BK virus infection: an update on diagnosis and treatment

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1 Nephrol Dil Trnsplnt (2015) 30: doi: /ndt/gfu023 Advnce Access publiction 25 Februry 2014 BK virus infection: n updte on dignosis nd tretment Deirdre Swinski nd Simin Gorl Renl, Electrolyte, nd Hypertension Division, University of Pennsylvni Medicl Center, Phildelphi, PA, USA Correspondence nd offprint requests to: Simin Gorl; E-mil: gorls@uphs.upenn.edu ABSTRACT BK virus, first isolted in 1971, is significnt risk fctor for renl trnsplnt dysfunction nd llogrft loss. Unfortuntely, tretment options for BK virus infection re limited, nd there is no effective prophylxis. Although overimmunosuppression remins the primry risk fctor for BK infection fter trnsplnttion, mle gender, older recipient ge, prior rejection episodes, degree of humn leukocyte ntigen mismtching, prolonged cold ischemi time, BK serosttus nd ureterl stent plcement hve ll been implicted s risk fctors. Routine screening for BK hs been shown to be effective in preventing llogrft loss in ptients with BK viruri or viremi. Reduction of immunosuppression remins the minsty of BK nephropthy tretment nd is the best studied intervention. Lbortory-bsed methods such s ELISPOT ssys hve provided new insights into the immune response to BK nd my help guide therpy in the future. In this review, we will discuss the epidemiology of BK virus infection, screening strtegies, tretment options nd future reserch directions. Keywords: BK virus, dignosis, kidney, trnsplnttion, tretment INTRODUCTION With the introduction of more potent immunosuppression regimens nd decresed cute rejection rtes, virl infections fter renl trnsplnttion hve emerged s n importnt cuse of llogrft loss. BK is common posttrnsplnt opportunistic virl infection, ffecting 15% of renl trnsplnt recipients in the first posttrnsplnt yer nd lcking n effective prophylxis strtegy. Tretment options re limited nd if unddressed, BK nephropthy (N) will progress to llogrft filure. In this review, we will ddress the utility of BK screening, methods of detection, new dignostic tools nd current mngement options. BK VIRUS The BK virus ws first isolted from the urine of renl trnsplnt recipient with ureteric stenosis in 1971 [1], but it ws not until 20 yers lter tht BK ws recognized s cuse of interstitil nephritis nd llogrft filure in renl trnsplnt recipients [2, 3]. BK is circulr, double-strnded DNA virus from the polyomvirus fmily, which includes JC virus nd SV40. The BK genome encodes three cpsid structurl proteins, such s virl cpsid protein 1 (VP1), VP2 nd VP3, s well s the lrge T nd smll t ntigens [4]. Bsed on DNA sequence vritions, BK cn be divided into six subtypes or genotypes. Genotype I is the most frequent worldwide (80%), followed by genotype IV (15%) [5]. Phylogenetic nlysis hs further identified four subgroups of subtype I (I/, I/b-1, I/b-2 nd I/c), nd six subgroups of subtype IV (IV/-1, IV/-2, IV/b-1, IV/b-2, IV/c-1 nd IV/c-2) [6]. As with subtype 1 subgroups, ech of the subtype 4 subgroups hs specific geogrphicl distribution pttern. Primry infection is often subclinicl or mnifests s mild respirtory illness nd is cquired in childhood; BK is ner ubiquitous in dults with seroprevlence of >80% [7]. After primry infection, the virus estblishes ltency in the uroepithelium nd renl tubulr epithelil cells. In the setting of immunosuppression, the virus rectivtes nd begins to replicte, triggering cscde of events strting with tubulr cell lysis nd viruri. The BK virus then multiplies in the interstitium nd crosses into the peritubulr cpillries, cusing viremi nd eventully invding the llogrft, leding to vrious tubulointerstitil lesions nd N. The outcome depends on the degree of dmge, inflmmtion nd fibrosis. Approximtely one-third of ptients with viruri will develop BK viremi () nd, without intervention, could progress to N (rtes rnging from 1 to 10%). We summrized the prevlence of viruri, viremi nd N reported in contemporry studies in Tble 1. BK rectivtion nd urinry shedding of BK virus hve been reported in otherwise helthy, immunocompetent ptients, but it is uncommon. Outside of renl trnsplnttion, BK is mostly encountered in bone mrrow trnsplnt recipients [15]; in these ptients, BK infec- The Author Published by Oxford University Press Downloded from on behlf of ERA-EDTA. All rights reserved. 209

