CD13-specific autoimmunity in cytomegalovirus-infected immunocompromised patients

Associations between early-life and in utero infections and cytomegalovirus-positive acute lymphoblastic leukemia in children

Childhood infections and cytomegalovirus (CMV) are associated with pediatric acute lymphoblastic leukemia (ALL). CMV dysregulates the host immune system and alters the immune response to subsequent antigenic exposures. We suspect that this immune dysregulation contributes to increased numbers of symptomatic infections in childhood allowing for expansion of pre-leukemic clones. We explored the association between childhood infections, maternal infections during pregnancy and CMV-positive ALL. Using a droplet digital PCR assay, we screened diagnostic ALL bone marrow samples from the California Childhood Leukemia Study (1995-2015) for the presence of CMV DNA identifying CMV-positive and CMV-negative cases. We performed a case-only analysis (n = 524) comparing the number and types of childhood infections and maternal infections during pregnancy between CMV-positive and CMV-negative ALL cases using logistic regression. With increasing numbers of infections in the first 12 months of life, children were more likely to classify to the highest tertile of CMV DNA in the bone marrow at diagnosis (OR: 1.04, 95% CI: 1.01-1.08). Specifically, those reporting cough or flu in the first 12 months were more likely to be CMV-positive at ALL diagnosis (OR: 2.15, 95% CI: 1.06-4.37 and OR: 2.06, 95% CI: 1.17-3.63 respectively). Furthermore, those with a history of maternal infection during pregnancy were more likely to be CMV-positive (OR: 2.12, 95% CI: 1.24-3.62). We hypothesize that children with underlying immune dysregulation develop more symptomatic infections in childhood and ultimately CMV-positive ALL; this underlying immune dysregulation may be due to early immune system alterations via CMV exposure (in utero or early infancy) proposing a potential link between CMV and ALL etiology.

Campylobacter jejuni and Postinfectious Autoimmune Diseases: A Proof of Concept in Glycobiology

Glycans, one of the most diverse groups of macromolecules, are ubiquitous constituents of all cells and have many critical functions, including the interaction between microbes and their hosts. One of the best model organisms to study the host-pathogen interaction, the gastrointestinal pathogen Campylobacter jejuni dedicates extensive resources to glycosylation and exhibits a diverse array of surface sugar-coated displays. The first bacterium where N-linked glycosylation was described, C. jejuni can additionally modify proteins by O-linked glycosylation, has extracellular capsular polysaccharides that are important for virulence and represent the major determinant of the Penner serotyping scheme, and has outer membrane lipooligosaccharides that participate in processes such as colonization, survival, inflammation, and immune evasion. In addition to causing gastrointestinal disease and extraintestinal infections, C. jejuni was also linked to postinfectious autoimmune neuropathies, of which Guillain-Barré syndrome (GBS) and Miller Fisher syndrome (MFS) are the most extensively characterized ones. These postinfectious autoimmune neuropathies occur when specific bacterial surface lipooligosaccharides mimic gangliosides in the host nervous system. C. jejuni provided the first proof of concept for the involvement of molecular mimicry in the pathogenesis of an autoimmune disease and, also, for the ability of a bacterial polymorphism to shape the clinical presentation of the postinfectious autoimmune neuropathy. The scientific journey that culminated with elucidating the mechanistic details of the C. jejuni-GBS link was the result of contributions from several fields, including microbiology, structural biology, glycobiology, genetics, and immunology and provides an inspiring and important example to interrogate other instances of molecular mimicry and their involvement in autoimmune disease.

Effect of Cytomegalovirus Infection on the Central Nervous System: Implications for Psychiatric Disorders

Cytomegalovirus (CMV) is a common herpesvirus that establishes lifelong latent infections and interacts extensively with the host immune system, potentially contributing to immune activation and inflammation. Given its proclivity for infecting the brain and its reactivation by inflammatory stimuli, CMV is well known for causing central nervous system complications in the immune-naïve (e.g., in utero) and in the immunocompromised (e.g., in neonates, individuals receiving transplants or cancer chemotherapy, or people living with HIV). However, its potentially pathogenic role in diseases that are characterized by more subtle immune dysregulation and inflammation such as psychiatric disorders is still a matter of debate. In this chapter, we briefly summarize the pathogenic role of CMV in immune-naïve and immunocompromised populations and then review the evidence (i.e., epidemiological studies, serological studies, postmortem studies, and recent neuroimaging studies) for a link between CMV infection and psychiatric disorders with a focus on mood disorders and schizophrenia. Finally, we discuss the potential mechanisms through which CMV may cause CNS dysfunction in the context of mental disorders and conclude with a summary of the current state of play as well as potential future research directions in this area.

Posttransplant cyclophosphamide is associated with increased cytomegalovirus infection: a CIBMTR analysis

Prior studies suggest increased cytomegalovirus (CMV) infection after haploidentical donor transplantation with posttransplant cyclophosphamide (HaploCy). The role of allograft source and posttransplant cyclophosphamide (PTCy) in CMV infection is unclear. We analyzed the effect of graft source and PTCy on incidence of CMV infection, and effects of serostatus and CMV infection on transplant outcomes. We examined patients reported to the Center for International Blood and Marrow Transplantation Research between 2012 and 2017 who had received HaploCy (n = 757), matched related (Sib) with PTCy (SibCy, n = 403), or Sib with calcineurin inhibitor-based prophylaxis (SibCNI, n = 1605). Cumulative incidences of CMV infection by day 180 were 42%, 37%, and 23%, respectively (P < .001). CMV disease was statistically comparable. CMV infection risk was highest for CMV-seropositive recipients (R+), but significantly higher in PTCy recipients regardless of donor (HaploCy [n = 545]: hazard ratio [HR], 50.3; SibCy [n = 279]: HR, 47.7; SibCNI [n = 1065]: HR, 24.4; P < .001). D+/R- patients also had increased risk for CMV infection. Among R+ or those developing CMV infection, HaploCy had worse overall survival and nonrelapse mortality. Relapse was unaffected by CMV infection or serostatus. PTCy was associated with lower chronic graft-versus-host disease (GVHD) overall, but CMV infection in PTCy recipients was associated with higher chronic GVHD (P = .006). PTCy, regardless of donor, is associated with higher incidence of CMV infection, augmenting the risk of seropositivity. Additionally, CMV infection may negate the chronic GVHD protection of PTCy. This study supports aggressive prevention strategies in all receiving PTCy.

