The heart is one of the least regenerative organs in the body. During a heart attack, blood flow to the heart is temporarily blocked, leading to muscle cell death. This damaged tissue is primarily replaced with scar tissue that is unable to beat, reducing the overall pumping capacity of the heart.
'And at the moment all of our treatments are... dancing around the root problem, which is that you don't have enough muscle cells,' study author Dr Charles Murry, director of the Institute for Stem Cell and Regenerative Medicine at the University of Washington told CNN.
Dr Murry's team induced severe heart attacks in macaque monkeys two weeks before the injection of around 750 million heart muscle cells (cardiomyocytes) derived from human embryonic stem cells into the damaged tissue.
Within one month, treated animals showed an improvement of 10 percent in the left ventricular ejection fraction, a widely used measure for the heart's pumping efficiency. In contrast, only a two percent improvement was observed in animals that did not receive the cells. Further improvements were seen in two treated animals that were observed for an additional two months, suggesting that the treatment effects could be sustainable.
'Our findings show that human embryonic stem cell-derived cardiomyocytes can remuscularise infarcts in macaque monkey hearts and, in doing so, reduce scar size and restore a significant amount of heart function,' said Dr Murry.
Previous studies have shown a similar benefit of using these human stem cell-derived cardiomyocytes in small animals, such as mice and guinea pigs, this is the first time the treatment has been tested in a larger animal.
This study also follows related work from Dr Murry's group in 2014, which suggested that these derived cardiomyocytes were able to integrate into the macaques' heart tissue, forming electromechanical junctions with the host heart and even beat in synchrony.
Although both papers show promising results, it remains unclear if and how they would scale to humans. The team is currently hoping to begin clinical trials in 2020, but there are concerns requiring further research before that can happen. Notably, several of the monkeys also experienced irregular heartbeats following the treatment.