Contraceptive vaccines

The basic principle of a contraceptive (or anti-fertility) vaccine is to use the body's own immune defence mechanisms to provide protection against an unplanned pregnancy. Factors such as: economic production, convenience of use, relatively long-lasting but reversible action, low failure rate, and the avoidance of mechanical devices or exogenous hormones make this approach a potentially attractive option for family planning programmes in both developing and developed countries. The major efforts in research and development have involved the prospect of active immunization against specific antigens of sperm, ovum, zygote and early embryo, and the pregnancy hormone hCG. Several anti-hCG vaccines have entered clinical trials and show promising results. These vaccines operate by preventing or interrupting pregnancy at the peri-implantation stage probably by neutralizing the luteotrophic action of hCG. The most refined vaccine is one directed against the unique C-terminal peptide on the beta-subunit of hCG. This vaccine provokes antibodies that are specific for hCG and do not cross react with hLH. Future research efforts aim to optimize the anti hCG approach, utilize new vaccine delivery systems, and broaden the spectrum of target antigens of potential utility for contraceptive vaccines.

Vaccination for birth control

The global population is currently expanding at the unprecedented rate of nearly 1 billion per decade, with 94% of the increase occurring in the developing world. New methods of fertility regulation are urgently needed, and the development of birth control vaccines by active immunization against antigens specific for reproduction has made substantial progress during the last two decades. These vaccines are meant to have an outstanding impact on future control of worldwide population growth by providing safe, effective, long-lasting and reversible contraception. The most advanced of these vaccines are based on the placental pregnancy hormone human chorionic gonadotropin (hCG), and have already entered clinical trials. However, immunological cross-reactivity and lack of efficacy of anti-hCG antibodies seriously challenge this strategy. Conversely, efforts to understand the molecular events involved in the fusion of sperm and egg have led to the identification of new target structures for the development of fertility-regulating vaccines. Herein, we summarize the current state of birth control vaccines and discuss the risks and drawbacks of this approach to fertility regulation.

Reproductive rights and population control in Zimbabwe

The author argues that population control in Zimbabwe, in other developing countries, and even in developed countries is targeted at non-whites and at the poorer classes. She discusses fertility vaccines and male sterilization in this context, and makes the point that while the technology of population control flows from the North to the South, resources from the South are flowing North to maintain the economic status quo. "I think that the real population problem is the widening gap between a few greedy, irresponsible people, most of whom happen to be located in the North, and the rest of humankind, whose lives have been so denigrated that they are now merely statistics.... We can easily see that what should be feeding, clothing, housing, healing, pleasing Africans, goes North, all in the name of ¿development'."

The suitability of human chorionic gonadotropin (hCG)-based birth-control vaccines

It has been widely hoped that immunological methods of fertility regulation by active immunization against specific antigens of the oocyte, sperm, zygote and early embryo, and the placental pregnancy hormone human chorionic gonadotropin (hCG), will provide a means to control the problem of worldwide population growth. The most advanced candidate vaccines are based on hCG immunogens and have entered clinical trials. However, during the past few years, increasing evidence has emerged that the current approaches using hCG as the target molecule may have some major drawbacks. On the basis of their recent findings, Stephan Dirnhofer and colleagues raise doubts on the suitability, safety and efficacy of gonadotropin-based immunological contraceptive vaccines.

Vaccination for contraception

Vaccination for birth control has several advantages over currently available methods of family planning and should prove an attractive addition to the contraceptive armamentarium both in developing countries and in a developed country such as Australia. Concerns have been voiced by consumer health advocates that vaccines, like other long acting contraceptive methods, may be abused by health authorities in developing countries and by their use in vulnerable groups such as aborigines in our own country. These concerns need to be recognised and addressed. More difficult to accommodate are the anxieties expressed by feminist groups about the 'loss of control' and 'lack of body awareness' inherent in a method, such as a vaccine, that is relatively easily administered and has no overt side effects. There is no evidence that these concerns are shared by women in general. The antifertility vaccine that will most likely be applied first in family planning programmes is one directed against the pregnancy hormone hCG. A WHO vaccine directed against the C-terminal peptide of beta-hCG provokes a specific and safe immune response and will enter Phase 2 trials in Sweden this year. Subsequent developments with this vaccine will include the replacement of the current emulsion vehicle by a delivery system based on biodegradeable microspheres which will give a more sustained antigen release and duration of effectiveness.

