Gene Therapy Injection Could Prevent Pregnancy in Cats Without Spaying

A new gene therapy could soon eliminate the need for invasive surgeries to spay cats. Researchers have developed an injected gene therapy that prevents female cats from getting pregnant. The therapy targets anti-Müellerian hormone, a protein that helps fetal sex organs develop. A modified virus introduces the gene that makes this hormone into the cat's cells, which then produce more anti-Müellerian hormone than normal. This high level of protein may prevent the ovaries from releasing eggs, thereby keeping the follicles, which house and release eggs, in a dormant state.

Results of the study, published in Nature Communications, show that none of the six treated cats became pregnant even after mating with a fertile male. In contrast, the control cats gave birth to litters after mating with males only once. The therapy could provide a more efficient way to control the global population of feral cats that numbers in the hundreds of millions. Feral cats kill billions of birds and small mammals around the world every year. Spaying both feral and pet cats help keep feline populations under control.

The therapy, if successful in further testing, may eliminate the need for surgery and multiple doses of medication, especially for controlling feral populations. Vaccines targeting hormones that spark ovulation have so far proven ineffective over the long term. The gene therapy, on the other hand, does not rely on the immune system and can last in the body for a lifetime. It can be a better approach because it produces more of something the body already has.

Males pursuing a ready-to-breed female are incredibly persistent if she’s in estrus, he says. A male will become restless, endlessly following a female and attempting to mount her if he thinks it’s possible to breed. “It’s like velociraptors in Jurassic Park testing the fence. All the time they’re testing these cats if they’re in estrus.”  

That’s the kind of annoying behavior that makes people not want cats in their neighborhoods, Levy says. For her, the ideal cat contraception would keep females from allowing any males to breed with them. Hopefully that would stop fertile, disruptive males from yowling, spraying urine to mark territory and fighting other males when chasing a female rendered infertile by gene therapy. 

It will still be years before the treatment makes it to vet offices, if approved by the U.S. Food and Drug Administration and similar agencies around the world. Swanson, Pépin and colleagues are still tweaking the gene and method of delivery, exploring how to make it as effective as possible as well as cost-effective to make. Clinical studies with more cats are also required to verify the injection’s safety and efficacy.

Still, “it’s a really different way to do contraception,” Pépin says. And anti-Müellerian hormone is common among animals, so it may be possible to expand to other invasive species. Pépin and others are even exploring ways to leverage the hormone in humans as a nonpermanent form of contraception (SN: 8/22/17). There’s still a lot to learn, “but I think there’s a great opportunity here.”

Our mission is to provide accurate, engaging news of science to the public. That mission has never been more important than it is today.

As a nonprofit news organization, we cannot do it without you.

Your support enables us to keep our content free and accessible to the next generation of scientists and engineers. Invest in quality science journalism by donating today.