Hematopoietic SCT Recipients Research Articles

DAS181 Treatment of Severe Parainfluenza Virus 3 Pneumonia in Allogeneic Hematopoietic Stem Cell Transplant Recipients Requiring Mechanical Ventilation.

Parainfluenza virus (PIV) may cause life-threatening pneumonia in allogeneic hematopoietic stem cell transplant (HSCT) recipients. Currently, there are no proven effective therapies. We report the use of inhaled DAS181, a novel sialidase fusion protein, for treatment of PIV type 3 pneumonia in two allogeneic hematopoietic SCT recipients with respiratory failure.

Long-term persistence of the immune response to antipneumococcal vaccines after Allo-SCT: 10-year follow-up of the EBMT-IDWP01 trial

The guidelines for immunization of hematopoietic SCT (HSCT) recipients recommend three doses of antipneumococcal conjugate vaccine (PCV) from 3 to 6 months after transplant, followed by a dose of polysaccharide 23-valent (PPV23) vaccine at 12 months in the case of no GVHD or an additional PCV dose in the case of GVHD. Due to the lack of long-term data in the literature, there is no recommendation for boosts after 12 months. Our goal was to assess the maintenance of the immune response to pneumococcal vaccines in patients vaccinated 10 years ago according to current guidelines. Thirty surviving patients of the IDWP01 (Infectious Diseases Working Party 1) trial were assessed for antibody levels against the seven antigens of the PCV7 and against two of the PPV23-specific antigens. When compared with 24 months after transplant, the immune response did not significantly decrease but with important serotype-specific variability. There was no evidence that an additional dose of PPV23 given to 11/30 patients 2-11 years after transplant was beneficial. In long-term HSCT survivors with no or few GVHD vaccinated against Streptococcus pneumoniae according to the current guidelines, the specific immunity is not fully maintained a decade later. The optimal schedule of antipneumococcal vaccination in HSCT recipients after 12 months remains to be established.

Evaluation of pretransplant influenza vaccination in hematopoietic SCT: a randomized prospective study.

Pretransplant influenza vaccination of the donor or allogeneic hematopoietic SCT (HSCT) candidate was evaluated in a randomized study. One hundred and twenty-two HSCT recipients and their donors were assigned to three randomization groups: no pretransplant vaccination (n=38), donor pretransplant vaccination (n=44) or recipient pretransplant vaccination (n=40). Specific IgG was assessed by both hemagglutinin inhibition (HI) and, in 57 patients, by an indirect influenza-specific ELISA at specified times after HSCT. Vaccinated donors had seroprotective HI titers for Ags H1 and H3 (P<0.001) compared with the other groups at the time of donation. The titers against H1 (P=0.028) and H3 (P<0.001) were highest in the pretransplant recipient vaccination group until day 180 after transplantation. A significant difference was found in the specific Ig levels against pandemic H1N1 at 6 months after SCT (P=0.02). The mean IgG levels against pandemic H1N1 and generic H1N1 and H3N2 were highest in the pretransplant recipient vaccination group. We conclude that pretransplant recipient vaccination improved the influenza-specific seroprotection rates.

Incidence and Risk Factors of Invasive Fungal Infection in Adult Patients Receiving Allogeneic Hematopoietic SCT Recipients

