Persistent Increased Epstein-Barr Virus Loads After Solid Organ Transplantation

Epstein-Barr virus (EBV) is an important pathogen after organ transplantation causing a variety of clinical syndromes, including posttransplantation lymphoproliferative disease (PTLD). Clinically important EBV infections and PTLD occur 5-7 times more frequently in patients who are seronegative before transplantation compared with those who are EBV seropositive at the time of liver transplantation.1, 2 As much as 60% of EBV-seronegative children undergoing organ transplantation will seroconvert during the first 3 months after transplantation. Although many children who seroconvert will not have clinically recognizable disease, high rates of PTLD have been reported after pediatric liver transplantation under both cyclosporine- and tacrolimus-based immunosuppression.3, 4 The high prevalence of EBV infection, and its associated morbidity and mortality, have resulted in efforts to identify children at risk for these complications. In addition, tools have been sought to facilitate early diagnosis and prevention of EBV disease. Initially, these efforts were limited to the performance of serial serologic studies aimed at identifying those children who experience primary infection after transplantation. More recently, these serologic studies have been replaced by the longitudinal measurement of EBV load in the peripheral blood by using DNA amplification techniques.5 The EBV load has proven to be a highly sensitive test for the identification of patients at risk for, or presenting with, EBV disease. Unfortunately, the presence of increased EBV loads in children has been shown to lack specificity for the presence of EBV-associated disease.5, 6 This is particularly true in transplant recipients who undergo virus load monitoring long after their primary EBV infection. These patients frequently have persistent increases in their EBV loads, even though most are asymptomatic. The possibility that these persistent increases will subsequently be associated with the development of late-onset EBV disease and PTLD creates anxiety for transplant recipients, their families, and the clinical team. In this issue of Liver Transplantation, D'Antiga and colleagues7 address several potentially important questions relevant to the role of longitudinal EBV monitoring in children undergoing transplantation. The goals of their retrospective study were (1) to identify which patients (if any) will benefit from long-term monitoring, (2) to determine how long EBV monitoring should be carried out, and (3) to attempt to ascertain the clinical significance of sustained EBV detection. The authors reviewed their experience with 34 children undergoing liver transplantation at the University of Padova who had a minimum of 12 months' follow-up, availability of pretransplantation serologic EBV status of the recipient, and availability of at least 3 EBV monitoring tests per year. Monitoring between 1986 and 1997 consisted of performance of EBV serologies. After 1997, monitoring was carried out through the determination of EBV virus load in peripheral blood lymphocytes (PBL) as measured by a real-time polymerase chain reaction assay. The authors found that 14 of 18 patients who experienced primary EBV infection after transplantation had sustained virus detection, compared with 0 of 13 children who were seropositive before transplantation. Sustained virus detection was defined as more than 6 months of either positive viral capsid antigen–immunoglobulin M or early antigen antibody or a positive reverse transcriptase–polymerase chain reaction test. Three of the 14 with sustained virus detection were subsequently found to develop PTLD more than 1 year after transplant. No PTLD was identified among the 13 children who were EBV seropositive before transplantation, and no cases of late PTLD were found among the 4 children who experienced primary infection but did not manifest sustained detection of EBV. Thus, this study shows that primary infection after transplantation represents a risk for persistent detection of EBV infection (according to the authors' definition) and for the development of late PTLD. The observation that primary EBV infection after organ transplantation in children is associated with sustained virus detection is consistent with our own experience in children undergoing many types of solid organ transplantation.6, 8, 9 There are some limitations to the present study. First, the definition of sustained virus detection in 8 of 14 patients was made on the basis of serology alone. Second, the definition of sustained virus detection by using EBV load did not require any prespecified level of load. Although the authors state that all patients with sustained virus detection reached a load of 500 genome copies/105 PBL, it is not clear whether this level of load was maintained throughout the period of sustained virus detection. This information is critical in determining whether patients with lower levels of sustained detectable EBV load have similar risks compared with those with persistently high loads. Despite these limitations, the importance of the work of D'Antiga et al. should not be underestimated. Although the presence of patients manifesting persistent increases of EBV load for prolonged periods has been previously identified,5, 6, 8 we are unaware of published data that explore the clinical significance of persistent EBV load carriage. Our own experience at the Children's Hospital of Pittsburgh adds information—and perhaps also some confusion—to this issue. It is our practice to differentiate persistent carriage states according to the height of load. We have defined persistent high-load carriers as those children who maintain a load of >200 genome copies per 105 PBL (or >16,000 copies/mL whole blood) for more than half of the measurements over a period of 6 months or more. It is worth noting that many of our children developed the high-load carrier state after experiencing complete recovery from an episode of EBV disease or PTLD. Among our pediatric heart transplant recipients, we observed that 6 (30%) of 20 patients with persistently high loads subsequently developed late de novo PTLD (including monomorphic disease/Burkitt's lymphoma), and 3 others developed recurrent polymorphic disease.9 In contrast, only 1 of 32 patients who carried high loads among our pediatric liver transplant recipients have gone on to develop PTLD or lymphoma in association with a persistent high load carrier state (unpublished data). The reason for this difference is unclear, but it might reflect lower levels of immunosuppression in the long term after liver transplantation and a more aggressive approach to reduction in immunosuppression when a diagnosis of chronic high-load state is made in this population. Aggressive reduction in immunosuppression in the cardiac population can lead to sudden death associated with undiagnosed acute rejection. The extent to which the high virus load state and risk of late PTLD can be safely ameliorated by reduction in immunosuppression remains to be determined. A preemptive reduction of immune suppression in response to a sustained EBV infection was performed in several patients in the current study. Although virus loads tended to decrease, one patient developed rebound acute rejection, and another went on to develop PTLD. Logically, the appropriate strategy for managing a high load state will depend on whether high EBV load carriers are globally overimmunosuppressed, or whether they have a relatively specific failure of T cell immunity against EBV antigens. ELISPOT (enzyme-linked immunosorbent spot-forming cell), tetramer staining, and other modern immune monitoring techniques might be used in the future to more accurately assess the state of the immune system in individual patients over time, contrasting responses to EBV antigens to those against alloantigens. In the meantime, there seems to be mounting evidence that in certain populations, a chronic high EBV load state may not always be benign, and careful long-term follow-up of such patients seems warranted.