To test this hypothesis, we used in vitro cultured Pax5Jak2/+ and Pax5Prd*‐Jak2/+ B‐ALL cells, which lost the wild‐type Pax5 allele, for ChIP‐seq analysis with an antibody detecting the N‐terminal paired domain of Pax5. Here, JAK2 is linked to acute lymphoblastic leukemia.