2 tion cn present either s N or hemorrhgic cystitis. There hve been scttered cse series reporting detectble nd BK viruri in nonrenl solid orgn trnsplnt recipients [16 19] (hert, lung nd liver), but in generl the presence of BK in blood or urine hs not been ssocited with impired renl function in these ptients. RISK FACTORS The most consistent risk fctor identified cross studies for the development of N is the overll degree of immunosuppression [20]. Other hypothesized risk fctors for nd N include mle gender, older recipient ge, rejection episodes, degree of humn leukocyte ntigen (HLA) mismtching, prolonged cold ischemi, BK serosttus nd ureterl stent plcement [20, 21], but these hve not been uniformly observed in ll studies (Tble 2). Induction nd lso mintennce immunosuppression ppers to influence N risk. An nlysis of the Orgn Procurement nd Trnsplnttion Network (OPTN) dt from the USA by Dhrnidhrk et l. [25] surveyed the outcomes of over kidney trnsplnts performed between 2003 nd 2006; they demonstrted tht the use of rbbit nti-thymocyte globulin induction nd tcrolimus- or mycophenolte mofetil (MMF)-bsed immunosuppression incresed the risk for the development of. Interestingly, induction with lemtuzumb ws not significnt risk fctor in lrge registry study [25], congruent with other single-center retrospective cohort studies which lso filed to show n incresed incidence of in ptients dministered lemtuzumb [26 28]. The observtion tht mintennce immunosuppression impcts N risk is bolstered by secondry nlysis of dt from the DIRECT tril. The DIRECT tril ws prospective, rndomized tril of cyclosporine versus tcrolimus in conjunction with bsiliximb induction, designed to study the development of new-onset dibetes mellitus or impired fsting glucose in renl trnsplnt recipients. Hirsch et l. [14] performed secondry nlysis of the dt nd demonstrted tht ptients in the cyclosporine rm hd lower rte of t 6 nd 12 months posttrnsplnt, compred with the tcrolimus group. High-titer (>4 log) nd the overll medin BK virl lods were higher in the tcrolimus group. This study is suggestive of n effect of mintennce immunosuppression on BK rectivtion, but s it is secondry dt nlysis should be interpreted with cution; furthermore, ptients in the tcrolimus group were mintined t high trough levels (10 15 ng/ml during Months 1 3 nd 5 10 ng/ml during Months 4 6) nd exposed to higher doses of steroids erly on fter trnsplnt, which my hve ffected their risk of developing. The nlysis of ntionl registry dt [25] hs lso suggested n effect of mintennce steroids on the development of, lthough the hzrd rtio ssocited with steroid use ws modest (HR 1.16, 95% CI ). Prospective studies designed to ddress the effect of induction nd mintennce immunosuppression on N re wrrnted. Donor nd recipient chrcteristics my lso ply role in the development of nd N. An ssocition hs been described between specific HLA lleles nd the risk for BK; single-center report [22] noted tht the bsence of the HLA C7 llele in the donor or recipient incresed the risk for sustined in the recipient t lest 3-fold. Recipient rce my lso ffect ptient s risk of developing ; in prospective study designed to identify risk fctors for BK infection, Sood et l. [13] demonstrted tht lower proportion of Africn Americns developed, independent of other confounding risk fctors. Nonimmunosuppression-bsed interventions, such s ureterl stent plcement, cn lso confer the risk of developing BK. Atlest three single-center reports [9,23,24] hve described n incresed risk of in ptients who hd ureterl stent (OR ), suggesting tht perhps these ptients should be screened erlier or more often. Currently, unlike testing for cytomeglovirus, pretrnsplnt screening of donors nd recipients for BK seropositivity is neither mndtory nor routinely performed. Pretrnsplnt BK ntibodies re not clerly protective; pretrnsplnt BK seropositivity in dult recipients hs not been shown to influence the development of N fter trnsplnttion [8, 29]. However, there is growing evidence to suggest tht the donor kidney my be the source of posttrnsplnt nd N [22], nd tht pretrnsplnt screening of donors could identify which recipients re t gretest risk of developing BK. Bohl et l. [22] identified BK virus ntibody-positive donors s risk for posttrnsplnt in recipients; in their study, ptients who received kidney from BK-seropositive donor were more likely to develop BK infection (46%), compred with those whose kidney cme from seronegtive donor (15%). Overll, they found higher thn expected concordnce between donor nd recipient BK serosttus. Interestingly, ll of the pirs in which both donor nd recipients were BK ntibody-positive shred the sme virl subtype nd sequence, suggesting donor origin of the BK virus. Recipients of BK Tble 1. Summry of BK prevlence in contemporry studies employing prospective screening Reference Decoy cells (%) BK viruri (%) (%) BKNV (%) Grft loss due to BK (%) Hirsch et l. [8] Brennn et l. [9] Koukoulki et l. [10] Almers et l. [11] Thkur et l. [12] Sood et l. [13] Hirsch et l. [14] Prevlence of event not reported. 210 D. Swinski nd S. Gorl

