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Recent studies from WHO indicated that a large proportion of human contraceptive needs cannot be covered by the already existing means for different reasons (medical, economical, political, and cultural). Therefore, development of new effective methods targeting birth control methods affordable by under-privileged populations turns out to be necessary. Over the last 20 years, a large number of strategies have been used for contraceptive vaccines and thus multiple antigens have been identified as potential targets for immunocontraception. Nowadays, the most acute researches are based on suppression of the secretion and the activity of gonadotropic hormones (GnRH, LH/hCG, FSH) or the targeting of antibodies specific to sperm surface (RSA-1, SP10, SP17, TCLe-1, PH-20) and oocyte antigens (ZP1, ZP2, ZP3). We developed a contraceptive vaccine against FSH receptor. Adult male monkeys (Macaca radiata) were immunized with filamentous phages displaying at their surface N-terminal peptides of the FSH receptor. Long term male contraception has been achieved without any alteration of circulating testosterone levels, sexual behaviour or of any other discernable metabolic changes. Interruption of vaccination resulted in full recovery of sperm production and male fertility. Contraceptive vaccines are aimed to block an essential step in the reproductive process. From this point of view, efforts have to be focused on the challenge to raise is to ally our knowledge on reproductive physiology and protein biochemistry for a better understanding of the target antigen's function.

Male contraception is still an unresolved problem because scientists do not yet clearly understand spermatogenesis, particularly hormonal regulation and identification of growth factors responsible for spermatozoa development. Suppression of luteinizing hormone and of follicle stimulating hormone is a possible approach. Yet, it takes 60 days to achieve azoospermia and it is necessary to substitute an androgen. Despite the fact that many trials using steroids (androgens, progestins and androgens) or a gonadotropin releasing hormone (GnRH) agonist with androgens have been conducted, not every subject achieves azoospermia. Initial trials of GnRH antagonists in association with testosterone enanthate show that this combination achieved azoospermia in almost all subjects. This approach must be improved by developing long acting antagonists and a more physiological testosterone substitution. Another approach, which inhibits reversible secretion of gonadotropins, leans toward the production of an anti-GnRH vaccine. So far, studies have not produced acceptable results, despite a reduction in the production of spermatids. No animal achieves azoospermia. Isolation and cloning of human sperm surface glycoproteins would lead to another type of contraceptive vaccine. This antigen would prevent sperm from joining with the egg.

Sperm surface antigens may induce an immune response in mammals. In humans, the presence of antisperm antibodies has been noted in the blood, seminal plasma, cervical mucus, and follicular liquid. Because they provoke immobilization and/or agglutination of sperm and a diminution of the rate of fertilization in vitro, these antibodies are believed to be a factor in some unexplained infertility, as for example after surgical reversal of vasectomy. These observations have led to research oriented toward development of a nonhormonal contraceptive method based on the immunological capacities of some sperm antigens. Possible secondary effects and the modes of action remain poorly understood. Antisperm immunoglobulins in the male should be induced by epitopes that are specific to sperm excluding the proteins of the sperm membrane, so that they will be without effect on functions other than fertilization. The epitopes should be located on the sperm surface and should be of post-testicular origin because of the risk of orchitis posed by testicular antigens. The antisperm immunoglobulins should also be present in the area surrounding he sperm in the male genital tract because of the limited permeability of the tract to immunoglobulins and other large molecules. The antisperm immunoglobulins should not be inhibited in the male by the immunosuppressive activities of the seminal plasma or in the female by capacitation. In vivo and in vitro observations indicate that various functions may be altered by antisperm antibodies. The antibodies may immobilize the sperm, block interaction with the oocyte at the level of the zona pellucida, block adherence to the vitelline membrane, or cause anomalies in embryonic development. In rats, isoimmunization against epididymal cofactor of the sperm zona pellucida receptor results in reduced sperm mobility and reduced fertility. The same study was conducted in 12 rams selected for homogeneity of sperm characteristics. Isoimmunization of rams induced transient asthenospermia. Most sperm antigens involved in fertilization are poorly understood. Observations in the ram suggest that embryonic mortality following isoimmunization should be studied.

The immunological contraceptive methods whose development is described in this work appear to inhibit the action of antigenic molecules necessary for fertilization. Antigens in the gametes or their envelopes that intervene in reconnaissance or fusion of the gametes appear to be more promising targets than those at the level of gamete production in the gonads. Clinical examples show that infertility may be spontaneously acquired in both sexes through active immunization. Contraceptive action can only be sought if the gametes carry specific antigens, so that other physiological functions will not be disturbed, and if the antigens play a determining role in fertilization. Research currently is oriented toward 3 complementary targets, the sperm and the 2 envelopes of the oocyte, the zona pellucida and the cumulus oophorus. Possibilities appear to exist of preventing the intervention of several different molecules in fertilization, although most of them are still poorly understood. In the past 10 years, various monoclonal antibodies have been produced against sperm of different animal species, some of which are capable of inhibiting fertilization in the same species and also in human beings. But in vivo effects of these antibodies have not been valuated, even in the same species. Active immunization of male or female guinea pigs with a sperm surface antigen has led to sterility, through inhibition of attachment of sperm to the zona pellucida, but the monoclonal antibody against the protein does not recognize the human sperm. Polyclonal antibodies against the same protein might be possible for human contraception. The biochemical and physiological study of monoclonal antibodies against human sperm is facilitated if the antibodies cross with rodent sperm. 2 such antibodies directed against proteins secreted by the human testicles are capable of inhibiting murine and human fertilization in vitro. Attempts to achieve active or passive immunization by targeting antigens of the zona pellucida have been underway for 2 decades in different animal species using ever more selective antigenic material. But in vivo animal studies caused serious ovarian disorders that would be unacceptable in contraception. A polyclonal antibody against the intercellular matrix of the human cumulus oophorus is capable of inhibiting fertilization in vitro, with the action resulting from a strong reduction in the number of sperm attached to the zona pellucida. Numerous aspects of immunocontraception are still at the research stage. Apart from the choice of the moist appropriate antigens, active immunization in human subjects must be preceded by massive production of purified antigens. Research is needed on the adjuvant, the possibility of maintaining high levels of antibodies, and the return of fertility. Despite the obvious public health need, few laboratories are engaged in this type of research.

