A chimeric sperm peptide induces antibodies and strain-specific reversible infertility in mice

A mouse testis serine protease, TESP1, as the potential SPINK3 receptor protein on mouse sperm acrosome

Serine protease inhibitor Kazal type 3 (SPINK3) from mouse seminal vesicles is a Kazal-type trypsin inhibitor. It has been shown to bind to the sperm acrosome and modify sperm activity by influencing the sub-cellular Ca2+ influx. Previously, SPINK3 was reported to suppress in vitro sperm capacitation. However, under natural coitus, SPINK3 is removed from the mouse acrosome in the female reproductive tract, leading to successful fertilisation. Identification of the SPINK3 binding partner becomes essential to develop a contraceptive that works by prolonging the binding of SPINK3 to the sperm acrosome. We identified the SPINK3 receptor by using recombinant SPINK3 (rSPINK3). Testicular serine protease 1 (TESP1) was identified as the receptor for SPINK3 by 2D gel electrophoresis coupled with western blot analysis. To authenticate TESP1 as the receptor for SPINK3, sperm cells were incubated with TESP1 peptide antibody followed by determining the intracellular [Ca2+]i concentration by flow cytometry using Fluo-3 AM as a calcium probe. Furthermore, the 3D structures of SPINK3 and TESP1 were predicted by homology modelling (Schrodinger suite) using the crystal structure of pancreatic secretory trypsin inhibitor (PDB ID-1TGS) and human prostasin (PDB ID-3DFJ) as templates. The modelled protein structures were validated and subjected to molecular dynamics simulation (MDS) using GROMACS v5.0.5. Protein-protein docking was performed using HDOCK and the complex was validated by MDS. The results predicted that SPINK3 and TESP1 had strong binding affinity, with a dock score of -430.70 and 14 hydrogen bonds as key active site residues. If the binding affinity between SPINK3 and TESP1 could be increased, the SPINK3-TESP1 association will be prolonged, which will be helpful in the development of a male contraceptive.

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.

Vaccination with an Epitope Peptide of IZUMO1 to Induce Contraception in Female Mice

PROBLEM

The development of a new and suitable contraceptive methods, as well as in-depth and systematic research into underlying contraceptive mechanisms, is crucial. IZUMO1 plays an important role in the fusion of the sperm and ovum during fertilization. Izumo(-/-) mice are infertile. Therefore, IZUMO1 may be a potential target for the development of a contraceptive vaccine.

METHOD OF STUDY

Linear B-cell epitopes (BCE) were identified in IZUMO using biosynthetic peptides and used to immunize female mice.

RESULTS

Five IZUMO BCE were identified: DLVLDCL177-183, YSFYRV196-201 (named BCE-2), YLT217-219, SMVGPED221-227, and DAGNY228-232. Active immunization with the BCE-2 vaccine sharply decreased the fertility rate in female mice in a safe and reversible manner. In vitro fertilization showed that the BCE-2 vaccine interferes with and blocks the fusion of the sperm and the ovum.

CONCLUSIONS

B-cell epitopes-2 may be a new candidate for the development of contraceptive vaccine due to its effectiveness, safety, and reversibility.

Immunocontraceptives: How far from reality?

Despite high expectations of safer, effective, economical, longer acting contraceptives, to date, there are no licensed contraceptive vaccines available in the market. Nevertheless, a role for vaccines undoubtedly exists as an aid to birth spacing and as a nonsurgical means of generating sterility. The research concerned in the area so far has been successful on the feline population, with room still for exhaustive studies on humans. The future of contraceptive vaccines holds great promise in terms of comfort, price, efficacy, rare complications, and possibly nonselective action on animal populations as well as on humans. This brief review deals with the basic aspects of immunocontraceptives along with the efforts done so far. There is a need for further research in aspects involving the rate of evolution of contraception resistance based on genetics, resistance phenotypes, or cross generation effects. Gonadotropin-releasing hormone and luteinizing-hormone have not been investigated in humans, as both reported impotency in animals; the follicle-stimulating hormone has been shown to cause oligospermia; zona pellucida has also not been studied in humans as it causes irreversible oophoritis, while the sperm has the potential for success in humans based on the data from immunoreproductive studies. Even as the position of the human chorionic gonadotropin vaccine looks hopeful, research on other possible targets continue with an eventual aim of discovering a vaccine that is more immunogenically effective.

Fertility control in wildlife: review of current status, including novel and future technologies

Overpopulation of selected groups of animals is widely recognised as an issue that can have adverse effects on several current global problems, such as animal and human health, conservation and environmental changes. This review will, therefore, focus on recent novel contraception together with future technologies that may provide additional contraceptive methods.

Milestones in contraceptive vaccines development and hurdles in their application

Contraceptive vaccines have been proposed for controlling the growing human population and wildlife population management. Multiple targets such as gonadotropin releasing hormone (GnRH), luteinizing hormone, follicle stimulating hormone, gonadotropin receptors, sperm-specific proteins and zona pellucida glycoproteins have been exploited to develop contraceptive vaccine and their efficacy investigated and shown in various experimental animal models. Vaccines based on GnRH have found application in immuno-castration of male pigs for prevention of boar-taint. Vaccines based on zona pellucida glycoproteins have shown promising results for population management of wild horses and white-tailed deer. Phase II clinical trials in women with β-human chorionic gonadotropin (β-hCG)-based contraceptive vaccine established proof of principle that these can be developed for human application. Block in fertility by β-hCG contraceptive vaccine was reversible. Further research inputs are required to establish the safety of contraceptive vaccines, improve their immunogenicity and to develop novel vaccine delivery platforms for providing long lasting immunity.