Human Cytomegalovirus and Autoimmune Diseases: Where Are We?

Human cytomegalovirus (HCMV) is a ubiquitous double-stranded DNA virus belonging to the β-subgroup of the herpesvirus family. After the initial infection, the virus establishes latency in poorly differentiated myeloid precursors from where it can reactivate at later times to cause recurrences. In immunocompetent subjects, primary HCMV infection is usually asymptomatic, while in immunocompromised patients, HCMV infection can lead to severe, life-threatening diseases, whose clinical severity parallels the degree of immunosuppression. The existence of a strict interplay between HCMV and the immune system has led many to hypothesize that HCMV could also be involved in autoimmune diseases (ADs). Indeed, signs of active viral infection were later found in a variety of different ADs, such as rheumatological, neurological, enteric disorders, and metabolic diseases. In addition, HCMV infection has been frequently linked to increased production of autoantibodies, which play a driving role in AD progression, as observed in systemic lupus erythematosus (SLE) patients. Documented mechanisms of HCMV-associated autoimmunity include molecular mimicry, inflammation, and nonspecific B-cell activation. In this review, we summarize the available literature on the various ADs arising from or exacerbating upon HCMV infection, focusing on the potential role of HCMV-mediated immune activation at disease onset.

CD13/Aminopeptidase N Is a Potential Therapeutic Target for Inflammatory Disorders

CD13/aminopeptidase N is a widely expressed ectoenzyme with multiple functions. As an enzyme, CD13 regulates activities of numerous cytokines by cleaving their N-terminals and is involved in Ag processing by trimming the peptides bound to MHC class II. Independent of its enzymatic activity, cell membrane CD13 functions by cross-linking-induced signal transduction, regulation of receptor recycling, enhancement of FcγR-mediated phagocytosis, and acting as a receptor for cytokines. Moreover, soluble CD13 has multiple proinflammatory roles mediated by binding to G-protein-coupled receptors. CD13 not only modulates development and activities of immune-related cells, but also regulates functions of inflammatory mediators. Therefore, CD13 is important in the pathogenesis of various inflammatory disorders. Inhibitors of CD13 have shown impressive anti-inflammatory effects, but none of them has yet been used for clinical therapy of human inflammatory diseases. We reevaluate CD13's regulatory role in inflammation and suggest that CD13 could be a potential therapeutic target for inflammatory disorders.

CD13 Autoantibodies Are Elevated in Sera From Mothers of Infants With Neonatal Cholestasis of Different Causes

OBJECTIVES

Human cytomegalovirus (HCMV) infection induces production of CD13-specific autoantibodies, which may promote inflammation and tissue damage. HCMV infection has been suggested as a cause of biliary atresia (BA), but little is known of its role in other forms of neonatal cholestasis. We studied serum levels of CD13-specific autoantibodies in mothers of infants with neonatal cholestasis of different causes, including BA, and in mothers of healthy, term infants without cholestasis, as well as in healthy blood donors.

METHODS

Using fluorescence-activated cell sorting, we measured CD13-specific autoantibody levels in serum from the above-mentioned groups. In addition, the effect of serum from mothers of infants with neonatal cholestasis was tested on the differentiation of monocytes into macrophages.

RESULTS

CD13-specific autoantibodies were found in mothers of infants with neonatal cholestasis, but not in mothers of infants without cholestasis and healthy blood donors, and were associated with HCMV seropositivity. Sera from mothers of infants with all forms of neonatal cholestasis inhibited differentiation of monocytes into macrophages, but this was not dependent on CD13-specific autoantibodies.

CONCLUSIONS

The significantly higher frequency of CD13-specific autoantibodies in mothers of infants with neonatal cholestasis of all forms compared with mothers of healthy infants without cholestasis suggests an association, but does not prove that they are pathogenic. The presence of CD13-specific autoantibodies does not correlate with HCMV IgG serostatus, suggesting a more complicated mechanism that possibly reflects active HCMV infection in these individuals. Further studies are needed to elucidate whether these autoantibodies contribute to the development of cholestasis or represent an epiphenomenon.

A Cytomegalovirus Peptide-Specific Antibody Alters Natural Killer Cell Homeostasis and Is Shared in Several Autoimmune Diseases

Human cytomegalovirus (hCMV), a ubiquitous beta-herpesvirus, has been associated with several autoimmune diseases. However, the direct role of hCMV in inducing autoimmune disorders remains unclear. Here we report the identification of an autoantibody that recognizes a group of peptides with a conserved motif matching the Pp150 protein of hCMV (anti-Pp150) and is shared among patients with various autoimmune diseases. Anti-Pp150 also recognizes the single-pass membrane protein CIP2A and induces the death of CD56(bright) NK cells, a natural killer cell subset whose expansion is correlated with autoimmune disease. Consistent with this finding, the percentage of circulating CD56(bright) NK cells is reduced in patients with several autoimmune diseases and negatively correlates with anti-Pp150 concentration. CD56(bright) NK cell death occurs via both antibody- and complement-dependent cytotoxicity. Our findings reveal that a shared hCMV-induced autoantibody is involved in the decrease of CD56(bright) NK cells and may thus contribute to the onset of autoimmune disorders.

The Cell Biology of Cytomegalovirus: Implications for Transplantation

Interpretation of clinical data regarding the impact of cytomegalovirus (CMV) infection on allograft function is complicated by the diversity of viral strains and substantial variability of cellular receptors and viral gene expression in different tissues. Variation also exists in nonspecific (monocytes and dendritic cells) and specific (NK cells, antibodies) responses that augment T cell antiviral activities. Innate immune signaling pathways and expanded pools of memory NK cells and γδ T cells also serve to amplify host responses to infection. The clinical impact of specific memory T cell anti-CMV responses that cross-react with graft antigens and alloantigens is uncertain but appears to contribute to graft injury and to the abrogation of allograft tolerance. These responses are modified by diverse immunosuppressive regimens and by underlying host immune deficits. The impact of CMV infection on the transplant recipient reflects cellular changes and corresponding host responses, the convergence of which has been termed the "indirect effects" of CMV infection. Future studies will clarify interactions between CMV infection and allograft injury and will guide interventions that may enhance clinical outcomes in transplantation.

