Infectious complications following allogeneic HLA-identical sibling transplantation with antithymocyte globulin-based reduced intensity preparative regimen

Abstract

In the setting of reduced-intensity conditioning (RIC) regimens for allogeneic stem cell transplantation (allo-SCT), the epidemiology of transplant-related infections is still poorly defined. In 101 high-risk patients who received an HLA-identical sibling allo-SCT after RIC, including fludarabine, busulfan and antithymocyte globulin (ATG), we report during the first 6 months a cumulative incidence of positive CMV antigenemia of 42% (95% CI 32–52%), developing at a median of 37 (range 7–116) days without evidence of CMV disease (median follow-up, 434 days). The cumulative incidence of bacteremia was 25% (95% CI 17–33%), occurring at a median of 67 (range 7–172) days, while patients had recovered a full neutrophil count. In all, 65% of the bacteremia (95% CI 49–81%) were gram negative. The cumulative incidence of fungal infections was 8% (95% CI 3–13%), with a median onset of 89 (range 7–170) days. In multivariate analysis, stem cell source (bone marrow; P=0.0002) was significantly associated with the risk of positive CMV antigenemia, while higher doses of prednisone (>2 mg/kg) represented the major risk factor for bacteremia (P=0.0001). Infectious-related mortality was 5% (95% CI 1–9%), with aspergillosis being the principal cause. Collectively, these results suggest that prospective efforts are warranted to develop optimal antimicrobial preventive strategies after RIC allo-SCT.

Introduction

Standard allogeneic stem cell transplantation (allo-SCT) from HLA-identical siblings has become a curative treatment option for some patients with hematological malignancies. Extensive data support an important role for a graft-versus-tumor (GVT) effect in eradicating tumor cells in patients who receive allo-SCT.1,2 However, because of the high incidence of procedure-related toxicities such as infections and graft-versus-host disease (GVHD), this procedure is often limited to younger patients in good medical condition. In an attempt to reduce procedure-related toxicity in elderly patients or in patients with medical comorbidities precluding the use of standard preparative regimens, or in patients with nonhematological malignancies not eligible for standard regimens, different reduced-intensity conditioning (RIC) regimens aiming to induce an allogeneic GVT effect have been investigated, and could result in durable donor cell engraftment.3,4,5,6,7,8,9,10,11 All of these protocols have been shown to be highly immunosuppressive, but because of the variability in the degree of myeloablation, the toxicity profile might vary from one protocol to another. In the standard myeloablative allo-SCT setting, early bacterial infections during the aplastic period and later cytomegalovirus (CMV) and fungal infections are important causes of morbidity and mortality.12,13 Although promising preliminary results have been reported with regard to feasibility and engraftment after RIC allo-SCT, only a few studies have specifically focused on the incidence and severity of infectious complications in this setting.14,15,16 Moreover, risk factors for bacterial, CMV and fungal infections are still sparse and poorly defined after RIC. Some observations, including the initial report from our group, suggested that the kinetic and risk factors for infections might be modified after RIC allo-SCT.17,18,19,20 However, our current knowledge of infectious complications after allo-SCT is still primarily based on results of analyses performed in the standard allo-SCT setting. This report describes an analysis of infectious complications (CMV antigenemia, documented bacteremia and fungal infections) in 101 patients with hematological and nonhematological malignancies, who received an antithymocyte globulin-(ATG), fludarabine- and busulfan-based RIC prior to allo-SCT from HLA-identical siblings. The aim of this analysis was to define the incidence and potential risk factors predicting the development of these infectious complications in the first 6 months following RIC allo-SCT, and to assess its impact on clinical outcome.

Patients and methods

Patients and donors

Study design

In all, 101 consecutive patients who received a RIC allo-SCT from HLA-identical donors for hematological and nonhematological malignancies were included in this study. Patients were treated in a joint program between the Institut Paoli-Calmettes, Marseille (n=75), and the Centre Jean-Perrin, Clermont-Ferrand (n=26), between April 1998 and June 2002. Written informed consent was obtained from each patient and donor. The study was approved by institutional review boards at both participating centers. All the donors were HLA-A-, HLA-B- and HLA-DR-identical siblings. All the patients were treated with a RIC before allo-SCT, because of high-risk clinical features that made them ineligible for our ‘standard’ allo-SCT program. ‘High-risk’ was defined by the presence of one or more of the following features that preclude the use of standard myeloablative allo-SCT: (1) patient age older than 50 years; (2) patients with high-risk diagnoses for allo-SCT such as lymphoma and myeloma; (3) heavily pretreated patients with more than two lines of chemotherapy before allo-SCT, including patients with metastatic solid tumors; and (4) patients with poor performance status due to significant medical comorbidities. All the patients received the preparative regimen as in-patients in private rooms, and remained admitted until hematopoietic and clinical recovery. The primary aim of the study was to analyze engraftment, toxicity, infections and transplant-related mortality (TRM). Other objectives were reported previously, and included the incidence of GVHD and disease response.21

