1．Diagnosis of AA confirmed by bone marrow aspirate and biopsy, myelodysplastic syndrome and paroxysmal nocturnal hemoglobinuria were excluded. To confirm severe AA, the patient must fulfill at least two of the criteria: i) ANC<0.5×109/L,ii)PLT<20×109/L and iii) Ret<20×109/L ,in addition, ANC<0.5×109/L must be included.