Antibody response against three epitopic domains on human chorionic gonadotropin (hCG) in women and rodents immunized with a beta hCG-based immunocontraceptive vaccine

The antibody repertoire generated against human chorionic gonadotropin (hCG), following immunization with an immunocontraceptive vaccine based on the beta subunit of the hormone, in humans was compared with that generated in rats. Three epitopic domains represented by the beta hCG loop peptide 38-57, the carboxy-terminal peptide (CTP) 109-145, and a region defined by monoclonal antibody (MAb) 206 were probed. In both species, the titer of antibodies against the MAb 206-defined epitopic domain had a good correlation with the total anti-hCG antibody titers. However, the antibody response against the beta hCG loop peptide (38-57) was not observed in human subjects and there was a weak response against this peptide in rats. Despite the good anti-hCG antibody titers in all animals (n = 8), only two had antibodies against this domain. A good antibody response was observed against CTP in rats, whereas in humans this region was weakly immunogenic. Antibodies against CTP were detected in random samples in only 57% of the subjects and this response had no correlation with the total anti-hCG antibody titers. The high antibody response against CTP in rodents compared to humans may be due to its recognition as a foreign determinant. Our results demonstrate that contraception can be achieved in women despite a poor antibody response against the CTP (109-145) and a receptor binding domain (38-57) of beta hCG.

The value and use of different contraceptive methods

Reductions in the rates of maternal and child mortality as well as in demographic growth are directly linked to contraceptive usage. The development and availability of safer, improved contraceptives which are convenient to use could be expected to be used by a larger group of individuals and thus make an impact on reproductive health as well as on population growth rates. Such arguments have been used to support contraceptive research. This article deals with some of the developments that have occurred as a consequence of such efforts.

Tissue specificity of the acrosomal protein SP-10: a contraceptive vaccine candidate molecule

The tissue specificity of the intra-acrosomal protein SP-10 was examined by Northern blot and polymerase chain reaction (PCR) analysis. Messenger RNA from 36 tissues in the female baboon (Papio papio) was isolated, separated on agarose gels, transferred to nylon, and probed with either SP-10, beta-actin, or cyclophilin cDNA. Northern blots, which were processed at both low and high stringency, showed SP-10 to be expressed exclusively in the testis. The mRNA from each tissue was also reverse transcribed, and both SP-10 and beta-actin were amplified by PCR from the resulting cDNA. Ethidium bromide-stained agarose gels of the SP-10 PCR products showed three clear bands from the testis but no co-migrating bands from the other tissues. Southern blots of the PCR products showed that only the three bands in the testis were related to SP-10. The data demonstrate that the SP-10 gene products are testis specific, a characteristic essential for a contraceptive vaccine candidate molecule.

Salmonella may offer contraceptive

A reversible, inexpensive birth control vaccine for men and women may come from an unlikely source--genetically altered salmonella bacteria. The bacteria cause food poisoning, typhoid and diarrhea. But with some genes removed and others spliced in, an altered form produces proteins that make the immune system reject sperm and does not cause disease, says Dr. Roy Curtiss, a biology professor at Washington University in St. Louis, Missouri, US. The approach was announced in November at a US meeting of the Council for the Advancement of Science Writing. "Salmonella act as the factory, making specific antigens. It is a slow-release system," he says. The altered bacteria produce sperm antigens, and both male and female immune systems make antibodies against them. To sustain immunity, a booster vaccine might be necessary every 6 to 12 months. Numerous concerns, however, have been raised over the use of such live vaccines. A live vaccine, for example, could accidentally immunize people through fecal contamination of water or food. Researchers are testing the vaccine approach in mice and are scheduled to begin experiments soon with macaque monkeys and baboons. Experiments among humans are not yet scheduled and would not begin until ethical and health issues are resolved. The contraceptive vaccine could be inexpensive to produce and would require no refrigeration, making it easy to store. It would probably be administered orally, eliminating costs and risks associated with injections, Dr. Curtiss says.

Contraceptive vaccine development

Recent advances in antigen definition and production have made the development of a contraceptive vaccine more attainable. Such a vaccine must evoke an immune response that blocks an indispensable step in the reproductive process. Vaccine research involves many approaches to fertility prevention. Vaccines are being developed that could interrupt fertility by inhibition of gonadotrophin release, the function of follicle-stimulating hormone or the effects of human chorionic gonadotrophin (hCG); alternatively, they may prevent fertilization by interfering with the transport of spermatozoa or with sperm-zona pellucida binding. The most advanced prototype is a vaccine based on antibodies to beta hCG. Such vaccines are being studied for clinical efficacy. Many hurdles remain in contraceptive vaccine development. Since the antigens are peptides or small proteins, the resultant immune response is usually moderate, and better adjuvants and delivery systems must be developed to enhance and maintain the immune response. Improvement of the mucosal immune response may be necessary for vaccines incorporating sperm antigens. Research on vaccines that control fertility has resulted in a fascinating base of scientific knowledge that, it is hoped, can be converted into products that will allow another option for individuals who wish to control their fertility.

Vaccines against fertility

The first evidence for the efficacy of a birth control vaccine in humans is now available from the Phase II trials on the human chorionic gonadotrophin vaccine in India. Several sperm antigens have been identified as potential contraceptive immunogens and zona pellucida antigens have been reported that reversibly control fertility.