Dampened hopes for transplanting bone marrow stem cells in heart attacks

There is little, if any, evidence that adult stem cells can build other cells in an adult organism than those formed in the organs they themselves come from. At any rate, blood stem cells do not convert to heart muscle cells in a damaged heart, which was previously hoped. This has been shown by a research team from the Stem Cell Center at Lund University in Sweden in an article in Nature Medicine.

During the end of the 1990s and early 2000s scientists nourished great hopes that adult stem cells would be able to develop into all sorts of cells. If so, it would not be necessary to use the ethically more problematic embryonic stem cells. However, newer studies have shown that while adult stem cells are very good at producing different types of cells in their own respective organs, they have little or no ability to form cells in other organs.

“Both we and two American research teams have used various methods to replicate a study from three years ago that appeared in Nature. It was about transplanting blood stem cells to create new heart muscle cells to repair a heart after a heart attack. But all of our results univocally indicate that this is not possible,” says Jens Nygren. He is a doctoral student and part of research team headed by Professor Sten Eirik Jacobsen at the Stem Cell Center.

What the Lund scientists have found is that the transplanted cells that remain in the infarcted area retain their identity as blood cells. On the other hand, outside the infarcted area a so-called fusion did occur between the transplanted cells and heart muscle cells.

Such fused cells can sometimes look as if they had been formed from a transplanted stem cell. In other words, fusions may explain the first promising studies: the scientists believed they were looking at cells produced by maturation of blood stem cells, whereas in actual fact they were seeing a tiny number of fused cells.

Now it is time for second thoughts, and these might affect the many large-scale patient trials that were initiated during the hopeful period. In Sweden there is only one entirely new trial underway, and it can easily be discontinued, but in Germany and elsewhere a huge number of patients have already had blood stem cells transplanted into their heart, and more transplants are in planned. The question is whether there is any reason to continue these trials, or whether they should be ended. There are some indications that bone marrow transplants have a certain positive effect on the heart function after an infarction, but the mechanism behind this remains an open question.

Sten Eirik Jacobsen’s research team is now primarily focusing on how blood production from stem cells is regulated. They are also going to carry on their work to understand what fusion between bone marrow cells and heart musculature might entail, both in adult hearts and in fetal development.