3 Tble 2. Summry of proposed risk fctors for BK virus infection Donor risk fctors BK virus seropositive donor [22] Degree of HLA mismtching [21] HLA C7 [22] Recipient risk fctors Older recipient ge [21] Mle recipient [21] Recipient rce (non-africn Americn) [21] Dibetes [21] Trnsplnt risk fctors Acute rejection episodes [8] Cold ischemi time [21] Delyed grft function [21] Ureterl stent plcement [9,23,24] Anti-thymocyte globulin induction [25] Tcrolimus nd/or MMF-bsed mintennce immunosuppression [14] seropositive donor kidneys developed t erlier posttrnsplnt timepoints, hd higher virl titers nd were slower to cler the virus. These dt suggest role for donor pretrnsplnt serotyping s mens of BK risk ssessment nd immunosuppression mngement. SCREENING As N hs limited tretment options, the gol of screening is to fcilitte erly dignosis of ptients when viruric or viremic, nd to intervene prior to the development of overt nephropthy. Prospective screening studies hve demonstrted tht N is predominntly n erly compliction of renl trnsplnttion with most cses occurring within the first posttrnsplnt yer. In cohort of Greek renl trnsplnt recipients followed prospectively for 18 months fter trnsplnt [10], the incidence of viremi nd viruri peked t Month 3 with 28 nd 31%, respectively, of ptients testing positive. Incidence of BK peked second time t 12 months posttrnsplnt, but fewer cses overll were dignosed, nd only one cse ws reported with first detection of BK t 18 months posttrnsplnt. The French experience is similr; Almers et l. [11] followed 119 ptients for 12 months; in tht time period, 10.9% of ptients hd detectble nd the medin time to detectble virl lod ws 90 (23 214) dys. All viremic ptients hd llogrft biopsies nd only one ws dignosed with N; ll ptients hd n initil virl lod <4 log copies per ml (rnge log). Similr findings were noted by Thkur et l. [12]; of the 32 ptients they followed prospectively with BK virl lods nd protocol biopsies, the highest incidence of positive BK virl lods ws noted t 1 month posttrnsplnt nd none of the protocol biopsies demonstrted histology consistent with N. Bsed on these reports nd others, we routinely screen ll renl trnsplnt ptients t our center for strting t 3 months posttrnsplnt nd hve found tht new onset fter 24 months posttrnsplnt is rre [30]; we do not recommend screening beyond 24 months unless renl dysfunction is present. However, s per the recently published AST Infectious Disese Community of Prctice guidelines [21] nd older KDIGO guidelines [31], erlier (strting t 1 month posttrnsplnt) nd more frequent Tble 3. Summry of screening methods Screening method Positive predictive vlue (%) screening (monthly plsm screening for the first 6 months, then every 3 months until 2 yers posttrnsplnt) my be more pproprite in high incidence trnsplnt centers. Our center nd others [32, 33] hve found prospective screening for with subsequent immunosuppression reduction to be n effective mens of preventing llogrft loss due to N. Reported cute rejection rtes fter decrese in immunosuppression rnged from 8 to 12% nd most were responsive to steroid tretment [33, 34]. We recommend tht ptients who hve their immunosuppression reduced for should be monitored crefully with serum cretinine checked every 1 2 weeks nd BK virl lods repeted t 2 4 week intervls. SCREENING TESTS Negtive predictive vlue (%) Sensitivity (%) Decoy cells [8] Hufen [35] BK urine PCR [8, 36, 37] BK serum PCR [8, 36, 37] Specificity (%) BK virus is detectble in both blood nd urine. After BK rectivtion, the virus is first detectble in the urine, with viremi developing severl weeks lter. There hve been isolted cse reports of ptients developing viremi without viruri, but this is unusul. hs higher positive predictive vlue (PPV) for N (50 60%) thn BK viruri [34]; hence screening for is the preferred screening strtegy t mny institutions. Tble 3 summrizes the screening methods commonly used. BK virl lods re mesured by rel-time PCR; BK-specific sequence is mplified with fluorescent probe nd the number of mplicons produced is compred with stndrd curve generted with seril dilutions of known concentrtion of BK DNA. There is no