Male Immuno Contraceptives
Groups of researchers in Europe, India, and the US have been working to develop a contraceptive vaccine that triggers an immune response to part of the human reproductive system. The immunocontraceptive closest to market has been developed for women by New York’s Population Council. An immunocontraceptive for men could target sperm cells or sex hormones.
Advantages of a hypothetical male immunocontraceptive include safe, affordable, and infrequent administration, long periods of efficacy, and eventual natural reversal. Some formulations being studied do not interfere at all with secondary sex characteristics such as muscle mass and libido. Furthermore, the existing widespread immunization infrastructure could make an immunocontraceptive accessible where other methods are not.
Disadvantages include a 3-6 week delay to the onset of action and lack of user control over the end of contraceptive effect. Furthermore, a man wouldn’t have any direct indication of when the contraceptive started working, or when it stopped. As a way to overcome this uncertainty, some suggest regular pin-prick tests to monitor blood-antibody levels. Constant monitoring of this sort would make immunocontraceptives considerably less affordable and convenient.
How would it work?
In order to understand how an immunocontraceptive would work, here is a very simplified description of the immune system. When a foreign material enters the body, specialized cells in the lymph system recognize it as alien. The recognition of this foreign material (“antigen”) triggers a chain reaction of immune responses. Cells in the lymph system known as type B lymphocytes produce an antibody made to match that particular antigen. The antibodies help lymph cells recognize the antigen. Several different types of lymphocytes then work together to remove the antigen from circulation by killing or encapsulating it.
The body develops an immunological memory of the antigens it encounters, so it will be better prepared to fend off antigens when next encountered. This is why immunizations work. For example, polio immunization is a weakened form of poliovirus. When injected, the body’s B cells create antibodies against polio. Lymphocytes built to recognize the poliovirus remain in the body for many years. When the poliovirus is next encountered, these cells will recognize it quickly and react vigorously to prevent infection.
An immunocontraceptive works by directing the immune system against cells in the reproductive system. For the immune system to recognize cells from its own body as foreign, a foreign substance must be bound onto the targeted cell. This essentially tricks the body into thinking that its own cell is an antigen. The duration of contraception depends on how long the antigenicity-inducing substance sticks.
There is a naturally occurring precedent for immunocontraception. “Relatively large numbers of overtly healthy men and women” are naturally infertile due to “the presence of anti-sperm antibodies” in their blood. The causes and mechanisms of this infertility are not well understood, and researchers have called for a more complete mapping of the surface of sperm cell membranes.
Challenges to developing an immunocontraceptive
Male immunocontraceptives are largely in the basic science stages, many years away from the market. Researchers are identifying possible targets in the reproductive system and testing synthetic immune response-inducing compounds in animals. This field struggles with the typical difficulties of translating animal research into an effective human equivalent. Development of an immunocontraceptive is especially challenging because the response to the same antigen varies not only between species but among individuals within the same species.
One notable exception is the work that received media attention in November of 2004. A group of scientists at the University of North Carolina, the University of California at Davis, and the Indian Institute of Science have identified a human protein called “eppin” which is found only in the tissues of the testes and epididymis. They found that 7 of 9 monkeys inoculated with eppin they manufactured developed high levels of eppin antibodies. The monkeys were given eppin injections every 3 weeks for 23 months and were infertile during the treatment period. Five of the 7 monkeys regained fertility from 2 weeks to 6 months after inoculations stopped. Eppin is an interesting human target, but this study shows that its effectiveness and reversibility are still unpredictable.