Over the millennia, people have come up with some very effective ways to avoid having babies. The ancient Egyptians and Greeks used linen sheaths and animal bladders, precursors to modern latex condoms and diaphragms. Now we’ve got spermicides, sponges, intrauterine devices, pills, and implants to keep sperm and egg apart. There’s just one problem: The people who want to avoid pregnancy aren’t always using contraception.
“The big fact here is that about half of all pregnancies are unintended,” says Deborah Anderson, a professor at Boston University Medical School who specializes in obstetrics, gynecology, and infectious diseases. “Even though we have a really good method in hormonal contraception, it’s not penetrating as well as we’d like.”
There are plenty of reasons why some people don’t want to use hormonal contraception: It requires a prescription, it can cause unpleasant side effects, it puts the onus of contraception on women, and it requires remembering a daily pill or getting a shot every three months, or having a more invasive procedure to put in an implant. Other methods have their drawbacks, too: Some require partner consent, are easy to forget or use incorrectly in the heat of the moment, or have a lower success rate.
So scientists have been working on a new method that would be easy to use, discreet, and effective without changing women’s hormones. This strategy uses manufactured proteins called monoclonal antibodies to mimic antibodies used by the immune system and attack sperm before they make it to the egg. Recent papers—one published in Science Translational Medicine in August and another published in EBioMedicine in July—demonstrate that these antibodies can latch onto sperm and render them impotent. Other studies have investigated whether these antibodies could be used to fight off HIV or the virus that causes herpes, and whether they are safe to apply as a topical contraceptive or as an insert like a vaginal ring.
“The timing is right,” says Anderson, a coauthor on the EBioMedicine paper, which showed that manufactured antibodies were effective at binding to sperm.
If monoclonal antibodies sound familiar, that’s because they’ve recently gotten a lot of attention as a treatment for fighting Covid-19. Antibodies are proteins that the human immune system makes to combat infections. They bind to specific sites on specific invaders and neutralize them, while also signaling to the body that it’s under attack and needs to make more defensive agents. We’re born with some of our antibodies. Others are created after we’re exposed to a new germ and get sick—think of the itchy, hard-won immunity that comes from having the chickenpox. And some are created after exposure to a vaccine that trains the body to fend off certain invaders without the misery of actual illness.
And now, some are created in the lab. These are meant to be short-term defenders, not a permanent immune system alteration; kind of like temporary bouncers who can block unwanted guests—sperm—from joining the party.
Anderson envisions a vaginal film that could be purchased at a pharmacy without a prescription. Each film would last for about a day. “I think it might be popular for use by women who have occasional intercourse,” she says. “They don’t want to be on something like a hormonal method that is a constant method. They would want to use a product only when they need it.”
Some people naturally produce anti-sperm antibodies, which don’t kill the sperm, but make them coagulate into a giant tangle. When the sperm can’t swim out of the vagina’s inhospitable, acidic environment, they die. In the 1970s, scientists started trying to reproduce those antibodies in the lab. But “at that time, the ability to manufacture antibodies and give them at specific dosages just was not possible,” says Samuel Lai, director of the pharmacoengineering program at the University of North Carolina at Chapel Hill and coauthor on the August paper. It was also incredibly expensive to synthesize enough of them. “That’s why all of the early work was focused on a contraceptive vaccine,” he continues.
Such a vaccine would have trained the body to make its own antibodies. It wouldn’t require a daily pill or for users to even tell their partners that they were using contraception. It seemed like a promising solution, and in the 1980s the World Health Organization created a Contraceptive Vaccine Task Force. But the project ran into trouble. First, there was the risk that a vaccine could make people permanently infertile, something that wasn’t acceptable for users who wanted to have children eventually. Then there was the problem of variability. People generate different levels of immune response to vaccines, and there was no way to guarantee equal protection for all users. Eventually, the WHO abandoned the project.
But three decades later, the cost of making antibodies has plummeted. Scientists have gotten better at growing antibodies in animal cultures and even on plants. They can be attached to a film, like Anderson imagines, or delivered via a vaginal ring that would dispense them over a few days or weeks. “It literally will be costing pennies per day,” Lai says, which is important because contraceptives need to be affordable and easy to use.
Plus, scientists have gotten better at tinkering with them. Lai takes advantage of new techniques that allow researchers to edit proteins and give them more adhesive binding sites that latch on tightly to proteins on the outside of the sperm. In his lab’s recent paper, which tested their engineered antibodies in sheep, they showed that they are 10 to 16 times more potent than the ones found in nature, and faster and more effective at binding to sperm.
Meanwhile, Anderson’s group has conducted a Phase I clinical trial, which tests for safety and dosage in a small group of healthy human volunteers. Nine women applied the antibodies via a vaginal film every day for a week. The researchers also ran a placebo study with 29 women, giving some participants a film that had no antibodies. They found that the women in the antibody group had the same vaginal pH as the placebo group, didn’t contract any bacterial infections, and that the antibody concentrations stayed strong and active for 24 hours, giving women protection for about a full day after they applied the film. But the team still has to prove that the film will work in larger trials among sexually active women, and Anderson estimates it could be a decade before there’s a product on the market. She’s also starting research on how to administer the antibodies as a contraceptive gel that could be applied to the penis. Unlike a spermicide, which is typically applied in the vagina, this would give men a contraceptive option beyond condoms and vasectomies.
Lai’s work is a little behind Anderon’s. He’s still in animal testing and has to run other preclinical safety tests before he can get permission to start a trial with people, likely in 2023.
“All these things look good,” says Daniel Johnston, chief of the Contraceptive Research Branch of the National Institute on Child Health and Development (NICHD). But he is still only cautiously optimistic because, as he points out, “at some point somebody has to get up there to the clinic and show us that it’s safe and that it works.” That means larger trials including a post-coital test that would count how many sperm make it to the cervix after a woman using the antibody contraception has sex.
The NICHD has funded both Lai and Anderson’s projects, and Johnston points out there are other new forms of birth control being developed, too. Phexxi, a non-hormonal contraceptive, was approved by the FDA and went on sale last September. It works by lowering the pH in the vagina so it is inhospitable for sperm. Hormonal contraceptives for men that use synthetic hormones to block the production of testosterone and sperm are in Phase 2 clinical trials.
But even if those options all become available, there may still be a need for monoclonal antibody contraceptives. Birth control advocates say that it’s best to have a range of options, from short-term to long-lasting, or that don’t require prescriptions or hormones for people who don’t want to use those things. “It’s about giving women options as their reproductive needs change over the course of their reproductive lifetime, and providing some better options for men,” Johnston says.
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