A prospective multicenter study of unrelated bone marrow transplants using a reduced-intensity conditioning regimen with low-dose ATG-F

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Since Slavin et al.1 introduced a reduced-intensity conditioning (RIC) regimen using fludarabine (Flu), busulfan (Bu) and anti-T-lymphocyte globulin (ATG), similar regimens have been used worldwide.2, 3 Finke et al.4 reported that following a myeloablative conditioning regimen, ATG-Fresenius (ATG-F) administered as prophylaxis for GvHD reduced the incidences of acute and chronic GvHD without compromising survival in patients with unrelated hematopoietic stem cell transplantations.5 The major unresolved issue is the optimal dose of ATG in different conditioning regimens and populations. First, in terms of the conditioning regimen, Soiffer et al.6 reported that the addition of ATG to a RIC regimen was associated with inferior overall survival (OS) due to increased rates of relapse and non-relapse mortality (NRM),4 in contrast to the beneficial impact found with a myeloablative regimen.4 A large European Society for Blood and Marrow Transplantation (EBMT) study did not observe a negative impact of ATG<6 mg/kg on the outcome following a RIC regimen.7 Thus, the adverse effects might be the consequence of profound immunosuppression due to an excessive dose of ATG. These results suggest the possibility that the reduced dose of ATG might be appropriate in the setting of RIC. Second, in terms of ethnicity, it is well known that the risk of GvHD is lower in Asian than in Caucasian populations.8, 9, 10 Therefore, the dose of ATG might be reduced in Asian populations. Our group previously reported the clinical outcome in patients who underwent unrelated bone marrow transplantation (BMT) using low-dose ATG-F.11, 12 The incidence of acute and chronic GvHD were low considering patient characteristics such as HLA disparity and the low dose of ATG-F.

To confirm the feasibility of this RIC regimen containing low-dose ATG-F in combination with Flu plus Bu, we prospectively conducted a multicenter study in patients with hematological malignancies. This was a multicenter prospective study that assessed the feasibility of a RIC regimen containing Flu (30 mg/kg x 6 days), IV Bu (3.2 mg/kg x 2 days), and ATG-F (5 mg/kg per day at day −2). Twenty-seven patients were enrolled from January 2009 to March 2012. This study was approved by the Institutional Review Board of the National Cancer Center, Tokyo, Japan.

The primary end point was the probability of survival with neutrophil engraftment at day 100 after unrelated BMT (expected 90% and threshold 70%). Secondary end points included neutrophil recovery, OS, NRM, acute GvHD and chronic GvHD. Neutrophil recovery and graft failure were defined as previously reported.13 The probability of OS was calculated by the Kaplan–Meier method. A Cox proportional-hazards regression model was used to analyze OS. The cumulative incidences of engraftment, NRM, GvHD, and discontinuation of immunosuppressive drugs were evaluated using a model by Fine and Gray. The variables evaluated in these analyses were as follows: sex, patient age (age 55 years vs age <55 years), disease AML and myelodysplastic syndrome (MDS) vs malignant lymphoma), and HLA disparity assessed by allele typing of HLA A, B, C and DRB1. All statistical analyses were performed with EZR (Saitama Medical Center, Jichi Medical University, Saitama, Japan), which is a graphical user interface for R (The R Foundation for Statistical Computing, version 2.13.0).14

The characteristics of the 27 patients are shown in Table 1. In indolent lymphoma, only four patients (40%) were in CR (CR1, n=1; CR3, n=3) before unrelated BMT. In aggressive lymphoma, three patients (50%) were in CR.

Table 1 Patient characteristics

Surviving patients were followed-up for a median of 1316 days post transplant (range, 284−1826 days). Three patients were excluded from the analysis of survival with engraftment at day 100 after unrelated BMT because they received chemotherapy for the progression of disease before day 100 post transplant. Twenty of 24 evaluable patients (83.3%, 95% confidence interval (CI) 62.6−95.3%) fulfilled the criteria of the primary end point. The causes of failure were idiopathic pulmonary syndrome (n=1), secondary graft failure (n=1) and neutropenia associated with the progression of the underlying disease (n=2).

Neutrophil engraftment was observed in all patients (median 16 days, range 12−22 days, Figure 1a). The median percentages of donor T-cell chimerism at day 28, day 56 and day 84 were 100% (range, 0–100%), 98.5% (range, 0–100%) and 99.5% (range, 12–100%), respectively. The median percentages of donor granulocyte chimerism at day 28, day 56 and day 84 were 100% (range, 64–100%), 100% (range, 0–100%), and 100% (range, 75–100%), respectively.

Figure 1
figure1

(a) Engraftment, (b) grade II acute GvHD, (c) grade II acute GvHD grouped according to the number of HLA mismatches, (d) moderate/severe chronic GvHD, (e) discontinuation of immunosuppressive drugs is indicated by the lower curve (The competing risks of relapse and death are shown by the upper curve), (f) Non-relapse mortality, (g) relapse, (h) OS and (i) OS grouped according to disease type (AML/MDS vs lymphoma). IS=immunosuppressive.

