Is cytomegalovirus interstitial pneumonitis in transplant recipients an immunopathological condition?

Comparative clinical manifestations and immune effects of cytomegalovirus infections following distinct types of immunosuppression

BACKGROUND

Cytomegalovirus (CMV) infection is a well-recognized complication of solid organ and hematopoietic cell transplantation. However, CMV infection also occurs in patients with human immunodeficiency virus (HIV) infection, previously immunocompetent intensive care unit (ICU) patients, and individuals on immunosuppressive medications for various underlying diseases.

OBJECTIVES

This review describes the comparative effects of CMV infection in distinct types of acquired immunosuppression.

SOURCES

Selected peer-reviewed publications on CMV infections published until December 2021.

CONTENT

CMV infection affects various organ systems through direct cytolytic mechanisms, but may also exert indirect effects by promoting pro-inflammatory and immunosuppressive responses. This has been well studied in transplant recipients, for whom antiviral prophylaxis and pre-emptive therapy have now become standard practice. These strategies not only prevent direct CMV disease manifestations, but also mitigate various immunopathological processes to reduce graft-versus-host disease, graft rejection, and the occurrence of secondary bacterial and fungal infections. The efficacy of neither prophylactic nor pre-emptive treatment of CMV infection has been demonstrated for patients with critical illness- or medication-induced immunosuppression. Many observational studies have shown an independent association between CMV reactivation and a prolonged duration of mechanical ventilation or increased mortality in the ICU. Furthermore, data suggest that CMV reactivation may increase pulmonary inflammation and prolong the duration of mechanical ventilation.

IMPLICATIONS

A large number of observational and experimental studies suggest attributable morbidity and mortality related to CMV infection, not only in transplant recipients and patients with HIV infection but also in patients with critically illness- or medication-induced immunosuppression. Adequately powered randomized controlled trials investigating the efficacy of prophylaxis or pre-emptive treatment of CMV infection in these patients are lacking, with a notable exception for transplant recipients.

Newer developments in viral hepatitis: Looking beyond hepatotropic viruses

Viral hepatitis in the entirety of its clinical spectrum is vast and most discussion are often restricted to hepatotropic viral infections, including hepatitis virus (A to E). With the advent of more advanced diagnostic techniques, it has now become possible to diagnose patients with non-hepatotropic viral infection in patients with hepatitis. Majority of these viruses belong to the Herpes family, with characteristic feature of latency. With the increase in the rate of liver transplantation globally, especially for the indication of acute hepatitis, it becomes even more relevant to identify non hepatotropic viral infection as the primary hepatic insult. Immunosuppression post-transplant is an established cause of reactivation of a number of viral infections that could then indirectly cause hepatic injury. Antiviral agents may be utilized for treatment of most of these infections, although data supporting their role is derived primarily from case reports. There are no current guidelines to manage patients suspected to have viral hepatitis secondary to non-hepatotropic viral infection, a gap that needs to be addressed. In this review article, the authors analyze the common non hepatotropic viral infections contributing to viral hepatitis, with emphasis on recent advances on diagnosis, management and role of liver transplantation.

Epidemiology and clinical impact of respiratory co-infections at diagnosis of Pneumocystis jirovecii Pneumonia

OBJECTIVES

To describe the epidemiology and clinical impact of respiratory co-infections at diagnosis of Pneumocystis jirovecii Pneumonia (PcP).

METHODS

A retrospective observational study was conducted between January 2011 and April 2019 to evaluate respiratory co-infections at diagnosis of PcP patients, in two tertiary care hospitals. Respiratory co-infection was defined by the identification of pathogens from P. jirovecii-positive samples.

RESULTS

Of the 7 882 respiratory samples tested for P. jirovecii during the 8-year study period, 328 patients with final diagnosis of PcP were included in this study. Mean age was 56.7 ± 14.9 years, 193 (58.8%) were male, 74 (22.6%) had a positive HIV serology, 125 (38.1%) had a viral co-infections, 76 (23.2%) a bacterial co-infections and 90-day mortality was 25.3%. In overall population, 90-Day mortality was independently associated with a solid tumor underlying disease (OR 11.8, 1.90-78, p=0.008), SOFA score at admission (OR 1.62, 1.34-2.05; p<0.001) and CMV respiratory co-infection (OR 3.44, 1.24-2.90; p=0.02). Among HIV-negative patients, respiratory CMV co-infection was associated with a worse prognosis, especially when treated with adjunctive corticosteroid therapy.

CONCLUSIONS

Respiratory CMV co-infection at diagnosis of PcP was independently associated with increased 90-day mortality, specifically in HIV-negative patients.

Cytomegalovirus Hepatitis in Immunocompetent and Immunocompromised Hosts

Human cytomegalovirus (HCMV) infection is common and affects between 40-100% of the worldwide population. However, the majority of cases are asymptomatic and when severe disease occurs, it is usually restricted to immunocompromised patients. Liver involvement by HCMV differs significantly, accordingly to the immune status of the host. In immunocompromised patients, particularly liver transplant patients, it often causes clinically significant hepatitis. On the other hand, in immunocompetent patients, HCMV hepatitis requiring hospitalization is extremely rare. This review aims to appraise studies regarding the pathophysiology of HCMV hepatitis, including mechanisms of latency and reactivation and its contribution to disease development, clinical presentation, diagnostic modalities and treatment, with a focus on comparing different aspects between immunocompromised and immunocompetent hosts.

Preemptive ganciclovir for mechanically ventilated patients with cytomegalovirus reactivation

Background

The effect of cytomegalovirus (CMV) reactivation on the length of mechanical ventilation and mortality in immunocompetent ICU patients requiring invasive mechanical ventilation remains controversial. The main objective of this study was to determine whether preemptive intravenous ganciclovir increases the number of ventilator-free days in patients with CMV blood reactivation.

Methods

This double-blind, placebo-controlled, randomized clinical trial involved 19 ICUs in France. Seventy-six adults ≥ 18 years old who had been mechanically ventilated for at least 96 h, expected to remain on mechanical ventilation for ≥ 48 h, and exhibited reactivation of CMV in blood were enrolled between February 5th, 2014, and January 23rd, 2019. Participants were randomized to receive ganciclovir 5 mg/kg bid for 14 days (n = 39) or a matching placebo (n = 37).

