Immunobiology of human cytomegalovirus: From bench to bedside. Clin Microbiol Rev. 2009;22:76-98, Table of Contents. [PMID: 19136435 DOI: 10.1128/cmr.00034-08]

Differentiation between polymorphisms and resistance-associated mutations in human cytomegalovirus DNA polymerase

Specific mutations in the human cytomegalovirus (HCMV) DNA polymerase (pUL54) are known to confer resistance against all currently licensed drugs for treatment of HCMV infection and disease. Following the widespread use of antivirals, the occurrence of HCMV drug resistance is constantly increasing. Recently, diagnostic laboratories have started to replace phenotypic drug resistance testing with genotypic resistance testing. However, the reliability and success of genotypic testing highly depend on the availability of high-quality phenotypic resistance data for each individual mutation and for combinations of mutations, with the latter being increasingly found in patients' HCMV isolates. We performed clonal marker transfer experiments to investigate the impacts of 7 different UL54 point mutations and also of combinations of these mutations on drug susceptibility and viral replicative fitness. We show that several mutations-S695T, A972V, K415R, S291P, and A692V-of suspected but uncertain drug susceptibility phenotype, either alone or in combination, were not relevant to antiviral drug resistance. In contrast, the combination of two mutations individually characterized previously-E756K and D413E-conferred high-grade loss of susceptibility to all three antivirals. Our results have been added to the newly available database of all published HCMV resistance mutations (http://www.informatik.uni-ulm.de/ni/mitarbeiter/HKestler/hcmv/index.html). These data will allow better interpretation of genotypic data and further improve the basis for drug resistance testing.

Chromatin-mediated regulation of cytomegalovirus gene expression

Following primary infection, whether Human cytomegalovirus (HCMV) enters either the latent or lytic lifecycle is dependent on the phenotype of the cell type infected. Multiple cell types are permissive for lytic infection with HCMV whereas, in contrast, well characterized sites of latency are restricted to a very specific population of CD34+ cells resident in the bone marrow and the immature myeloid cells they give rise to. It is becoming increasingly clear that one of the mechanisms that promote HCMV latency involves the recruitment of histone proteins to the major immediate early promoter (MIEP) which are subject to post-translational modifications that promote a transcriptionally inactive state. Integral to this, is the role of cellular transcriptional repressors that interact with histone modifying enzymes that promote and maintain this repressed state during latency. Crucially, the chromatin associated with the MIEP is dynamically regulated-myeloid cell differentiation triggers the acetylation of histones bound to the MIEP which is concomitant with the reactivation of IE gene expression and re-entry into lytic infection. Interestingly, this dynamic regulation of the MIEP by chromatin structure in latency extends not only into lytic infection but also for the regulation of multiple viral promoters in all phases of infection. HCMV lytic infection is characterised by a timely and co-ordinated pattern of gene expression that now has been shown to correlate with active post-translational modification of the histones associated with early and late promoters. These effects are mediated by the major IE products (IE72 and IE86) which physically and functionally interact with histone modifying enzymes resulting in the efficient activation of viral gene expression. Thus chromatin appears to play an important role in gene regulation in all phases of infection. Furthermore, these studies are highly suggestive that an intrinsic cellular anti-viral response to incoming viral genomes is to promote chromatinisation into a transcriptionally repressed state which the virus must overcome to establish a lytic infection. What is becoming evident is that chromatin structure is becoming as increasingly important for the regulation of viral gene expression as it is for cellular gene expression and thus understanding the mechanisms employed by HCMV to modulate chromatin function could have broader implications on our understanding of the control of gene expression in general.

Virological and immunological features of active cytomegalovirus infection in nonimmunosuppressed patients in a surgical and trauma intensive care unit

Cytomegalovirus (CMV) reactivation occurs frequently in critically ill patients. The natural course of CMV infection and the interaction between CMV and the adaptive immune system in this setting remain poorly defined. Fifty-three CMV-seropositive patients in a surgical and trauma intensive care unit were included in this study. The CMV DNA load in tracheal aspirates (TA) and plasma (PL) was monitored by qPCR. CMV-specific T-cell immunity was assessed by intracellular cytokine staining. Plasma TNF-alpha levels were determined by ELISA. CMV reactivation occurred in 39.7% of patients (23% had CMV DNA detected only in TA). The analysis of TA allowed an earlier diagnosis in 28% of patients. Clearance of CMV DNAemia preceded that of CMV DNA in TA in some episodes. Peak CMV DNA levels were significantly higher in TA than in PL (P = 0.02). CMV reactivation developed in the presence of CMV-specific T cells. Termination of CMV reactivation was associated with an expansion of functional CMV-specific T cells. Plasma levels of TNF-alpha did not allow for the prediction of the occurrence of CMV reactivation. CMV-specific T-cell immunity is preserved in most critically ill patients experiencing CMV reactivation. Analysis of respiratory specimens is imperative for an optimal monitoring of CMV reactivation in this setting.