Analysis of cellular and humoral immune responses against cytomegalovirus in patients with autoimmune Addison's disease

Background

Autoimmune Addison’s disease (AAD) is caused by multiple genetic and environmental factors. Variants of genes encoding immunologically important proteins such as the HLA molecules are strongly associated with AAD, but any environmental risk factors have yet to be defined. We hypothesized that primary or reactivating infections with cytomegalovirus (CMV) could represent an environmental risk factor in AAD, and that CMV specific CD8⁺ T cell responses may be dysregulated, possibly leading to a suboptimal control of CMV. In particular, the objective was to assess the HLA-B8 restricted CD8⁺ T cell response to CMV since this HLA class I variant is a genetic risk factor for AAD.

Methods

To examine the CD8⁺ T cell response in detail, we analyzed the HLA-A2 and HLA-B8 restricted responses in AAD patients and healthy controls seropositive for CMV antibodies using HLA multimer technology, IFN-γ ELISpot and a CD107a based degranulation assay.

Results

No differences between patients and controls were found in functions or frequencies of CMV-specific T cells, regardless if the analyses were performed ex vivo or after in vitro stimulation and expansion. However, individual patients showed signs of reactivating CMV infection correlating with poor CD8⁺ T cell responses to the virus, and a concomitant upregulation of interferon regulated genes in peripheral blood cells. Several recently diagnosed AAD patients also showed serological signs of ongoing primary CMV infection.

Conclusions

CMV infection does not appear to be a major environmental risk factor in AAD, but may represent a precipitating factor in individual patients.

Electronic supplementary material

The online version of this article (doi:10.1186/s12967-016-0822-z) contains supplementary material, which is available to authorized users.

CD13/aminopeptidase N is a negative regulator of mast cell activation

Antigen-induced mast cell (MC) activation via cross-linking of IgE-bound high-affinity receptors for IgE (FcεRI) underlies type I allergy and anaphylactic shock. Comprehensive knowledge of FcεRI regulation is thus required. We have identified a functional interaction between FcεRI and CD13 in murine MCs. Antigen-triggered activation of IgE-loaded FcεRI results in cocapping and cointernalization of CD13 and equivalent internalization rates of up to 40%. Cointernalization is not unspecific, because ligand-driven KIT internalization is not accompanied by CD13 internalization. Moreover, antibody-mediated cross-linking of CD13 causes IL-6 production in an FcεRI-dependent manner. These data are indicative of a functional interaction between FcεRI and CD13 on MCs. To determine the role of this interaction, CD13-deficient bone marrow-derived MCs (BMMCs) were analyzed. Intriguingly, antigen stimulation of CD13-deficient BMMCs results in significantly increased degranulation and proinflammatory cytokine production compared to wild-type cells. Furthermore, in a low-dose model of passive systemic anaphylaxis, antigen-dependent decrease in body temperature, reflecting the anaphylactic reaction, is substantially enhanced by the CD13 inhibitor bestatin (-5.9 ± 0.6°C) and by CD13 deficiency (-8.8 ± 0.6°C) in contrast to controls (-1.2 ± 1.97°C). Importantly, bestatin does not aggravate anaphylaxis in CD13-deficient mice. Thus, we have identified CD13 as a novel negative regulator of MC activation in vitro and in vivo-Zotz, J. S., Wölbing, F., Lassnig, C., Kauffmann, M., Schulte, U., Kolb, A., Whitelaw, B., Müller, M., Biedermann, T., Huber, M. CD13/aminopeptidase N is a negative regulator of mast cell activation.

Autoimmune haemolytic anaemia emerging during Campath treatment in a patient with CD5 negative chronic lymphocytic leukaemia

Campath is being employed for the treatment of autoimmune haemolytic anemia (AIHA) whether or not associated to B cell chronic lymphoid leukaemia (CLL). CD5 negative CLL is relatively uncommon and runs an indolent course. We report a CD5 negative CLL patient who developed AIHA associated with cytomegalovirus infection reactivation whilst on treatment with Campath for progressive disease.

Dendritic cell biology in human cytomegalovirus infection and the clinical consequences for host immunity and pathology

Human cytomegalovirus (HCMV), a member of the herpesvirus family, establishes life-long persistence and latency after primary infection and can be reactivated later in life. In immunosuppressed patients, it is an important pathogen that can cause severe disease. HCMV is also thought to play a causative role in inflammatory diseases and cancer. The virus can infect different immune cells, including dendritic cells (DCs) and can take advantage of host immune functions to avoid immune recognition. These characteristics have sparked major interest in understanding HCMV and its interaction with immune cells and their relevance to disease pathogenesis. In this review, we focus on the complex host-pathogen relationship between HCMV and DCs, including the persistence of the virus in these cells, their function in the immune response to HCMV infection and the potential clinical consequences of HCMV infection in DCs.

CMV-associated encephalitis and antineuronal autoantibodies--a case report

Background

Human cytomegalovirus (CMV) is an ubiquitous pathogen capable of modulating the host immune system. Immune dysfunction is common during CMV infection and includes autoimmune phenomena. Here we focus on a case of primary CMV infection associated with encephalopathy in a patient with a rudimentary spleen. We discuss diagnostic challenges and immunological aspects as well as the hypothesis that CMV may break tolerance and induce potentially encephalitogenic autoantibodies.

Case presentation

A 33-year-old woman was admitted with features of encephalitis, rapidly progressing into a catatonic state. The patient tested negative for presence of herpes simplex virus DNA in cerebrospinal fluid (CSF), and had elevated liver enzymes and hepatomegaly at computed tomography scan (CT) examination. CT scan and magnetic resonance imaging (MRI) showed only a rudimentary spleen. Initially, serum was negative for anti-CMV IgM, but borderline for anti-CMV IgG by enzyme-linked immunosorbent assay. However, a more sensitive assay resulted in a positive specific IgM Western blot profile and low IgG avidity, suggesting primary CMV infection. Further, CMV DNA was retrospectively detected in a CSF sample collected at admission. We also detected antineuronal autoantibodies, which stained GAD-positive neurons in the hippocampus. The patient was treated by a combination of prednisone, intravenous immunoglobulins (IVIg) and antivirals, which resulted in a dramatic amelioration of the patient’s neurological status. One year after admission the patient exhibited a nearly complete recovery with mild deficits in attention and memory.

Conclusions

A possible reason for the critical course of CMV infection could be the lack of a functional spleen in this patient, a condition previously associated with severe CMV infection. Prompt treatment with antiviral drugs, steroids and IVIg was most likely important for the positive outcome in this case and should be considered for similar cases of severe primary CMV infection associated with immunopathological phenomena.