▪To investigate the incidence and risk factors for the occurrence of proven or probable invasive fungal infection (IFI) in adult patients receiving allogeneic hematopoietic stem cell transplantation (HSCT), 421 patients undergoing HSCT between 2002 and 2013 in our hospital were retrospectively analyzed. Thirty-one patients with the median age of 42 years (range: 19-60) developed IFI after HSCT. The post-HSCT IFI incidence was 7.4% and median time from HSCT to the diagnosis of IFI was 139 days (range: 2-1809). The risk factors for the occurrence of IFI were analyzed using Cox regression models.Of the pretransplant factors, European Group for Blood and Marrow Transplantation (EMBT) risk>2 (P=0.001) and prior history of IFI (P=0.006) or DM (P=0.042) were the significant predictors for post-HSCT IFI by univariate analyses. In multivariate analysis, EMBT risk>2 (P=0.015) and prior history of IFI (P=0.006) retained significance. Of the post-transplant factors, acute graft-versus-disease (aGVHD) overall grade III-IV (P<0.001), extensive chronic GVHD (cGVHD) (P=0.002), post-transplant lymphoproliferative disorders (PTLD) (P=0.005) and the use of high-dose steroids (P<0.001) were statistically significant in univariate analyses. After multivariate analysis, high-dose steroids (P<0.001) and aGVHD overall grade III-IV (P=0.045) retained significance. These results suggest that risk group stratification prior HSCT and monitoring of IFI in patients with severe GVHD and receiving high-dose steroids is mandatory to decrease the risk of post-HSCT IFI, especially in those with prior history of IFI. Abstract 2476. Table 1Possible factors for the occurrence of invasive fungal infection (IFI) after adult allogeneic HSCTIFIUnivariate analysisMultivariate analysisFactorsNo. of patientsN%HR95%CIP-valueHR95%CIP-valueEMBT risk=<216952.9>22522610.35.0381.930-13.1510.0013.3901.273-9.0290.015Prior history IFINo406276.6Yes15426.64.4571.551-12.8060.0065.8071.675-20.1290.006Prior history DMNo402286.9Yes19315.73.4901.045-11.6530.042aGVHDNo or Overall Gr. I-II379236.0Gr. III-IV42819.06.9363.046-15.796<0.0012.6271.023-6.7480.045High steroids*No367123.2Yes541935.111.1485.401-23.008<0.00111.1853.875-32.289<0.001cGVHDNo or limited364195.2Extensive571221.03.1311.518-6.4590.002PTLDNo405276.6Yes164254.6271.607-13.3200.005Abbreviations: CI = confidence interval; HR = hazard ratio; EBMT = European Group for Blood and Marrow Transplantation; HSCT = hematopoietic stem cell transplantation; GVHD = graft-versus-host disease; aGVHD = acute GVHD; cGVHD = chronic GVHD; Gr.= grade; PTLD = Post-transplant lymphoproliferative disorders. DM = Diabetes mellitus. High steroids* = post-HSCT high-dose steroid; Significant values (P<0.05) are given in bold. [Display omitted] [Display omitted] DisclosuresNo relevant conflicts of interest to declare.

Optimizing drug therapy in pediatric SCT: Focus on pharmacokinetics

Given age-related differences in drug metabolism and indications for hematopoietic SCT (HSCT), personalized drug dosing of the conditioning regimen and post-transplant immunosuppression may reduce graft rejection, relapse rates and toxicity in pediatric HSCT recipients. This manuscript summarizes the pharmacokinetic/dynamic data of HSCT conditioning and post-grafting immunosuppression, presented at the First Annual Pediatric Bone Marrow Transplant Consortium (PBMTC) meeting in April 2013. Personalized dosing of BU to a target plasma exposure reduces graft rejection in children and improves relapse/toxicity rates in adults. Current weight-based dosing achieves the target BU exposure in only a minority (24.3%) of children. The initial BU dose should be based on the European Medicines Agency nomogram or population pharmacokinetic models to improve the numbers of children achieving the target exposure. There are limited pharmacokinetic data for treosulfan, CY, fludarabine and alemtuzumab as HSCT conditioning in children. For post-grafting immunosuppression, mycophenolic acid (MPA) clearance may be increased in younger children (<12 years). The preferred MPA pharmacokinetic monitoring parameters and target range are still evolving in HSCT recipients. Multi-institutional trials incorporating properly powered pharmacokinetic/dynamic studies are needed to assess the effect of variability in the plasma exposure of drugs/metabolites on clinical outcomes in pediatric HSCT recipients.

Pulmonary complications in hematopoietic SCT: a prospective study.

Pulmonary complications are common and often lethal in hematopoietic SCT recipients. The objective of this prospective interventional study was to evaluate the etiology, diagnostic procedures, risk factors and outcome of pulmonary complications in a cohort of hematopoietic SCT recipients followed up for 1 year. For patients suffering from a pulmonary complication, a diagnostic algorithm that included non-invasive and bronchoscopic procedures was performed. We identified 73 pulmonary complications in 169 patients: 50 (68%) were pneumonias; 21 (29%) were non-infectious complications and 2 (3%) were undiagnosed. Viruses (particularly Rhinovirus) and bacteria (particularly P. aeruginosa) (28 and 26%, respectively) were the most common causes of pneumonia. A specific diagnosis was obtained in 83% of the cases. A non-invasive test gave a specific diagnosis in 59% of the episodes. The diagnostic yield of bronchoscopy was 67 and 78% in pulmonary infections. Early bronchoscopy (⩽5 days) had higher diagnostic yield than late bronchoscopy (78 vs 23%; P=0.02) for pulmonary infections. Overall mortality was 22 and 32% of all fatalities were due to pulmonary complications. Pulmonary complications are common and constitute an independent risk factor for mortality, stressing the importance of an appropriate clinical management.Supplementary informationThe online version of this article (doi:10.1038/bmt.2014.151) contains supplementary material, which is available to authorized users.

