Colinear synthesis of an antigen-specific B-cell epitope with a 'promiscuous' tetanus toxin T-cell epitope: a synthetic peptide immunocontraceptive

The sperm-specific form of lactate dehydrogenase is required for fertility and is an attractive target for male contraception (a review)

There has been a recent upsurge in the interest about contraceptive development, evidenced by the Contraceptive Special Issue of Biology of Reproduction [1], with research funding from the Male Contraceptive Initiative and the Bill and Melinda Gates Foundation. Support from the Contraceptive Research Branch of the Eunice Kennedy Shriver National Institutes of Child Health and Human Development continues with a marked change in focus in the funding announcements. This has motivated me to reflect on research, mostly from my laboratory starting in the 1960s to the present, on the development of a male contraceptive based on the sperm-specific glycolytic enzyme, lactate dehydrogenase C (LDHC4). This review considers the rationale behind this research, the development paths pursued, obstacles encountered, and the renewed interest in going forward toward development of a male contraceptive mediated by the inhibition of the sperm-specific form of LDHC. I will address how some papers published many years ago are relevant to the present goals of non-hormonal contraception and will mention about innovative technology now available that can advance this project. This review presumably will serve as an instructive guide for a research program with a focused program related to contraception. As an aside, many of the citations in this review are to most of the 26 publications in Biology of Reproduction co-authored by this investigator and collaborators from 1974 through 2020 not long after the first issue of BOR which was published in April 1969.

Promiscuous T cell epitopes boosts specific IgM immune response against a P0 peptide antigen from sea lice in different teleost species

The development of vaccines employing conserved protein antigens, for instance ribosomal protein P0, has as disadvantage the high degree of identity between pathogen and host proteins due to possible induction of tolerance or auto antibodies in the host organism. To overcome this drawback, peptide-based vaccines have been designed with a proved high efficacy. The use of defined peptides as antigens has the problem that they are generally poor immunogenic unless coupled to a carrier protein. Several studies have established the potential for promiscuous T cell epitopes incorporated into chimeric peptides to enhance the immunogenicity in mammals. On the contrary, studies about the role of these epitopes on teleost immune system are scarce. Therefore, the main objective of our present study was to evaluate the potential of promiscuous T cell epitopes to boost specific IgM immune response in teleost fish against a peptide antigen. With this aim, we used a peptide of 35 amino acids from the ribosomal P0 protein of Lepeophtheirus salmonis, an important parasite in salmon aquaculture. We fused this peptide to the C-terminal of T cell epitopes from tetanus toxin and measles virus and produced the chimeric protein in Escherichia coli. Following vaccination, IgM antibody production was monitored in different immunization schemes in Tilapia, African catfish and Atlantic salmon. The results demonstrated for first time that the addition of T cell epitopes at the N-terminal of a target peptide increased IgM specific response in different teleost species, revealing the potential of this approach to develop peptide-based vaccines for aquaculture. The results are also of great importance in the context of vaccine development against sea lice using ribosomal protein P0 as antigen taking into account the key role of P0 in protein synthesis and other essential physiological processes.

Detection of sperm-reactive antibodies in wild sika deer and identification of the sperm antigens

Antisperm antibodies potentially inhibit sperm functions causing the sterility in humans and experimentally treated animals. However, there is no information about antisperm antibodies emerging spontaneously in wildlife. In this study, we searched for the sperm-reactive antibodies, spontaneously produced in wild sika deer (Cervus nippon), and identified the sperm antigens. We collected 529 fecal masses of sika deer in Japanese cities, from which we extracted the mucosal antibodies to test them for reactivities to deer sperm proteins by ELISA. Two of the extracts contained IgAs that were highly reactive to the sperm proteins. The molecular weights of the active IgAs, partially purified by DEAE-sephadex A-50, were estimated at more than 100 kDa, suggesting that the IgAs evaded drastic digestion in the gastrointestinal tract. Two-dimensional electrophoresis and immunoblotting detected three major antigens, and the following LC-MS/MS analysis identified them as alpha-enolase, phosphoglycerate kinase 2 and acrosin-binding protein. The antibodies were cross-reactive to a recombinant human acrosin-binding protein. To our knowledge, this is the first research to find that the sperm-reactive antibodies are produced spontaneously in wildlife and they recognize a common antigen found in humans.

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.

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.