Conditioning regimen

The preparative regimen was adapted from that reported by Slavin et al,4 with fludarabine (Fludara; Schering AG, Lys-Lez-Lannoy, France) 30 mg/m2 for 6 consecutive days (administered intravenously over 30 min), oral busulfan 4 mg/kg/day for 2 consecutive days and ATG (thymoglobuline; IMTIX-Sangstat, Lyon, France) 2.5 mg/kg/day for 4, 3 or 1 day, as indicated hereinafter (administered intravenously over 6–8 h between day −4 and −1). As part of the protocol, the ATG dose administered during conditioning was progressively decreased from initially 10 to 2.5 mg/kg. The first 25 patients received the higher total ATG dose of 10 mg/kg, while the next 21 patients received a total dose of 7.5 mg/kg. The remaining last 55 patients received the lower total ATG dose of 2.5 mg/kg. For comparison of ‘low’ vs ‘high’ ATG dose, the limit of 2.5 mg/kg was defined as the median ATG dose received by the patients. Therefore, patients receiving 10 or 7.5 mg/kg of ATG were considered as the ‘high’ ATG dose group, while patients receiving 2.5 mg/kg represented the ‘low’ ATG dose group.21

GVHD prophylaxis

GVHD prophylaxis included cyclosporine A (CsA) only at a dose of 3 mg/kg/day by continuous intravenous infusion starting from day −2, and changed to twice daily oral dosing as soon as tolerated. CsA doses were adjusted to achieve blood levels between 150 and 250 ng/ml, and to prevent renal dysfunction. CsA was tapered starting on day 90 if no GVHD appeared. CsA delivery (initial dose and route of administration) was comparable between the two participating centers.

Graft source

In total, 47 patients (47%) received a bone marrow (BM) graft collected under general anesthesia, whereas 54 patients (53%) received peripheral blood stem cells (PBSC). For PBSC collection, donors were treated with granulocyte-colony-stimulating factor (G-CSF) (Filgrastim, Amgen, Neuilly-sur-Seine, France) at a dose of 10 μg/kg/day for 5 days. Apheresis procedures were performed starting from day 5 of G-CSF treatment.22 The day of BM or PBSC infusion was designated as day 0. The graft was analyzed for content of hematopoietic progenitors (CD34+ cells) and CD3+ lymphoid cells, using standard flow cytometry procedures.

Infection prophylaxis and supportive care

Supportive care included antibacterial prophylaxis with intravenous vancomycin at 2 g daily, starting at day −2 (vancomycin was stopped as soon as the absolute neutrophil count (ANC) exceeded 500/μl). Pneumocystis carinii prophylaxis consisted of trimethoprim/sulfamethoxazole (10 mg/kg/day trimethoprim) administered pretransplantation and when the ANC exceeded 500/μl twice weekly. As soon as ANC exceeded 500/μl, patients received daily oral penicillin (1 × 106 UI × 2/day) prophylaxis against encapsulated bacteria. Penicillin prophylaxis was discontinued at the time of systemic immunosuppressive therapy discontinuation. Prophylaxis against herpes simplex virus included intravenous acyclovir (250 mg × 3/day) or oral valacyclovir (500 mg × 2/day) during the first month after allo-SCT. Empiric broad-spectrum antibiotics were begun for temperatures greater than 38.5°C or clinical signs of infection. Bacteremia was diagnosed on the basis of positive results of blood cultures. Hemoglobin was maintained through packed red blood cell transfusions at a level of 7 g/dl, and the platelet count was maintained at 10 000/μl. All blood products were irradiated. All patients received intravenous heparin (100 UI/kg) until ANC reached 500/μl, to prevent venoocclusive disease (VOD).17 No specific measures or prophylaxis were given for mucositis prevention. Patients in this protocol did not receive systematic specific oral digestive decontamination or systemic antifungal prophylaxis.