Cytomegalovirus-induced immunopathology and its clinical consequences

Human cytomegalovirus (CMV) is a ubiquitous DNA virus that causes severe disease in patients with immature or impaired immune systems. During active infection, CMV modulates host immunity, and CMV-infected patients often develop signs of immune dysfunction, such as immunosuppression and autoimmune phenomena. Furthermore, active viral infection has been observed in several autoimmune diseases, and case reports have linked primary CMV infection and the onset of autoimmune disorders. In addition, CMV infection promotes allograft rejection and graft-versus-host disease in solid organ and bone marrow transplant recipients, respectively, further implicating CMV in the genesis and maintenance of immunopathological phenomena. The mechanisms by which CMV could induce inhibition of host defense, inflammation, and autoimmunity are discussed, as is the treatment of virus-induced immunopathology with antivirals.

Anti-CD13 Abs in children with extensive chronic GVHD and their relation to soluble CD13 after allogeneic blood and marrow transplantation from a Children's Oncology Groups Study, ASCT0031

Our group previous demonstrated a strong association between elevated plasma soluble CD13 enzyme activity and newly diagnosed extensive chronic graft-versus-host disease (cGVHD) in children. Since cytotoxic anti-CD13 antibodies have been documented after blood and marrow transplant in association with cytomegalovirus infection and cGVHD, we hypothesized soluble CD13 contributes to cGVHD pathogenesis by induction of CD13 reactive antibodies and that anti-CD13 antibodies could be additional biomarkers for newly diagnosed pediatric extensive cGVHD. Using prospectively collected plasma samples from pediatric allogeneic blood and marrow transplant subjects with cGVHD and controls without cGVHD enrolled in a large multi-institution Children's Oncology Group cGVHD therapeutic trial we evaluated whether soluble CD13 correlates with induction of anti-CD13 antibodies. We found that CD13 reactive antibodies are present in a proportion of patients after allogeneic BMT, but did not appear to correlate with the presence of soluble CD13. Anti-CD13 antibodies also did not meet our criteria as a diagnostic biomarker for cGVHD. These data are not able to confirm that induction of CD13 reactive antibodies is a mechanism for cGVHD in children nor are part of the pathogenesis of cGVHD associated with elevated soluble CD13. The exact role of CD13 in cGVHD remains to be determined.

CD13 is a novel mediator of monocytic/endothelial cell adhesion

During inflammation, cell surface adhesion molecules guide the adhesion and migration of circulating leukocytes across the endothelial cells lining the blood vessels to access the site of injury. The transmembrane molecule CD13 is expressed on monocytes and endothelial cells and has been shown to mediate homotypic cell adhesion, which may imply a role for CD13 in inflammatory monocyte trafficking. Here, we show that ligation and clustering of CD13 by mAb or viral ligands potently induce myeloid cell/endothelial adhesion in a signal transduction-dependent manner involving monocytic cytoskeletal rearrangement and filopodia formation. Treatment with soluble recombinant (r)CD13 blocks this CD13-dependent adhesion, and CD13 molecules from monocytic and endothelial cells are present in the same immunocomplex, suggesting a direct participation of CD13 in the adhesive interaction. This concept is strengthened by the fact that activated monocytic cells adhere to immobilized recombinant CD13. Furthermore, treatment with anti-CD13 antibodies in a murine model of peritonitis results in a decrease in leukocyte infiltration into the peritoneum, suggesting a potential role for CD13 in leukocyte trafficking in vivo. Therefore, this work supports a new direction for CD13 biology, where these cell surface molecules act as true molecular interfaces that induce and participate in critical inflammatory cell interactions.

Human cytomegalovirus differentially controls B cell and T cell responses through effects on plasmacytoid dendritic cells

Plasmacytoid dendritic cells (PDCs), the main producers of type I IFN in response to viral infection, are essential in antiviral immunity. In this study, we assessed the effect of human CMV (HCMV) infection on PDC function and on downstream B and T cell responses in vitro. HCMV infection of human PDCs was nonpermissive, as immediate-early but not late viral Ags were detected. HCMV led to partial maturation of PDCs and up-regulated MHC class II and CD83 molecules but not the costimulatory molecules CD80 and CD86. Regardless of viral replication, PDCs secreted cytokines after contact with HCMV, including IFN-alpha secretion that was blocked by inhibitory CpG, suggesting an engagement of the TLR7 and/or TLR9 pathways. In the presence of B cell receptor stimulation, soluble factors produced by HCMV-matured PDCs triggered B cell activation and proliferation. Through PDC stimulation, HCMV prompted B cell activation, but only induced Ab production in the presence of T cells or T cell secreted IL-2. Conversely, HCMV hampered the allostimulatory ability of PDCs, leading to decreased proliferation of CD4(+) and CD8(+) T cells. These findings reveal a novel mechanism by which HCMV differentially controls humoral and cell-mediate immune responses through effects on PDCs.

Aminopeptidase N in arterial hypertension

Aminopeptidase N (APN) or CD13 is a conserved type II integral membrane zinc-dependent metalloprotease in the M1 family of ectoenzymes. APN is abundant in the kidneys and central nervous system. Identified substrates include Angiotensin III (Ang III); neuropeptides, including enkephalins and endorphins; and homones, including kallidan and somatostatin. It is developmentally expressed, a myelomonocytic marker for leukemias, and a receptor for coronovirus. There is evolving support for APN in the regulation of arterial blood pressure and the pathogenesis of hypertension. In rodent strains, intracerebraventricular (i.c.v.) infusions of APN reduces, while inhibitors of APN activity have a pressor effect on blood pressure. Dysregulation of central APN has been linked to the pathogenesis of hypertension in the spontaneously hypertensive rat. There is evidence that renal tubule APN inhibits Na flux and plays a mechanistic role in salt-adaptation. A functional polymorphism of the ANP gene has been identified in the Dahl salt-sensitive rat. Signaling by APN impacting on blood pressure is likely mediated by regulation of the metabolism of Ang III to Ang IV. Whether APN regulates arterial blood pressure in humans or is a therapeutic target for hypertension are subjects for future exploration.

Purification of infectious human herpesvirus 6A virions and association of host cell proteins

BACKGROUND

Viruses that are incorporating host cell proteins might trigger autoimmune diseases. It is therefore of interest to identify possible host proteins associated with viruses, especially for enveloped viruses that have been suggested to play a role in autoimmune diseases, like human herpesvirus 6A (HHV-6A) in multiple sclerosis (MS).

