Transient mobilization of lymphocytes in MCL patients treated with ibrutinib. The mean percentage change of ALC (over baseline) is graphed against treatment time. (A) Ibrutinib treatment was in 35-day cycles of 28 days on and 7 days off. Mean percentage ALC change and percentage of the sum of perpendicular diameters (SPD) change are plotted to treatment cycles (n = 9). (B) Ibrutinib treatment was continuous with no gap in treatment. Mean percentage ALC change compared with baseline (plotted as mean + standard error [SE]; n = 17) is plotted against treatment time. Time points plotted are D0 (day zero), D1, D8, D15, D22, and end of cycles 1, 2, 3, 4, and 5. (C) The absolute count (ABS) and percentage of CD19⁺CD5⁺ vs CD19⁺CD5^– cells following 1 week of ibrutinib treatment. Note the statistically significant change in the absolute count of CD19⁺CD5⁺ cells of MCL patients following treatment. *P < .05 (paired t test; n = 16). (D) Flow plot of gated lymphocytes of PBMC samples from a representative MCL patient before and after ibrutinib treatment (560 mg per day) for 7 days. PBMCs were stained with CD3, CD19, and CD5. Note increase of CD19⁺CD3^– and CD19⁺CD5⁺ population after 7 days of drug treatment. (E) Fluorescent probe occupancy assay of BTK in PBMCs isolated from a representative MCL patient before treatment (predose), and after 4 hours, 24 hours after first dose, before treatment on the eighth day (Day 8, predose), and 4 hours after the eighth day dose (Day 8, 4HR). The arrows point to the 75 kDa BTK band on a scanned fluorescent gel (top) and a western blot (bottom). (F) An average of >90% occupancy of BTK by drug is achieved in MCL patients who were administered ibrutinib in the first week, determined by fluorescent probe assays (n = 6).