A domestic research team published in an international journal the results of a study confirming a therapeutic effect by administering embryonic stem cells to Parkinson's disease patients whose hands and feet tremble and whose bodies gradually become paralyzed.
A joint team from Yonsei University Severance Hospital and S.Biomedics said on the 14th in the international journal Cell that a phase 1/2a clinical trial of transplanting midbrain dopamine neurons derived from human embryonic stem cells into Parkinson's disease patients confirmed safety and efficacy.
◇Differentiate embryonic stem cells into dopamine cells
Parkinson's disease is a degenerative brain disorder first identified in 1817 by British physician James Parkinson. As dopamine-secreting neurons decrease, motor symptoms such as trembling of the hands and feet and a heavy gait appear. Dopamine is a neurotransmitter that controls motor function.
The research team conducted a clinical trial to transplant dopamine neurons made from embryonic stem cells into patients, the first in Asia and the second in the world. Embryonic stem cells in a fertilized egg, where sperm and egg meet, are primitive cells that grow into all cells of the human body. Currently marketed Parkinson's disease treatments only alleviate symptoms, making fundamental treatment limited. Cell therapy can replace damaged neurons with healthy ones, enabling fundamental treatment.
The clinical trial divided patients into groups of six and administered a dopamine cell therapy into the brain at low dose (3.15 million cells) and high dose (6.3 million cells), respectively, followed by one year of follow-up. Patients enrolled in the trial had not responded to existing treatments and had side effects, but their symptoms improved significantly after dopamine cell therapy.
One patient had stopped conducting an orchestra due to hand tremors from Parkinson's disease but was able to take up the baton again after cell therapy. Another patient who had struggled even to walk is now enjoying table tennis and badminton after the therapy, the researchers said.
Parkinson's disease patients experience "wearing-off," in which, over time, the effects of medication diminish and symptoms such as tremor, rigidity, and pain occur more frequently. The research team said all patients improved in this phenomenon after cell therapy.
"Freezing of gait," in which the body stiffens and cannot move when walking or changing direction, improved in four of five patients in the low-dose group. Among them, two saw the freezing symptoms disappear completely. In the high-dose group, all six patients improved in freezing of gait, and four had the symptoms disappear entirely.
The research team said that brain imaging taken one year later showed increased signals from dopamine neurons, confirming that the transplanted cells had engrafted well. Jang Jin-woo, a neurosurgery professor at Korea University and first author of the paper, said, "The transplanted cells appear to have engrafted well and to be functionally well connected with the existing dopamine circuitry."
Lee Pil-hyu, a neurology professor at Severance Hospital and corresponding author of the paper, explained, "The increased signal on dopamine brain imaging is evidence showing the mechanism of action of cell therapy," adding, "It is highly significant that it shows a direct association with patients' clinical improvement."
◇Symptoms improved 43% in the high-dose group
The research team quantified the therapeutic effect. On the Hoehn & Yahr scale, which classifies Parkinson's symptoms by severity, the low-dose group improved by an average of 27.8% one year after transplantation. A lower stage indicates milder symptoms, and the average decreased from stage 3.7 to 2.7. The high-dose group improved by an average of 43.1%, decreasing from stage 3.8 to 2.2.
On the MDS-Unified Parkinson's Disease Rating Scale (MDS-UPDRS Part 3), which evaluates motor symptoms across 33 items, the low-dose group's score fell by 12.7 points for an average improvement of 21.8%. The high-dose group saw a decrease of 15.5 points, an average improvement of 26.9%.
No unusual side effects related to cell transplantation were observed. Among the 12 transplanted patients to date, one showed mild bleeding in an area adjacent to, but not related to, the transplant site; however, no notable neurological abnormalities or side effects were observed, the researchers said.
In the United States alone, more than 1 million people have Parkinson's disease. The resulting economic burden reaches $5.19 billion (about 74 trillion won) per year. The world-renowned boxer Muhammad Ali and actor Michael J. Fox, famous for the film "Back to the Future," also developed Parkinson's disease. If cell therapy succeeds, a huge market is expected to emerge.
Kim Dong-wook, professor in the Department of Physiology at Yonsei University College of Medicine and the overall lead and corresponding author of the paper (chief technology officer of S.Biomedics), said, "By differentiating embryonic stem cells, we secured the world's highest-purity dopamine neurons, and in animal experiments the survival rate of transplanted dopamine cells was superior to international competitors." Based on these results, the research team plans to proceed to phase 2b/3 clinical trials with more patients.
References
Cell (2025), DOI: https://doi.org/10.1016/j.cell.2025.09.010