Notably, the Pax5Jak2/+ B‐ALL cells still depend on IL‐7 signaling even in the presence of the constitutively active Pax5‐Jak2 protein, which may explain why the Pax5Jak2/+ tumors are preferentially located in the IL‐7‐rich environment of lymph nodes (Link et al, 2007). This evidence concerns the gene JAK2 and acute lymphoblastic leukemia.