Emerging viral infections after hematopoietic cell transplantation

Detection of human herpes virus 6 DNA and chromosomal integration after allogeneic hematopoietic stem cell transplantation: a retrospective single center analysis

INTRODUCTION

Human herpes virus 6 (HHV-6) can reactivate after allogeneic hematopoietic stem cell transplantation (allo-HSCT) and may be associated with significant morbidity and mortality.

METHODS

The epidemiology of HHV-6 infections and their impact on outcome after allo-HSCT were retrospectively analyzed in 689 adult allo-HSCT recipients (January 2015-December 2018). Chromosomal integration of HHV-6 (ciHHV-6) in the donor was retrospectively investigated to critically evaluate antiviral treatment strategies.

RESULTS

HHV-6 DNA in any specimen was found in 89 patients. HHV-6 infections (encephalitis (1), gastroenteritis (44), dermatitis (2), hepatitis (1) or pneumonitis (5)) were diagnosed in 53/689 patients (7.7%). Elevated levels of HHV-6 DNA were found in 38 patients (5.5%). CiHHV-6, analyzed in patients with HHV-6 viral loads ≥10⁴ copies/mL, was identified in 4 patients (10/38 patients; 10.5%). Two of those displayed copy numbers of HHV-6 ranging from ≥ 2 × 10⁵ to 2.5 × 10⁶ copies/mL (HHV-6A). Here, ciHHV-6 was integrated into donor and not into the patients' cells. In this series of allo-HSCT recipients, 10.5% of patients with blood viral loads of HHV-6 showed ciHHV-6.

CONCLUSION

Screening of the donor for chromosomal integration of HHV-6 (ciHHV-6) before initiation of antiviral therapy is recommended. This article is protected by copyright. All rights reserved.

Harnessing T Cells to Control Infections After Allogeneic Hematopoietic Stem Cell Transplantation

Dramatic progress in the outcome of allogeneic hematopoietic stem cell transplantation (allo-HSCT) from alternative sources in pediatric patients has been registered over the past decade, providing a chance to cure children and adolescents in need of a transplant. Despite these advances, transplant-related mortality due to infectious complications remains a major problem, principally reflecting the inability of the depressed host immune system to limit infection replication and dissemination. In addition, development of multiple infections, a common occurrence after high-risk allo-HSCT, has important implications for overall survival. Prophylactic and preemptive pharmacotherapy is limited by toxicity and, to some extent, by lack of efficacy in breakthrough infections. T-cell reconstitution is a key requirement for effective infection control after HSCT. Consequently, T-cell immunotherapeutic strategies to boost pathogen-specific immunity may complement or represent an alternative to drug treatments. Pioneering proof of principle studies demonstrated that the administration of donor-derived T cells directed to human herpesviruses, on the basis of viral DNA monitoring, could effectively restore specific immunity and confer protection against viral infections. Since then, the field has evolved with implementation of techniques able to hasten production, allow for selection of specific cell subsets, and target multiple pathogens. This review provides a brief overview of current cellular therapeutic strategies to prevent or treat pathogen-related complications after HSCT, research carried out to increase efficacy and safety, including T-cell production for treatment of infections in patients with virus-naïve donors, results from clinical trials, and future developments to widen adoptive T-cell therapy access in the HSCT setting.

Viral reactivations following hematopoietic stem cell transplantation in pediatric patients - A single center 11-year analysis

Viral reactivation occurs frequently in the context of immunodeficiency and immunosuppression after allogeneic hematopoietic stem cell transplantation (allo-HSCT) and can cause severe complications. The aim of this single-center retrospective analysis was to characterize viral infections in the first year after HSCT, to investigate risk factors and to study the impact of viral infections on transplantation outcome. This will facilitate the identification of at-risk patients and the development of new preventive strategies. 107 pediatric allo-HSCT from January 2005 through December 2015 were analyzed for infections with Epstein-Barr virus (EBV), cytomegalovirus (CMV), human herpesvirus 6 (HHV-6), adenovirus (ADV), herpes simplex virus (HSV) and varicella zoster virus (VZV). Viral infections were detected after 68.2% of transplantations. The viruses most commonly encountered were HHV-6 (36/107) and EBV (30/107). Severe viral disease was rare (7/107) and none of the patients died as result of viral reactivation. Important risk factors for viral infections were higher age at HSCT, donor type and occurrence of acute graft-versus-host disease (aGvHD). Especially for EBV, transplant from an unrelated donor and in-vivo T-cell depletion (TCD) had a significant effect on infection rates, whereas for CMV the strongest effect was seen by donor and recipient serostatus with recipient seropositivity most predictive for reactivation. The occurrence of severe aGvHD was associated with EBV and ADV infections. For HSV, the recipient serostatus was identified as prognostic factor for HSV infections, while we found higher age at time of HSCT as risk factor for VZV infections. The overall survival of patients with or without viral infections did not differ significantly. Interestingly, when looking at the 85 patients in our cohort who had received an HSCT for a malignant disease, a tendency towards lower relapse rates was seen in patients affected by viral infections (HR 0.51, 95% CI 0.25 - 1.06, p = 0.072). Viral reactivations are common after pediatric allo-HSCT, though severe complications were rare in our collective. Determining risk factors for viral reactivations may help to identify patients in need of intensified monitoring and to individualize preventive strategies.

