The scientists, who were from Memorial Sloan-Kettering Cancer Centre in New York, started with embryonic stem cells. They matured those cells into precursors of the ones that disappear in people with Parkinson's disease — so-called dopiminergic neurons. This step was hard-won. The Guardian quotes the lead author talking about the development:
"Previously we did not fully understand the particular signals needed to tell stem cells how to differentiate into the right type of cells," said Dr Lorenz Studer at the Memorial Sloan-Kettering Cancer Centre in New York.Discover Magazine described how they tested the cells:
"The cells we produced in the past would produce some dopamine but in fact were not quite the right type of cell, so there were limited improvements in the animals. Now we know how to do it right, which is promising for future clinical use."
The researchers then injected over 100,000 of these newly grown neurons into the brains of mice that had a rodent equivalent of Parkinson’s disease: damaged dopamine-producing cells and the resulting difficulties controlling muscle movement. Over the course of three to five months, the transplanted neurons thrived, connecting with surrounding brain cells, and the mice’s motor function greatly improved. When the team repeated the experiment in rats, the result was the same: A few months later, the stem cell-derived neurons had integrated into the brain and the rats were moving around just fine.Maturing embryonic stem cells into a cell type that can be transplanted to treat Parkinson's disease has been one of the great hopes for the field of stem cell research. There is currently no treatment for the 500,000 people living with Parkinson's disease in the U.S. CIRM has invested almost $40 million into 20 projects aimed at developing stem cell-based therapies for the disease. (You can see a complete list of those awards here.)
This technique produced enough neurons that the researchers were able to inject two rhesus monkeys with Parkinson’s-like damage with 7 million new dopamine-producing brain cells each, far closer to the number a human patient would need. A month later, the transplanted neurons were alive and well in the monkeys’ brains—though it was too early to tell whether the new neurons would restore normal movement.
Scientists still have the difficult task ahead of providing evidence to the Food and Drug Administration that these cells are safe to test in human trials. Even then, humans are quite different from mice, rats and even monkeys and there is no way of predicting whether a therapy that works in animals will be similarly successful in humans. The Guardian quoted Studer discussing the future of this research:
"We now have the right cells, but to put them into humans requires them to be produced in a specialised facility rather than a laboratory, for safety reasons. We have removed the main biological bottleneck and now it's an engineering problem."A.A.