_C -GnRH₂ (12.5 μg/injection/mouse) along with Sp17_C -GnRH₂ entrapped in PLA-MPs (12.5 μg/injection/mouse) in alum showed higher antibody titres and contraceptive efficacy as compared to mice immunized with Sp17_C -GnRH₂ entrapped in PLA-MPs alone in alum. Immunization with recombinant Sp17_C -GnRH₂ led to long-term infertility as second mating (150 days after immunization) of various groups of immunized mice showed similar infertility as observed during first mating.

CONCLUSION

Single-dose immunization with PLA-MPs entrapping Sp17_C -GnRH₂ along with soluble recombinant protein in alum generated long-lasting infertility in female mice.