Contraceptive vaccines targeting sperm

Identification of Arvicola terrestris scherman Sperm Antigens for Immune Contraceptive Purposes

The cyclical proliferation of the wild fossorial rodent Arvicola terrestris scherman (ATS) is critical in mid-mountain ecosystems of several European countries. Our goal is to develop an immunocontraceptive vaccine to control their fertility, as a sustainable alternative to chemical poisons currently used. Indeed, these chemicals cause the death of ATS predators and animals sharing their ecosystem, and current laws progressively limit their use, making the development of a targeted vaccination strategy an interesting and efficient alternative. In order to identify species-specific sperm antigens, male and female ATS received subcutaneous injections of whole ATS spermatozoa to elicit an immune response. The analysis of the immune sera led to the identification of 120 immunogenic proteins of sperm cells. Of these, 15 were strictly sperm-specific and located in different regions of the male gamete. Some of these antigens are proteins involved in molecular events essential to the reproductive process, such as sperm–egg interaction, acrosomal reaction, or sperm motility. This approach not only identified a panel of immunogenic proteins from ATS sperm cells, but also demonstrated that some of these proteins trigger an immune response in both male and female ATS. These spermatic antigens are good candidates for the development of a contraceptive vaccine.

Bioinformatic prediction of the structure and characteristics of human sperm acrosome membrane-associated protein 1 (hSAMP32) and evaluation of its antifertility function in vivo

Human sperm acrosome membrane-associated protein 1 (hSAMP32) plays an important role in the acrosome reaction, sperm-egg primary binding, secondary binding and fusion processes. However, its spatial structural and invivo antifertility function remain unknown. In this study, we first analysed the physical and chemical characteristics and antigenic epitopes of immunised mice using bioinformatics. Then, we constructed the prokaryotic expression vector pcDNA3.1-hSAMP32 to immunise BALB/c mice invivo. IgG antibodies in the serum were detected, and the litter size of female mice and the number of the hamster eggs penetrated were counted. hSAMP32 was found to contain six hydrophilic regions and a signal peptide beginning at amino acid position 29. The transmembrane region of hSAMP32 was located within amino acids 217-239 with α-helices and random coil structures. We predicted five antigenic epitopes. The molecular weight of hSAMP32 was 59 kDa. Moreover, the results of invivo studies revealed that 56 days after the first immunisation, the litter size was significantly smaller for female pcDNA-3.1(+)-hSAMP32-immunised (mean±s.d. 4.33±1.21) than control mice (9.50±0.55), indicating that the immunocontraception vaccine had an antifertility effect. This experiment presents a theoretical and experimental basis for in-depth study of the hSAMP32 mechanism within the sperm-egg fusing process and for the screening of antigenic epitopes with immunocontraceptive properties.

Concurrence of HOST to some conventional sperm quality parameters and seminal enzymes of Jersey bulls semen

In this study, hypoosmotic swelling test (HOST) was correlated with sperm quality such as motility, acrosome integrity, morphological abnormality and seminal enzymes including AST, ALT and ALP. Results revealed positive concurrence of HOS test to motility and acrosomal integrity and negative correlation between ALP and ALT in both the freezable and nonfreezable ejaculates. Since the HOS test is quick, easy and inexpensive method so it can be deployed as routine semen assessment procedure in semen stations to differentiate between the freezable and non-freezable bull semen.

In vitro study evaluating the instantaneous treatment of ozonised olive oil on human sperm

OBJECTIVE

The aim of our study was to evaluate the effects of ozonised olive oil (OOO) on human sperm in vitro.

METHODS

Human sperm was incubated with OOO for 20 s in vitro. The lowest concentration that completely immobilised all the sperm in 20 s without subsequent recovery of motility was recorded as the minimum effective concentration (MEC). The effects of OOO at MEC on human sperm viability, mitochondrial and acrosomal status, DNA integrity and transmission electron microscopy were observed.

RESULTS

Our findings demonstrate that OOO dose-dependently inhibits sperm motility. The MEC of OOO for 100% sperm immobilisation in 20 s was 6 μg/ml. Further experiments showed that sperm ultrastructure, function and DNA integrity were significantly affected after treatment with 6 μg/ml OOO in vitro.

CONCLUSIONS

OOO has spermicidal potential and may be explored as a promising vaginal contraceptive agent.

