stem-cell-therapy-parkinsonism

Introduction

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Atypical parkinsonian disorders—collectively known as Parkinson-plus syndromes—represent a group of neurodegenerative diseases characterized by parkinsonism (bradykinesia, rigidity, tremor) accompanied by additional neurological features that distinguish them from Parkinson’s disease. These include:

• Progressive supranuclear palsy (PSP): Characterized by vertical gaze palsy, postural instability, and cognitive decline

• Corticobasal syndrome (CBS): Featuring asymmetric rigidity, apraxia, alien limb phenomena, and cortical sensory loss

• Multiple system atrophy (MSA): Divided into MSA-P (parkinsonian) and MSA-C (cerebellar) subtypes, with autonomic dysfunction

• Dementia with Lewy bodies (DLB): Fluctuating cognition, visual hallucinations, and parkinsonism

Unlike idiopathic Parkinson’s disease, which primarily involves loss of dopaminergic neurons in the substantia nigra pars compacta, atypical parkinsonism involves more widespread neurodegeneration affecting multiple brain regions and neuronal populations. This complexity presents both unique challenges and opportunities for stem cell-based therapies.

Rationale for Cell Therapy in Atypical Parkinsonism

Dopaminergic Neuron Replacement

The foundational rationale for stem cell therapy in parkinsonian disorders stems from the successful proof-of-concept established in Parkinson’s disease: replacing lost dopaminergic neurons can restore motor function. While atypical parkinsonism involves additional neurotransmitter systems and brain regions, dopaminergic neuron transplantation may still provide symptomatic benefit for the parkinsonian components of these disorders.

Current clinical trials in Parkinson’s disease have demonstrated that both embryonic stem cell (ESC)-derived and iPSC-derived dopaminergic progenitors can survive, produce dopamine, and improve motor symptoms^{1Long term results of venetoclax combined with FLAG-IDA induction and consolidation for newly diagnosed and relapsed or refractory acute myeloid leukemia.2025 · Leukemia · DOI 10.1038/s41375-025-02531-8 · PMID 40000842Open reference}

Neuroprotective and Trophic Support

Beyond direct cell replacement, stem cells—particularly mesenchymal stem cells (MSCs)—exert neuroprotective effects through:

• Paracrine secretion of neurotrophic factors: BDNF, GDNF, NGF, and VEGF

• Immunomodulation: Suppression of pro-inflammatory microglia and reduction of neuroinflammation

• Anti-apoptotic effects: Secretion of factors that protect surviving neurons from cell death

• Promotion of endogenous repair: Stimulation of native neural stem cell proliferation and differentiation

These mechanisms are particularly relevant for atypical parkinsonism, where neuroinflammation plays a documented role in disease progression.

Disease-Specific Considerations

Each atypical parkinsonian disorder presents unique considerations for cell therapy:

Progressive Supranuclear Palsy: Neurodegeneration extends beyond the basal ganglia to include the subthalamic nucleus, pedunculopontine nucleus, and brainstem structures. While dopaminergic cell therapy may address bradykinesia and rigidity, the oculomotor deficits and gait freezing require approaches targeting additional neuronal populations.

Corticobasal Syndrome: Asymmetric cortical and subcortical degeneration affects frontoparietal regions. Cell therapy approaches may need to consider both motor cortex involvement and the cognitive deficits associated with cortical pathology.

Multiple System Atrophy: Both MSA-P and MSA-C involve autonomic dysfunction related to brainstem and spinal cord pathology. Cell therapy must address the broader neurodegenerative process affecting multiple neurotransmitter systems.

Dementia with Lewy Bodies: The presence of alpha-synuclein pathology throughout the cortex and peripheral nervous system presents challenges for cell replacement, though cholinergic neuron replacement may benefit cognitive symptoms.

Stem Cell Types and Applications

Induced Pluripotent Stem Cells (iPSCs)

iPSC technology offers particular advantages for atypical parkinsonism:

• Patient-specific modeling: iPSCs derived from patients can reveal disease-specific mechanisms

• Autologous transplantation potential: Patient-derived cells may reduce immune rejection risk

• Genetic correction: CRISPR-based gene editing can correct disease-causing mutations before transplantation (e.g., in GBA-associated cases)

iPSC-derived dopaminergic neurons have entered clinical trials for Parkinson’s disease^{1Long term results of venetoclax combined with FLAG-IDA induction and consolidation for newly diagnosed and relapsed or refractory acute myeloid leukemia.2025 · Leukemia · DOI 10.1038/s41375-025-02531-8 · PMID 40000842Open reference} and are expected to follow for atypical parkinsonism as the technology matures.

