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Cleveland MH, He HJ, Milavec M, Bae YK, Vallone PM, Huggett JF. Digital PCR for the characterization of reference materials. Mol Aspects Med 2024; 96:101256. [PMID: 38359699 DOI: 10.1016/j.mam.2024.101256] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2023] [Revised: 01/31/2024] [Accepted: 02/07/2024] [Indexed: 02/17/2024]
Abstract
Well-characterized reference materials support harmonization and accuracy when conducting nucleic acid-based tests (such as qPCR); digital PCR (dPCR) can measure the absolute concentration of a specific nucleic acid sequence in a background of non-target sequences, making it ideal for the characterization of nucleic acid-based reference materials. National Metrology Institutes are increasingly using dPCR to characterize and certify their reference materials, as it offers several advantages over indirect methods, such as UV-spectroscopy. While dPCR is gaining widespread adoption, it requires optimization and has certain limitations and considerations that users should be aware of when characterizing reference materials. This review highlights the technical considerations of dPCR, as well as its role when developing and characterizing nucleic acid-based reference materials.
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Affiliation(s)
- Megan H Cleveland
- Material Measurement Laboratory, National Institute of Standards and Technology, 100 Bureau Drive, Gaithersburg, MD, 20899, USA.
| | - Hua-Jun He
- Material Measurement Laboratory, National Institute of Standards and Technology, 100 Bureau Drive, Gaithersburg, MD, 20899, USA
| | - Mojca Milavec
- Department of Biotechnology and Systems Biology, National Institute of Biology, Večna Pot 111, 1000, Ljubljana, Slovenia
| | - Young-Kyung Bae
- Korea Research Institute of Standards and Science (KRISS), Daejeon, Republic of Korea
| | - Peter M Vallone
- Material Measurement Laboratory, National Institute of Standards and Technology, 100 Bureau Drive, Gaithersburg, MD, 20899, USA
| | - Jim F Huggett
- National Measurement Laboratory (NML), LGC, Queens Road, Teddington, TW11 0LY, Middlesex, UK; School of Biosciences & Medicine, Faculty of Health & Medical Science, University of Surrey, Guildford, UK
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He Z, Kwee EJ, Cleveland MH, Cole KD, Lin-Gibson S, He HJ. Quantitation and integrity evaluation of RNA genome in lentiviral vectors by direct reverse transcription-droplet digital PCR (direct RT-ddPCR). Sci Rep 2023; 13:14470. [PMID: 37660227 PMCID: PMC10475045 DOI: 10.1038/s41598-023-41644-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2023] [Accepted: 08/29/2023] [Indexed: 09/04/2023] Open
Abstract
Lentiviral vectors (LV) have proven to be powerful tools for stable gene delivery in both dividing and non-dividing cells. Approval of these LVs for use in clinical applications has been achieved by improvements in LV design. Critically important characteristics concerning quality control are LV titer quantification and the detection of impurities. However, increasing evidence concerning high variability in titration assays indicates poor harmonization of the methods undertaken to date. In this study, we developed a direct reverse transcription droplet digital PCR (Direct RT-ddPCR) approach without RNA extraction and purification for estimation of LV titer and RNA genome integrity. The RNA genome integrity was assessed by RT-ddPCR assays targeted to four distant regions of the LV genome. Results of the analyses showed that direct RT-ddPCR without RNA extraction and purification performs similarly to RT-ddPCR on purified RNA from 3 different LV samples, in terms of robustness and assay variance. Interestingly, these RNA titer results were comparable to physical titers by p24 antigen ELISA (enzyme-linked immunosorbent assay). Moreover, we confirmed the partial degradation or the incomplete RNA genomes in the prepared 3 LV samples. These results may partially explain the discrepancy of the LV particle titers to functional titers. This work not only demonstrates the feasibility of direct RT-ddPCR in determining LV titers, but also provides a method that can be easily adapted for RNA integrity assessment.
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Affiliation(s)
- Zhiyong He
- Material Measurement Laboratory, National Institute of Standards and Technology, 100 Bureau Drive, MS 8312, Gaithersburg, MD, 20899, USA.
| | - Edward J Kwee
- Material Measurement Laboratory, National Institute of Standards and Technology, 100 Bureau Drive, MS 8312, Gaithersburg, MD, 20899, USA
| | - Megan H Cleveland
- Material Measurement Laboratory, National Institute of Standards and Technology, 100 Bureau Drive, MS 8312, Gaithersburg, MD, 20899, USA
| | - Kenneth D Cole
- Material Measurement Laboratory, National Institute of Standards and Technology, 100 Bureau Drive, MS 8312, Gaithersburg, MD, 20899, USA
| | - Sheng Lin-Gibson
- Material Measurement Laboratory, National Institute of Standards and Technology, 100 Bureau Drive, MS 8312, Gaithersburg, MD, 20899, USA
| | - Hua-Jun He
- Material Measurement Laboratory, National Institute of Standards and Technology, 100 Bureau Drive, MS 8312, Gaithersburg, MD, 20899, USA.
