Safety and Preliminary Efficacy of Donor-derived Anti-leukemia Cytotoxic T Lymphocytes for the Prevention of Leukemia Relapse in Children Given Haploidentical Hematopoietic Stem Cell Transplantation

Patient Inclusion Criteria: 1. Age ≤ 18 years and ≥ 1 months 2. Life expectancy \> 12 weeks 3. Patients affected by life-threatening acute lymphoblastic leukemia (ALL) or acute myeloid leukemia (AML) with high risk of relapse after HSCT, namely: Patients affected by ALL: * in first morphological remission but with a positive minimal residual disease ≥ 1 x 10-3 before HSCT; * in second morphological remission after a high-risk relapse (patients belonging to the S3-S4 BFM risk group), independently of the level of minimal residual disease; * in second morphological remission with any positivity of minimal residual disease before HSCT; * in third or subsequent morphological remission, independently of the level of minimal residual disease; * patients not in morphological remission at time of HSCT. Patients affected by AML: * in first morphological remission and with a flow cytometry MRD at the end of induction therapy ≥ 0.1%; * in first morphological remission and with high-risk disease according to cytogenetics aberrations; * in first morphological remission after a primary induction failure; * in second morphological remission; * in third or subsequent morphological remission; * patients not in morphological remission at time of HSCT. 4. Pre-HSCT Lansky / Karnofsky score ≥ 40%. 5. HIV negativity. 6. Written informed consent signed by the parents or legal guardians (in case of patients \< 18 years) or by the patients (in the case of patients = 18 years). Patient Exclusion Criteria: 1. Ongoing active ≥ grade II acute GvHD or chronic extensive GvHD due to a previous allograft 2. Current clinically active infectious disease (including positive HIV serology or viral RNA) 3. Severe cardiovascular disease (arrhythmias requiring chronic treatment, congestive heart failure or left ventricular ejection fraction \<40%) 4. Liver dysfunction (AST/ALT ≥ 3 times institutional upper limit normal value -ULN- or bilirubine \> 3 times ULN) 5. Renal dysfunction: serum creatinine \> 1.5 times ULN or calculated creatinine clearance \< 60 ml/min/1.73 m2 6. End stage irreversible multi-system organ failure. 7. Other active malignancy. 8. Pregnant or breast feeding female patient 9. Lack of parents'/guardian's written informed consent for minors or lack of written informed consent for patients aged 18 y. Donor inclusion criteria: Eligible donors are the HSCT donors, i.e. HLA-haploidentical relative, including but not limited to biological parents, siblings, or half-siblings. Matching will be determined by class I and class II DNA typing. 1. Age between 18 and 65 years. 2. The donor should be sufficiently healthy not to be at increased risk from the leukapheresis procedure. 3. Donors must meet the selection criteria as defined by the European Directive 2006/17/CE) and according to the FACT-JACIE International Standards and local regulations for donor selection. 4. Donor must have adequate peripheral venous access for leukapheresis or must agree to placement of a central venous catheter. 5. Signed informed consent. Donor exclusion criteria: 1. Evidence of active infection (including urinary tract infection, or upper respiratory tract infection) or viral hepatitis exposure (on screening), unless HBs Ab+ and HBV DNA negative. 2. Factors which place the donor at increased risk for complications from leukapheresis (e.g. autoimmune disease, symptomatic sickle cell trait, symptomatic coronary artery disease requiring therapy, previous thrombotic events). 3. Pregnancy or breastfeeding female donor. 4. Lack of written informed consent.