Non-hormonal contraceptive supercharges antibodies against sperm
Contraceptives like the pill may be effective, but messing with hormones has a range of unpleasant side effects. Now researchers are experimenting with a new non-hormonal contraceptive based on antibodies, which stops sperm swimming through mucus.
The new technique is based on monoclonal antibodies, synthetic versions of the antibodies that our bodies naturally produce against various pathogens. These treatments are currently being tested against a variety of diseases, such as asthma, malaria, COVID-19, rabies, and acne.
For the new study, researchers at the University of North Carolina at Chapel Hill started with antibodies with a target that might be surprising – sperm. Antisperm antibodies can arise in anyone who engages in sexual activity with men, and may play a role in infertility in up to 30 percent of affected couples.
The team took samples of these antibodies from infertile women, and engineered them to be even more potent against sperm. Normally, each antibody molecule only has two binding arms to attach to their targets, but the scientists boosted that to between six and 10 arms. Essentially that means the antibodies can catch hold of more sperm and clump them together.
“We engineered antibodies that were at least 10- to 16-fold more potent at agglutinating sperm and reducing sperm permeation through mucus than the best known antibody,” says Bhawana Shrestha, first author of the study. “This in turn prevents sperm from swimming through mucus and reaching the egg altogether, enabling potent, non-hormonal contraception with a pharmacological mechanism that has already been validated in women.”
The team tested the antibodies in sheep, which have a similar-sized reproductive tract to humans. Solutions containing just a few dozen micrograms of the antibodies were injected into the animals’ vaginas, followed by injections of sperm. Samples were removed and analyzed after two minutes, showing a 99.9 percent drop in motile sperm compared to control groups.
The researchers say that this contraceptive could be applied through a few different methods. It could take the form of a ring placed into the vagina that releases the antibodies slowly over weeks, or it could be used as a dissolvable film inserted just before sex.
Of course, it’s still early days for the technique, and trials have yet to be conducted in humans. One potential hurdle is that monoclonal antibodies have proven prohibitively expensive in the past, but the team says that this could potentially be overcome in this case because far smaller doses are used. Further work will investigate whether it can be a viable contraceptive.
The research was published in the journal Science Translational Medicine.