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Vierbaum L, Wojtalewicz N, Grunert HP, Zimmermann A, Scholz A, Goseberg S, Kaiser P, Duehring U, Drosten C, Corman V, Niemeyer D, Rabenau HF, Obermeier M, Nitsche A, Michel J, Puyskens A, Huggett JF, O'Sullivan DM, Busby E, Cowen S, Vallone PM, Cleveland MH, Falak S, Kummrow A, Schellenberg I, Zeichhardt H, Kammel M. Results of German external quality assessment schemes for SARS-CoV-2 antigen detection. Sci Rep 2023; 13:13206. [PMID: 37580353 PMCID: PMC10425338 DOI: 10.1038/s41598-023-40330-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2022] [Accepted: 08/08/2023] [Indexed: 08/16/2023] Open
Abstract
The COVID-19 pandemic illustrated the important role of diagnostic tests, including lateral flow tests (LFTs), in identifying patients and their contacts to slow the spread of infections. INSTAND performed external quality assessments (EQA) for SARS-CoV-2 antigen detection with lyophilized and chemically inactivated cell culture supernatant of SARS-CoV-2 infected Vero cells. A pre-study demonstrated the suitability of the material. Participants reported qualitative and/or quantitative antigen results using either LFTs or automated immunoassays for five EQA samples per survey. 711 data sets were reported for LFT detection in three surveys in 2021. This evaluation focused on the analytical sensitivity of different LFTs and automated immunoassays. The inter-laboratory results showed at least 94% correct results for non-variant of concern (VOC) SARS-CoV-2 antigen detection for viral loads of ≥ 4.75 × 106 copies/mL and SARS-CoV-2 negative samples. Up to 85% had success for a non-VOC viral load of ~ 1.60 × 106 copies/mL. A viral load of ~ 1.42 × 107 copies/mL of the Delta VOC was reported positive in > 96% of results. A high specificity was found with almost 100% negative SARS-CoV-2 antigen results for HCoV 229E and HCoV NL63 positive samples. Quantitative results correlated with increasing SARS-CoV-2 viral load but showed a broad scatter. This study shows promising SARS-CoV-2 antigen test performance of the participating laboratories, but further investigations with the now predominant Omicron VOC are needed.
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Affiliation(s)
- Laura Vierbaum
- INSTAND E.V., Society for Promoting Quality Assurance in Medical Laboratories, Ubierstr. 20, 40223, Düsseldorf, Germany.
| | - Nathalie Wojtalewicz
- INSTAND E.V., Society for Promoting Quality Assurance in Medical Laboratories, Ubierstr. 20, 40223, Düsseldorf, Germany
| | - Hans-Peter Grunert
- GBD Gesellschaft für Biotechnologische Diagnostik mbH, Berlin, Potsdamer Chaussee 80, 14129, Berlin, Germany
| | - Anika Zimmermann
- IQVD GmbH, Institut für Qualitätssicherung in der Virusdiagnostik, Berlin, Potsdamer Chaussee 80, 14129, Berlin, Germany
| | - Annemarie Scholz
- IQVD GmbH, Institut für Qualitätssicherung in der Virusdiagnostik, Berlin, Potsdamer Chaussee 80, 14129, Berlin, Germany
| | - Sabine Goseberg
- INSTAND E.V., Society for Promoting Quality Assurance in Medical Laboratories, Ubierstr. 20, 40223, Düsseldorf, Germany
| | - Patricia Kaiser
- INSTAND E.V., Society for Promoting Quality Assurance in Medical Laboratories, Ubierstr. 20, 40223, Düsseldorf, Germany
| | - Ulf Duehring
- GBD Gesellschaft für Biotechnologische Diagnostik mbH, Berlin, Potsdamer Chaussee 80, 14129, Berlin, Germany
| | - Christian Drosten
- Institute of Virology, Charité - University Medicine Berlin; National Consultant Laboratory for Coronaviruses; German Centre for Infection Research, Berlin, Berlin, Germany
| | - Victor Corman
- Institute of Virology, Charité - University Medicine Berlin; National Consultant Laboratory for Coronaviruses; German Centre for Infection Research, Berlin, Berlin, Germany
| | - Daniela Niemeyer
- Institute of Virology, Charité - University Medicine Berlin; National Consultant Laboratory for Coronaviruses; German Centre for Infection Research, Berlin, Berlin, Germany
| | - Holger F Rabenau
- Institute of Virology, Charité - University Medicine Berlin; National Consultant Laboratory for Coronaviruses; German Centre for Infection Research, Berlin, Berlin, Germany
| | - Martin Obermeier
- Institute for Medical Virology, University Hospital, Goethe University Frankfurt, Frankfurt, Hessen, Germany
| | | | - Janine Michel
- Robert Koch Institute, Highly Pathogenic Viruses, Centre for Biological Threats and Special Pathogens, WHO Reference Laboratory for SARS-CoV-2 and WHO Collaborating Centre for Emerging Infections and Biological Threats, Robert Koch Institute, Berlin, Germany
| | - Andreas Puyskens
- Robert Koch Institute, Highly Pathogenic Viruses, Centre for Biological Threats and Special Pathogens, WHO Reference Laboratory for SARS-CoV-2 and WHO Collaborating Centre for Emerging Infections and Biological Threats, Robert Koch Institute, Berlin, Germany
| | - Jim F Huggett
- National Measurement Laboratory, LGC, Teddington, Middlesex, UK
- School of Biosciences and Medicine, Faculty of Health and Medical Science, University of Surrey, Guildford, UK
| | | | - Eloise Busby
- National Measurement Laboratory, LGC, Teddington, Middlesex, UK
| | - Simon Cowen
- National Measurement Laboratory, LGC, Teddington, Middlesex, UK
| | - Peter M Vallone
- NIST, National Institute of Standards and Technology, Applied Genetics Group, Biomolecular Measurement Division, Materials Measurement Laboratory, Gaithersburg, MD, USA
| | - Megan H Cleveland
- NIST, National Institute of Standards and Technology, Applied Genetics Group, Biomolecular Measurement Division, Materials Measurement Laboratory, Gaithersburg, MD, USA
| | - Samreen Falak
- Physikalisch-Technische Bundesanstalt, Berlin, Germany
| | | | - Ingo Schellenberg
- INSTAND E.V., Society for Promoting Quality Assurance in Medical Laboratories, Ubierstr. 20, 40223, Düsseldorf, Germany
- Institute of Bioanalytical Sciences, Center of Life Sciences, Anhalt University of Applied Sciences, Bernburg, Saxony-Anhalt, Germany