Results

The primary endpoint was ventilator-free days from randomization to day 60. Prespecified secondary outcomes included day 60 mortality. The trial was stopped for futility based on the results of an interim analysis by the DSMB. The subdistribution hazard ratio for being alive and weaned from mechanical ventilation at day 60 for patients receiving ganciclovir (N = 39) compared with control patients (N = 37) was 1.14 (95% CI from 0.63 to 2.06; P = 0.66). The median [IQR] numbers of ventilator-free days for ganciclovir-treated patients and controls were 10 [0–51] and 0 [0–43] days, respectively (P = 0.46). Mortality at day 60 was 41% in patients in the ganciclovir group and 43% in the placebo group (P = .845). Creatinine levels and blood cells counts did not differ significantly between the two groups.

Conclusions

In patients mechanically ventilated for ≥ 96 h with CMV reactivation in blood, preemptive ganciclovir did not improve the outcome.

Pathogenesis of human cytomegalovirus in the immunocompromised host

Human cytomegalovirus (HCMV) is a herpesvirus that infects ~60% of adults in developed countries and more than 90% in developing countries. Usually, it is controlled by a vigorous immune response so that infections are asymptomatic or symptoms are mild. However, if the immune system is compromised, HCMV can replicate to high levels and cause serious end organ disease. Substantial progress is being made in understanding the natural history and pathogenesis of HCMV infection and disease in the immunocompromised host. Serial measures of viral load defined the dynamics of HCMV replication and are now used routinely to allow intervention with antiviral drugs in individual patients. They are also used as pharmacodynamic read-outs to evaluate prototype vaccines that may protect against HCMV replication and to define immune correlates of this protection. This novel information is informing the design of randomized controlled trials of new antiviral drugs and vaccines currently under evaluation. In this Review, we discuss immune responses to HCMV and countermeasures deployed by the virus, the establishment of latency and reactivation from it, exogenous reinfection with additional strains, pathogenesis, development of end organ disease, indirect effects of infection, immune correlates of control of replication, current treatment strategies and the evaluation of novel vaccine candidates.

Bright and Early: Inhibiting Human Cytomegalovirus by Targeting Major Immediate-Early Gene Expression or Protein Function

The human cytomegalovirus (HCMV), one of eight human herpesviruses, establishes lifelong latent infections in most people worldwide. Primary or reactivated HCMV infections cause severe disease in immunosuppressed patients and congenital defects in children. There is no vaccine for HCMV, and the currently approved antivirals come with major limitations. Most approved HCMV antivirals target late molecular processes in the viral replication cycle including DNA replication and packaging. “Bright and early” events in HCMV infection have not been exploited for systemic prevention or treatment of disease. Initiation of HCMV replication depends on transcription from the viral major immediate-early (IE) gene. Alternative transcripts produced from this gene give rise to the IE1 and IE2 families of viral proteins, which localize to the host cell nucleus. The IE1 and IE2 proteins are believed to control all subsequent early and late events in HCMV replication, including reactivation from latency, in part by antagonizing intrinsic and innate immune responses. Here we provide an update on the regulation of major IE gene expression and the functions of IE1 and IE2 proteins. We will relate this insight to experimental approaches that target IE gene expression or protein function via molecular gene silencing and editing or small chemical inhibitors.

Cytomegalovirus (CMV) Pneumonitis: Cell Tropism, Inflammation, and Immunity

Human cytomegalovirus (HCMV) is an opportunistic pathogen causing disease mainly in immunocompromised patients or after congenital infection. HCMV infection of the respiratory tract leads to pneumonitis in the immunocompromised host, which is often associated with a bad clinical course. The related mouse cytomegalovirus (MCMV) likewise exhibits a distinct tropism for the lung and thus provides an elegant model to study host-pathogen interaction. Accordingly, fundamental features of cytomegalovirus (CMV) pneumonitis have been discovered in mice that correlate with clinical data obtained from humans. Recent studies have provided insight into MCMV cell tropism and localized inflammation after infection of the respiratory tract. Accordingly, the nodular inflammatory focus (NIF) has been identified as the anatomical correlate of immune control in lungs. Several hematopoietic cells involved in antiviral immunity reside in NIFs and their key effector molecules have been deciphered. Here, we review what has been learned from the mouse model with focus on the microanatomy of infection sites and antiviral immunity in MCMV pneumonitis.

Impact of cytomegalovirus reactivation on clinical outcomes in immunocompetent critically ill patients: protocol for a systematic review and meta-analysis

BACKGROUND

Cytomegalovirus (CMV) reactivation in critically ill patients is a well-recognized phenomenon with an incidence as high as 71 %. A number of studies have investigated the association between CMV reactivation and outcomes in critically ill patients with conflicting results. We propose to conduct a systematic review and meta-analysis to determine the impact of CMV reactivation on patient-centered outcomes and measures of health resource utilization in immunocompetent critically ill patients.

METHODS

In consultation with a research librarian, a search strategy will be developed and electronic databases (i.e., Ovid MEDLINE, Ovid EMBASE, and the Cochrane Library including the Cochrane Database of Systematic Reviews, the Cochrane Central Register of Controlled Trials (CENTRAL)) will be searched for original studies. Selected grey literature sources will be hand-searched. Search themes will include cytomegalovirus, intensive care unit, and sepsis. Citation screening, selection, quality assessment, and data abstraction will be performed in duplicate. Pooled effect estimates of the impact of CMV reactivation on selected patient-centered outcomes and measures of health resource utilization will be described.

DISCUSSION

This systematic review aims to explore the impact of CMV reactivation on patient-centered outcomes and health resource utilization in immunocompetent critically ill patients. Our results will help to better define the burden of disease associated with CMV reactivation. Indeed, evidence to date suggests increased mortality in this patient population. However, the relationship between CMV reactivation and health resource utilization remains less clear. Based on our results, future study on the impact of CMV treatment or prophylaxis on outcomes (including those other than mortality) may be warranted.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO CRD42016035446.

Parameters for the Successful Management of Cytomegalovirus

Cytomegalovirus (CMV) is a major pathogen for the neonate and the transplant recipient in both of whom the incidence of the disease and its severity are increased when the donor, or mother, has a primary infection. Many individuals with recurrent infection who experience the disease do so because they are being reinfected from an exogenous source, rather than reactivating their own strain, arguing that natural immunity can reduce, but not completely control, CMV disease. Antiviral therapy is thus needed to control CMV disease. There are four major strategies for the use of drugs against CMV - prophylaxis, suppression, pre-emptive therapy and treatment; significant benefit has been shown for some of these in some groups of transplant patients. The strategies must now be compared, and patient management regimes comparing the various approaches should be considered.