Prospects for immunocontraception in feral horse population control: exploring novel targets for an equine fertility vaccine

Feral horses populate vast land areas and often induce significant ecological and economic damage throughout the landscape. Non-lethal population control methods are considered favourable in light of animal welfare, social and ethical considerations; however, no single effective, safe and species-specific contraceptive agent is currently available for use in free-ranging wild and feral horses. This review explores aspects of equine reproductive physiology that may provide avenues for the development of specific and long-lasting immunocontraceptive vaccines and some of the novel strategies that may be employed to facilitate appropriate antigen discovery in future research. Potential antigen targets pertaining to spermatozoa, the ovary and oocyte, as well as the early conceptus and its associated factors, are reviewed in the context of their suitability for immunocontraceptive vaccine development.

Construction of a catsper1 DNA vaccine and its antifertility effect on male mice

Cation channel of sperm 1 (CATSPER1) is a unique sperm cation channel protein, and essential for sperm function and male fertility. CATSPER1 exclusively expresses in meiotic and postmeiotic spermatogenic cells, thus belongs to the spermatogenesis-specific antigen that escape central tolerance. We have previously demonstrated the immunocontraceptive potential of its transmembrane domains and pore region, and reported the antifertility effects of its B-cell epitopes on male mice. Aiming to develop DNA vaccine targeting CATSPER1 for male contraception, here the whole open reading frame of mouse Catsper1 was cloned into the plasmid pEGFP-N1 to obtain a DNA vaccine pEGFP-N1-Catsper1. The vaccine was confirmed to be transcribed and translated in mouse N2a cell in vitro and mouse muscle tissue in vivo. Intramuscular injection with the vaccine on male mice induced specific immune reaction and caused significant inhibition on sperm hyperactivated motility and progressive motility (P<0.001 for both), and consequently reduced male fertility. The fertility rate of experimental group was 40.9%, which was significant lower (P=0.012) than control group (81.8%). No significant change in mating behavior, sperm production and histology of testis/epididymis was observed. Given that Catsper1 exhibits a high degree of homology among different species, Catsper1 DNA vaccine might be a good strategy for developing an immunocontraceptive vaccine for human and animal use.

Antisperm antibodies: invaluable tools toward the identification of sperm proteins involved in fertilization

The identification of sperm proteins involved in fertilization has been the subject of numerous investigations. Much interest has been dedicated to naturally occurring antisperm antibodies (ASA) and their impact in fertility. Their presence in men and women has been associated with 2-50% of infertility cases. ASA may impair pre- and post-fertilization steps. Experimental models have been developed using sperm proteins as immunogens to evaluate their involvement in sperm function. Our team has pursued investigations to assess ASA presence in biological fluids from patients consulting for infertility and their effect on fertilization. We found ASA in follicular fluids with ability of inducing the acrosome reaction and blocking sperm-zona pellucida interaction and used them to identify sperm entities involved in these events. We generated and utilized antibodies against proacrosin/acrosin to characterize the sperm protease system. We implemented an ELISA to detect proacrosin/acrosin antibodies in human sera and evaluated their impact upon fertility by developing in vitro assays and a gene immunization model. This review presents a summary of ASA history, etiology, current approaches for detection and effects upon fertility. ASA (naturally occurring, generated by animal immunization and/or of commercial origin) are invaluable tools to understand the molecular basis of fertilization, better diagnose/treat immunoinfertility and develop immunocontraceptive methods.

In vitro effects of nicotine on human spermatozoa

Washed human spermatozoa from 12 normozoospermic donors were treated with different concentrations of nicotine 0.1, 1.0, 5.0 and 10.0 mm and were compared to spermatozoa suspended in nutrient medium only (control). Computer-aided sperm analysis was used to assess sperm kinematic properties after 30, 60, 120 and 180 min of incubation. Viability was assessed by means of a dye exclusion staining technique (eosin/nigrosin), while acrosome-reacted cells were identified under a fluorescent microscope using fluorescein isothiocyanate-Pisum sativum agglutinin as a probe. Nicotine significantly reduced total motility, progressive motility, curvilinear velocity, amplitude of lateral head displacement, beat cross-frequency, viability and caused spontaneous acrosome reaction at concentrations of ≥5.0 mm after 2 and 3 h of exposure. Nicotine concentrations of 0.1 and 1.0 mm had no significant effect (P < 0.05) on spermatozoa except that 1.0 mm significantly decreased (P < 0.05) sperm progressive motility at 2 and 3 h of incubation as well as viability after 3 h of incubation. This study concludes that the occurrence of high levels of nicotine in the body and seminal fluid might adversely affect fertilisation capacity of human spermatozoa through a mechanism that involves decreased motility, viability and premature induction of the acrosome reaction.

