异基因造血干细胞移植后EB病毒再激活的危险因素分析

背景：异基因造血干细胞移植后EB病毒再激活可导致致死性的移植后淋巴细胞增殖性疾病及相关疾病,目前国内尚未建立完整的EB病毒再激活及其相关性疾病的诊疗体系。 目的：前瞻性研究异基因造血干细胞移植后患者EB病毒再激活的发生和相关危险因素。 方法：纳入129例接受异基因造血干细胞移植的患者,采用实时定量PCR方法定期测定外周血中EB病毒载量,Kaplan-Meier模型分析其再激活的发生率,Logistic回归分析模型分析其再激活的相关危险因素。 结果与结论：异基因造血干细胞移植后EB病毒再激活及其相关疾病发生率高,EB病毒再激活发生的危险因素有HLA配型不合、应用抗胸腺细胞球蛋白、Ⅲ~Ⅳ度急性移植物抗宿主病及年龄小于20岁。     

The impact of human herpesvirus 6B reactivation on early complications following allogeneic hematopoietic stem cell transplantation.

Although human herpesvirus 6 (HHV-6) has been considered an important opportunistic and potentially fatal pathogen for allogeneic hematopoietic stem cell transplantation (HSCT), the clinical significance of HHV-6 reactivation remains controversial. In this study, we monitored HHV-6 DNAemia in 72 consecutive allogeneic HSCT recipients by real-time quantitative polymerase chain reaction. A total of 680 peripheral blood specimens were collected from the recipients before HSCT or at weekly intervals after HSCT. As the predominant variant, HHV-6B was detectable at least once in 47.2% (34/72) of HSCT recipients on the median day 21 (range, 7-84 days); HHV-6A reactivation occurred in only 1 recipient (1.4%). Detectable HHV-6B reactivation was associated with increased probability of skin rash by day 30 after HSCT (hazard ratio [HR], 3.68; 95% confidence interval [CI], 1.24-10.92; P = .019), cytomegalovirus (CMV) antigenemia (HR, 2.35; 95%CI, 1.32-4.19; P = .004), and hemorrhagic cystitis (HC) (HR, 2.59; 95%CI, 0.96-6.98; P = .061) by day 100 after HSCT. Neutrophil and platelet engraftment, mortality for 100 days after HSCT were not affected by HHV-6B reactivation. In conclusion, HHV-6 reactivation is a common event, and this study demonstrates a correlation between HHV-6B infection and CMV reactivation, early rash, and possibly increased incidence of HC after transplantation.     

Early human herpesvirus type 6 reactivation after allogeneic stem cell transplantation: a large-scale clinical study

This study investigated the impact of human herpesvirus type 6 (HHV6) reactivation within 100 days of allogeneic stem cell transplantation (allo-SCT) on patient outcomes. HHV6 plasma loads were monitored weekly by quantitative PCR. Of 235 consecutive patients, 112 (48%) had an early positive HHV6 PCR test (group A) and 123 (52%) did not (group B). HHV6 reactivation was less frequent in patients who received reduced-intensity conditioning (P = .028). In group A, only 6 patients (5%) were asymptomatic; the most common clinical manifestations were fever (n = 60), skin rash (n = 57), diarrhea (n = 51), pulmonary complications (n = 19), and neurologic disorders (n = 12). Compared with the patients in group B, those in group A experienced delayed platelet engraftment (P = .003) and more frequent grade II-IV acute graft-versus-host disease (GVHD) (47% versus 30% in group B; P = .009). In multivariate analysis, the most important factors influencing the development of grade II-IV acute GVHD development were early HHV6 reactivation (P = .03) and unrelated donor status (P < .001). HHV6 reactivation adversely influenced 6-month survival (P = .04). Of?the 38 evaluable patients receiving antiviral treatment, 34 had a significantly decreased HHV6 load. Our findings indicate that HHV6 reactivation after allo-SCT is associated with delayed platelet engraftment, early posttransplantation mortality, and the development of acute GVHD. Careful monitoring of HHV6 by PCR is warranted during the early posttransplantation period.     

Risk factors for moderate-to-severe chronic graft-versus-host disease after allogeneic hematopoietic stem cell transplantation.

