He explained that, by generating transgenic mice mimicking the PAX5‐ETV6 translocation that occurs in BCP‐ALL, the PAX5 fusion protein arrests lymphopoiesis at the pro‐B‐to‐pre‐B cell transition and did not interfere with the expression of most of the regulated PAX5 target genes. The gene discussed is PAX5; the disease is acute lymphoblastic leukemia.