Phage display--a powerful technique for immunotherapy: 2. Vaccine delivery

Phage display is a powerful technique in medical and health biotechnology. This technology has led to formation of antibody libraries and has provided techniques for fast and efficient search of these libraries. The phage display technique has been used in studying the protein-protein or protein-ligand interactions, constructing of the antibody and antibody fragments and improving the affinity of proteins to receptors. Recently phage display has been widely used to study immunization process, develop novel vaccines and investigate allergen-antibody interactions. This technology can provide new tools for protection against viral, fungal and bacterial infections. It may become a valuable tool in cancer therapies, abuse and allergies treatment. This review presents the recent advancements in diagnostic and therapeutic applications of phage display. In particular the applicability of this technology to study the immunization process, construction of new vaccines and development of safer and more efficient delivery strategies has been described.

Immunization with ovarian autoantigens leads to reduced fertility in mice following follicular dysfunction

Immunoproteomics using sera of women with ovarian autoimmune diseases such as primary ovarian insufficiency and IVF embryo transfer recruits led to identification of three proteins namely alpha actinin 4 (α-ACTN4), heat-shock 70 protein 5 (HSPA5), and actin beta (ACTB). This study deals with the establishment of a peptide ELISA for screening sera of antiovarian antibody (AOA)-positive patients and further delves into understanding the role of these three proteins in ovarian autoimmunity in a mouse model. Using in silico approach, antigenic peptides of these proteins were identified and used for peptide ELISA. ELISA results indicated that AOA-positive sera showed reactivity with only specific peptides. The functional significance of the dominant peptides was studied by active immunization of female mice with these peptides. All immunized mice generated high antibody titers and profound effect on ovaries with few primordial (2.4±0.1, 2.4±0.2, and 2±0.1), primary (2.4±0.5, 1.7±0.3, and 2.4±0.3), preantral (2.3±0.5, 3.4±0.3, and 2.9±0.3), antral (0.9±0.2, 1.6±0.8, and 2.3±0.6) follicles, and corpora lutea (2.8±0.8, 2.9±1.7, and 4.6±2.3), and increased number of atretic follicles (5.5±0.4, 4.9±1.8, and 7.5±1.0) in ACTN4-, HSPA5-, and ACTB-immunized mice compared with control animals (3.0±0.2, 3.5±0.6, 3±0.1, 3.6±0.2, 4.7±0.3, and 1.5±0.3) respectively. These mice when mated with fertile male mice showed an overall 25–43% reduction in fertility compared with controls. The data clearly suggest that the dominant antigenic epitopes of the three proteins play critical role in fertility and could possibly be the key autoimmune targets. These epitopes could be used to develop a more specific and sensitive diagnostic test for women with ovarian autoimmune diseases and to design therapy for disease management for reinstatement of ovarian function.

Induction of specific immune response and suppression of fertility by B-cell-epitope-based mimovirus vaccine

SPINLW1 (previously known as eppin (epididymal protease inhibitor)) is a target under intense scrutiny in the study of male contraceptive vaccines. B-cell-dominant epitopes are now recognized as key parts of the induction of humoral immune responses against target antigens. The generation of robust humoral responses in vivo has become a crucial problem in the development of modern vaccines. In this study, we developed a completely novel B-cell-dominant-epitope-based mimovirus vaccine, which is a kind of virus-size particulate antigen delivery system. The mimovirus successfully self-assembled from a cationic peptide containing a cell-penetrating peptide of TAT49-57 and a plasmid DNA encoding both three SPINLW1 (103-115) copies and adjuvant C3d3. The male mice were immunized with the epitope-based mimovirus vaccine, which resulted in a gradual elevation of specific serum IgG antibody levels. These reached a peak at week 4. Mating for the fertility assay showed that the mimovirus vaccine had accomplished a moderate fertility inhibition effect and investigation into the mechanism of action showed that it did so by interfering with the reproductive function of the sperm but that it did not damage the structures of the testes or cause serum testosterone to decline. Our results suggest an ideal protocol for suppressing fertility in mice by an engineered mimovirus vaccine.

Antisperm contraceptive vaccines: where we are and where we are going?

This is a review of current status and future perspectives on the development of antisperm contraceptive vaccines (CV) and immunocontraceptives. The development of antisperm CV is an exciting proposition. There is a strong rationale and recent data indicating that this proposition can translate into reality. The search for novel sperm-specific antigens/genes, that can be used for CV, continues using various recent developing technologies. Various approaches of proteomics, genomics, reproductive biology, mucosal immunity and vaccinology and several novel technologies such as gene knockout technology, phage display technology, antibody engineering, differential display technique, subtractive hybridization, and hybridoma technology are being used to delineate sperm-specific antigens and construct CV. Various sperm antigens/genes have been delineated, cloned, and sequenced from various laboratories. Vaccination with these sperm antigens (recombinant/synthetic peptide/DNA) causes a reversible contraceptive effect in females and males of various animal species, by inducing a systemic and local antisperm antibody response. The efficacy is enhanced by combination vaccination, including peptides based on various sperm antigens. Several human novel scFv antibodies with unique complementarity-determining regions (CDRs), that react with specific well-defined fertility-related sperm antigens, have been synthesized. These human infertility-related antibodies may find application in the development of novel immunocontraceptives. Besides finding the novel sperm antigens, the present and future focus is on enhancing the immunogenicity, bioefficacy, and on obliterating the inter-individual variability of the immune response, and proceeding for primate and human clinical trials. Multi-epitope vaccines combining sperm proteins involved in various steps of fertilization cascade have been found to enhance the immunogenicity and bioefficacy of the contraceptive effect. The in vitro synthesis of infertility-related human scFv antibodies may provide unique once-a-month immunocontraceptives, the first of its kind, for human use. The multi-epitope CV and preformed engineered human antibodies of defined specificity may obliterate the concern related to inter-individual variability of the immune response.

