Development and analytical characterization of novel tau Simoa assays targeting full‐length tau in CSF and mid‐tau in CSF and plasma

Abstract

AbstractBackgroundBiofluid markers of neurodegeneration and neural injury have great potential to elucidate disease mechanisms and accelerate development of experimental therapeutics. Cerebrospinal fluid (CSF) tau and phosphorylated tau are established biomarkers for AD, while plasma (N‐terminal) tau and phosphorylated tau (p‐tau) are being evaluated as complementary markers in a more accessible biofluid.Tau is present in CSF and plasma in both full‐length and truncated forms, with great interest in characterizing and advancing these different forms as biomarkers to support clinical development. To contribute to the emerging research on tau fragments as biomarker, novel ultra‐sensitive immunoassays were developed targeting low‐abundant, non‐truncated full‐length (FL) tau in CSF and a mid‐region tau fragment in CSF and plasma.MethodSimoa assays were developed using monoclonal antibodies (mAbs) targeting mid‐region tau epitopes or epitopes on full‐length tau.Resulting assays were qualified and partially validated for analytical performance parameters: measuring range, specificity, repeatability, reproducibility and parallelism were assessed. Reagent and analyte stability were investigated by assessing hold time and freeze/thaw (F/T) stability. Paired clinical routine CSF and plasma samples were analysed (20 controls and 20 AD based upon CSF Aβ1‐42, t‐tau and p‐tau(T181) profile).ResultFL‐ and mid‐tau Simoa assays were analytically characterized, upscaled to bulk volumes and partially validated. Both assays had acceptable repeatability and reproducibility (%CV <20%) for plasma and/or CSF. Parallelism was within acceptance criteria (ACC of 75‐125%; %CV <20%) for FL‐tau in 4 CSF samples and for mid‐tau in 4 CSF and 4 plasma samples. Analyte stability was demonstrated up to 5 F/T cycles and for a hold‐time of 24h at 21°C with a %CV<20%. Testing of clinical samples showed an increased CSF FL‐ (p<0.005) and mid‐Tau (p<0.0001) concentration in AD versus controls, whereas plasma mid‐tau did not increase.ConclusionA novel CSF assay for full length tau and a novel CSF/plasma assay for the mid‐tau fragment was developed, qualified and partially validated. The generated data indicated well‐performing tau assays available as RUO kits in pre‐clinical and clinical use in drug development programs.