Etiology, clinical features and outcomes of pre-engraftment and post-engraftment bloodstream infection in hematopoietic SCT recipients

We conducted an observational study to assess the etiology, clinical features and outcomes of bloodstream infection (BSI) in 172 hematopoietic SCT (HCST) recipients. One hundred episodes of BSI in the pre-engraftment period (early onset) were compared with 89 episodes in the post-engraftment phase (late onset). More patients with late-onset BSI received an allogeneic HSCT, had GVHD and had received corticosteroids, whereas patients with early-onset BSI were more likely to have neutropenia, severe mucositis and a central venous catheter (CVC) in place. CVC was the most frequent site of infection, followed by an endogenous source. Pneumonia and gastrointestinal infection were particularly frequent in late-onset BSI, whereas mucositis was more frequent in the early-onset group. Gram-positive organisms predominated over Gram negatives. Streptococcus pneumoniae was more frequent in patients with late-onset BSI. Patients with late-onset BSI presented worse outcomes regarding septic shock, intensive care unit admission and early and overall case-fatality rates. Early-onset BSI was mainly related to the presence of neutropenia, mucositis and CVC, whereas late-onset BSI mainly affected severely immunosuppressed allogeneic HSCT recipients with GVHD and corticosteroids. Late-onset BSI caused high case-fatality rates. BSI due to S. pneumoniae was especially frequent late after transplantation. The development of better vaccination strategies is needed.

Risk factors for thrombotic microangiopathy in allogeneic hematopoietic stem cell recipients receiving GVHD prophylaxis with tacrolimus plus MTX or sirolimus

Transplantation-associated thrombotic microangiopathy (TA-TMA) is a feared complication of allogeneic hematopoietic SCT (HSCT) owing to its high mortality rate. The use of calcineurin inhibitors or sirolimus (SIR) for GVHD prophylaxis has been suggested as a potential risk factor. However, the impact of tacrolimus (TAC) and SIR combinations on the increased risk of TA-TMA is currently not well defined. We retrospectively analyzed the incidence of TA-TMA in 102 allogeneic HSCT recipients who consecutively received TAC plus SIR (TAC/SIR) (n=68) or plus MTX (TAC/MTX)±ATG (n=34) for GVHD prophylaxis. No significant differences were observed in the incidence of TA-TMA between patients receiving TAC/SIR vs TAC/MTX±ATG (7.4% vs 8.8%, P=0.8). Only grade III-IV acute GVHD, previous HSCT and serum levels of TAC >25 ng/mL were associated with a greater risk of TA-TMA. Patients developing TA-TMA have significantly poorer survival (P<0.001); however, TA-TMA ceased to be an independent prognostic factor when it was included in a multivariate model. In conclusion, the combination of TAC/SIR does not appear to pose a higher risk of TA-TMA. By contrast, we identified three different risk groups for developing TA-TMA.

Predictors of invasive fungal infection in pediatric allogeneic hematopoietic SCT recipients

This study was aimed at finding predictors of invasive fungal infection (IFI) after pediatric allogeneic hematopoietic SCT (HSCT). All children who received allogeneic HSCT in the Wilhelmina Children's Hospital Utrecht between 2004 and 2012 were included. HSCT data were prospectively collected. Patients were retrospectively classified into high- or low-risk groups for developing IFI using criteria based on available literature. Predictors for the occurrence of IFI were analyzed using Cox regression models. We used logistic regression models to analyze the association between other HSCT-related complications and IFI. Secondary outcomes were overall survival and treatment-related mortality (TRM). Two-hundred nine patients were included in the analysis; median age was 6.6 years. The cumulative incidence of IFI was 12%. In patients classified as 'low risk' (n=75), only 5.3% developed IFI (odds ratio (OR): 0.325; P=0.047). In multivariate analysis, a predictor for the occurrence of IFI was an a priori determined HSCT TRM risk >20% (based on EBMT-risk score). Post-HSCT, the administration of high-dose steroids was associated with IFI (OR: 4.458; P=0.010). Patients who developed IFI showed an increased risk of TRM (OR: 3.773; P=0.004). These results confirm that risk group stratification should guide intensity of monitoring for IFI and use of antifungal prophylaxis.

