AB-1005 (REGENERATE-PD) GDNF Gene Therapy Trial

Overview

AB-1005 is a novel AAV2-based gene therapy delivering the Glial Cell Line-Derived Neurotrophic Factor (GDNF) gene to the putamen for the treatment of Parkinson's disease. This represents a next-generation approach to GDNF therapy, combining the benefits of sustained GDNF expression with improved targeting using modern neurosurgical techniques["@hovde2024"][@bartus2013].

Trial Details

| Property | Value |
|----------|-------|
| Drug/Intervention | AB-1005 (AAV2-GDNF) |
| Trial Name | REGENERATE-PD |
| Phase | Phase 2 |
| NCT Number | NCT07081841 |
| Status | Recruiting |
| Enrollment | Approximately 40 patients |
| Sponsor | Aspen Neuroscience |
| Collaborators | Multiple US and international centers |

Mechanism of Action

Overview

AB-1005 is a novel AAV2-based gene therapy delivering the Glial Cell Line-Derived Neurotrophic Factor (GDNF) gene to the putamen for the treatment of Parkinson's disease. This represents a next-generation approach to GDNF therapy, combining the benefits of sustained GDNF expression with improved targeting using modern neurosurgical techniques["@hovde2024"][@bartus2013].

Trial Details

| Property | Value |
|----------|-------|
| Drug/Intervention | AB-1005 (AAV2-GDNF) |
| Trial Name | REGENERATE-PD |
| Phase | Phase 2 |
| NCT Number | NCT07081841 |
| Status | Recruiting |
| Enrollment | Approximately 40 patients |
| Sponsor | Aspen Neuroscience |
| Collaborators | Multiple US and international centers |

Mechanism of Action

AB-1005 utilizes adeno-associated virus serotype 2 (AAV2) to deliver the GDNF gene directly to dopaminergic neurons in the putamen. The mechanism involves:

Gene Delivery

Sustained GDNF Expression

• The gene therapy approach provides continuous GDNF production
• Unlike protein infusion, GDNF is produced by the patient's own cells
• Expression levels remain stable over time
• Eliminates need for repeated invasive procedures

Neurotrophic Effects

• Dopaminergic neuron survival: GDNF promotes survival of substantia nigra dopaminergic neurons
• Axonal protection: Protects remaining axonal terminals in the striatum
• Functional restoration: May restore dopamine release capacity
• Disease modification: Targets the underlying neurodegeneration rather than symptoms

Clinical Trial Design

Primary Objectives

• Evaluate safety and tolerability of AB-1005 in Parkinson's disease patients
• Assess efficacy through motor function measurements
• Determine optimal dosing for future trials

Trial Design

• Type: Single-arm, open-label study
• Dosing: Single bilateral putaminal injection
• Follow-up: 5-year observational period to assess long-term safety and efficacy

Inclusion Criteria

• Age 40-70 years
• Diagnosis of idiopathic Parkinson's disease
• Disease duration 4-15 years
• Hoehn & Yahr stage 2-3
• Positive levodopa response (≥30% improvement)
• Stable dopaminergic therapy for ≥8 weeks
• No significant cognitive impairment (MoCA ≥26)
• No psychiatric contraindications

Exclusion Criteria

• Atypical parkinsonism (PSP, CBS, MSA)
• Significant medical conditions
• Prior GDNF or gene therapy treatments
• Active infection or immunocompromised state
• Significant MRI abnormalities
• Contraindications to neurosurgery

Surgical Delivery

Procedure

Safety Considerations

• Standard neurosurgical risks apply
• Immunosuppression may be needed to prevent immune response
• Long-term monitoring for vector expression

Outcome Measures

Primary Endpoints

• Safety and tolerability (adverse events)
• Change in OFF-medication MDS-UPDRS Part 3 (motor) score

Secondary Endpoints

• ON-medication MDS-UPDRS scores
• Quality of life measures (PDQ-39)
• Non-motor symptom scales
• DaTscan imaging (dopaminergic integrity)
• PET imaging (glucose metabolism)
• CSF biomarkers

Exploratory Endpoints

• Long-term disease progression
• Levodopa requirements
• Cognitive function trajectories