Management of Hematuria in Children

Purpose of Review

This paper provides a review of the diagnostic evaluation of both microscopic and gross hematuria, as well as an update on the pathogenesis, clinical features, and treatment strategies for several diseases of the kidneys and urinary tract in which hematuria is a prominent finding. The goal is to provide pediatric providers with a framework through which appropriate and expeditious referral to subspecialty care may be made for definitive treatment.

Recent Findings

Although there has been great heterogeneity in published treatment strategies for many causes of hematuria, the Kidney Diseases Improving Global Outcomes (KDIGO) initiative has recently set forth guidelines for glomerular diseases in particular to provide evidence-based strategies for treatment. In addition, recent advances in the understanding of molecular pathogenesis and long-term clinical outcomes for other non-glomerular diseases has led to updates in treatment strategies summarized in this review.

Summary

As the pediatric primary care provider is often the first point of contact for children with microscopic or gross hematuria, updated knowledge as to the epidemiology and management of several of the various causes of hematuria will improve the care of children by both avoiding extraneous testing and interventions and implementing definitive care (either by expectant management and reassurance or by subspecialty referral) in a timely manner.

Dissecting the mechanisms involved in anti-human T-lymphocyte immunoglobulin (ATG)-induced tolerance in the setting of allogeneic stem cell transplantation - potential implications for graft versus host disease

Polyclonal anti-human thymocyte globulins (ATG) have been recently shown to significantly reduce the incidence of graft versus host disease (GVHD) post allogeneic stem cell transplantation (HSCT) from both sibling and unrelated donors. Induction of regulatory T cells has been suggested as one of the possible mechanisms. The aim of current study was to further characterize the T cell populations induced by ATG treatment and to delineate the mechanisms involved in ATG-induced tolerance. Phenotypic characterization revealed a significant increase in the expression of FoxP3, GITR, CD95, PD-1 and ICOS as well as the complement inhibitory molecules CD55, CD58 and CD59 on CD4+CD25+ T cells upon ATG treatment. Addition of ATG-treated cells to autologous and allogeneic peripheral blood mononuclear cells (PBMCs) stimulated with anti-CD3/anti-CD28 antibodies resulted in significant inhibition of proliferation. Moreover, T-cell activation and IFNγ secretion were reduced in the presence of ATG-induced Treg cells. The CD4+CD25+CD127-low Treg fraction sorted from ATG-treated culture demonstrated greater suppressive potency than negative fraction. Conditioned medium produced by ATG-treated but not IgG-treated cells contained TGFβ and suppressed T cell proliferation and activation in a TGFβ receptor-dependent manner. TGFβ receptor kinase inhibitor SB431542 interfered with the suppressive activity of ATG-primed cells, enabling partial rescue of proliferation and IFNγ secretion. Moreover, SB431542 prevented Treg phenotype induction upon ATG treatment. Altogether, our data reveal the role of TGFβ signaling in ATG-mediated immunosuppression and further support the use of ATG, a potent inducer of regulatory T cells, for prevention of GVHD post HSCT and potentially other therapeutic applications.

Cytomegalovirus-Specific T Cells Isolated by IFN-γ Secretion Assay Do Not Induce Significant Graft-Versus-Host Reactions In Vitro

BACKGROUND

Graft-versus-host (GvH) disease (GvHD) remains a serious concern for patients undergoing antiviral cellular therapy. Despite the major improvements in cellular immunotherapy, the immunogenicity of virus-specific T cells has not yet been fully defined. This present study aims to examine how cytomegalovirus (CMV)-specific cytotoxic T lymphocytes (CTLs) respond to allogeneic antigen stimulation and whether they give rise to GvHD target tissue damage.

METHODS

Cytomegalovirus-specific CTLs were isolated by the IFN-γ secretion assay (gamma-catch) from healthy seropositive volunteers and expanded in vitro. The levels of intracellular IFN-γ, cytotoxic activity, IFN-γ and granzyme B secretion, and CD25 expression were measured using flow cytometry (fluorescence-activated cell sorting). The ability of CMV-CTLs to induce GvHD target tissue damage was evaluated using the human in vitro skin explant assay (skin explant assay).

RESULTS

Cytomegalovirus-specific CTLs responded specifically to CMV-phosphoprotein 65 stimulation by secreting IFN-γ and killing virus peptide loaded autologous phytohemagglutinin (PHA) blasts. Compared with unselected peripheral blood mononuclear cells, CMV-CTLs induced significantly less severe cutaneous GvH tissue damage. This observation coincided with low levels of CD25 expression, as well as IFN-γ and granzyme B secretion after allogeneic antigen stimulation in both the mixed lymphocyte reaction and in the skin explant assay.

CONCLUSIONS

Cytomegalovirus-specific CTLs isolated by the IFN-γ secretion assay from HLA-unmatched healthy donors exhibited a high level of anti-CMV potency without inducing significant cutaneous GvH tissue damage in vitro. This finding provides novel evidence supporting the safe use of in vitro expanded CMV-CTLs as an antiviral therapy in transplant patients with refractory CMV infections.