| | - Heinz Zeichhardt
- INSTAND E.V., Society for Promoting Quality Assurance in Medical Laboratories, Ubierstr. 20, 40223, Düsseldorf, Germany
- IQVD GmbH, Institut für Qualitätssicherung in der Virusdiagnostik, Berlin, Potsdamer Chaussee 80, 14129, Berlin, Germany
- GBD Gesellschaft für Biotechnologische Diagnostik mbH, Berlin, Potsdamer Chaussee 80, 14129, Berlin, Germany
| | - Martin Kammel
- INSTAND E.V., Society for Promoting Quality Assurance in Medical Laboratories, Ubierstr. 20, 40223, Düsseldorf, Germany
- IQVD GmbH, Institut für Qualitätssicherung in der Virusdiagnostik, Berlin, Potsdamer Chaussee 80, 14129, Berlin, Germany
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Govind S, Fritzsche M, Jenkins A, Cleveland MH, Vallone PM, Almond N, Morris C, Berry N. Deep Sequencing and Molecular Characterisation of BK Virus and JC Virus WHO International Reference Materials for Clinical Diagnostic Use. Viruses 2023; 15:1289. [PMID: 37376589 DOI: 10.3390/v15061289] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2023] [Revised: 05/24/2023] [Accepted: 05/27/2023] [Indexed: 06/29/2023] Open
Abstract
BACKGROUND Reactivation of JC and BK polyomaviruses during immunosuppression can lead to adverse clinical outcomes. In renal transplant recipients, BKV-associated nephropathy can result in graft loss, while in patients with autoimmune disorders, prolonged immunomodulatory drug use can cause rare onset of progressive multifocal leukoencephalopathy due to JCV reactivation. In such patients, accurate BK and JC viral load determinations by molecular technologies are important for diagnosis and clinical management; however, comparability across centres requires effective standardisation of diagnostic molecular detection systems. In October 2015, the WHO Expert Committee for Biological Standardisation (ECBS) established the 1st WHO International Standards (ISs) for use as primary-order calibrants for BKV and JCV nucleic acid detection. Two multi-centre collaborative studies confirmed their utility in harmonising agreement across the wide range of BKV and JCV assays, respectively. Previous Illumina-based deep sequence analysis of these standards, however, identified deletions in different regions, including the large T-antigen coding region. Hence, further detailed characterization was warranted. METHODS Comprehensive sequence characterisation of each preparation using short- and long-read next-generation sequencing technologies was performed with additional corroborative independent digital PCR (dPCR) determinations. Potential error rates associated with long-read sequencing were minimised by applying rolling circle amplification (RCA) protocols for viral DNA (circular dsDNA), generating a full validation of sequence identity and composition and delineating the integrity of full-length BK and JC genomes. RESULTS The analysed genomes displayed subpopulations frequently characterised by complex gene re-arrangements, duplications and deletions. CONCLUSIONS Despite the recognition of such polymorphisms using high-resolution sequencing methodologies, the ability of these reference materials to act to enhance assay harmonisation did not appear significantly impacted, based on data generated by the 2015 WHO collaborative studies, but highlights cautionary aspects of IS generation and commutability for clinical molecular diagnostic application.
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Affiliation(s)
- Sheila Govind
- Division of Infectious Disease Diagnostics, National Institute for Biological Standards and Control (NIBSC), South Mimms EN6 3QG, UK
| | - Martin Fritzsche
- Division of Analytical and Biological Sciences, National Institute for Biological Standards and Control (NIBSC), Medicines and Healthcare Product Regulatory Agency (MHRA), South Mimms EN6 3QG, UK
| | - Adrian Jenkins
- Division of Infectious Disease Diagnostics, National Institute for Biological Standards and Control (NIBSC), South Mimms EN6 3QG, UK
| | - Megan H Cleveland
- Applied Genetics Group, National Institute of Standards and Technology, Gaithersburg, MD 20899, USA
| | - Peter M Vallone
- Applied Genetics Group, National Institute of Standards and Technology, Gaithersburg, MD 20899, USA
| | - Neil Almond
- Division of Infectious Disease Diagnostics, National Institute for Biological Standards and Control (NIBSC), South Mimms EN6 3QG, UK
| | - Clare Morris
- Division of Infectious Disease Diagnostics, National Institute for Biological Standards and Control (NIBSC), South Mimms EN6 3QG, UK
| | - Neil Berry
- Division of Infectious Disease Diagnostics, National Institute for Biological Standards and Control (NIBSC), South Mimms EN6 3QG, UK
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Cleveland MH, Romsos EL, Steffen CR, Olson ND, Servetas SL, Valiant WG, Vallone PM. Rapid production and free distribution of a synthetic RNA material to support SARS-CoV-2 molecular diagnostic testing. Biologicals 2023; 82:101680. [PMID: 37178559 PMCID: PMC10154543 DOI: 10.1016/j.biologicals.2023.101680] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2023] [Accepted: 04/24/2023] [Indexed: 05/15/2023] Open
Abstract
In response to the COVID-19 pandemic, the National Institute of Standards and Technology released a synthetic RNA material for SARS-CoV-2 in June 2020. The goal was to rapidly produce a material to support molecular diagnostic testing applications. This material, referred to as Research Grade Test Material 10169, was shipped free of charge to laboratories across the globe to provide a non-hazardous material for assay development and assay calibration. The material consisted of two unique regions of the SARS-CoV-2 genome approximately 4 kb nucleotides in length. The concentration of each synthetic fragment was measured using RT-dPCR methods and confirmed to be compatible with RT-qPCR methods. In this report, the preparation, stability, and limitations of this material are described.
