title: High Specificity in Circulating Tumor Cell Identification Is Required for Accurate Evaluation of Programmed Death-Ligand 1.
abstract: BACKGROUND
  Expression of programmed-death ligand 1 (PD-L1) in non-small cell lung cancer (NSCLC) is typically evaluated through invasive biopsies; however, recent advances in the identification of circulating tumor cells (CTCs) may be a less invasive method to assay tumor cells for these purposes. These liquid biopsies rely on accurate identification of CTCs from the diverse populations in the blood, where some tumor cells share characteristics with normal blood cells. While many blood cells can be excluded by their high expression of CD45, neutrophils and other immature myeloid subsets have low to absent expression of CD45 and also express PD-L1. Furthermore, cytokeratin is typically used to identify CTCs, but neutrophils may stain non-specifically for intracellular antibodies, including cytokeratin, thus preventing accurate evaluation of PD-L1 expression on tumor cells. This holds even greater significance when evaluating PD-L1 in epithelial cell adhesion molecule (EpCAM) positive and EpCAM negative CTCs (as in epithelial-mesenchymal transition (EMT)).
  
  
  METHODS
  To evaluate the impact of CTC misidentification on PD-L1 evaluation, we utilized CD11b to identify myeloid cells. CTCs were isolated from patients with metastatic NSCLC using EpCAM, MUC1 or Vimentin capture antibodies and exclusion-based sample preparation (ESP) technology.
  
  
  RESULTS
  Large populations of CD11b+CD45lo cells were identified in buffy coats and stained non-specifically for intracellular antibodies including cytokeratin. The amount of CD11b+ cells misidentified as CTCs varied among patients; accounting for 33-100% of traditionally identified CTCs. Cells captured with vimentin had a higher frequency of CD11b+ cells at 41%, compared to 20% and 18% with MUC1 or EpCAM, respectively. Cells misidentified as CTCs ultimately skewed PD-L1 expression to varying degrees across patient samples.
  
  
  CONCLUSIONS
  Interfering myeloid populations can be differentiated from true CTCs with additional staining criteria, thus improving the specificity of CTC identification and the accuracy of biomarker evaluation.
authors.affiliation: Carbone Cancer Center, University of Wisconsin-Madison, Madison, Wisconsin, United States of America.
authors.forename: Jennifer L
authors.identifier: http://orcid.org/0000-0003-2123-997X
authors.initials: JL
authors.lastname: Schehr
authors.affiliation: Carbone Cancer Center, University of Wisconsin-Madison, Madison, Wisconsin, United States of America.
authors.forename: Zachery D
authors.initials: ZD
authors.lastname: Schultz
authors.affiliation: Department of Biomedical Engineering, University of Wisconsin-Madison, Madison, Wisconsin, United States of America.
authors.forename: Jay W
authors.initials: JW
authors.lastname: Warrick
authors.affiliation: Department of Biomedical Engineering, University of Wisconsin-Madison, Madison, Wisconsin, United States of America.
authors.forename: David J
authors.initials: DJ
authors.lastname: Guckenberger
authors.affiliation: Department of Biomedical Engineering, University of Wisconsin-Madison, Madison, Wisconsin, United States of America.
authors.forename: Hannah M
authors.initials: HM
authors.lastname: Pezzi
authors.affiliation: Carbone Cancer Center, University of Wisconsin-Madison, Madison, Wisconsin, United States of America.
authors.forename: Jamie M
authors.initials: JM
authors.lastname: Sperger
authors.affiliation: Carbone Cancer Center, University of Wisconsin-Madison, Madison, Wisconsin, United States of America.
authors.forename: Erika
authors.initials: E
authors.lastname: Heninger
authors.affiliation: Carbone Cancer Center, University of Wisconsin-Madison, Madison, Wisconsin, United States of America.|Department of Medicine, University of Wisconsin-Madison, Madison, Wisconsin, United States of America.
authors.forename: Anwaar
authors.initials: A
authors.lastname: Saeed
authors.affiliation: Carbone Cancer Center, University of Wisconsin-Madison, Madison, Wisconsin, United States of America.|Department of Medicine, University of Wisconsin-Madison, Madison, Wisconsin, United States of America.
authors.forename: Ticiana
authors.initials: T
authors.lastname: Leal
authors.affiliation: Carbone Cancer Center, University of Wisconsin-Madison, Madison, Wisconsin, United States of America.
authors.forename: Kara
authors.initials: K
authors.lastname: Mattox
authors.affiliation: Carbone Cancer Center, University of Wisconsin-Madison, Madison, Wisconsin, United States of America.|Department of Medicine, University of Wisconsin-Madison, Madison, Wisconsin, United States of America.
authors.forename: Anne M
authors.initials: AM
authors.lastname: Traynor
authors.affiliation: Carbone Cancer Center, University of Wisconsin-Madison, Madison, Wisconsin, United States of America.|Department of Medicine, University of Wisconsin-Madison, Madison, Wisconsin, United States of America.
authors.forename: Toby C
authors.initials: TC
authors.lastname: Campbell
authors.affiliation: Department of Biomedical Engineering, University of Wisconsin-Madison, Madison, Wisconsin, United States of America.
authors.forename: Scott M
authors.initials: SM
authors.lastname: Berry
authors.affiliation: Department of Biomedical Engineering, University of Wisconsin-Madison, Madison, Wisconsin, United States of America.
authors.forename: David J
authors.initials: DJ
authors.lastname: Beebe
authors.affiliation: Carbone Cancer Center, University of Wisconsin-Madison, Madison, Wisconsin, United States of America.|Department of Medicine, University of Wisconsin-Madison, Madison, Wisconsin, United States of America.
authors.forename: Joshua M
authors.initials: JM
authors.lastname: Lang
mesh_terms: D060890:B7-H1 Antigen / Q000378:metabolism*; D014408:Biomarkers, Tumor; D002289:Carcinoma, Non-Small-Cell Lung / Q000175:diagnosis* / Q000378:metabolism*; D006801:Humans; D016130:Immunophenotyping / Q000379:methods / Q000592:standards; D008175:Lung Neoplasms / Q000175:diagnosis* / Q000378:metabolism*; D009362:Neoplasm Metastasis; D009367:Neoplasm Staging; D009360:Neoplastic Cells, Circulating / Q000378:metabolism*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
chemical_list: D060890:B7-H1 Antigen; D014408:Biomarkers, Tumor