The cumulative incidence of grade II acute GvHD was 37.0% (Figure 1b). No patient developed grade III–IV acute GvHD. Stratified according to the number of HLA mismatches, the incidences of grade II acute GvHD were 23.5% in patients without an HLA mismatch, 40.0% in those with a one-locus mismatch and 80.0% in those with a 2-loci mismatch, respectively (P=0.024, Figure 1c). Multivariate analysis showed that the presence of HLA 2-loci mismatches was associated with an increased risk of grade II acute GvHD (HLA one-locus mismatch, hazard ratio 1.64, 95% CI 0.36–7.39, P=0.52; HLA 2-loci mismatch, hazard ratio 6.33, 95% CI 1.46–27.5, P=0.014).

The cumulative incidence of moderate/severe chronic GvHD according to the National Institutes of Health criteria was 37% (Figure 1d). Two patients developed severe chronic GvHD (lung (n=1) and poor performance status (n=1)). Following the classical criteria of limited/extensive chronic GvHD, the cumulative incidence of extensive chronic GvHD was 18.5%. The cumulative incidences of the discontinuation of immunosuppressive drugs are shown in Figure 1e.

The cumulative incidence of 3-year NRM was 7.4% (Figure 1f). The cumulative incidence of 3-year relapse/progression was 29.8% (Figure 1g). The probability of 3-year OS was 73.7% (Figure 1h). Grouped according to the underlying hematological malignancy (AML/MDS vs lymphoma), the probabilities of 3-year OS were 53.0 and 87.5% in patients with AML/MDS and lymphoma, respectively (Figure 1i).

Here, we conducted a multicenter prospective phase II study of a RIC regimen containing Flu, IV Bu and low-dose ATG-F. There were no cases of severe acute GvHD, and the incidence of NRM at 3 years was only 7.4%. These results are consistent with those of our previous single-center retrospective study.11 The promisingly low incidence of NRM in the ATG-F group is an important finding in this study, considering unfavorable patient characteristics such as old age and HLA disparity.

The major limitation of this study was the low number of patients included and their heterogeneity (various diagnoses and various HLA-compatibility). The benefit of low-dose ATG-F should be confirmed in a randomized trial.

In Western countries, the total dose of ATG-F for GvHD prophylaxis is usually 30–60 mg/kg.4 In Asian countries, a smaller dose of ATG is commonly used as the incidence of GvHD itself in Asian patients has been shown to be lower than that in Caucasian patients.8, 9, 10 In our previous study, we used ATG-F at a dose of 5 mg/kg or 10 mg/kg.11, 12 Use of the lower dose of ATG (5 mg/kg) did not increase the incidence of GvHD and was associated with similar clinical outcomes compared with the higher dose (10 mg/kg), although the study size was limited.11, 12 A French study showed that 5 mg/kg of thymoglobulin (ATG-T) was associated with a lower incidence of GvHD compared with 2.5 mg/kg of ATG-T in combination with a RIC regimen using Flu and Bu, suggesting that 5 mg/kg of ATG-T could be appropriate in this population.15 Therefore, the optimal dosage of ATG would depend on the type of ATG, conditioning regimen and ethnicity.

The beneficial impact of ATG on the reduction of chronic GvHD has been a popular topic recently because chronic GvHD is now considered to be an important complication after allogeneic hematopoietic stem cell transplantation, causing late NRM and decreased quality of life. In this study, the incidence of extensive chronic GvHD was reasonably low. Importantly, bronchiolitis obliterans was observed in only one patient. Furthermore, most patients were able to discontinue immunosuppressive drugs, suggesting a low frequency of uncontrolled/persistent chronic GvHD using this regimen, as we previously reported.11

In this study, malignant lymphoma was unexpectedly the most common indication, and the clinical outcomes of these patients were favorable, taking their high-risk pretransplant disease status into consideration. In patients with malignant lymphoma, the optimal RIC regimen is still undetermined. Therefore, a conditioning regimen including Flu, Bu and low-dose ATG-F may be an option for patients with malignant lymphoma.

In conclusion, the use of low-dose ATG-F in combination with a Flu plus Bu−based RIC regimen was associated with a promisingly low incidence of acute GvHD without compromising OS. The role of low-dose ATG-F as prophylaxis for GvHD should be further assessed with a uniform conditioning regimen in a prospective randomized-control trial.

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Acknowledgements

We thank the medical, nursing, data-processing, laboratory and clinical staff at the participating centers for their important contributions to this study and their dedicated patient care. This work was supported by grants from the Japanese Ministry of Health, Labour and Welfare and the National Cancer Research and Development Fund (23-A-28).

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Correspondence to S Fuji.

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Fuji, S., Kim, S., Yano, S. et al. A prospective multicenter study of unrelated bone marrow transplants using a reduced-intensity conditioning regimen with low-dose ATG-F. Bone Marrow Transplant 51, 451–453 (2016) doi:10.1038/bmt.2015.268

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