Among 810 consecutive hematopoietic stem cell transplantation (HSCT) patients, 679 survived more than 3 months and were evaluated for chronic GVHD. The aim of this study was to find predisposing factors increasing the risk of development of moderate-to-severe chronic GVHD. Many of the donors were HLA-identical siblings or related (n = 435), 185 were HLA-matched unrelated, and 59 were mismatched related or unrelated donors. Most of the patients had a hematological malignancy (n = 568), but 111 patients with a nonmalignant disease were included. Two hundred twenty-three patients (33%) developed mild, 41 (6%) moderate, and 15 (2.2%) severe chronic GVHD. The 5-year probability of development of moderate-to-severe chronic GVHD was 10%. We analyzed 30 potential risk factors for chronic GVHD. In the multivariate analysis, acute GVHD) grades II to IV (relative hazard [RH], 2.30; 95% CI, 1.29-4.10; P = .005), CML diagnosis (RH, 2.37; CI, 1.38-4.08; P = .002) and transplantation from an immunized female donor to a male recipient (RH, 2.16; CI, 1.14-4.11; P = .02) were independent risk factors for moderate-to-severe chronic GVHD. Recipient age also was significant (RH, 2.42; CI, 1.23-4.77; P = .01) if CML was not included in the analysis. In patients with no risk factors, the 5-year probability of development of moderate-to-severe chronic GVHD was 5%. In patients with 1 risk factor, the probability was 13%; 2 risk factors, 23%; and 3 risk factors, 45%. Among patients who developed chronic GVHD (n = 279), acute GVHD grades II to IV (RH, 2.18; CI, 1.23-3.86; P < .01) was the only predictive factor for moderate-to-severe chronic GVHD versus mild disease. Patients with previous acute GVHD grades II to IV may benefit from more aggressive initial treatment. This possibility would have to be examined in clinical trials.     

Human herpesvirus type 6 reactivation after haematopoietic stem cell transplantation

Human herpesvirus type 6 (HHV6) is known to reactivate after hematopoetic stem cell transplantation (HSCT) and has been suggested to be associated with increased mortality and severe clinical manifestations, including graft versus host disease (GvHD). The exact etiological role of HHV6 reactivation in increased morbidity and mortality after HSCT remains unclear. This review will focus on the current available evidence of HHV6 reactivation after HSCT and its immuno-modulatory capacities, with particular emphasis on the severe complication GvHD. At present, no effective specific antiviral treatment for HHV6 reactivation has been identified. The currently available antiviral agents are outlined, as well as possible future strategies for the treatment of HHV6 reactivation. Non-toxic, specific treatment or prevention of HHV6 reactivation might improve the safety and efficacy of the HSCT procedure.     

异基因造血干细胞移植后的相关并发症及危险因素

背景：有效预防和治疗异基因造血干细胞移植后并发症是提高患者存活率的重要因素。 目的：分析异基因造血干细胞移植后相关并发症的发生和危险因素。 方法：应用文献检索的方法获取异基因造血干细胞移植后相关并发症研究的文献,对符合研究标准的文献进行深入的数据分析,文章选取异基因造血干细胞移植后极易发生的并发症进行分析,如肺部并发症、真菌性败血症、巨细胞病毒感染以及中枢神经系统并发症等。 结果与结论：异基因造血干细胞移植后易出现肺部并发症,而且死亡率较高,肺部并发症的发病机制可能与移植物抗宿主病和巨细胞病毒抗原血症相关。异基因造血干细胞移植后真菌性败血症病原菌以假丝酵母菌属为主,死亡率较高,应二级预防性和早期经验性抗真菌治疗。更昔洛韦、膦甲酸钠对异基因造血干细胞移植后巨细胞病毒感染的治疗有效。中枢神经系统并发症在异基因造血干细胞移植后发生率较低,但在治疗过程也不容忽视。异基因造血干细胞移植后相关并发症的发生与多种危险因素有关,在临床治疗过程中要对相关因素采取预防措施,减少并发症的发生,提高患者的存活率。     

Risk factors for late infections after allogeneic hematopoietic stem cell transplantation from a matched related donor.

