CDKN2A and acute lymphoblastic leukemia: Under these conditions, healthy C57BL/6 mice receiving only 20 Arf-null, Bcr-Abl+ donor pro-B cells succumb to lethal ALL within 30 days of infusion, whereas mice receiving 2 × 105Arf+/+, Bcr-Abl+ donor pro-B cells develop no disease [4, 5].