A Study Comparing Haploidentical Hematopoietic Stem Cell Transplantations (HSCTs) From Young Non-first-degree and Older First-degree Donors in Hematological Malignancies

Patient Inclusion Criteria: * Patient age 13-78 years * Absence of a suitable HLA identical related or unrelated hematopoietic stem cell donor * Absence of a suitable partially HLA-mismatched (haploidentical), first-degree related donor aged between 18 and 50 * Presence of both HLA haploidentical young non-first-degree (age ≤ 40) and older first-degree (age \>50) donors Eligible diagnoses: AML（excluding APL） with at least one of the following: * median- or high- risk according to the WHO prognostic stratification system * failure to achieve CR after 2 cycles of induction chemotherapy * AML arising from MDS or a myeloproliferative disorder, or secondary AML * patients in CR2 or beyond Mixed-phenotype acute leukemia (MPAL) in morphological remission Acute lymphoblastic leukemia (T or B) in morphological remission MDS with at least one of the following: * IPSS score of INT-2 or greater * IPSS score of INT-1 with life-threatening cytopenias, including those generally requiring greater than weekly transfusions * A first allo-HCT * Adequate end-organ function * ECOG performance status \< 2 * No other contraindications for HSCT * Signature of the informed consent Patient Exclusion Criteria * Availability of suitable HLA identical related or unrelated hematopoietic stem cell donors * Availability of suitable partially HLA-mismatched (haploidentical), first-degree related donor aged between 18 and 50 * Not the first allo-HCT * Presence of uncontrolled bacterial, viral, or fungal infection * Patients with severe heart, lung, liver and kidney insufficiency * HIV-positive patients * Women of childbearing potential who are pregnant (β-HCG+) or breast feeding * Patients with a psychiatric history * ECOG performance status ≥ 2 * Patients with malignancies other than the primary disease * Refusal to sign the informed consent Donor Inclusion Criteria: * The donor and recipient must be HLA haploidentical * Meets institutional selection criteria and medically fit to donate * Lack of recipient anti-donor HLA antibody Donor Exclusion Criteria: * The donor and recipient are HLA identical * Has not donated blood products to recipient