A new complication has been seen in a patient with kidney disease who received stem cell therapy, scientists have warned.
Stem cells were injected into the kidney, but the patient suffered tissue damage and died from an infection.
The patient in this case had been treated by a private clinic.
Dr Duangpen Thirabanjasak, from Chulalongkorn University, who led the research, said: "This type of lesion has never been described before in patients, and we believe that this is either formed directly by the stem cells that were injected or that the stem cells caused these masses to form."
The authors conclude that their findings should serve as a warning to clinical investigators that the development of blood vessel and bone marrow masses may be a possible complication of stem cell therapy.
Writing in the journal, Andras Nagy, of Toronto's Mount Sinai Hospital, and Susan Quaggin, of the University of Toronto, said caution was needed over stem cell therapies - especially if they were being offered by unregulated private clinics.
They added: "Premature enthusiasm and protocols that are not fully vetted are dangerous and result in negative publicity for the field of stem cell research, and more importantly, may result in disastrous outcomes with no benefit to the patient.
"Although there is promise, a large gap still exists between scientific knowledge and clinical translation for safe and effective stem cell-based therapies.