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Affiliation(s)
- Megan H Cleveland
- National Institute of Standards and Technology, 100 Bureau Dr, Gaithersburg, MD, 20899, USA.
| | - Erica L Romsos
- National Institute of Standards and Technology, 100 Bureau Dr, Gaithersburg, MD, 20899, USA
| | - Carolyn R Steffen
- National Institute of Standards and Technology, 100 Bureau Dr, Gaithersburg, MD, 20899, USA
| | - Nathan D Olson
- National Institute of Standards and Technology, 100 Bureau Dr, Gaithersburg, MD, 20899, USA
| | - Stephanie L Servetas
- National Institute of Standards and Technology, 100 Bureau Dr, Gaithersburg, MD, 20899, USA
| | - William G Valiant
- National Institute of Standards and Technology, 100 Bureau Dr, Gaithersburg, MD, 20899, USA
| | - Peter M Vallone
- National Institute of Standards and Technology, 100 Bureau Dr, Gaithersburg, MD, 20899, USA
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Vierbaum L, Wojtalewicz N, Grunert HP, Lindig V, Duehring U, Drosten C, Corman V, Niemeyer D, Ciesek S, Rabenau HF, Berger A, Obermeier M, Nitsche A, Michel J, Mielke M, Huggett J, O’Sullivan D, Busby E, Cowen S, Vallone PM, Cleveland MH, Falak S, Kummrow A, Keller T, Schellenberg I, Zeichhardt H, Kammel M. RNA reference materials with defined viral RNA loads of SARS-CoV-2-A useful tool towards a better PCR assay harmonization. PLoS One 2022; 17:e0262656. [PMID: 35051208 PMCID: PMC8775330 DOI: 10.1371/journal.pone.0262656] [Citation(s) in RCA: 24] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2021] [Accepted: 01/03/2022] [Indexed: 12/19/2022] Open
Abstract
SARS-CoV-2, the cause of COVID-19, requires reliable diagnostic methods to track the circulation of this virus. Following the development of RT-qPCR methods to meet this diagnostic need in January 2020, it became clear from interlaboratory studies that the reported Ct values obtained for the different laboratories showed high variability. Despite this the Ct values were explored as a quantitative cut off to aid clinical decisions based on viral load. Consequently, there was a need to introduce standards to support estimation of SARS-CoV-2 viral load in diagnostic specimens. In a collaborative study, INSTAND established two reference materials (RMs) containing heat-inactivated SARS-CoV-2 with SARS-CoV-2 RNA loads of ~107 copies/mL (RM 1) and ~106 copies/mL (RM 2), respectively. Quantification was performed by RT-qPCR using synthetic SARS-CoV-2 RNA standards and digital PCR. Between November 2020 and February 2021, German laboratories were invited to use the two RMs to anchor their Ct values measured in routine diagnostic specimens, with the Ct values of the two RMs. A total of 305 laboratories in Germany were supplied with RM 1 and RM 2. The laboratories were requested to report their measured Ct values together with details on the PCR method they used to INSTAND. This resultant 1,109 data sets were differentiated by test system and targeted gene region. Our findings demonstrate that an indispensable prerequisite for linking Ct values to SARS-CoV-2 viral loads is that they are treated as being unique to an individual laboratory. For this reason, clinical guidance based on viral loads should not cite Ct values. The RMs described were a suitable tool to determine the specific laboratory Ct for a given viral load. Furthermore, as Ct values can also vary between runs when using the same instrument, such RMs could be used as run controls to ensure reproducibility of the quantitative measurements.
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Affiliation(s)
- Laura Vierbaum
- INSTAND e.V., Society for Promoting Quality Assurance in Medical Laboratories, Duesseldorf, North Rhine-Westphalia, Germany
| | - Nathalie Wojtalewicz
- INSTAND e.V., Society for Promoting Quality Assurance in Medical Laboratories, Duesseldorf, North Rhine-Westphalia, Germany
| | | | - Vanessa Lindig
- IQVD GmbH, Institut fuer Qualitaetssicherung in der Virusdiagnostik, Berlin, Germany
| | - Ulf Duehring
- GBD Gesellschaft fuer Biotechnologische Diagnostik mbH, Berlin, Germany
| | - Christian Drosten
- Institute of Virology, Charité - University Medicine Berlin; National Consultant Laboratory for Coronaviruses; German Centre for Infection Research, Berlin, Germany
| | - Victor Corman
- Institute of Virology, Charité - University Medicine Berlin; National Consultant Laboratory for Coronaviruses; German Centre for Infection Research, Berlin, Germany
| | - Daniela Niemeyer
- Institute of Virology, Charité - University Medicine Berlin; National Consultant Laboratory for Coronaviruses; German Centre for Infection Research, Berlin, Germany
| | - Sandra Ciesek
- Institute for Medical Virology, University Hospital, Goethe University Frankfurt, Frankfurt, Hesse, Germany
- German Centre for Infection Research, External partner site Frankfurt, Hesse, Germany
- Fraunhofer Institute for Molecular Biology and Applied Ecology, Branch Translational Medicine and Pharmacology, Frankfurt, Hesse, Germany
| | - Holger F. Rabenau
- Institute for Medical Virology, University Hospital, Goethe University Frankfurt, Frankfurt, Hesse, Germany
| | - Annemarie Berger
- Institute for Medical Virology, University Hospital, Goethe University Frankfurt, Frankfurt, Hesse, Germany
| | | | - Andreas Nitsche
- Robert Koch-Institute, Centre for Biological Threats and Special Pathogens, Berlin, Germany
| | - Janine Michel
- Robert Koch-Institute, Centre for Biological Threats and Special Pathogens, Berlin, Germany
| | - Martin Mielke
- Robert Koch-Institute, Department for Infectious Diseases, Berlin, Germany
| | - Jim Huggett
- National Measurement Laboratory, LGC, Teddington, Middlesex, United Kingdom
- Faculty of Health & Medical Science, School of Biosciences & Medicine, University of Surrey, Guildford, United Kingdom
| | - Denise O’Sullivan
- National Measurement Laboratory, LGC, Teddington, Middlesex, United Kingdom
| | - Eloise Busby
- National Measurement Laboratory, LGC, Teddington, Middlesex, United Kingdom
| | - Simon Cowen
- National Measurement Laboratory, LGC, Teddington, Middlesex, United Kingdom
| | - Peter M. Vallone
- Materials Measurement Laboratory, Biomolecular Measurement Division, NIST, National Institute of Standards and Technology, Applied Genetics Group, Gaithersburg, Massachusetts, United States of America
| | - Megan H. Cleveland
