Thomas S. May, M.A.

Medical Writer

Transplantation of embryonic stem cells in Parkinson's disease

Thomas S May

Researchers at Harvard Medical School (Boston, MA, USA) have shown that when low doses of embryonic stem cells are transplanted into the rat striatum, some of these cells develop into fully-differentiated dopaminergic neurons. Although this research is still in its preliminary stages, it could have significant implications for the treatment of Parkinson's disease.

Lars Björklund and colleagues injected a small number of embryonic stem cells (1000–2000) into the right striatum of 25 rats with Parkinson-like symptoms experimentally induced by intracerebral injections of the neurotoxin 6-hydroxydopamine. Several weeks later, five of the rats had developed teratoma-like tumours and six showed no graft survival. But 14 (56%) of the animals had graft-derived, functionally-integrated, dopaminergic neurons in their striatum. Furthermore, motor function gradually recovered in these animals to a significant degree in the 9 weeks following transplantation (Proc Natl Acad Sci USA 2002; 99: 2344–49).

“Previous work in our lab has shown significant numbers of dopamine neurons from grafted embryonic stem cells, but due to the high number of embryonic stem cells grafted, they also had numerous other types of cells”, says Björklund. “In our latest study, we were able to get rid of such unwanted cells [by using a lower dose of embryonic stem cells], which allowed the dopamine cells to functionally integrate and extend axons in the target area.”

While the experiment by Björklund's team showed that embryonic stem cells can develop into functional dopaminergic neurons in the brain, the results are far from perfect, according to Curt Freed (University Of Colorado School of Medicine, CO, USA).

He notes, for example, that there was a high tumour rate (20%) among the grafted animals, which occurred after only a few weeks of follow-up. “For a human application, the FDA [US Food and Drug Administration] would probably insist on zero tumours for at least one year after transplant into a large number of subjects. That level of protection will only come from cells that have been permanently differentiated in vitro.”

Nevertheless, Freed says that the use of embryonic stem cells for Parkinson's disease has great therapeutic potential. “If differentiation of human embryonic stem cells to dopamine neurons can be successfully performed in tissue culture, with no residual embryonic stem cells, this strategy could provide a safe source of dopamine neurons for transplantation into patients with Parkinson's disease.”

Volume 1, Issue 1, May 2002, Page 6

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