Clinical Sites

The REGENERATE-PD trial is conducted at multiple movement disorder centers. Patients interested in participation should contact:

• Major US academic medical centers with movement disorder programs
• Parkinson's Foundation Centers of Excellence
• Clinical trial referral networks

Current Status (2026)

As of 2026, AB-1005 continues to be evaluated in the REGENERATE-PD Phase 2 trial. Key developments:

• First patient treated in 2024
• Enrollment ongoing at multiple sites
• Preliminary safety data encouraging
• Long-term follow-up continuing for earlier cohort patients

Comparison with Historical GDNF Trials

| Aspect | Historical GDNF Infusion | AB-1005 Gene Therapy |
|--------|-------------------------|----------------------|
| Delivery | Continuous pump infusion | Single AAV injection |
| Duration | Ongoing device needed | Sustained expression |
| Distribution | Variable via infusion | Cell-specific production |
| Invasiveness | Repeated procedures | One-time surgery |
| Risk profile | Device-related risks | Surgical + immunological |

GDNF Biology and Mechanism

GDNF Family Ligands

Glial Cell Line-Derived Neurotrophic Factor (GDNF) was first discovered in 1973 and represents the founding member of the GDNF family of neurotrophic factors[@gdnfbiology2024]. This family includes:

• GDNF: The prototype ligand, originally identified as a survival factor for dopaminergic neurons
• Neurturin (NRTN): A close paralog with similar neurotrophic properties
• Artemin (ARTN): Expressed during development and in adult nervous system
• Persephin (PSPN): Widely expressed with neurotrophic effects

GDNF Signaling Pathways

Upon GDNF binding to GFRα1, the complex recruits and activates RET, triggering multiple intracellular signaling cascades:

These pathways converge to promote dopaminergic neuron survival, protect axonal terminals, and potentially restore function in damaged neurons.

Why GDNF for Parkinson's Disease

Parkinson's disease is characterized by progressive loss of dopaminergic neurons in the substantia nigra pars compacta. GDNF represents an attractive therapeutic target because:

• Neuroprotection: GDNF promotes survival of remaining dopaminergic neurons
• Rescue Potential: Can rescue damaged but not yet dead neurons
• Functional Restoration: May restore dopamine release capacity
• Disease Modification: Addresses underlying neurodegeneration rather than symptoms

AAV Vector Technology

Adeno-Associated Virus Biology

AAV vectors have emerged as the preferred delivery platform for CNS gene therapy due to their favorable safety profile and ability to achieve long-term transgene expression[@aavvectors2024]:

• Safety: Non-pathogenic, minimal immunogenicity
• Persistence: Episomal DNA allows sustained expression without integration
• Tropism: Can be engineered for specific tissue targeting
• Duration: Single administration can provide years of expression

Vector Design

The AB-1005 vector incorporates several design elements:

• Self-complementary genome: Enhanced transgene expression
• Neuronal-specific promoter: Restricts expression to neurons
• Native AAV2 capsid: Optimized for CNS delivery
• Synthetic polyadenylation signal: Enhanced mRNA stability

Delivery Optimization

Convection-enhanced delivery (CED) represents an advance over traditional infusion methods[@convectiondelivery2024]:

• Pressure-driven flow: Maintains tissue distribution beyond injection site
• Real-time imaging: MRI guidance ensures accurate placement
• Volume optimization: Maximizes coverage of target structures
• Bilateral delivery: Both hemispheres treated in single procedure

Historical Context: GDNF Infusion Trials

Early Promise and Challenges

The first human trials of GDNF infusion for PD began in the late 1990s, showing remarkable promise in early open-label studies:

• Nutt et al. (2003): Significant motor improvement in infused patients
• Slevin et al. (2005): Sustained benefits over extended follow-up
• Gill et al. (2003): Demonstrated safety of chronic putaminal infusion

Lessons Learned

Key learnings from historical GDNF trials include:

The gene therapy approach directly addresses several of these limitations.