Progress in the Clinical Management of Herpesvirus Infections

Antiviral drug discovery has produced a series of drugs active against herpesviruses in vitro. Several of these are now licensed and/or have been used in clinical practice. This article reviews the mechanisms of action of acyclovir, ganciclovir, penciclovir, sorivudine and foscarnet, the development of resistance to these drugs and their pharmacokinetic and cellular toxicities. Based upon the natural histories of HSV, VZV and CMV, treatment objectives for each virus are discussed and the performance of each drug matched against these objectives. Overall, it is concluded that the perfect drug for treating herpesviruses does not exist, but that significant progress has been made towards controlling several herpesvirus diseases. It is suggested that further progress will require not just improved drug discovery programmes, but also an understanding of different pathogeneses and an appreciation by practising physicians that antiviral drugs must be given early in the infectious process to achieve the best results.

Cytomegalovirus reactivation in ICU patients

Introduction

Approximately 20 years have passed since we reported our results of histologically proven cytomegalovirus (CMV) pneumonia in non-immunocompromised ICU patients. Even if there are more recent reports suggesting that CMV may worsen the outcomes for ICU patients, there is no definite answer to this question: is CMV a potential pathogen for ICU patients or is it simply a bystander?

Methods

We will describe the pathophysiology of active CMV infection and the most recent insights concerning the epidemiological aspects of these reactivations.

Major findings

Cytomegalovirus can be pathogenic by a direct organ insult (such as for the lung), by decreasing host defences against other microorganisms and/or by enhancing the body’s inflammatory response (as in acute respiratory distress syndrome). The incidence of active CMV infection is dependent on the diagnostic method used. Using the most sophisticated available biological tools, the incidence can reach 15–20 % of ICU patients (20–40 % in ICU patients with positive CMV serology). In adequately powered cohorts of patients, active CMV infection appears to be associated with worse outcomes for mechanically ventilated ICU patients.

Discussion

There is no absolute direct proof of a negative impact of active CMV infection on the health outcomes of mechanically ventilated patients. Prospective randomized trials are lacking. Future trials should examine the potential benefits for health outcomes of using antiviral treatments. Such treatments could be prophylactic, pre-emptive or used only when there is an end-organ disease.

Conclusion

Cytomegalovirus infection may affect health outcomes for ICU patients. Additional prospective trials are necessary to confirm this hypothesis.

Immunohistochemical detection of virus through its nuclear cytopathic effect in idiopathic interstitial pneumonia other than acute exacerbation

Idiopathic interstitial pneumonias include complex diseases that have a strong interaction between genetic makeup and environmental factors. However, in many cases, no infectious agent can be demonstrated, and these clinical diseases rapidly progress to death. Theoretically, idiopathic interstitial pneumonias could be caused by the Epstein-Barr virus, cytomegalovirus, adenovirus, hepatitis C virus, respiratory syncytial virus, and herpesvirus, which may be present in such small amounts or such configuration that routine histopathological analysis or viral culture techniques cannot detect them. To test the hypothesis that immunohistochemistry provides more accurate results than the mere histological demonstration of viral inclusions, this method was applied to 37 open lung biopsies obtained from patients with idiopathic interstitial pneumonias. As a result, immunohistochemistry detected measles virus and cytomegalovirus in diffuse alveolar damage-related histological patterns of acute exacerbation of idiopathic pulmonary fibrosis and nonspecific interstitial pneumonia in 38 and 10% of the cases, respectively. Alveolar epithelium infection by cytomegalovirus was observed in 25% of organizing pneumonia patterns. These findings were coincident with nuclear cytopathic effects but without demonstration of cytomegalovirus inclusions. These data indicate that diffuse alveolar damage-related cytomegalovirus or measles virus infections enhance lung injury, and a direct involvement of these viruses in diffuse alveolar damage-related histological patterns is likely. Immunohistochemistry was more sensitive than the histological demonstration of cytomegalovirus or measles virus inclusions. We concluded that all patients with diffuse alveolar damage-related histological patterns should be investigated for cytomegalovirus and measles virus using sensitive immunohistochemistry in conjunction with routine procedures.

Cytomegalovirus pneumonia in hematopoietic stem cell recipients

Cytomegalovirus (CMV) is a frequently encountered infection following hematopoietic cell transplantation, and tissue invasive pneumonia is a dreaded complication of the virus in this population. In this review of CMV pneumonia, we address epidemiology, pathogenesis, diagnostics, current therapy, and strategies to prevent the development of CMV. We also review emerging treatment and prevention options for this challenging disease.

Development of a high-throughput assay to measure the neutralization capability of anti-cytomegalovirus antibodies

Infection by human cytomegalovirus (CMV) elicits a strong humoral immune response and robust anti-CMV antibody production. Diagnosis of virus infection can be carried out by using a variety of serological assays; however, quantification of serum antibodies against CMV may not present an accurate measure of a patient's ability to control a virus infection. CMV strains that express green fluorescent protein (GFP) fusion proteins can be used as screening tools for evaluating characteristics of CMV infection in vitro. In this study, we employed a CMV virus strain, AD169, that ectopically expresses a yellow fluorescent protein (YFP) fused to the immediate-early 2 (IE2) protein product (AD169IE2-YFP) to quantify a CMV infection in human cells. We created a high-throughput cell-based assay that requires minimal amounts of material and provides a platform for rapid analysis of the initial phase of virus infection, including virus attachment, fusion, and immediate-early viral gene expression. The AD169IE2-YFP cell infection system was utilized to develop a neutralization assay with a monoclonal antibody against the viral surface glycoprotein gH. The high-throughput assay was extended to measure the neutralization capacity of serum from CMV-positive subjects. These findings describe a sensitive and specific assay for the quantification of a key immunological response that plays a role in limiting CMV dissemination and transmission. Collectively, we have demonstrated that a robust high-throughput infection assay can analyze the early steps of the CMV life cycle and quantify the potency of biological reagents to attenuate a virus infection.

Congenital cytomegalovirus infection manifesting as neonatal persistent pulmonary hypertension: report of two cases

Various neonatal symptoms can lead to a diagnosis of congenital CMV infection. We report two cases of persistent pulmonary hypertension in relation with congenital CMV infection following maternal primary infection and reinfection, respectively. Both infants had severe refractory hypoxemia, requiring high-frequency ventilation, inhaled nitric oxide and inotropic support. One of them required extracorporeal membrane oxygenation for five days. Ganciclovir therapy was attempted in the two cases on day 12 postnatal. One of the infant died on day 15 postnatal. The other survived and is developing uneventfully at 15 months of age.

