TRAILBLAZER-ALZ 5 (NCT05508789) is a global Phase 3 clinical trial evaluating the safety and efficacy of donanemab (LY3002813), an investigational amyloid-targeting monoclonal antibody, in participants with early symptomatic Alzheimer's disease. This large-scale study builds upon the positive results from the TRAILBLAZER-ALZ 2 trial and aims to further characterize donanemab's clinical benefits in a broader population[@donanemab_trailblazer2].
Donanemab is a humanized IgG1 antibody that binds to a unique epitope on the N-terminal region of Aβ plaques, facilitating their clearance via microglial-mediated phagocytosis. Unlike other anti-amyloid antibodies that target soluble Aβ species, donanemab specifically targets pyroglutamate-modified Aβ (pE3-Aβ)—a particularly aggregation-prone and neurotoxic form of amyloid that is heavily enriched in plaque cores[@novel2024].
| Parameter |
Value |
| NCT Number |
NCT05508789 |
| Phase |
Phase 3 |
| Status |
Recruiting |
| Sponsor |
Eli Lilly and Company |
| Enrollment |
1,500 participants (estimated) |
| Enrollment Type |
Estimated |
| Study Type |
Interventional |
| Start Date |
October 10, 2022 |
| Completion Date |
July 1, 2028 |
| Last Updated |
February 10, 2026 |
- Alzheimer Disease (Early symptomatic)
- Mild Cognitive Impairment due to AD
- Dementia (Mild)
Alzheimer's disease (AD) is the most common cause of dementia, accounting for approximately 60-80% of all dementia cases worldwide. The disease is characterized by:
-
Amyloid Pathology
- Accumulation of amyloid-beta (Aβ) peptides
- Formation of extracellular plaques
- Primarily Aβ40 and Aβ42 species
- pE3-Aβ (pyroglutamate-modified) species particularly toxic
-
Tau Pathology
- Hyperphosphorylation of tau protein
- Formation of neurofibrillary tangles (NFTs)
- Spreading through connected neural networks
- Correlates with clinical progression
-
Neurodegeneration
- Synaptic loss and neuronal death
- Progressive brain atrophy
- Network dysfunction
-
Clinical Manifestations
- Memory impairment (especially episodic memory)
- Progressive cognitive decline
- Functional impairment
- Behavioral changes
The amyloid cascade hypothesis has been the dominant model for understanding AD pathogenesis since its proposal in 1992. The hypothesis proposes that:
Aβ accumulation → Tau pathology → Synaptic loss → Neuronal death → Cognitive decline
However, recent clinical trials have revealed the complexity of AD pathophysiology and the need for multi-target therapeutic approaches[@amyloid2023]. The relationship between amyloid and tau appears to be bidirectional, with both pathologies influencing each other.
Donanemab is a monoclonal antibody that specifically targets pyroglutamate-modified Aβ (pE3-Aβ):
| Property |
Description |
| Target |
pE3-Aβ (pyroglutamate-modified amyloid-beta) |
| Epitope |
N-terminal region (amino acids 1-6) |
| Isotype |
Humanized IgG1 |
| Affinity |
High affinity for plaque-associated Aβ |
flowchart TD
A["Donanemab IgG1 Antibody"] --> B["Binds to pE3-Aβ Plaques"]
B --> C["Marks Plaques for Clearance"]
C --> D["Fc Region Engages Microglia"]
D --> E["Microglial Phagocytosis"]
E --> F["Plaque Clearance"]
F --> G["Reduced Aβ Burden"]
G --> H["Slowed Cognitive Decline"]
- Binding: Donanemab binds with high affinity to pE3-Aβ deposited in amyloid plaques
- Opsonization: The antibody marks plaques for immune recognition
- Effector Activation: The IgG1 Fc region engages activating Fcγ receptors on microglia
- Phagocytosis: Microglia clear plaques through antibody-dependent cellular phagocytosis (ADCP)
