Validation of ELISA Methods for Quantification of Total Tau and Phosphorylated-Tau181 in Human Cerebrospinal Fluid with Measurement in Specimens from Two Alzheimer's Disease Studies
Affiliations: [a] Eli Lilly and Company, Windlesham, UK | [b] PPD, Richmond, VA, USA | [c] Lilly Research Laboratories, Indianapolis, IN, USA | [d] Innogenetics NV, Gent, Belgium
Correspondence:
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Correspondence to: Dr. DR Lachno, Eli Lilly and Company, Erl Wood Manor, Sunninghill Road, Windlesham, Surrey, GU20 6PH, UK. Tel.: +44 1276 483508; Fax: +44 1276 483416; Email: drlachno@lilly.com.
Note: [1] Present address: American International Biotechnology Services, Richmond, VA, USA.
Abstract: Tau measurements in cerebrospinal fluid (CSF) are gaining acceptance as aids to diagnosis of Alzheimer's disease (AD) and differentiation from other dementias. Two ELISA assays, the INNOTEST® hTAU Ag and the INNOTEST® PHOSPHO-TAU(181P) for quantification of t-tau and p-tau181 respectively, have been validated to regulatory standards. Validation parameters were determined by repeated testing of human CSF pools. Specimens from Phase 2 studies of the γ-secretase inhibitor semagacestat and the therapeutic antibody solanezumab at baseline and following 12–14 weeks of treatment were also tested. Estimated intra-assay CV for repeated testing of 3 CSF pools were ≤11.5% and RE varied between −14.1% and +6.4%. Inter-assay CV for t-tau was <5% and RE was within ±8%. For p-tau181, inter-assay CV was <9% and RE was within ±2.5%. Total CV (intra-assay plus inter-assay) were below 10% for both analytes. Up to 20-fold dilutional linearity was demonstrated for both analytes. Stability of t-tau and p-tau181 was demonstrated in CSF during five freeze-thaw cycles at ≤−20°C and ≤−70°C and at 18–22°C for up to 24 h. Neither semagacestat nor solanezumab interfered with either assay. Inter-individual t-tau and p-tau181 concentrations were highly variable but intra-individual variations were small. These assays are suitable for analysis of CSF t-tau and p-tau181 in a single laboratory supporting multi-center AD clinical trials. No effect of treatment with semagacestat or solanezumab was observed in response to three months of drug administration.
