Improved monitoring of cytomegalovirus infection after allogeneic hematopoietic stem cell transplantation by an ultrasensitive plasma DNA PCR assay

Detection of human cytomegalovirus DNA in various blood components after liver transplantation

The quantification of human cytomegalovirus (HCMV DNA) by real-time PCR is currently a primary option for laboratory diagnosis of HCMV infection. However, the optimal sample material remains controversial due to the use of different PCR assays. To explore the best blood component for HCMV DNA surveillance after liver transplantation, whole blood (WB), serum (SE), and plasma (PL) specimens were collected simultaneously from targeted patients and examined for HCMV DNA using one commercially available assay. The HCMV DNA-positive rate with WB (16.67%) was higher than that with either SE or PL (8.33%, both P<0.01). Quantitative DNA levels in WB were of greater magnitude than those in SE (WB-SE mean log-transformed difference, 0.99; 95%CI=0.74-1.25; P<0.0001) and PL (WB-PL mean log-transformed difference, 1.37; 95%CI=1.07-1.66; P<0.0001). Dynamic monitoring revealed that HCMV DNA in WB was positive sooner and had higher values for a longer period of time during therapy. With earlier positive detection, higher sensitivity, and yield of greater viral loads, WB compared favorably to SE or PL and hence is recommended as the superior material for HCMV DNA surveillance after liver transplantation. In addition, infant recipients require more intensive monitoring and prophylactic care because of their higher susceptibility to primary HCMV infection.

Clinical significance of low cytomegalovirus DNA levels in human plasma

The clinical significance of the detection of low copy numbers of cytomegalovirus (CMV) DNA in immune-suppressed patients remains unclear. In this study, we compared the artus CMV Rotor-Gene PCR, utilizing an automated nucleic acid extraction and assay setup (the artus CMV protocol), with the COBAS Amplicor CMV Monitor test (our reference protocol). We then analyzed the results of all CMV PCR tests ordered following the implementation of the artus CMV protocol at our institution and followed 91 adult patients with positive test results. The artus CMV protocol had a linear range extending from 2.0 to 7.0 log(10) copies/ml and had a lower limit of 95% detection of 57 copies/ml. With archived plasma samples, this protocol demonstrated 100% sensitivity and 94% specificity for the detection of CMV DNA. Following implementation of the artus CMV protocol, 320 of 1,403 (22.8%) plasma samples tested positive (compared with 323/3,579 [9.0%] samples in the preceding 6 months), and 227 (16.2%) samples had copy numbers of <400/ml. Ninety-one adult patients had at least one positive test. The data were analyzed using a threshold of 200 copies/ml, and in 22 episodes, the viral load increased from <200 copies/ml to ≥ 200 copies/ml on sequential tests. In 21 of these 22 episodes, either the viral load continued to increase or antiviral treatment was initiated in response to the repeat value. In summary, we evaluate the performance characteristics of a protocol utilizing the artus CMV PCR and identify clinically meaningful changes in CMV DNA copy numbers even when they are initially detected at a low level.

Lack of evidence for systemic cytomegalovirus reactivation in maintenance hemodialysis patients

The risk of cytomegalovirus (CMV) reactivation among hemodialysis (HD) patients is unknown. In 52 HD patients from a single center, CMV serology and quantitative PCR were performed. The detection limit of PCR was 20 copies/ml. Here, PCR ruled out CMV viremia, despite CMV-IgM seropositivity in 15.4% patients.

Clinical relevance of cytomegalovirus viraemia(*,†)

BACKGROUND

Using new sensitive quantitative polymerase chain reaction (PCR) assays, cytomegalovirus (CMV) DNA is often detectable in the plasma of immunosuppressed patients. We investigated the prognostic value of a positive CMV DNA test for the development of CMV end-organ disease, other AIDS-defining events and mortality.

METHODS

A survival analysis was performed, using the Kaplan-Meier method and Cox proportional hazards models, for patients prospectively followed in the Swiss HIV Cohort Study, from January 1996 to December 2007, who were CMV-seropositive, had a CD4 count of ≤ 100 cells/μL, and had a plasma sample available for the measurement of baseline CMV DNA with an ultrasensitive PCR. The outcome analysed was an AIDS-defining event, including CMV end-organ disease, or death. Variables analysed at the time of CMV measurement were demographic variables, CD4 cell counts, HIV-1 RNA loads, and use and type of highly active antiretroviral therapy (HAART).