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.

Vaccines for immunological control of fertility

Vaccines have been proposed as one of the strategies for population control. Immunocontraceptive vaccines can be designed to inhibit: (1) production of gametes (sperm and egg); (2) functions of gametes, leading to blocking of fertilization; and (3) gamete outcome (pregnancy). Immunization with gonadotropin-releasing hormone coupled to different carriers has shown curtailment in the production of sperm with concomitant infertility in various species. Immunization of nonhuman primates and men with ovine follicle stimulating hormone has also resulted in reduced sperm output. Various spermatozoa-specific proteins such as FA1, PH-20, LDH-C₄, SP-10, SP-17, sp56, SPAG9, and Izumo have been proposed as candidate antigens to develop contraceptive vaccines, which have shown efficacy in inhibiting fertility in different animal models. Immunization with zona pellucida glycoproteins-based immunogens also results in curtailment of fertility in a variety of species. However, ways to overcome the observed oophoritis associated with zona proteins immunization have yet to be discovered, a necessary step before their proposal for control of human population. Nonetheless, this is a very promising approach to control wildlife animal population. Phase II clinical trials of β-human chorionic gonadotropin-based vaccine in women have established the proof of principle that it is possible to inhibit fertility without any untoward side-effects by vaccination. Further scientific inputs are required to increase the efficacy of contraceptive vaccines and establish their safety beyond doubt, before they can become applicable for control of fertility in humans.

Development of genetically engineered human sperm immunocontraceptives

Contraceptive vaccines targeting sperm are an exciting proposition. This review is focused on anti-sperm contraceptive vaccines and genetically engineered human antibodies that can be used as immunocontraceptives. Various methods of vaccinology and antibody engineering have been used to obtain multi-epitope contraceptive vaccines and human single chain variable fragment (scFv) antibodies from immunoinfertile and vasectomized men. Contraceptive vaccines comprised of various sperm antigens, peptide epitopes or DNA have shown various degrees of reversible contraceptive effect in the mouse model and their efficacy is enhanced with the multi-epitope combination vaccine. Failure to achieve a complete fertility block is probably due to variability in the host immune response. Using phage display technology, our laboratory has synthesized in vitro at least four novel scFv antibodies with unique complementarity determining regions (CDRs) that react with specific fertility-related sperm antigens employing cDNA from immunoinfertile and vasectomized men. These antibodies inhibit human sperm function in vitro, and their immunocontraceptive effect in vivo is being investigated. If these human scFv antibodies block fertility in vivo they may provide unique and novel immunocontraceptives, a first-in-kind for human use. The multi-epitope contraceptive vaccines and preformed engineered antibodies of defined specificity may eliminate concern related to inter-individual variability of the immune response.

Status of contraceptive vaccines

PROBLEM

This is a review of anti-sperm contraceptive vaccines (CV), and synthesis of human scFv antibodies that can be used as immunocontraceptives.

METHOD OF STUDY

Various methods of proteomics and genomics, peptide synthesis, phage display technology, and antibody engineering were used to obtain multi-epitope vaccines and human scFv antibodies from immunoinfertile and vasectomized men. The present review primarily focuses on the effect of multi-epitope vaccines and Izumo on fertility, and synthesis and characterization of sperm specific human scFv antibodies.

RESULTS

The immunization with Izumo peptides causes a contraceptive effect in female mice. The efficacy is enhanced by combination vaccination, including peptides based on other sperm antigens. Using phage display technology, we were able to synthesize at least four novel scFv antibodies with unique complementarity determining regions (CDRs) that reacted with specific fertility-related sperm antigens. These antibodies inhibited human sperm function in vitro, and their immunocontraceptive effect in vivo by these antibodies is currently being investigated.

CONCLUSION

The multi-epitope vaccines may provide an efficacious and viable approach to contraception. The human scFv antibodies, if they block fertility in vivo, may provide unique and novel immunocontraceptives, the first of its kind for human use. The multi-epitope CV and preformed engineered antibodies of defined specificity may obliterate the concern related to inter-individual variability of the immune response.

Experimental immunological infertility effect of anti-GAPDH-2 antibodies on the fertility of female mice

OBJECTIVE

To examine the relationship between an antibody against GAPDH-2, a sperm-specific protein, and infertility of female mice.

DESIGN

Basic research.

SETTING

National Research Institute for Family Planning Beijing, World Health Organization Collaboration Center of Human Reproduction.

ANIMAL(S)

New Zealand rabbit, NIH and ICR mice.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Enzyme-linked immunoabsorbent assay, Western blot and indirect immunostaining assays, standard fertility assay, and sperm agglutination assay.

RESULT(S)

Antibodies against the full-length GAPDH-2 were raised. Its specificity was assessed by immunoblotting and indirect immunostaining assays. The antibody immunoreacted with human sperm GAPDH-2 and the mouse homolog GAPDS but did not cross-react with GAPDH. Treatment of female mice with IP injection of anti-GAPDH-2 serum significantly reduced their fertility. Anti-GAPDH-2 serum caused the agglutination of normal mice sperm in vitro. The anti-GAPDH-2 antibody was detectable in the sera and uterine fluid of the mice immunized with GAPDH-2.

CONCLUSION(S)

These results show that GAPDH-2 should be further evaluated as a promising candidate in the development of an antifertility immunogen. Detecting anti-GAPDH-2 antibodies in the bodily fluid of subjects afflicted with indeterminate infertility may be a new diagnostic index.

