PARIS - Excited talk about the use of the versatile tissue known as stemcells to cure crippling diseases has been dampened by the discovery that ageing lab-dish cells pose a potential cancer threat.
The concern focuses on adult stemcells, viewed as an uncontroversial alternative to stemcells from early embryos -- the most versatile source of all.
Two new studies suggest that if adult stemcells replicate too many times in a lab dish, they risk becoming tumourous, New Scientist says.
Cells that divided between 90 and 140 times in a lab formed cancers when they were transplanted into test animals, according research by a team at the Autonomous University of Madrid, Spain.
University Hospital of Odense doctors in Denmark suspect that, after a certain number of divisions, genes get switched on in the cell that start making an enzyme called telomerase, and this eventually turns them cancerous.
Further research is therefore needed to determine what is a safe number of divisions before the ageing stemcell poses this risk.
Adult bonemarrow stemcells are currently being used in experimental treatment to repair damaged hearts.
However, they should be safe because the cells are only briefly grown outside the body before being inserted back into human tissue, according to the New Scientist report, which appears in this Saturday's issue of the weekly British magazine.
Until now, only embryonic cells were believed to pose a cancer risk. At their very earliest stage, they can form aggressive cancers called teratomas if injected into a laboratory animal.
Stem cells are immature cells that are like blank slates. In this early state, they have yet to differentiate into the specific cells that make up the body's tissues.
The goal among scientists is to harvest these cells and coax them into growing into fresh, replacement tissue which can then be transplanted into the body to reverse brain, nerve, muscle and organ damage.
The most versatile stem cells come from embryos in their early stage, for they can differentiate into any part of the body.
But embryonic cells have also ignited fierce objections from conservative religious groups who say that a cluster of embryonic cells has the same value as the life of a grown human being.
As a result, many countries, including the United States, have imposed restrictions on the use and sources of embryonic stem cells and research funding.
Scientists are looking at potential stem cells from adult tissue, such as blood, bone marrow and the liver, in order to skirt the problem.
In a separate study, published in the British journal Nature on Thursday, French-based researchers said they had identified a new population of progenitor muscle cells in mice, a discovery that may help in developing therapies to combat muscle disease.
04/20/2005 18:01 GMT