Detection of human cytomegalovirus in peripheral mononuclear cells and urine samples using PCR

Cytomegalovirus viral load within blood increases markedly in healthy people over the age of 70 years

BACKGROUND

Cytomegalovirus (CMV) is a highly prevalent herpesvirus, which maintains lifelong latency and places a significant burden on host immunity. Infection is associated with increased rates of vascular disease and overall mortality in the elderly and there is an urgent need for improved understanding of the viral-host balance during ageing. CMV is extremely difficult to detect in healthy donors, however, using droplet digital PCR of DNA from peripheral blood monocytes, we obtained an absolute quantification of viral load in 44 healthy donors across a range of ages.

RESULTS

Viral DNA was detected in 24 % (9/37) of donors below the age of 70 but was found in all individuals above this age. Furthermore, the mean CMV load was only 8.6 copies per 10,000 monocytes until approximately 70 years of age when it increased by almost 30 fold to 249 copies in older individuals (p < 0.0001). CMV was found within classical CD14+ monocytes and was not detectable within the CD14-CD16+ subset. The titre of CMV-specific IgG increased inexorably with age indicating that loss of humoral immunity is not a determinant of the increased viral load. In contrast, although cellular immunity to the structural late protein pp65 increased with age, the T cell response to the immediate early protein IE1 decreased in older donors.

CONCLUSION

These data reveal that effective control of CMV is impaired during healthy ageing, most probably due to loss of cellular control of early viral reactivation. This information will be of value in guiding efforts to reduce CMV-associated health complications in the elderly.

Systematic microRNA analysis identifies ATP6V0C as an essential host factor for human cytomegalovirus replication

Recent advances in microRNA target identification have greatly increased the number of putative targets of viral microRNAs. However, it is still unclear whether all targets identified are biologically relevant. Here, we use a combined approach of RISC immunoprecipitation and focused siRNA screening to identify targets of HCMV encoded human cytomegalovirus that play an important role in the biology of the virus. Using both a laboratory and clinical strain of human cytomegalovirus, we identify over 200 putative targets of human cytomegalovirus microRNAs following infection of fibroblast cells. By comparing RISC-IP profiles of miRNA knockout viruses, we have resolved specific interactions between human cytomegalovirus miRNAs and the top candidate target transcripts and validated regulation by western blot analysis and luciferase assay. Crucially we demonstrate that miRNA target genes play important roles in the biology of human cytomegalovirus as siRNA knockdown results in marked effects on virus replication. The most striking phenotype followed knockdown of the top target ATP6V0C, which is required for endosomal acidification. siRNA knockdown of ATP6V0C resulted in almost complete loss of infectious virus production, suggesting that an HCMV microRNA targets a crucial cellular factor required for virus replication. This study greatly increases the number of identified targets of human cytomegalovirus microRNAs and demonstrates the effective use of combined miRNA target identification and focused siRNA screening for identifying novel host virus interactions.

Human cytomegalovirus is a prevalent pathogen. Like other herpesviruses, human cytomegalovirus expresses small regulatory RNAs called microRNAs. The focus of this study was to understand the role of these RNAs in the context of viral infection and to use this information to identify novel host factors involved in human cytomegalovirus biology. We used a biochemical approach that allowed us to systematically identify cellular genes targeted by virus microRNAs. Because the virus targets these genes, it is reasonable to propose that these genes play an important role during infection. We confirmed this hypothesis using a second screen in which we knocked down expression of a number of the identified targets of the virus microRNAs. Knock down of one of the targets, a cellular factor called ATP6V0C, resulted in an almost complete block in production of infectious virus. These data suggest that endosomal acidification is crucial to HCMV replication, and the virus targets this process by microRNA regulation.

Spontaneous resolution of intravitreal steroid-induced bilateral cytomegalovirus retinitis

A 73-year-old woman underwent vitrectomy and intravitreal triamcinolone acetonide (IVTA) of the right eye and cataract surgery with IVTA of the left eye, for bilateral diabetic macular edema. The patient presented with visual loss in both eyes three-months postoperatively. The fundoscopic examination revealed white-yellow, necrotic peripheral lesions in the superotemporal quadrant of both eyes. Although bilateral acute retinal necrosis was suspected, azotemia resulting from diabetic nephropathy limited the use of acyclovir. Antiviral treatment was not started. A sample of the aqueous humor for polymerase chain reaction (PCR) analysis was obtained. One week later, the PCR results indicated the presence of cytomegalovirus (CMV). Since the retinal lesions did not progress and did not threaten the macula, the patient was followed without treatment for CMV. The retinal lesions progressively regressed and completely resolved in both eyes by six months of follow-up. Patients with IVTA-induced CMV retinitis may not require systemic treatment with ganciclovir.