RESULTS

We have established a method for rapid and morphology preserving purification of HHV-6A virions, which in combination with parallel analyses with background control material released from mock-infected cells facilitates qualitative and quantitative investigations of the protein content of HHV-6A virions. In our iodixanol gradient purified preparation, we detected high levels of viral DNA by real-time PCR and viral proteins by metabolic labelling, silver staining and western blots. In contrast, the background level of cellular contamination was low in the purified samples as demonstrated by the silver staining and metabolic labelling analyses. Western blot analyses showed that the cellular complement protein CD46, the receptor for HHV-6A, is associated with the purified and infectious virions. Also, the cellular proteins clathrin, ezrin and Tsg101 are associated with intact HHV-6A virions.

CONCLUSION

Cellular proteins are associated with HHV-6A virions. The relevance of the association in disease and especially in autoimmunity will be further investigated.

Biomarkers in newly diagnosed pediatric-extensive chronic graft-versus-host disease: a report from the Children's Oncology Group

Numerous chronic graft-versus-host disease (cGVHD) biomarkers have been identified in limited, single-institution studies without validation. We hypothesized that plasma-derived biomarkers could diagnose, classify, and evaluate response in children with cGVHD. We performed a concomitant analysis of a number of known and predicted peripheral blood cGVHD biomarkers from a Children's Oncology Group (COG) phase 3 cGVHD therapeutic trial. A total of 52 newly diagnosed patients with extensive cGVHD were compared for time of onset after blood and marrow transplantation (BMT) (early, 3-8 months; late, > or = 9 months) with 28 time-matched controls with no cGVHD (early, 6 months after BMT; late, 12 months after BMT). Soluble B-cell activation factor (sBAFF), anti-dsDNA antibody, soluble IL-2 receptor alpha (sIL-2Ralpha), and soluble CD13 (sCD13) were elevated in patients with early-onset cGVHD compared with controls. sBAFF and anti-dsDNA were elevated in patients with late-onset cGVHD. Some of the biomarkers correlated with specific organ involvement and with therapeutic response. These 4 biomarkers had high specificity with higher sensitivity in combination. Changes in biomarker concentrations with immune reconstitution after transplantation significantly affected interpretation of results. The identified biomarkers have the potential for improved classification, early response evaluation, and direction of cGVHD treatment, but require validation in larger studies. This study is registered at www.cancer.gov/clinicaltrials as no. COG-ASCT0031.

Risk assessment in haematopoietic stem cell transplantation: viral status

Viral infections have been important complications in the transplant procedure from the early days of stem-cell transplantation, causing significant morbidity and mortality. It is important for the management of patients to assess the risk for viral infections that might develop after the stem-cell transplantation. This can be exemplified by cytomegalovirus (CMV) and other herpesviruses, but risk assessment is also important for other viral infections. The aim of this review is to describe current knowledge regarding recipient and donor serological status for viral infections.

The development of autoantibodies after allogeneic stem cell transplantation is related with chronic graft-vs-host disease and immune recovery

OBJECTIVE

Chronic graft-vs-host disease (GVHD) has certain similarities with autoimmune diseases and is associated with the development of various autoantibodies in some patients. In this study, we analyzed the occurrence of autoantibodies in 63 patients surviving longer than 3 months after an allogeneic haematopoietic stem cell transplantation (HSCT), with the aim of detecting a possible association between occurrence of autoantibodies and development of chronic GVHD and immune recovery after HSCT.

PATIENTS AND METHODS

The patients were screened every 3 months for the occurrence of the following autoantibodies: anti-nuclear (ANA), anti-mitochondrial (AMA), anti-smooth muscle (ASMA), anti-cardiolipin (ACLA), anti-liver-kidney microsomal (LKM), anti-DNA, anti-neutrophil cytoplasmatic (ANCA), and anti-thyroid antibodies. Peripheral blood immunophenotyping with anti-CD3, CD4, CD8, CD19, CD20, CD16, and CD56 antibodies was evaluated at the same intervals.

RESULTS

Autoantibodies were not found in 18 patients (29%), at least in one screening in 29 patients (46%), and in all screenings in 16 patients (25%). ANA were found in 41 patients (65%), AMA in 4 (6%), ASMA in 4 (6%), ANCA in 7 (11%), ACLA in 1 (2%), anti-thyroid antibodies in 3 (5%), and anti-DNA in 2 (3%). More than one antibody occurred in 16/63 (25%) positive patients. ANA was significantly more frequent in patients with chronic GVHD and, among these, in those with the extensive form. The nucleolar pattern of immunofluorescence of ANA but not its titer was correlated with the extension of chronic GVHD. Patients who developed autoantibodies had higher CD20(+) cell blood counts than negative patients in the third month (p=0.006), ninth month (p=0.061), and twelfth month (p=0.043).

CONCLUSION

We conclude that patients with chronic GVHD, particularly those with an extensive involvement, were likely to develop autoantibodies and have a faster B-cell recovery, suggesting a role of B cells in the pathogenesis of chronic GVHD.

Detection of cytotoxic CD13-specific autoantibodies in sera from patients with ulcerative colitis and Crohn's disease

Recent evidence suggests an association between inflammatory bowel disease (IBD) and human cytomegalovirus (HCMV) infection, but the exact pathogenic role of HCMV in this disease remains unclear. HCMV infection has for a long time been known to be associated with various autoimmune manifestations and the formation of autoantibodies. Previous studies from our group have shown that HCMV is associated with a human protein, CD13 (aminopeptidase N) and that autoantibodies against this protein are frequently found in HCMV infected bone marrow transplant patients with chronic graft versus host disease. We have recently observed that 90% of IBD patients have an active HCMV infection. In this study, we examined the presence and cytotoxicity of CD13-specific autoantibodies in sera obtained from 28 patients with ulcerative colitis and 26 patients with Crohn's disease, and in sera obtained from healthy blood donors by using flow cytometric assays against mouse cells transfected with human CD13 or a microcytotoxicity assay against different CD13 positive human cells. Cytotoxic CD13-specific autoantibodies were identified in 66% of the sera obtained from HCMV-IgG positive patients with ulcerative colitis and in 58% of the sera obtained from HCMV-IgG positive patients with Crohn's disease, but not in control individuals. These cytotoxic autoantibodies may interfere with biological cell functions and could thereby contribute to the chronic inflammation in patients with IBD.

