The Alzheimers Association Global Biomarker Standardization Consortium (GBSC) Plasma Phospho-Tau Round Robin Study

BACKGROUND: Phosphorylated tau (p-tau) is a specific blood biomarker for Alzheimers disease (AD) pathology. Multiple p-tau biomarkers on several analytical platforms are poised for clinical use. The Alzheimers Association Global Biomarker Standardisation Consortium plasma phospho-tau Round Robin study engaged assay developers in a blinded case-control study on plasma p-tau, aiming to learn which assays provide the largest fold-changes in AD compared to non-AD, have the strongest relationship between plasma and cerebrospinal fluid (CSF), and show the most consistent relationships between methods (commutability) in measuring both patient samples and candidate reference materials (CRM). METHODS: Thirty-three different p-tau biomarker assays, built on eight different analytical platforms, were used to quantify paired plasma and CSF samples from 40 participants. AD biomarker status was categorised as AD pathology (n=25) and non-AD pathology (n=15) by CSF Aβ42/Aβ40 (US-FDA; CE-IVDR) and p-tau181 (CE-IVDR) methods. The commutability of four CRM, at three concentrations, was assessed across assays. FINDINGS: Plasma p-tau217 consistently demonstrated higher fold-changes between AD and non-AD pathology groups, compared to other p-tau epitopes. Fujirebio LUMIPULSE G, UGOT IPMS, and Lilly MSD p-tau217 assays provided the highest median fold-changes. In CSF, p-tau217 assays also performed best, and exhibited substantially larger fold-changes than their plasma counterparts, despite similar diagnostic performance. P-tau217 showed the strongest correlations between plasma assays (rho=0.81 to 0.97). Plasma p-tau levels were weakly-to-moderately correlated with CSF p-tau, and correlations were non-significant within the AD group alone. The evaluated CRM were not commutable across assays. INTERPRETATION: Plasma p-tau217 measures had larger fold-changes and discriminative accuracies for detecting AD pathology, and better agreement across platforms than other plasma p-tau variants. Plasma and CSF markers of p-tau, measured by immunoassays, are not substantially correlated, questioning the interchangeability of their continuous relationship. Further work is warranted to understand the pathophysiology underlying this dissociation, and to develop suitable reference materials facilitating cross-assay standardisation. FUNDING: Alzheimers Association (#ADSF-24-1284328-C) ### Competing Interest Statement All biomarker measurements were performed by the assay developers in-house without cost. ALZpath p-tau217 was performed at the University of Gothenburg (UGOT) and Lilly immunoassays were performed at the University of Lund. C2N Diagnostics declined to participate in the study. N.J.A. has given lectures in symposia sponsored by Eli-Lilly, Roche Diagnostics, and Quanterix. NJA has declined paid opportunities from ALZpath. A.K. has no conflicts of interest. W.S.B. has no conflicts of interest. L.G. has no conflicts of interest. U.A. has no conflicts of interest. B.A. has no conflicts of interest. M.D. is an employee of AbbVie and holds stock or stock options. S.B. is an employee of AbbVie and holds stock or stock options. J.V. is employee of ADx NeuroSciences. C.L. is an employee of ADx NeuroSciences. M.V.L. is an employee of ADx NeuroSciences. E.S. is an employee of ADx NeuroSciences. S.I. is an employee of Alamar Biosciences H.Y.J. is an employee of Alamar Biosciences X.Y. is an employee of Alamar Biosciences A.F-H. is an employee of Alamar Biosciences B.Z. is an employee of Alamar Biosciences Y.L. is an employee of Alamar Biosciences A.Jeromin is an employee of ALZpath, Inc., and has stock options. M.V. is an employee of Fujirebio Europe N.V. N.L.B. is an employee of Fujirebio Europe N.V H.K. is a former employee of Janssen R&D