Immunocontraceptives: new approaches to fertility control

The rapidly increasing global population has bowed the attention of family planning and associated reproductive health programmes in the direction of providing a safe and reliable method which can be used to limit family size. The world population is estimated to exceed a phenomenal 10 billion by the year 2050 A.D., thus presenting a real jeopardy of overpopulation with severe implications for the future. Despite the availability of contraceptive methods, there are over one million elective abortions globally each year due to unintended pregnancies, having devastating impact on reproductive health of women worldwide. This highlights the need for the development of newer and improved contraceptive methods. A novel contraceptive approach that is gaining substantial attention is "immunocontraception" targeting gamete production, gamete outcome, or gamete function. Amongst these, use of sperm antigens (gamete function) seems to be an exciting and feasible approach. However, the variability of immune response and time lag to attain titer among vaccinated individuals after active immunization has highlighted the potential relevance of preformed antibodies in this league. This review is an attempt to analyze the current status and progress of immunocontraceptive approaches with respect to their establishment as a future fertility control agent.

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.

Generation of monoclonal antibodies to the AML1-ETO fusion protein: strategies for overcoming high homology

The chromosomal translocation t(8;21) often found in acute myeloid leukemia generates an oncogenic fusion protein AML1-ETO. This chimeric oncoprotein disrupts wild-type AML1 function and dysregulates genes important for normal myelopoiesis. Monoclonal antibodies that can capture and detect the AML1-ETO fusion protein would help with early diagnosis and treatment prognosis of acute myeloid leukemia. We report the development of murine monoclonal antibodies (MAbs) that specifically bind epitopes encoded by either AML1 or ETO. Since alignment to the human ETO protein indicated almost 100% homology to the mouse ortholog, a strategy was needed to instruct humoral immunity in mice to focus and respond to self-epitopes. Our strategy to develop capture/detector reagents involved producing MAbs that would bind to epitopes within the non-fused myelopic protein (i.e., either AML1 or ETO). This included a process to select antibodies for their ability to also recognize the translocated chromosomal AML1-ETO fusion protein and to identify complementary capture/detector antibody pairs. Construction of a peptide hapten-carrier complex and use of a rapid immunization protocol resulted in IgM-IgG ETO specific MAbs. These MAbs bound specifically to a recombinant form of AML1-ETO fusion protein expressed in HEK and to an endogenous AML1-ETO form of the fusion protein expressed in Kasumi-1. We report the development of murine hybridoma MAbs derived from immunizations with a peptide "self-epitope." Our findings provide a potential strategy to instruct humoral immunity in mice to focus and respond to self-epitopes. This strategy has been validated with the oncogenic fusion protein AML1-ETO involved in acute myeloid leukemia.

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.

A heterologous helper T-cell epitope enhances the immunogenicity of a multiple-antigenic-peptide vaccine targeting the cryptic loop-neutralizing determinant of Bacillus anthracis protective antigen

We previously showed that a multiple antigenic peptide (MAP) displaying amino acids (aa) 305 to 319 from the 2beta2-2beta3 loop of protective antigen (PA) can elicit high-titered antibody that neutralizes lethal toxin (LeTx) in vitro and that this loop-neutralizing determinant (LND) specificity is absent in PA-immune rabbits. Some immune rabbits were, however, nonresponders to the MAP. We hypothesized that the immunogen elicited suboptimal major histocompatibility complex (MHC) class II-restricted T-cell help and that introduction of a functional helper T-cell epitope would increase MHC-restricted responsiveness and the magnitude and affinity of the antibody responses. In the current study, we characterized the T- and B-cell responses to LND peptides in mice, then designed second-generation MAP immunogens for eliciting LND-specific immunity, and tested them in rabbits. The 305-319 sequence was devoid of helper T-cell epitopes in three strains of mice; however, a T-B peptide comprising aa 305 to 319, colinearly synthesized with the P30 helper epitope of tetanus toxin, elicited robust LeTx-neutralizing immunity in mice. T-B MAPs displaying B-cell epitopes 304 to 319 (MAP304) or 305 to 319 (MAP305) elicited high-titer, durable antibody responses in rabbits which exhibited potent neutralization of LeTx in vitro. All MAP304-immune rabbits demonstrated neutralization titers exceeding that of hyperimmune sera of rabbits immunized with PA in Freund's adjuvant, with peak neutralization titers 23-, 6-, and 3-fold higher than that of the PA antiserum. Overall, immunization with MAPs containing the P30 epitope elicited higher antibody and toxin neutralization titers and peptide-specific affinity than immunization with an LND MAP lacking a helper epitope. P30-containing MAP304 represents a promising LND-specific vaccine for anthrax.