Requirement for neutralizing antibodies to control bone marrow transplantation-associated persistent viral infection and to reduce immunopathology

Bone marrow transplantation (BMT) is commonly used in the treatment of leukemia, however its therapeutic application is partly limited by the high incidence of associated opportunistic infections. We modeled this clinical situation by infecting mice that underwent BMT with lymphocytic choriomeningitis virus (LCMV) and investigated the potential of immunotherapeutic strategies to counter such infections. All mice that received BMT survived LCMV infection and developed a virus carrier status. Immunotherapy by adoptive transfer of naive splenocytes protected against low (200 PFU), but not high (2 x 10(6) PFU), doses of LCMV. Attempts to control infection of high viral titers using strongly elevated frequencies of activated LCMV-specific T cells failed to control virus and resulted in immunopathology and death. In contrast, virus neutralizing Abs combined with naive splenocytes were able to efficiently control high-dose LCMV infection without associated side effects. Thus, cell transfer combined with neutralizing Abs represented the most effective means of controlling BMT-associated opportunistic viral infection in our in vivo model. These data underscore the in vivo efficacy and immunopathological "safety" of neutralizing antibodies.

Co-purification of soluble membrane cofactor protein (CD46) and human herpesvirus 6 variant A genome in serum from multiple sclerosis patients

The association of human herpesvirus 6 (HHV-6) and multiple sclerosis (MS) has been supported by several immunological and molecular studies. Recently, membrane cofactor protein (CD46) has been identified as the cellular receptor for the A and B variants of HHV-6. Elevated levels of soluble CD46 (sCD46) have been reported in the serum and CSF of MS patients. The aim of this study was to investigate a possible correlation between elevated levels of soluble CD46 and the presence of serum HHV-6 DNA in MS patients. An immunoaffinity column comprised of immobilized monoclonal antibodies to CD46 was developed to isolate sCD46 from cell free body fluids of MS patients and controls. After immunoaffinity purification, DNA was extracted from anti-CD46 column eluates and subjected to PCR amplification. Of the 42 MS samples tested, 4 serum samples were HHV-6 positive, 3 of which were typed as HHV-6A. The co-purification of sCD46 and HHV-6 DNA from MS sera indicates that HHV-6 is tightly connected to its receptor, CD46, in the serum of MS patients.

CD13/aminopeptidase N and murine cytomegalovirus infection

CD13/aminopeptidase N is a membrane-bound metalloproteinase implicated in human cytomegalovirus (HCMV) infection and pathogenesis. Anti-CD13 antibodies can neutralize HCMV infectivity, and HCMV viremia after bone marrow transplantation induces anti-CD13 autoantibodies which correlate with development of chronic graft vs. host disease. We examined whether murine CD13/APN was similarly implicated in murine cytomegalovirus (MCMV) disease. MCMV infection did induce anti-CD13 antibodies in mice in a strain-specific manner. ICR and 129S mice developed high titers of anti-CD13 antibodies and anti-MCMV antibodies after MCMV infection, whereas CBA and CBAxC57BL/6 f1 hybrid mice produced antibodies against MCMV only. Unlike HCMV, no evidence was found for a correlation between host cell CD13/APN expression and infection, or for the presence of CD13/APN on MCMV particles, although APN inhibitors decreased MCMV plaque formation. Reproduction of CD13/APN autoantibody production in the murine system should make it possible to determine if these antibodies contribute to CMV pathogenesis.

Human cytomegalovirus inhibits the migration of immature dendritic cells by down-regulating cell-surface CCR1 and CCR5

Dendritic cells (DC) play a key role in the host immune response to infections. Human cytomegalovirus (HCMV) infection can inhibit the maturation of DC and impair their ability to stimulate T cell proliferation and cytotoxicity. In this study, we assessed the effects of HCMV infection on the migratory behavior of human DC. The HCMV strain TB40/E inhibited the migration of immature monocyte-derived DC in response to inflammatory chemokines by 95% 1 day after infection. This inhibition was mediated by early viral replicative events, which significantly reduced the cell-surface expression of CC chemokine receptor 1 (CCR1) and CCR5 by receptor internalization. HCMV infection also induced secretion of the inflammatory chemokines CC chemokine ligand 3 (CCL3)/macrophage inflammatory protein-1alpha (MIP-1alpha), CCL4/MIP-1beta, and CCL5/regulated on activation, normal T expressed and secreted (RANTES). Neutralizing antibodies for these chemokines reduced the effects of HCMV on chemokine receptor expression and on DC migration by approximately 60%. Interestingly, the surface expression of the lymphoid chemokine receptor CCR7 was not up-regulated after HCMV infection on immature DC, and immature-infected DC did not migrate in response to CCL19/MIP-3beta. These findings suggest that blocking the migratory ability of DC may be a potent mechanism used by HCMV to paralyze the early immune response of the host.

Consequences of human cytomegalovirus mimicry

The HCMV genome has evolved with its host by incorporating a series of genes that are homologous to, or functionally mimic, cellular genes. Some are designed to counteract the stress of infection on the host cell, notably the viral antiapoptotic proteins (vICA, vMIA). Others potentially help the infected cell maintain a low immunologic profile. These include virus-encoded chemokine receptors (UL33, UL78, US27, US28), FcRs (gp TRL11/IRL11, gp UL119-118), and proteins that directly or indirectly thwart natural killer cell activity (UL16, gpUL40). In addition, some viral proteins may play a role in immunopathology because of fortuitous cross-reactivity with host cell proteins. This overview discusses how these proteins affect the life of the host cell and its immediate neighbors.

Chronic graft-versus-host disease

Chronic graft-versus-host disease (GVHD) remains a vexing and dangerous complication of allogeneic stem cell transplantation. Mild forms of chronic GVHD are often manageable with local or low-dose systemic immunosuppression and do not affect long-term survival. In contrast, more severe forms of chronic GVHD require intensive medical management and adversely affect survival. This report reviews current concepts of the pathogenesis, clinical risk factors, classification systems, organ manifestations, and available treatments for chronic GVHD. It also provides a comprehensive listing of the published clinical trials aimed at prevention and primary treatment of chronic GVHD.

