Scientists are closing in on ways to help patients grow new heart muscle after a heart attack, as well as new lung tissue to treat fibrosis, corneas to erase eye pain and other body parts to gain a new chance at life.
If the science works, it could represent a new approach to medicine: reversing rather than alleviating chronic illnesses.
The idea “is really to restore function to the organ such that the quality of life of that person is normalized,” says Peter Schultz, president and chief executive of Scripps Research, a nonprofit scientific institute in La Jolla, Calif., that is testing medicines to regenerate hearts, lungs and other organs.
These treatments eventually might also be used to reverse the effects of aging, Schultz says. If they prove effective in people with disease, he says, they could be tested in healthy people to see if they can, say, “turn a 70-year-old heart into a 40-year-old heart.”
The need for regenerated hearts alone is huge. Up to 3% of the world’s population suffers from heart failure, in which a heart whose muscle has been damaged by a heart attack or another disease gradually loses its ability to pump blood. The condition affects about 6.5 million people in the U.S. and is the leading cause of hospitalization among Medicare patients.
Certain salamanders and zebrafish can regenerate their hearts, along with limbs and other organs. Humans have only a limited capacity to regenerate, with skin and the liver as the main examples. They die with most of the same heart-muscle cells they were born with. “We’re built for performance and not repair,” says Dr. Chuck Murry, director of the Eli and Edythe Broad Center of Regenerative Medicine and Stem Cell Research at the University of Southern California’s Keck School of Medicine.
Scientists are testing different approaches to regenerate the heart.
Some, like Murry, are working with stem cells. Others are working on stimulating existing heart-muscle cells—those that survive a heart attack—to proliferate.
One billion heart-muscle cells—about 25% of muscle cells in the left ventricle—can die as a result of a major heart attack, when blood flow to the heart muscle is abruptly cut off, says Dr. Mauro Giacca, head of the School of Cardiovascular and Metabolic Medicine & Sciences at King’s College London. The left ventricle is the heart’s main pumping chamber.
Giacca is developing a therapeutic that uses microRNA, molecules that help regulate how genes are expressed, to induce surviving cardiac cells to multiply. Tests in pigs showed the therapeutic improved the heart’s pumping function, increasing muscle and reducing scar tissue. But he needed to find a better way to deliver the therapeutic and control the dosage than the viral vectors he first tried. A company he founded, Heqet Therapeutics, is testing delivering the therapeutic by injection to the heart in pigs, he says, using two types of lipid nanoparticles similar to those in messenger RNA vaccines for Covid-19.
Scripps Research scientists are working on a drug to grow new heart muscle from surviving heart-muscle cells. It targets proteins that activate cell growth and control the size of the organ, so that new cells form but proliferation stops before the heart gets too big, says Michael Bollong, associate professor of chemistry.
After a heart attack, the immune system clears out dead heart-muscle cells, leaving gaps that are normally filled with scar tissue. The drug, in a hydrogel form, would be injected into the sac that surrounds the heart and slowly bathe the damaged area for a week, instructing the surviving cells to multiply and fill in the gaps.
“We all came from a single cell in our mothers’ wombs,” Bollong says. “We know that those genetic instructions are there for repair.”
The drug restored heart-pumping capacity almost back to normal in mice and pigs, according to Scripps. The research institute’s drug discovery arm, Calibr-Skaggs, aims to begin testing the drug in humans in early 2026.
Some studies have associated the protein used to activate heart-muscle cell growth with tumor growth as well. Scripps has addressed that by administering the drug for a short time, in a one-time injection, Bollong says. It would likely be administered three to five days after a heart attack, when a patient has been stabilized and acute inflammation has subsided, he says.
Murry at USC is developing a therapeutic in which new heart muscle is grown in a lab using stem cells, then injected into a damaged heart to allow it to “remuscularize,” he says. A focus is putting new heart muscle into the left ventricle.
Murry and his team have tested the treatment in several types of animals. Macaques that received it regained full pumping function in their hearts, he says. In more than 40 years in heart research, “I’ve never seen anything that could do this before,” he says.
He had to overcome one big problem: The young new heart cells initially beat to their own rhythms “like stressed-out adolescents” when grafted onto the macaques’ hearts, causing arrhythmias. Murry developed a method to control the beating with a cocktail of antiarrhythmic drugs and genome editing to change the cells’ electrical circuitry.
He hopes to begin clinical trials of the treatment in humans in early 2026, through a company he co-founded called StemCardia. “Society has become OK with the notion of dying from heart disease,” Murry says. “It does not have to be this way, because we can do something about this now.”
Another scientist, Doris Taylor, is working on growing entire hearts. Her company, Organamet Bio, grows heart cells using stem cells cultured from a patient’s blood. Those cells are engrafted into a scaffold created with a pig’s heart—a white mass that contains the heart’s structure and framework of its blood vessels.
“We can give you a heart that matches your body,” says Taylor, CEO and a stem-cell biologist. The pig heart closely resembles the human heart anatomically.
The company is testing its heart’s durability in the lab, Taylor says. It plans to study it in animals and hopes to begin clinical trials in humans in five years.
Clinical trials in humans are already under way to regenerate cells in another organ: the lungs. Scripps and Calibr-Skaggs are testing a drug to repair lungs damaged by idiopathic pulmonary fibrosis, or IPF, a disease that scars the lungs, restricting breathing. The drug, inhaled directly into the lungs, works by stimulating stem cells in the lower airway so that they produce cells on the surface of the lung that handle gas exchange. It is a new drug from a class used to treat diabetes.
An early-stage clinical trial began in September at the Fraunhofer Institute for Toxicology and Experimental Medicine in Hannover, Germany. The drug’s safety and how it gets into the lung are being studied in healthy volunteers and a small number of IPF patients, says Dr. Jens Hohlfeld, division director for airway research. Researchers there also hope to learn about the drug’s effectiveness in the IPF patients, he says.
Jannik Bruns, a 26-year-old data scientist, held an inhaler to his mouth and took in his dose of the drug or a placebo—he isn’t sure which—in a hospital room at the institute, surrounded by nurses wearing masks. Over three days, Bruns—one of the healthy volunteers—underwent blood, oxygen saturation and other tests, working from his room in between.
He has felt no side effects and returned to the institute a few times for more tests. “Supporting science is something I really want to do,” he says.
Write to Betsy McKay at [email protected]
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