Venetoclax-Enhanced BUCY vs. Standard BUCY Conditioning in High-Risk AML and MDS Patients Undergoing Allo-HSCT (Ven-BUCY Study)

Inclusion Criteria: * Diagnosis of acute myeloid leukemia (AML) or myelodysplastic syndrome (MDS) according to 2022 WHO classification * Age between 12 and 60 years * High-risk MDS as defined by at least one of the following: * IPSS intermediate-2/high risk or IPSS-R intermediate/high/very high risk * TP53 mutation * RAS pathway mutation (e.g., NRAS, KRAS, PTPN11, CBL, NF1, RIT1, FLT3, KIT) * Therapy-related MDS * High-risk AML as defined by at least one of the following: * TP53, RUNX1, or ASXL1 mutation * t(6;9)(p23;q34.1)/DEK-NUP214 * KMT2A rearrangement * BCR-ABL1 fusion * inv(3)(q21.3q26.2) or t(3;3)(q21.3;q26.2) * -5/del(5q), -7, -17/abn(17p) * Complex or monosomal karyotype * FLT3-ITD high with wild-type NPM1 * Initial WBC ≥ 10×10\^9/L * Secondary AML with history of MDS/MPN or therapy-related AML * AML with specific mutations (SRSF2, SF3B1, U2AF1, ZRSR2, ASXL1, EZH2, BCOR, STAG2) * MRD positive before transplantation * For AML: must have achieved CR or CRi prior to transplantation; for MDS: bone marrow blasts \< 20% * Availability of a matched related or unrelated donor (10/10 or 9/10 HLA match) * ECOG performance status 0-2 * Creatinine clearance ≥ 60 mL/min (Cockcroft-Gault) * AST/ALT ≤ 3 × ULN and total bilirubin ≤ 2 × ULN * LVEF ≥ 50% by echocardiogram * Life expectancy \> 8 weeks * Willingness to use effective contraception methods during and for a specified period after the study * Signed informed consent Exclusion Criteria: * Uncontrolled cardiovascular disease or New York Heart Association class III/IV heart failure * Other severe comorbid conditions that may interfere with study participation * Known HIV infection or uncontrolled active hepatitis B or C * Pregnant or breastfeeding women * More than one prior hematopoietic stem cell transplantation * Inability to understand the study protocol or provide informed consent * History of grade ≥ 3 non-hematologic adverse reaction to prior venetoclax therapy * Receipt of chemotherapy (except hydroxyurea/dexamethasone) or radiotherapy within 14 days before study treatment * Ongoing use of BCR-ABL1, IDH, or FLT3 inhibitors without proper washout (≥ 7 days)