Aspects of human cytomegalovirus latency and reactivation

Primary infection of healthy individuals with human cytomegalovirus (HCMV) is usually asymptomatic and results in the establishment of a lifelong latent infection of the host. Although no overt HCMV disease is observed in healthy carriers, due to effective immune control, severe clinical symptoms associated with HCMV reactivation are observed in immunocompromised transplant patients and HIV sufferers. Work from a number of laboratories has identified the myeloid lineage as one important site for HCMV latency and reactivation and thus has been the subject of extensive study. Attempts to elucidate the mechanisms controlling viral latency have shown that cellular transcription factors and histone proteins influence HCMV gene expression profoundly and that the type of cellular environment virus encounters upon infection may have a critical role in determining a lytic or latent infection and subsequent reactivation from latency. Furthermore, the identification of a number of viral gene products expressed during latent infection suggests a more active role for HCMV during latency. Defining the role of these viral proteins in latently infected cells will be important for our full understanding of HCMV latency and reactivation in vivo.

Latency and reactivation of human cytomegalovirus

Human cytomegalovirus (HCMV) persists as a subclinical, lifelong infection in the normal human host, maintained at least in part by its carriage in the absence of detectable infectious virus – the hallmark of latent infection. Reactivation from latency in immunocompromised individuals, in contrast, often results in serious disease. Latency and reactivation are defining characteristics of the herpesviruses and key to understanding their biology. However, the precise cellular sites in which HCMV is carried and the mechanisms regulating its latency and reactivation during natural infection remain poorly understood. This review will detail our current knowledge of where HCMV is carried in healthy individuals, which viral genes are expressed upon carriage of the virus and what effect this has on cellular gene expression. It will also address the accumulating evidence suggesting that reactivation of HCMV from latency appears to be linked intrinsically to the differentiation status of the myeloid cell, and how the cellular mechanisms that normally control host gene expression play a critical role in the differential regulation of viral gene expression during latency and reactivation.

Importance of simultaneous active cytomegalovirus and Epstein-Barr virus infection in renal transplantation

BACKGROUND

Although being the most common infective complication after transplantation, cytomegalovirus (CMV) infection does not always produce disease symptoms in immunosuppressed patients. Development of CMV disease may depend on different factors such as virulence of particular CMV strains and impairment of CMV-specific immune reactions.

OBJECTIVE

Demonstration of the importance of simultaneous Epstein-Barr virus (EBV) activation for development of symptomatic CMV infections.

STUDY DESIGN

208 renal transplantation patients were monitored for 3 years with respect to (i) CMV and EBV replications, and (ii) clinical symptoms associated with combined and single infections, respectively.

RESULTS

CMV and EBV replications were observed in 22% and 19% of the patients, respectively. Many of these active virus infections were found to overlap in time (59% and 74% of all active CMV and EBV infections, respectively). The increased detection of combined CMV and EBV infections probably does not result from higher initial immunosuppression in these patients, since the percentage of patients receiving OKT3 or ATG was almost identical in the groups of single and combined infections. In 18 cases of combined infections, CMV replication preceeded EBV replication, while EBV replication prior to CMV replication was observed in one case only, indicating that activation of latent EBV infection may be induced during active CMV infection.

CONCLUSIONS

Simultaneous replication of both viruses seems to be clinically important, since severe clinical symptoms were observed only in the group of combined CMV and EBV infections. Symptoms were similar to the clinical pictures of CMV disease. Thus, simultaneous EBV replication may be an important co-factor for the development of CMV disease, possibly by further decreasing the number of functional CD4 T cells or enhancing the CD8-positive cytolytic/suppressor T-cell subset as reflected by the comparatively stronger decrease of CD4/CD8 ratio during simultaneous CMV and EBV replication, particularly in the case of symptomatic infections.

The human eye (retina): a site of persistent HCMV infection?

BACKGROUND

Human cytomegalovirus (HCMV) retinitis frequently occurs in severely naturally and iatrogenically immunocompromised patients. It has been shown that the immune-privileged retina is a major site of HCMV infection in AIDS patients. It is conceivable either that during the immunosuppression HCMV infection reactivates in various other organs viremically affecting the retina or that HCMV persisting in the retina may locally reactivate and result in HCMV retinitis.