Cytomegalovirus in inflammatory bowel disease: pathogen or innocent bystander?

The role of cytomegalovirus (CMV) in exacerbations of inflammatory bowel disease (IBD) remains a topic of ongoing debate. Current data are conflicting as to whether CMV worsens inflammation in those with severe colitis, or is merely a surrogate marker for severe disease. The interpretation of existing results is limited by mostly small, retrospective studies, with varying definitions of disease severity and CMV disease. CMV colitis is rare in patients with Crohn's disease or mild-moderate ulcerative colitis. In patients with severe and/or steroid-refractory ulcerative colitis, local reactivation of CMV can be detected in actively inflamed colonic tissue in about 30% of cases. Where comparisons between CMV+ and CMV- steroid-refractory patients can be made, most, but not all, studies show no difference in outcomes according to CMV status. Treatment with antiviral therapy has allowed some patients with severe colitis to avoid colectomy despite poor response to conventional IBD therapies. This article reviews the immunobiology of CMV disease, the evidence for CMV's role in disease severity, and discusses the outcomes with antiviral therapy.

Contribution of herpesvirus specific CD8 T cells to anti-viral T cell response in humans

Herpesviruses infect most humans. Their infections can be associated with pathological conditions and significant changes in T cell repertoire but evidences of symbiotic effects of herpesvirus latency have never been demonstrated. We tested the hypothesis that HCMV and EBV-specific CD8 T cells contribute to the heterologous anti-viral immune response. Volume of activated/proliferating virus-specific and total CD8 T cells was evaluated in 50 patients with acute viral infections: 20 with HBV, 12 with Dengue, 12 with Influenza, 3 with Adenovirus infection and 3 with fevers of unknown etiology. Virus-specific (EBV, HCMV, Influenza) pentamer+ and total CD8 T cells were analyzed for activation (CD38/HLA-DR), proliferation (Ki-67/Bcl-2(low)) and cytokine production. We observed that all acute viral infections trigger an expansion of activated/proliferating CD8 T cells, which differs in size depending on the infection but is invariably inflated by CD8 T cells specific for persistent herpesviruses (HCMV/EBV). CD8 T cells specific for other non-related non persistent viral infection (i.e. Influenza) were not activated. IL-15, which is produced during acute viral infections, is the likely contributing mechanism driving the selective activation of herpesvirus specific CD8 T cells. In addition we were able to show that herpesvirus specific CD8 T cells displayed an increased ability to produce the anti-viral cytokine interferon-gamma during the acute phase of heterologous viral infection. Taken together, these data demonstrated that activated herpesvirus specific CD8 T cells inflate the activated/proliferating CD8 T cells population present during acute viral infections in human and can contribute to the heterologous anti-viral T cell response.

Cytomegalovirus in hematopoietic stem cell transplant recipients

This article examines the clinical manifestations of and risk factors for cytomegalovirus (CMV). Prevention of CMV infection and disease are also explored. Antiviral resistance and management of CMV are examined.

Prevalence and prognostic implications of active cytomegalovirus infection in patients with acute heart failure

AHF (acute heart failure) causes significant morbidity and mortality. Recent studies have postulated that the expression of inflammatory mediators, such as cytokines and chemokines, plays an important role in the development and progression of heart failure. A pro-inflammatory state has been postulated as a key factor in triggering CMV (cytomegalovirus) reactivation. Therefore we sought to determine the prevalence of active CMV infection in immunocompetent patients admitted for AHF and to quantify the association with the risk of the combined end point of death or AHF readmission. A total of 132 consecutive patients admitted for AHF were enrolled in the present study. Plasma CMV DNAaemia was assessed by qRT-PCR (quantitative real-time PCR), and cytokine measurements in plasma were performed by ELISA. Clinical data were evaluated by personnel blinded to CMV results. The independent association between active CMV infection and the end point was determined by Cox regression analysis. During a median follow-up of 120 [IQR (interquartile range), 60–240] days, 23 (17.4%) deaths, 34 (24.2%) readmissions for AHF and 45 (34.1%) deaths/readmissions for AHF were identified. Plasma CMV DNAaemia occurred in 11 (8.3%) patients, albeit at a low level (<100 copies/ml). The cumulative rate of the composite end point was higher in patients with CMV DNAaemia (81.8 compared with 29.8%; P<0.001). After adjusting for established risk factors, the occurrence of CMV DNAaemia was strongly associated with the clinical end point [hazard ratio = 4.39 (95% confidence interval, 2.02–9.52); P<0.001]. In conclusion, active CMV infection occurs, although uncommonly, in patients with AHF, and may be a marker of disease severity.

