Working toward nonsurgical pet sterilization

Harvard bioengineer David Mooney spends lots of time thinking about novel ways to fight cancer. An implantable device he developed that activates the immune system to shrink tumors is now being tested at Dana-Farber Cancer Institute in patients with melanoma.

Which is why it might seem surprising, at first, to hear Mooney talk about his latest project: creating a swift, simple vaccine that will help save the lives of stray cats and dogs, not cancer patients. Mooney recently received a three-year, $700,000 grant to fund the development of a contraceptive vaccine that could avoid the need for surgery and help decrease the number of animals killed in shelters each year.

“I’ve had dogs that need to be neutered,” said Mooney, who currently owns two Labradoodles, Casper and Ruger. “Even for house pets, it’s a pretty major surgery; there’s a lot of pain and issues with that, and I thought it would be great if we could do something to help dogs and cats avoid going through the surgery.”

The work is funded by the Los Angeles-based nonprofit Michelson Found Animals Foundation, which also offers a $25 million prize for the first team to come up with an effective nonsurgical sterilization technique.

Now, the procedure is cumbersome and invasive for stray animals.

“Someone goes out and traps them and transports them to the clinic,” Aimee Gilbreath, executive director of Michelson Found Animals, said. “It would be so much easier if instead of driving to the clinic and having to [perform] surgery you could do a quick injection right in the trap and let it go.”

According to the American Society for the Prevention of Cruelty to Animals, only 10 percent of the 7.6 million pets that enter shelters each year are spayed or neutered, and many animals in shelters are euthanized.

But what could that issue possibly have in common with Mooney’s main thread of research — immunotherapies that trigger the immune system to attack cancer?

Mooney, a core faculty member at Harvard’s Wyss Institute for Biologically Inspired Engineering, had seen the foundation’s call for research proposals but knew little about reproductive biology.

He began to read the literature and made a connection: The same technique he was using to help the body’s immune cells recognize and kill cancer cells might be repurposed to effectively sterilize cats and dogs. To create a contraceptive vaccine, Mooney would simply need to find a way to get the immune system to attack the hormone that controls reproduction in male and female cats and dogs.

Robert Langer, a bioengineer at the Massachusetts Institute of Technology not involved in the research, said the new application was a good idea. Solving the contraceptive problem in pets might also provide insights that could help in developing the technology to treat human diseases.

“You always learn things and some of it is translatable,” Langer said. “Certainly you learn a lot about safety and certain things about efficacy and a lot of practical things, like manufacturing and stability.”

Mooney is far from a successful vaccine now but says that it should be possible to adapt his cancer-fighting strategy for veterinary medicine.

In treating cancer, a chip surgically implanted in the patient attracts immune cells and then activates those cells and teaches them to recognize a particular antigen protein found on the surface of tumor cells.

Once educated, those immune cells go back to the lymph nodes and pass on the message to other immune cells capable of killing those cancer cells. For dog and cat contraception, the same general principle would apply — but the animal’s immune cells would be taught to attack the reproductive hormone instead of a tumor.

Mooney would like to design a one-time injection for animals, instead of an implant. That requires some new bioengineering tricks, and he is considering a range of options. One approach being considered is a “shape memory polymer” that can deform enough to be injected with a needle but in the body, it can pop back into its original shape.

Mooney hopes that what he learns in the process of designing the vaccine might help as he develops the approach for use in a variety of diseases.

“We’re taking a target in the body and we’re saying, ‘Can we generate a potent and long-lasting immune response against this particular molecule?’ ” Mooney said. “If we can do it here, you can probably do it against many other molecules you might target for other reasons.”