Researchers Implant Dopamine-Producing Stem Cells in Parkinson’s Patients Across Multiple Trials
A wave of clinical trials is now testing dopamine stem cell therapy for Parkinson’s disease, surgically implanting lab-grown neurons into patients’ brains to replace the cells destroyed by the disease.
The Story at a Glance:
- Multiple clinical trials are now testing dopamine stem cell therapy for Parkinson’s disease by surgically implanting lab-grown neurons into the brain’s putamen region.
- Bemdaneprocel (BlueRock/Bayer) showed a favorable safety profile and motor improvements through 36 months in a Phase 1 trial; a Phase 3 trial (exPDite-2) is now enrolling.
- A Japanese iPS cell trial reported a 44.7% average increase in dopamine activity in the putamen at 24 months, with both studies published in Nature in April 2025.
- Kenai Therapeutics dosed the first patient in its Phase 1 REPLACE trial (RNDP-001) in December 2025, with another trial underway at Keck Medicine of USC.
- No serious cell therapy-related adverse events have been reported across any of these programs to date.
What Happened
After decades of preclinical research, dopamine stem cell therapy for Parkinson’s disease has entered a period of rapid clinical testing. Several independent research groups are now surgically transplanting laboratory-grown dopamine-producing neurons directly into the brains of patients, aiming to replace the cells that the disease destroys.
The most clinically advanced program is bemdaneprocel (BRT-DA01), developed by BlueRock Therapeutics, a Bayer subsidiary. Eighteen-month results from its Phase 1 exPDite trial (n=12) were published in Nature in April 2025, showing the transplanted cells survived and continued to produce dopamine with no serious adverse events related to the therapy. A companion study from Kyoto University Hospital, also published in Nature the same day, reported similar safety findings using induced pluripotent stem (iPS) cells in 7 patients.
More recently, Kenai Therapeutics dosed the first patient in its Phase 1 REPLACE trial of RNDP-001 in December 2025, using a different iPSC-based platform. In February 2026, Keck Medicine of USC began enrolling patients in yet another early-phase trial using iPSCs, with the FDA granting both programs Fast Track designation.
Why Dopamine Stem Cell Therapy for Parkinson’s Matters
Parkinson’s disease affects more than 10 million people worldwide and over 1 million in the United States. The condition is driven by the progressive loss of dopamine-producing neurons in the brain, causing tremors, stiffness, and slowed movement. Current treatments — primarily levodopa and related medications — manage symptoms by replenishing dopamine levels, but they do not stop or slow neuronal loss, and their effectiveness typically diminishes over years of use.
The goal of stem cell transplantation is fundamentally different: to rebuild the dopamine-producing neural circuitry itself. If successful, this approach could reduce patients’ dependence on medication, extend the period of effective symptom control, and potentially alter the disease’s trajectory in ways no current treatment can.
Key Details: Active Dopamine Stem Cell Therapy Trials
| Program | Developer | Cell Source | Phase | n | Key Findings / Status |
|---|---|---|---|---|---|
| Bemdaneprocel (exPDite) | BlueRock / Bayer | Human embryonic stem cells (hESC) | Phase 1 (complete); Phase 3 enrolling | 12 (Ph1); ~102 (Ph3) | No serious AEs at 36 months; MDS-UPDRS Part III reduced 17.9 points (high dose); cells survived post-immunosuppression |
| iPS cell trial (Kyoto) | Kyoto University Hospital | Induced pluripotent stem cells (iPSC) | Phase I/II | 7 | 44.7% average increase in putamen dopamine activity at 24 months; no serious AEs; no tumor formation |
| RNDP-001 (REPLACE) | Kenai Therapeutics | iPSC (allogeneic, off-the-shelf) | Phase 1 | Up to 12 | First patient dosed December 2025; FDA Fast Track; initial data expected 2026 |
| USC iPSC trial | Keck Medicine of USC | iPSC | Phase 1 | Enrolling | FDA Fast Track; MRI-guided implantation; 12–15 month monitoring + 5-year follow-up |
| ANPD001 (autologous) | Mass General Brigham | Autologous iPSC (patient’s own cells) | Phase 1 | Up to 6 | 3 patients treated; no immunosuppression needed; first autologous iPSC trial for Parkinson’s |
What Experts Are Saying
“Rebuilding brain networks lost to disease is compelling.”
