Cells in the fetal brain that produce the chemical dopamine can be transplanted into Parkinson’s patients to keep their symptoms at bay for many years.

Transplanting fetal dopamine cells into the brains of patients with Parkinson’s disease may be the key to treating the illness, according to a study published this week in Cell Reports.

Researchers at Harvard-affiliated McLean Hospital found that these cells remained healthy and functional in patients with Parkinson’s for up to 14 years. This discovery could lead researchers to develop stem cell-based dopamine replacement therapies, making it easier and faster to treat patients.

“These results show that the vast majority of transplanted neurons remain healthy for the long term in Parkinson’s disease patients, consistent with clinical findings that fetal dopamine neuron transplants maintain function for up to 15 to 18 years in patients,” the study authors wrote.

Seven to 10 million people are living with Parkinson’s disease worldwide—more than the number of people diagnosed with multiple sclerosis, muscular dystrophy, and Lou Gehrig’s disease combined, according to the Parkinson’s Disease Foundation. There is still no cure for this debilitating disease.

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Lead study author Dr. Ole Isacson and his team examined the brains of five patients who had received fetal cell transplants in the late stages of Parkinson’s, over the course of 14 years. They found that “their dopamine transporters, proteins that pump the neurotransmitter dopamine, and mitochondria, the power plants of cells, were still healthy at the time the patients died, in each case of causes other than Parkinson’s,” according to the study press release.

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Until now, there was little proof that transplanted cells could remain healthy and keep symptoms at bay for long periods, the authors wrote.

“Previous studies have shown that when best practices are used, implanting neurons can make a functional improvement in patients,” Isacson told Healthline. “The latest controversy has been whether or not the implanted cells also become sick when they live and grow inside the patient’s brain. This paper shows that this is not the case, and the cells survive and grow very well for a long period of time without accumulating any significant Parkinson’s pathology.”

“We wanted to establish that the implanted new dopamine neurons could survive for a long time and correct the parkinsonism, but also sustain health on their own for a significant time, in anticipation of significant work by stem cell derived dopamine neurons, not fetal,” Isacson added.

While this study offers hope for treating patients with Parkinson’s, Isacson said the treatment is still controversial amongst scientists because it involves cells harvested from human fetuses, unlike induced pluripotent stem cells (iPSCs), which are grown in the lab.

“The controversy in the field has subsided somewhat, since now most experts believe these cells can work and help patients restore function,” he said.

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Fetal cell transplants can reduce Parkinson’s motor symptoms, as well as reduce the need for dopamine replacement drugs, the study authors wrote.

And while it may take months or even years for the newly transplanted dopamine cells to mature and begin to function in a host brain, researchers said that most fetal cell transplants improve motor symptoms in patients about one year after transplantation.

“Primarily, [our study] shows that this method is viable and potentially very helpful in the long run,” Isacson said. “It also means that stem cell-based methods such as those made from the patient’s own stem cells [iPSCs] to create new neurons, have a reasonable chance of succeeding.”

“The next step is to develop the same type of dopamine neurons from IPS cells for patients to be able to transplant in clinical settings in the future,” he said.

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