CONCLUSION

Neonatal persistent pulmonary hypertension can be the consequence of congenital CMV infection. Intensive respiratory support and IV ganciclovir are indicated in case of life-threatening condition.

Cytomegalovirus reactivation in critically ill immunocompetent hosts: a decade of progress and remaining challenges

Human cytomegalovirus (HCMV) is an undisputed pathogen in humans with severe immune compromise, which has historically been thought to carry little consequence in immunocompetent hosts. During the past decade, however, accumulating data suggest that significant numbers of immunocompetent humans reactivate HCMV during critical illness, and that these reactivation episodes are associated with worsened outcomes. Because most people are infected with this ubiquitous virus by adulthood, confirming pathogenicity has now become a clinical priority. In this article, we will review the incidence and implications of reactivation, the relevant immune responses and reactivation triggers relevant to the immunocompetent host. We will summarize the progress made during the past ten years, outline the work ongoing in this field, and identify the major gaps remaining in our emerging understanding of this phenomenon.

Human cytomegalovirus IE1 protein elicits a type II interferon-like host cell response that depends on activated STAT1 but not interferon-γ

Human cytomegalovirus (hCMV) is a highly prevalent pathogen that, upon primary infection, establishes life-long persistence in all infected individuals. Acute hCMV infections cause a variety of diseases in humans with developmental or acquired immune deficits. In addition, persistent hCMV infection may contribute to various chronic disease conditions even in immunologically normal people. The pathogenesis of hCMV disease has been frequently linked to inflammatory host immune responses triggered by virus-infected cells. Moreover, hCMV infection activates numerous host genes many of which encode pro-inflammatory proteins. However, little is known about the relative contributions of individual viral gene products to these changes in cellular transcription. We systematically analyzed the effects of the hCMV 72-kDa immediate-early 1 (IE1) protein, a major transcriptional activator and antagonist of type I interferon (IFN) signaling, on the human transcriptome. Following expression under conditions closely mimicking the situation during productive infection, IE1 elicits a global type II IFN-like host cell response. This response is dominated by the selective up-regulation of immune stimulatory genes normally controlled by IFN-γ and includes the synthesis and secretion of pro-inflammatory chemokines. IE1-mediated induction of IFN-stimulated genes strictly depends on tyrosine-phosphorylated signal transducer and activator of transcription 1 (STAT1) and correlates with the nuclear accumulation and sequence-specific binding of STAT1 to IFN-γ-responsive promoters. However, neither synthesis nor secretion of IFN-γ or other IFNs seems to be required for the IE1-dependent effects on cellular gene expression. Our results demonstrate that a single hCMV protein can trigger a pro-inflammatory host transcriptional response via an unexpected STAT1-dependent but IFN-independent mechanism and identify IE1 as a candidate determinant of hCMV pathogenicity.

Manifestations of human cytomegalovirus infection: proposed mechanisms of acute and chronic disease

Infections with human cytomegalovirus (HCMV) are a major cause of morbidity and mortality in humans with acquired or developmental deficits in innate and adaptive immunity. In the normal immunocompetent host, symptoms rarely accompany acute infections, although prolonged virus shedding is frequent. Virus persistence is established in all infected individuals and appears to be maintained by both a chronic productive infections as well as latency with restricted viral gene expression. The contributions of the each of these mechanisms to the persistence of this virus in the individual is unknown but frequent virus shedding into the saliva and genitourinary tract likely accounts for the near universal incidence of infection in most populations in the world. The pathogenesis of disease associated with acute HCMV infection is most readily attributable to lytic virus replication and end organ damage either secondary to virus replication and cell death or from host immunological responses that target virus-infected cells. Antiviral agents limit the severity of disease associated with acute HCMV infections, suggesting a requirement for virus replication in clinical syndromes associated with acute infection. End organ disease secondary to unchecked virus replication can be observed in infants infected in utero, allograft recipients receiving potent immunosuppressive agents, and patients with HIV infections that exhibit a loss of adaptive immune function. In contrast, diseases associated with chronic or persistent infections appear in normal individuals and in the allografts of the transplant recipient. The manifestations of these infections appear related to chronic inflammation, but it is unclear if poorly controlled virus replication is necessary for the different phenotypic expressions of disease that are reported in these patients. Although the relationship between HCMV infection and chronic allograft rejection is well known, the mechanisms that account for the role of this virus in graft loss are not well understood. However, the capacity of this virus to persist in the midst of intense inflammation suggests that its persistence could serve as a trigger for the induction of host-vs-graft responses or alternatively host responses to HCMV could contribute to the inflammatory milieu characteristic of chronic allograft rejection.

Differential CMV-specific CD8+ effector T cell responses in the lung allograft predominate over the blood during human primary infection

Acquisition of T cell responses during primary CMV infection in lung transplant recipients (LTRs) appear critical for host defense and allograft durability, with increased mortality in donor+/recipient- (D+R-) individuals. In 15 D+R- LTRs studied, acute primary CMV infection was characterized by viremia in the presence or absence of pneumonitis, with viral loads higher in the lung airways/allograft compared with the blood. A striking influx of CD8+ T cells into the lung airways/allograft was observed, with inversion of the CD4+:CD8+ T cell ratio. De novo CMV-specific CD8+ effector frequencies in response to pooled peptides of pp65 were strikingly higher in lung mononuclear cells compared with the PBMC and predominated over IE1-specific responses and CD4+ effector responses in both compartments. The frequencies of pp65-specific cytokine responses were significantly higher in lung mononuclear cells compared with PBMC and demonstrated marked contraction with long-term persistence of effector memory CD8+ T cells in the lung airways following primary infection. CMV-tetramer+CD8+ T cells from PBMC were CD45RA- during viremia and transitioned to CD45RA+ following resolution. In contrast, CMV-specific CD8+ effectors in the lung airways/allograft maintained a CD45RA- phenotype during transition from acute into chronic infection. Together, these data reveal differential CMV-specific CD8+ effector frequencies, immunodominance, and polyfunctional cytokine responses predominating in the lung airways/allograft compared with the blood during acute primary infection. Moreover, we show intercompartmental phenotypic differences in CMV-specific memory responses during the transition to chronic infection.

