JAK2 inhibition increases the Treg:effector T-cell ratio in human allogeneic MLRs and does not impair IL-2 signaling. (A) Representative contour plots of Tregs (gating on CD3⁺CD4⁺CD25^bright and then assessing for absence of CD127 and presence of Foxp3)^24,25  and CD8⁺CD25⁺ effector T cells identified in allogeneic MLRs with DMSO (0.01%) or the JAK2 inhibitor TG101348 (1μM). Five day allogeneic MLRs used DC:T cell ratio of 1:30. Drug or control was added once on day 0. (B) Percent expression of CD25 among the Tregs identified in the DMSO (0.01%) or TG101348 (1μM)–treated allogeneic MLRs. Bar graphs show means ± SD from 5 independent experiments; **P = .001-.01; NS, not significant by paired t test. (C) Effect of JAK2 inhibition on the ratio of Tregs to CD8⁺CD25⁺ effector T cells in allogeneic MLRs compared with DMSO. Bar graphs show means ± SD from 5 independent experiments; **P = .001-.01; NS, not significant by paired t test. (D-F) Representative contour plots and bar graphs depict STAT5 phosphorylation in Con A–stimulated T cells with or without rhuIL-2 (50IU/mL) treated with TG101348 (1μM) or DMSO (0.01%). The IL-2–induced STAT5 phosphorylation index was measured by dividing the percentage of pSTAT5 in the sample by the percentage of pSTAT5 in its respective baseline. Bar graphs show means ± SD from 3 independent experiments; *P < .05; NS, not significant by paired t test.