The investigators will conduct this prospective and randomized clinical trial, to evaluate the hematopoietic reconstitution, GVHD and relapse rate of patients after allo-HSCT with decitabine containing conditional regimen and NAC treatment.

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is the main curative treatment for hematological malignancy. Relapse, graft versus host disease (GVHD) and graft failure are the main causes of treatment failure. Acetylcysteine (NAC) was found to be able to enhance defective HSCs by repairing dysfunctional bone marrow endothelial cells, and overcome the exhaustion of HSCs and enhance the engraftment of HSCs. Decitabine could restore bone marrow microenvironment by repairing endothelial cells and endothelial progenitor cells, as well as cytokines and chemokines which are crucial to HSCs proliferation and differentiation, thereby promote platelet recovery after HSCT. Besides, decitabine therapy was shown to be associated with reduced incidence of GVHD, lower relapse rate, and increased overall survival in several studies. Thereby the investigators will conduct this clinical trial to evaluate the hematopoietic reconstitution, GVHD and relapse rate of patients with hematological malignancy after allo-HSCT with decitabine containing conditional regimen and NAC treatment.

Inclusion Criteria:

1. Diagnosed as hematopoietic malignancy;
2. Achieved complete remission since the last chemotherapy;
3. Age 10-70 years；
4. Be willing to receive allo-HSCT, with HLA matched related or HLA matched unrelated, or HLA mismatched related donor.

Exclusion Criteria:

1. Active infections, severe organ damage (cardiac, renal and/or hepatic dysfunction greater than grade 2 according to the Common Terminology Criteria for Adverse Events V5.0), or any other conditions that make patients ineligible for allo-HSCT;
2. Allergic to acetylcysteine or decitabine.