Although a myeloablative dose of i.v.BU/fludarabine ( i.v. BU/Flu) has been widely accepted as a reduced toxicity myeloablative regimen for Allo-SCT from a related or unrelated donor,1 little information is available on the feasibility of the i.v.BU/Flu regimen in cord blood transplantation (CBT).Studies from Duke University, in which i.v.BU/Flu was used as the conditioning regimen followed by double CBT, demonstrated that only 2 of 10 patients engrafted with donor hematopoietic cells.2.BU/Flu-conditioning regimen in CBT, we retrospectively reviewed 62 consecutive adult CBT recipients with i.v.To evaluate the safety and efficacy of the i.v. BU/Flu-based conditioning regimens at our institute from Feb. 2007 to March 2010.The patients' characteristics are summarized in Table 1.Their median age was 59 years (range, 21-72), with a median hematopoietic cell transplant-specific comorbidity index score of 2 (0-5).All were considered not to be proper candidates for conventional myeloablative therapy.Fifty-seven (92%) patients were not in remission and 16 (36%) had a prior history of Allo-SCT.All were transplanted with a single cord blood unit, and all received fludarabine (Flu; 25-30 mg/m2 once daily for 5-6 days, 125-180 mg/m2 per total) and i.v.BU (0.8 mg/kg four times a day for 2-4 days, 6.4-12.8 mg/kg per total).Melphalan (Mel; 40-70 mg/m2 once daily for 2 days, 80-140 mg/m2 per total) or TBI (2-8 Gy per total) were used in combination with i.v.BU/Flu regimens in all the patients.Pre-transplant conditioning was determined by each attending physician according to the patient's condition, disease status and history of prior therapy.Engraftment, regimen-related toxicities (RRT), chimerism, GVHD, nonrelapse mortality (NRM), OS and disease-free survival (DFS) were assessed as previously reported.3, 4.All patients gave written informed consent for transplant, and this study was approved by the institutional review board.Forty-eight patients achieved neutrophil recovery on a median of day 21 (range, 12-52) post transplant.Among 14 who failed to achieve neutrophil recovery, 5 experienced early disease progression, 6 showed graft rejection, and 3 died before engraftment.The cumulative incidences of neutrophil and platelet recoveries were 77.4% and 56.5%, resp.All patients who achieved engraftment showed complete donor chimerism within 28 days post transplant.In multivariate anal., more mismatches in HLA (2/6 vs 1/6) was the only significant factor neg. affecting neutrophil engraftment rate (Hazard ratio (HR) =0.65, 95% confidence interval (CI), 0.44-0.96, P=0.03).RRT and GVHD were summarized in Table 1.At the time of anal., 27 of 62 patients survived for a median of 33.5 (range, 21-55) months after transplant.Seventeen patients died of nonrelapse causes.Six of them were from infections, four from GVHD, two from engraftment failure and five from idiopathic pneumonia syndrome.The cumulative incidences of NRM at day 100 and 2 years were 23.4% (13.5-34.8%) and 28.6% (17.6-40.4%), resp.Twenty-five patients relapsed at a median of 7.5 mo (range; 1-21) after transplant.The cumulative incidences of relapse at day 100 and 2 years were 15.1% (7.4-25.4%) and 40.9% (28.1-53.3%), resp.Two-year actual OS and DFS were 46.8% (34.0-58.5%) and 32.1% (20.9-43.8%), resp.Patients were divided into two groups: those received a myeloablative doses of i.v.BU (12.8 mg/kg, FB 4 group), and those received lower doses of i.v.BU (6.4-9.6 mg/kg, FB 2-3 group).No statistically significant differences were observed in patients' characteristics between the FB 4 and FB 2-3 groups (Table 1).The incidences of neutrophil engraftment, RRT and GVHD did not differ between the FB 4 and FB 2-3 groups, as summarized in Table 1.Remarkably, the incidences of NRM did not differ between the two groups (Figure 1a).In contrast, relapse rate at 2 years for the patients in the FB 4 group was 31.0% (15.9-47.5%), whereas 53.8% (32.3-71.3%) in the FB 2-3 group (P=0.03, Figure 1b).Interestingly, patients who received 8 Gy of TBI (n=8) showed a significantly higher incidence of relapse compared with those who had 0-4Gy of TBI (75 vs 35.5% at 2 years, P =<0.01), which could be a reflection of the fact that the TBI 8 Gy group included patients who received a lower dose of i.v.BU.Other pretransplant factors including age (≥55 vs <55 years), disease status (high vs standard), HCT-CI (≥2 vs <2 score), HLA disparities (2/6 vs 1/6), number of TNC infused (≥2.5x10*7/kg vs <2.5x10*7/kg), GVHD prophylaxis (TAC alone vs TAC+MMF) and dose of Mel (80 vs 120-140 mg/m2) did not correlate with incidence of NRM and relapse (data not shown).Prior Allo-SCT was the only significant factor associated with a higher NRM in univariate anal. (P<0.01) and in multivariate anal. (HR=6.66, 95% CI 2.29-19.3, P<0.01).FB 4 group was the only significant factor associated with a lower relapse rate even in multivariate anal. (HR=0.88, 95% CI 0.80-0.97, P=0.01).Two-year OS of FB 4 and FB 2-3 were 58.3% (40.7-72.4%) and 30.8% (14.6-48.5%), resp., and 2-yr DFS of FB 4 and FB 2-3 were 41.3% (25.2-56.7%) and 19.2% (7.0-36.0%), resp. (Figure 1c and d).The differences reached statistical significance for both OS (P=0.04) and DFS (P=0.04) in univariate anal., but not in multivariate anal.Prior Allo-SCT was the only significant factor for poor OS rate in multivariate anal. (HR=2.72, 95% CI 1.09-6.79, P=0.03).This study clearly demonstrated feasibility of i.v.BU/Flu+Mel or TBI regimen in CBT.In the setting of CBT, a lower engraftment rate using BU/Flu-based regimen was reported,2, 5, 6 likely owing to insufficient immunoablation associated with BU.7.As cord blood contains functionally immature lymphocytes and the total number of T cells are small,8 more intensive immune suppression before transplant would be crucial to ensure engraftment compared with BM or PB SCT.9.Our data here demonstrated that addition of Mel or TBI to BU/Flu regimen, expected to increase lymphoablative effect, is sufficient for engraftment following CBT.Secondly, our data confirmed that no addnl. toxicities were observed by increasing dose of i.v.BU from 6.4-9.6 to 12.8 mg/kg, even for patients having high-risk disease with old age and/or comorbidities.Some investigators confirmed its safety even in patients with higher age (up to 70 years old) and/or comorbidities.10, 11, 12 Finally, FB 4 regimens could also have an impact on reducing relapse rate.Despite the fact that higher doses of TBI or Mel were added to patients in the FB 2-3 group than to those in the FB 4 group, the relapse rate was lower in the FB 4 group, which could possibly indicate that a myeloablative dose of i.v.BU is more potent in disease control.Previous attempts to decrease the intensity of conditioning regimens have not resulted in improved survival, because any reduction in NRM was offset by higher relapse.13.Myeloablative doses of i.v. BU could be an ideal in this regard.In conclusion, our results clearly demonstrated that an i.v.BU/Flu+Mel or TBI regimen is feasible in CBT.Myeloablative dose of i.v. BU does not increase NRM even in patients having high-risk disease with old age and/or comorbidities, and could possibly be associated with decrease of relapse.As this is a retrospective study including small and heterogeneous groups of patients with various characteristics, the results should be re-confirmed by larger-scale prospective studies, which are now going on throughout Japan.
