Stem cell therapy can safely and effectively treat Parkinson’s disease

Two independent clinical trials demonstrate the safety of stem cell therapy for Parkinson’s disease. The papers, published this week in Nature, examine the use of cells derived from induced human pluripotent stem cells and human embryonic stem cells, respectively. However, further research is needed to verify the efficacy and clinical benefits of these treatments.

Parkinson‘s disease is a neurodegenerative disease characterized by the progressive loss of neurons that produce the neurotransmitter dopamine. While existing treatments, such as levodopa, can alleviate symptoms in the early stages, their effectiveness diminishes over time, and treatment is often accompanied by side effects such as dyskinesia (involuntary movements).

Cell therapy, particularly replenishing dopamine-producing (dopaminergic) neurons in the brain, may be a potentially more effective treatment option with fewer side effects.

To investigate the safety and potential side effects of cell therapy for Parkinson’s disease, Ryosuke Takahashi, Jun Takahashi, and colleagues conducted a phase I/II study. Seven patients (aged 50 to 69 years) underwent transplantation of dopaminergic neuronal precursors derived from human induced pluripotent stem cells into the brain on both sides.

No serious adverse events were reported during the 24-month study, and the transplanted cells produced dopamine without growing or forming tumors, one of the dangers associated with stem cell therapy.

The researchers also noted a reduction in motor symptoms associated with Parkinson’s disease (a secondary outcome of the study) in four of the six participants who continued the study to the efficacy evaluation without taking standard medication, and in five patients who continued taking medication. However, these outcomes varied depending on the measurements taken, and some showed minimal change.

In a separate Phase I clinical trial, Vivian Tabar and her colleagues studied the safety of a preparation of dopaminergic neuronal progenitor cells (bemdaneprocel) derived from human embryonic stem cells. Twelve patients with a mean age of 67 years underwent surgical transplantation of bemdaneprocel into the basal nucleus region on both sides of the brain. Five participants received a low dose (0.9 million cells per basal nucleus) and seven received a high dose (2.7 million cells per basal nucleus).

The cell preparation was generally well tolerated, and no serious therapy-related adverse events were reported during 18 months of follow-up. No cases of dyskinesia, which has previously been associated with fetal tissue transplantation as a treatment for Parkinson’s disease, were noted.

In addition, some improvement in motor function (a secondary outcome of the study) was observed in patients in both the low- and high-dose treatment cohorts. However, the degree of improvement varied across the different parameters measured.

Both clinical trials confirm the safety of allogeneic (“unrelated”) transplantation of stem cell-derived cell products for the treatment of Parkinson’s disease. Some limitations are noted, including the small sample size and the open nature of both trials (meaning that both researchers and patients knew who was receiving which treatment).

However, the fact that both independent trials showed safety and hinted at possible efficacy is an important step towards the introduction of this cell therapy for Parkinson’s disease.

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Published: 18.04.2025

Updated: 17.04.2025

Medical author, Medical editor:

Stepan Yuk

Medical expert:

PhD. Olexandr Voznyak