A-kinase anchoring proteins as potential drug targets

A-kinase anchoring proteins (AKAPs) crucially contribute to the spatial and temporal control of cellular signalling. They directly interact with a variety of protein binding partners and cellular constituents, thereby directing pools of signalling components to defined locales. In particular, AKAPs mediate compartmentalization of cAMP signalling. Alterations in AKAP expression and their interactions are associated with or cause diseases including chronic heart failure, various cancers and disorders of the immune system such as HIV. A number of cellular dysfunctions result from mutations of specific AKAPs. The link between malfunctions of single AKAP complexes and a disease makes AKAPs and their interactions interesting targets for the development of novel drugs. LINKED ARTICLES This article is part of a themed section on Novel cAMP Signalling Paradigms. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2012.166.issue-2.

The blood-testis barrier and its implications for male contraception

The blood-testis barrier (BTB) is one of the tightest blood-tissue barriers in the mammalian body. It divides the seminiferous epithelium into the basal and the apical (adluminal) compartments. Meiosis I and II, spermiogenesis, and spermiation all take place in a specialized microenvironment behind the BTB in the apical compartment, but spermatogonial renewal and differentiation and cell cycle progression up to the preleptotene spermatocyte stage take place outside of the BTB in the basal compartment of the epithelium. However, the BTB is not a static ultrastructure. Instead, it undergoes extensive restructuring during the seminiferous epithelial cycle of spermatogenesis at stage VIII to allow the transit of preleptotene spermatocytes at the BTB. Yet the immunological barrier conferred by the BTB cannot be compromised, even transiently, during the epithelial cycle to avoid the production of antibodies against meiotic and postmeiotic germ cells. Studies have demonstrated that some unlikely partners, namely adhesion protein complexes (e.g., occludin-ZO-1, N-cadherin-β-catenin, claudin-5-ZO-1), steroids (e.g., testosterone, estradiol-17β), nonreceptor protein kinases (e.g., focal adhesion kinase, c-Src, c-Yes), polarity proteins (e.g., PAR6, Cdc42, 14-3-3), endocytic vesicle proteins (e.g., clathrin, caveolin, dynamin 2), and actin regulatory proteins (e.g., Eps8, Arp2/3 complex), are working together, apparently under the overall influence of cytokines (e.g., transforming growth factor-β3, tumor necrosis factor-α, interleukin-1α). In short, a "new" BTB is created behind spermatocytes in transit while the "old" BTB above transiting cells undergoes timely degeneration, so that the immunological barrier can be maintained while spermatocytes are traversing the BTB. We also discuss recent findings regarding the molecular mechanisms by which environmental toxicants (e.g., cadmium, bisphenol A) induce testicular injury via their initial actions at the BTB to elicit subsequent damage to germ-cell adhesion, thereby leading to germ-cell loss, reduced sperm count, and male infertility or subfertility. Moreover, we also critically evaluate findings in the field regarding studies on drug transporters in the testis and discuss how these influx and efflux pumps regulate the entry of potential nonhormonal male contraceptives to the apical compartment to exert their effects. Collectively, these findings illustrate multiple potential targets are present at the BTB for innovative contraceptive development and for better delivery of drugs to alleviate toxicant-induced reproductive dysfunction in men.

ZP-binding peptides identified via phage display stimulate production of sperm antibodies in dogs

Zona pellucida (ZP) glycoproteins play a central role in sperm-oocyte binding and fertilization. Sperm protein sequences that are involved in sperm-ZP recognition and have an important role in fertilization represent attractive targets for development of contraceptive vaccines, yet are currently unknown. To identify peptide sequences that recognize and bind to ZP proteins, we developed a novel selection procedure from phage display libraries that utilizes intact oocytes surrounded by ZP proteins. The major advantage of this procedure is that ZP proteins remain in their native conformation unlike a selection protocol previously published that utilized solubilized ZP on artificial solid support. Several peptides of 7 and 12 amino acids with binding specificity to canine ZP proteins were identified. Four of them (LNSFLRS, SSWYRGA, YLPIYTIPSMVY, and NNQSPILKLSIH) plus a control ZP-binding peptide (YLPVGGLRRIGG) from the literature were synthesized and tested for antigenic properties in dogs. NNQSPILKLSIH peptide stimulated production of anti-peptide antibodies. These antibodies bind to the acrosomal region of the canine sperm cell, demonstrating ability to act as sperm antibodies. The identified ZP-binding peptides (mimicking sperm cell surface antigens) may be useful in the design of immunocontraceptive agents for dogs.

