Several groups have demonstrated very low incidence of acute and chronic graft-versus-host disease (GVHD) with post-transplantation cyclophosphamide (PTCy) in haploidentical, unrelated and related allogeneic stem cell transplantation (SCT). Nonetheless for majority of the grafts, except for 10/10 HLA-matched bone marrow, with this type of prophylaxis require concomitant administration of calcineurin inhibitors±MMF, which delays immune reconstitution and development of graft-versus-leukemia (GVL) effect. So, despite reduction of transplant-related mortality, use of PTCy doesn't lead to the reduction of relapse incidence. This is particularly important for relapsed or refractory acute leukemia patients, where, despite all efforts to intensify conditioning regimens, relapses after SCT occur in more than 50% of patients, and long-term survival rarely exceeds 10-20%. In preclinical model of haploidentical SCT the substitution of post-transplantation cyclophosphamide with bendamustine, led to comparable GVHD control, but significantly augmented GVL effect. To test this hypothesis and improve the outcome of allogeneic SCT in refractory acute leukemia patients we initiated a pilot trial with high-dose post-transplantation bendamustine for GVHD prophylaxis. The selection of doses is based on the previous dose-escalation studies. Additional immunosuppression could be added for mismatched grafts.

Inclusion Criteria:

- Diagnosis: Acute Myeloblastic Leukemia Acute Lymphoblastic Leukemia Mixed-Lineage Acute Leukemias

• Disease, refractory to at list one course of induction chemotherapy or immunotherapy
• More than 5% clonal blasts in the bone marrow or peripheral blood at the time of inclusion
• Signed informed consent
• Matched related, 8-10/10 HLA-matched unrelated or haploidentical donor available. The HLA typing is performed by the following genetic loci: HLA-A, HLA-B, HLA-Cw, HLA-DRB1, and HLA-DQB1.
• No second tumors
• No severe concurrent illness
• No previous autologous or allogeneic stem cell transplantations

Exclusion Criteria:

• Karnofsky index <70%
• Moderate or severe cardiac dysfunction, left ventricular ejection fraction <50%
• Moderate or severe decrease in pulmonary function, FEV1 <70% or DLCO<70% of predicted
• Respiratory distress >grade I
• Severe organ dysfunction: AST or ALT >5 upper normal limits, bilirubin >1.5 upper normal limits, creatinine >1.5 upper normal limits
• Creatinine clearance < 60 mL/min
• Uncontrolled bacterial or fungal infection at the time of enrollment, defined by CRP level >70 mg/L or positive procalcitonin in patient with adequate empirical antibacterial and antifungal therapy.
• Requirement for vasopressor support at the time of enrollment
• Pregnancy
• Somatic or psychiatric disorder making the patient unable to sign informed consent

Consultations are ongoing about how IPD initiative fits the local law "About personal data 152-fz".