Quantitative analysis of Epstein-Barr virus load by using a real-time PCR assay

Molecular diagnosis of Epstein-Barr virus-related diseases

Epstein-Barr virus (EBV) is the causative agent of infectious mononucleosis, and it may also be found in a wide variety of benign and malignant lesions including oral hairy leukoplakia, inflammatory pseudotumor, Hodgkin's disease, non-Hodgkin's lymphoma, nasopharyngeal carcinoma, and gastric carcinoma. Molecular testing is increasingly important in the diagnosis and monitoring of patients affected by these diseases. In biopsy tissues, molecular detection of EBV-encoded RNA transcripts by in situ hybridization remains the gold standard for proving that a histopathological lesion is EBV-related. EBV-encoded RNA hybridization and EBV LMP1 immunostains are used routinely to detect latent EBV in tissues affected by posttransplant lymphoproliferative disorder (PTLD) or in enlarged nodes from patients with infectious mononucleosis. Traditional serology is the best test for evaluating acute versus remote infection in healthy individuals. High serological titers serve as a tumor marker for some EBV-related malignancies, but titers are not a dependable tumor marker in immunocompromised hosts. EBV viral load testing by quantitative DNA amplification of blood samples is a promising new laboratory test that has proven useful for early diagnosis and monitoring patients with PTLD. Recent studies suggest a role for EBV viral load testing in nasopharyngeal carcinoma, Hodgkin's disease, and AIDS patients with brain lymphoma. Further research is needed to define more fully the clinical utility of viral load tests in the full spectrum of EBV-associated diseases. Gene expression profiling is on the horizon as a means to improve subclassification of EBV-related diseases and to predict response to therapy.

Characterization of Epstein-Barr virus–infected B cells in patients with posttransplantation lymphoproliferative disease: disappearance after rituximab therapy does not predict clinical response

Post-transplantation lymphoproliferative disease (PTLD) is associated with Epstein-Barr virus (EBV). Quantitative and qualitative differences in EBV in peripheral blood mononuclear cells (PBMCs) of PTLD patients and healthy controls were characterized. A quantitative competitive polymerase chain reaction (QC-PCR) technique confirmed previous reports that EBV load in PBMCs is increased in patients with PTLD in comparison with healthy seropositive controls (18 539 vs 335 per 106 PBMCs, P = .0002). The average frequency of EBV-infected cells was also increased (271 vs 9 per 106 PBMCs, P = .008). The distribution in numbers of viral genome copies per cell was assessed by means of QC-PCR at dilutions of PBMCs. There was no difference between PTLD patients and healthy controls. Similarly, no differences in the patterns of viral gene expression were detected between patients and controls. Finally, the impact of therapy on viral load was analyzed. Patients with a past history of PTLD who were disease-free (after chemotherapy or withdrawal of immunosuppression) at the time of testing showed viral loads that overlapped with those of healthy seropositive controls. Patients treated with rituximab showed an almost immediate and dramatic decline in viral loads. This decline occurred even in patients whose PTLD progressed during therapy. These results suggest that the increased EBV load in PBMCs of PTLD patients can be accounted for by an increase in the number of infected B cells in the blood. However, in terms of viral copy number per cell and pattern of viral gene expression, these B cells are similar to those found in healthy controls. Disappearance of viral load with rituximab therapy confirms the localization of viral genomes in PBMCs to B cells. However, the lack of relationship between the change in viral load and clinical response highlights the difference between EBV-infected PBMCs and neoplastic cells in PTLD.

Characterization of Epstein-Barr virus–infected B cells in patients with posttransplantation lymphoproliferative disease: disappearance after rituximab therapy does not predict clinical response

