Sezary syndrome (SS) is an aggressive leukemic form of cutaneous T-cell lymphoma with neoplastic CD4(+) T cells present in skin, lymph nodes, and blood. Despite advances in therapy, prognosis... Show moreSezary syndrome (SS) is an aggressive leukemic form of cutaneous T-cell lymphoma with neoplastic CD4(+) T cells present in skin, lymph nodes, and blood. Despite advances in therapy, prognosis remains poor, with a 5-year overall survival of 30%. The immunophenotype of Sezary cells is diverse, which hampers efficient diagnosis, sensitive disease monitoring, and accurate assessment of treatment response. Comprehensive immunophenotypic profiling of Sezary cells with an in-depth analysis of maturation and functional subsets has not been performed thus far. We immunophenotypically profiled 24 patients with SS using standardized and sensitive EuroFlow-based multiparameter flow cytometry. We accurately identified and quantified Sezary cells in blood and performed an in-depth assessment of their phenotypic characteristics in comparison with their normal counterparts in the blood CD4(+) T-cell compartment. We observed inter- and intrapatient heterogeneity and phenotypic changes over time. Sezary cells exhibited phenotypes corresponding with classical and nonclassical T helper subsets with different maturation phenotypes. We combined multiparameter flow cytometry analyses with fluorescence-activated cell sorting and performed RNA sequencing studies on purified subsets of malignant Sezary cells and normal CD4(+) T cells of the same patients. We confirmed pure monoclonality in Sezary subsets, compared transcriptomes of phenotypically distinct Sezary subsets, and identified novel downregulated genes, most remarkably THEMIS and LAIR1 , which discriminate Sezary cells from normal residual CD4(+) T cells. Together, these findings further unravel the heterogeneity of Sezary cell subpopulations within and between patients. These new data will support improved blood staging and more accurate disease monitoring. Show less