Clinical significance of sperm protein 17 expression and immunogenicity in esophageal cancer

We recently identified sperm protein 17 (Sp17) transcripts in esophageal squamous cell carcinomas (ESCCs) by differential display. This study was designed to determine the clinical significance of Sp17 protein in different stages of esophageal tumorigenesis and to test the hypothesis that aberrant localization of Sp17 protein to immunosurveillant site may lead to production of anti-Sp17 antibodies in serum, which may be of clinical relevance in ESCCs. Sp17 transcripts were detected by RT-PCR in 26 of 30 (86%) ESCCs, while no transcripts were detected in normal esophageal tissues. Rabbit polyclonal antibody was raised against an immunogenic peptide of Sp17 and used to evaluate protein expression by immunohistochemistry. Expression of Sp17 protein was observed in 60/80 (75%) of ESCCs and 27/30 (90%) dysplastic tissues, while no detectable Sp17 expression was observed in 13 distant histologically normal epithelia. Sixteen of the 60 immunopositive ESCCs showed nuclear expression in addition to cytoplasmic localization of the protein. The circulating levels of anti-Sp17 antibodies, determined by ELISA, were significantly elevated in ESCC patients when compared with normal subjects (p < 0.001). Increasing Sp17 antibody titers were observed to be associated with the progressive disease in 4 patients. In conclusion, the study demonstrates expression of Sp17 protein in esophageal tumor as well as dysplastic tissues, suggesting it to be an early event in the development of ESCC. To our knowledge, this is the first report showing elevated levels of anti-Sp17 antibodies in ESCC patients.

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.

Effect of sperm DNA vaccine on fertility of female mice

Our laboratory has identified a sperm-specific dodecamer peptide sequence, designated as YLP(12), vaccination with which causes a long-term reversible immunocontraceptive effect in female mice. In the present study, the effects of YLP(12) DNA vaccine were examined. YLP(12) 36 bp cDNA was cloned into pVAX1 vector to prepare the DNA vaccine. Two additional vaccine constructs were made by in frame cloning of one and two CpG repeats in the YLP(12)-cDNA vaccine. Five groups of female mice were immunized intradermally by using gene gun with YLP(12)-cDNA, YLP(12)-cDNA-CpG, YLP(12)-cDNA-CpG-CpG, YLP(12)-cDNA mixed with exogenous synthetic CpG oligodeoxynucleotide (ODN), or vector DNA alone, respectively. Vaccination with all three constructs and the YLP(12) vaccine mixed with exogenous ODN raised antibody response both in the sera as well as locally in the vaginal tract. There was no antibody response in the mice injected with the vector alone. In sera, the highest titers were obtained for the IgG class for all constructs and formulation followed by IgA class. In vaginal washings the highest titers were obtained for the IgA class followed by IgG class. Within the IgG class, the titers for the IgG2a subclass were significantly greater than the IgG1 subclass. Immunization with all constructs and formulation caused a significant (P < 0.05 to <0.001) reduction (20-43%) in fertility of female mice. The highest reductions were seen in mice immunized with YLP(12)-cDNA-CpG-CpG (two repeats) (43% reduction) and with the YLP(12) vaccine administered with exogenous CpG ODN (42% reduction). T lymphocytes obtained from DNA-vaccinated mice showed clearly distinguished comparative RT-PCR analysis of cytokine mRNA expression for Th1 and Th2 immune responses compared to T lymphocytes obtained from control animals injected with vector DNA. Expression of both Th1 cytokines (IL-2 and IFN-gamma) and Th2 cytokines (IL-4 and IL-10) was enhanced after DNA vaccination as compared to controls, with a bias towards Th1 response. The immunocontraceptive effects were long-lasting observed up to 1.3 years of the observation period and increased with time. These novel findings indicate that the intradermal immunization with a sperm-specific DNA vaccine causes a long-term circulating and local immune response resulting in immunocontraceptive effects in female mice.

Antisperm Vaccine for Contraception

PROBLEM

This study is a review of antisperm contraceptive vaccine (CV) development with the main focus on research going on in our laboratory.

METHOD OF STUDY

Various methods of proteomics and genomics, hybridoma technology, substractive libraries, differential display method, and phage display technology were used to obtain sperm-specific genes and proteins. The present study will primarily focus on the sequences obtained by using the phage display technology and their role in CV development and human immunoinfertility.

RESULT

Four novel peptides, delineated by using the phage display technology, were found to be involved in human immunoinfertility. The vaccine based on one of these peptides, designated as YLP(12), caused a reversible contraception in female mice.

CONCLUSIONS

The vaccine targeting sperm is a feasible and exciting approach to contraception. The phage display technology is a powerful tool to delineate sperm-specific peptide sequences that can be used for the CV development and in the diagnosis and treatment of infertility mediated through antisperm antibodies.

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.

