Studies Suggest Stem Cell Therapies May Treat Parkinson’s Disease by Restoring Brain Circuitry

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Two small clinical trials tested the safety of injecting stem cells into the brains of Parkinson’s patients and found no adverse effects

Lillian Ali – Staff Contributor

April 21, 2025 1:23 p.m.

A recent advancement in the management of Parkinson’s disease has emerged through two small-scale clinical trials that investigated the safety of stem cell injections into patients’ brains. These trials provide promising insights suggesting that stem cell transplants might effectively counteract the cellular degeneration responsible for Parkinson’s symptoms.

The clinical trials involved the injection of neurons derived from stem cells directly into the brains of individuals diagnosed with Parkinson’s disease, focusing primarily on evaluating the safety of the procedure. Published in the journal Nature, the trials engaged a modest group of participants—12 in one study and 7 in the other—preventing any conclusive statements regarding the efficacy of stem cell therapies for Parkinson’s as of yet.

Experts view these findings as a significant progression in the research landscape. Malin Parmar, a stem cell biologist at Lund University in Sweden, remarked on the studies, stating, “These cell products are safe and show signs of cell survival.” The findings suggest that the introduced cells did not exhibit harmful effects, an essential step in the potential development of stem cell treatments for neurodegenerative diseases.

Parkinson’s disease is a debilitating condition that predominantly affects individuals over the age of 60, with an estimated prevalence of at least 1 percent worldwide. The disorder primarily impacts the basal ganglia, an area of the brain essential for motor control, leading to symptoms such as tremors, stiffness, and slow movement due to the loss of dopamine-producing neurons.

Most current treatments aim to alleviate symptoms by increasing dopamine levels through various medications, which either enhance the levels of available dopamine, mimic its effects, or inhibit its breakdown. While these options can slow the progression of the disease, they do not offer a cure, prompting researchers to explore alternative treatment strategies.

Stem cell therapy represents a groundbreaking approach, with the potential not only to substitute the lost dopamine but also to restore the damaged neural circuits caused by the disease. Neurosurgeon Viviane Tabar, the primary author of the trial involving 12 patients, explained that the goal is to place neuron progenitors derived from stem cells at precise locations in the brain to facilitate connections with existing neurons.

Stem cells, often referred to as “master cells,” have the unique ability to differentiate into various cell types throughout the body. This characteristic positions them as critical components in the field known as regenerative medicine, which aims to replace or repair weakened or dysfunctional cells. For instance, stem cell transplants are commonplace in treating leukemia, as they can restore healthy blood cells within the bone marrow.

The trials were designed to monitor the survival of the injected cells and to assess any increase in dopamine production post-therapy. In the larger trial conducted across the U.S. and Canada, researchers tested varying dosages of stem cells—administering 0.9 million cells as a low dose and 2.7 million cells as a high dose. Initial estimates anticipated a notable cell death rate post-surgery, but results showed a surprising degree of cell survival.

Evaluation methods included standardized scales for measuring Parkinson’s disease progression. Typically, patients experience a decline of two to three points on this scale annually; however, those receiving higher doses in the trials exhibited an improvement of approximately 20 points, while the low-dose group saw about nine points of progress.

In the smaller study, results also indicated symptom improvements along with no significant adverse effects, such as tumor formation or excessive bleeding. Jun Takahashi, the senior author of this trial, confirmed that the data collected reinforced the safety of the employed stem cells.

While the concept of utilizing stem cell therapies for Parkinson’s is not novel, previous trials had raised concerns about the potential for healthy implanted cells to acquire Parkinson’s-like symptoms. “There have been times of hype versus hope in this field,” Tabar added, acknowledging the mixed results experienced in the past.

However, the current studies suggest renewed optimism. Their safety findings and preliminary signs of symptom improvement are directing researchers toward larger clinical trials which may provide robust evidence of efficacy and broaden access to this innovative treatment approach.

Mya Schiess, a neurosurgeon at the University of Texas Health Science Center in Houston, emphasized the potential of these findings, stating, “now we have the potential to really, really halt this disease in its tracks.”

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