- Materials Measurement Laboratory, Biomolecular Measurement Division, NIST, National Institute of Standards and Technology, Applied Genetics Group, Gaithersburg, Massachusetts, United States of America
| | - Samreen Falak
- Physikalisch-Technische Bundesanstalt, Berlin, Germany
| | | | | | - Ingo Schellenberg
- INSTAND e.V., Society for Promoting Quality Assurance in Medical Laboratories, Duesseldorf, North Rhine-Westphalia, Germany
- Institute of Bioanalytical Sciences, Center of Life Sciences, Anhalt University of Applied Sciences, Bernburg, Saxony-Anhalt, Germany
| | - Heinz Zeichhardt
- INSTAND e.V., Society for Promoting Quality Assurance in Medical Laboratories, Duesseldorf, North Rhine-Westphalia, Germany
- GBD Gesellschaft fuer Biotechnologische Diagnostik mbH, Berlin, Germany
- IQVD GmbH, Institut fuer Qualitaetssicherung in der Virusdiagnostik, Berlin, Germany
| | - Martin Kammel
- INSTAND e.V., Society for Promoting Quality Assurance in Medical Laboratories, Duesseldorf, North Rhine-Westphalia, Germany
- IQVD GmbH, Institut fuer Qualitaetssicherung in der Virusdiagnostik, Berlin, Germany
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7
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Milavec M, Cleveland MH, Bae YK, Wielgosz RI, Vonsky M, Huggett JF. Metrological framework to support accurate, reliable, and reproducible nucleic acid measurements. Anal Bioanal Chem 2021; 414:791-806. [PMID: 34738220 PMCID: PMC8568362 DOI: 10.1007/s00216-021-03712-x] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2021] [Revised: 09/05/2021] [Accepted: 10/01/2021] [Indexed: 11/29/2022]
Abstract
Nucleic acid analysis is used in many areas of life sciences such as medicine, food safety, and environmental monitoring. Accurate, reliable measurements of nucleic acids are crucial for maximum impact, yet users are often unaware of the global metrological infrastructure that exists to support these measurements. In this work, we describe international efforts to improve nucleic acid analysis, with a focus on the Nucleic Acid Analysis Working Group (NAWG) of the Consultative Committee for Amount of Substance: Metrology in Chemistry and Biology (CCQM). The NAWG is an international group dedicated to improving the global comparability of nucleic acid measurements; its primary focus is to support the development and maintenance of measurement capabilities and the dissemination of measurement services from its members: the National Metrology Institutes (NMIs) and Designated Institutes (DIs). These NMIs and DIs provide DNA and RNA measurement services developed in response to the needs of their stakeholders. The NAWG members have conducted cutting edge work over the last 20 years, demonstrating the ability to support the reliability, comparability, and traceability of nucleic acid measurement results in a variety of sectors.
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Affiliation(s)
- Mojca Milavec
- Department of Biotechnology and Systems Biology, National Institute of Biology, Večna pot 111, 1000, Ljubljana, Slovenia.
| | - Megan H Cleveland
- National Institute of Standards and Technology, 100 Bureau Drive, Gaithersburg, MD, 20899, USA
| | - Young-Kyung Bae
- Korea Research Institute of Standards and Science (KRISS), Daejeon, Republic of Korea
| | - Robert I Wielgosz
- Bureau International Des Poids Et Mesures (BIPM), Pavillon de Breteuil, 92312, Sèvres Cedex, France
| | - Maxim Vonsky
- D.I. Mendeleev Institute for Metrology, Moskovsky pr., 19, Saint-Petersburg, 190005, Russian Federation
| | - Jim F Huggett
- National Measurement Laboratory (NML), LGC, Queens Road, Teddington, TW11 0LY, Middlesex, UK.,School of Biosciences & Medicine, Faculty of Health & Medical Science, University of Surrey, Guildford, UK
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8
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Williams PM, Forbes T, P. Lund S, Cole KD, He HJ, Karlovich C, Paweletz CP, Stetson D, Yee LM, Connors DE, Keating SM, Destenaves B, Cleveland MH, Lau CJ, Barrett JC, Kelloff GJ, McCormack RT. Validation of ctDNA Quality Control Materials Through a Precompetitive Collaboration of the Foundation for the National Institutes of Health. JCO Precis Oncol 2021; 5:PO.20.00528. [PMID: 34250423 PMCID: PMC8232894 DOI: 10.1200/po.20.00528] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2020] [Revised: 03/05/2021] [Accepted: 04/20/2021] [Indexed: 12/18/2022] Open
Abstract
We report the results from a Foundation for the National Institutes of Health Biomarkers Consortium project to address the absence of well-validated quality control materials (QCMs) for circulating tumor DNA (ctDNA) testing. This absence is considered a cause of variance and inconsistencies in translating ctDNA results into clinical actions. METHODS In this phase I study, QCMs with 14 clinically relevant mutations representing single nucleotide variants, insertions or deletions (indels), translocations, and copy number variants were sourced from three commercial manufacturers with variant allele frequencies (VAFs) of 5%, 2.5%, 1%, 0.1%, and 0%. Four laboratories tested samples in quadruplicate using two allele-specific droplet digital polymerase chain reaction and three (amplicon and hybrid capture) next-generation sequencing (NGS) panels. RESULTS The two droplet digital polymerase chain reaction assays reported VAF values very close to the manufacturers' claimed concentrations for all QCMs. NGS assays reported most single nucleotide variants and indels, but not translocations, close to the expected VAF values. Notably, two NGS assays reported lower VAF than expected for all translocations in all QCM mixtures, possibly related to technical challenges detecting these variants. The ability to call ERBB2 copy number amplifications varied across assays. All three QCMs provided valuable insight into assay precision. Each assay across all variant types demonstrated dropouts at 0.1%, suggesting that the QCM can serve for testing of an assay's limit of detection with confidence claims for specific variants. CONCLUSION These results support the utility of the QCM in testing ctDNA assay analytical performance. However, unique designs and manufacturing methods for the QCM, and variations in a laboratory's testing configuration, may require testing of multiple QCMs to find the best reagents for accurate result interpretation.