Response to steroids in de novo autoimmune hepatitis after liver transplantation

Graft dysfunction associated with autoimmune phenomena has been recently described in liver transplant recipients without previous autoimmune disease. However, the natural history, diagnostic criteria, and definitive therapeutic approach of de novo autoimmune hepatitis (de novo AIH) are poorly understood. We report 12 cases of de novo AIH 27.9 +/- 24.5 months after liver transplantation: the outcome of 7 patients treated with steroids is compared with a group of 5 nontreated patients. Nontreated patients lost the graft after 5.8 +/- 2.6 months from de novo AIH onset. All treated patients were alive after 48.4 +/- 14 (29-65) months from de novo AIH onset, and none of them lost the graft. However, 5 patients relapsed in relation to steroid tapering. All patients presented an atypical antiliver/kidney cytosolic autoantibody, associated to classical autoantibodies in 10 cases. Histological study showed several degrees of lobular necrosis and inflammatory infiltrate. HLA antigen frequencies and matching were compared with 2 control groups (16 orthotopic liver transplantation [LTX] patients without de novo AIH and 929 healthy blood donors); de novo AIH patients showed a higher prevalence of HLA-DR3 (54.5% vs. 25.9%, P =.04) than healthy controls, which was not observed in LTX patients without de novo AIH. In conclusion, this new disease should be included in the differential diagnosis of unexplained graft dysfunction. In addition, treatment with steroids results in a dramatically improved outcome. However, maintenance therapy is usually required.

Autoantibody appearance in cytomegalovirus-infected liver transplant recipients: correlation with antigenemia

The presence of anti-endothelial cells (AECA), smooth muscle (SMA), antinuclear (ANA) and antimitochondrial (AMA) autoantibodies, and liver/kidney microsomal antibody type 1 (LKM1) was investigated retrospectively in sera of liver transplant patients and correlated with cytomegalovirus (CMV) infection as determined by the antigenemia test and with the appearance of acute or chronic allograft rejection. Indirect immunofluorescence analysis was carried out in sequential sera from 40 liver transplant patients. Ten out of 23 antigenemia-positive and none of the antigenemia-negative patients developed serum autoantibodies (P = 0.002, Fisher's exact test). Anti-endothelial cell autoantibodies were found in nine cases and SMA in four patients. Antinuclear antibodies were detected in one otherwise autoantibody-negative patient. All but one case of autoantibody positivity were observed in the high antigenemia group (P < 0.0001, Fisher's exact test). In all but one case, autoantibodies were detected in blood during the antigenemia phase and in most cases in coincidence with or after the antigenemia peak. Even though a statistically significant correlation was not found between autoantibody production and the development of acute or chronic allograft rejection, proportionally more acute rejection cases were observed in the autoantibody-positive than in the autoantibody-negative group. It has been speculated that CMV-induced endothelial damage may be a potent antigenic stimulus, which leads to the production of anti-endothelial cells autoantibodies. Anti-endothelial cell autoantibodies may represent not only a marker of cell injury but also contribute to the progression of the inflammatory response leading to the exposure of tissue-privileged self antigens and the induction of other autoantibodies such as SMA.

Molecular determinants of species specificity in the coronavirus receptor aminopeptidase N (CD13): influence of N-linked glycosylation

Aminopeptidase N (APN), a 150-kDa metalloprotease also called CD13, serves as a receptor for serologically related coronaviruses of humans (human coronavirus 229E [HCoV-229E]), pigs, and cats. These virus-receptor interactions can be highly species specific; for example, the human coronavirus can use human APN (hAPN) but not porcine APN (pAPN) as its cellular receptor, and porcine coronaviruses can use pAPN but not hAPN. Substitution of pAPN amino acids 283 to 290 into hAPN for the corresponding amino acids 288 to 295 introduced an N-glycosylation sequon at amino acids 291 to 293 that blocked HCoV-229E receptor activity of hAPN. Substitution of two amino acids that inserted an N-glycosylation site at amino acid 291 also resulted in a mutant hAPN that lacked receptor activity because it failed to bind HCoV-229E. Single amino acid revertants that removed this sequon at amino acids 291 to 293 but had one or five pAPN amino acid substitution(s) in this region all regained HCoV-229E binding and receptor activities. To determine if other N-linked glycosylation differences between hAPN, feline APN (fAPN), and pAPN account for receptor specificity of pig and cat coronaviruses, a mutant hAPN protein that, like fAPN and pAPN, lacked a glycosylation sequon at 818 to 820 was studied. This sequon is within the region that determines receptor activity for porcine and feline coronaviruses. Mutant hAPN lacking the sequon at amino acids 818 to 820 maintained HCoV-229E receptor activity but did not gain receptor activity for porcine or feline coronaviruses. Thus, certain differences in glycosylation between coronavirus receptors from different species are critical determinants in the species specificity of infection.

Immune reconstitution after allogeneic marrow transplantation compared with blood stem cell transplantation

Allogeneic peripheral blood stem cell grafts contain about 10 times more T and B cells than marrow grafts. Because these cells may survive in transplant recipients for a long time, recipients of blood stem cells may be less immunocompromised than recipients of marrow. Immune reconstitution was studied in 115 patients randomly assigned to receive either allogeneic marrow or filgrastim-mobilized blood stem cell transplantation. Between day 30 and 365 after transplantation, counts of most lymphocyte subsets were higher in the blood stem cell recipients. The difference was most striking for CD4 T cells (about 4-fold higher counts for CD45RA(high) CD4 T cells and about 2-fold higher counts for CD45RA(low/-)CD4 T cells; P <.05). On assessment using phytohemagglutinin and herpesvirus antigen-stimulated proliferation, T cells in the 2 groups of patients appeared equally functional. Median serum IgG levels were similar in the 2 groups. The rate of definite infections after engraftment was 1.7-fold higher in marrow recipients (P =.001). The rate of severe (inpatient treatment required) definite infections after engraftment was 2.4-fold higher in marrow recipients (P =.002). The difference in the rates of definite infections was greatest for fungal infections, intermediate for bacterial infections, and lowest for viral infections. Death associated with a fungal or bacterial infection occurred between day 30 and day 365 after transplantation in 9 marrow recipients and no blood stem cell recipients (P =.008). In conclusion, blood stem cell recipients have higher lymphocyte-subset counts and this appears to result in fewer infections. (Blood. 2001;97:3380-3389)

The use of granulocyte colony-stimulating factor for treatment of autoimmune neutropenia

The advent of better diagnostic tools, molecular techniques, and cytokine therapies have come together at the end of the 20th century to provide an improved outlook for patients with autoimmune neutropenia. Severe chronic neutropenia is no longer idiopathic in most cases, and growth factor therapy can be safely offered to selected patient groups. Previously unsuccessful and even dangerous forms of treatment are no longer appropriate, and G-CSF treatment appears to be safe when administered long term. Fears about transformation of these disorders into acute myeloblastic leukemia probably relate to the underlying natural history of these disorders rather than to their treatment.