Metapneumovirus Infections and Respiratory Complications

Acute respiratory tract infections (ARTIs) are the most common illnesses experienced by people of all ages worldwide. In 2001, a new respiratory pathogen called human metapneumovirus (hMPV) was identified in respiratory secretions. hMPV is an RNA virus of the Paramyxoviridae family, and it has been isolated on every continent and from individuals of all ages. hMPV causes 7 to 19% of all cases of ARTIs in both hospitalized and outpatient children, and the rate of detection in adults is approximately 3%. Symptoms of hMPV infection range from a mild cold to a severe disease requiring a ventilator and cardiovascular support. The main risk factors for severe disease upon hMPV infection are the presence of a high viral load, coinfection with other agents (especially human respiratory syncytial virus), being between 0 and 5 months old or older than 65 years, and immunodeficiency. Currently, available treatments for hMPV infections are only supportive, and antiviral drugs are employed in cases of severe disease as a last resort. Ribavirin and immunoglobulins have been used in some patients, but the real efficacy of these treatments is unclear. At present, the direction of research on therapy for hMPV infection is toward the development of new approaches, and a variety of vaccination strategies are being explored and tested in animal models. However, further studies are required to define the best treatment and prevention strategies.

Preventing stem cell transplantation-associated viral infections using T-cell therapy

Hematopoietic stem cell transplantation is the treatment of choice for many hematologic malignancies and genetic diseases. However, viral infections continue to account for substantial post-transplant morbidity and mortality. While antiviral drugs are available against some viruses, they are associated with significant side effects and are frequently ineffective. This review focuses on the immunotherapeutic strategies that have been used to prevent and treat infections over the past 20 years and outlines different refinements that have been introduced with the goal of moving this therapy beyond specialized academic centers.

Antiviral T-cell therapy

Serious viral infections are a common cause of morbidity and mortality after allogeneic stem cell transplantation. They occur in the majority of allograft recipients and are fatal in 17–20%. These severe infections may be prolonged or recurrent and add substantially to the cost, both human and financial, of the procedure. Many features of allogeneic stem cell transplantation contribute to this high rate of viral disease. The cytotoxic and immunosuppressive drugs administered pretransplant to eliminate the host hematopoietic/immune system and any associated malignancy, the delay in recapitulating immune ontogeny post‐transplant, the immunosuppressive drugs given to prevent graft versus host disease (GvHD), and the effects of GvHD itself, all serve to make stem cell transplant recipients vulnerable to disease from endogenous (latent) and exogenous (community) viruses, and to be incapable of controlling them as quickly and effectively as most normal individuals.

The development of new therapies for human herpesvirus 6

Human herpesvirus 6 (HHV-6) infections are typically mild and in rare cases can result in encephalitis. A common theme among all the herpesviruses, however, is the reactivation upon immune suppression. HHV-6 commonly reactivates in transplant recipients. No therapies are approved currently for the treatment of these infections, although small studies and individual case reports have reported intermittent success with drugs such as cidofovir, ganciclovir, and foscarnet. In addition to the current experimental therapies, many other compounds have been reported to inhibit HHV-6 in cell culture with varying degrees of efficacy. Recent advances in the development of new small molecule inhibitors of HHV-6 will be reviewed with regard to their efficacy and spectrum of antiviral activity. The potential for new therapies for HHV-6 infections will also be discussed, and they will likely arise from efforts to develop broad spectrum antiviral therapies for DNA viruses.

Accelerating immune reconstitution after hematopoietic stem cell transplantation

Viral infections remain a significant cause of morbidity and mortality after hematopoietic stem cell transplantation. Pharmacologic agents are effective against some pathogens, but they are costly and can be associated with significant toxicities. Thus, many groups have investigated adoptive T-cell transfer as a means of hastening immune reconstitution and preventing and treating viral infections. This review discusses the immunotherapeutic strategies that have been explored.

Epidemiology of viral respiratory tract infections in an outpatient haematology facility

Viral respiratory tract infections (VRTI) are an important cause of morbidity and mortality in haematology patients, particularly after haematopoietic stem cell transplantation (HSCT). The incidence, clinical presentation and outcome of symptomatic and asymptomatic VRTI in HSCT outpatient unit were prospectively evaluated during a single influenza season (January–March 2011). Pharyngeal swabs were performed at the first visit and if new symptoms were present. Molecular multiplex assay for 12 respiratory viruses was performed by the regional reference laboratory. Among 264 swabs from 193 outpatients, 58 (22 %) resulted positive for 61 viruses (influenza, n = 20; respiratory syncytial virus [RSV], n = 21; rhinovirus, n = 12; coronavirus, n = 4; adenovirus, n = 3; parainfluenza, n = 1). VRTI were detected more frequently in the presence of symptoms than in asymptomatic patients: 49 out of 162 (30 %) vs. 9 out of 102 (9 %), p < 0.001. Influenza-like illness syndrome (ILI) was significantly associated with a VRTI if compared to other presentations (42 %), while the European Centre for Disease Prevention and Control definition was not (30 %). Positive predictive value (PPV) of ILI for influenza was 17 %. Influenza and RSV peak periods were contemporary. Influenza prophylaxis was given to 25 patients following exposure. Low rate of progression from upper to lower respiratory tract infection (approximately 5 % for influenza and RSV), no nosocomial epidemics and no VRTI-related deaths were observed. VRTI are very frequent in high-risk haematology outpatients, but symptoms are aspecific and PPV of ILI is low. Symptoms of influenza and RSV overlap. Thus, microbiological diagnosis and contact preventive measures are crucial. Rather than universal influenza prophylaxis, prompt diagnosis and treatment of only documented infections could be pursued.