Hepatitis E virus infection in a hematopoietic stem cell donor

Hepatitis E virus (HEV) is an important cause of viral hepatitis, especially in immunocompromised patients.1 Versluis et al.2 recently studied the incidence and course of HEV-infection in a large cohort of patients undergoing allogeneic hematopoietic SCT (HSCT). In contrast to previously published studies from our group3 and others,4 they identified a considerable number of patients with chronic HEV infection with a significant lethality. Therefore, they suggested pretransplant HEV screening for HSCT recipients. Reconsidering these important new results we now even extend our position, strongly suggesting HEV screening in HSCT.

Outcomes of hematopoietic SCT recipients with rhinovirus infection: a matched, case–control study

The impact of rhinovirus in hematopoietic SCT (HSCT) recipients is not well defined. A retrospective, matched, case–control study of HSCT recipients with rhinovirus was conducted between 2009 and 2011. Controls were matched for timing relative to transplant, malignancy, and stem cell source. There were 47 cases and 94 controls. The cases and controls did not differ with respect to age, gender, ethnicity, donor source, malignancy, conditioning regimen, immunosuppression, antimicrobial prophylaxis or significant comorbidities. There were no differences in need for intensive care unit care, 100 day mortality, hospice discharge, relapse of disease, GVHD or development of disease or infection due to CMV or EBV. Other infectious complications after rhinovirus diagnosis were also equal. However, there was an increased number of recurrent hospitalizations from any cause among the cases (46.8% vs 24.5%, P=0.007). Recurrent hospitalizations due to any infection were also more common in cases (34% vs 14.9%, P=0.015). For patients who were diagnosed with rhinovirus pre-transplant (n=13), there was no difference in outcome compared with matched controls. HSCT recipients with rhinovirus have an increased risk of hospital readmission. However, there was no difference in outcome compared with matched controls. Transplantation in patients with active rhinovirus infection appears to be safe.

Translating the HLA-DPB1 T-cell epitope-matching algorithm into clinical practice

A simple online tool can predict HLA-DPB1 T-cell epitope (TCE) matching. At least a quarter of hematopoietic SCT recipients could benefit from a better outcome by including HLA-DPB1 in unrelated donor (UD) selection algorithms.

Herpesviruses and oral ulcerations in hematopoietic SCT recipients

We have read with great interest an article by van der Beek et al.1 published in Bone Marrow Transplantation. The authors reported that HSV-1 shedding in oral fluid after hematopoietic SCT (HSCT) is a significant predictor for oral mucosal ulcerations in adult patients, thus being a promising marker of the epithelial lesion. However, the conditioning regimen proved to be a non-significant predictor of ulcerative mucositis (UM) in this study. Therefore, we would like to discuss some interrelations between intensity of conditioning therapy, viremia rates and UM frequency in our pediatric setting. Some of these cases were reported elsewhere.2 Our study involved 120 patients of 1–21 years old (a mean of 12.4±5.9), comprising 56% males and 44% females, treated at R. Gorbacheva Memorial Institute of Children Hematology and Transplantology from 2002 to 2010. The patients with oncohematological disorders (mostly, acute leukemias, 73% of the total) underwent allo-HSCT from HLA-matched related or unrelated donors (38% and 62% of total group, respectively). The patients received peripheral blood stem cells or BM (60% and 40% of the total, respectively). Sixty-one recipients (51%) underwent myeloablative conditioning treatment (basically, BuCy protocols), while other patients were subjected to reduced-intensity conditioning (RIC), mostly, fludarabine-based treatment. GVHD prophylaxis was performed with CYA and MTX, at a standard schedule. In non-related HSCTs, antilymphocyte globulin treatment was added in 91 cases (76%), at 20 mg/m2 daily. Acyclovir prophylaxis since day 0 was performed in 31 patients (26% of total).