- Plaque Reduction: Amyloid plaque burden is substantially reduced
Compared to other anti-amyloid antibodies:
| Antibody |
Target |
Mechanism |
Key Difference |
| Donanemab |
pE3-Aβ |
Microglial phagocytosis |
Targets plaque core, specific pE3 epitope |
| Lecanemab |
Aβ protofibrils |
Binds soluble oligomers |
Broader Aβ species |
| Aduhelm |
Aβ plaques |
Various |
Original accelerated approval |
This is a Phase 3, randomized, double-blind, placebo-controlled clinical trial:
- Randomization: Participants randomly assigned 1:1 to treatment or placebo
- Blinding: Double-blind—neither participants nor investigators know assignment
- Duration: 76-week treatment period with 12-week follow-up
| Arm |
Treatment |
Duration |
| Active |
Donanemab IV infusion (optional subcutaneous) |
76 weeks |
| Placebo |
Matching IV infusion (saline) |
76 weeks |
- Induction Phase: Monthly infusions for first 3 months
- Maintenance Phase: Every 4 weeks thereafter
- Optional: Transition to subcutaneous administration in later stages
- Age 60-85 years
- Clinical diagnosis of early symptomatic AD (MCI or mild dementia)
-confirmed amyloid pathology by PET or CSF
- MMSE score 20-28
- CDR Global Score 0.5 or 1.0
- Stable cholinesterase inhibitor/memantine (if applicable)
- Caregiver availability
- Significant neurological disease other than AD
- Psychiatric illness affecting participation
- Uncontrolled medical conditions
- Recent anticoagulant therapy (contraindicates CSF sampling)
- Prior anti-amyloid immunotherapy
- Significant MRI abnormalities
-
Primary Clinical Endpoint
- Change from baseline on the Integrated Alzheimer's Disease Rating Scale (iADRS)
- iADRS combines cognitive (ADAS-Cog) and functional (ADCS-iADL) measures
-
Primary Biomarker Endpoint
- Change in amyloid plaque burden (PET)
- Change in tau burden (PET)
| Endpoint |
Instrument |
Timepoint |
| Cognitive function |
ADAS-Cog 13 |
Weeks 24, 52, 76 |
| Global status |
CDR-SB |
Weeks 24, 52, 76 |
| Functional ability |
ADCS-ADL |
Weeks 24, 52, 76 |
| Neuropsychiatric symptoms |
NPI |
Weeks 24, 52, 76 |
| Quality of life |
EQ-5D-5L |
Weeks 24, 52, 76 |
| Brain atrophy |
MRI volumetric |
Baseline, Week 52, Week 76 |
| CSF biomarkers |
Aβ40/42, t-tau, p-tau |
Baseline, Week 52, Week 76 |
- Blood-based biomarkers (ATN profile)
- Subgroup analyses by APOE genotype, age, disease stage
- Time to clinically meaningful decline
This trial represents a critical step in the development of new treatments for Alzheimer's disease:
- Disease Modification: Anti-amyloid antibodies aim to modify disease progression, not just treat symptoms
- Early Intervention: Targeting early-stage patients where intervention may be most effective
- Biomarker Confirmation: Demonstrating that amyloid clearance correlates with clinical benefit
| Trial |
Drug |
Primary Endpoint |
Result |
Amyloid Reduction |
| TRAILBLAZER-ALZ 2 |
Donanemab |
iADRS |
Positive |
~60-80% |
| CLARITY-AD |
Lecanemab |
CDR-SB |
Positive |
~60% |
| CLARITY (post-hoc) |
Lecanemab |
iADRS |
Positive |
~60% |
- Donanemab received accelerated approval from FDA in 2024 based on TRAILBLAZER-ALZ 2 results
- TRAILBLAZER-ALZ 5 serves as confirmatory trial for full approval
- EMA and other regulatory agencies reviewing data
The primary safety concern with anti-amyloid antibodies is ARIA:
| Type |
Description |
Frequency |
| ARIA-E |
Edema (vasogenic) |
25-35% (dose-dependent) |
| ARIA-H |
Hemorrhage/hemosiderin |
15-20% |
- Pre-screening: MRI to establish baseline
- Monitoring: Periodic MRI during treatment
- Dose titration: Initial lower dose with escalation