Post-transplantation lymphoproliferative disease (PTLD) is associated with Epstein-Barr virus (EBV). Quantitative and qualitative differences in EBV in peripheral blood mononuclear cells (PBMCs) of PTLD patients and healthy controls were characterized. A quantitative competitive polymerase chain reaction (QC-PCR) technique confirmed previous reports that EBV load in PBMCs is increased in patients with PTLD in comparison with healthy seropositive controls (18 539 vs 335 per 106 PBMCs, P = .0002). The average frequency of EBV-infected cells was also increased (271 vs 9 per 106 PBMCs, P = .008). The distribution in numbers of viral genome copies per cell was assessed by means of QC-PCR at dilutions of PBMCs. There was no difference between PTLD patients and healthy controls. Similarly, no differences in the patterns of viral gene expression were detected between patients and controls. Finally, the impact of therapy on viral load was analyzed. Patients with a past history of PTLD who were disease-free (after chemotherapy or withdrawal of immunosuppression) at the time of testing showed viral loads that overlapped with those of healthy seropositive controls. Patients treated with rituximab showed an almost immediate and dramatic decline in viral loads. This decline occurred even in patients whose PTLD progressed during therapy. These results suggest that the increased EBV load in PBMCs of PTLD patients can be accounted for by an increase in the number of infected B cells in the blood. However, in terms of viral copy number per cell and pattern of viral gene expression, these B cells are similar to those found in healthy controls. Disappearance of viral load with rituximab therapy confirms the localization of viral genomes in PBMCs to B cells. However, the lack of relationship between the change in viral load and clinical response highlights the difference between EBV-infected PBMCs and neoplastic cells in PTLD.

Monitoring four herpesviruses in unrelated cord blood transplantation

Cord blood transplantation, which has lower risk of graft-versus-host disease than bone marrow transplantation, might have higher risk of infections. A system to quantify four herpesviruses, CMV, human herpesvirus 6 (HHV6), EBV, varicella-zoster virus using the real-time PCR assay was established and applied for prospective viral load monitoring in three recipients undergoing cord blood transplantation. CMV and HHV6 were detected in peripheral blood from all three recipients, while EBV was detected in two. Varicella-zoster virus was not detected at all. At the peak of HHV6 or CMV, each patient showed virus-related symptoms. During the pre-transplant period, CMV DNA was detected in two recipients who later developed CMV-related diseases. These observations indicate that our system is not only useful for managing herpesviruses infections in transplant recipients, but also a powerful method for clarifying the relationships between the viral load and clinical symptoms.

Quantitative analysis of circulating cell-free Epstein-Barr virus (EBV) DNA levels in patients with EBV-associated lymphoid malignancies

Cell-free Epstein-Barr virus (EBV) DNA has recently been detected in the plasma and serum of patients with Hodgkin's disease, post-transplant lymphoproliferative disease (PTLD) and acquired immunodeficiency syndrome-related lymphoma. However, no data are available on the temporal variation of plasma/serum EBV DNA levels in patients with EBV-associated lymphoid malignancies during the course of therapy. Using a real-time quantitative polymerase chain reaction assay, we studied the plasma EBV DNA levels in 13 patients with EBV-associated lymphoid malignancies (six patients with Hodgkin's disease, four with nasal natural killer/T-cell lymphoma, two cases of PTLD and one patient with Burkitt's lymphoma) at presentation and during therapy. Plasma EBV DNA was detected in 12 of the 13 patients (median 2,266 copies/ml; interquartile range 181-8,379 copies/ml), but not in any of 35 healthy control subjects (P < 0.0001). The EBV status in tumour cells was also examined in 12 of these patients using in situ hybridization for EBV-encoded small RNAs (EBERs). EBER positivity was observed in 11 patients, all of whom had EBV DNA detectable in plasma. The one patient who had no detectable plasma EBV DNA was also negative for EBERs in tumour tissue. Serial measurements of plasma EBV DNA levels were performed in nine of the patients during the course of therapy. All patients who responded to therapy demonstrated a significant reduction of plasma EBV DNA to low or undetectable levels, whereas in two patients with ineffective therapy, disease progression was associated with a rapid increase in plasma EBV DNA levels. We concluded that plasma EBV DNA is detectable in a wide range of EBV-associated lymphoid malignancies. As plasma EBV DNA levels correlate well with the therapeutic response, such analysis may be a valuable tool for monitoring clinical progress.

