Clinical Trials

Influence of two different doses of antithymocyte globulin in patients with standard-risk disease following haploidentical transplantation: a randomized trial

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Abstract

To evaluate the effect of the different doses of antithymocyte globulin (ATG) on the incidence of acute GVHD among patients receiving hematopoietic SCT without ex vivo T-cell-depletion from haploidentical donors, 224 patients with standard-risk hematological malignancy were randomized in this study. One hundred and twelve patients received 6 mg/kg ATG, whereas the remaining patients received 10 mg/kg ATG. This study was registered at http://www.chictr.org as No. ChiCTR-TRC-11001761. The incidence of grade III–IV acute GVHD was higher in the ATG-6 group (16.1%, 95% confidence interval (CI), 9.1–23.1%) than in the ATG-10 group (4.5%, CI, 0.7–8.3%, P=0.005, 95% CI for the difference, −19.4% to −3.8%). EBV reactivation occurred more frequently in the ATG-10 group (25.3%, 17.1–33.5%) than in the ATG-6 group (9.6% (4.0–15.2%), P=0.001). The 1-year disease-free survival rates were 84.3% (77.3–91.3%) and 86.0% (79.2–92.8%) for the ATG-6 group and ATG-10 groups, respectively (P=0.88). In conclusion, although 6 mg/kg ATG applied in haploidentical transplantation decreased the risk of EBV reactivation compared with 10 mg/kg ATG, this treatment exposes patients to a higher risk for severe acute GVHD.

Introduction

Antithymocyte globulin (ATG) has been used in the conditioning regimen to prevent severe GVHD in haploidentical hematopoietic SCT (HSCT), and our previous study presented encouraging results.1 However, the limitations associated with the use of ATG as a regimen for in vivo T-cell depletion (TCD) include the occurrence of delayed immune reconstitution and an increased risk of severe infections, depending on the dose of ATG administered.2 Several previous studies have suggested suitable doses of ATG in matched unrelated transplantations.3, 4 However, to date, the optimal dose of ATG with respect to the prevention of severe GVHD following the haploidentical transplantation is unknown.

In our recently reported retrospective study, we reduced the total dose of ATG from the traditional 10 mg/kg in our classic regimen to 6 mg/kg for refractory/relapsed patients undergoing haploidentical HSCT. We observed that the reduction of the total dose of ATG to 6 mg/kg produced similar rates of engraftment, GVHD and survival compared with the 10 mg/kg dose of ATG.5 Based on these findings, we set out to extend the use of 6 mg/kg ATG to standard-risk patients. Therefore, we initiated the current prospective randomized study to evaluate the effect of the two different doses of ATG in conditioning regimens on graft failure, GVHD, relapse and survival among standard-risk patients receiving haploidentical HSCT. We postulated that the use of 6 mg/kg ATG might reduce adverse events without increasing the risk of GVHD.

Patients and methods

Study design

This was an open-label, prospective, randomized trial initiated by Peking University People’s Hospital, Institute of Hematology, Beijing, China. The aim of the study was to compare two different total doses of ATG (6 mg/kg vs 10 mg/kg) in patients receiving myeloablative conditioning before allogeneic (allo)-HSCT from haploidentical donors in our center. Patients were recruited between December 2010 and May 2012. All research subjects were enrolled on a protocol approved by the Institutional Review Board of Peking University and signed informed consent. This study was conducted in accordance with the Declaration of Helsinki. The study was registered at http://www.chictr.orgas no. ChiCTR-TRC-11001761.

The primary end points were the occurrence of grades III–IV acute GVHD (aGVHD). The secondary end points were the rates of engraftment, aGVHD grades II–IV, chronic GVHD (cGVHD), infection, relapse, non-relapse mortality (NRM), disease-free survival (DFS), and OS. Analyses of individual secondary end points were exploratory assessments and not prospectively defined and were not intended to be a primary determination of outcome superiority.

