This is a retrospective study. Between January 1995 and December 2009, 261 under 18-year-old patients received unrelated HSCT at the Hospital de Clínicas, Universidade Federal do Paraná (UFPR), Brazil. Of the 261 patients, nine were excluded from the analysis for the following reasons: seven patients had insufficient data for analysis and two patients were recipients of peripheral blood transplants. One hundred and eighteen patients received BM and 134 UCB grafts. The characteristics of the 252 cases that were assessed are listed in Table 1.

The units were selected on the basis of best HLA matching and a critical minimum cell dose at the discretion of the treating physicians and source from National and International Public Banks. Class I typing was performed by serological or molecular techniques and Class II typing by molecular techniques; it was only in 2008 that the analysis of the locus C was frequently performed.

The conditioning regimen and prophylaxis for acute GVHD varied according to the underlying disease, stem cell source and HLA incompatibilities (Table 1).

The units of BM grafts used for transplantation contained an average of 4.39×108 total nucleated cells (TNC) (range: 0.3–10.8 cells) per kilogram of recipient's body weight after thawing. The units of UCB grafts used for transplantation contained an average of 5.2×107 TNC (range: 1.4–36.5 cells) and 1.3×105 CD34 cells (range: 0.1–11.4 cells) per kilogram of recipient's body weight after thawing.

Central venous catheters were inserted in all patients. Patients received acyclovir for antiviral prophylaxis, fluconazole or amphotericin-B for antifungal prophylaxis, and trimethoprim-sulfamethoxazole for prophylaxis against Pneumocystis carinii. Empirical broad spectrum antibiotic therapy was started at the first sign of fever.

Hematologic recovery was defined as the time when the absolute neutrophil count was equal to or greater than 0.5×109cells/L in three consecutive laboratory counts on different days and platelet count equal to or greater than 20×109cells/L (after seven days without transfusion support).6

Patients were evaluated and considered at risk for acute GVHD when there was evidence of neutrophil recovery. Diagnosis of acute GVHD was based on clinical criteria, with histopathologic confirmation when possible. Overall staging was assessed according to previously published criteria.15 Only those patients with sustained engraftment of donor hematopoiesis surviving for more than 90 days after transplant were assessed for chronic GVHD according to the criteria described in previous studies.16

Relapse was characterized by morphological evidence of malignant disease at any site. Transplant-related mortality (TRM) was determined to be every cause of death that was not death by relapse. OS was the time between transplantation and death due to any cause or between transplantation and the day of the last follow-up.

All statistical analyses were carried out using the STATA v.12.0 computer program. Survival rates were calculated using the Kaplan–Meier method. The log-rank test was used for testing differences in survival between groups in the univariate analysis. Cumulative incidence curves were used for engraftment and GVHD endpoints with death as a competing risk factor. The Cox proportional hazards model with backward elimination was used for multivariate testing of co-variables (statistical significance was based on p-values≤0.05). Differences between subgroups were compared using the Fine and Gray test with death as a competing risk. The association between dichotomous variables was calculated using Fisher's exact test.

From 1995 to 2009, 252 patients were treated with unrelated HSCT. The mean age of the patients was eight years (range: 0.2–18 years) with 34 patients being one year old or less. Most patients were male (61.1%). A total of 96 patients were transplanted for malignant diseases with 64 (66.7%) being at an early stage. A total of 150 (59.5%) donor-graft pairs were matched for ABO and 124 (49.8%) were matched for gender. BM was used for HSCT in 118 patients (46.8%) and UCB in 134 patients (53.2%). The patients as well as treatment are listed in Table 1.

Neutrophil engraftment occurred in 181 of the 234 (77.4%) avaliable (18 patients died before) cases (BM: 89.47% and UCB: 65.83%). In the BM group, 102 of the 118 patients achieved neutrophil engraftment in an average time of 24 days (range: 11–1696 days). The cumulative incidence by Day 30 was 80%. In the UCB group, 79 of the 134 patients achieved neutrophil engraftment in a mean time of 32 days (range: 14–4037 days). The cumulative incidence by Day 42 was 62%. In the univariate analysis, neutrophil engraftment was influenced by cell source (p-value<0.001) and patient age (p-value=0.002). In the multivariate analysis only cell source (p-value<0.001) was a significantly favorable factor for neutrophil engraftment (Table 2 and Figure 1).

Figure 1.

Cumulative incidence of neutrophil engraftment over time.

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In the BM group, patients achieved platelet engraftment in an average of 25 days (range: 10–96 days). The cumulative incidence by Day 30 was 50%. In the UCB group, patients achieved platelet engraftment in a mean time of 43 days (range: 19–158 days). The cumulative incidence by Day 42 was 38%. In the univariate analysis, platelet engraftment was influenced by cell source (p-value<0.001), patient age (p-value=0.022) and HLA match (p-value=0.027). In the multivariate analysis cell source (p-value<0.001) and HLA match (p-value=0.013) were significantly favorable factors for platelet engraftment (Table 2 and Figure 2).

Figure 2.

Cumulative incidence of platelet engraftment over time.

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Acute GVHD occurred in 88 (48.6%) patients of the total of 181 (on average within 90 days) and was scored as Grade II (54.5%) and Grade III–IV (45.5%). By Day 100 after transplantation, the cumulative incidence was 44% in the BM group and 43% in the UCB group (p-value=0.653 – Figure 3). HLA match (p-value=0.004) and ATG (p-value=0.005) were significant in the univariate analysis; this was the same in the multivariate analysis (p-value=0.003 and p-value=0.006, respectively – Table 2).

Figure 3.

Cumulative incidence of acute graft-versus-host disease over time.

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Chronic GVHD occurred in 13 (9.2%) patients out of the total of 142 (on average within 90 days). The disease was classified as limited in six cases (46.2%) and extensive in seven cases (53.8%). At one year after transplantation, the cumulative incidence was 14% in the BM group and 2.5% in the UCB group (p-value=0.053).

Hematological relapse was detected between 21 and 1228 days (mean: 181 days; 95% confidence interval: 94.0–670.0) after transplantation in 23 of 96 patients treated for malignant disease. Relapse was observed in 29.31% of the patients in the BM group and 15.79% in the UCB group (p-value=0.117). The cumulative incidences of relapse were 45% in the BM group and 25% in the UCB group at two years (Figure 4). The stage of the disease was found to be significant (p-value=0.005) however cell source, GVHD, CMV and ABO incompatibility were not (Table 2).

Figure 4.

Cumulative incidence of relapse over time.

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With an average follow-up time of surviving patients of 1207 days (3.3 years), the cumulative proportions of surviving patients at one year and five years were 55% and 47%, respectively. The cumulative proportions of surviving patients at one year and five years after unrelated HSCT with BM were 55% and 45%, respectively and for UCB they were 52% and 45%, respectively (p-value=0.466) (Figure 5). In a multivariate analysis, the factors that most influenced of negative form the OS were higher ages (p-value<0.001), non-use of ATG (p-value=0.029), and GVHD (p-value=0.007 – Table 2).

Figure 5.

Cumulative incidence of overall survival over time.

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In this series, 131 (52.0%) patients died, 59 (50.0%) in the BM group and 72 (53.73%) in the UCB group (p-value=0.614). Death was associated with infection (n=47), graft failure (n=29), GVHD (n=25), relapse (n=18) and others (n=12).