Fatal human metapneumovirus infection following allogeneic hematopoietic stem cell transplantation

Respiratory viruses are an important yet underestimated cause of infectious morbidity and mortality in immunocompromised children and adolescents. Here, we report the occurrence of fatal lower respiratory tract disease associated with human metapneumovirus (HMPV) infection in a 10-year-old girl with chronic graft-versus-host disease following allogeneic hematopoietic stem cell transplantation (HSCT) for secondary chronic myeloid leukemia. Symptoms occurred 8 months after HSCT while on immunosuppression with 0.2 mg/kg/day of prednisone, and presented as dry cough, bilateral pneumonitis, and progressive respiratory distress. Non-invasive and invasive microbiological investigations revealed HMPV type B as the sole pathogen. Histopathological findings showed interstitial and intra-alveolar pneumonitis with profound alveolar cell damage. The patient was treated with intravenous and oral ribavirin and polyvalent immunoglobulins, but ultimately died from respiratory failure. The case reflects the potentially fatal impact of infections by respiratory viruses in immunocompromised patients and the need for effective approaches to their prevention and treatment.

Respiratory syncytial virus disease: prevention and treatment

Respiratory syncytial virus (RSV) is one of the most clinically important viruses infecting young children, the elderly, and the immunocompromised. Over the past decade, the most significant advance in the prevention of RSV disease has been the development of high-titered antibody products. Infection control is the only other strategy to prevent RSV disease. A humanized monoclonal antibody directed against the fusion (F) protein palivizumab, (Synagis®, MedImmune, Inc., Gaithersburg, MD), is given routinely on a monthly basis to premature infants and young children less than 24 months of age with underlying medical problems including prematurity, chronic lung disease, or cardiac disease to prevent RSV disease and hospitalization. Other products utilizing polyclonal or monoclonal antibodies or antibody fragments against the F protein have been developed and some already tested in patient populations. The only licensed antiviral treatment available today is ribavirin, a guanosine analogue generally administered as a small particle aerosol to immunocompromised patients with lower respiratory tract disease due to RSV. This drug has also been utilized in oral and intravenous forms, again mainly in immunocompromised patients. Promising new antiviral agents under development by multiple pharmaceutical and biotechnology companies include small molecule fusion inhibitors, attachment inhibitors, inhibitors of RNA synthesis, and small interfering RNA particles (siRNA).

Human Metapneumovirus: lessons learned over the first decade

It has been 10 years since human metapneumovirus (HMPV) was identified as a causative agent of respiratory illness in humans. Since then, numerous studies have contributed to a substantial body of knowledge on many aspects of HMPV. This review summarizes our current knowledge on HMPV, HMPV disease pathogenesis, and disease intervention strategies and identifies a number of areas with key questions to be addressed in the future.

Multiplex polymerase chain reaction for six herpesviruses after hematopoietic stem cell transplantation

BACKGROUND

Herpesviruses cause life-threatening diseases after hematopoietic stem cell transplantation (HSCT). It is necessary that viral diseases are identified early and safely diagnosed. The purpose of this study was to evaluate the efficacy of multiplex polymerase chain reaction (PCR) for qualitative detection of the six herpesviruses simultaneously: herpes simplex virus type 1 and type 2, varicella-zoster virus, cytomegalovirus, Epstein-Barr virus (EBV) and human herpesvirus 6B.

METHODS

Multiplex PCR was applied to patients with various clinical manifestations including central nervous system, cutaneous and mucosal complications after allogeneic HSCT, and the data were retrospectively analyzed.

RESULTS

Patients positive for cytomegalovirus in peripheral blood by multiplex PCR might need pre-emptive treatment, but a positive result for EBV had no specific correlation with EBV-associated post-transplant lymphoproliferative disease, and positive result for human herpesvirus 6B failed to show any clinical significance. The multiplex PCR was safe and helpful to diagnose viral diseases of local regions, for example, the central nervous system, skin and mucosa.

CONCLUSIONS

It may be worthwhile to survey the six herpesviruses with multiplex PCR after HSCT.

Molecular impact and inducible factors associated with adenovirus infection in hematopoietic stem [corrected] cell transplant patients

BACKGROUND AND PURPOSE OF STUDY

Latent and active adenovirus infections are detected in 5% to 20% of hematopoietic stem cell transplant (HSCT) patients. In addition to the significant role of adenoviral infection in the pathogenesis of late-onset hemorrhagic cystitis in HSCT patients, adenovirus infections may have possible roles in undefined posttransplant clinical complications. Therefore, pre- and posttransplantation we studied the prevalence and role of adenoviral infections among HSCT clinical syndromes using molecular methods.