METHODS

As there is still controversy about the sites of HCMV latency and persistence we investigated 75 eyes of HIV-seronegative patients undergoing enucleation due to a variety of malignant and non-viral benign ophthalmic disorders for the retinal presence of HCMV antigen and DNA.

RESULTS

None of the analyzed patients had symptoms of HCMV retinitis. Immunohistologic staining as well as Taq Man DNA PCR analysis showed all samples to be free of HCMV.

CONCLUSIONS

Our data suggest that the human eye is rather unlikely to be a site of productive or latent HCMV persistence.

Quantitation of CMV by real-time PCR in transfusable RBC units

BACKGROUND

CMV is one of the most significant pathogens infecting immunocompromised individuals. CMV is transmissible through transfusion of blood components. The goal of this study was to measure CMV levels in RBC units using a sensitive and quantitative DNA amplification assay.

STUDY DESIGN AND METHODS

An assay to measure CMV load was developed by using real-time PCR to target the major immediate early viral gene. A probe (TaqMan, Applied Biosystems) was used to confirm product specificity and to permit quantitation of CMV in blood samples on a sequence detection system (ABI Prism 7700, Applied Biosystems).

RESULTS

The assay was shown to be accurate, linear, and sensitive to as few as five copies of CMV DNA per PCR. The assay was applied to aliquots of RBC units from 203 healthy donors, 110 of whom were seropositive for CMV. CMV DNA was not detected in any of the 203 RBC samples.

CONCLUSION

The findings statistically imply that at least 98.5 percent of RBC units have a CMV load of less than 250 copies per mL. Future clinical studies on larger numbers of units are required to determine the utility of real-time PCR in evaluating the risk of CMV transmission and in confirming the efficacy of WBC reduction.

Human cytomegalovirus latency-associated protein pORF94 is dispensable for productive and latent infection

Human cytomegalovirus latency in bone marrow-derived myeloid progenitors is characterized by the presence of latency-associated transcripts encoded in the ie1/ie2 region of the viral genome. To assess the role of ORF94 (UL126a), a conserved open reading frame on these transcripts, a recombinant virus (RC2710) unable to express this gene was constructed. This virus replicated at wild-type levels and expressed productive as well as latency-associated ie1/ie2 region transcripts. During latency in granulocyte-macrophage progenitors, RC2710 DNA was detected at levels indistinguishable from wild-type virus, latent-phase transcription was present, and RC2710 reactivated when latently infected cells were cocultured with permissive fibroblasts. These data suggest pORF94 is not required for either productive or latent infection as assayed in cultured cells despite being the only known nuclear latency-associated protein.

Polymerase chain reaction assays for the detection of cytomegalovirus in organ and bone marrow transplant recipients

Cytomegalovirus (CMV) infection is ubiquitous and results in a wide spectrum of clinical manifestations ranging from asymptomatic infection to severe life threatening disease. Infection in normal children and adults usually causes no symptoms but in the immunocompromised host, CMV may result in severe opportunistic infections with high morbidity and mortality. Historically, virus detection was dependent on culture of the virus or on a centrifugation culture system referred to as a shell vial assay. The shell vial assay frequently lacked sensitivity and was unable to detect infection in its early phase. Also, as with culture assays, the results were affected by antiviral therapy. The CMV antigenemia assay was developed to provide more rapid results and has gained wide usage. This assay is limited to detection of the virus in white blood cells and is more sensitive than culture or the shell vial assay. Application of the polymerase chain reaction (PCR) to these problems has resulted in the development of assays for CMV which are more sensitive than previously available methods. This method employs liquid hybridization with 32P labeled probes and gel retardation analysis for detection of amplified DNA specific for each virus. A comparison of the detection of CMV by an antigenemia assay or the PCR method in the leukocytes of renal transplant patients revealed that the PCR assay detects cytomegalovirus earlier and more consistently than the antigenemia assay. Finally, the application of a fluorescent dye detection system and image analysis of the acrylamide gel with a laser scanner provides additional sensitivity to the detection of cytomegalovirus, as well as avoiding the use of radioactivity, making the assay more adaptable to the clinical laboratory.

