CRLF2 and precursor B-cell acute lymphoblastic leukemia: Eμ-Crlf2-mediated overexpression of Crlf2 alone did not constitutively activate downstream pStat5Y694 (Supplemental Fig. S2B), and these mice did not develop B-ALL by 18 mo of age (data not shown), demonstrating that Crlf2 overexpression alone was insufficient to induce B-cell leukemia.