Ruxolitinib reduces spleen size but lacks antileukemic activity in vivo. (A) cells per femur and wet spleen weight (data normalized to control). (B) Flow cytometry gating strategy for bone marrow analysis of human hematopoietic engraftment by gating on human hCD45⁺ cells, detecting exclusively myeloid hCD33⁺ cells, and excluding hCD3⁺ cells for each experimental condition. (C) Human AML engraftment in bone marrow, peripheral blood, and spleen (n = 4 different primary AML samples; 2-4 mice per group per sample. Data normalized to control). (D) Representative images of reticulum staining on femur sections. Arrowheads indicate reticular fibers. Scale bars, 50 µm. (E) Peripheral blood counts of ruxolitinib- or vehicle-treated leukemic NSG mice (data normalized to control). Data are shown as mean ± SEM. See also supplemental Figure 5. *P < .05; **P < .01 determined by Wilcoxon signed-rank test.