Coinfection rates and clinical outcome data for cytomegalovirus and Epstein‐Barr virus in post‐transplant patients: A systematic review of the literature

Abstract Background In transplant recipients, cytomegalovirus (CMV) infection increases morbidity and mortality; furthermore, coinfection with other human herpesviruses like the Epstein‐Barr virus (EBV) may complicate their management. This systematic literature review aimed to summarize rates of CMV‐EBV coinfection and associated clinical outcomes among solid organ transplant (SOT) and hematopoietic stem cell transplant (HSCT) recipients. Methods An electronic literature search was performed using pre‐specified search strategies (January 1, 2010‐October 31, 2018) and following established/best practice methodology. Of 316 publications identified, 294 did not report CMV‐EBV coinfection and were excluded. Studies meeting the inclusion criteria were further analyzed. Due to limited reporting/heterogeneity, data were not meta‐analyzable. Results Nine studies (six SOT; three HSCT) reported CMV‐EBV coinfection; rates of coinfection post transplantation varied between 2.6% and 32.7%. Two studies indicated CMV reactivation to be an independent variable associated with EBV reactivation. Among SOT studies, higher rates of graft dysfunction (47.4% vs 22.9%), rejection episodes (20.0% vs 8.9%), or acute rejection (50.0% vs 31.0%) were reported for patients with coinfection than without. In HSCT studies, patients with graft‐vs‐host disease were not reported separately for coinfection. Two studies described cases of post‐transplant lymphoproliferative disorder (PTLD) in patients with CMV‐EBV coinfection and reported rates of PTLD of 92% and 100%. Conclusion The CMV‐EBV coinfection rate in HSCT and SOT recipients varied and was associated with increased graft rejection and PTLD compared with patients without coinfection. Further research may improve understanding of the burden of CMV‐EBV coinfection among transplant recipients.


| INTRODUC TI ON
Ubiquitous in the general population, infection with cytomegalovirus (CMV) is a serious complication of transplantation that increases the risk for allograft rejection, morbidity, and mortality. 1 The frequency of symptomatic CMV infection among transplant recipients ranges from approximately 8%-41% in the literature, depending on the allograft received, 1 serostatus of the donor and recipient, and the use and type of antiviral prophylaxis. 2 CMV exerts direct cytopathic effects on various organ systems, causing conditions such as pneumonia, gastrointestinal tract disease, and hepatitis. 3,4 Like other human herpesviruses (HHV), CMV is highly cell-associated, and transmission requires either intimate mucosal contact or physical transfer of a latent virus via an allograft or leukocyte-containing blood product. 4,5 While cytotoxic T lymphocytes form the key host defense system against CMV, failure to reconstitute CMV-specific cellular immunity following alteration of cell-mediated immunity heightens the risk of acute CMV disease. 1 CMV infection can also lead to indirect immunosuppressive effects-including aberrations in T-cell synthesis, the expression of major histocompatibility antigens, and cytokine and chemokine activity-further increasing the risk of opportunistic infections. 4,6 CMV is also an active inducer of other HHV. 1

| MATERIAL S AND ME THODS
This study was defined a priori, including the protocol, screening forms, and data extraction templates. The study was performed adhering to the best methods established in the peer-reviewed science of systematic review research, 9  Prospective or retrospective studies reporting either of the following outcomes for patients undergoing SOT or HSCT were selected: (a) rate of CMV-EBV coinfection or (b) clinical outcomes of patients with CMV-EBV coinfection following transplantation. Studies documenting coinfections defined as symptomatic clinical infections as well as those citing cases of asymptomatic viremia were considered. White papers, editorials/commentaries, reviews or models without presentation of primary data, news articles, and editorials were excluded.

| Study screening and data extraction
All references were screened using a two-level process. First, titles and abstracts were screened (ERB) and then the full text of studies meeting the preliminary criteria (reports, coinfection rates, and/or clinical outcomes associated with CMV-EBV coinfection). A second author (CA-S) screened a 10% random sample of excluded articles. Pre-specified study-level data were extracted and summarized (Appendix S1).

| Studies
The PubMed and EMBASE ® searches generated 2027 records.
Three additional studies were included from other sources, such as manual searches. After the exclusion of duplicates, conference abstracts, case reports, and reviews, 316 articles were screened for relevance ( Figure 1). Of those records, 22 (7%) publications were reviewed in full, and 9 of the 22 (41%) studies were deemed eligible for inclusion. Table 2 presents an overview of the nine studies identified; six studies assessed SOT recipients (one liver and five renal transplantations), 8,[13][14][15][16][17] and three studies assessed HSCT recipients. [18][19][20] Two studies estimated infection rates based on retrospective reviews of clinical data. 13,20 All other studies monitored patients prospectively.
Study samples primarily comprised adults (mean or median age >18 years) with one study in pediatric liver transplantation. 13 Males represented the majority (52.3%-86%) of patients across all study cohorts. Two studies of renal transplant and HSCT recipients, respectively, selected patients at high risk for EBV disease. 14,19 Another study included only HSCT recipients who had prior CMV exposure (immunoglobulin [Ig]G-positive, IgM-negative CMV). 18 Table 3 presents the available study data on patient and treat-

| CMV-EBV coinfection post transplantation
The published rates of CMV-EBV coinfection during the post-transplantation period varied ( Figure 2).