An investigation into the heparin-binding properties of a synthetic peptide deduced from the antigenic domain 2 of human cytomegalovirus glycoprotein B

An investigation was performed into the heparin-binding properties of a synthetic peptide deduced from the sequence of human cytomegalovirus glycoprotein B. The peptide, T7-13:3, amino acids 69-78, which was previously shown to contain a neutralization epitope was able to bind heparin coated onto microtitre plates as well as immobilized on agarose beads. Conversely, labelled heparin could be used to specifically detect the immobilized peptide. The peptide bound to human cells in a manner which suggested an interaction with extracellular matrix, and binding of the peptide to human fibroblasts could be inhibited both by adding soluble heparin and by enzymatic pretreatment of the cells with heparinase. The sequence of T7-13:3 shows similarity to several proteins with known or supposed ability to bind heparin, e.g. basic fibroblast growth factor, the heparin-binding capacity of which could also be inhibited by T7-13:3. The peptide was also found to bind DNA, probably due to the similarities between DNA and heparin in terms of structure and charge. Because heparin is a chemical homologue of heparan sulfate, the results strongly indicate that the sequence represented by T7-13:3 is involved in the binding of virus to cell surface heparan sulfate. The described region of gB may have the potential to contribute to a subunit vaccine although possible hazards, such as the induction of auto-antibodies to heparin, and thus also to DNA, need to be considered.

High levels of antiphospholipid antibodies are associated with cytomegalovirus infection in unrelated bone marrow and cord blood allogeneic stem cell transplantation

Antiphospholipid antibodies (APA) are a family of autoimmune and alloimmune immunoglobulins recognizing protein-phospholipid complexes in in vitro laboratory test systems. These antibodies have been associated with several conditions (malignancies, autoimmune diseases, infections, use of drugs); moreover, a syndrome capable of inducing thromboembolic disease has recently been associated with the presence of these antibodies. The aim of this prospective study was to investigate the levels of APA in subjects affected by haematological malignancies undergoing allogeneic haematopoietic stem cell transplantation (ASCT). Between March 1996 and December 1997, 32 patients undergoing ASCT were studied prospectively until day +180 from transplant. The mean values of IgG and IgM anticardiolipin antibodies (ACA) increased in recipients of stem cells from anunrelated donor, and a statistically significant difference inACA IgG mean value between unrelated and related transplanted patients was demonstrated between days +95 and +180. All of the subjects who received stem cells from an unrelated donor had APA levels higher than the mean normal value +3 SD vs. 35% of those receiving stem cells from a related donor (P < 0.01). The reason for such a difference may be a result of the different incidence in documented cytomegalovirus (CMV) infection in the two groups (83% vs. 23%; P < 0.01), as indicated by the significant correlation between APA positivity and CMV infection (P < 0.05). No relationship was found between APA, conditioning regimen and acute or chronic graft vs. host disease (GVHD). Moreover, we did not observe any thromboembolic disorder or veno occlusive disease (VOD).

Mechanisms for induction of autoimmunity in humans

The triggering or immunogenic stimulus for human autoimmune diseases is unknown. It is not even known whether the stimulus is endogenous, i.e. truly "self" or exogenous, "non-self". Many autoimmune diseases are human lymphocyte antigen (HLA)-associated and demonstrate linkage to the HLA chromosome in family investigations. For most of these diseases, evidence is strong that the association is directly dependent on specific HLA class I or II molecules rather than on other genes located in the HLA region. Since HLA polymorphic HLA molecules have so far only been shown to have two distinct functions, both of which are immunological, a HLA association supports the notion that a particular disease is autoimmune. Furthermore, an association to a specific HLA allele implies that the immunogenic stimulus for autoimmunity would be one specific HLA-binding peptide and that, at least initially, autoimmunity is dependent on the reactivity of one or a limited number of potentially autoaggressive T cell clones. These findings are encouraging and formin the basis for future preventive measures. One current theory is that autoimmune disease is precipitated by an environmental agent, such as a viral infection. Several different mechanisms to explain how a viral infection could induce autoimmune disease in humans are described and one specific example is presented for a virus-induced autoimmune disease in humans. The question of whether ITP could also be dependent on such a mechanism is briefly discussed.

A novel mechanism for virus-induced autoimmunity in humans

A novel mechanism for virus-induced autoimmunity in humans is described. Infection of immunocompromised bone marrow-transplanted patients with human CMV results in the formation of autoantibodies specific for the cell-surface protein CD13 (aminopeptidase N). CD13 is present on all CMV-susceptible cells and infection can be specifically blocked by antibodies against CD13. CMV particles carry CD13, which is incorporated in the viral envelope during budding of viral nucleo-capsids into Golgi-derived vacuoles. Antibodies against CD13 are virus-neutralizing, in efficiency comparable to antibodies against viral envelope glycoproteins. Autoantibodies against CD13 are present in patients who develop chronic GVHD following allogeneic bone marrow transplantation. This lesion shows striking similarities to certain autoimmune diseases in humans, of which scleroderma is one example. In vivo binding of antibodies to tissue structures known to be targets for chronic GVHD has been demonstrated in patients with chronic GVHD. Finally, patient serum containing CD13-specific antibodies binds to skin and mucosa tissue sections in vitro, a binding which is inhibited by CD13-specific monoclonal antibodies. Thus a virus infection can activate an immune response against a specific autoantigen, providing possibilities for destruction of non-infected host cells, as originally proposed by Fujinami & Oldstone (1985), and also for the molecular mimicry model for induction of autoimmunity. Our findings lend support to the idea that inhibiting the transfer of CMV infection in bone marrow transplants will reduce morbidity and mortality from CMV infection but will also reduce the incidence of chronic GVHD. Elimination of CD13+ cells in bone marrow is not believed to interfere with the chance of recipient repopulation, and may be a way to decrease morbidity and mortality substantially following BMT. For all patients, every effort should be taken to prevent a post-BMT CMV infection in order to reduce the risk of the later development of chronic GVHD.