The prognosis for children affected by acute leukemia and transplanted in an advanced disease stage, in the presence of MRD or with unfavorable cytogenetic abnormalities, is still poor. Optimizing post-transplant management to maintain durable remission represents the greatest challenge to improve the outcome of pediatric patients with acute leukemia given an allogeneic HSCT.

The pivotal therapeutic role of immunity against acute leukemia has been highlighted by the immunological effect of donor T cells (GVL) observed following allogeneic HSCT, which is considered the only curative strategy for this type of cancer. Moreover, circulating leukemia-specific CTLs have been detected in patients with different forms of acute leukemia, and the presence of these specific T-cell responses in peripheral blood and bone marrow samples of leukemic patients has been associated with improved disease control and longer survival. This body of data suggests that immunological interventions could have an effect in preventing relapse and improving transplant outcome.

Unmanipulated donor lymphocyte infusion (DLI) is used after stem cell transplantation to treat and prevent relapse, to prevent infections and to establish full donor chimerism. However, an expected side effect of the presence of mature T cells is the potential occurrence of acute GvHD. Evidence has emerged that escalating DLI has achieved higher clinical response rates with lower GvHD occurrence. Optimization of DLI dose and schedule as well as strategies of donor T-cell manipulation may lead to the consistent ability to separate GvHD from GvL activity and improve the safety of DLI treatment. One way to manipulate donor lymphocytes to reduce GVHD is leukemia antigen stimulation, in order to increase antileukemia activity while reducing the number of alloreactive T cells by specific culture.

The aim of this study is to enhance the GVL effect, and reduce the rate of post-transplant relapse, with preventive post-HSCT infusions of donor anti-leukemia CTLs specifically directed to patient's leukemic blasts. The leukemia-reactive CTLs obtained by stimulation with patients' leukemia blasts are specific for each individual blast signature, and, due to their physiological recognition and effector mechanism through their natural T cell receptor, exert leukemia-specific killing with less severe adverse reactions than CAR-T cells. Moreover, due to their potential to recognize multiple leukemia-associated antigens present on the blast surface, they should be less prone to immune evasion strategies exerted by leukemic stem cells. Additionally, the risk of GVHD should be reduced by the culture procedure, which decreases the number of alloreactive T cells. For the reasons stated, the use of these T cells after HSCT in a highly personalized approach may be a safer and more efficient option than unmanipulated donor lymphocyte infusions (DLIs) to prevent leukemia relapse after HSCT.

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.