STAT6 regulates proliferation but not survival of malignant lymphocyte in MF and SS patient samples. Peripheral blood SS CD4⁺ T cells were cultured for 5 days with/without AS1517499. (A) Representative images from the cell culture conditions indicated on day +5. (B) Cell proliferation by CSFE assay. The cellular division capacity was determined by flow cytometry. Gates are set in the dividing cell population. A representative experiment and the mean percentage of divided (CFSE^low) cells ± standard deviation (SD) from 5 SS patients are shown. (C) Cell metabolic activity was measured by MTT assay. Results are expressed as percent change of absorbance from untreated control cells, which is set at 100% and represents mean values of triplicate measurements from 11 independent samples. Data are shown as mean ± SD compared with untreated cells. (D) Annexin V and propidium iodide (PI) staining followed by flow cytometry after 48 hours of treatment. Annexin V-positive, PI-negative cells were considered apoptotic. Representative examples and mean percentage of apoptotic cells from 5 SS patients are shown. (E) Cell viability determined by Cellometer Auto 2000 Cell Viability Counter. (F) Representative examples of double-color immunofluorescence microscopy for Ki67/TOX from ex vivo skin explants (MF, n = 5; NS, n = 5) cultured for 5 days with/without STAT6 inhibition as indicated, ×1000. Statistics in panels B-E by Student t test.