— Claire Henchcliffe, MD, DPhil, Chair of Neurology, UC Irvine School of Medicine; exPDite principal investigator
Henchcliffe noted that while early signals are encouraging, particularly in patients who received higher cell doses, caution is warranted when interpreting these uncontrolled Phase 1 results, according to a BlueRock Therapeutics statement. Brian Lee, MD, PhD, a neurosurgeon at Keck Medicine of USC and principal investigator of the USC trial, stated that restoring normal dopamine levels could potentially slow the disease and improve motor function.
What’s Next
The most pivotal near-term milestone is BlueRock’s Phase 3 exPDite-2 trial, a multicenter, double-blind, sham-controlled study enrolling approximately 102 patients with moderate Parkinson’s disease. Data from this registrational trial are expected in 2027 and could support regulatory approval of bemdaneprocel, which holds both RMAT (Regenerative Medicine Advanced Therapy) and Fast Track designations from the FDA.
Kenai Therapeutics expects initial safety and brain imaging data from all 12 REPLACE trial patients in 2026. The Keck Medicine trial will monitor patients for up to 5 years. The Mass General Brigham autologous iPSC program remains the only trial that does not require immunosuppression, a potential advantage if efficacy is confirmed.
The Bigger Picture
The convergence of multiple dopamine stem cell therapy programs entering clinical testing marks a notable shift in the Parkinson’s treatment landscape. Previous attempts at cell transplantation using fetal tissue in the 1990s and 2000s showed mixed results and raised ethical concerns about tissue sourcing. The current generation of trials uses standardized, scalable stem cell-derived products — either from embryonic stem cells or iPSCs — and has so far avoided the graft-induced dyskinesia that complicated earlier approaches. If the Phase 3 data confirm what early trials suggest, cell replacement could become the first regenerative therapy for a major neurodegenerative disease.
Bottom Line
- Multiple clinical trials are now testing dopamine stem cell therapy for Parkinson’s by implanting lab-grown neurons directly into the brain.
- Early data across programs show acceptable safety, evidence of cell survival, and preliminary motor improvements — particularly at higher doses.
- BlueRock’s Phase 3 sham-controlled trial (exPDite-2) will be the first rigorous efficacy test, with results expected in 2027.
- Long-term durability, optimal dosing, immunosuppression requirements, and whether cell therapy can truly modify disease progression remain open questions.
Sources
- Sawamoto N, Doi D, Nakanishi E, et al. Phase I/II trial of iPS-cell-derived dopaminergic cells for Parkinson’s disease. Nature. 2025;641:971–977. DOI: 10.1038/s41586-025-08700-0
- BlueRock Therapeutics. Publication in Nature of 18-month data from Phase 1 exPDite trial for bemdaneprocel. Press release. April 16, 2025. Link
- BlueRock Therapeutics. Positive 36-month results from Phase I trial of bemdaneprocel. Press release. October 7, 2025. Link
- Kenai Therapeutics. First patient dosed in Phase 1 REPLACE trial of RNDP-001. Press release. December 15, 2025. Link
- University of Southern California. Doctors test brain cell implants to restore movement in Parkinson’s. ScienceDaily. February 6, 2026. Link
- ClinicalTrials.gov. A Study to Investigate the Efficacy and Safety of Bemdaneprocel (exPDite-2). NCT06944522
- ClinicalTrials.gov. Phase 1 REPLACE Trial of RNDP-001. NCT07106021