| SOT studies
In the study of pediatric liver transplant recipients, 6.5% (4/62) of patients had CMV-EBV coinfections detected within the first 21 days after transplantation. 13 Three of the five studies in renal transplantation detected low (≤5% of patients) CMV-EBV coinfection rates. 8,15,16 Of these, two studies monitored patients for 12 months post transplantation and found coinfection rates of 4.2% and 2.6%, respectively. 8,16 In the third study, 3.2% of patients followed for 36 months had CMV-EBV coinfection 15 ; however, the two cases reported were identified within 12 months post transplantation (at 8 and 10 months, respectively). 15 Additionally, triple infection with BK polyomavirus (CMV-EBV-BK) was reported at a rate of 2.4%. 16 The remaining two renal transplantation studies reported higher CMV-EBV coinfection rates of 10.0% 17 and 21.3%. 14 In the latter study, infections were categorized as "immediate" (0-3 months), "late" (>3-12 months), or "very late" (>12 months) based on the time of assessment relative to transplantation. 14 The rates of immediate, late, and very late coinfections were 24% (5/21), 17.6% (3/17), and 21.6% (11/51), respectively. That study, however, specifically included patients with symptoms suggestive of end-organ disease, graft dysfunction, or renal dysfunction (without symptoms), who may have harbored a high risk for infection. 14

Antiviral prophylaxis
Duration of follow-up Barani

| Graft dysfunction or loss
Three studies specifically reported on the frequency of graft dysfunction, rejection, or loss among CMV-EBV-coinfected patients. 13,14,17 In the study reporting the largest cohort with coin-

| PTLD
Of the seven studies that reported on PTLD, one liver transplantation study reported a single case of PTLD in the subgroup with EBV monoinfection only. 13 A study in renal transplantation reported a severe case of PTLD in a patient with EBV monoinfection and a case of mild PTLD in a patient without EBV infection. 16 Two studies in renal transplantation 8,17 and a single HSCT study 20 reported no cases of PTLD during the study period (Table 4).
Two studies described cases of PTLD in renal and HSCT recipients with CMV-EBV coinfection, respectively. 15,19 In the random-  Two studies reported a relationship between donor/recipient serostatus and the propensity for CMV-EBV coinfection in renal transplant recipients. In the first study, all five CMV-EBV coinfections occurred in donor-positive/recipient-positive cases. 17 The second study identified donor CMV seropositivity as the only clinical variable significantly associated with combined CMV-EBV reactivation (P = .0127). 16 CMV-EBV coinfection was also significantly associated with CMV and EBV viral loads greater than detectable levels (250 copies/mL) (P = .0237) and with elevated CMV and EBV DNAemia (P = .0416). 16

F I G U R E 2
Post-transplantation CMV-EBV coinfection rates in SOT and HSCT recipients a Cases also included in the separate CMV and EBV cohorts. CMV, cytomegalovirus; EBV, Epstein-Barr virus; HSCT, hematopoietic stem cell transplant; SOT, solid organ transplant Another study found that CMV disease occurred slightly more frequently in renal transplant recipients with EBV reactivation. 8

| Timing of coinfection post transplantation
The time interval between transplantation and the detection of CMV-EBV coinfection was not the focus of the studies included in the SLR. However, a study of renal transplant recipients found that the subgroup presenting during the "immediate" post-transplantation period featured a higher proportion of patients with CMV-EBV coinfection (24%) compared with the subgroups presenting during later periods (<22% of patients). 14 A study of HSCT recipients with coinfection reported that the median time between CMV and EBV infection was 26 days. 20 In the two studies reporting the order of detection of CMV and EBV in patients with coinfection, detection of EBV preceded that of CMV in approximately 50% of patients in each study (Table 6). 16,18 One study reported only one case of concomitant detection of CMV and EBV. 18 Eight studies disclosed the time of detection for CMV or EBV  (Table 6). 8,13,14,[16][17][18][19][20] Only one study (renal transplantation) found that EBV DNAemia was detected in a higher proportion of patients assessed >1 year post transplantation than in those evaluated during earlier time periods. 14 However, patients were not TA B L E 4 Studies reporting on graft rejection/loss or PTLD as posttransplantation outcomes for CMV-EBV coinfection CMV-EBV coinfection rates (2.6%-33.0%). It was apparent, however, that the impact that CMV and EBV infections had on clinical outcomes, the viability of the allograft, and the development of PTLD represented a common primary concern for healthcare providers and in terms of patient outcomes. Despite these concerns, guidelines for the management of CMV and EBV monoinfection in transplant recipients do not include recommendations for the treatment of coinfections. [21][22][23][24] Graft dysfunction/loss is a major concern in transplant patients. respectively, for the two cases in one study, 15  in the SLR were conducted at single centers; and while most studies were prospective, very few aimed to establish the rate of infections or examine the outcomes of coinfected patients. Furthermore, in the studies, assessment of the differences between groups involved limited hypothesis testing, and the analyses conducted were not adjusted for covariates, potentially affecting outcomes. These factors may have contributed to the variances reported across the studies, notably regarding differences in coinfection rates.
A key finding of this SLR was that CMV and EBV infections seem to have an impact on the viability of the allograft that differs from monoinfection, which together with the development of PTLD represent a primary concern for the management of transplant recipients. As knowledge of the interplay of HHVs in the transplant setting continues to evolve, additional research specifically evaluating the rate of coinfection and outcomes of CMV-EBV coinfection is needed.
A better understanding of differing outcomes based on coinfection status could provide optimal methods for applying antiviral therapies and strategies aimed at CMV-EBV or other HHV combinations. and Consulting Services, which was funded by Shire, a Takeda company, to conduct this study.

AUTH O R CO NTR I B UTI O N S
All authors contributed to the conception or design of the work and interpretation of the data. All authors contributed to drafting of the work and revising it critically for intellectual content. The manuscript was drafted, critically revised, and finally approved by all of the named authors.

DATA AVA I L A B I L I T Y S TAT E M E N T
All data reported in this systematic literature review were obtained from the published literature.