Treatment strategies for Epstein-Barr virus-associated hemophagocytic lymphohistiocytosis (EBV-HLH)

In Epstein-Barr virus (EBV) infection, the virus immortalizes B lymphocytes and cytotoxic T lymphocytes (CTLs) are directed toward both latent and lytic viral antigens expressed on EBV-infected B-cells. Various EBV-associated diseases occur as a result of this disruption of immune surveillance. In the majority of EBV-associated hemophagocytic lymphohistiocytosis (EBV-HLH) cases, the major cell types containing EBV DNA are not B-cells, but clonally proliferating T-cells or NK-cells. Proliferation of these cells produces severe immune reactions in the host, and the clinical features related to massive cytokine production at the onset of disease are unique and distinct from other EBV-associated diseases. In the treatment of EBV-HLH, therapeutic infusion of EBV-specific CTLs appears to be ineffective, and eradication of EBV-containing cells is useful but not sufficient to save lives, because of high incidence of acute mortality due to cytokine-induced multiple organ failure and neutropenia-associated opportunistic infections. The optimal treatment strategy for this disease consists of three steps: (1) control of cytokine storm including coagulopathy and multiple organ failure, (2) control of opportunistic infections, and (3) eradication of clonally proliferating EBV-containing T- or NK- cells by immunochemotherapy and, if necessary, hemopoietic stem cell/bone marrow transplantation (SCT/BMT).

Predictive negative value of persistent low Epstein-Barr virus viral load after intestinal transplantation in children

BACKGROUND

The correlation between an elevated Epstein-Barr virus (EBV) viral load in the peripheral blood and the subsequent development of EBV-associated posttransplant lymphoproliferative disease (PTLD) is the basis for strategies using serial measurements of the EBV viral load to guide preemptive therapy (PT). Neither the frequency, duration of monitoring, nor the predictive negative value of viral load monitoring for asymptomatic patients with persistent low or nondetectable viral loads against the development of PTLD has been established.

METHODS

Since April 1994, children undergoing intestinal transplantation (ITx) underwent serial monitoring of the EBV viral load in their peripheral blood using a quantitative competitive EBV polymerase chain reaction assay (PCR). Samples were obtained every 2 weeks for the first 3 months and then every 1-3 months depending on the patients clinical condition. EBV viral loads > or =40 (for patients who were EBV seronegative pre-ITx) and > or =200 (for those who were seropositive) genome copies/10(5) peripheral blood lymphocytes were felt to identify patients at increased risk for PTLD and generally prompted PT.

RESULTS

A total of 30 ITx recipients were compliant with our monitoring protocol; 23/30 are alive 6-59 months post-ITx. A total of 12/30 never had a viral load >40 and did not receive PT. In contrast, 18/30 had > or =1 high viral load (> or =200); the first high viral load was measured a median of 59 days post-ITx (range 1-440). A late rise (>6 months post-ITx) was seen in only 2/18 children. A total of 0/12 patients with persistently low viral loads received PT and none developed PTLD. In contrast, 5/18 with > or =1 one high viral load (including 2/14 who received and 3/4 who did not receive PT) developed PTLD. All five children with PTLD were EBV seropositive pre-ITx and experienced their first high EBV PCR within the first 3 months after ITx.

CONCLUSIONS

The predictive negative value of persistently low or nondetectable EBV viral loads was 100% in this study. Patients with nondetectable or low viral loads for the first 6 months after ITx did not develop PTLD regardless of their pretransplant EBV serological status. The frequency of viral load monitoring can be safely decreased for patients whose viral loads remain low for the first 6 months ITx.

Molecular methods in the diagnosis of infections in the immunocompromised host

Despite recent developments, infection remains a major obstacle to a successful outcome in transplantation. Molecular methods have allowed for earlier diagnosis and have proven to be powerful tools for analysing the epidemiology of infectious diseases. More recently, some of these molecular methods have been commercialized, enabling standardized diagnostic techniques to be used in multicentre trials.

Bax is downregulated in inflamed colonic mucosa of ulcerative colitis

BACKGROUND AND AIMS

One form of epithelial cell injury in inflamed colonic mucosa in ulcerative colitis (UC) is reported to involve apoptosis of these cells. Bcl-2 family proteins Bax and Bcl-2 are the major regulators of apoptosis. The aim of this study was to elucidate the involvement of the Bax/Bcl-2 system in induction of apoptosis of the inflamed colonic epithelium in UC.