MATERIALS AND METHODS

In this cross-sectional study between 2005 and 2008. We collected 470 EDTA-treated blood samples from 125 HSCT recipients, including 70 (56%) men and 55 (44%) women. The 52 (41.6%) HSCT patients underwent autologous grafts and the other 73 (58.4%), from related donors. One EDTA-treated blood sample was collected from all recipients pretransplantation. Also once per week for 3 months we were collected blood samples from HSCT patients to evaluate the prevalence of adenovirus DNA infection by a qualitative in house polymerase chain reaction method.

RESULTS

The adenovirus genome was diagnosed in 2/75 (2.7%) HSCT patient samples pretransplantation. There were 28/395 (7.1%) plasma samples of transplant patients infected with adenovirus DNA. Graft-versus-host disease (GVHD) clinical complications were observed in six adenovirus-infected transplant recipients; there was a significant correlation between these viral infections and GVHD clinical presentation.

CONCLUSION

The high prevalence of adenovirus infection in HSCT recipients pre- and posttransplantation, was significantly related to GVHD symptoms, enforcing the important pathogenic role of these viral infections in clinical complications post-HSCT.

Benzimidazole analogs inhibit human herpesvirus 6

Several benzimidazole nucleoside analogs, including 1H-β-D-ribofuranosyl-2-bromo-5,6-dichlorobenzimidazole (BDCRB) and 1H-β-L-ribofuranosyl-2-isopropylamino-5,6-dichlorobenzimidazole (maribavir [MBV]), inhibit the replication of human cytomegalovirus. Neither analog inhibited the related betaherpesvirus human herpesvirus 6 (HHV-6). Additional analogs of these compounds were evaluated against both variants of HHV-6, and two L-analogs of BDCRB had good antiviral activity against HHV-6A, as well as more modest inhibition of HHV-6B replication.

NKT cells, Treg, and their interactions in bone marrow transplantation

Bone marrow transplantation (BMT) is a potentially curative treatment for patients with leukemia and lymphoma. Tumor eradication is promoted by the anti-tumor activity of donor T cells contained in the transplant; however, donor T cells also mediate the serious side effect of graft-versus-host disease (GVHD). Separation of GVHD from graft anti-tumor activity is an important goal of research in improving transplant outcome. One approach is to take advantage of the immunomodulatory activity of regulatory NKT cells and CD4(+)CD25(+) Treg of host and/or donor origin. Both host and donor NKT cells and donor Treg are able to prevent GVHD in murine models. In this review, we summarize the mechanisms of NKT cell- and Treg-mediated protection against GVHD in mice while maintaining graft anti-tumor activity. In addition, we also examine the interactions between NKT cells and Treg in the context of BMT, and integrate the data from murine experimental models with the observations made in humans.

Cytomegalovirus, adenovirus, and polyomavirus co-infection among pediatric recipients of allogeneic stem cell transplantation: characteristics and outcome

ADV and PMV infection have increasingly been documented as significant complications following allo-HSCT. Despite increasing recognition, characteristics and outcome of CMV, ADV, and PMV viral co-infection remain obscured. In this study, a retrospective quantitative PCR analysis of ADV, PMV (BKV and JCV) was performed from pediatric patients' stored blood samples previously tested for CMV viremia after allo-HSCT. Clinical and virological characteristics and outcome among patients with and without viral co-infection were analyzed and compared. From 2001 to 2006, 219 blood samples from 69 patients were studied. Viral DNA was present in 119 samples (52.9%).The proportion of viremia was highest for BKV (30.6%), followed by CMV (20.9%), ADV (9.1%), and JCV (0.5%). Viral co-infection occurred in 17 patients (24.6%), with CMV/BKV as the most common type (11.6%), followed by CMV/ADV (4.3%) and ADV/BKV (2.9%). From multivariate analysis, factors associated with viral co-infection were acute GVHD (OR 4.57; 95% CI 1.9-10.96, p = 0.001), level of blood CMV viral load (OR 1.53; 95% CI 1.24-1.89, p < 0.001), and level of blood ADV viral load (OR 1.56; 95% CI 1.05-2.32, p = 0.027). Higher probability of developing viral disease was strongly associated with more types of virus detected in blood (p < 0.001). Significant difference in the causes of death was observed among patients with and without viral co-infection (p = 0.014). Infection (87.5%) was the major cause of death of patients with viral co-infection, whereas relapse of hematologic disease (70%) was the major cause of death of patients with mono-viral infection. Viral co-infection is a common and significant infectious complication in pediatric recipients of allo-HSCT. Blood monitoring of CMV, ADV, and BKV is suggested among pediatric patients who develop GvHD or who have rising of CMV or ADV viremia following allo-HSCT.

Challenges of T cell therapies for virus-associated diseases after hematopoietic stem cell transplantation

IMPORTANCE OF THE FIELD

Hematopoietic stem cell transplantation (HSCT) is the treatment of choice for many hematological malignancies and genetic disorders. The majority of patients do not have a human leukocyte antigen (HLA) identical sibling donor, and alternative stem cell sources include HLA-matched or mismatched unrelated donors and haploidentical related donors. However, alternative donor HSCT are associated with three major complications i) graft rejection; ii) graft-versus-host disease (GvHD); and iii) delayed immune reconstitution leading to viral infections and relapse.

