Decreasing donor chimerism is considered as an early sign of graft failure or relapse in patients undergoing allogeneic stem cell transplantation. The treatment option included tapering or stop of immunosuppression and or donor lymphocyte infusion (DLI) which may restore a full donor chimerism but subsequent graft versus host disease (GVHD) is the major complications. In this single arm prospective study, the investigator evaluate the effect and safety of low-dose decitabine alone or with DLI in patients with decreased donor chimerism after allo-HSCT.

Decreasing donor chimerism is considered as an early sign of graft failure or relapse in patients undergoing allogeneic stem cell transplantation. The treatment option included tapering or stop of immunosuppression and or donor lymphocyte infusion (DLI) which may restore a full donor chimerism but subsequent GVHD is the major complications. In this single arm prospective study, the investigator plan to evaluate the effect and safety of low-dose decitabine treatment alone in patients with decreased donor chimerism after allo-HSCT. The investigators expect an overall response rate of 80% without serious toxicity such as grade III-IV aGVHD, ext cGVHD and lethal infection event associated with low-dose decitabine (LD-DAC) treatment. In case of donor chimerism decreasing, 5-day low-dose decitabine (5mg/m2) will given every 6 to 8 weeks until full donor chimerism is achieved (>98%). Fast withdraw of immuno-suppression or stop of immunosupression is not carried out in the study.

Inclusion Criteria:

• all patients after allogeneic stem cell transplantation
• decreasing of donor chimerism to less than 97%
• providing inform consent

Exclusion Criteria:

• patients with documented relapse disease
• patients with documented positive MRD+ (>0.1% via flowcytometry or PCR)
• patients with active infection or grade III-IV GVHD