Delivering non-hormonal contraceptives to men: advances and obstacles

There have been major advances in male contraceptive research during the past two decades. However, for a contraceptive to be used by men, its safety requires more stringent scrutiny than therapeutic compounds for treatment of illnesses because the contraceptives will be used by healthy individuals for an extended period of time, perhaps decades. A wide margin is therefore required between the effective dose range and doses that cause toxicity. It might be preferable that a male contraceptive, in particular a non-hormone-based compound, is delivered specifically and/or directly to the testis and has a rapid metabolic clearance rate, reducing the length of exposure in the liver and kidney. In this article, we highlight the latest developments regarding contraceptive delivery to men and with the aim of providing useful information for investigators in future studies.

Evaluation of acrosomal status and sperm viability in fresh and cryopreserved specimens by the use of fluorescent peanut agglutinin lectin in conjunction with hypo-osmotic swelling test

OBJECTIVE

In this study, we evaluated whether the hypo-osmotic swelling test (HOST) can be used as a vital marker in combination with peanut agglutinin (PNA) - labeling in fresh and cryopreserved spermatozoa.

MATERIALS AND METHODS

Human sperm populations were exposed to a hypo-osmotic medium for 60 minutes, and then incubated in a 1 microg/mL solution of the fluorescent dye Hoescht 33258 (H33258) for 10 minutes. Excess stain was removed by washing in phosphate-buffered saline (PBS) solution, and the pellet was resuspended in 100 microL of culture medium. Twenty microliters of this solution were subsequently smeared on a microscope slide, and fixed in ice-cold methanol to permeabilize the sperm membranes. The fixed smears were finally incubated in a 40-microg/mL FITC-PNA solution for 20 minutes. Simultaneous assessment of acrosome and viability scores was done in a fluorescent microscope equipped with appropriate filters and phase contrast illumination. The same slide was examined for FITC-PNA labeling, tail swelling, and for Hoechst-33258 staining by interchanging the filters and phase contrast optics.

RESULTS

In fresh specimens, HOST was found to provide viability assessments comparable to those obtained using the H33258 method (r = 0.95). However, the results of HOST and H33258 were not correlated in cryopreserved specimens (r = 0.22). There was no alteration of PNA-labeling due to the HOST or H33258.

CONCLUSIONS

FITC-PNA labeling in conjunction with the visualization of the morphological change induced by exposure to hypo-osmotic solution provides a simple but effective method for establishing the state of acrosomal membrane and viability in fresh human spermatozoa, but this technique is not reliable for cryopreserved ones.

Evolutionary diversification of SPANX-N sperm protein gene structure and expression

The sperm protein associated with nucleus in the X chromosome (SPANX) genes cluster at Xq27 in two subfamilies, SPANX-A/D and SPANX-N. SPANX-A/D is specific for hominoids and is fairly well characterized. The SPANX-N gave rise to SPANX-A/D in the hominoid lineage ∼7 MYA. Given the proposed role of SPANX genes in spermatogenesis, we have extended studies to SPANX-N gene evolution, variation, regulation of expression, and intra-sperm localization. By immunofluorescence analysis, SPANX-N proteins are localized in post-meiotic spermatids exclusively, like SPANX-A/D. But in contrast to SPANX-A/D, SPANX-N are found in all ejaculated spermatozoa rather than only in a subpopulation, are localized in the acrosome rather than in the nuclear envelope, and are expressed at a low level in several nongametogenic adult tissues as well as many cancers. Presence of a binding site for CTCF and its testis-specific paralogue BORIS in the SPANX promoters suggests, by analogy to MAGE-A1 and NY-ESO-1, that their activation in spermatogenesis is mediated by the programmed replacement of CTCF by BORIS. Based on the relative density of CpG, the more extended expression of SPANX-N compared to SPANX-A/D in nongametogenic tissues is likely attributed to differences in promoter methylation. Our findings suggest that the recent duplication of SPANX genes in hominoids was accompanied by different localization of SPANX-N proteins in post-meiotic sperm and additional expression in several nongonadal tissues. This suggests a corresponding functional diversification of SPANX gene families in hominoids. SPANX proteins thus provide unique targets to investigate their roles in the function of spermatozoa, selected malignancies, and for SPANX-N, in other tissues as well.

