JAK3 M511I cells are sensitive to the JAK3 inhibitor tofacitinib in vivo. (A) Four BALB/c mice that received a primary transplant of cells expressing JAK3 M511I were treated for 6 days with tofacitinib, 2 times per day with a total concentration of 30 mg/kg per day. WBC count was determined before, during, and after treatment. The graph shows WBC count over time, indicating days post-transplant. (B) Eleven BALB/C mice received a primary transplant of cells expressing JAK3 M511I. Mice were randomly divided into 2 groups. One group was treated with tofacitinib for 5 weeks, twice daily, with a total concentration of 40 mg/kg per day. The other group received vehicle (DMSO) treatment. WBC count was determined at the start and end of treatment. The graph shows differences in WBC counts over the 5 weeks of treatment. (C) Ten BALB/c mice received a secondary transplant of cells expressing JAK3 M511I. Afterward, mice were randomly divided into 2 groups. Both groups were treated for 14 days, one group with tofacitinib and the second group with vehicle (DMSO). Treatment was performed 2 times per day with a total concentration of 20 mg/kg per day. WBC count was determined at the start and the end of the experiment. The graph shows the difference in WBC count over the 14 days of treatment. (D) Graphs show the spleen, thymus, and lymph node weights of secondary transplanted mice with JAK3 M511I after 18 days of treatment with tofacitinib or vehicle. Significance was determined by Student t test. (E) Cleaved caspase-3 staining of the spleen and thymus samples retrieved from the experiment shown in (C). H&E staining of the thymus after treatment with placebo or tofacitinib. The scale bars represent 100 μm. Pathology images were obtained using a Leica DM2500 microscope and a Leica DFC290HD camera and analyzed using the Leica Application suite LAS v4.1 software. Images were processed with Adobe Photoshop CS5.