METHODS

Colonic epithelium was isolated from colonic biopsy specimens. Expression of CD95, Bax, Bcl-xL, and Bcl-2 proteins was determined by western blotting. Bax gene expression was assessed by both reverse transcription-polymerase chain reaction (RT-PCR) followed by Southern hybridisation and a real time PCR assay.

RESULTS

Equal levels of expression of CD95, Bcl-xL, and Bcl-2 proteins were noted in normal and UC colonic epithelia. Equal levels of expression of Bax protein and mRNA were noted in epithelia of normal colon and inactive UC. Levels of expression of Bax protein and mRNA were markedly reduced in inflamed UC colonic epithelium.

CONCLUSIONS

Our study showed for the first time downregulation of Bax in inflamed colonic epithelium of UC. The Bax/Bcl-2 system did not seem to be involved in induction of apoptosis of epithelial cells in the inflamed colonic mucosa of UC.

Usefulness of quantitative real-time polymerase chain reaction in following up patients with Epstein-Barr virus infection after liver transplantation

BACKGROUND

Post-transplant lymphoproliferative disease (PTLD), which is mainly induced by Epstein-Barr virus (EBV) infection, is a cause of significant morbidity and mortality for patients undergoing liver transplantation, especially when it is detected at such an advanced stage as monoclonal malignant lymphoma.

METHODS

In this series, 6 of 22 liver transplant patients suffered from EBV infection. We tested quantitative DNA (Qt-DNA) by real-time polymerase chain reaction (PCR), qualitative DNA in plasma (Q1-pDNA) by PCR, and EBV-encoded mRNA 1 (EBER 1) by in situ hybridization to clarify which of them is a better marker for the early diagnosis and prediction of EBV-associated disorders.

RESULTS

Four had signs or symptoms of PTLD, but 2 did not develop individualized lymphoid lesions. In all patients, both Qt-DNA and EBER 1 exceeded the cut-off level of 10(2.5) copies/microg DNA and 0.002%, respectively, at the time of diagnosis. In 2 patients, when Qt-DNA had a poor decline, EBER 1, even if it seemed to decrease after antiviral therapy, increased again after a few months and the clinical symptoms recurred. In 2 patients, Qt-DNA and EBER 1 increased again after a few months of antiviral therapy, and Q1-pDNA remained positive, whereas, in 3 patients, no reaction of EBV could be detected once Q1-pDNA became negative, even after the cessation of therapy.

CONCLUSIONS

These results suggest that real-time PCR for Qt-DNA was more sensitive to the real-time activity of EBV and that Q1-pDNA could indicate when to stop antiviral therapy.

Early intervention in post-transplant lymphoproliferative disorders based on Epstein-Barr viral load

Using a real-time quantitative PCR assay, we identified two patients with EBV-related lymphoproliferative disorders at a very early stage. Both had received an unmanipulated bone marrow transplant with anti-thymocyte globulin for conditioning. To estimate virus-specific immunity, the frequencies of EBV-specific CD8+ T cells were measured using an enzyme-linked immunospot assay. The frequencies of EBV-specific CD8+ T cells of the two were 3.2 and 7.7%, respectively, which had possibly expanded in vivo. After withdrawing the immunosuppressive agents or administering donor lymphocytes transfusion, their symptoms regressed in parallel with the viral load.

Development of a real-time quantitative RT-PCR for the detection of HIV-2 RNA in plasma

An assay is described for the quantification of human immunodeficiency virus type 2 (HIV-2) RNA in EDTA plasma based on RT-PCR using the Taqman real-time PCR detection method. As standard, an electron microscopically counted virus stock of HIV-2 strain NIHZ was used. The lower detection limit is 5 # 102 HIV-2 RNA copies per ml of EDTA plasma. The assay is linear within the range required (5 # 102-106 HIV-2 RNA copies/ml of EDTA plasma) with an intra assay variability of 2.5% and an inter-assay variability ranging from 2% at 106 copies to 7.5% at the lower detection limit. Three primer/probe combinations were developed to circumvent false negative samples due to nucleotide variation in the target sequence. Using these primer/probe sets enabled the detection of HIV-2 DNA sequences from all HIV-2 seropositive individuals and two out of five dual human immunodeficiency virus type 1 (HIV-1) and HIV-2 seropositive individuals visiting the University Hospital Rotterdam.