Immunization with autologous CD46 generates a strong autoantibody response in rats that targets spermatozoa

CD46, a membrane complement regulator, has been implicated as pathogen receptor, T cell activator and contributor to spermatozoa-egg interactions. In man, a role in the fertilization process was suggested by its localization on the acrosome. In rodents, CD46 is expressed only on the spermatozoal acrosome, suggesting an essential role at this site. This restricted expression led us to ask whether immunization with CD46 would generate anti-CD46 antibody responses that might target spermatozoa and influence fertility. We immunized male and female rats with rat CD46. Strong immune responses were generated in all rats and immune sera stained CD46 in testis extracts and in situ in testis and sperm. Incubation of spermatozoa with immune sera caused deposition of immunoglobulin and C3b in an acrosome pattern and reduced motility. We mated immune male rats with naïve females and female immune rats with naïve males. The incidence of pregnancy and number of fetuses were not different in matings involving immune male or female rats compared to controls. Testis sections from immune rats revealed no immunoglobulin deposition on CD46-positive sperm precursors, suggesting that acrosomal CD46 was inaccessible in this location. A minority of spermatozoa harvested from epididymis of immune rats had immunoglobulin and C3b bound to the acrosome, suggesting that anti-CD46, present in genital tract fluids, bound after acrosome reaction. These data demonstrate that the restricted expression of CD46 allows strong anti-CD46 responses in rats that target spermatozoa in vitro and in vivo. The anti-CD46 response did not influence fertility, perhaps reflecting the considerable redundancy for fertilization in rodents.

Prospects for immunocontraception in the European red fox (Vulpes vulpes)

The European red fox is an introduced pest species in Australia for which improved means of control are urgently needed. Research efforts have focussed recently on the development of novel biological control methods to reduce the serious impact this species continues to have on both native fauna and the sheep industry. The ultimate goal has been to generate an antifertility vaccine for use on foxes that relies on a process termed ‘immunocontraception’. A variety of proteins derived from sperm and oocytes, together with different delivery vectors, have been experimentally assessed for their ability to induce immunocontraceptive responses in foxes. Vaccine vectors screened have included Salmonella typhimurium, vaccinia virus and canine herpesvirus but suppression of fertility has yet to be achieved with any combination of antigen and delivery vector. Downregulation of fox mucosal antibodies during oestrus, lack of vector replication and low antibody responses to the target antigens have been the main constraints in successful fertility control. The fox is not well known as an experimental animal and the logistics of dealing with this difficult-to-handle species proved to be a major challenge when compared with other species, such as rabbits and mice. Despite these difficulties, research on fox immunocontraception has generated important insights into the reproductive biology, husbandry, biology and basic immunology of viral vectors in European red foxes. This information represents a valuable knowledge base should antifertility vaccination for foxes be revisited in the future.

Biological control of vertebrate pests using virally vectored immunocontraception

Species-specific viruses are being genetically engineered to produce contraceptive biological controls for pest animals such as mice, rabbits and foxes. The virus vaccines are intended to trigger an autoimmune response in the target animals that interferes with their fertility in a process termed virally vectored immunocontraception. Laboratory experiments have shown that high levels of infertility can be induced in mice infected with recombinant murine cytomegalovirus and ectromelia virus expressing reproductive antigens as well as in rabbits using myxoma virus vectors. The strategies used to produce and deliver species-specific immunocontraceptive vaccines to free-living wildlife are presented in this review. Discussion includes coverage of the likely safety of the proposed vaccines as well as the implications of the approach for fertility control in other species.

Immunogenicity study of recombinant human sperm-associated antigen 9 in bonnet macaque (Macaca radiata)

BACKGROUND

The human sperm-associated antigen 9 (hSPAG9) is of special interest attributing to the findings indicating that SPAG9 is an acrosomal molecule. SPAG9 is not only restricted to acrosomal compartment but also persists in equatorial segment post-acrosome reaction, which is a key location in sperm-egg interaction.

METHODS AND RESULTS

Immunogenicity studies in macaques were carried out with recombinant hSPAG9 (rhSPAG9) adsorbed on alum, which resulted in high titres of anti-rhSPAG9 antibodies as determined by enzyme-linked immunosorbent assay (ELISA). Immunoblotting analysis employing anti-rhSPAG9 antibodies generated in monkeys indicated that antibodies specifically reacted with native SPAG9 from macaque and human sperm and rhSPAG9 protein. Furthermore, indirect immunofluorescence experiments demonstrated SPAG9 localization in the acrosomal compartment of macaque and human sperm. In addition, monkey antibodies against rhSPAG9 significantly inhibited the human spermatozoa adherence or penetration in zona-free hamster oocytes.