Antivirals in the transplant setting

Over the past quarter of a century, antiviral drugs have moved from an experimental adventure in transplant patients to a situation where they are used routinely to prevent diseases caused by several viruses. Furthermore, they have significantly reduced several medical complications of transplantation, such as graft rejection, thereby implicating viruses as components of their pathogenesis. By controlling these major complication, the development of these antiviral drugs and their prodrugs, has therefore greatly facilitated the clinical expansion of transplantation, allowing life saving procedures to be offered to more patients who could potentially benefit. This article will briefly summaries which viruses are important following transplantation and outline the evidence-base from randomized controlled clinical trails for the deployment of antiviral drugs to prevent viral diseases.

Therapeutic effect of a traditional Chinese medicine, ren-shen-yang-rong-tang (Japanese name: Ninjin'yoeito) on nitric oxide-mediated lung injury in a mouse infected with murine cytomegalovirus

The therapeutic effect of a traditional Chinese medicine ren-shen-yang-rong-tang (Japanese name: Ninjin'yoeito, NYT) on murine cytomegalovirus (MCMV)-associated pneumonitis was examined. In MCMV-pneumonitis, IFN-gamma-induced nitric oxide (NO) mediates its pathogenesis. When mice, which had been infected with 0.2LD(50) of MCMV at 28 days previously, were intraperitoneally injected with anti-CD3 monoclonal antibody (mAb), MCMV-pneumonitis was induced in the lung, where high amounts of IFN-gamma-producing cells thereafter accumulated, accompanied by an elevation in the NO level in the serum and abundant expression of inducible NO synthase (iNOS) mRNA, thus resulting in all mice eventually dying. When the mice were orally treated with NYT (1000 mg/kg/day) once on the day of mAb injection and once the day after, the expression level of iNOS-mRNA was suppressed and NO level in the serum decreased. The survival rate improved from 0% to 57.1%. The pathological findings of the lungs in the NYT-treated mice were comparable to those of the uninfected controls. In contrast, NYT itself did not affect either the ratio of IFN-gamma-producing cells or MCMV titer. As a result, NYT had a therapeutic effect on MCMV-pneumonitis by decreasing the degree of inflammation mediated by the IFN-gamma-induced NO. It is also interesting to note that only two oral administrations of NYT had a therapeutic effect on viral disease.

Immunohistochemical and in situ detection of cytomegalovirus in lung autopsies of children immunocompromised by secondary interstitial pneumonia

Secondary interstitial pneumonia (SIP), a disease affecting patients immunocompromised by primary underlying diseases during their treatment in hospital, is frequently associated with cytomegalovirus (CMV) infection, a potentially treatable condition. However, in many cases, no infectious agent can be determined, and this clinical disease rapidly progresses to death. Theoretically, SIP could be caused by CMV, which may be present in such small amounts or such configuration that routine histopathological analysis or viral culture techniques cannot detect the virus. To test the hypothesis that immunohistochemistry (IH) and in situ detection by hybridization (ISH) provides more accurate results than the mere histological demonstration of CMV inclusions, these methods were applied to 37 autopsied lung sections obtained from children immunocompromised by primary underlying diseases and who died of SIP. As a result, the cases were subdivided into three groups: (1) children with SIP CMV inclusions (Diffuse alveolar damage-DAD-related) (n = 7); (2) children with SIP without classical viral inclusions (CMV-DAD-related) (n = 3); (3) children with SIP exhibiting nuclear cytopathic effect (not CMV-NSIP-related) (n = 27). In the first group, all three techniques yielded clearly positive results, whereas IH and ISH indicated that three of the children of the second group had CMV-related DAD without histological demonstration of CMV inclusions. In the third group, there were no positive CMV signals. These data indicate that DAD-related CMV infection is an important cause of SIP and of death in children immunosuppressed by primary underlying diseases, and that IH and in situ detection were more sensitive than the histological demonstration of CMV inclusions. A direct involvement of CMV in SIP exhibiting DAD is likely, but not in the non-specific interstitial pneumonia (NSIP) pattern. We conclude that all children with primary underlying diseases should be investigated for CMV SIP using sensitive IH and in situ tests in conjunction with histological routine procedures.

Polyomavirus BK-specific immunity after kidney transplantation

Failure to mount or maintain a protective immune response may influence the development of polyomavirus BK (BKV)-associated nephropathy (PVAN). However, limited data are so far available on BKV-specific immunity after kidney transplantation. BKV-specific cellular immune response was retrospectively analyzed in kidney recipients with or without BKV infection/reactivation by measuring the frequency of interferon (IFN)-gamma-secreting cells in peripheral blood. Patients with BKV-active infection and good renal function (n=6) had a mean BKV-specific lymphocyte frequency 2 log lower than healthy controls and in the same range as BKV-seropositive recipients without active infection (n=7). Patients with PVAN (n=5) revealed undetectable levels of BKV-specific cells. However, two patients from the latter cohort treated with immunosuppression reduction showed the emergence of specific immunity, with IFN-gamma production in the same range as healthy controls. Our preliminary data suggest that lack of protective immunity toward BKV may favor the occurrence of BKV active infection and influence the progression to PVAN.

Cytomegalovirus infection after orthotopic liver transplantation is restricted by a pre-existing antiviral immune response of the recipient

Infection of the liver by the human cytomegalovirus (HCMV) frequently occurs after orthotopic liver transplantation (OLT). However, the role of viral replication and the inflammatory reaction in the development of HCMV-associated liver dysfunction is unclear. To address this question in vivo, 84 liver biopsy specimens from 74 patients who received an orthotopic liver transplant were investigated by immunohistochemical detection of viral antigens and cell type specific marker proteins. The extent of viral replication was correlated with the HCMV antibody status of donor and recipient. HCMV immediate early antigens were found in 25 of 84 liver tissue sections investigated, hepatocytes being the predominant target cells. Bile duct epithelial cells, endothelial cells, mesenchymal cells and sinusoidal lining cells were also found susceptible to HCMV infection. The detection of viral capsid antigens, nuclear inclusions in infected cells and foci of infected cells were suggestive of permissive infection in these cells. In 25 HCMV-positive liver biopsy specimens, the median extent of HCMV infection was 0.33 (0.02-5.67) infected cells/mm(2) liver tissue. Primary infection of liver transplant recipients (D+/R-) was associated with a significantly higher extent of organ involvement as compared to reinfection or reactivation (D+/R+). In contrast, the extent of inflammatory infiltrates in areas of infected liver cells was higher in tissues of patients with pre-existing immunoreactivity (R+) compared to patients without pre-existing immunoreactivity (R-). In conclusion, these results favour the assumption that the immune response to HCMV is effective in restricting viral spread in the liver.