Non-inferiority was predefined as a difference in the incidence of grades III–IV aGVHD between the ATG-6 and ATG-10 groups of no more than 15 percentage points (by reference to the reported prospective studies regarding the effect of ATG on GVHD2). On the assumption of an incidence of grades III–IV aGVHD of 15%, a sample of 89 patients who could be evaluated in each treatment group (a total of 178) was required to demonstrate non-inferiority at the two-sided significance level of 5% with a power of 80%. Thus, a 95% confidence interval (CI) for the difference in the incidence of grades III–IV aGVHD within 15% was required for ATG-6 to be considered not inferior to ATG-10. On the assumption of a 20% loss of patients, a total sample size of 214 subjects was required. We intentionally over-recruited patients because of a delay in primary events compared with our original expectations. All comparisons were performed according to the intention-to-treat principle. Figure 1 presents the trial profile.

Figure 1
figure1

Study flow diagram.

To guarantee a correct and consistent assessment of aGVHD and cGVHD, adverse events and detailed structured data of organ involvement related to aGVHD and cGVHD were recorded in the case report form. A panel of blinded investigators with expertise in the study reviewed and classified all documented GVHD. To ensure data uniformity, this panel composed of hematologists was blinded as to the patients’ treatment assignments. Independent clinical monitoring was performed regularly, and the data recorded in the case report forms were all verified by inspection of the source data in the patients’ charts.

Patient eligibility

Patients aged 15–60 years-old with standard-risk hematological malignancies who were scheduled to receive haploidentical HSCT were eligible for inclusion in this trial. Patients were eligible for haploidentical HSCT if a matched sibling donor or a suitable closely HLA-matched unrelated donor was unavailable or if there was insufficient time for an unrelated donor search due to disease status (acute leukemia in the second CR (CR2), myelodysplastic syndrome with >10% blasts or CML in the second chronic phase). For the patients transplanted in CR1, when a suitable donor was available, eligible patients proceeded to HSCT after receiving 2–4 cycles of consolidation therapy.6 Patients with malignancies were categorized as ‘standard risk’ if they were in the first or second CR (CR1 or CR2) of acute leukemia, were in the chronic phase of CML or had myelodysplastic syndrome with <20% blasts.

HLA-A and HLA-B alleles were determined using low-resolution molecular typing with PCR sequence-specific primers (PCR-SSPs). HLA-DRB1 was determined using high-resolution molecular typing with PCR-SSPs. Family mismatched donors and recipients were required to at least share complete haplotypes.

Patients who had received previous allo-HSCT and/or autologous transplantation were not eligible for inclusion in this trial. Patients were not included if they had existing contraindications to HSCT or a known hypersensitivity to rabbit immunoglobulin antibodies.

Randomization and masking

After obtaining written consent, the donor–recipient pairs were randomly assigned in a 1:1 ratio to the two treatment arms (the 6 mg/kg ATG group or the 10 mg/kg ATG group) by the sub-investigator (treating physician of our transplant center) according to a computer-generated randomization system. Patients and independent individuals assessing outcomes and analyzing data were masked to treatment allocation to eliminate the subjective aspects of assessment and care that could potentially affect the outcome of such a comparison.

Transplant procedures

Patients were conditioned with intensive chemotherapy-based regimen (regimen 1). Patients with T-cell ALL (T-ALL) and incompletely eradicated tumor masses were conditioned with a TBI-based regimen (regimen 2). Regimen 1 consisted of the following: Ara-C (4 g/m2 per day i.v.) on days −10 and −9; BU, 12 mg/kg p.o. or 9.6 mg/kg i.v. in 12 doses on days −8, −7 and −6; CY, 1.8 g/m2 per day i.v. on days −5 and −4; and simustine (250 mg/m2) on day −3. Regimen 2 consisted of TBI (770 cGy in a single fraction) with particle shielding of the lungs on day −6, and the treatment from days −5 to −3 was the same as regimen 1.

Two different doses of ATG (Thymoglobulin; rabbit ATG, Imtix Sangstat, Lyon, France) were administered from days −5 to −2; patients in the ATG-10 group received 2.5 mg/kg per day, and patients in the ATG-6 group received 1.5 mg/kg per day. Patients received scheduled dexamethasone 5 mg/day as part of the administration of ATG. ATG-related diarrhea and grade III fever (according to the Common Terminology Criteria for Adverse Events), when present, were treated with additional dexamethasone, and the speed of the ATG infusion was reduced.