Contraceptive vaccines

The world's population is growing at a tremendous rate, affecting growth and development. Apart from this population growth, unintended pregnancies resulting in elective abortions continue to be a major public health issue. In over half of these unintended pregnancies, the women have used some type of contraception. Thus, there is an urgent need for a better method of contraception that is acceptable, effective and available. The contraceptive choices available to women at this time include steroid contraceptives, intrauterine devices, barrier methods, spermicides, natural family planning, male and female sterilisation, and recently available emergency contraceptives. Contraceptive vaccines (CVs) may provide viable and valuable alternatives that can fulfill most, if not all, properties of an ideal contraceptive. Since both the developed and most of the developing nations have an infrastructure for mass immunisation, the development of vaccines for contraception is an exciting proposition. The molecules that are being explored for CV development either target gamete production (gonadotropin releasing hormone, follicle-stimulating hormone and luteinising hormone), gamete function (zona pellucida [ZP] proteins and sperm antigens) or gamete outcome (human chorionic gonadotropin [hCG]). Disadvantages of CVs targeting gamete production are that they affect sex steroids and/or show only a partial effect in reducing fertility. CVs targeting gamete function are better choices. Vaccines based on ZP proteins are quite efficacious in producing contraceptive effects. However, they invariably induce oophoritis affecting sex steroids. Sperm antigens constitute the most promising and exciting targets for CVs. Several sperm-specific antigens have been delineated in several laboratories and are being actively explored for CV development. Antisperm antibody-mediated immunoinfertility provides a naturally occurring model to indicate how an antisperm vaccine will work in humans. 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 the efficacy and the lack of immunotoxicity have been reasonably well demonstrated for this vaccine. The present studies focus on increasing the immunogenicity and efficacy of this birth control vaccine.

Identification of a New, Testis-Specific Sperm Antigen Localized on the Principal Piece of the Spermatozoa Tail in the Fox (Vulpes vulpes)1

Fox (Vulpes vulpes) sperm antigens were identified to assess them as a potential target for a contraceptive vaccine. We report here the cloning and sequencing of fSP13, a fox sperm protein of 97 kDa. The fSP13 protein was both auto- and iso-antigenic in foxes; it was recognized by sera of foxes immunized with fox sperm proteins and vasectomized foxes. The NH2-terminal sequence of fSP13 was determined, and a piece of cDNA was amplified from testicular RNA by reverse transcription polymerase chain reaction. This piece was used to screen a cDNA library from fox testis by Southern blot. A sequence of 1662 base pairs was obtained, including a major open reading frame coding for 498 amino acid. Mass spectrometry analysis confirmed the position of the open reading frame and the presence of posttranscriptional modifications. Analysis of the predicted amino acid sequence revealed no apparent transmembrane regions. Comparison of the protein sequence with the Prosite database demonstrated the presence of four potential N-linked glycosylation sites. The fSP13 bears the closest amino acid similarity to two human sperm proteins: fibrousheathin 2 and testis-specific calcium binding protein 86-VII. The deduced 80 N-terminal amino acid sequence also presents similarity with the RIIalpha domain. By using a serum against fSP13, this antigen was localized on the principal piece of the fox spermatozoa. Northern blot analysis showed that fSP13 is specifically expressed in testis. The fSP13 is one of the first fox sperm antigens to be cloned and sequenced.

Reversible immunocontraception in male monkeys immunized with eppin

Various forms of birth control have been developed for women; however, there are currently few options for men. The development of male contraceptives that are effective, safe, and reversible is desired for family planning throughout the world. We now report contraception of male nonhuman primates (Macaca radiata) immunized with Eppin, a testis/epididymis-specific protein. Seven out of nine males (78%) developed high titers to Eppin, and all of these high-titer monkeys were infertile. Five out of seven (71%) high-anti-Eppin titer males recovered fertility when immunization was stopped. This study demonstrates that effective and reversible male immunocontraception is an attainable goal. This method of immunocontraception may be extended to humans.

Development of mouse-specific contraceptive vaccines: infertility in mice immunized with peptide and polyepitope antigens

Mouse-specific immunocontraceptive peptides have been identified in mouse proteins with key roles in reproduction from sequence comparisons to other species and tested for efficacy as immunocontraceptive antigens. Peptides were derived from granulocyte-macrophage colony-stimulating factor (GMCSF), the placental 27 kDa heat-shock protein (HSP), leukemia inhibitory factor receptor (LIFR), oviduct glycoprotein (OGP), proliferin (PLF), prolactin (PRL), sperm protein SP56 and mouse zona pellucida subunits 1 and 3 (ZP1, ZP3). Fertility of female BALB/c mice was reduced after immunization with several peptides either conjugated to a carrier protein or in the form of recombinant polyepitopes. The most effective conjugated peptides (SP56, GMCSF and PRL) induced peptide-specific serum antibodies and reduced fertility by 50%. Fertility of mice was also reduced after immunization with polyepitope antigens containing up to five different peptides fused to maltose-binding protein, but antibodies were not produced against all the encoded peptides. The most effective polyepitope antigen (containing PLF, SP56, ZP1 and ZP3 peptides) reduced fertility by 50% but induced only SP56 and ZP1 antibodies. We demonstrate that lack of antibody response to a given peptide epitope (ZP3) can be overcome if repeated copies are used in the polyepitope antigen construct, but the effect varies between mouse strains. We conclude that infertility induced in mice with a range of peptide-based vaccines is dependent on antigen formulation and genetic factors but does not necessarily correlate with peptide-specific antibody levels. In light of these results, strategies to improve the efficacy of peptide-based antifertility vaccines are discussed.