Pre-emptive CMV therapy

CMV infection management was similar at the two participating centers. All blood products were filtered but not CMV screened. In the first 100 days post allo-SCT, patients were assessed twice per week for CMV infection by antigenemia assay23 (CINAkit, Argene Biosoft, France; this method uses a monoclonal antibody pool that recognizes the lower matrix structural phosphoprotein pp65; in a positive specimen, results were reported as number of antigen-positive cells). A patient was considered positive when having at least two infected cells out of 2 × 105 leukocytes, in order to initiate pre-emptive ganciclovir therapy. All patients with a positive CMV antigenemia received pre-emptive ganciclovir therapy (5 mg/kg intravenously twice daily) for 14 days. Since CMV antigenemia testing is a semiquantitative technique, and those patients who have a higher number of antigenemia-positive leukocytes are at a higher risk for developing CMV disease,24 in case of rising or persistent CMV antigenemia after 5 days of ganciclovir pre-emptive therapy, patients were switched to foscarnet therapy (180 mg/kg/day) for 14 days.25 Patients did not receive systematic maintenance therapy after pre-emptive therapy or routine prophylactic intravenous immunoglobulins. CMV-positive antigenemia recurrence was defined as a new positive CMV antigenemia occurring after at least 15 days of the end of a successful pre-emptive ganciclovir or foscarnet therapy course. CMV disease was defined as described previously.14

Bacterial and fungal infections diagnosis

Blood cultures were performed to identify the etiology of bacterial and fungal infections. Specimens were submitted for microbial cultures according to standard methods. A diagnosis of invasive aspergillosis was made as previously described.26 Candidemia was diagnosed on the basis of positive results of blood cultures performed according to standard methods.

Clinical outcomes and definitions

Clinical outcomes after transplantation that were analyzed included time of neutrophil and platelet engraftment, time to start and severity of acute GVHD and time to onset of an infection that was defined as the day when the diagnostic test was performed.24 Time to neutrophil engraftment was defined as the first of 3 consecutive days in which the ANC exceeded 500/μl. Time to platelet engraftment was defined as the first of 3 consecutive days with 20 000/μl, without a need for platelet transfusion during a 5-day period. Acute GVHD was graded according to standard criteria.27 The diagnosis of chronic GVHD was made based on both clinical and/or histology criteria of skin and other affected sites, as previously described.28,29,30 Upon diagnosis of grade II–IV acute GVHD, all patients were primarily treated or continued on CsA and a corticosteroid-based regimen (prednisone or methylprednisolone 2 mg/kg/day). Tapering schedules of prednisone or methylprednisolone were individualized at the discretion of the attending physicians for disease status and activity of GVHD. A second-line immunosuppressive regimen was defined as the initiation of secondary systemic immunosuppressive treatment replacing or being in addition to primary first-line systemic therapy because of refractory or progressive GVHD. Patients received various second-line therapies such as higher doses of prednisone or methylprednisolone (>2 mg/kg/day), ATG, mycophenolic acid mofetil (MMF), extracorporeal photopheresis, or low-dose total lymphoid irradiation. For the purpose of this analysis, detailed data relating to GVHD and infectious complications were captured on designated report forms from medical charts by MM, WJ and JOB.

Statistics

All data were computed using SPSS for Windows (SPSS, Inc., Chicago, IL, USA) and SEM software (SILEX, Mirefleurs, France). The Mann–Whitney test was used for comparison of continuous variables. Categorical variables were compared using the χ2 test. The probability of developing an infectious complication (CMV, bacteremia or fungal infection) was determined by calculating the cumulative incidence.31 Probability of overall survival (OS) was estimated from the time of transplantation, using the Kaplan–Meier product–limit estimates.32 Differences between groups were tested using the log-rank test when Kaplan–Meier analysis was performed. Potential risk factors for CMV-positive antigenemia or bacteremia were considered only if their onset occurred concomitantly or before the diagnosis of infection. The association of time to onset of an infection with selected variables was evaluated in a multivariate analysis, using the Cox proportional hazards regression model.33