The G-CSF-mobilized, fresh and unmanipulated BM (G-BM) and peripheral blood (G-PB) harvests were infused into the recipients on the day of collection. Each patient received both G-BM and G-PB as previously described.1 G-CSF (5–10 μg/kg per day s.c.) was provided to all of the recipients from day 6 after transplantation until their WBC count exceeded 2 × 109 cells/L for 3 consecutive days.

GVHD prophylaxis and treatment

All of the transplant recipients received CsA, mycophenolate mofetil (MMF) and short-term MTX for GVHD prophylaxis.1 The primary dosage of CsA was 2.5 mg/kg/day i.v. from day −9 until bowel function returned to normal. At that point, the patient was switched to oral CsA. The whole blood CsA concentration was monitored weekly using a fluorescence polarization immunoassay (Cayman Chemical Company, Ann Arbor, MI, USA), and the dosage was adjusted to maintain a blood trough concentration of 150–250 ng/mL. In cases with no evidence of GVHD by day 180, the CsA dosage was gradually reduced. In cases with GVHD, CsA was continued. MMF was administered orally, 0.5 g every 12 h, from day 9 before transplantation to day 30 after transplantation. MMF was tapered from 0.5 g every 12 h to 0.25 g every 12 h on day 30 and was discontinued over days 45–60. The dosage of MTX was 15 mg/m2 i.v. on day 1 and 10 mg/m2 on days 3, 5 and 11 after transplantation. aGVHD was treated with steroids (methylprednisolone (MP) 1 mg/kg per day). If there was either inadequate or no response to primary therapy, anti-CD25 mAbs (basiliximab, Novartis Pharma AG, Basel, Switzerland) were administered to the patient. cGVHD was treated with CsA and steroids.

CMV and EBV monitoring

CMV and EBV monitoring was performed once a week using a real-time Taqman CMV DNA PCR and EBV DNA PCR (Sino-American Biotech, Beijing, China) until day 100 after allo-HSCT, then once every 2 weeks until day 180 after HSCT, followed by once every month until 1 year after HSCT. However, in patients with a CMV or EBV reactivation, monitoring was performed twice a week before day 100. CMV or EBV reactivation was defined as a CMV DNA viral load >600 copies/mL or an EBV DNA viral load >500 copies/mL at any time after HSCT for at least one measurement.

CMV disease and post-transplant lymphoproliferative disease (PTLD) prophylaxis

For prophylaxis against CMV disease, ganciclovir (10 mg/kg/day) was administered i.v. twice daily from day 9 to day 2 before transplantation. And pre-emptive ganciclovir therapy (10 mg/kg/day) or foscarnet (90–120 mg/kg/day) was administered to patients who had two consecutive positive tests for CMV and was continued until the CMV DNA monitoring was negative on two occasions.

For prophylaxis against PTLD, we administered anti-CD20 antibody (Rituximab) to all patients who were positive with >103 copies of EBV as a pre-emptive therapy.

DLI

Reasons for giving DLI were as follows: (1) intervention for leukemia relapse: modified DLI was administered to minimal residual disease-positive patients without active GVHD;7 (2) treatment of leukemia relapse: when a hematological relapse was diagnosed after HSCT, the relapse was treated with chemotherapy followed by a therapeutic DLI;8 (3) G-CSF-mobilized peripheral blood cells for poor engraftment; and (4) DLI for severe CMV or EBV infection. The number of patients receiving DLI for various reasons is listed in Table 1.

Table 1 Patient and donor characteristics GVHD distribution and relapse rate according to ATG dose

Definitions and evaluation

aGVHD was defined and graded from 0 to IV based on the pattern and severity of organ involvement;9 grades III–IV aGVHD manifest as serious clinical features on the skin, liver and/or gut. CMV or EBV reactivation was defined as described above. cGVHD was defined and graded according to the National Institute of Health criteria:10 that is, mild cGVHD reflects the involvement of no more than 1 or 2 organs/sites (except for lung) with a maximum score of 1; moderate cGVHD involves at least 1 organ/site with a score of 2 or 3 organs/sites with a score of 1 (or lung score 1); and severe cGVHD is diagnosed when a score of 3 is given to any organ (or lung score 2). The diagnosis is mainly based on clinical manifestations. Grades and severity of aGVHD/cGVHD are maximal. Primary engraftment failure was defined as a slow recovery of ANC counts 0.5 × 109/L and platelet counts 20 × 109/L by +30 day after allo-HSCT. Secondary engraftment failure was defined as a decrease in blood cell counts to the above-mentioned levels for at least 30 consecutive days after successful and prompt hematopoietic engraftment. Relapse was defined by the morphological evidence of disease in the peripheral blood, BM or extramedullary sites. Patients exhibiting minimal residual disease (for example, the presence of BCR/ABL RNA transcripts by PCR) were not classified as having relapsed. NRM was defined as death without preceding relapse, and OS referred to patients who survived until the final follow-up time point. DFS was defined as survival in continuous CR.