After allogeneic hematopoietic stem cell transplantation (HSCT), early infections represent a major cause of morbidity and mortality but little information has been previously reported on late infections. Late infection incidence and risk factors were retrospectively determined in 196 long-term survivors after HLA matched related HSCT. Patients transplanted for aplastic anemia, chronic myelogenous leukemia (CML), and acute myelogenous leukemia (AML) were included. Median follow-up was 8 years. Thirty patients died beyond the first year, causes of death were relapse (n = 10) and infections (n = 19, associated with graft-versus-host disease [GVHD] in 16 patients). Late severe bacterial (LSB) and fungal infections occurred in 30 and 8 patients, yielding to an 8-year cumulative incidence of 15 (95%CI: 10-20) and 4% (95%CI: 1-6), respectively. The majority of viral infections were hepatitis C (HCV) and VZV (8-year cumulative incidence: 10 (95%CI: 5-14) and 27% (95%CI: 20-34), respectively. Three risk factors for LSB have been identified in multiple Cox analysis: CMV status (positive recipient and negative donor) (hazard ratio [HR]: 2.5, 95%CI: 1.1-5.9, P = .033), irradiation-based conditioning regimen (HR: 3.1, 95%CI: 1.2-7.8, P = .016), and extensive chronic GVHD (cGVHD; HR: 2.9, 95%CI: 1.3-6.9, P = .013). Extensive cGVHD was the only risk factor for non-HCV viral infections in patients transplanted for AML or CML (HR: 2.7, 95%CI: 1.4-5.1, P = .002). After HSCT, patients remain at high risk of infections even late after transplantation, in particular, with the above risk factors, and required a prolonged follow-up.     

Risk factors for progression from cytomegalovirus viremia to cytomegalovirus disease after allogeneic hematopoietic stem cell transplantation

Cytomegalovirus (CMV) disease is a major cause of infectious complications in allogeneic hematopoietic stem cell transplantation (allo-HSCT). Although patients undergoing allo-HSCT receive prophylactic and preemptive treatment for CMV, a subset of patients experience clinically significant CMV disease. This study investigated the risk factors for progression from CMV viremia to CMV disease during or after preemptive therapy in patients undergoing allo-HSCT. Between January 2006 and August 2010, 43 patients received preemptive therapy for CMV viremia after allo-HSCT. These patients experienced 74 episodes of CMV viremia. Nine of the patients (21%) and 12 of the episodes (16%) progressed to CMV disease. Univariate analysis identified several risk factors for progression to CMV disease, including high initial viral load (P?=?.020), leukopenia (P = .012), and neutropenia (P = .033) at the time of detection of CMV viremia. On multivariate analysis, leukopenia remained an independent predictor (hazard ratio, 4.347; P = .045). The rate of failure to clear CMV viremia after 1 cycle of preemptive therapy was higher in the leukopenia group than in the non-leukopenia group (60.0% versus 16.9%; P = .002). This indicates that leukopenia initially?documented with CMV viremia is related to lower viral response to preemptive therapy and is a notable risk factor for progression from CMV viremia to CMV disease.     

Early central nervous system complications after reduced-intensity stem cell transplantation.

To investigate clinical characteristics of early central nervous system (CNS) complications after reduced-intensity stem cell transplantation (RIST), we reviewed the medical records of 232 patients who had undergone RIST for hematologic diseases at our institutions between September 1999 and June 2003. All patients had received purine analog-based preparative regimens. Stem cell sources comprised granulocyte colony-stimulating factor-mobilized blood from HLA-identical or 1 locus-mismatched related donors (n = 151), unrelated bone marrow (n = 44), or unrelated cord blood (n = 37). Graft-versus-host disease prophylaxis incorporated cyclosporine with or without methotrexate. Diagnosis of CNS complications was based on clinical, radiologic, and microbiological findings. CNS complications occurred in 18 patients (7.8%), with a median onset of 22 days, and were infectious (n = 1), metabolic (n = 15), or cerebrovascular (n = 2). Symptoms included seizures (n = 7), visual disturbance (n = 2), headache (n = 8), nausea (n = 8), vomiting (n = 6), impaired consciousness (n = 16), and hemiparesis (n = 3). Complications improved promptly in 10 patients, and 8 patients died without improvement within 30 days. Multivariate analysis with logistic regression identified umbilical cord blood transplantation as a significant risk factor for early CNS complications (odds ratio, 14.5; 95% confidence interval, 3.7-56.9; P <.0001). CNS complications are a significant problem after RIST, particularly with umbilical cord blood. Limbic encephalopathy is an unrecognized subtype of neurotoxicity after umbilical cord blood transplantation.     