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.

Immunogenicity of a multi-component recombinant human acrosomal protein vaccine in female Macaca fascicularis

A vaccine formula comprised of five recombinant human intra-acrosomal sperm proteins was inoculated into female monkeys to test whether specific antibodies to each component immunogen could be elicited in sera and whether antibodies elicited by the vaccine affected in vitro fertilization. Acrosomal proteins, ESP, SLLP-1, SAMP 32, SP-10 and SAMP 14, were expressed with his-tags, purified by nickel affinity chromatography and adsorbed to aluminum hydroxide. Five female cynomolgus monkeys were inoculated intramuscularly three times at monthly intervals. All five monkeys developed both IgG and IgA serum responses to each recombinant immunogen on Western blots. Each serum stained the acrosome of human sperm and bound to the cognate native protein on Western blots of human sperm extracts. By ELISA, all monkeys developed IgG to each immunogen, with the highest average absorbance values to ESP, SAMP 32 and SP-10, followed by lower values for SLLP-1 and SAMP 14. IgA was also generated to each component immunogen with the highest average absorbance values to SLLP-1 and SP-10. For antigens that induced an IgA response, the duration of the IgA response was longer than the IgG response to the same antigens. This study supports the concept that a multivalent contraceptive vaccine may be administered to female primates evoking both peripheral (IgG) and mucosal (IgA) responses to each component immunogen following an intramuscular route of inoculation with a mild adjuvant, aluminum hydroxide, approved for human use.

Study on the antifertility effects of the plasmid DNA vaccine expressing partial brLDH-C4′

Partial cDNA sequence coding forMicrotus brandti radde(Brandt’s vole) testes-specific lactate dehydrogenase (brLDH-C4) was amplified by reverse transcription-polymerase chain reaction (RT-PCR). By inserting the product into the eukaryotic expression vector pCR3.1, pCR3.1-brLDH-C4′ was obtained as the prototype of contraceptive DNA vaccine. Immunization with pCR3.1-brLDH-C4′ in BALB/c mice generated antibodies specific to purified brLDH-C4′ and native mouse LDH-C4 protein. The birth rate of the pCR3.1-brLDH-C4′ immunized mice was found to be decreased significantly (80% lower than that of those immunized with pCR3.1). Functions of the elicited antibodies in sera from pCR3.1-brLDH-C4′ inoculated mice were further explored. The results indicated that the antibodies from the mice injected with pCR3.1-brLDH-C4′ could cause the agglutination of normal sperm suspension, while the ovarian structure and the development of ovarian follicles of these mice were not impaired, which gives a possible explanation for the immunocontraceptive effects of the pCR3.1-brLDH-C4′ DNA vaccine.

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.

Isolation and characterization of a haploid germ cell specific sperm associated antigen 9 (SPAG9) from the baboon

Previously, we cloned and sequenced a sperm specific antigen, designated as HSS (EMBL nomenclature human sperm associated antigen 9: hSPAG9) from human testis (Shankar et al.: Biochem Biophys Res Commun 243:561-565, 1998). The present study was conducted to isolate baboon proteomic homologue in order to find out whether the baboon can provide a suitable model for examining its immunocontraception effects. Baboon SPAG9 (bSPAG9) was cloned and sequenced from the baboon testis cDNA library. The baboon cDNA contained open reading frame encoding 760 amino acids. A 90.6 and 96.8% homology between baboon and human SPAG9 was found at protein and DNA levels. Analysis for tissue specificity by Northern blot procedure using various baboon tissues indicated that bSPAG9 was specifically expressed only in the baboon testis. Further, cell type expression analysis by in situ hybridization in baboon testis demonstrated the expression of bSPAG9 mRNA transcript only in the round spermatid suggesting haploid germ cell expression. Anti-human SPAG9 antibodies recognized the acrosomal compartment region of baboon sperm in indirect immunofluorescence (IIF). Flow cytometry analysis showed surface localization of bSPAG9 in live baboon sperm. The amino acid sequence data for nonhuman primate SPAG9 suggest that antibodies generated by vaccinating baboon with hSPAG9 will recognize nonhuman primate SPAG9, supporting the testing of SPAG9 contraceptive vaccine based on hSPAG9 in the nonhuman primate model.

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.

