Sperm vaccine contraceptive success

US researchers have developed a new, potentially reversible form of male contraception that targets a key protein involved in sperm production. The team, based at the University of North Carolina, have shown their approach to be effective in male monkeys. Details of the research are published in the journal Science.

The new technique works by triggering the body's immune system to disable a protein called Eppin, which sits on the 'outer coat' of sperm. The researchers injected nine monkeys with human Eppin protein, causing seven to become infertile. The scientists think that antibodies made by the monkeys after immunisation with the human protein stick to the sperm, and stop them from working properly. Two thirds of a control group injected with a placebo vaccine went on to father offspring.

Previous attempts to create an immune-based male contraceptive have 'universally failed', according to male reproduction expert Bernard Robaire, of McGill University in Canada. This is thought to be because antibodies that stick to sperm proteins can also affect other cells in the testes, causing inflammation. In the latest study, the researchers think that the antibody is targeting sperm further down the male reproductive tract, so the testes are unharmed.

Other groups are working on hormonal methods of male contraception. Earlier this year, drug companies Schering and Organon began a clinical trial of a contraceptive for men based on a progestogen implant, plus regular injections of testosterone. However, contraceptives based on hormones can have other effects on the body, as well as halting sperm production. The new immune-based approach is less likely to produce unwanted side effects, since its action is restricted to the testes.

UK expert Jonathan Millar, of the Medical Research Council's Human Reproductive Sciences Unit, says that the Eppin-based treatment looks unlikely to have any deleterious effects in other areas of the body. 'Importantly, it does seem that it is reversible', he added, since 71 per cent of the monkeys recovered fertility within a year of stopping treatment. However, he also pointed out that not all of the monkeys in the study developed antibodies against Eppin, showing that immune methods of contraception may not always be 100 per cent effective. Study leader Michael O'Rand admits that the sperm vaccine has a long way to go, but believes the research offers 'a proof of principle' for this approach to contraception.