International consensus guidelines on the management of cytomegalovirus in solid organ transplantation

Cytomegalovirus (CMV) remains one of the most common infections after solid organ transplantation, resulting in significant morbidity, graft loss, and occasional mortality. Management of CMV varies considerably among transplant centers. A panel of experts on CMV and solid organ transplant was convened by The Infectious Diseases Section of The Transplantation Society to develop evidence and expert opinion-based consensus guidelines on CMV management including diagnostics, immunology, prevention, treatment, drug resistance, and pediatric issues.

[Acute retinal necrosis from the virologist's perspective]

Acute retinal necrosis occurs in approximately one per million persons per year and is caused in approximately 70% of the cases by the varicella zoster virus or in about 30% of the cases by herpes simplex virus. The early diagnosis is primarily based on virus-specific polymerase chain reaction in fluid from the anterior chamber or vitreous humor and can be supported by the determination of specific antibody titers from fluid and serum. Virus detection provides the basis for early causative therapy which limits disease progression and risk of complications. Retinal infections by varicella zoster virus or herpes simplex virus are treated with aciclovir, ganciclovir, or famciclovir. Ganciclovir and valganciclovir are used for the therapy of retinal cytomegalovirus infections. In the case of resistance development, foscarnet or cidofovir are available as second line antiviral drugs. The early use of specific antiviral agents is a crucial prerequisite for optimized therapy of acute retinal necrosis.

CD8+ T-cell recognition of human cytomegalovirus latency-associated determinant pUL138

Recent studies have shown that long-term persistence of human cytomegalovirus (HCMV) in mononuclear cells of myeloid lineage is dependent on the UL138 open reading frame, which promotes latent infection. Although T-cell recognition of protein antigens from all stages of lytic HCMV infection is well established, it is not clear whether proteins expressed during latent HCMV infection can also be recognized. This study conducted an analysis of T-cell response towards proteins associated with HCMV latency. Ex vivo analysis of T cells from healthy virus carriers revealed a dominant CD8(+) T-cell response to the latency-associated pUL138 protein, which recognized a non-canonical 13 aa epitope in association with HLA-B*3501. These pUL138-specific T cells displayed a range of memory phenotypes that were in general less differentiated than that previously described in T cells specific for HCMV lytic antigens. Antigen-presentation assays revealed that endogenous pUL138 could be presented efficiently by HCMV-infected cells. However, T-cell recognition of pUL138 was dependent on newly synthesized protein, with little presentation from stable, long-lived protein. These data demonstrate that T cells targeting latency-associated protein products exist, although HCMV may limit the presentation of latent proteins, thereby restricting T-cell recognition of latently infected cells.

Short-term exposure to human cytomegalovirus-infected fibroblasts induces a proportional increase of active CD94/NKG2A(+) natural killer cells

Natural killer (NK) cells are essential components of the immune response against human cytomegalovirus (HCMV). As NK cells are part of the innate immune system providing an immediate defense against pathogens, short-term exposure to HCMV-infected cells may induce changes in the phenotype and function of these cells. To identify immediate reactions of NK cells to HCMV, we co-cultured peripheral blood mononuclear cells with HCMV-infected fibroblasts for 24 and 72 hours. A distinct, HCMV-mediated, proportional enlargement of a subset of NK cells expressing CD94/NKG2A was sustained throughout the period of incubation. As preceding studies have shown that HCMV can cause an increase in CD94/NKG2C(+) NK cells, our results were surprising. The NK cells showed intense upregulation of the early activation marker CD69 in response to HCMV. The CD94/NKG2A(+) NK cells demonstrated the highest expression of CD69. Studies of HCMV-induced interferon-gamma expression after 24 hours of co-culture showed that this cytokine was almost exclusively produced by the CD94/NKG2A(+) subset of NK cells. In summary, our data demonstrate that HCMV induces an immediate proportional enlargement of a functionally active CD94/NKG2A expressing subset of NK cells.