AREAS COVERED IN THIS REVIEW

Graft rejection and the risk of GvHD can be significantly reduced by using intensive conditioning regimens, including in vivo T cell depletion as well as ex vivo T cell depletion of the graft. However, the benefits of removing alloreactive T cells from the graft are offset by the concomitant removal of T cells with anti-viral or anti-tumor activity as well as the profound delay in endogenous T cell recovery post-transplant. Thus, opportunistic infections, many of which are not amenable to conventional small-molecule therapeutics, are frequent in these patients and are associated with significant morbidity and high mortality rates. This review discusses current cell therapies to prevent or treat viral infections/reactivations post-transplant.

WHAT THE READER WILL GAIN

The reader will gain an understanding of the current state of cell therapy to prevent and treat viral infections post-HSCT, and will be introduced to preclinical studies designed to develop and validate new manufacturing procedures intended to improve therapeutic efficacy and reduce associated toxicities.

TAKE HOME MESSAGE

Reconstitution of HSCT recipients with antigen-specific T cells, produced either by allodepletion or in vitro reactivation, can offer an effective strategy to provide both immediate and long-term protection without harmful alloreactivity.

Prospective, comprehensive, and effective viral monitoring in children undergoing allogeneic hematopoietic stem cell transplantation

Major advances in the monitoring and treatment of viral infections after hematopoietic stem cell transplantation (HSCT) have been achieved over the last decade. The appropriate extent of viral monitoring and antiviral therapy remains controversial, and reports in pediatric patients receiving allogeneic unmanipulated hematopoietic stem cells (HSCs) are sparse. A total of 40 pediatric patients who underwent HSCT with either peripheral blood stem cells (PBSCs, n = 30) or bone marrow (BM; n = 10) were prospectively monitored every week for viral DNAemia (VDNA) by simultaneous detection of cytomegalovirus (CMV), Epstein-Barr virus (EBV), human herpesvirus 6 (HHV6), human adenovirus (ADV), and polyoma BK virus (BKV) using real-time TaqMan polymerase chain reaction (PCR). All patients received prophylactic acyclovir and preemptive ganciclovir (GCV) when 500 copies/microg DNA (EBV/HHV6) or >1 copy/microg DNA (CMV) were detected on 2 consecutive measurements. VDNA occurred in 25 of 40 recipients (CMV, 11/40 patients [28%]; EBV, 19/40 [48%]; HHV6, 2/40 [5%]; ADV/BKV, 1/40) and was found exclusively after neutrophil engraftment and in most cases up to day +100. Recurrent VDNA (P = .028) and (readily treatable) viral disease (P = .003) were observed predominantly in patients suffering from nonmalignant diseases, a cohort characterized by delayed lymphocyte engraftment. VDNA occurred more frequently in HLA-mismatched HSCT and in the 24 of 40 patients receiving antithymocyte globulin (ATG). The incidence of EBV, but not that of CMV, was increased in the ATG group. Yet, in these patients, viral loads of both EBV and CMV were higher, but with prompt initiation of preemptive GCV, no posttransplantation lymphoproliferative disorder or other life-threatening morbidities occurred. HHV6 was typically detected at low viral loads (<10(2) copies/microg DNA), with only 5% of HSC recipients fulfilling our HHV6 criteria for triggering GCV treatment. In multivariate analysis, ATG treatment, HLA mismatch, recipient CMV seropositivity, and stem cell source, but not severe acute graft-versus-host disease were identified as independent risk factors for VDNA. This comprehensive viral monitoring program with defined thresholds for initiation of preemptive GCV effectively prevents the development of critical viral disease, even in high-risk patients receiving ATG.

Hematopoietic cell transplantation and emerging viral infections

Viral infections remain important causes of morbidity and mortality in hematopoietic cell transplant recipients. More recent developments in preparative regimens and graft manipulations, as well as the control of well-recognized post-transplant infections by the introduction of prophylaxis and preemptive strategies, have influenced the timing and the epidemiology of infections. As new pathogens, such as human metapneumovirus (HMPV), human bocavirus, human coronaviruses HCoV-NL63 and HCoV-HKU1, human herpesviruses HHV-6 and HHV-7, and polyomaviruses, have emerged, it is fundamental to determine the significance of the newly discovered viruses and their role in the transplantation field. This article summarizes recent data on epidemiology and laboratory diagnosis of new pathogens, as well as clinical features and management of the associated infectious complications. J. Med. Virol. 82:528-538, 2010. (c) 2010 Wiley-Liss, Inc.

Human metapneumovirus infection in hematopoietic stem cell transplant recipients

Human metapneumovirus (hMPV) was described in 2001 and has been associated with both upper and lower respiratory tract infection (URTI and LRTI, respectively), especially in children, the elderly, and in immunocompromised patients. The objective of this study was to identify hMPV as the etiological agent of acute respiratory infection in hematopoietic stem cell transplant (HSCT) patients and to determine the clinical features of hMPV infection in these patients.