Molecular cloning and characterization of the macaque sperm associated antigen 9 (SPAG9): an orthologue of human SPAG9 gene

The present study was conducted to isolate macaque proteomic homologue of human SPAG9 (EMBL nomenclature human sperm associated antigen 9: hSPAG9; Shankar et al., 1998: Biochem Biophys Res Commun 243:561-565) in order to find out whether the macaque can provide a suitable model for examining its immunocontraception effects. Macaque SPAG9 was cloned and sequenced from the macaque testis cDNA library. The macaque cDNA contained open reading frame encoding 712 amino acids. A 84.9% and 94% homology between macaque and human SPAG9 was found at protein and DNA levels. Northern analysis and RNA in situ hybridization experiments revealed testis- and stage-specific expressions of macaque SPAG9 mRNA, mainly confined to round spermatid suggesting haploid germ cell expression. Anti-human SPAG9 antibodies recognized native SPAG9 in macaque sperm extract in Western blotting and the acrosomal compartment region of macaque sperm in indirect immunofluorescence. Flow cytometry analysis further revealed surface localization of macaque SPAG9 in live macaque sperm. The amino acid sequence data for nonhuman primate SPAG9 suggest that antibodies generated by vaccinating macaque with hSPAG9 will recognize nonhuman primate SPAG9, supporting the testing of SPAG9 contraceptive vaccine based on hSPAG9 in the nonhuman primate model.

Contraceptive vaccines targeting sperm

Overpopulation is a global problem of significant magnitude, with grave implications for the future. Development of new contraceptives is necessary, as existing forms of birth control are unavailable, impractical and/or too expensive for many individuals due to sociological, financial or educational limitations. Immunocontraception and, in particular, the targeting of antibodies to sperm-specific antigens implicated in sperm-egg binding and fertilisation offers an attractive approach to control fertility. Sperm-specific antibodies may impair fertility by inhibiting sperm motility, by reducing penetration of the cervical mucus by sperm, or by interfering in sperm capacitation or the acrosome reaction; alternatively, antisperm antibodies may invoke the complement cascade, resulting in sperm lysis. The antibodies raised against sperm-specific antigens have proved to be extremely effective at reducing sperm-egg interactions in vitro; fertility trials in subhuman primates will eventually be needed to prove the effectiveness of the sperm antigens in terms of contraceptive efficacy before trials in humans can be justified. In addition, existing and emerging strategies (such as sperm proteomics, the determination of molecular and structural details of sperm proteins, and the modelling of protein-ligand interactions using X-ray and/or NMR structures to name a few) are expected to provide the experimental foundation for the design of small molecule inhibitors with antifertility effects. The technology underpinning vaccine development is constantly being developed and the introduction of DNA/RNA vaccines is certain to impact upon the field of immunocontraception.

Sperm specific proteins-potential candidate molecules for fertility control

The increase in population growth rate warrants the development of additional contraceptive methods that are widely acceptable, free from side effects and less expensive. Immunocontraception, and in particular the targeting of antibodies to gamete-specific antigens implicated in sperm egg binding and fertilization, offers an attractive approach to control fertility. The development of a contraceptive vaccine based on sperm antigen represents a promising approach to contraception. In mammals, fertilization is completed by the direct interaction of sperm and egg, a process mediated primarily by sperm surface proteins. Sperm have proteins that are unique, cell specific, immunogenic and accessible to antibodies. A few of the sperm specific proteins have been isolated and characterized. The antibodies raised against the sperm specific antigens have proved to be extremely effective at reducing sperm-egg interaction in vitro; fertility trials in sub-human primates would eventually prove the effectiveness of the sperm antigens in terms of contraceptive efficacy.

Contraceptive vaccines

The control of human fertility would be revolutionised by the development of a safe, effective, long-acting contraceptive vaccine. The pursuit of this objective has involved the selection of appropriate targets within the reproductive process that are amenable to interference with antibodies. To date, three major targets have been researched. The zona pellucida (ZP) plays key roles in folliculogenesis, fertilisation and early development, and is comprised of powerful cell-specific antigens. The induction of infertility requires high ZP antibody titres that are difficult to maintain without inducing ovarian pathology characterised by a premature loss of primordial follicles. As a premature menopause would be a high price to pay for long-term contraception, this approach to a vaccine cannot progress until the cause of the ovarian pathology has been resolved. Sperm surface antigens represent another promising approach to contraceptive vaccine development. While there is some clinical data to support the likely efficacy of this strategy, none of the gamete-specific molecules characterised to date have fulfilled this promise. Anti-human chorionic gonadotropin (hCG) vaccines terminate pregnancy by preventing the maternal recognition of pregnancy. This vaccine has reached the stage of clinical trials, and preliminary indications are that the approach is safe and potentially effective. However, reliability may be an issue, given the observed inter-individual variability in antibody generation. The future of contraceptive vaccine development will clearly involve a continuation of the intense search for suitable targets and the development of improved immunisation procedures that exploit the latest innovations in vaccine technology.

