JAK2 and acute lymphoblastic leukemia: Moreover, the p‐STAT5 levels in Pax5Jak2/+ B‐ALL cells were reduced at 30 min and lost at 1 h after ruxolitinib treatment (Appendix Fig S7D), while they were reduced at 2 h and lost at 4 h after IL‐7 withdrawal (Appendix Fig S7E), suggesting that STAT5 phosphorylation in these tumor cells depends on both the Pax5‐Jak2 kinase and IL‐7 signaling.