METHODS

The study was performed retrospectively in 769 respiratory samples obtained from immunocompromised patients submitted to HSCT over a period of 6 years. RNA was extracted by the guanidinium thiocyanate method, and reverse transcription polymerase chain reaction assay was performed to amplify a 928pb fragment of the hMPV N gene.

RESULTS

hMPV was present in 19 (2.5%) samples. The mean age of infected patients was 18.3+/-10.8 (range, 3-41). Sixty-six percent of hMPV infections occurred during autumn, winter, and spring months. Three episodes showed co-infection with more than 1 virus. Two patients (11.1%) were infected a few days into the conditioning period and 9 (50%) in the first 3 months after the transplant. The majority of patients (72.2%) presented URTI alone with flu-like symptoms (cough, fever, headache, wheezing), while 5 patients (27.8%) had LRTI (pneumonia). No patient died from complications associated with the hMPV infection.

CONCLUSIONS

hMPV has been reported as a respiratory pathogen in HSCT patients. We suggest that hMPV infection should be routinely investigated in this population, mainly in children, to prevent nosocomial transmission during transplant proceedings and to avoid the risk of progressing to complications due to LRTI.

Nucleofection of DCs to generate Multivirus-specific T cells for prevention or treatment of viral infections in the immunocompromised host

Viral infections cause morbidity and mortality in allogeneic hematopoietic stem cell transplant (HSCT) recipients. To prevent and treat these, we have produced and infused cytotoxic T lymphocytes (CTLs) with specificity for Epstein-Barr virus (EBV), cytomegalovirus (CMV), and adenovirus (Adv), and shown that small numbers of infused cells proliferate in vivo and protect against all three viruses. Despite these encouraging results, broader implementation of this approach is limited by the need for infectious virus material (EBV), expensive production of clinical grade adenoviral vectors, and a prolonged (8-12 weeks) period of manufacture. There is also competition between virus-derived antigens within antigen-presenting cells (APCs), limiting extension to additional agents. We now describe an approach that uses DNA nucleofection of dendritic cells (DCs) with DNA plasmids that encode a range of immunodominant and subdominant viral antigens from CMV, EBV, BK, and Adv. Within 10 days, this methodology provides multivirus-reactive CTLs that lack alloreactivity. We further demonstrate that nucleofected DC stimulation can be combined with interferon-gamma (IFN-gamma) capture technology to produce even more rapid multivirus-CTL products for treatment of acute infection. These CTL generation procedures should increase the feasibility and applicability of T-cell therapy.

Cytotoxic T lymphocytes as immune-therapy in haematological practice

Viral infections are a significant cause of morbidity and mortality, particularly in pediatric allogeneic haematopoietic stem cell transplant recipients. Effective therapies are limited and often associated with significant side effects. Adoptive transfer of virus-reactive T cells offers a means of reconstituting antiviral immunity and this approach has been successfully used to prevent and treat cytomegalovirus, Epstein-Barr virus, and adenovirus infections in vivo. This review outlines the clinical trials that have been performed to date, and will describe future initiatives to (a) develop strategies that can increase the breadth of the viruses that can be targeted, and (b) simplify the process to extend this technology to more centers so that cellular therapy to reconstitute immunity can be more widely applied.

Human herpesvirus 6A (HHV-6A) and HHV-6B alter E2F1/Rb pathways and E2F1 localization and cause cell cycle arrest in infected T cells

E2F transcription factors play pivotal roles in controlling the expression of genes involved in cell viability as well as genes involved in cell death. E2F1 is an important constituent of this protein family, which thus far contains eight members. The interaction of E2F1 with its major regulator, retinoblastoma protein (Rb), has been studied extensively in the past two decades, concentrating on the role of E2F1 in transcriptional regulation and the role of Rb in cell replication and cancer formation. Additionally, the effect of viral infections on E2F1/Rb interactions has been analyzed for different viruses, concentrating on cell division, which is essential for viral replication. In the present study, we monitored E2F1-Rb interactions during human herpesvirus 6A (HHV-6A) and HHV-6B infections of SupT1 T cells. The results have shown the following dramatic alterations in E2F1-Rb pathways compared to the pathways of parallel mock-infected control cultures. (i) The E2F1 levels were elevated during viral infections. (ii) The cellular localization of E2F1 was dramatically altered, and it was found to accumulate both in the cytoplasmic and nuclear fractions, as opposed to the strict nuclear localization seen in the mock-infected cells. (iii) Although E2F1 expression was elevated, two exemplary target genes, cyclin E and MCM5, were not upregulated. (iv) The Rb protein was dephosphorylated early postinfection, a trait that also occurred with UV-inactivated virus. (v) Infection was associated with significant reduction of E2F1/Rb complexing. (vi) HHV-6 infections were accompanied by cell cycle arrest. The altered E2F1-Rb interactions and functions might contribute to the observed cell cycle arrest.

