Fludarabine (NSC 118218) is a DNA synthesis inhibitor, which also inhibits phosphorylation of STAT1. Fludarabine, a pro-drug, is converted metabolically by dephosphorylation to the antimetabolite, F-ara-A. In Vitro: Fludarabine (5 μM; 48 hours) induces a decrease in p27kip1 expression^[4]. In Vivo: Fludarabine (0.8 mg/kg; i.p.; two cycles for 5 days every 2 weeks) in combination with Cyclophosphamide (400 mg/kg; i.p.; 2 weeks) decreases incidence of GVHD^[5].