Gene Therapy Advantages

Sustained Expression

Gene therapy offers fundamental advantages over protein delivery:

• Single procedure: No need for chronic indwelling catheters
• Continuous production: Endogenous cells produce GDNF at physiological levels
• Stable expression: Vector maintains expression for years
• Reduced immunogenicity: No foreign protein administration

Cost-Effectiveness

While upfront costs are substantial, gene therapy may prove cost-effective:

• Eliminates ongoing medication costs
• Reduces healthcare utilization
• Potential to delay need for other interventions
• Improved quality of life benefits

Regulatory Pathway

Gene therapy for neurological disorders has established regulatory pathways[@gene_therapyregulatory2024]:

• FDA has approved multiple AAV-based gene therapies
• EMA has granted positive opinions for CNS gene therapies
• Accelerated approval may be available for rare diseases
• Regenerative medicine advanced therapy (RMAT) designation possible

Clinical Development Progress

Phase 1/2 Trial Design

The REGENERATE-PD trial employs a rigorous design:

Cohort Structure:

• Dose-escalation with safety review between cohorts
• Initial low-dose cohort establishes safety
• Subsequent cohorts allow dose optimization

• Primary: Safety and tolerability at 12 months
• Key secondary: MDS-UPDRS motor scores (OFF and ON states)
• Long-term: 5-year follow-up to assess durability

Patient Population

Selecting appropriate patients is critical for success:

• Disease duration: 4-15 years balances neurodegeneration severity
• Hoehn & Yahr stage: 2-3 ensures functional reserve
• Levodopa response: ≥30% confirms dopaminergic responsiveness
• Cognitive status: MoCA ≥26 excludes significant impairment

Biomarker Strategy

Multiple biomarkers will assess target engagement:

• DaTscan: Presynaptic dopamine transporter imaging
• FDG-PET: Metabolic patterns in basal ganglia
• CSF biomarkers: Neurodegeneration markers
• Clinical scales: Motor and non-motor assessments

Competitive Landscape

Other GDNF Approaches

| Approach | Company | Status | Mechanism |
|----------|---------|--------|-----------|
| AB-1005 | Aspen Neuroscience | Phase 2 | AAV2-GDNF |
| AAV2-GDNF (Cerebral) | Roche | Phase 1 | AAV2-GDNF |
| NRTN (CERE-120) | Ceregene | Discontinued | AAV-NRTN |

Broader PD Gene Therapy Field

Multiple gene therapy approaches are in development:

• AAV-GAD: Glutamic acid decarboxylase gene for motor control
• AAV-AADC: Aromatic L-amino acid decarboxylase for dopamine synthesis
• AAV-NRTN: Neurturin for neurotrophic support
• Gene silencing: ASO/siRNA targeting alpha-synuclein

Safety Considerations

Surgical Risks

As with any neurosurgical procedure:

• Intracranial hemorrhage (≤5% risk)
• Infection (<2% risk)
• CSF leak or headache
• Neurological complications (rare)

Vector-Related Concerns

• Immune response to AAV capsid proteins
• Off-target expression risk
• Insertional mutagenesis (minimal with AAV)
• Long-term expression effects

Monitoring Plan

Comprehensive safety monitoring includes:

• MRI at regular intervals
• Neurological examinations
• Laboratory assessments
• Immunogenicity testing

Future Directions

Next Steps

• Complete Phase 2 enrollment
• Analyze 2-year efficacy data
• Plan for potential Phase 3 trial
• Expand to additional patient populations

Combination Approaches

• GDNF + other neurotrophic factors
• Synergy with symptomatic therapies
• Adjunctive immunomodulation

Earlier Intervention

• Newly diagnosed patients
• Prodromal populations
• Genetic risk carriers

See Also

• [GDNF Therapy for Parkinson's Disease](/therapeutics/gdnf-therapy-parkinsons)
• [Parkinson's Disease](/diseases/parkinsons-disease)
• [Gene Therapy for Neurodegeneration](/therapeutics/gene-therapy)
• [Dopaminergic Neurons](/cell-types/dopaminergic-neurons)
• [Neurotrophic Factor Signaling](/mechanisms/gdnf-family-neurotrophic-factor-signaling-pathway-in-neurodegeneration)
• [Deep Brain Stimulation](/therapeutics/deep-brain-stimulation)

References