Acute myeloid leukemia (AML) is the second most common type of leukemia in children and accounts for up to 20 % of all leukemias. Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is an effective, and sometimes the only therapeutic option in high-risk patients with AML. Graft-versus-host disease (GVHD) is a major complication of allo-HSCT and the main cause of transplant-related mortality. GVHD prophylaxis in children includes calcineurin inhibitors, either alone or in combination with other immunosuppressants, which can lead to grade II–IV acute GVHD in 40–85 % of cases. Alternatively, GVHD can be prevented with high-dose cyclophosphamide (50 mg/kg/day) administered on days +3, +4 after allo-HSCT, either alone or in combination with other immunosuppressive drugs depending on HLA compatibility of the donor. The aim of this study was to evaluate outcomes after allo-HSCT from an unrelated donor with GVHD prophylaxis with post-transplant cyclophosphamide (PTC) in children in their first and second remission of AML in comparison with a historical control group. We retrospectively analyzed patient outcomes after 53 first-time allo-HSCTs from HLA-matched (n = 40) and partially-matched (8–9/10) (n = 13) unrelated donors performed in pediatric patients (aged 0 to 18 years) in their 1st or 2nd remission of AML at the R. M. Gorbacheva Research Institute for Pediatric Oncology, Hematology and Transplantation from 2008 to 2018. The study was approved by the Independent Ethics Committee and the Scientific Council of the I. P. Pavlov First Saint Petersburg State Medical University of Ministry of Healthcare of the Russian Federation. Our group of interest included 26 patients preventively treated for GVHD with 50 mg/kg of cyclophosphamide on days +3 and +4 in combination with calcineurin inhibitors (cyclosporin A – 2 (7.7 %) patients, tacrolimus – 24 (92.3 %) patients), the mTOR inhibitor sirolimus (5 (19.2 %) patients) or mycophenolate mofetil (21 (80.8 %) patients). The historical control group was made up of 27 patients whose GVHD prophylaxis was based on antithymocyte globulin used in combination with calcineurin inhibitors (tacrolimus – 5 (18.5 %) patients, cyclosporin A – 21 (77.8 %) patients) or the mTOR inhibitor sirolimus (1 (3.7 %) patients) or methotrexate (25 (92.6 %) patients), or mycophenolate mofetil (2 (7.4 %) patients). The groups were matched for diagnosis, age, disease status before allo-HSCT, the matched-to-partially-matched donor ratio, the source of hematopoietic stem cells and conditioning regimen intensity (myeloablative conditioning regimen (MAC) or reduced intensity conditioning regimen (RIC)). The median age at the time of allo-HSCT was 8.6 (0.97–18) years in the PTC group and 6.55 (1.42–17.76) years in the historical control group. In the PTC group, 21 (80.8 %) patients were diagnosed with primary AML and 5 (19.2 %) – with secondary AML, while the historical control group included 22 (81.5 %) and 5 (18.5 %) patients with primary and secondary AML respectively. Disease status at the time of allo-HSCT: 21 (80.8 %) patients treated with PTC were in the 1st complete clinical and hematologic remission (CCHR) and 5 (19.2 %) – in the 2nd CCHR; among the controls, there were 19 (70.4 %) cases of the 1st CCHR and 8 (29.6 %) cases of the 2nd CCHR. In the PTC group, 18 (69.2 %) patients underwent allo-HSCT from 10/10 fully HLA gene-matched donors and 8 (30.8 %) – from 9/10 HLA-matched donors. In the historical control group, 19 (70.4 %) patients had allo-HSCT from 10/10 fully HLA gene-matched donors, 4 (14.8 %) – from 9/10 matched donors, and 1 (3.7 %) – from an 8/10 matched donor. In the PTC group, MAC was used in 14 (53.8 %) patients, RIC – in 12 (46.2 %) patients. In the control group, MAC and RIC were used in 14 (51.9 %) and 13 (48.1 %) patients respectively. In the group treated with PTC, hematopoietic stem cells were derived from the bone marrow in 14 (53.8 %) patients, from the peripheral blood – in 12 (46.2 %) patients. In the historical group, bone marrow was used in 13 (48.1 %) patients and peripheral blood - in 14 patients (51.9 %). The median graft cellularity (CD34+ × 106/kg) in the PTC group was 4.60 (1.7–10.9) × 106/kg, in the historical group – 6.60 (1.0–13.2) × 106/kg. The overall and relapse-free 5-year survival rates were higher in the PTC group than in the historical control group: 83.3 % (95 % confidence interval (CI) 60.9–93.5) vs 59.3 % (95 % CI 38.6–75.0), p = 0.0327 and 76.9 % (95 % CI 55.7–88.9) vs 48.1 % (95 % CI 28.7–65.2), respectively, p = 0.0198. The cumulative incidence of grade II–IV acute GVHD and grade III–IV acute GVHD by day +125 and of moderate and severe chronic GVHD, and the 2-year transplant-related mortality were significantly lower in the PTC group compared to the controls: 15.4 % (95 % CI 4.8–31.5) vs 51.8 % (95 % CI 31,9–68.5), p = 0.004; 7.7 % (95 % CI 1.3–21.7) vs 33.3 (95 % CI 16.8–50.9), p = 0.026; 23.4 % (95 % CI 9.5-41.0) vs 58.6 % (95 % CI 33.8–76.8), p = 0.022; 3.8 % (95 % CI 0.3–16.4) vs 25.9 % (95 % CI 11.5–43.1), p = 0.0232, respectively. GVHD-related mortality was higher in the historical control group than in the PTC group (3.8 % vs 18.5 %, p = 0.192). Thus, PTC-based GVHD prophylaxis was shown to be more effective in managing acute and chronic GVHD compared to antithymocyte globulin, with better overall, relapse-free and GVHD-free relapse-free survival rates and low transplant-related mortality.