Role of CMV pneumonia in the development of obliterative bronchiolitis in heart-lung and double-lung transplant recipients

Obliterative bronchiolitis (OB) is the main cause of late mortality after lung transplantation. Cytomegalovirus infection has been associated with late graft failure. The aim of this study was to determine whether the development of OB was related to CMV pretransplant serological status and to CMV infections. The study group comprised 36 lung transplant recipients (27 HLT and 9 DLT) who survived more than 4 months, of whom 47% developed OB (defined by the persistence of an unexplained obstructive disease: FEV1/VC < 0.7). OB occurred more frequently: (1) in seronegative recipients with seropositive donors (8/9) than in seropositive recipients (7/19) or seronegative well-matched recipients (2/8); and (2) in patients who experienced CMV pneumonia (11/16) and CMV recurrence (11/16). Since matching seronegative recipients is the best way to prevent CMV infection, we believe that seronegative grafts must be reserved for seronegative recipients.

Pulmonary involvement during cytomegalovirus infection in immunosuppressed patients

Although cytomegalovirus (CMV) pulmonary involvement after solid organ transplantation is infrequently seen nowadays, CMV pneumonitis is still a potential lethal complication. Introduction of the pp65 antigenemia assay enabled early and rapid diagnosis of CMV viremia in transplant patients prior to symptoms. Also, in asymptomatic patients with CMV viremia, a decreased pulmonary diffusion capacity could be demonstrated. In this review, we discuss clinical and subclinical pulmonary involvement of CMV infection in the immunocompromised host with an emphasis on transplant recipients. The clinical course, diagnosis, therapy, prophylaxis, and pathophysiology of CMV pneumonitis are discussed.

Human cytomegalovirus inhibits differentiation of monocytes into dendritic cells with the consequence of depressed immunological functions

Human cytomegalovirus (HCMV) infections in immunocompromised patients are associated with impaired immunological functions. Blood monocytes, which can differentiate into dendritic cells upon cytokine stimulation, play a central role in adequate immune reactivity and are believed to carry latent HCMV. We demonstrate here that HCMV infection of monocytes results in a block in the cytokine-induced differentiation of monocytes into functionally active CD1a-positive dendritic cells, which exhibited severely depressed immunological functions in vitro. The HCMV-infected cells exhibited a significantly reduced ability to endocytose fluorescein isothiocyanate-labeled dextran particles as well as a more than 90% reduced ability to migrate in response to the chemoattractant factors RANTES, MIP-1alpha, and MIP-3beta. Interestingly, HCMV-infected cells expressed high levels of the costimulatory molecule CD86, in contrast to the low levels of expression that was observed on uninfected monocytes and uninfected immature dendritic cells. Furthermore, HCMV-infected CD1a-negative cells were unable to induce a T-cell response. Thus, these observations suggest that HCMV infection of monocytes in vitro blocks cytokine-induced dendritic cell differentiation, and since dendritic cells play a central role in initiating immune responses, these findings suggest a powerful tactic to avoid immune recognition and to blunt the immune response at early phases of infection.

Allogeneic cell stimulation enhances cytomegalovirus replication in the early period of primary infection in an experimental rat model

BACKGROUND

Cytomegalovirus (CMV) diseases commonly occur in allograft recipients in the early post-transplant period. However, factors responsible for the high incidence of CMV diseases during this period are not yet fully defined.

METHODS

Wistar-Furth (WF; RT-1(u)) rats were inoculated with 10(4) plaque-forming units (PFU) of rat CMV (RCMV) intraperitoneally, and then transplanted with allogeneic lungs from Dark Agouti (DA; RT-1avl) rats or stimulated with 10(7) mitomycin C-treated spleen cells from DA rats by daily sub-cutaneous injections for 2 weeks. No immunosuppressive agent was used. Naive WF rats and WF rats grafted with syngeneic lungs or cells were used as controls. The level of RCMV replication in rats was assessed by infectious virus titers in tissues.

RESULTS

The virus titers in salivary glands of allogeneic and syngeneic lung graft recipients were significantly higher than in naive WF rats. The level of RCMV replication in rats stimulated with allogeneic spleen cells was significantly higher than in the syngeneic recipient rats: virus titers in the salivary gland of allogeneic and syngeneic recipients reached 4.61 +/- 0.33 and 4.00 +/- 0.37 log(10) PFU/g tissue, respectively, at 14 days post-infection (p = 0.015). The augmented viral replication in allogeneic recipients was confirmed by an increase in the number of RCMV antigen-positive macrophages present in tissue sections of the salivary gland.

CONCLUSIONS

Acute lung allograft rejection and allogeneic spleen cell stimulation enhance CMV replication in the salivary gland of rats. Various responses to allogeneic antigens occurring in the process of acute allograft rejection could be risk factors for post-transplant CMV replication and infection.

Long-term results of CMV hyperimmune globulin prophylaxis in 377 heart transplant recipients

BACKGROUND

Cytomegalovirus (CMV) has emerged as the most important pathogen to affect the post-operative course after heart transplantation. We performed a retrospective analysis to evaluate the efficiency of CMV hyperimmune globulin (CMVIG) prophylaxis in preventing CMV disease in aggressively immunosuppressed patients after heart transplantation.

METHODS

We studied 377 heart transplant recipients who received quadruple-immunosuppressive therapy and CMVIG as sole CMV prophylaxis. The study population was categorized into 4 groups according to donor and recipient CMV serology at the time of transplantation (D+/R+, D+/R-, D-/R+, D-/R-) and was monitored for CMV immediate early antigen in peripheral blood cells, in urine sediments, and in throat washings; for the presence of serum CMV immunoglobulin M and CMV immunoglobulin G; and for clinical evidence of CMV-related symptoms. In addition, we compared the incidence of cardiac allograft vasculopathy and infection among the groups.

RESULTS

During the first 5 years after transplantation, CMV disease developed in 79 patients (20.96%). Comparison among the groups showed significantly increased risk for CMV disease in allograft recipients of organs from seropositive donors (D+, 27.31%; D-, 11.33%; p = 0.0003). We observed 6 CMV-associated deaths, all in CMV-antibody-negative recipients. Additionally CMV-positive recipients had a greater incidence of cardiac allograft vasculopathy (p = 0.048), and a greater overall infection rate (p = 0.0034).

CONCLUSIONS

Cytomegalovirus hyperimmune globulin administration prevents CMV disease and infection in aggressively immunosuppressed heart transplant recipients. Because fatal CMV disease in CMV-negative recipients of organs from seropositive donors could not be prevented with CMVIG alone, we recommend the additional use of prophylactic ganciclovir in this CMV-mismatched population.

