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[Immunological aspects of the development of contraceptive vaccines].

Presently available contraceptive methods are not optimal with regard to either effectiveness or convenience and may cause various side effects especially in third-world countries where adequate health care is often lacking. In an effort to develop an oral contraceptive without many of the drawbacks associated with those currently on the market intensive research is now being conducted on substances which would activate the female immune system to produce antibodies to sperm in the uterus and vagina causing a preventive effect against pregnancy. It is theorized that antibodies bind themselves to sperm in the cervix canal and thereby hinder mobility and thus fertility. The genital tract has been shown to be part of the muscosal associated lymphoid tissue" with antigens in the intestine-stimulating lymphocytes mainly Peyersian plaque. If the lymphocytes which are stimulated in the Peyersian plaque are not stimulated by the same local antigens (for example in the cervix) there appears a clonal (multiplying) expansion and antibody production. If this theory is correct it should then be possible to induce antibody production locally in the cervix by giving sperm antigens orally by placing these antigens in a capsule which would be resistant to stomach acid and thereby obtain a potentially reversible oral contraceptive. In a recent study confirming this theory the fertility of female mice was reduced after oral administration of sperm. Usually however various bodily protective systems operate to counter immune responses to fertility and pregnancy since female seminal plasma contains potent immune-suppressive elements which directly hinder the lymphocyte function. The uterine secretion is also believed to have such immune-suppressive powers. Work is now concentrating on finding specific antibodies to the reproduction hormone HCG (human chorionic gonadotropin) as this has been shown to hinder the degenerating of corpus luteum and accordingly is responsible for maintaining high progesterone levels throughout early pregnancy. It has been know that the immune reaction to HCG interrupts pregnancy at an early point in animals. The is because neutralizing antibodies hinder progesterone production as corpus luteum degenerates. Cytotoxic anti-HCG antibodies or activated T-lymphocytes may also possibly destroy the early pre-or periimplantation blastocyte. It may be possible to cause production of an immunogen or antigen which could cause antibody production with a maximum specified for HCG. A study showed that baboons immunized with this in the form of a systematic peptide had a fertility rate of only 9.5% while the control groups was 71.4%. Recently it has been shown that it is possible to clone HCG genes by recombined DNA technology. This cloning will probably make the effort to induce specific anti-HCG antibodies has now progressed to the stage that clinical trials on women are underway. One such study using LDH-C4 (lactate dehydrogenace C4) for synthesis immunizing has show significant reduction in fertility in dogs and cats. After a drop in the antibody effect normal pregnancy was found to occur. The antibodies prevent fertility apparently by agglutinizing the spermatocytes thereby immobilizing them. Another promising direction of research is in biochemical characterizing of the unique glycoprotein forming the zona pellucida. Passive immunization with anti-zona antibodies has been show to reduce fertility in mice. Active immunization with zona antigens has also demonstrated longterm suppression is possible. Future research may teach more about the biochemistry regarding antigens in the embryo and placenta so that it may be possible to find which embryo determinants will lead to a safer and more effective antifertility vaccine.