Lung transplantation for bronchiolitis obliterans after allogeneic hematopoietic stem cell transplantation

Bronchiolitis obliterans (BO) is a late onset complication of allogeneic hematopoietic stem cell transplantation (HSCT), and treatment outcome is dismal if it does not respond to immunosuppressive therapy. A 21-year-old male diagnosed with acute myeloid leukemia received an allogeneic HSCT from human leukocyte antigen- identical sibling donor. Twenty one months after transplantation, he developed progressive dyspnea and was diagnosed BO. Despite standard immunosuppressive therapy, the patient rapidly progressed to respiratory failure and Novalung® interventional lung-assist membrane ventilator was applied in the intensive care unit. Three months after the diagnosis of BO, the patient underwent bilateral lung transplantation (LT) and was eventually able to wean from the ventilator and the Novalung®. Since the LT, the patient has been under a strict rehabilitation program in order to overcome a severe lower extremity weakness and muscle atrophy. Histologic findings of the explanted lungs confirmed the diagnosis of BO. Nine months after the LT, the patient showed no signs of rejection or infectious complications, but still required rehabilitation treatment. This is the first LT performed in a patient with BO after allogeneic HSCT in Korea. LT can be an effective therapy in terms of survival for patients with respiratory failure secondary to development of BO following HSCT.     

Etanercept (Enbrel) administration for idiopathic pneumonia syndrome after allogeneic hematopoietic stem cell transplantation.

Acute pulmonary dysfunction remains a frequent and severe complication of hematopoietic stem cell transplantation (SCT). Almost half of the pulmonary insults that occur in this seating are noninfectious in origin and are referred to as idiopathic pneumonia syndrome (IPS). In this series of 3 patients, etanercept (Enbrel; Immunex, Seattle, WA), a soluble, dimeric tumor necrosis factor alpha-binding protein, was administered to 3 consecutive pediatric allogeneic BMT recipients with IPS. The administration of etanercept, in combination with standard immunosuppressive therapy, was well tolerated and associated with significant improvements in pulmonary dysfunction within the first week of therapy. These data suggest that etanercept may represent a safe, non-cross-reactive, therapeutic option for patients with IPS and that clinical trials studying etanercept for this indication are warranted.     

Use of real-time PCR to monitor human herpesvirus 6 reactivation after allogeneic bone marrow transplantation

Reactivation of human herpesvirus 6 (HHV-6) is common following allogeneic marrow transplantation, however, little is known about the immune control and pathogenic potential of HHV-6 infection after transplantation. In order to determine whether reactivation of HHV-6 plays an important role in the development of complications in patients undergoing allogeneic bone marrow transplantation or not, we developed a very rapid quantification of viral DNA using a LightCycler. The amount of viral DNA was determined using a supernatant of a chronically infected cell line [TaY(OK)] which contains a known amount of viral DNA. Peripheral blood cells were collected from 5 patients undergoing allogeneic bone marrow transplantation once before transplant and once per week after transplant for 8-24 weeks. The real-time PCR system revealed that there was a linear correlation in the range of 101 to 105 molecules of reference. Using this system, we have found the presence of non-diagnosed HHV-6 reactivation as well as symptomatic infection, indicating the potential for routine implementation of this technology for laboratory diagnosis of HHV-6 infection. Our study shows that this method of rapid quantification of HHV-6 genomes by the real-time PCR using a LightCycler may be useful not only to understand the reconstitution of the immune system following marrow transplantation but also to manage the care of patients.     

Cidofovir for cytomegalovirus reactivation in pediatric patients after hematopoietic stem cell transplantation.

BACKGROUND: Cidofovir (CDV) is a nucleotide analogue with broad antiviral activity. This drug has a very favorable pharmacokinetic profile that enables intermittent dosing, but the potential for nephrotoxicity has hitherto restricted its use in stem cell transplant recipients. Data on pediatric patients are limited. OBJECTIVES: To report the efficacy and toxicity of CDV in a group of pediatric patients with cytomegalovirus (CMV) reactivation after allogeneic stem cell transplantation. STUDY DESIGN: Prospective evaluation of safety and efficacy of CDV used pre-emptively for CMV reactivation in 10 out of 30 children who underwent allogeneic hematopoietic stem cell transplantation from January 2000 to December 2001. In all the patients but one, CDV was used as second-line therapy (after foscarnet or ganciclovir) of CMV reactivation. RESULTS: Overall, 12 courses of CDV were administered with a median 5 doses per course, range 1-6 (two patients were treated twice). Considering the first CDV treatment episode, 8 out of 10 patients had positive CMV antigenemia assay when they started CDV. Five of eight antigenemic patients responded completely while three were switched to foscarnet or ganciclovir, respectively, due to increasing (one) or persistent CMV antigenemia (two). Overall, the therapy with CDV was well tolerated, but it was withdrawn in one patient due to a two-fold increase in the baseline creatinine level. This patient concurrently had a high tacrolimus blood level. CONCLUSION: Safety is the major concern regarding the use of CDV but the adoption of probenicid, intravenous hydration and anti-emetic therapy improved its tolerability profile. Our data suggest that CDV has an acceptable toxicity and would deserve further controlled studies in the setting of pre-emptive therapy for CMV.     