RESULTS

Of 1128 patients, 208 (18%) presented an AIDS-defining event and 246 (22%) died. A total of 368 patients (34% of samples) had detectable CMV DNA at baseline, with DNA concentrations of up to 38 800 copies/mL. In the multivariate analysis, CMV DNA predicted evolution not only towards CMV end-organ disease [hazard ratio (HR) 12.6; 95% confidence interval (CI) 4.27-37.41], but also towards other AIDS-defining events (HR 2.6; 95% CI 1.60-4.33) and death (HR 1.9; 95% CI 1.10-3.34).

CONCLUSION

Quantitative CMV DNA detected in the plasma of HIV-infected patients with CD4 counts ≤ 100 cells/μL is a predictor for HIV disease progression, CMV disease and death. A single low value of 80 copies/mL identifies patients at low but significantly increased risk during the following months, after the measurement.

Molecular detection of herpesviruses

In routine molecular diagnostics, detection of herpesviruses has made a major impact. Infection with herpesviruses is indicated by demonstrating the presence of the virus in selected specimens. Rapid and reliable detection of herpesvirus DNA helps to decrease the lethality as well as the sequelae of herpesvirus infection in patients at risk. This chapter discusses specimen types and both laboratory-developed and commercially available assays useful for molecular detection of herpesviruses. To meet the need for reliable laboratory results, it is advisable to employ maximum automated and standardized kits based on reagents and standards of reproducible high quality. In the routine diagnostic laboratory, introduction of IVD/CE and/or FDA-labeled tests is preferred.

Quantification of DNA in plasma by an automated real-time PCR assay (cytomegalovirus PCR kit) for surveillance of active cytomegalovirus infection and guidance of preemptive therapy for allogeneic hematopoietic stem cell transplant recipients

The performance of a plasma real-time PCR (cytomegalovirus [CMV] PCR kit; Abbott Diagnostics) was compared with that of the antigenemia assay for the surveillance of active CMV infection in 42 allogeneic hematopoietic stem cell transplantation (Allo-SCT) recipients. A total of 1,156 samples were analyzed by the two assays. Concordance between the two assays was 82.2%. Plasma DNA levels correlated with the number of pp65-positive cells, particularly prior to the initiation of preemptive therapy. Fifty-seven episodes of active CMV infection were detected in 37 patients: 18 were defined solely by the PCR assay and four were defined on the basis of the antigenemia assay. Either a cutoff of 288 CMV DNA copies/ml or a 2.42-log(10) increase of DNAemia levels between two consecutive PCR positive samples was an optimal value to discriminate between patients requiring preemptive therapy and those not requiring therapy on the basis of the antigenemia results. The real-time PCR assay allowed an earlier diagnosis of active CMV infection and was a more reliable marker of successful clearance of CMV from the blood. Analysis of the kinetics of DNAemia levels at a median of 7 days posttreatment allowed the prediction of the response to CMV therapy. Two patients developed CMV colitis. The PCR assay tested positive both before the onset of symptoms and during the disease period. The plasma real-time PCR from Abbott is more suitable than the antigenemia assay for monitoring active CMV infection in Allo-SCT recipients and may be used for guiding preemptive therapy in this clinical setting.

Clinical Utility of Autopsy after Hematopoietic Stem Cell Transplantation

Autopsy is the gold standard for establishing the cause of death. We present results of the largest retrospective review of complete autopsies of subjects after hematopoietic stem cell transplantation to better define the role of the autopsy in discovering a missed diagnosis. We reviewed the medical chart and autopsy records of 111 patients who had undergone hematopoietic stem cell transplantation from July 1986 to June 2003 from a single center. We compared the cause of death as charted by the clinical team with data obtained from postmortem chart review and autopsy reports. Of 29 (26%) cases when the premortem and postmortem major diagnoses did not agree, only 4 (4%) autopsy records provided data that might have led to the initiation of new treatments, and none of these diagnoses would be missed today with more sensitive and specific diagnostics and improved supportive care. Although autopsies after transplantation can be important educational, research, and epidemiologic tools and provide an emotional benefit to patient's families, in our series they rarely provided missed diagnoses that would alter the management of subsequent patients. Improvements in noninvasive tests for relapse or occult infections may further erode the role of autopsies in discovering missed diagnoses.

