Monoclonal Antibodies for Birth Control

Medically Reviewed by Traci C. Johnson, MD on June 16, 2022
4 min read

Many women cannot, or prefer not to, use hormonal birth control, such as the pill or an IUD. But convenient and easy hormone-free choices are limited. That’s why several research teams around the country are exploring a common cause of female infertility as a potential means of contraception.

Still in development, here’s what’s known about the use of monoclonal antibodies for birth control.

Some women who have trouble getting pregnant eventually learn from their doctor that their body is making antibodies to their partner’s sperm. They're called antisperm antibodies

Antibodies are proteins that your immune system makes to fend off outside invaders, like germs, bacteria, and viruses. When the germ enters your body, your immune system recognizes it as an unwelcome outsider and makes antibodies to fight it.

Believe it or not, sperm have some of the properties of germs and can prompt the immune system of the body that they enter to attack them. Research suggests that both men and women carry antisperm antibodies, but most people don’t carry enough of these proteins to cause infertility.

Scientists aren’t sure exactly how the antibodies develop, but they have some theories. One is that when sperm enters the digestive tract through oral or anal sex, the body mistakes it for a germ and then makes antibodies against it.

It’s not clear to what degree antisperm antibodies in women keep them from getting pregnant, but doctors find the proteins in about 9% to 12% of the women they treat for infertility.

Now that the manufacturing of synthetic antibodies, called monoclonal antibodies, is becoming increasingly common in the treatment of numerous conditions from cancer to COVID-19, researchers are exploring the use of these antibodies as a form of hormone-free contraception for women.

Teams of researchers around the country at various universities and drug companies have studies underway to advance the development of an antisperm antibody form of birth control. The various studies involve taking an antisperm antibody from an infertile woman and cloning it for use as contraception.

The experimental form of contraception can come in the form of a vaginal ring that continually delivers antibodies throughout a woman’s fertility window or a dissolvable film that is inserted in the vagina before sex.

When sperm enters the vagina, the antisperm antibodies recognize the sperm as an unwanted invader. The antibodies then latch onto the sperm and cause them to cluster together in large clumps. Sperm, by design, are able to pass through mucus in the female reproductive tract in order to reach and fertilize an egg. But when the antibodies herd the sperm up into larger masses, sperm are no longer able to get through the mucus and reach the egg. The antibodies effectively stop the sperm in their tracks.

Monoclonal antibodies are not a barrier form of birth control like condoms are, so these proteins alone wouldn’t prevent women from getting an STD from their partner. But some of the research into this form of birth control involves delivering other types of antibodies along with the antisperm antibodies.

Phase I clinical trials – the first step on the years-long road to FDA approval of a new drug –  have tested the safety of a dissolvable vaginal film that includes antibodies against sperm as well as one that contains antibodies against herpes types 1 and 2 and HIV. Early findings show that  it was generally safe and well tolerated without any serious side effects. Eventually, the researchers plan to combine the contraceptive and disease-preventing antibodies into one film.

All medications, whether prescription, over the counter, or herbal supplements, have side effects. Contraceptive monoclonal antibodies will be no exception, but it’s too early to know what those side effects may be.

Side effects may depend in part on the delivery method: ring versus film.

In the phase I clinical trial of the anti-herpes and anti-HIV film, the women in the trial didn’t report any significant side effects. Labs taken during the study found microscopic traces of blood in some women’s urine. But the women didn’t have any symptoms from this side effect.

It’s very early in the development of a monoclonal antibody approach to birth control. One group’s contraceptive film will soon advance to a phase II clinical trial. Other groups are not yet ready to test their contraceptives on humans. So far, they’ve done studies in large animals, including sheep.

After passing animal tests, experimental drugs must go through three to four phases of human clinical trials before the drugmaker can apply for FDA approval of the medication. Each phase includes more people and lasts longer than the phase before. Phase I trials take a few months and include fewer than 100 people. Phase III trials can take up to 4 years and can include 1,000 or more people.

Each phase of a clinical trial also weeds out the medicines that don’t pass muster. While 70% of experimental drugs make it through phase I. Just 25% to 30% advance past the later phases of human clinical trials.

Given this lengthy process, it’s unclear whether monoclonal antibodies could be a birth control option for the current generation of fertile women, but they may be one of many new choices available to the next.