Human parvoviruses B19, PARV4 and bocavirus in pediatric patients with allogeneic hematopoietic SCT

Among the immunocompetent, infections with parvovirus B19 (B19V) and human bocavirus (HBoV) 1 range clinically from asymptomatic to severe, while following allogeneic hematopoietic SCT (HSCT) B19V can cause a persistent severe illness. The epidemiology and clinical impact of HBoV1 and the other emerging parvovirus 4 (PARV4) among immunocompromised patients have not been established. To determine the occurrence and clinical spectrum of B19V, PARV4 and HBoV1 infections, we performed a longitudinal molecular surveillance among 53 allogeneic HSCT recipients for pre- and post-HSCT DNAemias of these parvoviruses. Quantitative real-time PCR showed B19V DNA in sera of 16 (30%) patients, at mean levels of 4.6 × 10(3), 9.9 × 10(7), 1.1 × 10(10) and 1.6 × 10(2) B19V DNA copies/mL pre-HSCT (9/53), and at 1 (6/53), 2 (4/53) and 3 months (1/25) post HSCT, respectively. However, no clinical manifestation correlated with the presence of B19V viremia. All B19V sequences were of genotype 1. None of the sera investigated contained PARV4 or HBoV1 DNAs. Our data demonstrate B19V viremia to be frequent among pediatric allogeneic HSCT recipients, yet without apparent clinical correlates. PARV4 or HBoV1 viremias were not seen in these immunocompromised patients.

Interleukin-15 administration increases graft-versus-tumor activity in recipients of haploidentical hematopoietic SCT

Utilizing a clinically relevant haploidentical (HI) murine transplant model, lethally irradiated B6D2F1 (H2K(b/d)) mice were transplanted with T cell-depleted (TCD) BM from B6CBAF1 (H2K(b/k)) mice. We found that administration of IL-15 significantly increases the numbers of CD8+ T and natural killer (NK) cells in spleen and BM after transplantion without GVHD. Graft-versus-tumor (GVT) potency of the graft was evaluated upon tumor challenge using P815 tumor cells (H2(d)). IL-15 administration without T-cell infusion did not result in any survival improvement. However, IL-15 in combination with very low-dose T-cell infusion (1 × 10(4)) significantly increased GVT activity and improved survival in recipients of HI hematopoietic SCT (HSCT). This effect was observed when IL-15 was given at a later time point, rather than immediately following transplantation. IL-15 administration also specifically increased slow-proliferative CD8+ T-cell proliferation and IFN-γ secretion in CD8+ T cells in recipients of CFSE (carboxyfluorescein succinimidyl ester)-labeled HI T-cell infusion, whereas there was no effect on CD4+ T-cell proliferation, suggesting the critical effect of IL-15 on CD8+ T-cell homeostasis in HI host. We conclude that IL-15 can be used for enhancing antileukemia effect of HI-HSCT, which requires presence of donor-derived T cells.

Monitoring of TNFR1, IL-2Rα, HGF, CCL8, IL-8 and IL-12p70 following HSCT and their role as GVHD biomarkers in paediatric patients

No predictive factors are currently available to establish patient-specific GVHD risk. A panel of six serum cytokines (TNF receptor 1, IL-2 receptor alfa (IL-2Rα), hepatocyte growth factor (HGF), monocyte chemo-attractant protein-2, IL-8, IL-12p70) were monitored at established time points (days -1, +1, +7, +14, +21, +28 and +60) in 170 paediatric hematopoietic SCT (HSCT) recipients. We found that higher concentrations of IL-2Rα on days +14 and +21 together with HGF on days +14 and +21 were significantly associated at a higher probability of both grade II-IV GVHD (on day +14 it was: 60% vs 28%, P=0.007) and grade III-IV (on day +14 it was: 40% vs 15%, P=0.001). The higher IL-8 serum concentration on day +28 was associated with a lower probability of chronic GVHD being 4% vs 29% (P=0.01) for patients with higher vs lower IL-8 serum concentration. These findings were confirmed when the analysis was restricted to the the matched unrelated donor group. In conclusion, even if the serum cytokine levels were related to several variables associated with HSCT, we identified two cytokines as predictors of GVHD II-IV and III-IV, translating into a higher TRM risk (17% vs 3%, P=0.004).

Adenoviral infections in adult allogeneic hematopoietic SCT recipients: a single center experience

Disseminated adenoviral infection (AI) is associated with profound immunosuppression and poor outcome after allogeneic hematopoietic SCT (allo-HSCT). A better understanding of AI in allo-HSCT recipients can serve as a basis to develop more effective management strategies. We evaluated all adult patients who received allo-HSCT at MD Anderson Cancer Center between 1999 and 2008. Among the 2879 allo-HSCT patients, 73 (2.5%) were diagnosed with AI. Enteritis (26%) and pneumonia (24%) were the most common clinical manifestations; pneumonia was the most common cause of adenovirus-associated death. A multivariable Bayesian logistic regression showed that when the joint effects of all covariates were accounted for, cord blood transplant, absolute lymphocyte count (ALC) ≤ 200/mm(3) and male gender were associated with a higher probability of disseminated AI. The OS was significantly worse for patients with AI that was disseminated rather than localized (median of 5 months vs median of 28 months, P<0.001) and for patients with ALC ≤ 200/mm(3) (P<0.001). Disseminated AI, in patients who received allo-HSCT, is a significant cause of morbidity and mortality. Strategies for early diagnosis and intervention are essential, especially for high-risk patients.

