The study subjects included 17 children who received tacrolimus and minidose MTX for the prevention of GVHD at the Pediatric HSCT Unit at Pusan National University Hospital. Patient records from March 2003 to February 2011 were reviewed retrospectively.

Tacrolimus was administered intravenously since the day before transplantation at 0.03 mg/kg/day via continuous infusion. Following engraftment, once the patient was able to consume oral medications, tacrolimus was administered as an oral dose at a concentration of 4 times the intravenous (IV) dose. The oral dose was administered in 2 doses every 12 h. Tacrolimus levels were monitored every second day, and the dosage was adjusted to maintain trough levels between 5 and 15 ng/mL. In the absence of GVHD, tacrolimus dosage was subsequently tapered by 25% per month and discontinued by day 180. Children with aGVHD continued to receive tacrolimus at the discretion of the physician. Dosage modifications of tacrolimus were also made in patients who developed serum creatinine levels that were >2 times the baseline value. Minidose MTX was administered intravenously on post-transplant days 1, 3, 6, and 11 at a dose of 5 mg/m². The dose on day 11 was reduced or omitted when the patient was unable to swallow due to severe oral mucositis.

Neutrophil engraftment was defined as the first of 3 consecutive days when the absolute neutrophil count of peripheral blood (PB) exceeded 0.5×10⁹/L; platelet engraftment was defined as the first day when the platelet count exceeded 20×10⁹/L without the need for platelet transfusions the following week. Toxicity was evaluated using the Common Terminology Criteria for Adverse Events v3.0 from the National Cancer Institute (NCI) [17].

aGVHD was graded according to the Glucksberg criteria [18]. cGVHD was categorized according to the criteria described by Shulman et al. [19].

Transplant-related complications were assessed by analyzing the survival and disease status at post-transplant day 100, 1 year, and the final follow-up.

Data was assessed for association by using Fisher's exact tests. Continuous variables between subgroups were compared by using Student's t-test. All P values were two-sided, and a P<0.05 was considered significant.

Seventeen patients (age, 17 months-17 years) undergoing allogeneic HSCT received tacrolimus and minidose MTX for the prevention of aGVHD. Fifteen patients had hematological malignancies (8 had acute myeloid leukemia, 7 had acute lymphoblastic leukemia (ALL), 1 had Fanconi anemia, and 1 had severe aplastic anemia) (Table 1). Related and unrelated donor transplants were received by 9, and 8 patients, respectively (Table 2). The degree of HLA matching was as follows: 7 matched sibling bone marrow (BM) or PB donors and 2 matched sibling cord blood (CB) donors had 6/6 HLA matches; 4 unrelated BM or PB donors had 8/8 HLA matches; 2 unrelated PB donors had 7/8 HLA matches; 2 unrelated CB donors had 5/6 HLA matches, 4/6 HLA matches in each. Patients were followed up for a median time of 55 months post-transplantation (range, 1-107 months). Chemotherapy-based conditioning regimens were administered to 16 patients; 8 received busulfan, fludarabine, and/or antithymocyte globulin (ATG); 4 received busulfan, melphalan, and ATG; and 2 received fludarabine, cyclophosphamide, and ATG. Only 1 patient with ALL received total body irradiation as a part of the preparatory conditioning (Table 2).

The median number of total nucleated cells (TNC) infused was 8.6×10⁸/kg (range, 1.8-23.3×10⁸/kg) and that of CD 34⁺ cells was 7.5×10⁶/kg (range, 1.9-17.2×10⁶/kg) in 13 patients with BM/PB stem cell transplant. The median number of infused TNC was 3.06×10⁷/kg (range, 1.9-5.7×10⁷/kg) and CD 34⁺ cells was 1.5×10⁵/kg (range, 0.95-3.4×10⁵/kg) for 4 patients who had undergone CB transplantation (CBT). With the exception of 1 patient who received an unrelated CBT, all the patients were successfully engrafted. The median time for neutrophil engraftment was 15 days (range, 9-24 days) post-transplantation, while platelet recovery occurred at a median of 19 days (range, 9-77 days). Three patients died before platelet recovery due to aGVHD, acute respiratory distress syndrome, and veno-occlusive disease (VOD) (Table 3).

aGVHD occurred in 5 (31.3%) of the 16 patients who received grafts. In the related donor group, 2 (22.2%) of a total of 9 patients developed aGVHD; in the unrelated donor group, 3 (42.9%) of a total of 7 patients developed aGVHD. Among the 4 patients who developed grade II aGVHD, 2 had received related transplants, and the rest had received unrelated transplants. Only 1 patient who had received an unrelated transplant developed grade IV aGVHD and died from hepatic failure (Table 3). Grade III-IV aGVHD did not occur in the related donor group. Cases that could be evaluated for cGVHD (engrafted and survived until post-transplantation day 100) were 13/17 transplant recipients. cGVHD was not found to occur in either group (Table 4).

The mean IV dose of administrated tacrolimus was 0.035±0.012 mg/kg/day (range, 0.025-0.050 mg/kg), and the mean blood concentration of tacrolimus was 7.12±0.49 ng/mL (range, 5.13-11.82 ng/mL). To maintain therapeutic levels of tacrolimus in the blood (5-15 ng/mL), an increased mean dose (0.042 mg/kg/day was administered to the younger group (<8 years old), compared to that administered (0.028 mg/kg/day to the older group (≥8 years old), P=0.0075) (Table 5). The mean blood concentration of tacrolimus in the children who did not develop aGVHD was higher (8.11±1.83 ng/mL) than in those who developed aGVHD (6.04±2.54 ng/mL) (P=0.038).

Hypomagnesemia (88.2%) was the most frequent adverse event associated with tacrolimus administration (Table 6), with the median time to peak being post-transplantation day 21 (range, days 4-39). Magnesium supplementation was required in all cases during the administration of tacrolimus. Four patients (23.5%) developed nephrotoxicity but no patient required hemodialysis. Hyperglycemia was observed in 4 patients (23.5%), but no patient required insulin management other than the adjustment of total parenteral nutrition formulation. Hypertension and pancreatitis occurred in 1 patient in each case (5.8%). Neurotoxicity symptoms such as tremor or seizure, hemolytic uremic syndrome (HUS), and thrombotic thrombocytopenic purpura (TTP) were not observed in this study. Oral mucositis was noted in all patients during the first 2 weeks of post-transplantation. Of these, 3 (18%) were grade 1; 5 (29%), grade 2; 8 (47%), grade 3; and 1 (6%) was grade 4.

With a median follow-up of 55 months (range, 1-107 months), the survival rates at 100 days post-transplantation and 1 year were 82% and 70%, respectively. Among the 15 patients who received transplants for leukemia, 3 patients experienced a relapse. Although 2 patients died from disease progression following the relapse, the third patient is alive and in remission at 100 months after chemotherapy. The causes of death of 6 patients included leukemic relapse, aGVHD, ARDS, VOD, and secondary engraftment failure (Table 3).