Stem cells grew into tumours in an Israeli child whose desperate parents brought him to a Moscow clinic for treatment. Doctors from Sheba Medical Center, in Tel Aviv, say that a boy with a rare genetic disease, ataxia telangiectasia, now has tumours in his brain and spinal cord.

Their report in PLoS Medicine is the first documented example of such a complication in a human following neural foetal stem cell therapy. The injected cells, which were obtained from two aborted human foetuses, were a mixture of glial cells, neurons, and progenitors – which would be regarded as substandard practice in the US. As one would expect, the resulting tumours contained a hodgepodge of different cell types.

Despite the result, the researchers insist that their findings "do not imply that the research in stem cell therapeutics should be abandoned", but that doctors must be careful. "Stem cell transplantations have a humongous potential," says Dr Marius Wernig, of Stanford University. But "if people rush out there without really knowing what they're doing... that really backfires and can bring this whole field to a halt." ~ Science Daily, Feb 17; AP, Feb 18, PLoS Medicine