Immune recovery after transplantation was assessed between December 2010 and May 2011 using the median number of absolute CD4+ cells, CD3+ cells and CD19+ cells on days 30, 60 and 90 based on lymphocyte immunophenotyping (four-color analysis).

Statistical analysis

Variables of the two groups were compared using the χ2 statistic for categorical variables and the Mann–Whitney test for continuous variables. Cumulative incidence curves were used in a competing risk setting, with death from relapse treated as a competing event to calculate the probabilities of NRM and with death from other causes as a competing risk for GVHD, engraftment, EBV and CMV reactivation and relapse. The time to GVHD was defined as the time from HSCT to the onset of any grade of GVHD; GVHD occurrences were studied as time-dependent variables. The probabilities of OS and DFS were estimated using the Kaplan–Meier method. Unless otherwise specified, all of the reported P-values were based on two-sided hypothesis tests. Alpha was set at 0.05. S Plus 2000 (Mathsoft, Seattle, WA, USA) was used for most of the analyses. The final follow-up was performed on 10 December 2012.

Results

Study population

A total of 224 patients were randomized in this trial. All of the patients completed the prescribed ATG dose regimen. The groups were balanced with respect to patient and donor characteristics (Table 1).

Lower dose of ATG in conditioning regimen increased the risk of aGVHD and cGVHD

The cumulative incidence of grade II–IV aGVHD on day 100 was 41.9% (CI, 32.5–51.3%) vs 25.0% (16.8–33.2%) in the ATG-6 and the ATG-10 groups, respectively (P=0.005, Figure 2b). Data, including the organ distribution, on grades II–IV aGVHD according to the ATG dose are presented in Table 1. The incidence of grade III–IV aGVHD was also higher in the ATG-6 group than in the ATG-10 group, 16.1% (9.1–23.1%) vs 4.5% (0.7–8.3%), respectively (P=0.005, Figure 2a, 95% CI for the difference, −19.4% to −3.8%). This 95% CI falls outside of the predefined lower limit of −15 percentage points. aGVHD developed at a median time of 25 days (range, 9–82 days) and 28 days (range, 9–100 days) after HSCT in the ATG-6 and ATG-10 groups, respectively (P=0.24). Five (4.5%) and none of the patients in the ATG-6 and ATG-10 groups died of aGVHD (P=0.02), respectively. Among the patients suffering from aGVHD, one patient in the ATG-10 group developed aGVHD after DLI. Univariate analyses of the risk factors for grade III–IV aGVHD are presented in Table 2.

Figure 2
figure2

The incidences of aGVHD grades III–IV (a), aGVHD grades II–IV (b), moderate-to-severe cGVHD (c), platelet engraftment (d), EBV reactivation (e), relapse (f), NRM (g), probabilities of OS (h) and DFS (i) for the two groups.

Table 2 Univariate analysis of risk factors for 100-day cumulative incidence of grades III–IV acute GVHD

The cumulative incidence of cGVHD within 1.5 years was 64.6% (CI, 54.6–74.6%) vs 44.8% (35.0–54.6%) in the ATG-6 and the ATG-10 groups, respectively (P=0.007). The cumulative incidence of moderate-to-severe cGVHD within 1.5 years was 33.5% (CI, 23.3–43.7%) vs 26.4% (17.6–35.2%) in the ATG-6 and the ATG-10 groups, respectively (P=0.28, Figure 2c). Data on the severity of cGVHD according to the ATG dose are presented in Table 1. Among the patients suffering from cGVHD, four and five patients in the ATG-6 and ATG-10 group developed cGVHD after DLI, respectively.