Successful immunotherapy of HCMV disease using virus-specific T cells expanded from an allogeneic stem cell transplant recipient

Opportunistic infection remains the principal cause of mortality in allogeneic stem cell transplant recipients with active extensive chronic graft-versus-host disease. Human cytomegalovirus (HCMV) represents an important cause of disease in this setting and the toxicity of protracted and recurrent antiviral treatment together with eventual drug resistance represents a significant limitation to therapy. Although the expansion and adoptive transfer of HCMV-specific T cells from the healthy original donor can be an effective strategy to control viral replication, this is not possible when donors are seronegative or are subsequently inaccessible. Here we demonstrate for the first time, the successful expansion of HCMV-specific T cells from a seropositive transplant recipient of a seronegative graft with active HCMV disease and the long-term reconstitution of protective antiviral immunity following their adoptive transfer back into the patient.

The CD94/NKG2C-expressing NK cell subset is augmented in chronic lymphocytic leukemia patients with positive human cytomegalovirus serostatus

Human cytomegalovirus (HCMV) manipulates the host immune system in various ways. Allegedly, HCMV infection is associated with increased percentages of a particular natural killer (NK) cell subset expressing the activating receptor CD94/NKG2C in both healthy individuals and in patients infected with human immunodeficiency virus (HIV). Whether the HCMV-mediated induction of this specific NK cell subset is also apparent for other diseases characterized by abnormal immune responses, such as malignant blood diseases, is unknown. By comparing the fractions of CD94/NKG2C(+) NK cells in B-cell chronic lymphocytic leukemia (B-CLL) patients having either positive or negative HCMV serostatus, a proportional increase of this cell subset was obvious in the HCMV-seropositive subjects. Therapeutic intervention in the patients with positive HCMV serostatus did not seem to reduce the percentage of CD94/NKG2C-expressing NK cells. Thus, HCMV infection seemingly shapes the NK cell system in healthy individuals, HIV patients, and B-CLL patients in a uniform manner, even though these involve different immunological challenges.

Human herpes virus 6 infection is a hallmark of cord blood transplant in adults and may participate to delayed engraftment: a comparison with matched unrelated donors as stem cell source

Occurrence of CMV, EBV and human herpes virus 6 (HHV6) infections and immune reconstitution were compared in 15 adult patients receiving a cord blood transplantation (CBT) and 40 patients who received an allogeneic transplantation from a matched unrelated donor (MUD). Herpes virus DNA quantifications in the blood (459 samples) were performed before and then monthly up to 9 months after transplant and the main lymphocytes populations were counted at 3, 6 and 9 months. Incidence of HHV6 infection was significantly higher in the CBT group (80 vs 42.5%; P<0.0001), with higher viral load (P<0.0001). In multivariate analysis, the use of a CBT and a myeloablative conditioning regimen were found to increase the risk of HHV6 infection (odds ratio (OR)=5.4, P=0.02 and OR=3.5, P=0.04, respectively). Incidences of CMV were similar between the two groups whereas MUD increased the risk of EBV infection, in univariate analysis only. HHV6 reactivation translated toward delayed neutrophils and plts engraftment in the two groups. MUD and CBT do not share the same immune reconstitution patterns, notably for B and CD8 lymphocytes and NK cells. There is a strong and specific relationship between HHV6 infection and the use of cord blood cells.

Analysis of latent viral gene expression in natural and experimental latency models of human cytomegalovirus and its correlation with histone modifications at a latent promoter

Human cytomegalovirus (HCMV) is an opportunistic human pathogen that establishes a lifelong latent infection, which can reactivate periodically. If unchecked by a robust immune response, this reactivation can result in severe disease in immunocompromised patients. Reactivation of latent virus in myeloid progenitor cells is concomitant with cellular differentiation through regulation of the major immediate-early promoter (MIEP) by chromatin remodelling. In this study, we analysed the expression of the latent gene transcript UL81-82as (LUNA). LUNA is expressed in latently infected CD34(+) cells and its expression decreases as CD34(+) cells differentiate to immature dendritic cells. Upon maturation (and HCMV reactivation), a second wave of transcription occurs, consistent with expression during lytic infection. Furthermore, we show that the LUNA promoter is associated with acetylated histones during HCMV latency in experimentally and naturally infected CD34(+) cells, thus suggesting that latent gene promoters are, like the MIEP, regulated by post-translational modifications of their associated histone proteins.