BK virus-associated hemorrhagic cystitis in pediatric cancer patients receiving high-dose cyclophosphamide

Hemorrhagic cystitis (HC) is a known complication of oxazophosphorine chemotherapy. BK virus (BKV) has been commonly found to be associated with hematuria in stem cell transplant patients; however, it has rarely been reported after cyclophosphamide chemotherapy alone. The authors present 3 cases of BK viruria with HC in nontransplant pediatric oncology patients. The 3 patients with BKV had more prolonged hematuria (14 to 16 wk) compared with 1 patient with BKV-negative HC (10 wk). The HC necessitated chemotherapy delays and also prolonged supportive care. One patient was treated with intravenous cidofovir with resolution of BK viruria and hematuria. BKV may have an association with the development of HC in nonstem cell transplant patients receiving high-dose oxazophosphorine chemotherapy. HC may present early and be more prolonged in patients with BK viruria. Patients with HC after cyclophosphamide or ifosfamide with negative bacterial cultures should be studied for BKV. Cidofovir may be beneficial in certain patients with BK viruria and HC; however, definitive data will require a clinical trial.

Successful outcome of human metapneumovirus (hMPV) pneumonia in a lung transplant recipient treated with intravenous ribavirin

Human metapneumovirus (hMPV) has recently been shown to be a prominent cause of respiratory infections in immunocompromised hosts, and is associated with high morbidity and mortality. We report a case of hMPV pneumonia in a lung transplant recipient presenting with respiratory failure and sepsis syndrome. hMPV was diagnosed by polymerase chain reaction, and treated with intravenous ribavirin with a successful outcome.

A recombinant human monoclonal antibody to human metapneumovirus fusion protein that neutralizes virus in vitro and is effective therapeutically in vivo

Human metapneumovirus (hMPV) is a recently discovered paramyxovirus that is a major cause of lower-respiratory-tract disease. hMPV is associated with more severe disease in infants and persons with underlying medical conditions. Animal studies have shown that the hMPV fusion (F) protein alone is capable of inducing protective immunity. Here, we report the use of phage display technology to generate a fully human monoclonal antibody fragment (Fab) with biological activity against hMPV. Phage antibody libraries prepared from human donor tissues were selected against recombinant hMPV F protein with multiple rounds of panning. Recombinant Fabs then were expressed in bacteria, and supernatants were screened by enzyme-linked immunosorbent assay and immunofluorescent assays. A number of Fabs that bound to hMPV F were isolated, and several of these exhibited neutralizing activity in vitro. Fab DS7 neutralized the parent strain of hMPV with a 60% plaque reduction activity of 1.1 mug/ml and bound to hMPV F with an affinity of 9.8 x10(-10) M, as measured by surface plasmon resonance. To test the in vivo activity of Fab DS7, groups of cotton rats were infected with hMPV and given Fab intranasally 3 days after infection. Nasal turbinates and lungs were harvested on day 4 postinfection and virus titers determined. Animals treated with Fab DS7 exhibited a >1,500-fold reduction in viral titer in the lungs, with a modest 4-fold reduction in the nasal tissues. There was a dose-response relationship between the dose of DS7 and virus titer. Human Fab DS7 may have prophylactic or therapeutic potential against severe hMPV infection.

Airflow decline after myeloablative allogeneic hematopoietic cell transplantation: the role of community respiratory viruses

We conducted a 12-year retrospective study to determine the effects that the community respiratory-virus species and the localization of respiratory-tract virus infection have on severe airflow decline, a serious and fatal complication occurring after hematopoietic cell transplantation (HCT). Of 132 HCT recipients with respiratory-tract virus infection during the initial 100 days after HCT, 50 (38%) developed airflow decline ⩽1 year after HCT. Lower-respiratory-tract infection with parainfluenza (odds ratio [OR], 17.9 [95% confidence interval {CI}, 2.0–160]; P=.01) and respiratory syncytial virus (OR, 3.6 [95% CI, 1.0–13]; P=.05) independently increased the risk of development of airflow decline ⩽1 year after HCT. The airflow decline was immediately detectable after infection and was strongest for lower-respiratory-tract infection with parainfluenza virus; it stabilized during the months after the respiratory-tract virus infection, but, at ⩽1 year after HCT, the initial lung function was not restored. Thus, community respiratory virus–associated airflow decline seems to be specific to viral species and infection localization

Viral Infections in Patients with Hematological Malignancies

Viral infections are important causes of morbidity and mortality for patients with a hematological malignancy. However, the true incidence and consequences of viral infections for these patients who undergo conventional nontransplant therapy are poorly defined. The difference in incidence and outcome of viral infections among patient groups is wide, but dependent upon the intensity and duration of T-cell–mediated immune suppression. Infections caused by cytomegalovirus (CMV), herpes simplex virus (HSV), varicella-zoster virus (VZV), respiratory syncytial virus (RSV), parainfluenza viruses and influenza viruses have been intensely studied, yet newly recognized aspects of these viral infections including late CMV infection; the emergence of new viral pathogens (human herpesvirus-6, BK virus, adenovirus, and human metapneumovirus); the development of molecular diagnostic techniques, and the potential of new agents for viral prophylaxis (maribavir), or preemptive therapy (valganciclovir) form the basis of this review. Well-designed prospective studies are needed to better clarify the spectrum of these viral infections and develop effective prevention and treatment strategies. Yet the increased use of agents like alemtuzumab that induce profound T-cell depletion demands that we develop a better understanding of viral infections that occur in patients with hematological malignancy who receive nontransplant therapy.