D.B. has no conflicts of interest. G.T-B. is an employee of Janssen R&D and has stock options. D.B. has no conflicts of interest. S.J. has no conflicts of interest. S-Y.Y is an employee of MagQu Co., Ltd.C.D. C.D. is employee of Meso Scale Diagnostics, LLC D.R. is an employee of Meso Scale Diagnostics, LLC G.S. is an employee of Meso Scale Diagnostics, LLC J.W. is an employee of Meso Scale Diagnostics, LLC K.M. is an employee of Quanterix M.K. is an employee of Quanterix A.Jethwa is a full-time employee of Roche Diagnostics GmbH, Penzberg, Germany. L.S. is a full-time employee of Roche Diagnostics GmbH, Penzberg, Germany. O.H. has acquired research support (for the institution) from AVID Radiopharmaceuticals, Biogen, C2N Diagnostics, Eli Lilly, Eisai, Fujirebio, GE Healthcare, and Roche. In the past 2 years, he has received consultancy/speaker fees from AC Immune, Alzpath, BioArctic, Biogen, Bristol Meyer Squibb, Cerveau, Eisai, Eli Lilly, Fujirebio, Merck, Novartis, Novo Nordisk, Roche, Sanofi and Siemens. R.R has no conflicts of interest. J.G. has no conflicts of interest. P.K. has no conflicts of interest. F.G-O. has no conflicts of interest. L.M-G. has no conflicts of interest. L.M.S. has served as a consultant or on advisory boards for Biogen, Roche Diagnostics, Fujirebio; receives grant support from NIA/ADNI with QC oversight responsibilities and in-kind support from Fujirebio and Roche Diagnostics automated immunoassay platforms and reagents. K.B. has served as a consultant, at advisory boards, or at data monitoring committees for Abcam, Axon, BioArctic, Biogen, JOMDD/Shimadzu, Julius Clinical, Lilly, MagQu, Novartis, Ono Pharma, Pharmatrophix, Prothena, Roche Diagnostics, and Siemens Healthineers, and is a cofounder of Brain Biomarker Solutions in Gothenburg AB (BBS), which is a part of the GU Ventures Incubator Program, outside the work presented in this paper. J.M.S. has received research funding from Avid Radiopharmaceuticals (a wholly owned subsidiary of Eli Lilly); consulted for Roche Pharmaceuticals, Biogen, Merck, and Eli Lilly; given educational lectures sponsored by GE Healthcare, Eli Lilly, and Biogen; and is Chief Medical Officer for ARUK. H.Z. has served at scientific advisory boards and/or as a consultant for Abbvie, Acumen, Alector, Alzinova, ALZPath, Amylyx, Annexon, Apellis, Artery Therapeutics, AZTherapies, Cognito Therapeutics, CogRx, Denali, Eisai, Merry Life, Nervgen, Novo Nordisk, Optoceutics, Passage Bio, Pinteon Therapeutics, Prothena, Red Abbey Labs, reMYND, Roche, Samumed, Siemens Healthineers, Triplet Therapeutics, and Wave, has given lectures in symposia sponsored by Alzecure, Biogen, Cellectricon, Fujirebio, Lilly, and Roche, and is a co-founder of Brain Biomarker Solutions in Gothenburg AB (BBS), which is a part of the GU Ventures Incubator Program (outside submitted work). ### Funding Statement Alzheimers Association (#ADSF-24-1284328-C) grant to Prof Henrik Zetterberg ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: National Research Ethics Service London Queen Square Committee gave ethical approval for the Wolfson CSF study 12/00344 in August 2013, from which the participant samples for this work originated. I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes Data available: Yes Data types: Deidentified participant data How to access data: Requests should be directed to the corresponding authors a.keshavan@ucl.ac.uk, h.zetterberg@clinchem.gu.se and j.schott@ucl.ac.uk. When available: With publication Supporting Documents Document types: None Who can access the data: Anonymized data will be shared by request from a qualified academic investigator. Types of analyses: Data will be shared for the sole purpose of replicating procedures and results. Mechanisms of data availability: Data will be available after approval of a proposal and with a signed data access agreement.