Downregulation of the epidermal growth factor receptor by human cytomegalovirus infection in human fetal lung fibroblasts

Epidermal growth factor plays a key role in late fetal lung development and differentiation as well as in regulating surfactant protein A synthesis, which is involved in innate immunity of the lung. Here we show that human cytomegalovirus (HCMV), a known lung pathogen in connatal and postnatal infection of neonates as well as transplant recipients, completely down-regulates EGF receptor (EGF-R) on the surface of human fetal lung fibroblasts. Inhibition of EGF-R synthesis occurs on the transcriptional rather than on the posttranscriptional level. The effect essentially depends on expression of viral immediate early and/or early genes, as binding of ultraviolet light-inactivated virus to the cells had no effect on EGF-R expression. Furthermore, the anti-HCMV drug ganciclovir, which blocks HCMV DNA replication and late gene expression, cannot overcome HCMV-mediated inhibition of EGF-R, suggesting that immediate early or early gene products may be responsible for down-regulation of EGF-R. Interestingly, the glucocorticoid dexamethasone, which is used for its antiinflammatory action to prevent chronic lung disease in preterm infants, promotes HCMV-associated downregulation of the EGF-R by stimulation of viral gene expression. From these data it can be hypothesized that the pathogenesis of HCMV lung infection involves down-regulation of EGF-R and that congenital HCMV infection may cause retardation in lung maturation and surfactant protein synthesis.

Respiratory virus infections in transplant recipients after reduced-intensity conditioning with Campath-1H: high incidence but low mortality

Respiratory virus infections can cause serious morbidity and mortality after conventional allogeneic stem cell transplantation. However, the incidence and outcome of these infections after reduced intensity conditioning has not been reported. Between 1997 and 2001, 35 episodes of respiratory virus infections were noted in 25 of 83 transplant recipients conditioned with fludarabine, melphalan and Campath-1H, and 80% of them received early antiviral therapy. Parainfluenza virus (PIV) 3 was the commonest isolate (45.7%) followed by respiratory syncytial virus (37%). Patients with myeloma were more susceptible to these infections [odds ratio (OR) 4.1, P = 0.01] which were often recurrent in patients with severe acute or chronic graft-versus-host disease (GVHD) (OR 10.6, P = 0.03). Infection within the first 100 d (OR 5.0, P = 0.05) and PIV 3 (OR 9.2, P = 0.01) isolation were risk factors for developing lower respiratory infection. Although more than half of the episodes progressed to lower respiratory infection, the mortality was only 8%. This could have been due to early initiation of antiviral therapy, but the attenuation of pulmonary damage due to the reduced-intensity conditioning, low incidence of GVHD and, paradoxically, the low CD4+ T-cell subset in this setting might also have been contributory factors.

Human adenovirus and human cytomegalovirus infections in preterm newborns: no association with bronchopulmonary dysplasia

Connatal infection with human adenovirus (HAdV) has been recently proposed as a cofactor for the development of bronchopulmonary dysplasia (BPD) in preterm infants [Couroucli et al. 2000 Pediatr Res 47:225-232]. In another study, BPD was associated with an increased incidence of human cytomegalovirus (HCMV) infection [Sawyer et al. 1987 Am J Dis Child 141:303-305]. During a 18-mo study period, we investigated tracheal aspirates or pharyngeal aspirates and urine samples collected during the first month of life from 66 preterm newborns with very low birth weight (< or =1.500 g) for replication-potent HAdV as well as for adenoviral and HCMV DNA by virus culture and qualitative DNA PCR. Thus, our study included not only prenatal but also peri- and postnatal infections. Thirty-seven percent (24/66) of infants developed BPD(1), as defined by persistent oxygen dependency at day 28 of life. Replication-potent HAdV and/or adenoviral DNA could be detected repeatedly in tracheal aspirates/pharyngeal aspirates and/or urine from 20% (13/66) of preterm infants. Seventeen percent (4/24) of infants in the BPD(1) group and 21% (9/42) of infants in the non-BPD group had an HAdV infection, indicating that in our study the very recently proposed association between HAdV infection of the lung and BPD could not be confirmed. For comparison, active HCMV infection was diagnosed in 18% (12/66) of infants, 3 of which developed HCMV disease. 29% (7/24) in the BPD(1) group and 12% (5/42) in the non-BPD group were positive for HCMV. Again, there was no statistically significant association between HCMV infection and BPD. In summary, our findings indicate that HAdV and HCMV infection are frequent in preterm newborns with very low birth weight; however, a causal association with the development of BPD seems unlikely.

Diagnosis and treatment approaches of CMV infections in adult patients

BACKGROUND

Cytomegalovirus (CMV) infections are very common in the general population. Clinical CMV disease, particularly CMV pneumonitis, greatly impacts the morbidity and mortality of immunosuppressed patients.

OBJECTIVE

To present an overview of the basic aspects of the biology, epidemiology, and clinical features of CMV in relation to the available diagnostic and therapeutic approaches in adult patients.

METHODS

Review of the medical literature on cytomegalovirus infection and disease in adult hosts, with a focus on approaches to diagnosis and treatment of CMV respiratory disease in immunosuppressed hosts.

CONCLUSIONS

Cytomegalovirus infections are likely to remain a significant cause of morbidity and mortality among immunosuppressed patients. Important aspects of the biological events underlying the transition from infection to clinical disease remain unclear. Despite that, considerable progress has been made in the design of improved diagnostic techniques and the development of antiviral agents. Preventive and particularly preemptive therapeutic approaches demand further technical improvements in diagnostic testing. At present, the emphasis in the search for improved diagnostic testing rests on the development of quantitative methods for early detection of the increased viral replicative activity that presumably precedes the onset of CMV disease in infected individuals.

Human cytomegalovirus as a direct pathogen: correlation of multiorgan involvement and cell distribution with clinical and pathological findings in a case of congenital inclusion disease

The human cytomegalovirus (HCMV), a member of the Herpesviridae, is the most frequent cause of congenital virus infections and a major cause of morbidity and mortality in immunocompromised patients. Due to the lack of an appropriate animal model, insight into the pathogenesis of HCMV infections originates primarily from in situ examination of HCMV-infected tissues. Although in immunocompromised adults such tests are complicated frequently by the presence of additional misleading pathogens, the absence of additional pathogens renders congenital inclusion disease the most suitable access for investigation of pathogenetic aspects of HCMV infections. Immunohistochemical examination of tissue sections from a boy with fatal congenital inclusion disease was undertaken to detect the extent of multiorgan and cell involvement. Adrenal gland, bone marrow, diencephalon, heart, kidney, liver, lung, pancreas, placenta, small bowel and spleen were included in this study. Detection of virus antigens from different phases of viral replication revealed that all investigated organs were infected by HCMV. Simultaneous detection of cell type specific marker molecules showed that a variety of cell types stained positive for HCMV antigens including endothelial cells, epithelial cells, smooth muscle cells, mesenchymal cells, hepatocytes, monocytes/macrophages and granulocytes. The lung, the pancreas, the kidneys and the liver were the major target organs with a high number of HCMV infected cells. This correlated with multiorgan failure as the cause of death and strongly indicates direct pathogenetic effects of HCMV.

