EBV Viral Load Monitoring: Unanswered Questions

Copyright C Blackwell Munksgaard 2002American Journal of Transplantation 2002; 2: 894–895

Blackwell Munksgaard ISSN 1600-6135

Editorial

EBV Viral Load Monitoring: Unanswered Questions

Michael Greena,* and Steven A. Webberb

a Department of Pediatrics and Surgery, University of

Pittsburgh School of Medicine, Division of Allergy,

Immunology and Infectious Diseases, and b Department of

Pediatrics, University of Pittsburgh School of Medicine,

Division of Cardiology, Children’s Hospital of Pittsburgh,

Pittsburgh, PA

*Correspondence: Michael Green, greemd@chp.edu

Received 28 June 2002, revised and accepted forpublication 7 August 2002

Measurement of the Epstein-Barr Virus (EBV) load in the pe-ripheral blood using DNA amplification techniques has be-come increasingly available for the management of organtransplant recipients (1). In this volume of the American

Journal of Transplantation, Tsai and colleagues add to ourknowledge of this test by exploring the use of EBV PCR forthe diagnosis and management of post-transplant lympho-proliferative disorders (PTLD) in adult solid organ transplant(SOT) recipients (2). As most published experience to datehas been derived from pediatric organ transplant or bonemarrow transplant recipients, analysis of data derived fromadult SOT is necessary to determine whether or not resultsobtained from this population will be similar to findings fromchildren and marrow recipients. The findings that EBV viralloads obtained from adult SOT recipients undergoing evalu-ation for PTLD were highly specific but only marginally sensi-tive contrast with previously published work, which has typic-ally found the EBV viral load to be extremely sensitive but tolack specificity for the presence of EBV-associated disease(1–3).

The differences between the current investigation and pre-viously published studies may be explained by a number ofreasons. One obvious explanation for these differences couldbe variations in PCR assay methods, units or cut-offs of posi-tivity. Published experience has been based on determinationof EBV viral load within peripheral blood lymphocytes (PBL),whole blood or plasma. Amplification of EBV genome hasbeen performed using a wide variety of primer sets and tar-get genes. Results of viral load detection using PCR havebeen reported as genome copies/105 PBL, genome copies/mL or genome copies/mg DNA. Definitions for ‘elevated’loads, ‘high’ loads or ‘positive’ loads have been arbitrarily de-termined and have varied between laboratories and publi-cations. Efforts to standardize methods, sites of sampling,

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and levels of load that denote risk have not been undertakenbut are urgently needed.

Differences in patient population may also explain the vari-ations in sensitivity and specificity observed between the cur-rent report and previously published studies. Obtaining re-sults from a cohort of patients in whom PTLD is clinicallysuspected may lead to enhanced specificity for the presenceof EBV disease compared with results obtained from patientsundergoing surveillance or random sampling in the absenceof a clinical illness. Specificity may also be affected by theEBV serostatus of the patient before transplantation. Experi-ence from our center suggests that children developing pri-mary EBV infection after transplantation are more likely tobecome chronic asymptomatic carriers of high EBV loadsthan those who are seropositive at the time of the transplant(4,5). As the majority of pediatric transplant recipients areseronegative before transplantation, high load carriers areseen frequently in this population. In contrast, adults arerarely EBV seronegative before transplantation, suggestingthat high low carriers will be observed infrequently in thesepatients. Thus elevated loads in adults may be more likelyto be associated with PTLD, possibly explaining the higherspecificity reported in the current study compared with pre-vious reports. Additional data are necessary to confirm thesehypotheses.

Not only the specificity but also the sensitivity of the EBVviral load could be affected by the EBV serostatus at the timeof the transplant. It is possible that EBV viral loads may behigher in patients with PTLD that develops in recipients whoexperience primary infection following their transplant com-pared with patients with PTLD who were EBV-seropositivebefore transplantation. ‘Low-load’ PTLD (where EBV viralloads at the time of diagnosis of PTLD fall below predictedcut-offs) may be seen more frequently in patients who areseropositive before transplantation than those who are sero-negative. Because the vast majority of children are EBV-sero-negative before transplantation, EBV viral loads at the time ofPTLD may be higher in children resulting in a greater sensi-tivity compared with adults where seropositive patients mayaccount for significant proportions of cases of PTLD. Again,this hypothesis has yet to be confirmed.

The availability of a noninvasive, accurate test that can predictrisk for, or presence of, EBV-associated PTLD is a highly de-sirable development for the field of transplantation. Unfortu-nately, the technology to acquire a result currently exceedsour understanding of its meaning. While one or more differ-ences in the test or patient populations may explain the con-

Editorial

trast between the results of Tsai et al. and previous publi-cations, neither this work nor previously published work clari-fies this for the transplant clinician. What we do know is thatthe EBV viral load is elevated in most pediatric patients withPTLD. However, an elevated EBV PCR alone in these patientsdoes not differentiate between asymptomatic infection,symptomatic EBV infection (not fulfilling the diagnostic cri-teria of PTLD) and PTLD. We do not know if elevated EBVviral loads will be detected less often in adults compared withpediatric organ transplant recipients with PTLD, though thecurrent study suggests this may be the case. We know thatdevelopment of a high EBV viral load occurs uncommonlyin patients who are EBV-seropositive before transplantation.However, we do not know if pre-existing immunity againstEBV before transplantation will affect the EBV viral load atthe time of diagnosis of EBV-associated PTLD. We know thatintermittent elevations in EBV viral load can be observed withtreatment of rebound rejection but that these transient elev-ations are not typically associated with relapsing disease. Wedo not know the significance of the high-load carrier statenor whether the use of EBV viral load monitoring plays anyrole in identifying relapse of PTLD. Finally, we do not knowwhether additional laboratory tests can be identified that mayadd to the sensitivity or specificity of the EBV viral load inorgan transplant recipients, though preliminary work charac-terizing viral gene expression in the load looks promising (4).Determining the answers to these questions about the EBVviral load for which we have no answers remains an import-

895American Journal of Transplantation 2002; 2: 894–895

ant challenge to all of us who care for patients undergoingtransplantation. Collaborative, prospective studies aimed atanswering these questions must be designed and as import-antly funded if we are to maximize the full potential of theEBV viral load to impact on the incidence and outcome ofEBV disease in organ transplant recipients.

References

1. Green M, Reyes J, Webber S, Michaels MG, Rowe D. The role of viralload in the diagnosis, management, and possible prevention ofEpstein Barr Virus-associated posttransplant lymphoproliferative dis-ease following solid organ transplantation. Current Opinion in OrganTransplantation 1999; 4: 292–296.

2. Tsai D, Nearey M, Hardy C, Tomaszewski J, Kotloff R. Use of EBV PCRfor the Diagnosis and Monitoring of Post-Transplant Lymphoproliferat-ive Disorder in Adult Solid Organ Transplant Recipients. Am J Trans-plant 2002; 2: 946–954.

3. Green M, Caccuarelli TV, Mazareigos GV et al. Serial measurements ofEpstein-Barr viral load in peripheral blood in pediatric liver transplantrecipient for posttransplant lymphoproferative disease. Transplantation1998; 66: 1641–1644.

4. Qu L, Green M, Webber S, Reyes J, Ellis D, Rowe D. Epstein-Barr virusgene expression in the peripheral blood of transplant recipients withchronic circulating viral loads. J Inf Dis 2000; 182: 1013–1021.

5. Boyle GJ, Law Y, Miller SA et al. Characterization of chronic high EBV-load carriers after pediatric thoracic transplantation. XIX InternationalCongress of the Transplantation Society, Miami. (Abstract). Transplan-tation, in press.