Acute leukemia, including acute myeloid leukemia (AML) and acute lymphoblastic leukemia (ALL), is the subtype of leukemia with the highest mortality, and leukemia relapse caused by the protective bone marrow microenvironment is the main cause of treatment failure. The chemokine receptor CXCR4 plays a crucial role in the homing and settling of leukemia cells into the bone marrow. Preclinical study of the investigators demonstrates that CXCR4 blockade can mobilize leukemia cells from their protective bone marrow microenvironment to periphery, thereby significantly enhancing the killing effect of allogeneic lymphocytes against leukemia cells. This study aims to preliminarily evaluate the efficacy and safety of donor lymphocyte infusion (DLI) plus CXCR4 antagonist plerixafor in the treatment of relapsed acute leukemia patients after allogeneic hematopoietic stem cell transplantation (allo-HSCT) through a prospective single arm study. The results may preliminarily confirm the effectiveness and safety of DLI combined with plerixafor in the treatment of recurrent acute leukemia patients after allo-HSCT, providing a reference basis for further research.

Patients with relapsed acute leukemia post allo-HSCT will be screened for the eligibility of this clinical trial. The participants will receive chemotherapy to reduce leukemia burden followed by DLI three days later. Ten days post DLI, plerixafor will be administrated to the participants (subcutaneous injection, twice per day) for a consecutive five days. The second round of DLI plus plerixafor will be given if the participants achieving partial remission or complete remission with positive minimal measurable disease. Short-term responses and long-term outcomes will be evaluated and safety of this therapeutic regimen will be assessed.

Inclusion Criteria:

• The age of the patients is ≥ 14 and ≤ 60 years old;
• Those with relapsed acute leukemia after allo-HSCT with bone marrow blasts less than 50%;
• The expected survival exceeds 3 months;
• At least 100 days post transplantation, and the immunosuppressants were discontinued;
• Those with no significant abnormalities of the main organ function: creatinine ≤ 176.8 μ Mol/L, bilirubin ≤ 51.3 μ Mol/L, aspartate aminotransferase and alanine aminotransferase ≤ 2.5 times the normal upper limit;
• Sign an informed consent form.

Exclusion Criteria:

• Those with patient-specific human leukocyte antigen (HLA) loss at relapse;
• Those with active graft-versus-host disease;
• Those with severe infection;
• Those with organ function failure;
• Those with an Eastern Cooperative Oncology Group (ECOG) score more than 2 points;
• Those who are allergic to experimental drugs;
• Those who use other anti-leukemia therapies, such as radiotherapy, cellular immunotherapy, or Chinese medical herbs;
• Those participate in other clinical trials simultaneously;
• Those having mental illness or other illnesses that cannot fully comply with treatment or follow-up requirements;
• Those with extramedullary leukemia;
• Those with other conditions that researchers evaluate who are not proper to participate in this clinical trial.