Different ATG dose did not affect engraftment

The median myeloid engraftment time was 12 days (range, 9–23 days) and 12 days (range, 9–26 days) in the ATG-6 (112 patients) and the ATG-10 groups (111 patients, P=0.88), respectively. The 100-day cumulative rate of platelet engraftment was comparable between the two groups (91.9% (86.7–97.1%) vs 88.7% (82.5–94.9%), P=0.19, Figure 2d). The median platelet engraftment time was 13 days (range, 7–169 days) and 14 days (range, 7–288 days) for the ATG-6 and the ATG-10 groups (P=0.36), respectively. One patient in the ATG-10 group did not achieve ANC engraftment until day 30 and underwent a second allo-HSCT, but treatment failed again, and the patient died on day 30 after the second HSCT. One and four patients in the ATG-6 and ATG-10 groups, respectively, suffered secondary engraftment failure (P=0.18).

Adverse events evaluation

Higher doses of ATG required higher levels of corticosteroids to resolve toxicity

Although the incidence, duration and severity of diarrhea and fever were comparable between the two groups, the patients in the ATG-10 group were treated with more corticosteroids between day −5 and day −1; the median total dose of dexamethasone (including the 5 mg/day scheduled dexamethasone) treatment was 20.0 mg (range, 20.0–34.2 mg) vs 23.0 mg (range, 20.0–45.0 mg) for the ATG-6 and ATG-10 groups, respectively (P=0.001). The proportion of patients requiring additional corticosteroids was 43% vs 68% (P=0.001). This additional dexamethasone contributed to the final equal toxicities with regard to diarrhea and fever between the two groups. The incidence and severity of other toxicities were comparable between the two treatment arms.

The reduced dose of ATG decreased the risk of EBV reactivation

The 1-year cumulative incidence of EBV reactivation was 9.6% (4.0–15.2%) vs 25.3% (17.1–33.5%) in the ATG-6 and the ATG-10 groups (P=0.001, Figure 2e), respectively. The incidence of PTLD was 1.8% (0–4.2%) vs 8.0% (3.0–13.0%) in the ATG-6 and the ATG-10 groups (P=0.03), respectively. The 1-year cumulative incidence of CMV reactivation was 75.0% (66.8–83.2%) vs 78.6% (75.2–82.0%) in the ATG-6 and the ATG-10 groups (P=0.40), respectively. Two (1.8%) and 9 (8.0%) patients in the ATG-6 and ATG-10 groups died of virus-related infections (P=0.03, Table 3), respectively. As shown in Table 3, one and three of the patients in the ATG-6 and ATG-10 groups died of PTLD, respectively. With respect to the incidences of septicemia or invasive fungal infection, there was no significant difference between the two treatment arms in our trial (P=0.093 and P=0.837, respectively), although there was a trend for a higher incidence of septicemia in the ATG-10 group than in the ATG-6 group (11.6% vs 5.4%, respectively).

Table 3 Causes of death

Higher dose of ATG delayed early immune reconstitution

A total of 65 patients (33 and 32 in the ATG-6 and ATG-10 arms) with complete sets of immunological data at defined end points were analyzed. At the end of the first month, patients in the ATG-6 group had significantly higher levels (cells/μl) of CD3+ and CD4+ T cells and CD19+ B cells (173.3 (range, 52.4–1428.1) vs 85.5 (4.0–1443.3), P=0.04; 41.9 (8.4–280.3) vs 21.7 (0.4–293.7), P=0.01; and 11.9 (0.7–28.6) vs 2.7 (0.1–731.8, P=0.002, respectively, Figure 3). However, no significant differences were observed between the two treatment arms at the end of the second and third months after HSCT.

Outcome of transplantation

Up to 10 December 2012, the median follow-up time was 474 days (range, 227–717) and 439 days (range, 216–720) after HSCT among survivors in the ATG-6 and the ATG-10 groups, respectively (as shown in Table 1). The 1-year incidence of relapse was 7.6% (2.8–12.4%) and 4.6% (0.8–8.4%) in the ATG-6 and the ATG-10 groups (P=0.38, Figure 2f), respectively. The effects of the ATG dose on the rates of leukemia relapse for each major diagnosis are presented in Table 1. The 1-year probabilities of NRM, OS and DFS did not differ between the ATG-6 and the ATG-10 groups (8.1% (2.9–13.3%) vs 10.3% (4.9–15.7%), P=0.50, Figure 2g; 88.4% (82.4–94.4%) vs 87.0% (80.4–93.6%), P=0.96, Figure 2h; and 84.3% (77.3–91.3%) vs 86.0% (79.2–92.8%), P=0.88, Figure 2i; respectively).