Large deletion of the X-linked lymphoproliferative disease gene detected by fluorescence in situ hybridization

The X-linked lymphoproliferative disease (XLP) is an inherited immunodeficiency characterized by an abnormal responses to infection with Epstein-Barr virus (EBV), resulting in fatal infectious mononucleosis, hypogammaglobulinemia, virus-associated hemophagocytic syndrome, and malignant lymphoma. Mutations in the gene coding for a T cell-specific SLAM-associated protein (SAP) have been recently identified in XLP patients. We report on a 1-year-old boy representing fulminant hemophagocytic syndrome. He developed high fever, lymphadenopathy, hepatosplenomegaly with liver dysfunction, and pancytopenia with marrow hemophagocytosis. EBV DNA was abnormally increased in the blood. Polymerase chain reaction failed to amplify SAP mRNA and genomic DNA products from the patient' As peripheral blood. A large deletion of the SAP gene was confirmed by fluorescence in situ hybridization (FISH). FISH analysis also disclosed that the patient's mother was a carrier. We conclude that FISH can be useful in the diagnosis of XLP with large deletions of the SAP gene and its carrier state.

[Malignant non-Hodgkins B lymphoma related to Epstein-Barr virus and chronic natural killer lymphocytosis in a immunocompromised patient]

INTRODUCTION

Immunocompromised patients are at high risk of Epstein-Barr virus (EBV)-related lymphoproliferative disorders. The lymphoproliferation affects B, T, and natural killer (NK) cells.

EXEGESIS

We report the case of a woman suffering from systemic lupus erythematous. She developed an opportunistic pneumonia while immunodepressed during long-term corticotherapy aimed at curing her auto-immune disease. Chronic lymphocytosis was also diagnosed at this time. Several months later, non-Hodgkin's lymphoma was diagnosed. Genomic amplification of the Epstein-Barr virus in the patient's blood and positive EBV latent membrane protein 1 on the lymph nodes provided evidence for a strong correlation between EBV reactivation and lymphoma.

CONCLUSION

Two distinct lymphoid diseases occurred during the immunosuppressive therapy for the auto-immune disease. PCR monitoring of Epstein-Barr virus allows for early screening of lymphoproliferative disorders in immunocompromised patients, leading to earlier and more efficient treatment.

Assessment of ribozyme cleavage efficiency using reverse transcriptase real-time PCR

Real-time PCR is a novel technology recently described to perform quantitative analysis of amplified products. Unlike classical quantitative PCR, this method is easy to standardize, does not required extensive manipulation, and is not reagent intensive, so that the risk of contamination is minimized. Therefore, we have chosen reverse transcriptase real-time PCR to quantitate CD95 (Fas) transcripts to test the cleavage efficiency of anti-Fas ribozymes in the mouse insulinoma cell line beta TC-3. Based on the melting-curve analysis of the amplified products, we determined the temperature at which to collect the fluorescent data used for quantification. After constructing a standard curve by plotting the log of the standards' copy number versus their fractional cycle number, the copy numbers of the unknown samples were automatically determined by interpolation of this curve. As we illustrate in this study, it is important, particularly while setting up the technique, to validate the melting-curve profile with standard gel electrophoresis analysis, achieved by matching melting temperature and size of the amplified product. The method is fast and reproducible: Excluding the isolation of RNA and synthesis of cDNA, the results can be obtained in less than 1 hr. The coefficient of variance is 15% in the range of 10(4)-10(6) gene copies. Accordingly, reverse transcriptase (RT) real-time PCR is a technique suitable for screening a large number of ribozymes.

