Advancing the Field: Stem Cell Therapies and the Future of Parkinson Disease Treatment

In a recently launched special NeurologyLive^® Roundtable Discussion developed in collaboration with the International Society for Stem Cell Research (ISSCR), two leading Parkinson disease experts explored the rapidly advancing field of stem cell medicine and its potential role in treating Parkinson disease.

Over five episodes, Roger Barker, MD, PhD, professor of clinical neuroscience at the University of Cambridge, and Claire Henchcliffe, MD, DPhil, chair of the Department of Neurology at the University of California, Irvine, School of Medicine, examined the science, clinical trial landscape, and practical implications of this emerging therapeutic frontier, anchored around ISSCR's newly launched educational course.

An Educational Resource Built for a Global Clinical Community

The conversation opened with an overview of the ISSCR course and why Parkinson disease was selected as a featured condition. As Barker explained, the ISSCR has increasingly shifted its focus from basic science toward clinical applications, and Parkinson disease, with its well-defined pathology centered on the loss of a specific cell population, emerged as a natural frontrunner. Developed in collaboration with Harvard Medical School, the course is designed as a rolling program and has already drawn more than 7,000 to 8,000 learners from around the world.

For Henchcliffe, the international scope was one of its most compelling qualities. "ISSCR really takes great pains to include people from different parts of the world," she said. "Although we originated in the same place, we work in completely different medical environments. The resources that we've got available are really quite different."

She also highlighted the course's inclusion of a patient with lived experience of Parkinson disease, someone who had undergone one of these novel interventions firsthand. "That made a world of difference to me," Henchcliffe said, "in terms of hearing someone's own experience, not us talking about it."

What Clinicians Stand to Gain

Both faculty noted that questions about stem cell therapies are now routine in clinic. Patients are arriving with pointed questions about trials they have read about, regulatory approvals abroad, and whether they are missing a window for treatment.

"Some people are actually coming in specifically with questions about stem cells, like, should I book my airline tickets? Is this something I need to jump onto now?" Henchcliffe said.

Barker emphasized the importance of helping clinicians distinguish between unproven commercial offerings, early investigator-led trials, and more advanced phase studies — a layered landscape that creates real confusion for patients and families. He also cautioned against the phenomenon of "stem cell tourism," where patients pay out of pocket for therapies with no clear scientific rationale.

Both panelists pointed to the ISSCR's website as a trusted, unbiased resource clinicians can direct patients to, a meaningful alternative to social media and company-generated content.

A Field That Has Exploded: The Clinical Trial Landscape

The specific focus of current trials is dopamine cell replacement, turning stem cells into the type of dopamine-producing nerve cells lost in Parkinson disease and surgically delivering them to the brain. Four trials have reported results to date, covering a combined total of roughly 30 patients. That number is growing, with many more patients currently enrolled in ongoing studies, and Barker estimated that at least a dozen to two dozen companies globally are now working in this space.

Among the most advanced programs, both panelists pointed to Blue Rock Therapeutics, which uses an embryonic stem cell-derived product and is now enrolling in a phase 3 trial targeting approximately 100 patients with a sham surgery control component. In Japan, a program using induced pluripotent stem (iPS) cell-derived dopamine cells has received conditional regulatory approval and has since entered clinical trials in the United States. An emerging area of interest involves autologous cell approaches, using a patient's own cells to eliminate the need for immunosuppression, with companies like Aspen Neuroscience presenting early data.

Barker cautioned against viewing all trials as interchangeable. "Blue Rock use an embryonic stem cell, they use a particular type of immunotherapy. The group in Japan used an iPS cell, it wasn't a frozen cell product, they use less immunotherapy," he noted. "These subtle differences may account for some of the differences you see in the trials themselves."

Despite the momentum, the field remains early. Results have been encouraging but inconsistent, particularly around cell survival on imaging. Both experts were equally quick to note the collaborative spirit driving the work. "We're all in this together," Barker said. "Let's see if we can learn from each other, work together, and lead together as a community."

How Stem Cell Therapies Differ From Current Treatments

Existing treatments, including the gold-standard levodopa, work by augmenting dopamine systemically. While effective early in the disease course, they become increasingly difficult to manage over time, with patients developing motor fluctuations, dyskinesias, and complications that consume significant clinic time.

"When people are having ups and downs all day long, and they can't control their symptoms smoothly, or they start getting dyskinesia, this is when we really start thinking very hard about what is that next advanced therapeutic going to be," Henchcliffe said.

Stem cell approaches offer the theoretical promise of a one-time surgical delivery of dopamine-producing cells placed precisely where they are needed, avoiding systemic side effects and indwelling hardware. "The ultimate would be to provide a one-time delivery of cells that is going to hold people for their lifetime for the motor symptoms," Henchcliffe said.

On the question of disease modification, Barker drew a useful distinction: stem cell therapies would not halt the underlying pathology of Parkinson disease, but they could meaningfully alter its natural history. "With the advent of levodopa, your life expectancy with Parkinson's is normal," he noted. "So, you actually have modified people's life and disease expectancy simply by giving them symptomatic treatments." Looking further ahead, both panelists envisioned cell replacement used alongside disease-modifying agents as a combination approach to treatment.

A Call to Action for the Clinical Community

Closing out the series, both faculty made a direct case for why clinicians should engage with the ISSCR course, regardless of subspecialty.

"Even if you are not interested yourself, I can tell you your patients and their families are," Barker said. "To have a resource where you can quickly get an up-to-date, realistic account of where this therapy has got to, I think is something everybody should do."

Henchcliffe added that the relevance extends well beyond Parkinson disease specialists. "It doesn't matter if you're a stroke specialist or a specialist in autoimmune neurological disorders, you are going to be seeing people who either have Parkinson's or know someone who's been affected by it." Barker echoed that broader view, noting that stem cell approaches are being explored across neurology, from stroke to autoimmune encephalitis. "The future of medicine and neurology is going to involve stem cells for different diseases, different types," he said. "This just happens to be one of the front runners."