A St. Paul-based gene editing company is partnering with Mayo Clinic to research methods of growing human cardiac cells inside pigs to treat children with potentially fatal heart defects.

Recombinetics announced the partnership on Thursday with Mayo, and a spinoff company, ReGen Theranostics, which develops human stem cell lines for transplant.

The partnership initially wants to use the stem cells to grow cardiomyocytes, the cells that form heart muscle, that can be safely implanted in children and delay their need for donor heart transplants. But Tammy Lee, Recombinetics’ chief executive and president, said this could be just the first step in the use of specially modified pigs to grow human cells, tissues and maybe even whole organs that could be safe for transplant and wouldn’t be rejected by recipients’ immune systems.

“The ability to grow human cells in the pig that don’t have the rejection issues?” she said. “This is a first-of-its-kind initiative.”

Lee called the genetically modified pigs her company’s “oinkubators,” which are needed to grow human cells in sufficient quantity for transplant. The first step is proving the stem cells can safely produce enough human cardiac cells inside pigs. Federal approval for human clinical trials of the pig-produced cells would follow.

Recombinetics, which recently raised $34 million in private research funding, has reported success in the use of gene editing for agricultural ventures. Examples include growing dairy cattle without horns, or that can withstand heat, and pigs that don’t require castration as part of the usual process in pork production.

The company also worked with Mayo to create pigs as human models of dilated cardiomyopathy disease. These pigs are used by researchers to study improved therapies for the disease, which occurs when the left ventricle of the heart is enlarged and weakened and can’t pump blood effectively.

Researchers globally have studied “exotransplantation,” which refers to the growth of human cells in animals for transplant, as well as “xenotransplantation,” which refers to the use of animal tissues and organs themselves for transplant.

A University of Minnesota researcher, for example, has studied whether pig islet cells could be safely transplanted into patients with severe, unmanaged diabetes. Pigs already are a source of heart valves for replacement procedures.

Lee said the Mayo project would start with an existing stem cell line, but her company’s long-term goal is to develop a method for growing patients’ own cells inside pigs for transplants. Recipients’ immune systems would be less likely to reject transplants of their own cells.

Lee said she is excited to pursue a therapy that could be an alternative to heart transplants, or could delay children’s’ needs for them.

“Today, only a small percentage of individuals requiring a transplant are matched with the right donor,” she said, “and those transplant recipients often face a life of anti-rejection drugs that come with serious side effects.”