Specific suppression of SATB1 expression in Sézary cells. (A) SATB1 RNA expression levels are significantly down-regulated in CD4⁺CD7⁻ primary Sézary cells from 6 SS patients with TCR clonality [SS(T)] and 3 SS patients without TCR clonality [SS(A)], as well as cultured Sézary cell lines (Hut78 and HH), compared with similarly purified T lymphocytes from normal volunteers (NC), and 2 cultured non-Sézary leukemic cell lines (Jurkat and CCL119). **P = .004. (B) SATB1 protein expressions are absent from patient-derived Sézary cells (SS1 and SS2) and Sézary cell lines, whereas the normal cells (NC1 and NC2) and 2 non-Sézary leukemia cell lines show abundant expression of SATB1 protein. GAPDH serves as the internal reference. (C) Immunofluorescence staining of SATB1 on CD4⁺ T cells in vitro. Cells were stained with mouse SATB1 monoclonal antibody (1:100) and Alexa-594-conjugated anti–mouse secondary antibody (1:200). DAPI was used to counterstain cell nucleus. Non-Sézary cells (NC, Jurkat and CCL119) showed strong SATB1 staining on the nucleus, whereas patient-derived SS and Sézary cell line (Hut78 and HH) cells showed nearly no staining on the nucleus. Original magnification ×630. Scale bar represents 10 μm.