Doubt cast on adult stem cell therapies

A new US study calls into question the existence of adult stem cells capable of transforming into insulin-producing pancreatic cells. Previous research in mice has suggested that such cells could be used to develop new treatments for diabetes. But the new study, carried out by scientists at Harvard University in Massachusetts, casts doubt on this idea. Their findings, published in Nature, show that new insulin-producing 'beta' cells arise from existing beta cells, rather than from stem cells. The discovery could pave the way for new treatments for the disease, and also emphasizes the importance of research into therapies based on embryo stem cells (ES cells) .

People with diabetes either do not produce enough insulin, or do not respond to the hormone's effects. Researchers are hoping to develop new treatments for this disorder by transplanting new, insulin-producing 'beta' cells into the pancreas. Previous work suggested that adult stem cells from the pancreas, spleen and bone marrow could transform into new pancreatic beta cells. But according to team leader Douglas Melton, the new study 'provides no evidence whatsoever for the existence of an adult pancreatic stem cell'.

The researchers developed a new 'tracking system' to see where new beta cells came from in normal mice with pancreas damage. They found that older beta cells themselves produced new cells, and that no stem cells were involved. Future diabetes research should focus on ways of getting these cells to produce enough new beta cells to treat the disease, the researchers say. But for people who have no beta cells left, the only source of new cells may be human ES cells. ES cells are the body's master cells, capable of growing into any type of body tissue.

Another study, published last week in Nature Medicine, has found little evidence that adult bone marrow stem cells can grow into heart cells, despite hopes that they could be used to treat damaged heart muscle. Researchers at Lund University in Sweden have found that bone marrow cells transplanted into hearts retain their 'blood cell' identity. However, they also found evidence of 'cell fusion' between some heart cells and transplanted bone marrow cells. This could explain the initial promising studies, say the scientists - several preliminary human trials have shown that bone marrow transplants can benefit heart failure patients.

The Swedish researchers ask whether current large scale trials should continue, since although there are 'some indications' that bone marrow transplants can heal damaged heart muscle, the underlying mechanism remains an open question. Many scientists are hoping to use adult stem cells to develop new therapies for a wide range of diseases, especially in countries where ES cell research is not permitted.