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.

Plasmodium vivax promiscuous T-helper epitopes defined and evaluated as linear peptide chimera immunogens

Clinical trials of malaria vaccines have confirmed that parasite-derived T-cell epitopes are required to elicit consistent and long-lasting immune responses. We report here the identification and functional characterization of six T-cell epitopes that are present in the merozoite surface protein-1 of Plasmodium vivax (PvMSP-1) and bind promiscuously to four different HLA-DRB1* alleles. Each of these peptides induced lymphoproliferative responses in cells from individuals with previous P. vivax infections. Furthermore, linear-peptide chimeras containing the promiscuous PvMSP-1 T-cell epitopes, synthesized in tandem with the Plasmodium falciparum immunodominant circumsporozoite protein (CSP) B-cell epitope, induced high specific antibody titers, cytokine production, long-lasting immune responses, and immunoglobulin G isotype class switching in BALB/c mice. A linear-peptide chimera containing an allele-restricted P. falciparum T-cell epitope with the CSP B-cell epitope was not effective. Two out of the six promiscuous T-cell epitopes exhibiting the highest anti-peptide response also contain B-cell epitopes. Antisera generated against these B-cell epitopes recognize P. vivax merozoites in immunofluorescence assays. Importantly, the anti-peptide antibodies generated to the CSP B-cell epitope inhibited the invasion of P. falciparum sporozoites into human hepatocytes. These data and the simplicity of design of the chimeric constructs highlight the potential of multimeric, multistage, and multispecies linear-peptide chimeras containing parasite promiscuous T-cell epitopes for malaria vaccine development.

Immunization of female cynomolgus macaques with a synthetic epitope of sperm-specific lactate dehydrogenase results in high antibody titers but does not reduce fertility

Previous studies have reported reduced fertility in female baboons immunized with a synthetic peptide derived from the sperm-specific isozyme of lactate dehydrogenase (LDH-C). In this study, a similar approach was used to immunize female cynomolgus macaques with the same peptide sequence (bC5-19) conjugated to a T-cell epitope from tetanus toxin (TT). Twelve female monkeys were immunized with bC5-19:TT delivered with Ribi MPL adjuvant vehicle, and 10 control female monkeys were injected with the adjuvant vehicle only. All 12 females in the treatment group developed LDH-C-specific serum antibodies as measured by ELISA, but anti-LDH-C antibodies were not detected in vaginal fluids of the immunized animals. After 4 months of timed mating immediately following the immunizations, five of the ten immunized females became pregnant, as did six of the ten control females. Anti-sera from both pregnant and nonpregnant bC5-19:TT-immunized females recognize a single band at 35 kDa on Western blots of whole sperm extracts, and purified Igs from the same sera localize along the principle piece of the flagellum of permeabilized sperm.

Immunological response of female macaques to the PH-20 sperm protein following injection of recombinant proteins or synthesized peptides

Because of its location on the sperm surface and its multiple functions during fertilization, the PH-20 protein is a potential target for contraceptive vaccines. Cynomolgus macaques were immunized using four different adjuvants together with synthesized peptides or recombinant proteins representing selected regions of macaque PH-20. The synthesized peptide (amino acids 387-412, designated Peptide 4) was used as a linear molecule in a 1:1 ratio with a peptide sequence of tetanus toxoid, as well as a multiple antigenic peptide (MAP) matrix held together by scaffolding lysine residues. In the MAP construct, the ratio of Peptide 4 to tetanus peptide was 4:1. To circumvent the poor production of recombinant PH-20 in bacterial cells, two truncated forms of the molecule were expressed in Escherichia coli, G18 (encoding amino acids 143-510) and E10 (encoding amino acids 291-510). The adjuvants were Montanide ISA 51, Titermax Gold, Syntex adjuvant formulation (SAF), and QS-21. All of the antigen/adjuvant combinations produced significant immune responses as measured by ELISA. The circulating antibodies from immunized animals recognized macaque sperm surface PH-20 on Western blots and were shown by indirect immunofluorescence to bind to the surface of macaque sperm. Montanide and Titermax were associated with higher titers of anti-PH-20 antibodies than QS-21 and SAF adjuvants. Immunization with Titermax, however, resulted in sterile abscesses in 4 of 8 animals injected. We conclude that antigens derived from synthesized peptides and recombinant proteins representing selected regions of the PH-20 molecule can be used as vaccine components in combination with the adjuvant Montanide to elicit a significant sperm-directed antibody response in immunized macaques.