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Affiliation(s)
- P. Mickey Williams
- Molecular Characterization Laboratory, Frederick National Laboratory for Cancer Research, Leidos Biomedical Research Inc, Frederick, MD
| | - Thomas Forbes
- Molecular Characterization Laboratory, Frederick National Laboratory for Cancer Research, Leidos Biomedical Research Inc, Frederick, MD
| | - Steven P. Lund
- National Institute of Standards and Technology, Gaithersburg, MD
| | - Kenneth D. Cole
- National Institute of Standards and Technology, Gaithersburg, MD
| | - Hua-Jun He
- National Institute of Standards and Technology, Gaithersburg, MD
| | - Chris Karlovich
- Molecular Characterization Laboratory, Frederick National Laboratory for Cancer Research, Leidos Biomedical Research Inc, Frederick, MD
| | - Cloud P. Paweletz
- Medical Oncology, Dana-Farber Cancer Institute, Boston, MA
- Belfer Center for Applied Cancer Science, Dana-Farber Cancer Institute, Boston, MA
| | - Daniel Stetson
- Translational Medicine, Oncology R&D, AstraZeneca, Waltham, MA
| | - Laura M. Yee
- Division of Cancer Treatment and Diagnosis, National Cancer Institute, National Institutes of Health, Bethesda, MD
| | - Dana E. Connors
- Foundation for the National Institutes of Health, Bethesda, MD
| | | | | | | | - Christie J. Lau
- Medical Oncology, Dana-Farber Cancer Institute, Boston, MA
- Belfer Center for Applied Cancer Science, Dana-Farber Cancer Institute, Boston, MA
| | - J. Carl Barrett
- Translational Medicine, Oncology R&D, AstraZeneca, Waltham, MA
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9
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He HJ, Das B, Cleveland MH, Chen L, Camalier CE, Liu LC, Norman KL, Fellowes AP, McEvoy CR, Lund SP, Almeida J, Steffen CR, Karlovich C, Williams PM, Cole KD. Development and interlaboratory evaluation of a NIST Reference Material RM 8366 for EGFR and MET gene copy number measurements. Clin Chem Lab Med 2020; 57:1142-1152. [PMID: 31112502 PMCID: PMC6875440 DOI: 10.1515/cclm-2018-1306] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2018] [Accepted: 02/21/2019] [Indexed: 01/04/2023]
Abstract
Background The National Institute of Standards and Technology (NIST) Reference Material RM 8366 was developed to improve the quality of gene copy measurements of EGFR (epidermal growth factor receptor) and MET (proto-oncogene, receptor tyrosine kinase), important targets for cancer diagnostics and treatment. The reference material is composed of genomic DNA prepared from six human cancer cell lines with different levels of amplification of the target genes. Methods The reference values for the ratios of the EGFR and MET gene copy numbers to the copy numbers of reference genes were measured using digital PCR. The digital PCR measurements were confirmed by two additional laboratories. The samples were also characterized using Next Generation Sequencing (NGS) methods including whole genome sequencing (WGS) at three levels of coverage (approximately 1 ×, 5 × and greater than 30 ×), whole exome sequencing (WES), and two different pan-cancer gene panels. The WES data were analyzed using three different bioinformatic algorithms. Results The certified values (digital PCR) for EGFR and MET were in good agreement (within 20%) with the values obtained from the different NGS methods and algorithms for five of the six components; one component had lower NGS values. Conclusions This study shows that NIST RM 8366 is a valuable reference material to evaluate the performance of assays that assess EGFR and MET gene copy number measurements.