Expression of sperm protein 17 (Sp17) in ovarian cancer

Sperm protein 17 (Sp17) is an antigenic protein highly expressed in spermatozoa. Sp17 expression was demonstrated recently in multiple myeloma, suggesting that it may be a novel cancer-testis antigen. Expression of Sp17 mRNA and protein was examined in human ovarian tumors. Sp17 mRNA was evaluated by reverse transcription-polymerase chain reaction (RT-PCR) and Northern blot analysis of RNA derived from epithelial ovarian tumors and normal tissues. RT-PCR analysis detected Sp17 transcripts in 15 of 18 (83%) primary ovarian tumors. The transcript was not detected in RNA derived from normal uterus or cervix, whereas weak expression was noted in some normal ovarian tissue samples. Northern blot analysis showed no detectable Sp17 mRNA expression in normal tissues, including normal ovary, but showed Sp17 expression in 17 of 25 ovarian tumors (68%). To evaluate protein expression, mouse monoclonal antibodies were produced against recombinant Sp17 protein and used in Western blot and immunohistochemical analyses of normal reproductive tissue and primary ovarian tumor samples. Sp17 protein was detected by Western blot analysis in normal spermatozoa and in 8 of 19 ovarian tumor samples. Immunohistochemical studies showed Sp17 expression in spermatozoa, ciliated cells of the female reproductive tract, and most ovarian tumors evaluated. Tumors showed a predominantly nuclear localization of Sp17 expression, with some cytoplasmic staining. These results demonstrate that Sp17, a protein with restricted expression in somatic tissues, is expressed in ovarian tumors. Because Sp17 is immunogenic, it may represent a novel target for immunotherapeutic interventions for ovarian cancer patients.

Immunocontraception for population control: will resistance evolve?

The prospect for successful biocontrol using immunocontraception is threatened if there is adaptation to the vaccine through natural selection of individuals that are genetically resistant to the contraceptive agent. To assess this possibility we examined the literature and found that little relevant data are available for any species on the appropriate trait, fertility variation among immunized individuals, or about appropriate population and genetic parameters influencing the likelihood of a selection response. Some data are available on variation in antibody response to immunocontraceptives, but the relationship between antibody response and fertility levels is poorly documented. The antibody response data indicate low heritability for this trait suggesting that fertility levels of contraceptive-resistant individuals will also have a low heritability. Slow evolution of contraception resistance might therefore be anticipated. The absence of information about relevant parameters makes the construction of quantitative models premature. We discuss factors in particular need of investigation if predictions about resistance evolution are to be made. These include: 1. the genetic basis of fertility retention, 2. the proportion of the population resistant to the contraceptive agent and how this is affected by gene flow from refuge populations, 3. the genetically-based fitness tradeoffs of resistant individuals that often accompany selection, 4. cross-generation effects that can thwart the effects of selection, and 5. the efficiency of delivery of the contraceptive agent. An understanding of the above for particular species, and the development of appropriate divergently acting multiple vaccines that can be used in temporal rotation or in mixtures, should facilitate the development of management options to minimize resistance evolution.

Molecular cloning and sequencing of cDNA encoding for human FA-1 antigen

The cDNA encoding for the human FA-1 sperm antigen was cloned and sequenced from the in-house constructed subtractive human testis cDNA expression library in lambda Ziplox using the FA-1 monoclonal antibody (mAb). The full--length sequence was obtained by using the 5' rapid amplification of 5'-cDNA end (5'-RACE) procedure. It is 1,576-bp long, and has an open reading frame (ORF) of 283 amino acids (aa) with the first ATG Met start codon at nucleotide (nt) 57 and the stop codon TAG at nt 906. It has two termination codons at the 5' end before the ATG start codon. The translated protein has a calculated molecular weight of 32.1 kDa and estimated isoelectric point (pI) of 11.59. It has one potential N-linked glycosylation site and one tyrosine phosphorylation site, besides several O-linked glycosylation and serine and threonine phosphorylation sites. Hydrophilicity analysis of the deduced aa sequence showed it to be a membrane-anchored protein. Extensive computer search in the database did not identify any known nt/aa sequence having homology with FA-1 cDNA or deduced aa, indicating it to be a novel gene. The Northern blot and reverse transcription-polymerase chain reaction (RT-PCR)-Southern blot analyses indicated the testis-specific expression of FA-1 antigen at the mRNA level. The ORF of the FA-1 was subcloned into pGEX- 1lambda T for expression. The expressed FA-1 recombinant protein had a molecular size of approximately 40 kDa, and was recognized by the FA-1 mAb, and not by the myeloma control Ig. The rabbit antibodies (Ab) raised against the recombinant (r) FA-1 antigen recognized the rFA-1 antigen as well as the native (n) FA-1 antigen. The rFA-1 Ab specifically recognized a protein band of approximately 50 kDa in human testis extract in the Western blot involving 11 types of human tissue extracts, indicating the testis-specific expression of FA-1 at the protein level. The Ab showed binding with live and methanol-fixed human sperm at the post-acrosomal, mid-piece, and tail regions. The Ab caused a significant (P < 0.001) and concentration-dependent inhibition of human sperm capacitation/acrosome reaction by blocking tyrosine phosphorylation of the FA-1 antigen. The sperm-specific human FA-1 recombinant antigen may find applications in immunocontraception, and diagnosis and treatment of immunoinfertility in humans.

The development of contraceptive vaccines

The use of vaccination as a means of controlling fertility was established during the last decade with the publication of a successful Phase II trial demonstrating the efficacy of this approach to family planning. However, only this one Phase II trial has been completed despite a plethora of hormonal and gamete antigens that have been proposed as candidate vaccines. Improvements in the design and formulation of contraceptive vaccines are underway and will be a necessary prelude to further clinical trials.

Human sperm-specific peptide vaccine that causes long-term reversible contraception

A novel dodecamer peptide sequence, YLP(12), was identified on human sperm that is involved in oocyte binding. We investigated its immunocontraceptive effects in a murine model. A vaccine was prepared by conjugating the synthetic YLP(12) peptide with the binding subunit of recombinant cholera toxin. Vaccination of female mice by i.m. or intranasal routes without any additional adjuvant induced a sperm-specific immune response in serum and the vaginal tract that caused a long-term contraceptive state. Fertility was fully regained when antibody reactivity diminished at 305-322 days. The contraceptive effect was also completely reversed voluntarily by intravaginal administration of the peptide. Antibodies affected fertility at the prefertilization stage by inhibiting sperm capacitation and the acrosome reaction, and sperm-oocyte binding. The peptide sequence is an epitope of a 50 +/- 5-kDa membrane protein localized on the acrosome and tail of spermatozoa. Thus, the sperm-specific YLP(12) is an attractive candidate for contraceptive vaccine.

