How far from a hormone-based 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.

[Male contraception]

Contraception allows within a heterosexual couple to have a more fulfilling as possible sexuality while protecting against the occurrence of unintended pregnancy. In a majority of couples, contraception is assumed by women. Currently, male contraceptive methods most commonly used are the male condom and vasectomy. Many other strategies, including hormonal contraceptive regimens, have been proposed and evaluated. The purpose of this review is to present an overview of the various current and future male contraceptive methods.

Passive transfer of maternal GnRH antibodies does not affect reproductive development in elk (Cervus elaphus nelsoni) calves

Gonadotropin-releasing hormone is intermittently released from the hypothalamus in consistent patterns from before birth to final maturation of the hypothalamic-pituitary-gonadal axis at puberty. Disruption of this signaling via GnRH vaccination during the neonatal period can alter reproduction at maturity. The objective of this study was to investigate the long-term effects of GnRH-antibody exposure on reproductive maturation and function in elk calves passively exposed to high concentrations of GnRH antibodies immediately after birth. Fifteen elk calves (eight males and seven females) born to females treated with GnRH vaccine or sham vaccine during midgestation were divided into two groups based on the concentration of serum GnRH antibodies measured during the neonatal period. Those with robust (>15 pmol (125)I-GnRH bound per mL of serum) titers (N = 10; four females and six males) were designated as the exposed group, whereas those with undetectable titers (N = 5; three females and two males) were the unexposed group. Onset of puberty, reproductive development, and endocrine function in antibody-exposed and unexposed male and female elk calves were compared. Neonatal exposure to high concentrations of GnRH antibodies had no effect on body weight (P = 0.968), endocrine profiles (P > 0.05), or gametogenesis in either sex. Likewise, there were no differences between groups in gross or histologic structure of the hypothalamus, pituitary, testes, or ovaries. Pituitary stimulation with a GnRH analog before the second potential reproductive season induced substantial LH secretion in all experimental elk. All females became pregnant during their second reproductive season and all males exhibited similar mature secondary sexual characteristics. There were no differences between exposure groups in hypothalamic GnRH content (P = 0.979), pituitary gonadotropin content (P > 0.05) or gonadal structure. We concluded that suppressing GnRH signaling through immunoneutralization during the neonatal period likely does not alter long-term reproductive function in this species.

Contraceptions masculines non déférentielles : revue de la littérature

OBJECTIVES

To review the state of progress of the various male contraceptive methods (with the exception of deferential methods).

MATERIAL AND METHODS

A review of the literature was performed by using the key words: male/contraception, limiting the search to original articles in English and French. Articles on vasectomy and the other deferential methods of contraception are not considered in the present review.

RESULTS

Three methods of male contraception are widely used at the present time: withdrawal, male condom and vasectomy, although other types of male contraception have been shown to be effective, including hormonal contraception, which appears to be the most promising technique and the subject of the majority of research. Other contraceptive methods (immunological, thermal...) could constitute possible alternatives.

CONCLUSION

Male contraception remains under-used, as only male condoms are commonly used (apart from withdrawal and vasectomy). Consequently, new research protocols in the field of male contraception must be strongly encouraged.

Prospects for virally vectored immunocontraception in the control of wild house mice (Mus domesticus)

The wild house mouse (Mus domesticus) is not native to Australia and was introduced from Europe with early settlement. It undergoes periodic population explosions or plagues, which place significant economic and social burdens on agricultural communities. Present control mechanisms rely on improvements to farm hygiene and the use of rodenticides. This review covers over a decade of work on the use of virally vectored immunocontraception (VVIC) as an adjunct method of controlling mouse populations. Two viral vectors, ectromelia virus (ECTV) and murine cytomegalovirus (MCMV) have been tested as potential VVIC vectors: MCMV has been the most widely studied vector because it is endemic to Australia; ECTV less so because its use would have required the introduction of a new pathogen into the Australian environment. Issues such as efficacy, antigen choice, resistance, transmission, species specificity and safety of VVIC are discussed. In broad terms, both vectors when expressing murine zona pellucida 3 (mZP3) induced long-term infertility in most directly inoculated female mice. Whereas innate and acquired resistance to MCMV may be a barrier to VVIC, the most significant barrier appears to be the attenuation seen in MCMV-based vectors. This attenuation is likely to prevent sufficient transmission for broad-scale use. Should this issue be overcome, VVIC has the potential to contribute to the control of house mouse populations in Australia.