Central nervous system complications after allogeneic hematopoietic stem cell transplantation: incidence, manifestations, and clinical significance.

The incidence of central nervous system (CNS) complications, their risk factors, and impact on outcome are not well defined in recipients of allogeneic hematopoietic stem cell transplant (aHSCT). We reviewed the medical records of 302 consecutive patients who underwent aHSCT for malignant and nonmalignant hematologic diseases at Princess Margaret Hospital between 2002 and 2005. The cumulative incidences of all CNS complications and posterior reversible encephalopathy syndrome (PRES) at days 100 and 365 were 18% (95% confidence interval [CI]: 14-22) and 23% (95% CI: 19-29), and 6% (95% CI: 4-9) and 7% (95% CI: 5-11), respectively. Seizures occurred in 37% of all CNS events in the first 100 days and 73% of PRES episodes. Female gender and high-dose total-body irridiation (TBI) were identified as independent risk factors for CNS complications in the first 100 days posttransplant. Survival at 1-year was significantly inferior in patients who developed CNS complications within 100 days of transplant (28% [95% CI: 17-41] versus 72% [95% CI: 66-77]) and PRES (27% [95% CI: 10-47] versus 67% [95% CI: 62-73]) compared to those who did not (P < .0001). Death from graft-versus-host disease (GVHD) was more common in patients with CNS complications in the first 100 days (P = .006) and PRES (P = .01) compared to patients without complications.     

Preemptive cellular immunotherapy after T-cell-depleted allogeneic hematopoietic stem cell transplantation.

GVHD is a life-threatening complication of allogeneic hematopoietic stem cell transplantation (HSCT). GVHD is due to donor lymphocytes that are cotransplanted with donor stem cells. These donor lymphocytes are primed by histocompatibility differences between donors and recipients and activated by a cytokine storm caused by the conditioning regimen. The most efficient method for prevention of GVHD consists of T-cell depletion (TCD) of the graft. However, TCD usually leads to an increased risk of leukemia relapse because of the loss of the graft-versus-leukemia (GVL) effect. Several groups have studied the feasibility of preemptive donor lymphocyte infusion (DLI) to lessen the impact of TCD on leukemia relapse. Preemptive DLI is given several weeks to months after the transplantation, ie, after the cytokine storm and after the patient has recovered from conditioning-regimen-related toxicities. After briefly discussing various techniques of TCD of the graft and the efficacy of DLI, this article reviews the first clinical studies evaluating a strategy of TCD of the graft followed by preemptive DLI.     

Chronic kidney disease after myeloablative allogeneic hematopoietic stem cell transplantation.

Because survival of recipients of allogeneic hematopoietic stem cell transplantation (HSCT) has improved, long-term complications become more important. We studied the incidence and risk factors of chronic kidney disease in these patients and evaluated associated posttransplant complications and mortality. We performed a retrospective cohort study of 266 adults who received myeloablative allogeneic HSCT and who survived for >6 months in an 11-year period at a Dutch university medical center. Primary outcome was the incidence of chronic kidney disease defined as a glomerular filtration rate (GFR) of <60 mL/min/1.73 m(2). Chronic kidney disease developed in 61 (23%) of 266 patients, with a cumulative incidence rate of 27% at 10 years. Severe kidney disease (GFR of <30 mL/min/1.73 m(2)) developed in 3% of patients. Only 6 patients developed the thrombotic microangiopathic syndrome SCT nephropathy, and 2 of them needed dialysis. Pretransplant risk factors for chronic kidney disease were lower GFR at day 0 (P < .0001, odds ratio [OR] 0.95 95% confidence interval [CI] 0.93-0.97), female gender, and higher age (P = .001 and P < .0001, respectively). The occurrence of hypertension after transplantation was associated with chronic kidney disease (P < .0001, OR 0.34 95% CI 0.18-0.62). Mortality was 39% after a mean follow-up of 5.1 years. There was no significant difference in survival between patients with and without chronic kidney disease. Chronic kidney disease is a common late complication of myeloablative allogeneic HSCT. Because of the natural decline in renal function with time there is a risk of developing end-stage renal disease in the future. SCT nephropathy seems to be a specific cause of chronic kidney disease that is typically associated with severe kidney disease.     