Immunointerruption of pregnancy consists of preventing pregnancy or terminating it at an early stage through antibodies. The antibodies may be obtained after administration of vaccine to induce their formation through active immunization, or by direct injection through passive immunization. Antigens that could potentially be used are found in sperm, the zona pellucida, and reproductive hormones, especially the chorionic gonadotropins. The sperm antigens are basically enzymes such as hyaluronidase and accrosine. 3 glucoproteins have been identified in the zona pellucida of mice and pigs. In vitro studies have shown that fertilization can be prevented if eggs are exposed to antizona-pellucida antibodies along with sperm. Active immunization could give longer term results, but ovarian function could also be affected if the antigens weren't purified. Much research has been devoted to identifying human embryonic antigens through analysis of the proteins of the cells of embryonic teratocarcinoma. Among placental antigens, the glucoprotein SP1 synthesized by the trophoblast is under study. Anti-SP1 antibodies appear to cause abortion in monkeys, but knowledge of these antigens is still fragmentary. Various reproductive hormones have been studied, but too many undesirable effects could result from the use of luteinizing hormone, luteinizing hormone releasing hormone, follicle stimulation hormone, or steroids. Human chorionic gonadotropin (hCG), however, is more promising. It is a glucoprotein formed of alpha and beta subunits, both of which are needed for hCG to interact with its receptor. The alpha subunit has the same sequence as that of other hormones of the same species, but the beta subunit is specific to each hormone. Studies are underway to determine the site of amino acids and peptide sequences capable of inducing an anti-hCG response which would inactivate the biological activity of hCG. Different teams have used synthetic peptides analogous to sequences of beta-hCG or fragments obtained by enzymatic cleavage of natural hCG to block pregnancy in rats and baboons. The presence of antibodies can block pregnancy without disturbing ovulation or modifying menstrual regularity. No toxic or secondary effect has been observed in animals. A multicenter phase 1 test using beta-hCG coupled with tetanus antitoxin caused almost all the women participating to develop antibeta-hCG and antitetanus anatoxin antibodies, but titres of antibodies varied greatly between different women, required 5-6 months to develop, and declined rapidly thereafter. Several pregnancies were observed, especially in women with low titres of antibodies. The approach of passive immunization through direct injection of antibodies has met with numerous obstacles, including lack of success in producing human monoclonal antibodies. Although a 2nd generation of vaccines in under study, the potential role of immunointerruption of pregnancy in fertility regulation remains to be clarified.

The contraceptive properties of antigonadotropin releasing hormone (GnRH) antibodies, and GnRH antagonists and agonists are examined, and their modes of action and possible therapeutic uses explored in this article. Maximum neutralization of GnRH in women through active immunization requires 2-3 months for the production of antibodies, although other fertility-related changes occur simultaneously; in addition, practical difficulties arise from the individual variability in immune response. Passive immunization is probably a more promising route for fertility suppression. In the past few years a number of GnRH agonists and antagonists have been synthesized and studied using rats and other animal models; the greatest progress in contraceptive development has occurred with GnRH agonists at high doses for short periods or at lower doses over a longer interval. The simplest approach would be to suppress ovulation entirely with a continuous dose of GnRH agonist, and trials among 90 women in Uppsala and Berlin using a nasal spray over 3-12 months did not produce any pregnancies or irreversible effects. Individual variations were noted in the response to treatment, with 20-25% experiencing amenorrhea. Potential problems with the method might be caused by exposure to estrogens in the absence of progesterone or by very low levels of estradiol. At present GnRH agonists do not appear suitable for widespread use in developing countries because of their difficulty of administration, but they may be appropriate for women seeking alternatives to oral contraceptives. Although they represent 1 of the most promising new approaches to contraception, several years of study are still required to resolve problems arising in treatment. They have potential future applications in treatment of conditions such as precocious puberty and tumors dependent on sexual hormones.

An anti-beta human chorionic gouadotropin (HCG) vaccine has been tested on rhesus monkeys and women to prevent pregnancy by Talwar and his colleagues in India. The beta subunit of HCG must be used since the HCG alpha subunit is identical to a part of the luteinizing hormone molecule. The HCG beta subunit is bonded to tetanus toxin, whose properties are known. There were observed side effects on menstruation, lactation, progesterone, nervous system, respiration, or blood pressure in women, or on metabolism, endocrine systems, or organs in animals. In women the antibody titer rose from 4-6 weeks to a maximum at 5 months, then dropped to zero in 11-16 months. A 2nd immunization brought on a rapid secondary response. Other workers have doubts about the reversibility of anti-beta HCG because abortions have been recorded after antibody levels were undetectable.