Stem cell therapy improves motor function in Parkinson’s trial, data show

XS411, Xellsmart’s experimental stem cell therapy, was generally well tolerated and associated with improved motor function in people with Parkinson’s disease, according to new Phase 1 clinical trial data.

The trial (NCT07080775) enrolled nine people with moderate to advanced Parkinson’s. It also showed that the treatment improved patients’ quality of life, and that the benefits were sustained through available follow-up.

The findings were presented at the 2026 International Congress of Parkinson’s Disease and Movement Disorders, held Oct. 4-8 in Seoul, South Korea, according to a company press release.

The company also announced the completion of patient enrollment in the Phase 2 part of the trial, with all patients in the treatment group having received the cell transplantation.

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XS411 designed to restore dopamine production

Parkinson’s is characterized by the loss of nerve cells, or neurons, that produce dopamine, a chemical messenger essential for controlling movement. As dopamine-producing neurons die, patients develop motor symptoms such as tremors, muscle stiffness, and slow movement.

Although current medications such as levodopa can help control these symptoms, they do not replace the dopamine-producing neurons lost to the disease.

XS411 is designed to restore dopamine production by replacing damaged nerve cells. It uses induced pluripotent stem cells – mature cells reprogrammed in the laboratory into a stem-cell-like state – that are engineered to develop into immature dopamine-producing neurons.

These cells are then surgically transplanted into the putamen, a brain region involved in movement control, where they are expected to mature into functional dopamine-producing neurons and integrate into the brain’s existing networks. This can potentially restore some of the patients’ lost functions.

The cell therapy is allogeneic, meaning it uses cells obtained from donors, allowing cells to be manufactured in advance and used to treat multiple patients. While XS411 does not require matching donor cells to each profile, patients receive a standardized immunosuppressive regimen to help prevent rejection of the transplanted cells.

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Motor function improvements seen 6 months after transplant

Participants in the Phase 1 study were living with Parkinson’s for about 10 years and had substantial movement difficulties despite receiving standard treatment. The trial evaluated progressively higher doses in three groups of three patients.

No dose-limiting toxicities, serious adverse events, or adverse events considered related to XS411 were reported during the study. MRI scans also showed no evidence of abnormal cell growth, and no involuntary movements caused by the transplanted cells were observed.

Six months after transplantation, scores on the Movement Disorder Society-Unified Parkinson’s Disease Rating Scale Part III, which evaluates motor symptoms, decreased by an average of more than 30 points, indicating improved motor function. Patients were assessed in the off state, when the effects of their usual Parkinson’s medications had worn off.

Patient diaries also showed that participants gained an average of over five hours of good on time each day, which refers to periods when Parkinson’s symptoms are adequately controlled without troublesome involuntary movements. Improvements were also reported in participants’ quality of life.

Brain scans using 18F-DOPA positron emission tomography, an imaging technique that assesses dopamine-related activity in the brain, also showed increased tracer uptake in the putamen. These findings are consistent with increased dopamine production in the treated region, supporting the therapy’s intended mechanism of action.

Phase 2 trial results will help inform future study

Building on these preliminary results, Xellsmart advanced to the Phase 2 part of the trial, which enrolled 30 participants randomly assigned to different treatment groups. All patients assigned to XS411 have undergone cell transplantation, and follow-up assessments are ongoing.

The company expects the results from this trial to help inform a future Phase 3 trial designed to provide more definitive evidence of the therapy’s safety and effectiveness, which may support regulatory submissions seeking the therapy’s approval.

According to the developer, the therapy has also shown benefits in a Phase 1/2 study (NCT07166757) enrolling people with early-onset Parkinson’s.

This year, the U.S. Food and Drug Administration awarded XS411 fast-track status, a designation that may provide a faster regulatory review if clinical data are positive. The FDA and regulators in China also cleared Phase 1/2 clinical trials testing XS411 in people with multiple system atrophy-Parkinsonian type, a form of atypical parkinsonism.