Scientists are trying furiously to harness different types of stem cells, the building blocks for other cells in the body, to regrow damaged tissue and thus treat devastating diseases. For all the promise, however, researchers long have warned that they must learn to control newly injected stem cells so they do not grow where they should not. Small studies in people are only just beginning.
Tuesday's report in the journal PLoS Medicine, the first documented case of a human brain tumor - albeit a benign, slow-growing one - after fetal stem cell therapy, and it hammers home the need for careful research. The journal is published by the Public Library of Science.
"Patients, please beware," said Dr. John Gearhart, a stem cell scientist at the University of Pennsylvania who was not involved in the Israeli boy's care but who sees similarly desperate U.S. patients head abroad to clinics that offer unproven stem cell injections.
"Cells are not drugs. They can misbehave in so many different ways, it just is going to take a good deal of time" to prove how best to pursue the potential therapy, Gearhart said.
The unidentified Israeli boy has a rare, fatal genetic disease with a tongue-twisting name - ataxia telangiectasia, or A-T. Degeneration of a certain brain region gradually robs children with the condition of movement. Plus, a faulty immune system leads to frequent infections and cancers. Most die in their teens or early 20s.
Israeli doctors pieced together the child's history: When he was 9, the family traveled to Russia, to a Moscow clinic that provided injections of neural stem cells from fetuses, immature cells destined to grow into a main type of brain cell. The cells were injected into his brain and spinal cord twice more, at ages 10 and 12.
Back home in Israel at age 13, the boy's A-T was severe enough to require that he use a wheelchair when he also began complaining of headaches. Tests at Sheba Medical Center in Tel Aviv uncovered a growth pushing on his brain stem and a second on his spinal cord. Surgeons removed the spinal cord mass when the boy was 14, in 2006.
Was the boy prone to tumors anyway, or were the fetal stem cells to blame? A Tel Aviv University team extensively tested the tumor tissue and concluded it was the fetal cells. Among other evidence, some of the cells were female and had two normal copies of the gene that causes A-T. The boy's underlying poor immune function could have allowed the growths to take hold.
Using stem cells from multiple fetuses that also were mixed with growth-spurring compounds "may have created a high-risk situation where abnormal growth of more than one cell occurred," wrote lead researcher Dr. Ninette Amariglio of Sheba Medical. She urged better research to "maximize the potential benefits of regenerative medicine while minimizing the risks."
This brain disease was not conducive to stem cell therapy in the first place, said stem cell specialist Dr. Marius Wernig of Stanford University in the United States, who said it is unclear exactly what was implanted.
"Stem cell transplantations have a humongous potential," Wernig said. 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."