Results

Patients' characteristics and engraftment

Baseline characteristics and other relevant outcomes for patients included in this analysis were reported in detail previously.21 Briefly, the median age of recipients was 50 (range 17–61) years. In all, 25 patients had a myeloid malignancy, whereas 45 patients were diagnosed with lymphoid malignancies. The remaining 31 patients were treated for metastatic nonhematological malignancies. In this series, 47 patients received donor BM, while the remaining 54 patients received PBSC. As part of the protocol, the total ATG dose administered during conditioning was progressively decreased from initially 10 to 2.5 mg/kg, with the aim of modulating GVHD. In total, 46 patients received the ‘high’ total ATG dose of 10 or 7.5 mg/kg, while the remaining 55 patients received the ‘low’ ATG dose of 2.5 mg/kg. Overall, patients in this series received a median ATG dose of 2.5 mg/kg (Table 1). A sustained ANC of more than 500/μl was reached at a median of 15 (range 9–23) days. Platelet engraftment occurred at a median of 14 (range 0–99) days.

Table 1 Patient and donor characteristics

CMV antigenemia

In this series, 42 patients (42%; 95% confidence interval (CI) 32–52%) developed at least one episode of CMV-positive antigenemia during the first 6 months after allo-SCT. The cumulative incidence of CMV-positive antigenemia is shown in Figure 1a. The median time to onset of the first CMV-positive antigenemia was 37 (range 7–116) days. Among the 42 patients experiencing a first episode of positive CMV antigenemia, 13 patients (31%; 95% CI 17–45%) had a second episode of positive CMV antigenemia despite a complete course of pre-emptive therapy, at a median time of 43 (range 16–91) days following the first episode and 87 (range 49–138) days after allo-SCT. Furthermore, in the latter 13 patients, four patients had a third episode of CMV-positive antigenemia despite two previous complete courses of pre-emptive therapy. In all, 12 cases (29%; 95% CI 15–43%) of CMV antigenemia occurred concomitantly or early after the onset of clinically significant grade II–IV acute GVHD. All the 42 patients with a positive CMV antigenemia received ganciclovir as pre-emptive therapy. However, four patients (10%) were switched to foscarnet, because of a rising or persistent CMV antigenemia after 5 days of ganciclovir frontline pre-emptive therapy. Moreover, four patients (31%) of the 13 patients who experienced recurrence of CMV antigenemia were treated with foscarnet as frontline pre-emptive therapy. Two of the four patients with a third episode of CMV antigenemia recurrence were also treated with foscarnet as frontline pre-emptive therapy.

Figure 1
figure1

Cumulative incidence of infections after ATG-based RIC allo-SCT: (a) CMV-positive antigenemia; (b) bacteremia; (c) fungal infections.

Risk factors for positive CMV antigenemia

None of the 17 CMV low-risk cases (both donor and recipient CMV seronegative)34 developed a positive CMV antigenemia as compared to the remaining 84 intermediate (donor CMV seronegative and recipient CMV seropositive) and high-risk (both donor and recipient CMV seropositive) patients (P=0.0001), further confirming the protective effect of a negative CMV donor–recipient serostatus against the development of CMV antigenemia.34 Since none of the CMV low-risk cases (donor and recipient CMV seronegative) developed a positive CMV antigenemia at any time after allo-SCT, we were unable to evaluate the effect of this factor in our statistical models. Thus, Table 2 presents the results of univariate analysis of risk factors for the development of a positive CMV antigenemia following RIC allo-SCT, in the remaining 84 intermediate- and high-risk patients.34 Stem cell source and the ATG dose received during conditioning were the only variables showing a significant association with the risk of development of a positive CMV antigenemia in univariate analysis (Table 2). In the multivariate analysis, only BM as the stem cell source was associated with an increased risk of development of a positive CMV antigenemia (Table 3).

Table 2 Univariate analysis of risk factors for positive CMV antigenemiaa
Table 3 Multivariate analysis of risk factors for time to positive CMV antigenemia and bacterial infection

