Doctors re-grow human heart

A Yale doctor’s innovative stem cell procedure may change the field of regenerative medicine.

4-year old Angela Irizarry was born with a single pumping chamber in her heart, a congenital birth defect that causes the heart to overwork itself trying to pump sufficient amounts of blood to the body. Six months ago, Christopher Breuer, associate professor of surgery and pediatrics and director of tissue engineering at the Yale School of Medicine, led a procedure to implant a bio-absorbable tube with bone marrow stem cells into her heart. On March 20, the Wall Street Journal reported that the tube has dissolved and Irizarry’s cells have begun to grow a conduit that functions like a normal blood vessel, the first successful procedure of its kind.

In a healthy heart, the left ventricle pumps blood around the body, while the right one pumps it to the lungs. But Irizarry’s left ventricle was non-functional, so her right had to do double duty. Her new blood vessel is now directing deoxygenated blood to her lungs, preventing the right ventricle from straining itself.

“It’s positive example of how research in the lab can be brought to the bedside,” said Sally Temple, Scientific Director at the Neural Stem Cell Institute, a nonprofit that supports stem cell research.

Current procedures use adult or bovine tissue or synthetic grafts made of Gore-Tex, both of which can lead to infection or clotting and require frequent replacement as the child outgrows them, said Peter Johnston, an assistant professor and cardiologist at the Johns Hopkins School of Medicine. A natural conduit that functions like a natural blood vessel would eliminate these complications and the need for surgical replacements, he said.

Breuer’s research has “incredible potential” for developing fully biological grafts that behave like a natural blood vessel one is born with, which would be “ideal” since it could grow over time, Johnston said.

“[If successful], it would be truly replacing the blood vessel as opposed to being a temporary fix,” he said.

Previous attempts to mimic normal blood vessels successfully implanted scaffolds with stem cells, but the engineered tissue eventually broke down, Temple said. Breuer’s procedure shows that a biodegradable tube with bone marrow cells significantly reduces the chance of shutting down, she said, making her optimistic that this trial would succeed where others have failed.

Kevin Whittlesey, science officer at the California Institute for Regenerative Medicine, said that the bone marrow stem cells do not themselves grow into the replacement blood vessel. Instead, the three-dimensional structure and stem cells together enable the heart tissue to regenerate itself. This means that the implanted cells are not permanently necessary, as long as they are present initially to modulate the environment, allowing host cells grow appropriately, Temple said. Now Breuer is researching these growth factors, which are key to understanding how these cells allow host cells to grow for a long time, she added.

Breuer’s approach was still a risky one, because tissue-engineered version can cause complications, such as blockages, Breuer said in the WSJ article. Stem cell therapy can also sometimes lead to cancer or a bad immune-system reaction. Breuer could not be reached for comment.

Breuer plans to repeat the procedure in a six-patient study to test the safety and see if the blood vessels in fact grow with the child, according to the article.

70 percent of newborns with Irizarry’s condition, hypoplastic left heart syndrome, die before their first birthday.

Comments