Reduced Post-transplant Cyclophosphamide Dose in Patients Undergoing Haploidentical Hematopoietic Stem Cell Transplantation for Hematological Malignancies

Inclusion Criteria: * Age ≥ 18 years * Confirmed hematological malignancy with an indication for allogeneic HSCT * Presence of a haploidentical donor willing to donate PBSC * Patient planned to receive a thiotepa-based conditioning regimen * Provision of written informed consent Affiliation to a social security system (excluding "Aide Médicale d'État") Exclusion Criteria: * Karnofsky performance status \< 70% * Life expectancy \< 1 month, as determined by the attending physician * Acute or chronic heart failure, defined as left ventricular ejection fraction \< 40% * Pulmonary dysfunction with diffusion capacity \< 50% of predicted values * Renal impairment with estimated glomerular filtration rate (eGFR) \< 45 mL/min (calculated using the CKD-EPI formula) * Decompensated hemolytic anemia * Fanconi anemia and other DNA breakage repair disorders * Acute urothelial toxicity due to cytotoxic chemotherapy or radiotherapy * Obstruction of urinary outflow * Concomitant use with yellow fever vaccine and with live virus and bacterial vaccines * Combination with products containing Hypericum perforatum * Combination with medicines that are substrates for the multidrug efflux transporter P-glycoprotein (P-gp) or the organic anion transporter proteins (OATP) and for which elevated plasma concentrations are associated with serious and/or life-threatening events, e.g., bosentan, dabigatran etexilate and aliskiren * Active non-controlled infectious disease * Positive HIV status * Pregnancy, breast-feeding, or refusal to use effective contraception for the duration of the study and 6 months after the last treatment dose * Individuals under legal protection measures or unable to provide consent (e.g., severe neurological or psychiatric disorders, or deprivation of liberty by judicial or administrative decision) * Hypersensitivity to the active substance or any of the excipients * Concurrent participation in another investigational therapeutic study * Inability to comply with study procedures as assessed by the investigator based on objective criteria, including but not limited to: * Significant language barrier in the absence of adequate translation support * Social or geographic situation preventing follow-up and adherence to visit schedule * Ongoing substance abuse likely to interfere with protocol compliance * Documented cognitive or functional impairment not otherwise covered under legal protection