Human cytomegalovirus latent gene expression in granulocyte-macrophage progenitors in culture and in seropositive individuals

Following infection with cytomegalovirus, human granulocyte-macrophage progenitors carry the viral genome but fail to support productive replication. Viral transcripts arise from a region encompassing the major regulatory gene locus; however, their structure differs significantly from productive phase transcripts. One class, sense transcripts, is encoded in the same direction as productive phase transcripts but uses two novel start sites in the ie1/ie2 promoter/enhancer region. These transcripts have the potential to encode a novel 94 aa protein. The other class, antisense transcript, is unspliced and complimentary to ie1 exons 2-4, and has the potential to encode novel 154 and 152 aa proteins. Consistent with a role in latency, these transcripts are present in bone marrow aspirates from naturally infected, healthy seropositive donors but are not present in seronegative controls. Sense latent transcripts are present in a majority of seropositive individuals. Consistent with the expression of latent transcripts, antibody to the 94 aa and 152 aa proteins is detectable in the serum of seropositive individuals. Thus, latent infection by cytomegalovirus is accompanied by the presence of latency-associated transcripts and expression of immunogenic proteins. Overall, these results suggest that bone marrow-derived myeloid progenitors are an important natural site of viral latency.

Significance of human cytomegalovirus DNA detection in immunocompromised heart transplant patients

Peripheral blood samples (n= 1240), obtained at variable intervals from 483 heart transplantation (HTx patients under immunosuppressive therapy, and blood samples (n=1013) obtained upon blood donation from 1013 healthy anti-human cytomegalovirus (HCMV) positive blood donors, were tested for HCMV DNA by nested polymerase chain reaction (PCR). The detection limit of the nested PCR was determined to be less than 10 copies of the plasmid pRR 47, containing the HCMV immediate early gene. HCMV DNA was detected in 79 of 483 HTx patient (17%). To the contrary' HCMV DNA was only detected in 1 of 1013 anti-HCMV positive, healthy blood donors (0.1%). This PCR positive donor had recently contracted a primary HCMV infection. The rate of HCMV PCR positive immunosuppressed HTx patients in our study was lower than the rate of HCMV PCR positive healthy blood donors in previous reports in the literature. Blood samples (269 from 117 HTx patients) were assayed for HCMV DNA in peripheral blood leukocytes, HCMV DNA in plasma, and HCMV tegument protein 65 kDa (pp 65 antigen). Three laboratory diagnostic patterns were observed and related to clinical findings: (1) HCMV DNA only in leukocytes was observed in 26 patients, 7 of whom had HCMV disease, 5 of whom had graft rejection, and 14 of whom had no specific symptoms; (2) HCMV DNA both in leukocytes and in plasma (viremia) was observed in 3 patients, who were all symptomatic with HCMV disease; (3) HCMV DNA in leukocytes and in plasma (viremia) and pp 65 antigen were observed in 13 patients, all of whom were symptomatic (10 patients had HCMV disease, and 3 patients had graft rejection). A similar sequence of diagnostic patterns was observed in all symptomatic HCMV infections and reactivations in this study: HCMV DNA appeared first in peripheral blood leukocytes, then also in plasma, followed by pp 65 antigen detectable in peripheral blood leukocytes. Upon clinical recovery, these findings disappeared in reverse order. However, HCMV DNA remained detectable in peripheral blood leukocytes for several weeks. The detection of HCMV DNA in the peripheral blood is an exception, not the rule, even in severely immunosuppressed HTx patients. It indicates a pathological condition, albeit without clinical symptoms in some patients, and it is the earliest signal of HCMV replication. Of 42 patients in whom HCMV DNA was initially detected only in peripheral blood leukocytes, 16 patients progressed into viremia. Thus, HCMV-specific PCR performed on nucleic acid extracts from lysed peripheral blood is an appropriate method for the monitoring of HCMV infections in immunosuppressed HTx patients.

Cell types involved in replication and distribution of human cytomegalovirus

As the number of patients suffering from severe HCMV infections has steadily increased, there is a growing need to understand the molecular mechanisms by which the virus causes disease. The factors that control infection at one time and the events leading to virus multiplication at another time are only beginning to be understood. The interaction of HCMV with different host cells is one key for elucidating these processes. Through modern techniques, much has been learned about the biology of HCMV infections in culture systems. In addition to endothelial cells, epithelial cells, and smooth muscle cells, fibroblasts are one cell population preferentially infected in solid tissues in vivo. From these sites of multiplication, the virus may be carried by peripheral monocytes and circulating endothelial cells to reach distant sites of the body. This would explain the multiorgan involvement in acute HCMV infection and the modes of viral transmission. From what has been learned mainly from human fibroblast culture systems, future studies will focus on how HCMV regulates the expression of its putative 200 genes in different host cells at different stages of cell differentiation and activation to result in viral latency and pathogenesis.