Immune response of male baboons to testis-specific LDH-C(4)

Four sexually mature male baboons (Papio sp.) were immunized with a chimeric peptide containing a B-cell epitope of the testis-specific lactate dehydrogenase (LDH-C(4)) and a promiscuous T-cell epitope of tetanus toxin. LDH-C(4) is the testis-specific isozyme of lactate dehydrogenase, and antibodies to this protein reduce fertility significantly in female nonhuman primates. Animals were immunized on Day 0 and received booster injections at Days 29, 61, and 344 after priming. Serum specific antibodies were determined at regular intervals during the initial 6 months and after the last booster. Testis biopsies were taken at Days 61, 127, and 183 after the primary immunization. Sperm-zona binding was assessed prior to and three times after the last booster. The present study demonstrated that this epitope of LDH-C(4) did not cause autoimmune disease and that sperm from these immunized males had a diminished zona binding capacity. These results suggest that a safe male immunocontraceptive based on development of anti-sperm antibodies may be feasible.

An efficacious recombinant subunit vaccine against the salmonid rickettsial pathogen Piscirickettsia salmonis

Piscirickettsia salmonis is the aetiological agent of salmonid rickettsial septicaemia, an economically devastating rickettsial disease of farmed salmonids. Infected salmonids respond poorly to antibiotic treatment and no effective vaccine is available for the control of P. salmonis. Bacterin preparations of P. salmonis were found to elicit a dose-dependent response in coho salmon (Oncorhynchus kisutch), which varied from inadequate protection to exacerbation of the disease. However, an outer surface lipoprotein of P. salmonis, OspA, recombinantly produced in Escherichia coli elicited a high level of protection in vaccinated coho salmon with a relative percent survival as high as 59% for this single antigen. In an effort to further improve the efficacy of the OspA recombinant vaccine, T cell epitopes (TCE's) from tetanus toxin and measles virus fusion protein, that are universally immunogenic in mammalian immune systems, were incorporated tandemly into an OspA fusion protein. Addition of these TCE's dramatically enhanced the efficacy of the OspA vaccine, reflected by a three-fold increase in vaccine efficacy. These results represent a highly effective monovalent recombinant subunit vaccine for a rickettsia-like pathogen, P. salmonis, and for the first time demonstrate the immunostimulatory effect of mammalian TCE's in the salmonid immune model. These results may also be particularly pertinent to salmonid aquaculture in which the various subspecies are outbred and of heterologous haplotypes.

Baboon spermatozoa-zona pellucida binding assay

This study developed a baboon in vitro system that allows transport of sperm from a treatment facility to an off-site location for subsequent evaluation of sperm functional capacity. We further described a sperm functional assay that evaluates baboon sperm binding to homologous zona pellucida, a baboon hemizona assay (HZA). Semen samples were collected from baboons via electroejaculation directly into refrigeration transport buffer. Postshipment semen characteristics were analyzed and each specimen prepared for assessment of sperm-zona pellucida interaction. Optimization of the baboon HZA included determination of the relationship between motile sperm concentration and zona pellucida binding. The effect of the sperm activators, caffeine and dbcAMP, on computerized sperm motion characteristics and HZ binding was also determined. A significant motile sperm concentration dependent increase was observed in sperm-zona pellucida binding. Maximal binding was observed at approximately 1-2 million motile sperm/mL. Treatment with the sperm activators, caffeine and dbcAMP, resulted in a significant increase in sperm progressive motility, straightline velocity (VSL), and amplitude of lateral head displacement (ALH), p <0.05 and a highly significant increase in curvilinear velocity (VCL), p <0.01. Treatment with caffeine and dbcAMP was not an absolute requirement for sperm-zona pellucida binding, inasmuch as binding did occur in the absence of activators. However, treatment with the two activators, caffeine and dbcAMP, resulted in a highly significant increase in HZ binding, p <0.0001. This system allows for the short-term maintenance of baboon sperm in a semiquiescent state until stimulation with the activators, caffeine and dbcAMP. It further provides a novel approach to delineating a contraceptive regimen's or agent's (ie, sperm vaccine) impact on specific cellular events occurring in the male gamete during fertilization.

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.