Embryonic Stem Cells (ESCs)

ESC-derived dopaminergic neurons are the most advanced cell therapy approach currently in clinical development:

• Bemdaneprocel (BlueRock Therapeutics): hESC-derived dopaminergic progenitors in Phase III for Parkinson’s disease

• STEM-PD: European trial of hESC-derived dopaminergic neurons^{2Heart failure with preserved ejection fraction.2024 · Nature reviews. Disease primers · DOI 10.1038/s41572-024-00540-y · PMID 39143132Open reference}

These programs establish the manufacturing, safety, and efficacy frameworks that will enable expansion to atypical parkinsonism.

Mesenchymal Stem Cells (MSCs)

MSCs offer a different therapeutic mechanism focused on neuroprotection rather than cell replacement:

• Delivery routes: Intravenous, intrathecal, or intracerebral administration

• Mechanisms: Paracrine trophic support, immunomodulation, anti-inflammatory effects

• Clinical trials: Multiple trials in Parkinson’s disease and ALS have established safety

For atypical parkinsonism, MSC therapy may be particularly valuable given the prominent role of neuroinflammation in these disorders.

Neural Stem Cells (NSCs)

Endogenous or derived neural stem cells can differentiate into multiple neuronal subtypes:

• Potential to replace multiple neurotransmitter systems affected in atypical parkinsonism

• Support for circuit reconstruction through axon guidance

• Limited clinical development to date but active preclinical research

Clinical Trial Landscape

Current Parkinson’s Disease Trials (Foundational)

Bemdaneprocel (exPDite-2, NCT05887418)

Sponsor: BlueRock Therapeutics (Bayer subsidiary)

Phase: Registrational Phase III (pivotal for approval)

Enrollment: ~102 patients at 24+ clinical sites internationally

Inclusion criteria:

• Age 50-75 years

• Parkinson’s disease diagnosis with Hoehn & Yahr stage II-III

• Motor complications inadequately controlled by levodopa

• No significant psychiatric or cognitive impairment

• Able to undergo stereotactic brain surgery

Results (Phase I/II): 21.9-point improvement in UPDRS Part III score at 24 months vs baseline

Expected readout: 2027-2028

Access options:

• Enroll in Phase III trial (clinicaltrials.gov NCT05887418)

• Expanded access program (contact BlueRock Medical Affairs)

• Post-approval access upon registration

STEM-PD (NCT05635409)

Sponsor: Lund University / University of Cambridge

Phase: Phase I/IIa, first-in-human

Clinical sites:

• Skåne University Hospital, Lund, Sweden

• UK sites (MHRA approved October 2023)

Cohort structure:

• Cohort 1 (completed): 4 patients, 3.5M cells per putamen (7M total), lower dose

• Cohort 2 (dosing underway): 4 patients, 7M cells per putamen (14M total), higher dose; first patient transplanted during 2024

Results:

• No concerning side effects reported; all patients doing well

• PET imaging at 6-12 months post-transplantation shows signs of dopamine cell survival

• 100,000-200,000 surviving dopamine neurons observed

• 36-month follow-up planned

Timeline: First patient transplanted February 2023; 3-year follow-up per patient

Kyoto University iPSC-DA Trial (NCT04995081)

Sponsor: Kyoto University / Center for iPS Cell Research and Application (CiRA)

Phase: Phase I/II, completed

Cell source: Autologous iPSC-derived midbrain dopamine progenitors

Results (published Nature 2025):

• 44.7% increase in putaminal dopamine on PET at 12 months

• Safety confirmed over 12-month observation period

• First-in-human demonstration of iPSC-derived DA neuron transplantation

Significance: Established proof-of-concept for iPSC approach; manufacturing protocols now being refined for larger-scale trials

Emerging Programs

Anticipated Applications in Atypical Parkinsonism

Based on the Parkinson’s disease foundation, clinical trials for atypical parkinsonism are expected to follow phases:

1. Phase I: Safety in small cohorts of PSP, CBS, or MSA patients (likely 2026-2028)

2. Phase II: Dose-finding and preliminary efficacy assessment (2028-2030)

3. Phase III: Registration-enabling trials if earlier phases show promise (2030+)

The choice of disorder for initial trials will likely prioritize:

• PSP: Relatively focal brainstem involvement, clear outcome measures (vertical gaze, postural stability)

• CBS: Asymmetric presentation adds complexity but clear motor endpoints

• MSA-P: Similar to Parkinson’s disease with autonomic complications

For CBS/PSP patients:

• Monitor PD trials as leading indicators of cell therapy feasibility

• First CBS/PSP-specific stem cell trials are expected approximately 2-3 years behind PD registrational timelines