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Affiliation(s)
- Hua-Jun He
- Biosystems and Biomaterials Division, National Institute of Standards and Technology, 100 Bureau Drive, MS 8312, Gaithersburg, MD 20899, USA, Phone: +301-975-2169, Fax: +301-330-3447
| | - Biswajit Das
- Molecular Characterization and Clinical Assay Development Laboratory, Frederick National Laboratory for Cancer Research, Frederick, MD, USA
| | - Megan H Cleveland
- Biomolecular Measurement Division, National Institute of Standards and Technology, Gaithersburg, MD, USA
| | - Li Chen
- Molecular Characterization and Clinical Assay Development Laboratory, Frederick National Laboratory for Cancer Research, Frederick, MD, USA
| | - Corinne E Camalier
- Molecular Characterization and Clinical Assay Development Laboratory, Frederick National Laboratory for Cancer Research, Frederick, MD, USA
| | | | | | | | | | - Steve P Lund
- Statistical Engineering Division, National Institute of Standards and Technology, Gaithersburg, MD, USA
| | - Jamie Almeida
- Biosystems and Biomaterials Division, National Institute of Standards and Technology, Gaithersburg, MD, USA
| | - Carolyn R Steffen
- Biomolecular Measurement Division, National Institute of Standards and Technology, Gaithersburg, MD, USA
| | - Chris Karlovich
- Molecular Characterization and Clinical Assay Development Laboratory, Frederick National Laboratory for Cancer Research, Frederick, MD, USA
| | - P Mickey Williams
- Molecular Characterization and Clinical Assay Development Laboratory, Frederick National Laboratory for Cancer Research, Frederick, MD, USA
| | - Kenneth D Cole
- Biosystems and Biomaterials Division, National Institute of Standards and Technology, 100 Bureau Drive, MS 8312, Gaithersburg, MD 20899, USA, Phone: +301-975-2169, Fax: +301-330-3447
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10
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Cleveland MH, Anekella B, Brewer M, Chin PJ, Couch H, Delwart E, Huggett J, Jackson S, Martin J, Monpoeho S, Morrison T, Ng SHS, Ussery D, Khan AS. Report of the 2019 NIST-FDA workshop on standards for next generation sequencing detection of viral adventitious agents in biologics and biomanufacturing. Biologicals 2020; 64:76-82. [PMID: 32094072 PMCID: PMC9987593 DOI: 10.1016/j.biologicals.2020.02.003] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2020] [Accepted: 02/13/2020] [Indexed: 02/06/2023] Open
Abstract
Adventitious virus testing assures product safety by demonstrating the absence of viruses that could be unintentionally introduced during the manufacturing process. The capabilities of next-generation sequencing (NGS) for broad virus detection in biologics have been demonstrated by the detection of known and novel viruses that were previously missed using the recommended routine assays for adventitious agent testing. A meeting was co-organized by the National Institute of Standards and Technology and the U.S. Food and Drug Administration on September 18-19, 2019 in Gaithersburg, Maryland, USA, to facilitate standardization of NGS technologies for applications of adventitious virus testing in biologics. The goal was to assess the currently used standards for virus detection by NGS and their public availability, and to identify additional needs for different types of reference materials and standards (natural and synthetic). The meeting focused on the NGS processes from sample preparation through sequencing but did not thoroughly cover bioinformatics, since this was considered to be the topic of a separate meeting.
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Affiliation(s)
- Megan H Cleveland
- National Institute of Standards and Technology, 100 Bureau Dr, Gaithersburg, MD, 20899, USA
| | - Bharathi Anekella
- LGC-Clinical Diagnostic Business Unit, 910 Clopper Road, Gaithersburg, MD, 20878, USA
| | - Michael Brewer
- Thermo Fisher Scientific, 35 Wiggins Ave, Bedford, MA, 01730, USA
| | - Pei-Ju Chin
- Center for Biologics Research and Evaluation, U.S. Food and Drug Administration, 10903 New Hampshire Ave, Silver Spring, MD, 20993, USA
| | - Heather Couch
- American Type Culture Collection, 10801 University Boulevard, Manassas, VA, 20110, USA
| | - Eric Delwart
- Vitalant Research Institute, 270 Masonic Ave, San Francisco, CA, 94118, USA
| | - Jim Huggett
- National Measurement Laboratory at LGC, Queens Road, Teddington, TW11 0LY, UK; School of Biosciences & Medicine, Faculty of Health & Medical Sciences, University of Surrey, Guildford, Surrey, GU2 7XH, UK
| | - Scott Jackson
- National Institute of Standards and Technology, 100 Bureau Dr, Gaithersburg, MD, 20899, USA
| | - Javier Martin
- National Institute for Biological Standards and Control, Blanche Ln, South Mimms, Potters Bar, EN6 3QG, UK
| | - Serge Monpoeho
- Regeneron Pharmaceuticals, 81 Columbia Turnpike, Rensselaer, NY, 12144, USA
| | - Tom Morrison
- AccuGenomics, 1410 Commonwealth Dr. Ste. 105, Wilmington, NC, 28403, USA
| | - Siemon H S Ng
- Analytical Sciences, Sanofi Pasteur, Analytical Research and Development, 1755, Steeles Avenue West, M2R 3T4, Toronto, Ontario, Canada
| | - David Ussery
- Department of Biomedical Informatics, University of Arkansas for Medical Sciences, Little Rock, AR, 72205, USA
| | - Arifa S Khan
- Center for Biologics Research and Evaluation, U.S. Food and Drug Administration, 10903 New Hampshire Ave, Silver Spring, MD, 20993, USA.
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Cleveland MH, Zook JM, Salit M, Vallone PM. Determining Performance Metrics for Targeted Next-Generation Sequencing Panels Using Reference Materials. J Mol Diagn 2018; 20:583-590. [PMID: 29959024 PMCID: PMC6172655 DOI: 10.1016/j.jmoldx.2018.04.005] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2018] [Revised: 03/28/2018] [Accepted: 04/26/2018] [Indexed: 11/20/2022] Open
Abstract
The National Institute of Standards and Technology has developed reference materials for five human genomes. DNA aliquots are available for purchase, and the data, analyses, and high-confidence small variant and homozygous reference calls are freely available on the web. These reference materials are useful for evaluating whole-genome sequencing methods and also can be used to benchmark targeted sequencing panels, which are used commonly in clinical settings. This article describes how to use the Genome in a Bottle samples to obtain performance metrics on any germline-targeted sequencing panel of interest, as well as the limitations of the reference materials. These materials are useful for understanding the limitations of, and optimizing, targeted sequencing panels and associated bioinformatics pipelines. Example figures are presented to illustrate ways to access the performance metrics of targeted sequencing panels, and a table of best practices is included.
