Results of hematopoietic stem cell transplantation in children with acute leukemia: a single-center experience

   Currently, allogeneic hematopoietic stem cell transplantation (allo-HSCT) is an effective treatment option for relapsed / refractory (R / R) acute leukemia (AL) and high-risk AL. In this article, we present our own experience of allo-HSCT in children with R / R AL. The study was approved by the Independent Ethics Committee and the Scientific Council of the N. N. Blokhin National Medical Research Center of Oncology. Fifty-one patients with R / R AL were included in the study: 32 patients had acute lymphoblastic leukemia (ALL), 17 patients had acute myeloid leukemia (AML) and 2 patients had biphenotypic leukemia (BL). All patients underwent allo-HSCT from January 2021 to October 2022. The median age was 8.7 years (5 months – 17 years). At the time of allo-HSCT, 26 patients were in the second (and further) remission, the rest were in the first clinical and hematologic remission (high-risk AML and refractory ALL). Twenty-one (41.2 %) patients received allo-HSCT from a haploidentical donor, 19 (37.2 %) patients underwent allo-HSCT from an HLA-matched related donor and 11 (21.6 %) patients – from an HLA-matched unrelated donor. Pre-transplant conditioning in ALL: 27 patients received regimens based on total body irradiation at a dose of 12 Gy, 4 patients received busulfan-based conditioning regimens, and in 1 patient we used treosulfan. In AML and BL, we used conditioning regimens based on treosulfan/thiotepa (n = 10), treosulfan/melphalan (n = 8) or busulfan / melphalan (n = 1). Bone marrow (in 14 patients) and peripheral blood stem cells (in 37 patients) were used as a source of hematopoietic stem cells. In haploidentical allo-HSCTs in order to prevent graft-versus-host disease (GVHD) we performed TCRab/CD19 depletion followed by additional administration of abatacept / tocilizumab / rituximab on day –1 in 15 patients, 6 patients received post-transplant cyclophosphamide. In transplantations from HLA-matched related and unrelated donors, patients received combined immunosuppressive therapy with abatacept and rituximab on day –1, and calcineurin inhibitors were used as basic immunosuppressive therapy. All patients engrafted with a median time to engraftment of 13 (range, 9 to 24) days after allo-HSCT. Eight (15.7 %) patients developed a relapse of AL at different times after HSCT (five of them are alive). At the median follow-up of 9 (5–25) months, the overall and disease-free survival survival rates were 76.4 % and 68.8 %, respectively, for patients with AL. Acute GVHD was observed in 72.5 % of children, grade 3–4 GVHD was observed in 5.3 % of patients, and 13.7 % of children developed chronic GVHD. Most patients developed infectious complications in the early post-transplant period: febrile neutropenia (96.0 %), reactivation of viremia (47.3 %,) oropharyngeal mucositis (78.4 %), acute cystitis (12.3 %). The overall mortality rate was 17.6 %. Late mortality was associated with a relapse of AL.