Bacterial infections

During the first 6 months after allo-SCT, 25 patients (25%; 95% CI, 17–33%) developed at least one episode of bacteremia. The cumulative incidence of bacteremia episodes is shown in Figure 1b. The median time to onset of the first bacteremia episode was 67 (range 7–172) days. Among the 25 patients developing an episode of bacteremia, six patients (24%; 95% CI, 7–41%) had a second episode of bacteremia at a median time of 40 (range 19–81) days following the first bacteremia episode and 134 (range 32–172) days after allo-SCT. Furthermore, in the latter six patients, three patients had a third episode of bacteremia. Only two cases of bacteremia occurred during the neutropenic phase, respectively, at days 7 and 13 following allo-SCT. The remaining 23 patients who developed a bacteremia episode had recovery of the neutrophil count at the time of bacteremia, and had no sign of mucositis. Apart from the two episodes developing during the neutropenic phase while patients were receiving vancomycin prophylaxis, all other episodes occurred while patients were receiving penicillin prophylaxis. Gram-negative bacteria (n=22; six Escherichia coli, four Enterobacter cloacae, three Pseudomonas aeruginosa, two Pseudomonas putida, three Xanthomonas maltophila, three Klebsiella pneumoniae and one Klebsiella oxytoca) represented the majority of the total 34 bacteremia episodes (65%; 95% CI, 49–81%). Among the 12 Gram-positive bacteria, five Staphylococcus epidermidis were considered related to the patients tunneled lines, while the source of other bacteria (four Staphylococcus aureus, two Streptococcus and one Enterococcus faecium) could not be determined.

Risk factors for bacteremia

Table 4 presents the results of univariate analysis of risk factors for the development of at least one bacteremia episode following RIC allo-SCT. Grade II–IV acute GVHD and use of high doses of prednisone or methylprednisolone (>2 mg/kg) were the only variables showing a significant association with the risk of development of a bacteremia episode in univariate analysis (Table 4). Median time for ANC>500/μl in patients who experienced a bacteremia episode was 15 (range 9–21) days, which was not significantly different from that of patients who did not experience any bacteremia (median 14 days (range 9–23); P=NS). In the multivariate analysis, the use of higher doses of prednisone or methylprednisolone (>2 mg/kg) because of refractory or progressive acute GVHD was the only factor associated with an increased risk of bacteremia (Table 3).

Table 4 Univariate analysis of risk factors for bacteremia development

Incidence and risk factors of fungal infections

During the first 6 months after allo-SCT, eight patients (8%; 95% CI, 3–13%) in this series developed a documented fungal infection. The cumulative incidence of fungal infections is shown in Figure 1c. The median time to onset of fungal infections was 89 (range 7–170) days. Systemic amphotericin B (1 mg/kg/day) was used as frontline therapy in all cases of fungal infections. Among the eight patients developing a fungal infection, six patients (75%) had a pulmonary invasive aspergillosis, while the remaining two patients had a documented candidemia (Candida albicans and Candida krusei). Owing to the relatively low number of fungal infections encountered in this series, we were not able to detect any statistically significant association between relevant risk factors (recipient age, diagnosis, disease status, stem cell source, ATG dose infused during conditioning, acute GVHD, immunosuppressive treatments, CMV-positive antigenemia and neutropenia duration) and the risk for development of fungal infections. However, three cases of fungal infections (two aspergillosis and one candidemia) occurred in patients with refractory grade IV acute GVHD, requiring high-dose prednisone or methylprednisolone (>2 mg/kg/day) and ATG. One patient with invasive pulmonary aspergillosis was neutropenic at the time of diagnosis (day 7 after allo-SCT); however, this patient had a long-lasting period (6 months) of chemotherapy-induced neutropenia before allo-SCT. The remaining seven patients who developed a fungal infection had recovered a full neutrophil count at the time of infection. In all cases, fungal infections occurred while patients were not receiving any systemic prophylaxis.

Morbidity and mortality following the development of infections

At the time of this analysis, 53 of the 101 patients included in this study died during the follow-up period, and 47 are still alive with a median follow-up of 434 days (range 196–1495). The majority of deaths (n=34) were directly attributed to disease progression or relapse.21 In all, 13 deaths were attributed to acute or chronic GVHD. In two of the 13 GVHD-related deaths, invasive pulmonary aspergillosis and candidemia were concomitant with grade IV acute GVHD. However, in these two patients, acute GVHD was still considered to be the main cause of death. Five deaths were directly attributed to infections. The overall cumulative incidence of infectious-related mortality was 5% (95% CI, 1–9%), occurring at a median time of 122 (range 46–193) days after allo-SCT. It is noteworthy that among these five patients, four were aged over 50 and one was aged 49. Two infectious-related deaths occurred before day 100. Four infectious-related deaths were directly attributed to pulmonary invasive aspergillosis. The other remaining infectious-related death patient died of an aspergillosis-compatible acute respiratory distress syndrome. In addition, this patient had a digestive hemorrhage of unknown origin on the day of his death. No bacteremia-related mortality was observed in this series. All patients with bacteremia responded rapidly to appropriate antimicrobial therapy. Moreover, none of the patients from this series developed signs of CMV disease at the time of the last follow-up. The Kaplan–Meier estimates of overall survival were not statistically significantly different between patients who experienced a positive CMV antigenemia as compared to patients without CMV antigenemia (P=NS; Figure 2a), or between patients experiencing a bacteremia episode in comparison to patients without bacteremia (P=NS; Figure 2b).