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.

Testis-specific antigen (TSA-1) is expressed in murine sperm and its antibodies inhibit fertilization

PROBLEM

We recently cloned and sequenced a sperm-specific antigen, designated as testis-specific antigen-1 (TSA-1), from human testis. The present study was conducted to examine its expression and function in murine sperm, in order to find out whether or not the mouse can provide a suitable model for examining its immunocontraceptive effects.

METHOD OF STUDY

The antibodies (Ab) were raised against purified human rTSA-1 in virgin female rabbits. The rTSA-1 was run in sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) and the gel containing the approximately 18 kDa band was cut, minced and used for immunization to obtain the specific Ab. The immunoglobulins from preimmune bleed and from animals injected with adjuvant alone served as control. These Ab were analysed in enzyme-linked immunosorbent assay (ELISA), Western blot procedure, immunoprecipitation procedure, immunocytochemical technique (ICT), immunobead binding technique (IBT), acrosome reaction and sperm-zona binding assay.

RESULTS

Active immunization of female rabbits with purified rTSA-1 protein of 18 kDa, produced high titer Ab against the recombinant antigen. These Ab to rTSA-1 were used in the present study. In Western blot procedure, rTSA-1 Ab recognized a specific protein band of approximately 24 +/- 3 kDa in murine sperm extract, the band similar to found in human sperm extract. In the immunoprecipitation procedure, rTSA-1 Ab immunoprecipitated the protein band of similar size from extracts of murine sperm and murine testis. The ICT and the IBT studies revealed the subcellular localization of TSA-1 on the surface of acrosome and tail regions of the non-capacitated and capacitated murine sperm cells. In functional bioassays, rTSA-1 Ab inhibited the acrosome reaction and sperm-egg binding in vitro.

CONCLUSIONS

These data indicate that the TSA-1 is expressed in murine sperm and may have a biological role in sperm function and sperm-egg binding. In vitro inhibition of capacitation/acrosome reaction and sperm-zona binding suggests that the mouse can provide a suitable model to examine the immunocontraceptive effects of TSA-1 in actively immunized animals.

Effect of antibodies to sperm-specific recombinant contraceptive vaccinogen (rCV) on murine fertilization: search for an animal model to examine its contraceptive potential

Recently, we cloned and sequenced a sperm-specific antigen, designated as Contraceptive Vaccinogen (rCV), from human testis (Naz et al., 2001). The present study was conducted to examine its proteomic homologue and function in murine sperm, in order to find out whether or not the mouse can provide a suitable model for examining its immunocontraceptive effects. This was examined by using purified antibodies (Ab) raised against the recombinant (r) human CV antigen of approximately 44 kD. In the Western blot procedure, rCV antibodies recognized a specific protein band of approximately 64 +/- 5 kD in murine testis and murine sperm extracts, the band similar to that found in human testis and human sperm. In the immunoprecipitation procedure, rCV Ab immunoprecipitated a protein band of similar size from murine sperm and murine testis extracts. The immunocytochemical (ICT), immunoscanning electronmicroscopic (ISEM) and the immunobead binding technique (IBT) revealed the subcellular localization of CV antigen on the surface of acrosome and tail regions of the noncapacitated and capacitated murine sperm cell. In functional bioassays, rCV Ab inhibited the acrosome reaction as well as sperm-egg binding in vitro. These data indicate that the CV antigen is expressed in murine sperm and has a biological role in sperm function and sperm-egg binding. In vitro inhibition of capacitation/acrosome reaction and sperm-zona binding suggest that the mouse can provide a suitable model to examine the immunocontraceptive effects of CV antigen in actively-immunized animals.

Sperm protein 17 (Sp17) in multiple myeloma: opportunity for myeloma-specific donor T cell infusion to enhance graft-versus-myeloma effect without increasing graft-versus-host disease risk

We recently found that sperm protein 17 (Sp17), a spermatozoa-restricted protein, is aberrantly expressed on the tumor cells in patients with multiple myeloma (MM). It may therefore be possible to generate donor-derived Sp17-specific CTL for administration following allogeneic stem cell transplant to augment graft-versus-myeloma (GVM) effect without inducing a global GVHD. To assess this approach, we have produced recombinant Sp17 protein and used Sp17 protein-pulsed dendritic cells to generate HLA class I-restricted Sp17-specific CTL from a previously unimmunized healthy donor. These CTL were able to lyse autologous Epstein-Barr virus-transformed lymphoblastoid cells in a Sp17-dependent manner. Target lysis was HLA-A1 and HLA-B27 restricted. Cytotoxicity could be blocked by antibodies against monomorphic HLA class I, HLA-A1 and HLA-B27 molecules but not HLA class II molecules. Most importantly, the CTL lysed HLA class I-matched Sp17-positive tumor cells, suggesting that Sp17 is processed and presented in association with the HLA class I molecules in Sp17-positive tumor cells in a concentration and configuration that could be recognized by recombinant protein-primed CTL. Analysis by flow cytometry of the CTL indicated that they were predominantly CD8 in phenotype and they produced IFN-gamma and very little IL-4. Our results suggest the potential for the generation and administration of donor-derived Sp17-specific CTL to augment GVM without inducing GVHD following allogeneic stem cell transplant for MM.

