MDS patients without identical sibling donor or unrelated donor would receive haplo-HSCT. Participants will receive either reduced-toxicity Bu/Flu/Cy/ATG conditioning regimen (for patients aged ≥55 years) or standard myeloablative modified Bu/Cy+ATG conditioning regimen (for patients aged <55 years) followed by unified post-transplant immunosuppression and supportive care.

RTC preconditioning regimen consisted of cytarabine (2g/m2/day, days -10 to -9), busulfan (3.2 mg/kg/day on days -8 to -6), cyclophosphamide (1.0 g/m2/day, days -5 to -4), fludarabine (30 mg/m2/day, days -6 to -2), semustine (250 mg/m2, day-3), and rabbit antithymocyte globulin (thymoglobulin, 2.5 mg/kg/d, days -5 to -2; Sanofi, France). Bu/Cy preconditioning regimen consisted of tandard institutional myeloablative busulfan + cyclophosphamide + rabbit ATG regimen per department routine dosing guidelines.

Death without disease progression or relapse

Neutrophil engraftment is defined as the first day of sustained absolute neutrophil count (ANC) ≥0.5×10⁹/L for 3 consecutive days; platelet engraftment is defined as the first day of sustained platelet count (PLT) ≥20×10⁹/L without transfusion support for 7 consecutive days. Cumulative incidence of neutrophil engraftment at Day 30 and platelet engraftment at Day 90 will be calculated.