Figure 2
figure2

(a) Overall survival in patients with and without (dashed lines) CMV-positive antigenemia after RIC allo-SCT; (b) overall survival in patients with and without (dashed lines) bacteremia after RIC allo-SCT.

Discussion

In this study, we have analyzed the incidence and characteristics of infectious complications in high-risk patients given HLA-identical allo-SCT following ATG-based RIC. Overall infectious-related mortality was relatively low, comparing favorably with the results reported with standard allo-SCT.35,36,37,38,39 Although this study focused on microbial-documented infections and did not analyze other infectious episodes without bacteremia or candidemia, or other viral non-CMV infections (HSV, VZV, adenoviruses…), one should bear in mind that other nonmicrobial documented infections such as pneumonitis might represent an important issue, since they can result in a high rate of morbidity, impairing patients of the quality of life. Nevertheless, our results suggest that a busulfan-, fludarabine- and ATG-based RIC would result in a different evolution of infections following allo-SCT, as compared to standard allo-SCT or to other RIC regimens.14,16,40 The stem cell source was the major determinant for the likelihood of developing positive CMV antigenemia that occurred mainly early (before day 45) after allo-SCT, without evidence of a high risk of CMV disease or detrimental effect on outcome. In contrast, bacteremia predominated after neutropenic recovery with higher doses of prednisone or methylprednisolone being the major risk factor. Also, although the incidence of fungal infections in this study did not allow us to define statistically significant risk factors, our results support a delayed onset, with invasive aspergillosis occurring mainly after resolution of the neutropenic period, different from that reported after standard allo-SCT.41,42,43,44

In standard allo-SCT, the transplant period is classically divided into three phases. The first phase is related to the aplastic period, with neutropenia and toxicity of the conditioning regimen favoring a majority of bacterial infections, but also favoring fungal infections.36,41,42,43,44 The second phase is characterized by neutrophil recovery, but a major T-cell dysfunction due to the immunosuppressive therapies used for acute GVHD management and thus favoring viral infections, especially CMV.13,34 A third phase might develop in some long-term surviving patients with several complex immune dysfunctions due to chronic GVHD and/or prolonged immunosuppression.45,46,47 In our study, the use of ATG as part of the preparative regimen could provide a certain level of in vivo T-cell depletion, modulating the kinetics of immune reactions and reconstitution after allo-SCT.21 In univariate analysis, a high ATG dose correlated with a significantly higher incidence of CMV-positive antigenemia. This is in line with previous studies from the standard myeloablative T-cell depletion setting, showing that combined in vivo/ex vivo T-cell depletion would influence the incidence of early active CMV infection and disease in the depleted patients.48,49 However, in multivariate analysis, the stem cell source (BM vs PBSC) was the only predictive factor for the development of positive CMV antigenemia. These data suggest that protection against CMV-positive antigenemia might be conferred by specific T lymphocytes transferred with the graft, at least in the early period after allo-SCT. Our preliminary basic research findings demonstrate that PBSC grafts are likely to contain a higher number of functional CMV-specific effectors as compared to BM (M Mohty, unpublished observations), further supporting a protective effect of PBSC transplantation against CMV-positive antigenemia and the overall major influence of stem cell source in transplant-related events.50

In our study, we report a relatively high incidence and recurrence of CMV-positive antigenemia. We cannot definitely exclude that the absence of ganciclovir maintenance therapy or regular prophylactic intravenous immunoglobulins might have favored CMV-positive antigenemia recurrence. However, most importantly, none of the patients included in our study developed clinical signs of CMV disease. This is somewhat at odds with a recent large case–control study from the Seattle group, suggesting that late onset of CMV disease still occurs after RIC allo-SCT.14 However, such differences can be explained by the differing and variable immunosuppressive potential of the major RIC regimens investigated at different centers. The Seattle RIC regimen, including fludarabine and low-dose total body irradiation, used a combination of CsA and MMF for GVHD prophylaxis,14 while our ATG-based regimen used CsA alone. It has already been shown that the combination of MMF and CsA provided potent synergistic immunosuppressive effects on T cells.51,52 Thus, it is possible that CsA/MMF combination would cause delayed CMV-specific immune recovery, favoring the delayed onset of CMV disease. In this context, our preliminary immune recovery data using the ELISPOT assay and CMV-specific HLA-peptide tetramers suggested that ATG-based RIC would result in a rapid recovery of functional CMV-specific effectors (M Mohty, unpublished observations), further enhancing the need for a stringent biological monitoring for assessment of the potential advantages of the different RIC regimens, in comparison with standard regimens.53