Development of a real-time quantitative assay for detection of Epstein-Barr virus

With the use of real-time PCR, we developed and evaluated a rapid, sensitive, specific, and reproducible method for the detection of Epstein-Barr virus (EBV) DNA in plasma samples. This method allowed us to screen plasma and serum samples over a range between 100 and 10(7) copies of DNA per ml using two sample preparation methods based on absorption. A precision study yielded an average coefficient of variation for both methods of less than 12%, with a coefficient of regression for the standard curve of a minimum of 0. 98. We detected EBV DNA in 19.2% of plasma samples from immunosuppressed solid-organ transplant patients without symptoms of EBV infections with a mean load of 440 copies per ml. EBV DNA could be detected in all transplant patients diagnosed with posttransplant lymphoproliferative disorder, with a mean load of 544,570 copies per ml. No EBV DNA could be detected in healthy individuals in nonimmunosuppressed control groups and a mean of 6,400 copies per ml could be detected in patients with infectious mononucleosis. Further studies revealed that the inhibitory effect of heparinized plasma could be efficiently removed by use of an extraction method with Celite as the absorbent.

Quantitation of Pseudomonas aeruginosa in wound biopsy samples: from bacterial culture to rapid 'real-time' polymerase chain reaction

STATEMENT OF FINDINGS: We developed a real-time detection (RTD) polymerase chain reaction (PCR) with rapid thermal cycling to detect and quantify Pseudomonas aeruginosa in wound biopsy samples. This method produced a linear quantitative detection range of 7 logs, with a lower detection limit of 103 colony-forming units (CFU)/g tissue or a few copies per reaction. The time from sample collection to result was less than 1h. RTD-PCR has potential for rapid quantitative detection of pathogens in critical care patients, enabling early and individualized treatment.

Antigen-Driven Expansion and Contraction of CD8+-Activated T Cells in Primary EBV Infection

The origin of the increased numbers of CD8+ atypical lymphocytes, expressing activated markers such as HLA-DR or CD45RO, in the peripheral blood of patients with infectious mononucleosis (IM) has been debated. Using a recently developed assay to detect intracellular accumulation of IFN-γ in EBV-reactive T cells by FACS, we have demonstrated that 34–54% of HLA-DR+/CD8+ and 34–60% of CD45RO+/CD8+ T cells in the PBMCs of febrile patients suffering from IM are EBV-specific. The EBV-specific CD8+ T cell counts in the PBMCs of four febrile patients suffering from IM ranged between 2260 and 8200/μl, decreasing to 5.1% and 7.9% of the counts in the first samples over 10 days in two donors. The decline of CD8+ T cell subpopulations, namely HLA-DR+, CD45RO+, and EBV-specific T cells, was in parallel with the drop in the EBV genome load. These data indicate that the Ag-driven expansion of CD8+ T cells and subsequent contraction with the Ag decline in vivo in humans is effective for clearing virus-infected cells with minimal disturbance of the homeostasis of the immune system.

Prevalence of maternal cytomegalovirus (CMV) antibody and detection of CMV DNA in amniotic fluid

The prevalence of cytomegalovirus (CMV) IgG antibody was determined in 573 pregnant women in the first trimester. The overall prevalence of CMV IgG antibody was 77.5%. The rate of seropositivity was 67.7% in women < 25 yr, and increased with age to 85.7% in women 40 yr. These results imply that young women in Japan are at increased risk for primary CMV infection during pregnancy and that congenital CMV infection rates might increase in the future. We conducted a prospective study of 75 pregnant women who underwent amniocentesis for various indications to determine if CMV DNA could be detected in the amniotic fluid. None had symptoms associated with CMV infection, CMV IgM antibody, or seroconversion to CMV IgG antibody during pregnancy. CMV DNA was not detected in the amniotic fluid using a polymerase chain reaction assay. The 65 fetuses, including 3 sets of twins, were followed through birth. CMV DNA was not detected in urine samples obtained within the first 2 weeks of life. In conclusion, CMV DNA was not detected in the amniotic fluid of women who did not have CMV infection. These results, however, suggest that the negative predictive value of prenatal amniotic fluid analysis is high and that the presence of CMV DNA in the amniotic fluid has clinical significance for the diagnosis of congenital CMV infection if detected in pregnant women.