Degradation of RIG-I following cytomegalovirus infection is independent of apoptosis

Many viruses have evolved strategies to either evade or hijack host cell immune programs, as a means of promoting their own reproduction. For example, the human cytomegalovirus (HCMV) immediate-early protein vMIA/UL37ex1 inhibits host cell apoptosis, and its expression during infection aids virus replication. Here it is shown that stable expression of vMIA/UL37ex1 reduces cleavage of the innate immune response-proteins MAVS and RIG-I by caspases during apoptosis. Unexpectedly, it is demonstrated that RIG-I, but not MAVS, is degraded during HCMV infection. This process occurs in a non-apoptotic manner, and provides new evidence that HCMV may have evolved a unique strategy to evade RIG-I-mediated immune responses.

Vaccines: the fourth century

Vaccine development, which began with Edward Jenner's observations in the late 18th century, has entered its 4th century. From its beginnings, with the use of whole organisms that had been weakened or inactivated, to the modern-day use of genetic engineering, it has taken advantage of the tools discovered in other branches of microbiology. Numerous successful vaccines are in use, but the list of diseases for which vaccines do not exist is long. However, the multiplicity of strategies now available, discussed in this article, portends even more successful development of vaccines.

The HLA-G 14 bp insertion/deletion polymorphism is a putative susceptible factor for active human cytomegalovirus infection in children

Human leukocyte antigen-G (HLA-G) expression is a potential factor for the pathogenesis of virus infection. A 14 bp insertion/deletion polymorphism (rs16375) in the 3'-untranslated region of the HLA-G gene is involved in the stability of HLA-G mRNA and HLA-G protein expression. Therefore, the HLA-G 14 bp polymorphism might be involved in human cytomegalovirus (hCMV) infection. To test a possible association between the HLA-G 14 bp deletion/insertion polymorphism and the active hCMV infection, in this study, a total of 54 patients with active hCMV infection and 165 age- and sex-matched, unrelated, normal Chinese Han population were genotyped for the 14 bp insertion/deletion polymorphism. Association of 14 bp polymorphism with hCMV urine DNA copies and the odds ratio (OR) of the polymorphism as a risk factor for active hCMV infection were analyzed. Our results showed that the prevalence of -14 bp/ -14 bp genotype in active hCMV patients was markedly increased [P(c) = 0.00034, OR = 3.31, 95% confidence interval (CI): 1.77-6.18], and similar significance was also observed for the frequency of -14 bp allele (P c = 0.0023, OR = 2.24, 95% CI: 1.38-3.64) when compared with that of healthy controls. Furthermore, urine hCMV DNA copies in patients with the -14 bp/ -14 bp genotype were significantly higher than those in patients with the +14 bp/ +14 bp genotype (P = 0.041). Our findings support a potential role of HLA-G 14 bp insertion/deletion polymorphism as a susceptible factor for the active hCMV infection.

Discerning regulation of cis- and trans-presentation of CD8+ T-cell epitopes by EBV-encoded oncogene LMP-1 through self-aggregation

Activation of the nuclear factor–κB pathway by Epstein-Barr virus–encoded latent membrane protein-1 (LMP-1) leads to an up-regulation of the major histocompatibility complex class I antigen–processing pathway. Paradoxically, LMP-1 itself induces a subdominant CD8+ T-cell response and appears to have evolved to avoid immune recognition. Here we show that, although expression of LMP-1 in human cells dramatically enhanced the trans-presentation of CD8+ T-cell epitopes, cis-presentation of LMP-1–derived epitopes was severely impaired. Testing of a series of LMP-1 mutants revealed that deletion of the first transmembrane domain of LMP-1, which prevented self-aggregation, significantly enhanced cis-presentation of T-cell epitopes from this protein, whereas it lost its ability to up-regulate trans-presentation. Interestingly, we also found that cis-presentation of LMP-1 epitopes was rescued by blocking the proteasome function. Taken together, these results delineate a novel mechanism of immune evasion, which renders a virally encoded oncogene inaccessible to the conventional major histocompatibility complex class I pathway limiting its cis-presentation to effector cells.