[Current status of human cytomegalovirus disease]

Human cytomegalovirus (HCMV) can establish lifelong persistence after primary infection with reactivation occurring as a result of immunosuppression. There is much evidence that molecular interactions between the immune system and the HCMV are responsible for immune escape. HCMV in many cells especially in mononuclear blood cells during latency are frequently the source of transmission and spreading and results in a variety of disorders. In this review some data about acute infection in immunocompetent host (mononucleosis, hepatitis), about intrauterine HCMV infection, about infection and endogenous reinfection in bone marrow and solid organ transplant recipients (pneumonitis) and about HCMV disease in AIDS patients (encephalitis, neuropathy, retinitis, colitis) are investigated. Moreover, HCMV associated vasculitis is described in patients with myocarditis, rheumatoid arthritis or polyradiculopathy. HCMV could play an important role in atherosclerosis. Several types of human malignancy have been linked to HCMV and it has been shown that HCMV ie genes upregulate expression of cellular oncogenes. The diagnosis of HCMV infection is carried out by viremia in cell culture using immediate early antigen staining, by antigenaemia which appears to be an early quantitative and predictive tool, by HCMV DNA detection using hybridization and PCR, and by IgM and IgG antibody evaluation. Two antiviral drugs are used for treatment: ganciclovir and phosphonoformic acid; few resistant clinical isolates have been reported. Specific gammaglobulin activity is discussed. HCMV vaccine is not available.

Human cytomegalovirus DNA is not detectable with nested double polymerase chain reaction in healthy blood donors

The PCR method was introduced to detect cytomegalovirus (CMV) DNA from 189 peripheral blood samples of volunteer donors. We adopted the nested double PCR method with primers specific for immediate early gene 1 followed by electrophoresis and ethidium bromide staining. This nested double PCR method was sensitive enough to detect approximately a single copy of CMV DNA. However, we failed to obtain positive amplification of CMV DNA from any of these donor samples. In contrast, CMV DNA could be detected in all 3 tested immunocompromised patients who had undergone bone marrow transplantation. These results support our previous report that the frequency of CMV DNA is of an order lower than 1 copy/10(5) leucocytes in the peripheral blood of healthy seropositive individuals.

Quantitation of human cytomegalovirus DNA in leukocytes by end-point titration and duplex polymerase chain reaction

The presence of human cytomegalovirus (CMV) DNA and cellular DNA in leukocytes was detected by duplex polymerase chain reaction (PCR) and quantitated by end-point titration. Two different duplex PCR methods were used to co-amplify CMV DNA and a 536 bp fragment of globin DNA. MIE-globin PCR amplified a 435 bp fragment of the major immediate early (MIE) gene of CMV DNA whereas the LA-globin PCR amplified a 200 bp fragment of the late antigen (LA) gene of CMV DNA. PCR products were separated by electrophoresis in 3% agarose gels and detected by ethidium bromide staining. Amplification of globin DNA was included in the PCR as a positive control to monitor the accuracy and reproducibility of the PCR assay and to provide a reference point for CMV DNA levels. End-point titration PCR using known amounts of recombinant CMV DNA and human placental DNA showed that the end-point titres of the amplified CMV DNA correlated directly with the amount of CMV DNA in the sample. The limit of detection of MIE-globin and LA-globin PCR was 1 ng for placental DNA, and 10 fg (1000 copies) for CMV-MIE DNA and 1 fg (100 copies) for CMV-LA DNA, respectively. The amount of CMV DNA was quantitated in leukocytic lysates of 16 immunocompromised patients, who were tested for the presence of CMV in blood by cell culture, and of four normal controls. The blood concentration of CMV DNA, calculated as the number of copies of CMV DNA per microgram of leukocyte DNA, varied between 10(4) and 10(7) in the seven bloods that were CMV-cell-culture-positive, and between 10(2) and 10(4) in the blood of five patients that were CMV-cell-culture-negative. CMV DNA was undetected by PCR in the blood of another eight CMV-negative cases. This study shows that end-point titration and duplex PCR can be used as a simple and rapid method to quantitate CMV DNA in blood of patients that are either CMV-positive or CMV-negative by cell culture. Quantitation of CMV DNA in blood by end-point titration PCR has potential to differentiate between asymptomatic CMV infection and symptomatic CMV disease, and to monitor viral load during viral therapy.