JAK inhibitor ruxolitinib upregulates CD38 expression and enhances DARA-mediated ADCC against MM cells. (A) RPMI 8226 cells were treated with solvent control or ruxolitinib (Ruxo; 1, 5 µM), in the absence or presence of BMSC-sup or IL-6 (1 ng/mL) for 48 hours. Whole-cell lysates were subjected to immunoblotting using indicated antibodies. (B-C) RPMI 8226 cells were treated with solvent control or ruxolitinib (1, 5 µM), in the absence or presence of BMSC-sup for 72 hours, and then subjected to flow cytometric analysis for CD38 expression (B) and DARA-mediated ADCC assay (C). (D) BMMCs of 5 MM patients were treated with solvent control, ruxolitinib (1, 5, 10 µM), ATRA (5, 25 nM), or panobinostat (Pano; 1, 5 nM) for 120 hours. After incubation, CD38 expression on 7-AAD⁻ and CD138⁺ MM cells was measured by flow cytometry. (E) CD138⁺ MM cells separated from BMMCs of 5 MM patients were treated with solvent control, ruxolitinib (1, 5, 10 µM), ATRA (5, 25 nM), or panobinostat (1, 5 nM) for 120 hours. After incubation, relative CD38 mRNA level was assessed by qRT-PCR. Relative CD38 MFI was calculated in comparison with MFI of control. Data are shown as mean plus or minus standard error of the mean. *P < .05; **P < .01; ***P < .001.