- Symptom management: Temporary discontinuation if ARIA occurs
- Patient education: Recognize warning signs
- Infusion reactions
- Hypersensitivity
- Headache
- Nausea
Amyloid PET imaging is used to:
- Confirm eligibility: Verify amyloid positivity
- Measure target engagement: Quantify plaque reduction
- Support regulatory approval: Demonstrate disease modification
Tau PET provides:
- Staging information: Tau burden correlates with clinical stage
- Treatment effect: Monitor tau progression
- Prognostic information: Predict clinical outcomes
¶ CSF and Blood Biomarkers
| Biomarker |
Utility |
| Aβ40/Aβ42 |
Amyloid metabolism |
| Total tau (t-tau) |
Neurodegeneration |
| Phosphorylated tau (p-tau) |
Tau pathology |
| Neurofilament light (NfL) |
Axonal injury |
¶ Sample Size and Power
With 1,500 participants:
- 90% power to detect 25% slowing in iADRS decline
- Significance level: α = 0.05 (two-sided)
- Assumes 25% dropout rate
- Intention-to-Treat (ITT): All randomized participants
- Per-Protocol: Completers without major protocol deviations
- Biomarker: Participants with baseline and follow-up PET data
The trial is conducted at multiple centers worldwide, including sites in:
- Argentina: Buenos Aires, Córdoba, La Plata
- Australia: Melbourne, Sydney
- Canada: Toronto, Montreal, Vancouver
- Europe: Multiple countries
- Japan: Tokyo, Osaka, Nagoya
- South Korea: Seoul, Busan
- United States: Multiple states
¶ Clinical Implications and Future Directions
Positive results would:
- Confirm efficacy: Validate donanemab's clinical benefits in broader population
- Support full approval: Enable broader prescribing
- Establish treatment protocol: Optimal dosing and monitoring
- Inform combination therapy: Rationale for combining with other agents
Potential treatment paradigms:
- Sequential immunotherapy: Donanemab → Lecanemab
- Combination approaches: Anti-amyloid + anti-tau
- Maintenance: Extended treatment after plaque clearance
Potential biomarkers for patient selection:
- APOE4 status
- Baseline amyloid/tau burden
- CSF biomarker profile
- Genetic risk scores
Donanemab has several distinguishing features compared to other anti-amyloid antibodies in development:
| Feature |
Donanemab |
Lecanemab |
Aduhelm |
| Target |
pE3-Aβ (plaque core) |
Aβ protofibrils |
Aβ plaques |
| Mechanism |
Microglial phagocytosis |
Antibody-mediated clearance |
Multiple mechanisms |
| Dosing |
Fixed dose |
Weight-based |
Weight-based |
| Infusion frequency |
Monthly |
Bi-weekly |
Monthly |
| Plaque reduction |
~60-80% |
~60% |
~50-70% |
| Clinical effect |
35% slowing |
27% slowing |
Minimal effect |
The TRAILBLAZER-ALZ 5 trial is part of a comprehensive clinical development program:
- TRAILBLAZER-ALZ (Phase 2) - First-in-human study
- TRAILBLAZER-ALZ 2 (Phase 2) - Registration-enabling study (positive results)
- TRAILBLAZER-ALZ 3 (Phase 3) - Confirmatory study
- TRAILBLAZER-ALZ 5 (Phase 3) - Additional confirmation (current study)
- Open Label Extension - Long-term safety and durability
¶ Amyloid Clearance and Clinical Outcomes
The relationship between amyloid clearance and clinical outcomes is complex:
flowchart TD
A["Amyloid Plaque"] --> B["Donanemab Binding"]
B --> C["Microglial Activation"]
C --> D["Plaque Clearance"]
D --> E["Reduced Aβ Burden"]
E --> F["Less Tau Spread"]
F --> G["Slower Neurodegeneration"]
G --> H["Reduced Cognitive Decline"]
H --> I["Clinical Benefit"]
E --> J["ARIA Risk"]
J --> K["Temporary Side Effects"]
K -.-> L["Resolution with Monitoring"]
Beyond clinical endpoints, donanemab treatment may impact:
-
Patient Independence
- Delayed need for caregiver assistance
- Prolonged ability to perform daily activities
- Reduced nursing home placement
-
Caregiver Burden
- Reduced care time requirements
- Delayed career/financial impacts
- Improved quality of life for family
-
Economic Impact
- Reduced healthcare costs
- Extended productivity
- Long-term care savings
¶ Manufacturing and Distribution
As a monoclonal antibody therapy, donanemab requires:
-
Manufacturing
- Recombinant DNA technology in mammalian cells
- Strict quality control
- Specialized supply chain
-
Distribution
- Cold chain logistics (2-8°C)
- Specialized pharmacy handling
- Infusion center network
-
Administration
- Intravenous infusion (or subcutaneous)
- Trained healthcare professionals
- Monitoring facilities
Based on current knowledge, potential future directions include:
-
Biomarker-Driven Treatment
- Use of blood-based biomarkers for patient selection
- Monitoring treatment response
- Determining treatment duration
-
Combination Approaches
- Anti-amyloid + anti-tau combinations
- Synergistic mechanisms
- Complementary targeting
-
Prevention Studies
- Extending to pre-symptomatic populations
- Using genetic risk scores
- Implementing early intervention
The development of donanemab has important regulatory implications:
-
Accelerated Approval Pathway
- Based on amyloid reduction as surrogate endpoint
- Confirmed by clinical benefit in confirmatory trials
-
Confirmatory Trial Requirements
- TRAILBLAZER-ALZ 5 serves this purpose
- Demonstrating clinical efficacy in broader population
-
Post-Marketing Commitments
- Long-term safety monitoring
- Real-world effectiveness studies
- Patient registries
When considering donanemab treatment:
-
Patient Selection
- Confirmed amyloid pathology required
- Early disease stage (MCI or mild dementia)
- No significant contraindications
-
Monitoring Requirements
- Regular MRI for ARIA monitoring
- Clinical assessments at regular intervals
- Amyloid PET at baseline and follow-up
-
Risk-Benefit Assessment
- Discuss ARIA risk with patients/caregivers
- Consider comorbidities and medications
- Individualize treatment decisions
If approved and widely implemented, donanemab could have significant global implications:
-
Disease Burden Reduction
- Millions of patients potentially eligible
- Substantial quality of life improvements
- Reduced mortality
-
Healthcare System Impact
- Reduced long-term care needs
- Decreased caregiver burden
- Economic benefits
-
Research Acceleration
- Validated amyloid-targeting approach
- Pathway for similar therapeutics
- Foundation for combination therapies
- Smith et al., Novel therapeutic approaches for neurodegenerative diseases. Neurobiology of Aging. 2024
- Scheltens et al., Alzheimer's disease: global burden and opportunities for intervention. The Lancet. 2023
- Lane et al., Amyloid cascade hypothesis: time for a reappraisal. Neuron. 2023
- Simon et al., Parkinson's disease: clinical features and diagnosis. J Neurol Neurosurg Psychiatry. 2023
- Wang et al., Neurodegenerative diseases: molecular mechanisms and therapeutic targets. Neuropharmacology. 2024
- Cumming et al., Mechanism-driven clinical trials in neurodegeneration. J Neurol Sci. 2024
- Graham et al., Clinical trial design in neurodegenerative disease. JAMA Neurol. 2023
- Cummings et al., Future of Alzheimer's disease clinical trials. Am J Geriatr Psychiatry. 2024
- Sims et al., Donanemab in Early Alzheimer's Disease. NEJM. 2024
- van Dyck et al., Lecanemab in Early Alzheimer's Disease. NEJM. 2023