Discussion

The current results demonstrated that in haploidentical HSCT without in vitro TCD, the use of 6 mg/kg ATG did not fulfill the protocol-defined criteria for non-inferiority to 10 mg/kg ATG with respect to the incidence of severe aGVHD. However, the significant difference in the rates of severe aGVHD and GVHD-related death between the ATG-6 and ATG-10 groups favors giving patients 10 mg/kg ATG at the present time.

Dose-finding studies for ATG have been performed in the HLA-identical sibling donor (ISD) setting11, 12, 13 and unrelated donor (URD) setting.2, 4, 14, 15, 16 A total dose of 4.5–5 mg/kg and 7.5 mg/kg ATG has been recommended in the ISD and the URD settings, respectively. In a recent report, a subset analysis of the URD HSCT recipients demonstrated a significantly higher (P=0.005) mortality rate in the 10 mg/kg ATG dose recipients (18/26, 69%) than in the 7.5 mg/kg dose recipients (7/17, 29%), and this large difference stemmed from a higher day-100 mortality mostly attributable to non-relapse and non-GVHD mortality in the high-dose ATG group (10/26, 39%) than in the low-dose group (1/24, 4%; P=0.003).16 In the haploidentical setting, ATG in the conditioning provided a major contribution to controlling alloreactivity.17 ATG has a key role in our unique haploidentical preparative regimen, and our recent reports validated its use in haploidentical HSCT both for patients with advanced-stage leukemia18 and for patients with severe aplastic anemia.19 The current report revealed that the dose of ATG in the haploidentical setting was as important as that in other HSCT settings. However, different transplant modalities may require different doses of ATG to effectively inhibit the target immune cells. In the current study, 6 mg/kg ATG resulted in a higher rate of severe GVHD and GVHD-related death than 10 mg/kg ATG. However, rates of moderate-to-severe cGVHD were comparable, and survival outcomes were similar between the two arms despite the different proportions of causes of death, suggesting that decreased mortality from non-GVHD complications in the ATG-6 group was offset by the increased severe GVHD.

Furthermore, we noted a much lower incidence of grade III–IV aGVHD in the control arm (4.5%) compared with that from our previous study, which reported a rate of 13.4%.1 The difference between the rate of the current report and the historical control may be due to the improvement in GVHD prevention and management over the years as well as the different proportions of donor gender and family relationships in the two reports, with more male donors and more child-to-parent pairs in the current study population (data not shown). These factors were found to influence the incidence of GVHD in our recent report regarding haploidentical HSCT using the same modality.20 Before that published report, since 2009, we intentionally chose young (especially offspring), male donors who were identified to be associated with a lower rate of GVHD20 under our protocol.

The prospective and randomized design of the current study laid the foundation for the results’ reliability. In our previous retrospective study, the incidence of aGVHD was comparable between patients with refractory/relapsed leukemia receiving 10 mg/kg ATG and patients receiving 6 mg/kg ATG.5 Disparate study designs and different study populations between the two studies may have contributed to the contradictory conclusions. The prospective and randomized design of the current study may make the current results more representative. It is unlikely that the reduction of GVHD in the ATG-10 group could be attributed to the higher dose of corticosteroids used between day −5 and day −1 for the resolution of toxicity. In our current study, the median total dosage of corticosteroids used between day −5 and day −1 in the ATG-10 group was only 3 mg more than that in the ATG-6 group, and the median time to GVHD occurrence was comparable between the two groups. Chao et al.21 reported a prospective randomized study comparing CsA, MTX and MP vs CsA and MTX in patients receiving HSCT from ISD. MP began on day 7 at 0.5 mg/kg/day and then increased to 1 mg/kg/day from day 15 to day 28. The results demonstrated that the use of MP appeared to delay the onset of GVHD (22 days for the two-drug regimen compared with 40.5 days for the three-drug regimen, P=0.02). The corticosteroid use in our current study occurred earlier, and the dosage gap between the two arms was much lower than that in Chao’s report. However, this variable cannot be completely excluded. In addition, the significantly lower rate of severe aGVHD in the ATG-10 group is particularly notable considering that this group required more DLI (as shown in Table 1), but GVHD did not increase as a result, which is in accordance with our previous report regarding our modified DLI modality.7, 18