The other important finding of this study was the low incidence of bacteremia following ATG-based RIC allo-SCT, which compares favorably with the 24–55% incidence encountered after autologous or standard allo-SCT.36,37,38,39 However, RIC-associated bacteremia had a late onset, independent of neutropenia or gastrointestinal mucositis, and consisted of mainly Gram-negative bacteria. The predominance of Gram-negative bacteria in our study might be explained by the vancomycin prophylaxis and the absence of Gram-negative bacteria prophylaxis usually used in other protocols. We also identified higher doses of prednisone or methylprednisolone given for refractory GVHD as a strong risk factor for the likelihood of development of bacteremia. Intuitively, this association is not surprising given the well-known deleterious immunosuppressive effects associated with high-dose steroids.54,55,56,57 Nevertheless, this unveils the major unresolved issue of GVHD management after RIC allo-SCT. Optimal management of GVHD after RIC allo-SCT is still poorly defined. Recent data suggested that RIC regimens might modify the natural history21 and presentation of GVHD, with a higher incidence of severe and ‘late onset’ acute forms after day 100,58 supporting the validity of prospective testing of new immunosuppressive modalities after RIC allo-SCT, in replacement of the classical steroid-based treatments. In our study, the cumulative incidence curves for bacteremia and fungal infections did not seem to have reached a plateau yet. Thus, one could hypothesize that the incidence of bacterial and fungal infections might be higher with longer periods of follow-up, especially in those patients receiving lengthy high-dose steroid treatments, challenging the long-term quality of life and survival of these patients.

In conclusion, in the first 6 months after allo-SCT, our data showed that fludarabine-, busulfan- and ATG-based RIC allo-SCT recipients from HLA-identical siblings are associated with a high incidence of early CMV-positive antigenemia without CMV disease occurrence. Although nearly abrogated during the postconditioning neutropenic phase, delayed bacterial infections still occur, being mainly associated with high-dose prednisone or methylprednisolone treatment for GVHD therapy. Late invasive fungal infections are the principal source of infectious-related mortality, warranting prospective efforts to develop optimal antimicrobial preventive strategies.

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Acknowledgements

Mohamad Mohty was supported by grants from ‘the Société Française de Greffe de Moelle et de Thérapie Cellulaire (SFGM-TC)’, the ‘Fondation de France’, the ‘Fondation pour la Recherche Médicale’, the ‘Association pour la Recherche sur le Cancer’, the ‘Association Cent pour Sang la Vie’ (Paris, France), the ‘Association Méditerranéenne pour le Développement de la Transplantation’ (Marseille, France) and from the ‘Ligue contre le Cancer du Gard’ (Nimes, France). We thank FB Petersen, MD (University of Utah Health Sciences Center, Salt Lake City, UT, USA) for critical reading of the manuscript, and B Gaugler (INSERM U119, Marseille) for helpful discussions. We thank the nursing staff for providing excellent care for our patients. We thank AG Le Coroller (INSERM U379, Marseille, France) for help with statistical analysis. We also thank the following physicians at the Institut Paoli-Calmettes for their important study contributions and dedicated patient care: A Gonçalves, F Viret, AC Braud, RT Costello, JM Schiano de Collela, A Charbonnier, R Bouabdallah, GL Damaj, V Ivanov, G Novakovitch, P Ladaique and C Chabannon.

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Mohty, M., Jacot, W., Faucher, C. et al. Infectious complications following allogeneic HLA-identical sibling transplantation with antithymocyte globulin-based reduced intensity preparative regimen. Leukemia 17, 2168–2177 (2003). https://doi.org/10.1038/sj.leu.2403105

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Keywords

  • infections
  • allogeneic stem cell transplantation
  • reduced-intensity conditioning

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