Cytomegalovirus (CMV)-specific CD8+ T cells in individuals with HIV infection: correlation with protection from CMV disease

CD8+ cytotoxic T cells play a key role in immunological protection from clinical cytomegalovirus (CMV) disease. Numbers of CMV-specific CD8+ T cells are increased in untreated and antiretroviral-treated HIV patients compared with healthy controls. Accumulation of CMV-specific CD8+ T cells during HIV infection may reflect persistent reactivation of CMV owing to suboptimal immune control and/or oligoclonal expansion of the limited populations of CMV-specific CD8+ T cells present before antiretroviral therapy (ART). CD8+ T cells directed against the CMV immediate early (IE)-1 protein may play an important role in preventing CMV replication to pathogenic levels. However, immunological protection from CMV disease in HIV-infected individuals on ART does not appear to depend on total numbers of CMV-specific CD8+ T cells but rather on the presence of both effector-memory and effector CMV-specific CD8+ T cells that produce interferon-gamma and/or perforin in response to CMV antigens.

Pretransplantation CMV-specific T cells protect recipients of T-cell-depleted grafts against CMV-related complications

We have studied cytomegalovirus (CMV) immunity in 17 CMV-positive recipients of T-cell-depleted or T-cell-replete grafts. In recipients of T-cell-replete grafts, the patient's CMV-specific T-cell response was completely ablated. Because primary anti-CMV responses were rare during the first year, immunity depended essentially on the transfer of donor CMV-specific T cells and, therefore, on the CMV positivity of the donor. In the recipients of T-cell-depleted grafts, CMV-specific cytotoxic T cells were of recipient origin in 2 patients who underwent transplantation with CMV-negative donors and in 3 of 8 patients who underwent transplantation with CMV-positive donors, and they were of mixed or donor origin in the other 5 patients studied. Recipient CMV-specific T cells responded vigorously to antigen ex vivo and persisted for several years without replenishment by donor cells. Furthermore, they appeared to have a protective effect because CMV-related complications were absent in the patients with CMV-specific T cells of recipient origin. Clinical outcomes of a cohort of 91 patients corroborated the experimental results. Patients with recipient T cells in their blood were protected regardless of the donor immune status. Hence, when a T-cell depletion protocol is used that favors the survival of recipient T cells, the patient's pretransplantation CMV-specific immunity protects against posttransplantation CMV-related complications.

Cytomegalovirus (CMV)-specific cellular immune responses

A large percentage of healthy individuals (50-90%) is chronically infected with Cytomegalovirus (CMV). Over the past few years, several techniques were developed in order to monitor CMV-specific T-cell responses. In addition to the identification of antigen-specific T cells with peptide-loaded MHC complexes, most of the current strategies to identify CMV-specific T cells are centered on the assessment of the functions of memory T cells including their ability to mediate effector function, to proliferate or to secrete cytokines following antigen-specific stimulation. The investigation of these functions has allowed the characterization of the CMV-specific T-cell responses that are present during different phases of the infection. Furthermore, it has also been shown that the combination of virus-specific CD4 and CD8 T-cell responses are critical components of the immune response in the control of virus replication.

Recent advances in the prevention of CMV infection and disease after hematopoietic stem cell transplantation

Cytomegalovirus (CMV) remains an important pathogen in hematopoietic stem cell transplant (HCT) recipients in the current era of antiviral prophylaxis and preemptive therapy, despite the almost complete elimination of CMV disease during the first 3 months after transplantation. Pretransplant CMV serostatus of the donor and/or recipient remains an important risk factor for poor post-transplant outcome, especially in highly immunodeficient patients (e.g. recipients of ex vivo or in vivo T-cell depletion). Prevention of late CMV disease continues to be a challenge in selected high-risk populations, and indirect immunomodulatory effects of CMV (e.g. invasive bacterial and fungal infections) appear to contribute to the poor outcome. The risk of developing antiviral resistance remains low in most patients; however, in a setting of intense immunosuppression (e.g. after transplantation from a haploidentical donor) the incidence may be as high as 8%. Transfusion-transmitted CMV infection can be reduced by the provision of seronegative or leukocyte-depleted blood products; however, a small risk of 1-2% of CMV disease remains. Surveillance and preemptive therapy is effective in preventing transfusion-related CMV disease. The development of new drugs and immunologic strategies (adoptive transfer of CMV-specific T-cells and donor/recipient vaccination strategies) are important goals for the elimination of the negative impact of CMV in the HCT setting.