Characterization of Sp17: a ubiquitous three domain protein that binds heparin

Sp17 is a protein that was originally thought to be expressed exclusively in the testis and whose primary function was binding to the extracellular matrix of the oocyte. Several recent reports have implicated Sp17 as having a role in cell-cell adhesion and/or cell migration in transformed, lymphocytic and haematopoietic cells, possibly through its interaction with extracellular heparan sulphate. In the present study, we report that Sp17's central domain (amino acids 61-117), spanning exon 3, is critical for heparin binding. Sp17 has two additional functional domains, an N-terminal domain similar to the dimer-interaction site in the cAMP-dependent protein kinase IIalpha regulatory subunit and a C-terminal calmodulin-binding domain. The mouse gene for Sp17 is 6.5 kb and contains four exons. Although Sp17 expression is highest in the testis, it is present in all of the mouse somatic tissues examined and is highly conserved throughout all mammalian species. Sp17's central domain, which is necessary for heparin binding, exhibits the greatest sequence divergence of all three domains. The Sp17 gene is induced in metastatic cells and during mucosal immune responses, and the protein appears to play an important role in cell migration and/or adhesion in somatic cells, as well as in male germ cells.

Molecular cloning and sequencing of a novel cDNA encoding for a protein involved in human sperm function

A cDNA encoding for an antigen, designated as NZ-3, was cloned and sequenced from human testis. The 1481-bp NZ-3 cDNA yielded an open reading frame (ORF) of 231 amino acids (aa) with the first ATG, Met start codon at nucleotide (nt) 104 and the stop codon TGA at nt 797. Extensive computer search indicated it to be a novel cDNA/protein. The ORF of NZ-3 cDNA was subcloned into pGEX-1lambdaT vector and expressed in glutathione S-transferase gene fusion system. The expressed recombinant protein had a molecular size of approximately 25 kDa, and the rabbit antibodies (Ab) against the recombinant antigen recognized a specific protein band of 63 +/- 3 kDa in the human testis extract. The NZ-3 antigen was located on the acrosomal and tail regions of human sperm cell and the NZ-3 Ab significantly (P < 0.001) inhibited human sperm capacitation and/or acrosome reaction. The novel recombinant NZ-3 antigen may find applications in immunocontraception and in specific diagnosis of human infertility.

Sperm protein 17 is a novel cancer-testis antigen in multiple myeloma

Various studies have demonstrated the aberrant expression of normal testicular proteins in neoplastic cells. These proteins collectively form the new class of tumor antigens called cancer-testis (CT) antigens. Their selective normal tissue expression makes them ideal antigens for immune targeting of the malignant disease. In this study, the expression of a spermatozoa protein, Sp17, in multiple myeloma was investigated. It was found that Sp17 is detectable in tumor cells from 12 of 47 (26%) myeloma patients. Reverse transcription polymerase chain reaction (RT-PCR) and Western blot analysis detected Sp17 transcripts and proteins, respectively. Northern blot analysis and RT-PCR demonstrated that Sp17 transcripts were detected only in normal testis, supporting its tissue specificity. Since a high proportion of normal individuals develop antibodies against Sp17 following vasectomy, Sp17 is likely to be a highly immunogenic protein in vivo. Sp17 is therefore a novel member of the CT antigen family and should be an ideal target for immunotherapy of multiple myeloma.

The potential use of sperm antigens as targets for immunocontraception; past, present and future

Immunocontraception, and in particular the targeting of antibodies to gamete-specific antigens implicated in sperm egg binding and fertilisation, offers an attractive approach to the growing global problem of overpopulation. Such an idea is not new; indeed several immunocontraception trials, using animal model systems, have been reported in recent years and a number are reviewed here. However, the results of these studies have been largely disappointing. We believe that two fundamental flaws attribute to the poor success of most of these preliminary immunocontraceptive trials. Firstly, loss of fertility has invariably been used as the assay. This presupposes that immuno-neutralisation of a single, gamete-specific antigen will be sufficient to cause a significant reduction in fertility; however, recent data suggests that such a premise may not be well-founded for a number of reasons. Secondly, and arguably the most important flaw, is the almost universal, but largely inappropriate, use of systemic immunisation as the sole route of antigen delivery. Whilst systemic immunisation regimes may lead to high serum IgG levels, these levels do not correlate with specific antibody levels in the reproductive tract or with contraceptive efficacy. Hence, an alternative antigen delivery approach is required which will induce an effective local immune response in the reproductive tract. Here we discuss the ways in which this might be achieved.

Expression of recombinant mouse sperm protein sp56 and assessment of its potential for use as an antigen in an immunocontraceptive vaccine

Recombinant mouse sp56 protein was produced for testing as an antigen in an immunocontraceptive vaccine. The coding sequence for the mature sp56 protein was cloned into the bacterial expression system pFLAG using a PCR-based method on mouse testis cDNA. Polyclonal antisera were raised in mice against affinity purified recombinant sp56 fusion protein (sp56FLAG) or an artificial sp56 peptide fused to a carrier protein (KLH) and shown to cross-react to a protein band of 75 kD in detergent extracts of mouse sperm by Western immunoblot analysis under reducing conditions. The antisera to sp56FLAG also immunolocalized over the entire acrosome of mouse sperm. Female BALB/c mice were immunized intraperitoneally with sp56FLAG in a fertility trial with 20 microg sp56FLAG in Freund's Complete Adjuvant and boosted three to five times with 20 microg sp56FLAG in Freund's Incomplete Adjuvant. Litter sizes of sp56FLAG-treated mice were significantly smaller than control-treated animals after five boosts.