Stem Cell Therapy for Parkinson’s: What We Know So Far

In a recent “Ask an Expert” webinar, neurologist and movement disorder specialist Dr. Saz Atari from UC Irvine Health shared insights into one of the most talked-about topics in Parkinson’s research today: stem cell therapy. Speaking from her clinic at the new UCI Advanced Care building, Dr. Atari explained the science behind stem cells and how they’re being studied as a potential treatment for Parkinson’s disease. To begin with, Dr. Atari walked the audience through the basics of Parkinson’s. It’s a progressive neurological condition that primarily affects a group of brain cells in a region called the substantia nigra—Latin for “black substance”—because these dopamine-producing neurons are dark in colour. Over time, these cells degenerate and die, reducing dopamine levels and leading to the classic motor symptoms of Parkinson’s: slowness, stiffness, tremor, and balance issues. However, many people may not realise that the main symptom used for diagnosis isn’t tremor, but slowness of movement. Non-motor symptoms—such as constipation, sleep issues, vivid dreams, changes in sense of smell, and blood pressure fluctuations—often appear years earlier but are not enough for diagnosis on their own. Current treatments, including medications like levodopa and dopamine agonists, aim to replace or mimic dopamine. While they’re usually effective for some time, patients eventually experience “off” periods when the medication wears off and symptoms return, or they develop side effects like dyskinesias (involuntary movements). When medications are no longer sufficient, advanced options like Deep Brain Stimulation (DBS) surgery can help. DBS involves implanting electrodes in the brain to improve symptoms, but even this doesn’t replace the lost dopamine-producing cells. This is where stem cell therapy enters the picture. The idea is simple in theory: if dopamine neurons are lost, why not replace them? In practice, it’s been a long and complicated road. For over 50 years, scientists have been exploring how to use cell therapy to treat diseases like Parkinson’s. In the early days, researchers experimented with fetal tissue transplants, but these raised ethical issues and gave inconsistent results. A major breakthrough came in 2006 when scientists discovered how to take adult cells (like those from skin) and “reprogram” them back into a more flexible state, similar to embryonic stem cells. These are called induced pluripotent stem cells (iPSCs) and don’t carry the same ethical concerns as using fetal tissue. Stem cells are unique because they can divide and become many different types of cells. Embryonic stem cells are the most versatile—they can become any cell type in the body. Adult stem cells are more limited but still useful. In recent years, scientists have succeeded in turning stem cells into dopamine-producing neurons in the lab. The challenge has been delivering them safely and effectively into the human brain. Dr. Atari described the decades of careful work that led to a recent major milestone: the first human clinical trials testing stem cell transplantation in Parkinson’s. These studies were designed to see whether the therapy is safe and well-tolerated. One such study, called the EXPLORE trial, used human embryonic stem cells to create dopamine neurons and implant them into the brains of people with Parkinson’s. UC Irvine was one of several centres involved in this international effort. The team’s chair, Dr. Claire Henchcliffe, led the study, which was published in the prestigious journal Nature and even made the cover. Twelve participants received cell transplants in a single three-hour surgery. Thin tubes were inserted into both sides of the brain, delivering cells to the area where dopamine is needed. Because the cells came from a donor, patients took immune-suppressing medication for a year to prevent rejection. The early results are promising. Not only did patients show improvements in their movement scores, but brain scans also revealed signs that the transplanted cells had survived and were functioning. The effect appeared to hold steady even six months after stopping immune suppression. At the same time, a similar trial using iPSCs took place in Japan, with equally encouraging results. The consistency between the two studies adds weight to the findings, even though the trials were small and designed mainly to test safety. Dr. Atari stressed that there is currently no FDA-approved stem cell therapy for Parkinson’s or any other neurological condition. Everything remains experimental. That said, a larger Phase 3 study is now underway, aiming to confirm whether the therapy is truly effective. If successful, this could lead to FDA approval sometime in the early 2030s. Until then, patients should be cautious of clinics offering unproven stem cell treatments, especially those charging large sums. Legitimate clinical trials are typically free and closely regulated, and patients should always ask for documentation and consult their neurologist before enrolling. Dr. Atari also addressed questions about the source of stem cells. While embryonic cells require immune suppression, future options may include using a patient’s own cells, which could eliminate the need for those medications. Studies using autologous cells are already underway at places like Stanford and Harvard, although they’re still in the early stages and often by invitation only. Stem cell therapy won’t be a silver bullet. It’s costly, complicated, and not suitable for everyone. But it may eventually offer a powerful new way to restore some of what Parkinson’s takes away. While more research is needed, the progress so far gives many scientists and patients alike a cautious but genuine sense of hope.