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Affiliation(s)
- Megan H Cleveland
- Material Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, Maryland.
| | - Justin M Zook
- Material Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, Maryland
| | - Marc Salit
- Material Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, Maryland; Joint Initiative for Metrology in Biology, Stanford, California
| | - Peter M Vallone
- Material Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, Maryland
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Hendley AM, Provost E, Bailey JM, Wang YJ, Cleveland MH, Blake D, Bittman RW, Roeser JC, Maitra A, Reynolds AB, Leach SD. p120 Catenin is required for normal tubulogenesis but not epithelial integrity in developing mouse pancreas. Dev Biol 2014; 399:41-53. [PMID: 25523391 DOI: 10.1016/j.ydbio.2014.12.010] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2014] [Revised: 12/03/2014] [Accepted: 12/04/2014] [Indexed: 12/20/2022]
Abstract
The intracellular protein p120 catenin aids in maintenance of cell-cell adhesion by regulating E-cadherin stability in epithelial cells. In an effort to understand the biology of p120 catenin in pancreas development, we ablated p120 catenin in mouse pancreatic progenitor cells, which resulted in deletion of p120 catenin in all epithelial lineages of the developing mouse pancreas: islet, acinar, centroacinar, and ductal. Loss of p120 catenin resulted in formation of dilated epithelial tubules, expansion of ductal epithelia, loss of acinar cells, and the induction of pancreatic inflammation. Aberrant branching morphogenesis and tubulogenesis were also observed. Throughout development, the phenotype became more severe, ultimately resulting in an abnormal pancreas comprised primarily of duct-like epithelium expressing early progenitor markers. In pancreatic tissue lacking p120 catenin, overall epithelial architecture remained intact; however, actin cytoskeleton organization was disrupted, an observation associated with increased cytoplasmic PKCζ. Although we observed reduced expression of adherens junction proteins E-cadherin, β-catenin, and α-catenin, p120 catenin family members p0071, ARVCF, and δ-catenin remained present at cell membranes in homozygous p120(f/f) pancreases, potentially providing stability for maintenance of epithelial integrity during development. Adult mice homozygous for deletion of p120 catenin displayed dilated main pancreatic ducts, chronic pancreatitis, acinar to ductal metaplasia (ADM), and mucinous metaplasia that resembles PanIN1a. Taken together, our data demonstrate an essential role for p120 catenin in pancreas development.
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Affiliation(s)
- Audrey M Hendley
- Department of Surgery, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA; The McKusick-Nathans Institute of Genetic Medicine, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA; Division of Gastroenterology, Hepatology and Nutrition, Department of Internal Medicine, The University of Texas Health Science Center at Houston, Houston, TX 77030, USA.
| | - Elayne Provost
- Department of Surgery, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA; The McKusick-Nathans Institute of Genetic Medicine, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA.
| | - Jennifer M Bailey
- Department of Surgery, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA; The McKusick-Nathans Institute of Genetic Medicine, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA; Division of Gastroenterology, Hepatology and Nutrition, Department of Internal Medicine, The University of Texas Health Science Center at Houston, Houston, TX 77030, USA.
| | - Yue J Wang
- Department of Surgery, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA; The McKusick-Nathans Institute of Genetic Medicine, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA.
| | - Megan H Cleveland
- Department of Surgery, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA; The McKusick-Nathans Institute of Genetic Medicine, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA.
| | - Danielle Blake
- Department of Surgery, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA; The McKusick-Nathans Institute of Genetic Medicine, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA.
| | - Ross W Bittman
- Department of Surgery, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA; The McKusick-Nathans Institute of Genetic Medicine, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA.
| | - Jeffrey C Roeser
- Department of Surgery, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA; The McKusick-Nathans Institute of Genetic Medicine, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA.
| | - Anirban Maitra
- Department of Pathology, The Sol Goldman Pancreatic Cancer Research Center, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA; Departments of Pathology and Translational Molecular Pathology, The University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA.
| | - Albert B Reynolds
- Department of Cancer Biology, Vanderbilt University Medical Center, Nashville, TN 37232, USA.
| | - Steven D Leach
- Department of Surgery, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA; The McKusick-Nathans Institute of Genetic Medicine, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA.
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13
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Cleveland MH, Sawyer JM, Afelik S, Jensen J, Leach SD. Exocrine ontogenies: on the development of pancreatic acinar, ductal and centroacinar cells. Semin Cell Dev Biol 2012; 23:711-9. [PMID: 22743232 DOI: 10.1016/j.semcdb.2012.06.008] [Citation(s) in RCA: 53] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2012] [Accepted: 06/13/2012] [Indexed: 02/07/2023]
Abstract
This review summarizes our current understanding of exocrine pancreas development, including the formation of acinar, ductal and centroacinar cells. We discuss the transcription factors associated with various stages of exocrine differentiation, from multipotent progenitor cells to fully differentiated acinar and ductal cells. Within the branching epithelial tree of the embryonic pancreas, this involves the progressive restriction of multipotent pancreatic progenitor cells to either a central "trunk" domain giving rise to the islet and ductal lineages, or a peripheral "tip" domain giving rise to acinar cells. This review also discusses the soluble morphogens and other signaling pathways that influence these events. Finally, we examine centroacinar cells as an enigmatic pancreatic cell type whose lineage remains uncertain, and whose possible progenitor capacities continue to be explored.
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Affiliation(s)
- Megan H Cleveland
- McKusick-Nathans Institute of Genetic Medicine, Johns Hopkins University, Baltimore, MD 21205, United States
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