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

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

Biological control of vertebrate pests using virally vectored immunocontraception

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

Epitope topology and removal of mouse acrosomal plasma membrane by P12-targeted immunoaggregation

P12 is a Kazal-type trypsin inhibitor that has been purified from mouse seminal vesicle secretion. We observed a slight impact of P12 on sperm capacitation, and demonstrated the removal of plasma membrane overlaying the acrosome region by immunoaggregation of P12 on mouse sperm. Further, we compared the immunoreactivity of P12 antibody to ten P12 variants, including six single-site mutated mutants (R19L, Y21V, D22G, R43G, K44S, and R45T), two multisite mutated mutants (R43G/K44S/R45T and L50H/R52G/K53A), and two deletion mutants (Nd10 and Cd8) in which 10 and 8 residues were deleted from the N- and C-terminals, respectively. We found that the N-terminal region, 43RKR45, and the C-terminal region, but not R19, Y21, and D22, are involved in the three epitopes that reside on one side and are three-dimensionally distant from R19, Y21, and D22 on the P12 molecule. Based on the epitope topology, we elucidated the structural basis by which P12 antibody immunoaggregated P12 on sperm head.

Fertility control in wildlife: humans as a model

In a time of accelerated extinction rates and biodiversity loss, it may seem illogical to be concerned with methods limiting the reproduction of wild populations; however, there is an urgent need to inhibit the proliferation of a wide variety of species. The range of animals for which fertility control is desired makes the development of a single method impossible. The various reproductive strategies used by individual species, the desired outcome of contraceptive programs (reversible or irreversible; male or female directed) and our ignorance of the reproductive biology of many endangered species necessitate thorough species-specific investigations. As fertility control in humans is a reality and research into methods of fertility control is more advanced, humans serve as a model for developing contraceptive approaches for wild species. Population control by traditional methods (indirect or direct intervention by culling, poisoning, translocation, etc.) is increasingly unacceptable to the public, making human studies even more valuable for finding solutions to overabundant wild populations. This review compares and contrasts the range of contraceptive methods used in both wildlife and humans.

Nonhormonal drugs for contraception in men: a systematic review

Nonhormonal drugs for contraception in men may have advantages over hormonal methods. The nonhormonal methods can have more rapid onset and less interference with androgen-dependent functions. This systematic review summarizes the clinical studies evaluating nonhormonal drugs administered to men for contraception. Relevant clinical results were found for gossypol, which is derived from the cotton plant, and for extracts of Tripterygium, a plant used in Chinese traditional medicine. Randomized, controlled trials were available on the efficacy of gossypol and on the effect of gossypol on potassium levels. Gossypol had problems with low efficacy and toxicity. For Tripterygium, 2 observational studies described men who were treated for rheumatoid arthritis. Although sperm density was lower among those taking Tripterygium, later reports indicated some toxicity. Nonclinical research continues on isolates of Tripterygium. No clinical studies for contraception in men were found for nonhormonal vaccines or neem, which is also a plant used for medicinal purposes. Clinical trials studied injecting styrene maleic anhydride into the vas deferens, but no comparative data were provided. At this time, no safe and effective nonhormonal drug is available for contraception in men.

TARGET AUDIENCE

Obstetricians & Gynecologists, Family Physicians.

LEARNING OBJECTIVES

After completion of this article, the reader should be able to state that the number of studies concerning the use of nonhormonal drugs for male contraception are very limited, point out that the two nonhormonal drugs used to a small degree have varying results and serious side effects, and recall that there are limited clinical studies on use of vas deferens injections and vaccines in humans.