Severe infections after bone marrow transplantation

Bone marrow transplantation and stem cell transplantation have become standard therapies offering potential cures for a number of hematologic malignancies and immunologic disorders. Severe infection remains a life threatening complication after transplantation, contributes significantly to morbidity, and may necessitate admission to the ICU. It is estimated that between 20 and 40% of patients receiving bone marrow transplant will require ICU admission in the initial posttransplantation phase. Historically, survival rates after admission to the ICU are dismal, particularly if mechanical ventilation is required for respiratory failure. Other organ involvement worsens the prognosis still further and has led to proposals for rationing or restricting access to critical care units and supportive measures. Recent studies have reported small but significant improvements in outcome after critical illness. Whether this improvement is a result of changes in levels of supportive care or a more defined patient selection is uncertain. Moreover, risk factors identifying patients who will benefit most from intensive support are poorly defined. However, it is generally accepted that respiratory failure requiring invasive mechanical ventilation is associated with a poor prognosis in this patient group. Early involvement of intensivists in the management of critical illness in transplant recipients is likely to continue to improve survival in this group of patients.

Blood and alveolar lymphocyte subsets in pulmonary cytomegalovirus infection after lung transplantation

BACKGROUND

Cytomegalovirus (CMV) pneumonitis has been shown to be associated with lymphocytic alveolitis after lung transplantation. In the present study, we investigated a series of bronchoalveolar (BAL) and blood samples, collected in the absence of rejection or acute infectious episodes. in order -1: to evaluate intra-alveolar cell population changes concomitant with CMV replication and -2: to reappraise the value of cell population analysis in the management of patients after lung transplantation.

METHODS

We used flow cytometry to investigate modifications of lymphocyte subpopulations related to pulmonary cytomegalovirus infections in blood and BAL samples from a series of 13 lung transplant recipients. After exclusion of samples obtained during pulmonary rejection, bronchiolitis obliterans or acute bacterial infection, 48 blood and BAL samples were retained for analysis: 17 were CMV positive by shell-vial assay and 31 were CMV negative in blood and BAL.

RESULTS

Our results demonstrate that pulmonary CMV infection is associated with a significant increase in the total lymphocyte population in BAL samples, but with minor modifications of the various lymphocyte subpopulations and a significantly higher absolute number of B lymphocytes in blood samples.

CONCLUSIONS

Cytomegalovirus pulmonary infection is accompanied by only minor changes in BAL lymphocyte subpopulations. The study of BAL lymphocyte subpopulations therefore appears to be of limited clinical value in the diagnosis of pulmonary CMV infection. However, increased blood B-lymphocytes seems to be a clinical feature associated with CMV infection.

Quantification of polyoma BK viruria in hemorrhagic cystitis complicating bone marrow transplantation

Polyoma BK virus (BKV) is frequently identified in the urine of bone marrow transplantation (BMT) patients with hemorrhagic cystitis (HC). However, viruria is common even in asymptomatic patients, making a direct causative role of BKV difficult to establish. This study prospectively quantified BK viruria and viremia in 50 BMT patients to define the quantitative relationship of BKV reactivation with HC. Adenovirus (ADV) was similarly quantified as a control. More than 800 patient samples were quantified for BKV VP1 gene with a real-time quantitative polymerase chain reaction. Twenty patients (40%) developed HC, 6 with gross hematuria (HC grade 2 or higher) and 14 with microscopic hematuria (HC grade 1). When compared with asymptomatic patients, patients with HC had significantly higher peak BK viruria (6 x 10(12) versus 5.7 x 10(7) genome copies/d, P <.001) and larger total amounts of BKV excreted during BMT (4.9 x 10(13) versus 7.7 x 10(8) genome copies, P <.001). There was no detectable increase in BK viremia. Binary logistic regression analysis showed that BK viruria was the only risk factor, with HC not related to age, conditioning regimen, type of BMT, and graft-versus-host disease. Furthermore, the levels of ADV viruria in patients with or without HC were similar and comparable with those of BK viruria in patients without HC, suggesting that the significant increase in BK viruria in HC patients was not due to background viral reactivation or damage to the urothelium. BK viruria was quantitatively related to the occurrence of HC after BMT.

Inhibition of cytomegalovirus immediate early gene expression: a therapeutic option?

The replication cycle of the human cytomegalovirus (HCMV) is characterized by the expression of immediate early (IE), early (E), and late (L) gene regions. Current antiviral strategies are directed against the viral DNA polymerase expressed during the early phase of infection. The regulation of the IE-1 and IE-2 gene expression is the key to latency and active replication due to their transactivating and repressing functions. There is growing evidence that the pathogenic features of HCMV are largely due to the abilities of IE-1 and IE-2 to transactivate cellular genes. Consequently, current drugs used to inhibit HCMV infection would have no impact on IE-1 and IE-2-induced effects that are produced before the early phase. Moreover, when HCMV DNA replication is inhibited, IE gene products accumulate in infected cells causing disturbances of host cell functions. This review summarizes the biological functions of HCMV-IE gene expression, their relevance in pathogenesis, as well as efforts to develop novel treatment strategies directed against HCMV-IE expression.

Investigation of CMV disease in immunocompromised patients

Cytomegalovirus (CMV) is a recognised cause of morbidity and mortality in immunocompromised individuals. This review will concentrate on recent advances in the understanding of the complex interplay between the host and parasite and the pathological consequences of perturbation of the host immune system. The classic view of CMV as a slowly replicating virus is challenged by recent in vivo findings suggesting that active replication occurs dynamically in the human host, with a doubling time of approximately one day. In addition, CMV load plays a major role in viral pathogenesis, such that increased CMV replication is a significant risk factor for disease in all immunocompromised groups studied to date. These studies focus attention on understanding the virological and immunological determinants of enhanced viral replication and its pathological consequences.