Sirolimus and thrombotic microangiopathy after allogeneic hematopoietic stem cell transplantation.

Thrombotic microangiopathy (TMA) may occur after allogeneic hematopoietic stem cell transplantation (HSCT) and is related in part to calcineurin inhibitor toxicity. We observed a higher-than-expected rate of TMA when calcineurin inhibitors were combined with sirolimus. To determine the incidence of and risk factors for TMA after HSCT, we performed a retrospective cohort analysis of myeloablative allogeneic HSCT recipients between 1997 and 2003. TMA diagnosis required the simultaneous occurrence of (1) creatinine increase >2 mg/dL or >50% above baseline, (2) schistocytosis, (3) increased lactate dehydrogenase, and (4) no evidence of disseminated intravascular coagulopathy. A total of 111 sirolimus-exposed subjects were compared with 216 nonexposed subjects after HSCT. TMA occurred in 10.8% of the sirolimus group and 4.2% in the nonsirolimus group (odds ratio, 2.79; P=.03). Sirolimus exposure was associated with TMA earlier than in nonsirolimus patients (25 versus 58 days; P=.04). Only the use of sirolimus (exact odds ratio, 3.49; P=.02) and grade II to IV acute graft-versus-host disease (exact odds ratio, 6.60; P=.0002) were associated with TMA in regression analyses. Treatment of TMA varied among affected individuals. Renal recovery was complete in 92% of sirolimus-treated patients. Overall survival after TMA diagnosis was better for sirolimus subjects than for nonsirolimus subjects (58.3% versus 11.1%; P=.02). Sirolimus seems to potentiate the effects of calcineurin inhibitors on TMA after HSCT. TMA associated with sirolimus seems reversible and has a favorable prognosis when compared with TMA associated with calcineurin inhibitors alone. A careful monitoring strategy for TMA should be used with a sirolimus-containing graft-versus-host disease prophylaxis regimen.     

Voriconazole and sirolimus coadministration after allogeneic hematopoietic stem cell transplantation.

Sirolimus is increasingly used in transplantation for prevention and treatment of graft-versus-host disease and organ rejection. Voriconazole is contraindicated when used concomitantly with sirolimus because of a substantial increase in sirolimus drug exposure with unadjusted dosing, but voriconazole is also considered the best initial treatment of invasive aspergillosis and other fungal infections. Patients who received voriconazole and sirolimus concomitantly were identified by a review of the medical records of all allogeneic hematopoietic stem cell recipients at our institution from September 1, 2002, to June 1, 2005. Data including baseline characteristics, indications for both drugs, and potential adverse effects were evaluated. Eleven patients received voriconazole and sirolimus concomitantly for a median of 33 days (range, 3-100 days). In 8 patients whose sirolimus dose was initially reduced by 90%, trough sirolimus levels were similar to those obtained before the administration of voriconazole; no obvious significant toxicity from either drug was observed during coadministration. Serious adverse events were observed in 2 patients in whom sirolimus dosing was not adjusted during voriconazole administration. Sirolimus and voriconazole may be safely coadministered if there is an empiric initial 90% sirolimus dose reduction combined with systematic monitoring of trough levels.     

First analysis of human herpesvirus 6T-cell responses: Specific boosting after HHV6 reactivation in stem cell transplantation recipients

Early human herpesvirus 6 (HHV6) reactivation after hematopoietic stem cell transplantation (HSCT) is associated with poor survival. We characterized HHV6 immuneresponses in HSCT patients during lymphopenia. Prospectively, HHV6 DNA-load was measured weekly by realtime-PCR. Numbers of IFNγ-producing HHV6-T-cells were retrospectively determined by enzyme-linked immunospot assay 2months after HSCT. HHV6-specific T-cell proliferative capacity was analyzed with a newly developed assay using antigen-presenting autologous HHV6-infected PBMC. Fifty-six patients were included (median age 4.6years; range 0.2-21.2years). HHV6-reactivation occurred in 29/56 (52%) patients with a median time of 14 (range 1-41) days after HSCT. The median number of IFN-γ producing HHV6-specific T-cells at 2months and the HHV6-specific CD8+ T-cell proliferative capacity at 6months after HSCT was increased after HHV6-reactivation compared to non-reactivating patients (P=0.006 and p=0.019). In conclusion, HHV6-specific immuneresponses can be initiated during lymphopenia early after HSCT, which implicates a potential window for development of HHV6-specific (immuno)therapy.