• Autologous iPSC programs (Japan) may offer near-term access via research protocols

Transplantation Approaches

Stereotactic Intracerebral Injection

The standard delivery method for dopaminergic progenitors:

• Target: Putamen primarily, with potential for substantia nigra

• Technique: Multiple injection tracks for broad coverage

• Advantages: Direct delivery to target region, high local cell concentration

• Challenges: Invasive neurosurgical procedure, risk of hemorrhage

Intravenous Administration

Common for MSC-based therapies:

• Target: Systemic, with cells migrating to sites of inflammation

• Technique: Peripheral infusion

• Advantages: Minimally invasive, suitable for repeated dosing

• Challenges: Blood-brain barrier limits CNS delivery, trapped in peripheral organs

Intrathecal Administration

Delivery into cerebrospinal fluid:

• Target: CSF-exposed brain surfaces and spinal cord

• Technique: Lumbar puncture or cisterna magna injection

• Advantages: Bypasses blood-brain barrier, broader distribution than intracerebral

• Challenges: Variable distribution, risk of infection

Combination Approaches

Emerging strategies combine multiple delivery methods:

• Initial intracerebral transplantation for cell replacement

• Follow-up intravenous or intrathecal MSC administration for neuroprotection

• Repeated dosing schedules to maintain therapeutic effects

Immunological Considerations

Allogeneic Transplantation

Current clinical trials use allogeneic (donor-derived) cells:

• Immunosuppression required: Tacrolimus, mycophenolate mofetil, or similar regimens

• Risks: Infection, metabolic side effects, long-term immunosuppression complications

• Benefits: Off-the-shelf availability, established manufacturing

Autologous Approaches

iPSC technology enables patient-derived cells:

• Reduced immunosuppression: Theoretical advantage of patient-matched cells

• Challenges: Manufacturing complexity, cost, time (several months for reprogramming)

• Current status: Not yet in clinical trials for neurodegeneration

HLA Engineering

Emerging technologies to create universal donor cells:

• HLA knockout: Removing HLA expression to reduce immune recognition

• HLA-E expression: Inhibiting NK cell responses

• Potential: Off-the-shelf cells with minimal immunosuppression

For atypical parkinsonism patients, who often have older age and may be on immunosuppressive medications, minimizing immunosuppression-related complications is particularly important.

Challenges and Limitations

Disease-Specific Challenges

1. Widespread neurodegeneration: Unlike Parkinson’s disease, atypical parkinsonism involves multiple brain regions beyond the dopaminergic system

2. Multiple proteinopathies: Tau pathology in PSP, alpha-synuclein in MSA and DLB may affect transplanted cells

3. Autonomic dysfunction: MSA patients may have cardiovascular instability affecting surgical risk

4. Cognitive impairment: Some patients may have difficulty providing informed consent

Technical Challenges

1. Cell survival: Only 5-20% of transplanted cells survive in typical protocols

2. Functional integration: Establishing appropriate synaptic connections with host circuitry

3. Optimal cell dose: Determining the cell number needed for therapeutic effect

4. Delivery precision: Ensuring accurate targeting within the brain

Long-Term Considerations

1. Durability: Will transplanted cells maintain function over years to decades?

2. Disease progression: Will underlying neurodegeneration affect grafts?

3. Aging: Age-related changes in the host brain microenvironment

4. Tumorigenicity: Long-term monitoring for teratoma formation (primarily ESC/iPSC concern)

Emerging Research Directions

Gene-Enhanced Stem Cells

Combining gene editing with stem cell therapy:

• Stress resistance: Engineering cells to resist oxidative stress and excitotoxicity

• Enhanced trophic factor secretion: Engineering MSCs to produce higher levels of GDNF or BDNF

• Disease-modifying secretion: Engineering cells to secrete alpha-synuclein antibodies or tau-targeted molecules

Biomaterial Scaffolds

3D scaffolds to support cell survival and integration:

• Hydrogel carriers: Provide structural support and controlled release of trophic factors

• Biodegradable matrices: Support initial survival while allowing natural integration

• Organoid systems: More complex tissue constructs for transplantation

Combination Therapies

Stem cell therapy combined with other approaches:

• With small molecules: Pharmacological support for cell survival and integration

• With immunotherapy: Targeting pathological proteins to protect grafts

• With physical therapy: Rehabilitation to enhance functional recovery

See Also

• Stem Cell Therapy for Neurodegenerative Diseases

• Parkinson’s Disease Treatment

• Progressive Supranuclear Palsy

• Corticobasal Syndrome

• Multiple System Atrophy

• Gene Therapy for Neurodegeneration

• Trophic Factor Therapy