Sperm stopper. Vaccinated monkeys suggest that a new kind of male contraceptive is possible.

Shots Make Monkeys Shoot Blanks

When the 1880s debut of vulcanized rubber and the 1930s advent of latex mark the latest advances, one quickly understands the sorry state of male contraceptives. Researchers in this beleaguered field have tried to supply men with other options but haven't had much success. Now a team in the United States and India reports promising preliminary results for its new contraceptive vaccine for males.

Reproductive biologist Michael O'Rand of the University of North Carolina, Chapel Hill, crafted the vaccine after reporting his discovery of a novel male-only protein in 2001. The protein, called Eppin, has been found so far on the surface of sperm cells and elsewhere in the testes and epididymis. Its function isn't clear. But O'Rand reasoned that if a male harbored antibodies to this protein, his sperm might malfunction.

O'Rand teamed up with colleagues at the Indian Institute of Science in Bangalore, which hosts a large primate research center. The researchers injected nine monkeys with human Eppin protein and gave six monkeys a sham vaccine. Two of the Eppin-vaccinated monkeys were dropped from the study, however, because they didn't produce sufficient antibodies to the protein, a mysterious problem other immunocontraceptives have encountered.

The monkeys got boosters of vaccine every 3 weeks. To test whether it worked, immunized males spent several days each with three different females during the fertile peak of the females' menstrual cycle. The upshot: None of the seven vaccinated monkeys managed to impregnate a female. Four of the six control monkeys did. Although the contraceptive effect of the vaccine was intended to be reversible, only five of the seven vaccinated monkeys, some of whom received the vaccine for nearly 2 years, recovered their fertility during the study, the group reports in the 12 November issue of Science. "It's hard to say" what that means, says O'Rand. "Maybe they recovered 2 weeks after we quit" testing them.

"There seems to be some real promise," says Ronald Swerdloff, a reproductive endocrinologist at the University of California, Los Angeles. Still, "it's just early in the game," with too few monkeys tested, to conclude whether the approach will pan out, he adds. O'Rand and his colleagues are now trying to understand how their vaccine disrupts fertility. One possibility is that it leaves sperm sluggish.

Related sites
O'Rand and colleagues' Science paper
Michael O'Rand's home page