Optimization of quantitative detection of cytomegalovirus DNA in plasma by real-time PCR

Previous studies have shown that detection of cytomegalovirus (CMV) DNA in plasma is less sensitive than the antigenemia assay for CMV surveillance in blood. In 1,983 blood samples, plasma PCR assays with three different primer sets (UL125 alone, UL126 alone, and UL55/UL123-exon 4) were compared to the pp65 antigenemia assay and blood cultures. Plasma PCR detected CMV more frequently in blood specimens than either the antigenemia assay or cultures, but of the three PCR assays, the double-primer assay (UL55/UL123-exon 4) performed best with regard to sensitivity, specificity, and predictive values compared to antigenemia: 122 of 151 antigenemia-positive samples were detected (sensitivity, 80.1%), and there were 122 samples that were PCR positive-antigenemia negative (specificity, 93%). Samples with discrepant results had a low viral load (median, 0.5 cells per slide; 1,150 copies per ml) and were often obtained from patients receiving antiviral therapy. CMV could be detected by other methods in 15 of 29 antigenemia positive-PCR negative samples compared to 121 of 122 PCR positive-antigenemia negative samples (P < 0.001). On a per-subject basis, 21 of 25 patients (antigenemia positive-PCR negative) and all 57 (PCR positive-antigenemia negative) could be confirmed at different time points during follow-up. The higher sensitivity of the double-primer assay resulted in earlier detection compared to antigenemia in a time-to-event analysis of 42 CMV-seropositive stem cell transplant recipients, and two of three patients with CMV disease who were antigenemia negative were detected by plasma PCR prior to the onset of disease. Interassay variability was low, and the dynamic range was >5 log(10). Automated DNA extraction resulted in high reproducibility, accurate CMV quantitation (R = 0.87, P < 0.001), improved sensitivity, and increased speed of sample processing. Thus, primer optimization and improved DNA extraction techniques resulted in a plasma-based PCR assay that is significantly more sensitive than pp65 antigenemia and blood cultures for detection of CMV in blood specimens.

Cytomegalovirus in hematopoietic stem cell transplant recipients: current status, known challenges, and future strategies

Cytomegalovirus (CMV) infection is a major cause of morbidity and mortality after hematopoietic stem cell transplantation. Significant progress has been made in the prevention of CMV disease over the past decade, but prevention of late CMV disease continues to be a challenge in selected high-risk populations. The pretransplantation CMV serostatus of the donor and/or recipient remains an important risk factor for posttransplantation outcome despite the use of antiviral prophylaxis and preemptive therapy; CMV-seropositive recipients of T cell-depleted grafts in particular continue to have a survival disadvantage compared with seronegative recipients with seronegative donors. The risk of developing antiviral drug resistance remains low in most patients; however, in a setting of intense immunosuppression (eg, after transplantation from a haploidentical donor), the incidence may be as high as 8%. Primary CMV infection via blood transfusion can be reduced by the provision of seronegative or leukocyte-depleted blood products; however, a small risk of 1% to 2% of CMV disease remains. Surveillance and preemptive therapy are effective in preventing the sequelae of transfusion-related CMV infection. Indirect immunomodulatory effects of CMV are increasingly recognized in hematopoietic stem cell transplant recipients. Strategies currently being investigated include long-term suppression of CMV with valganciclovir for the prevention of late CMV infection and disease, adoptive transfer of CMV-specific T cells, and donor and recipient vaccination strategies.

Monitoring of cytomegalovirus infection in solid-organ transplant recipients by an ultrasensitive plasma PCR assay

Early and accurate monitoring of cytomegalovirus (CMV) infection in solid-organ transplant recipients is of major importance. We have assessed the potential benefit of an ultrasensitive plasma-based PCR assay for renal transplant recipients. The pp65 CMV antigen (pp65 Ag) assay using leukocytes was employed as a routine test for the monitoring of CMV in 23 transplant recipients. We compared the pp65 antigenemia with the CMV load quantified by an ultrasensitive PCR (US-PCR) with a limit of detection of 20 CMV DNA copies/ml of plasma. CMV infection was detected in 215 (67%) of 321 plasma samples by the US-PCR compared with 124 (39%) of 321 samples by the pp65 Ag assay. The US-PCR assay permitted the detection of CMV infection episodes following transplantation a median of 12 days earlier than the pp65 Ag assay. Moreover, during CMV infection episodes, DNA detection by the US-PCR was consistently positive, whereas false negative results were frequently observed with the pp65 Ag assay. We found a good correlation between the two assays, and the peak viral loads were significantly higher in patients with CMV-related complications (median, 5000 DNA copies/ml) than in those without symptoms (1160 DNA copies/ml) (P = 0.048). In addition, patients that did not require preemptive therapy based on the results of the pp65 assay had CMV loads significantly lower (median, 36 DNA copies/ml) than those that needed treatment (median, 4703 DNA copies/ml) (P < 0.001). These observations provided cutoff levels that could be applied in clinical practice. The ultrasensitive plasma-based PCR detected CMV infection episodes earlier and provided more consistent results than the pp65 Ag assay. This test could improve the monitoring of CMV infection or reactivation in renal transplant recipients.