Bronchiolitis obliterans after allogeneic hematopoietic SCT: further insight—new perspectives?

Bronchiolitis obliterans (BO) is a late non-infectious pulmonary complication after allogeneic hematopoietic SCT. Among 982 patients after myeloablative hematopoietic SCT between January 2000 and October 2010, 68 were diagnosed with BO according to NIH criteria. The median onset of BO was 18 months post transplant, 5-year cumulative incidence was 5.8% and 5-year mortality 41%. BO prevalence rate was 10% among all long-term surviving hematopoietic SCT recipients and 12% among chronic GVHD-patients. Chronic GVHD, peripheral SCT and ABO blood group incompatibility were identified as risk factors associated with BO. IgG levels were significantly decreased at the onset of BO (6.7 g/L±0.7, P=0.001), the mean exhaled NO concentrations were lower in BO-patients than in stem cell recipients without BO (14 p.p.b.±0.9 vs 20 p.p.b.±2.1) or healthy controls (25 p.p.b.±2.4, P<0.001). Hypoxia-inducible factor 1 alpha (HIF-1α) was significantly elevated in BO as compared with healthy controls or GVHD-patients without lung involvement (340±61 vs 127±22 vs 140±32, P=0.02). Calculated 5-year survival was superior in female than in male BO-patients (86 vs 45%, P=0.04). These results emphasize the relevance of BO as serious late complication with substantial mortality and point to essential pathophysiological changes due to regulatory responses to hypoxia.

Citrulline and albumin as biomarkers for gastrointestinal mucositis in recipients of hematopoietic SCT

Gastrointestinal (GI) mucositis is a common side effect of intense chemotherapy to prepare patients for hematopoietic SCT. Measuring intestinal damage objectively remains difficult, and clinicians often rely on albumin levels as an indicator of GI mucositis, but citrulline might be a more specific marker, which has in the past been shown to correlate with clinical signs of GI mucositis. We evaluated the courses of albumin and citrulline following different conditioning regimens for SCT and studied their relatedness to the subsequent inflammatory response using C-reactive protein. Patterns of albumin and citrulline differed significantly between myeloablative and non-myeloablative conditioning regimens. After myeloablative regimens, decreasing citrulline levels preceded the occurrence of inflammation unlike albumin levels, which decreased thereafter. Albumin levels were greatly influenced by inflammation, confirming it to be a 'negative acute-phase protein', whereas citrulline levels were not. Citrulline appeared to be a better biomarker of GI mucositis than albumin. Measuring citrulline might prove useful in clinical decision making, in identifying GI mucositis, and it would also be of interest to see how it compares with other biomarkers in the setting of acute GI GVHD.

Viral-specific adoptive immunotherapy after allo-SCT: the role of multimer-based selection strategies

Recipients of hematopoietic SCT undergo a period of profound immunosuppression due to the chemotherapy and/or radiotherapy used for the conditioning and to the graft versus host reaction. SCT patients are highly susceptible to the development of viral infections such as CMV or EBV. The achievement of a competent immunological response, such as viral-specific T cells, is associated with a lower incidence of viral infections. Methods for direct identification of antigen-specific T cells have been based on the functional characteristics of these T cells. Techniques such as proliferation and ELISPOT assays, intracellular cytokine staining and IFN-γ capture have been used to quantitate and obtain viral-specific T cells. Multimers are composed of several MHC molecules loaded with immunodominant peptides joined to a fluorescent molecule, which signal can be quantified by a flow cytometer. Multimer technology together with recent advances in flow cytometry, have facilitated the monitoring and selection of antigen-specific T cells without the need for in vitro cultures and manipulation. This has resulted in a better characterization of the function and phenotype of the different subpopulations of T cells involved in the immune recovery post allogeneic SCT. It is becoming a distinct possibility to isolate individual antigen-specific T cells, without long-term culture techniques, and potentially use them as adoptive immunotherapy in the SCT setting.