Photo/IllutrationThe Asahi Shimbun

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A patient who received the world’s first transplant of cardiac muscle cells using artificially derived stem cells known as iPS cells this month is in stable condition, an Osaka University team said Jan. 27.

After surgery, doctors closely monitored the patient, who had ischemic cardiomyopathy, a condition in which clotted arteries cause heart muscles to malfunction. But the patient has been moved to a general hospital ward, the team said.

Yoshiki Sawa, a professor of cardiovascular surgery at the university, who led the team that conducted the transplant, said the team aims to put the technique into practical use.

Sawa said the team hopes transplants of heart muscle tissues derived from induced pluripotent stem cells “will be used to save many patients who have heart conditions.”

In the clinical trial, three sheets of heart muscle tissues made from iPS cells stocked at Kyoto University’s Center for iPS Cell Research and Application were attached to affected parts of the patient’s heart. The iPS cells were created from tissues provided by a healthy donor.

The sheets were 4 to 5 centimeters in diameter and 0.1 millimeter thick.

The transplant's goal is to regenerate cardiac blood vessels using a substance secreted by the sheets of muscle cells. The sheets are degradable and disappear from the body several months after they secrete the substance, according to the team.

The university plans to perform similar transplants on nine other patients who have serious heart problems.

The Osaka University team had planned to conduct the clinical trial of the transplant earlier after the government approved the plan in May 2018.

But it was postponed due to damage from a powerful earthquake that hit Osaka Prefecture the following month that rendered its facility to cultivate cells unusable.

The trial is part of the process toward the future distribution of medical products using cells.

Osaka University’s announcement of the successful transplant of tissues created from iPS cells marked the fourth such transplantation.

Including Osaka University's trial, Japanese surgeons have now successfully transplanted tissues created from iPS cells four times.

The world's first transplant of iPS-derived cells was conducted in 2014 when the Riken research institute transplanted retina cells for a patient with age-related macular degeneration.

In 2018, Kyoto University transplanted nerve cells for a Parkinson disease patient. Osaka University transplanted cornea cells into a patient with a disease of the cornea in 2019.

Patients who undergo transplants using iPS-derived cell must accept the risk that the cells may become cancerous.

The more iPS-derived cells a patient receives, the higher their risk.

Hundreds of thousands of retina cells were used in the 2014 retina transplant. In the 2018 and 2019 transplants, the number of nerve and cornea cells used soared to between 5 million to 6 million.

Osaka University's latest transplant utilized roughly 100 million tissues made from iPS cells.

Sawa acknowledged the transplanted heart muscle tissues could turn cancerous, but said the team “has made great efforts to remove potentially cancerous cells.”

Hideyuki Okano, professor of molecular neurobiology at Keio University, who is researching the application of iPS-derived nerve cells to treat patients with spinal cord damage, said the risk was worth it.

Okano said the Osaka University's transplant, using tissues made from iPS cells from a donor, could be more effective than the existing therapy, which uses the patient’s own muscle tissues.

“I understand that the transplanted tissues might become cancerous or cause an erratic heart rhythm, but the transplantation of the iPS-derived heart muscle tissues can be more effective than muscle tissue sheets made from the patient’s leg,” Okano said.

Keio University is also planning to conduct clinical research using iPS-derived cells to regenerate heart tissues.