In vivo Jak2 depletion in mice bearing Eμ-Crlf2/Jak2R683G leukemias using two different shRNAs resulted in significantly reduced peripheral WBC count, reduced leukemic burden in the spleen (Fig. 3D,E), and a marked survival benefit that correlated with knockdown efficiency of the Jak2 shRNAs (Fig. 3B,F). The gene discussed is CRLF2; the disease is leukemia.