All patients will be prepared by the NST protocol (I.V.fludarabine 30mg/m2/day [on days -10 to -5] and oral busulfan 4mg/kg in 4 divided daily doses [on days -6 and -5] or I.V. Busulfex a dose of 3.2 mg\kg on days -6 and -5,with or without I.V. ATG according to randomization group [on days -4 to -1]). ATG dosing schedule: a cumulative dose of 7.5 mg/kg ATG will be given with the following program - 0.5 mg/kg day -4, 2.0 mg/kg day -3, 2.5 mg/kg day -2, 2.5 mg/kg day -1. Each day's infusion time will be 8 hours. The last dose on day -1 should be given within 24 hours pre the stem cell infusion.