Cytometry Part B: Clinical Cytometry | 2021
Issue Highlights – March 2021
Abstract
This issue of the journal focuses on the flow cytometric detection of Sézary syndrome (SS) and mycosis fungoides (MF) in the peripheral blood (PB). As outlined in the editorial (Craig, 2021), flow cytometry has been used since the early 1980 s to immunophenotype SS and MF, and the characteristic CD7-negative, CD26-negative immunophenotype was readily adopted by dermatology groups. However, there is frustration among both clinicians and cytometrists. As outlined in the second article in this series on the clinicians perspective (Guitart, 2021), dermatologists and oncologists are frustrated by variability in flow cytometry practice and reports, which often lack mention of whether an abnormal population is present, if the phenotype is compatible with SS/MF, and the quantity of abnormal cells. There is also frustration among flow cytometry labs, who recognize the limitations of using individual evaluations for CD7 and CD26 and use a different multi-parameter immunophenotyping approach to evaluate for other hematologic malignancies. An international group of cytometrists convened to address these frustrations, and their work is outlined in three articles in this issue. The article by Pulitzer, Horna, & Almeida (2021), provides a detailed review of SS and MF, including definitions of the major categories of cutaneous T-cell lymphoma, and diagnosis of SS and MF in the skin and PB, and the role of immunophenotyping. The article by Horna and colleagues (2021) builds on this information to outline the characteristics necessary for an assay designed to evaluate PB for SS and MF using a multi-parameter immunophenotyping approach. This article includes consideration of the antigens to evaluate, a strategy for analysis, discussion about quantitation of abnormal populations, and mention of reporting, and is illustrated with supplemental examples. This article prompted a letter to the editor from Roelens et al. (2021) describing their favorable experience using evaluation of CD158k for the detection of SS and MF. However, in the reply (Almeida, Pulitzer, & Norna, 2021), the authors highlight that others have not reported the same success with this approach, and caution that the antibody recommended by Roelens is not available commercially as a flow-cytometry reagent. The next article in this issue (Illingworth, et al., 2021), describes how to develop an assay with the recommended characteristics, including instrument set-up, reagent selection and assessment of staining, validation of the optimized assay (including a detailed example validation template), and ongoing monitors of assay quality. This series of articles should help laboratories with every step of introducing an optimal assay for detection of SS and MF in the PB. The international guidelines also highlight areas where there are remaining gaps in our knowledge about the optimal approach to immunophenotyping for SS and MF, and invite further investigation. An example of such work is provided by the final article in this issue, by Lyapichev et al. (2021) who report a direct comparison of the multi-parameter immunophenotyping for aberrancies versus quantification of CD26− or CD7− CD4+ T-cells in SS/MF patients, and confirm that the former method (recommended by the international group) provides more accurate staging, particularly among patients with low stage disease (B0 and B1). Hopefully this issue of the journal will prompt further investigation, and decrease the widespread frustration experienced with the flow cytometric evaluation of PB for SS and MF.