Abstract
Simple SummaryTRBC1 expression analysis by flow cytometry (FCM) has been recently proved to be a useful, simple and fast approach to assessing Tαβ-cell clonality. The aim of this study was to validate the utility of this assay specifically for the diagnosis of T-cell clonality of T-large granular lymphocytic leukemias (T-LGLL), as more mature polyclonal Tαβ large granular lymphocytes (Tαβ-LGL) show broader TRBC1+/TRBC1− ratios vs. total Tαβ cells. Our results showed that a TRBC1-FCM assay is also a fast and easy method for detecting T-cell clonality in T-LGLL based on altered (increased or decreased) percentages of TRBC1+ Tαβ cells of LGL expansions (i.e., with lymphocytosis) suspected of T-LGLL, whereas in the absence of lymphocytosis (or in TαβCD4-LGLL), the detection of increased absolute cell-counts of more precisely defined subpopulations of T-LGL expressing individual TCRVβ families is required.Flow cytometric (FCM) analysis of the constant region 1 of the T-cell receptor β chain (TRBC1) expression for assessing Tαβ-cell clonality has been recently validated. However, its utility for the diagnosis of clonality of T-large granular lymphocytic leukemia (T-LGLL) needs to be confirmed, since more mature Tαβ cells (i.e., T-LGL normal-counterpart) show broader TRBC1+/TRBC1− ratios vs. total Tαβ cells. We compared the distribution and absolute counts of TRBC1+ and TRBC1− Tαβ-LGL in blood containing polyclonal (n = 25) vs. clonal (n = 29) LGL. Overall, polyclonal TRBC1+ or TRBC1− Tαβ-LGL ranged between 0.36 and 571 cells/μL (3.2–91% TRBC1+ cells), whereas the clonal LGL cases showed between 51 and 11,678 cells/μL (<0.9% or >96% TRBC1+ cells). Among the distinct TCRVβ families, the CD28− effector-memory and terminal-effector polyclonal Tαβ cells ranged between 0 and 25 TRBC1+ or TRBC1− cells/μL and between 0 and 100% TRBC1+ cells, while clonal LGL ranged between 32 and 5515 TRBC1+ or TRBC1− cells/μL, representing <1.6% or >98% TRBC1+ cells. Our data support the utility of the TRBC1-FCM assay for detecting T-cell clonality in expansions of Tαβ-LGL suspected of T-LGLL based on altered percentages of TRBC1+ Tαβ cells. However, in the absence of lymphocytosis or in the case of TαβCD4-LGL expansion, the detection of increased absolute cell counts by the TRBC1-FCM assay for more accurately defined subpopulations of Tαβ-LGL-expressing individual TCRVβ families, allows the detection of T-cell clonality, even in the absence of phenotypic aberrations.
Highlights
T-cell large granular lymphocytic leukemia (T-LGLL) is a rare chronic lymphoproliferative disorder (CLPD) characterized by the clonal expansion of mature cytotoxic T cell—i.e., large granular T lymphocytes (T-LGL)—in blood and potentially in other tissues [1,2,3]
We investigated the TRBC1 expression profile of the aberrant/ pathological cells from T-LGLL (n = 20) and HDc (n = 3) with that of the polyclonal effector memory (EM)-EE-terminal effector (TE) T cells from HD (n = 11) and patients with reactive conditions (n = 8) in a total of 42 blood samples
It may be concluded that the absolute count of pathological T-LGL cells identified by the TRBC1 expression profile within the whole population of Tαβ cells cannot be used as a universal criterion for clear-cut detection of clonal Tαβ-LGL, in T-LGLL cases that present without lymphocytosis and/or that carry relatively small (
Summary
T-cell large granular lymphocytic leukemia (T-LGLL) is a rare chronic lymphoproliferative disorder (CLPD) characterized by the clonal expansion of mature cytotoxic T cell—i.e., large granular T lymphocytes (T-LGL)—in blood and potentially in other tissues [1,2,3]. A threshold of 2 × 109 T-LGL/L of blood was initially mandatory for the diagnosis of T-LGLL, but lower LGL counts of ≥0.5–2 × 109 cells/L are currently recognized as a diagnostic criterion for T-LGLL when associated with typical clinical manifestations of the disease (i.e., cytopenias or autoimmune disorders) [4,5,6,7]. This indicates that no single T-LGL count cut-off allows for clear-cut discrimination between neoplastic and reactive expansions of T-LGL. Considering all the above, the demonstration of the clonal nature of the expanded T-LGL in the diagnostic work-up of T-LGLL still remains a challenge, in cases presenting without lymphocytosis [8,11]
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