In the current report, it appears that the higher dose increased EBV infection and virus-related death. These results were consistent with other researchers’ findings.2, 14 The propensity of patients receiving 10 mg/kg ATG to contract severe virus-related infections is associated with significantly lower lymphocyte counts on day 30. Duval et al.22 reported similar results. Although it was not prospectively subject to any hypothesis, the clinical significance of this result deserves further prospective investigation. Reducing the severity of aGVHD in the ATG-10 group was insufficient to reduce NRM. The incidence of severe aGVHD was not high in either the ATG-6 group (16.1%) or the ATG-10 group (4.5%); consequently, even in the ATG-6 group, GVHD-related death occurred in 4.5% of the patients, whereas none of the patients in the ATG-10 group died of GVHD. However, patients in the ATG-10 group had a higher incidence of infection-related death compared with the ATG-6 group. Therefore, a beneficial effect in the ATG-10 group in reducing severe aGVHD did not translate into lower NRM or higher OS because of the increased risk of death from causes other than GVHD, especially virus-related death. These results were inconsistent with the findings of two randomized studies in patients receiving or not receiving ATG.2, 23 Despite comparable NRM and OS between the two study groups, better GVHD prevention may still represent a reasonable approach. A further increase in dosage may result in poorer immune reconstitution and consequently increased incidence of infection.24

We hypothesized that the use of 6 mg/kg ATG might reduce adverse events. Although the number of patients who experienced diarrhea and fever was comparable between the two groups, one must keep in mind that the patients in the ATG-10 group were treated with more corticosteroids between day −5 and day −1. Therefore, these results suggest that the toxic effect regarding diarrhea and fever was actually more prominent among patients receiving 10 mg/kg ATG compared with that of the ATG-6 group. However, the toxic effects of ATG were temporary and did not result in an increased early death (within 30 days) or affect overall transplant outcomes.

There are some limitations to this study. First, the median follow-up time among survivors was relatively short for evaluating cGVHD and long-term outcomes. Long-term follow-up data must be analyzed in the future. Second, as the decreased mortality from non-GVHD complications in the ATG-6 group was offset by the increased severe GVHD, the optimal dose was left undetermined. A middle dose, such as 7.5 mg/kg ATG, the common dose for unrelated HSCT, need to be evaluated. Third, given that some other centers in China use our modality to treat haploidentical patients, a prospective, multi-center study is needed to confirm these results.

In conclusion, 6 mg/kg ATG applied in a conditioning regimen for haploidentical transplant recipients without in vitro TCD exposes patients to a higher risk for severe aGVHD compared with the 10 mg/kg ATG regimen. It appears that the higher-dose ATG regimen resulted in increased immunosuppression. Therefore, further studies are necessary to determine whether 7.5 mg/kg is appropriate before the optimal dose of ATG can be established.

Figure 3
figure3

Reconstitution of CD19+ cells, CD3+ cells and CD4+ cells for the two groups.

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Acknowledgements

This work was supported (in part) by the National High Technology Research and Development Program of China (Program 863) (Grant No. 2011AA020105), The Key Program of National Natural Science Foundation of China (Grant No. 81230013), the Scientific Research Foundation for Capital Medicine Development (Grant No. 2011-4022-08) and the National Natural Science Foundation of China (Grant Nos. 30971292 and 30725038). We thank American Journal Experts for reviewing the paper in English. We thank every faculty member who has participated in these studies.

Author contributions

XJH designed and performed the study. YW and HXF collected data. YW and XJH did the data analysis and wrote the paper. All the authors contributed to the interpretation of the data and approved the final version.

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Correspondence to X-J Huang.

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The authors declare no conflict of interest.

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Keywords

  • antithymocyte globulin
  • HLA-mismatched
  • transplantation

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