Primary Hypothesis: Blood-based biomarkers (p-tau217, p-tau181, NfL, GFAP) can serve as valid surrogates for tau PET in monitoring anti-tau therapeutic response, enabling more accessible and frequent monitoring in clinical trials and practice.
Secondary Hypotheses:
- Blood p-tau217 changes correlate with tau PET changes (r > 0.7) over 12-24 month treatment periods
- Blood biomarkers detect treatment effects earlier than tau PET due to higher sensitivity to change
- The relationship between blood biomarkers and tau PET differs by therapeutic mechanism (antibody vs ASO vs small molecule)
This experiment addresses the critical understanding gap identified in the CBS/PSP Cure Roadmap Phase 3:
- "Can blood biomarkers substitute for tau PET in monitoring treatment response?"
Also addresses the practical constraint that tau PET is:
- Expensive ($5,000-10,000/scan)
- Limited availability (fewer than 50 US centers)
- Involves radiation exposure
- Not suitable for frequent monitoring
- Type: Prospective longitudinal biomarker correlation study embedded within Phase 2 anti-tau clinical trials
- Cohort (pooled from multiple trials):
- Anti-tau antibody trial participants (E2814, BMS-986446, Posdinemab): n=200
- Tau ASO trial participants (BIIB080): n=100
- OGA inhibitor trial participants (FNP-223): n=80
- Total: n=380
| Timepoint |
Blood (p-tau217, NfL, GFAP) |
CSF (p-tau181, total tau, NfL) |
Tau PET |
| Baseline |
✓ |
✓ |
✓ |
| Month 1 |
✓ |
✓ |
|
| Month 3 |
✓ |
|
|
| Month 6 |
✓ |
✓ |
✓ |
| Month 9 |
✓ |
|
|
| Month 12 |
✓ |
✓ |
✓ |
| Month 18 |
✓ |
|
✓ |
| Month 24 |
✓ |
✓ |
✓ |
- Primary Endpoint: Correlation between blood p-tau217 % change and tau PET SUVr change at 12 months
- Secondary Endpoints:
- Correlation at other timepoints
- Correlation with clinical measures (PSP-RS, CDR, MMSE)
- Comparison across therapeutic mechanisms
- Lead/lag analysis (which biomarker changes first)
- Correlation analysis: Pearson and Spearman correlation between blood and PET biomarkers
- Mixed-effects models: Account for repeated measures within subjects
- Agreement analysis: Bland-Altman plots to assess agreement
- Sensitivity to change: Compare effect sizes (standardized mean differences) between biomarkers
- Lead/lag analysis: Cross-correlation functions to identify temporal relationships
- Subgroup analyses: By therapeutic mechanism, baseline disease severity, demographics
Using the FDA BIOMARKER qualification framework:
- Biological plausibility: Review evidence for causal relationship
- Association: Correlation between surrogate and true endpoint
- Predictive value: Ability to predict clinical outcome
- Modulation by therapy: Evidence that therapy affects surrogate
- Correlation coefficient: Blood p-tau217 vs tau PET at 12 months: r = 0.75 (95% CI: 0.65-0.82)
- Sensitivity to change: Blood p-tau217 shows 1.5x larger effect size than tau PET
- Minimum detectable effect: Blood biomarker can detect 20% treatment effect with n=100 per arm
- Lead time: Blood biomarkers show significant change 3-6 months before tau PET
- Mechanism-specific relationships: Different correlation patterns for antibody vs ASO vs OGAi
- Clinical prediction: Blood biomarker changes at 6 months predict clinical outcome at 24 months
- Optimal biomarker panel: Identify combination of biomarkers that best predicts PET
- Sampling frequency: Determine minimum sampling needed for adequate monitoring
- Cost-effectiveness: Model cost savings from blood-based vs PET-based monitoring
- Leverages existing clinical trial infrastructure (reduces costs)
- Multi-mechanism design enables mechanism-specific validation
- Industry partnerships provide access to trial data
- High clinical relevance for trial design
- Requires coordination across multiple pharma-sponsored trials
- Different trial designs may limit direct comparisons
- Blood biomarker assays lack standardization across labs
- Tau PET acquisition protocols vary across sites
| Milestone |
Expected Date |
| Protocol development (with pharma partners) |
Month 1-3 |
| Data sharing agreements |
Month 3-6 |
| First patient data (pooled) |
Month 6 |
| 50% enrollment |
Month 12 |
| Full enrollment |
Month 18 |
| 12-month primary analysis |
Month 24 |
| 24-month analysis |
Month 36 |
| FDA submission |
Month 42 |
| Category |
Cost (USD) |
| Personnel (1 FTE project manager, 1 biostatistician) |
$600,000 |
| Blood biomarker assays (p-tau217, NfL, GFAP) |
$400,000 |
| CSF biomarker assays |
$200,000 |
| Tau PET (central reads) |
$150,000 |
| Data management (harmonization across trials) |
$300,000 |
| Statistical analysis |
$200,000 |
| Regulatory consultation |
$150,000 |
| Indirect costs (20%) |
$400,000 |
| Total |
$2,400,000 |
Note: Major cost share provided by pharma partners (trial sponsors)
This experiment has implications for:
- AD (similar blood vs PET questions for amyloid)
- Clinical trial design (enabling more frequent monitoring)
- Clinical practice (accessibility for patients)
- Biomarker qualification (FDA/EMA regulatory pathways)