CONCLUSION

These results demonstrate that rhSPAG9 adsorbed on alum is highly immunogenic in subhuman primate model and therefore represents a suitable sperm-based vaccine immunogen for fertility trials in macaque.

Immunisation of the male tammar wallaby (Macropus eugenii) with spermatozoa elicits epididymal antigen-specific antibody secretion and compromised fertilisation rate

Immunocontraception has been proposed as an effective and humane means of controlling overabundant kangaroo populations in Australia. We have examined the feasibility of using a sperm-based vaccine for this purpose using a model macropod species, the tammar wallaby (Macropus eugenii). This study has demonstrated immunocontraception in a marsupial species following immunisation of males with homologous spermatozoa. Serum anti-sperm IgG titres were associated with a significant reduction in fertilisation rates following mating with superovulated female wallabies. Antigen-specific IgG penetrated the reproductive tract at the rete testis and bound spermatozoa in vivo. IgG was detected bound to the acrosome and midpiece regions of both epididymal and ejaculated spermatozoa. The absence of adverse testicular pathology and sperm movement effects suggests that contraception may have been achieved by antibody-mediated blocking of sperm surface antigens essential for fertilisation. This study demonstrates that a contraceptive vaccine targeting sperm antigens has potential for fertility control in male macropods.

Small interference RNA-mediated knockdown of sperm associated antigen 9 having structural homology with c-Jun N-terminal kinase-interacting protein

Recently, we reported a novel testis-specific sperm associated antigen 9 (SPAG9) protein, a new member of the JNK-interacting protein family, having a functional role in sperm-egg fusion [N. Jagadish, R. Rana, R. Selvi, D. Mishra, M. Garg, S. Yadav, J.C. Herr, K. Okumura, A. Hasegawa, K. Koyama, A. Suri, Biochem. J. 389 (2005) 73-82]. NCBI Blast searches revealed SPAG9 nucleotide sequence similarities with ESTs of various cancerous tissues. In the present study, we compared the efficiency of two independent SPAG9 specific small interfering RNA (siRNA) constructs, BS/U6/spag9 and BS/U6/spag9-I, to ablate the SPAG9 expression in mammalian cells. A positive correlation between the ratio of target gene versus siRNA and the suppression of SPAG9 expression was observed. Further, the cotransfection of BS/U6/spag9 with pcDNA-SPAG9 and pFlag-CMV2-JNK-3 resulted in specific suppression of SPAG9 without affecting JNK-3 expression. The present investigation will eventually extend the application of SPAG9 siRNA in in vivo targeting experiments that aim to define the SPAG9 functional genomics in tumor and reproductive biology.

Immunogenicity and contraceptive potential of recombinant human sperm associated antigen (SPAG9)

Human sperm-associated antigen 9 (hSPAG9) is a potential target for sperm-based contraceptive vaccine in lieu of its location on the sperm acrosomal compartment and its implication in sperm-egg interaction. SPAG9 is an acrosomal molecule which is not only restricted to a specific region (domain) of the acrosome but also undergoes relocation to the equatorial region in a stage-specific manner during acrosome reaction, demonstrating its potential role in sperm-egg binding. Human SPAG9 nucleotide sequence revealed 94% identity with macaque SPAG9 and 96.8% with baboon SPAG9 over the entire sequence. The amino acid sequence comparison of human SPAG9 with macaque and baboon revealed an overall homology of 84.9% and 90.6%, respectively. The presence of a high level of homology at the amino acid and nucleotide levels indicates that SPAG9 is conserved in macaque, baboon and human sharing common function and common origin in the biological past. Immunogenicity studies were carried in rats, which demonstrated that recombinant hSPAG9 protein adsorbed on alum is highly immunogenic. Antibodies thus generated after immunization reacted with recombinant human SPAG9 (rhSPAG9) and native SPAG9 protein from human sperm in Western blot analysis. In an in vitro assay, anti-rhSPAG9 antibodies inhibited sperm adherence to or penetration in zona-free hamster egg penetration test. Further, anti-SPAG9 antibodies inhibited the binding of human sperm to intact human oocyte as well as to matched hemi-zonae, indicating that the recombinant protein is a suitable contraceptive vaccinogen. Together these results demonstrate that the rhSPAG9 adsorbed on alum is immunogenic in nature, which is a permissible adjuvant for immunogenicity and fertility trials in non-human primates.