estblished stndrd ssy, nd intrlbortory vritions in the ssy stndrds or protocols used cn yield significnt differences in the mount virus quntified nd limits of ssy detection. Vritions in smple type/ source, DNA extrction techniques, primer nd probe sequences, nd BK strin DNA used for stndrd curve cretion cn ll impct ssy results nd introduce cliniclly significnt vribility [34, 38]. Most quntittive PCR ssys use the genotype I (Dunlop) strin s the reference sequence ginst which primers nd probes re designed [39]. In comprison of the PCR results generted from seven different commercilly vilble kits using the Dunlop strin or the mixed ptient stndrd (MPS) s the reference sequence, discordnt results (>1 log difference) were found in 23% of ssys using the MPS nd 94% of ssys using Dunlop s the stndrd [40]. This effect ws most pronounced in the subtype III nd IV isoltes [40], nd ws ttributed to primer/probe mismtch s well s DNA sequence BK virus infection 211

4 polymorphisms. Another group [39] confirmed tht BK PCR ssys using the genotype I strin s the reference cn be s much s 4-fold less sensitive for vrint strins (limit of detection copies per μl for the vrint strin compred with 10 copies per μl for genotype I). This is problemtic s rre BK virus subtype vrints re more frequently ssocited with N [4], perhps due to the difficulty in detecting them t low virl lods. To limit intrlbortory fluctutions in BK PCR results, we recommend using consistent lbortory fcility to monitor single ptient whenever fesible nd to hve low clinicl suspicion for rre vrints when ptient s clinicl course does not correlte with his virl lod. Blood BK detection by rel-time PCR of plsm is very sensitive nd specific for the development of N. Depending on the study, sensitivity cn pproch 100% nd specificity is 90%, with PPV of 50% nd negtive predictive vlue (NPV) of 100% [8, 41]. This is the preferred screening method t most trnsplnt centers, including our own. A definitive virl lod cutoff ssocited with nephropthy hs not been estblished, but retrospective studies hve suggested tht BK virl lod >4 log copies/ml is strongly ssocited with finding N on biopsy [42]. Urine shedding in the urine is common nd cn occur in up to 30% of renl trnsplnt recipients [20]. Urine cn be screened for BK by cytology or by quntifiction of urine BK DNA by PCR. Tubulr epithelil cells infected with BK virus re shed in the urine nd re clled decoy cells (Figure 1). They hve lrge, bsophilic nuclei with virl inclusions nd pper similr to those seen in uroepithelil cncer. Urine BK PCR is more sensitive thn urine cytology for detection nd dignosis of N. In comprison of urine cytology with urine PCR, decoy cells hd sensitivity of only 25% nd specificity of 84% for N compred with urine PCR which ws 100% sensitive nd 78% specific[41]. This is in contrst to n erlier study in which urine decoy cells were found to be 100% sensitive nd 71% specific for N with positive FIGURE 1: Decoy cells in the urine. predictive vlue (PPV) of 29% nd NPV of 100% [8]. If only urine BK screening is to be performed, we recommend urine BK PCR s the superior ssy, using the threshold of > copies/ml s suggestive of N. Given the widespred vilbility of the plsm PCR ssy nd its greter predictive vlue for N, it is unnecessry to perform urine BK screening first before plsm testing. EM Hufen Hufen re icoshedrl ggregtes of polyomvirus prticles nd Tmm-Horsfll protein tht cn be detected in the urine of kidney trnsplnt ptients with N using negtive-stining electron microscopy. In single-center study [35] of 21 kidney trnsplnt recipients with biopsy-proven N, the presence of Hufen in the urine ws highly correlted (k 0.98) with N nd hd PPV of 97% for N. These results re intriguing nd require further study, but if vlidted could offer noninvsive lterntive for dignosing N. Urine mrna There is growing interest in the use of mrna profiles in nephrology s biomrker for ntive renl disese, cute rejection nd chronic llogrft dysfunction. BK virl cpsid protein 1 (VP1) mrna derived from urinry cells hs been studied s N biomrker [35]. In previous publiction [43], cutoff vlue of VP1 mrna/ng RNA ws estblished s threshold tht ws predictive of N. This threshold ws vlidted in second cohort of ptients [44], 12 of whom hd biopsy-proven N. Urine grnzyme B mrna nd protese inhibitor-9 mrna levels were lso shown to be predictive of subsequent decline in llogrft function, suggesting new res of future investigtion. Urine mrna profiles my provide dditionl dignostic nd prognostic informtion in ddition to renl trnsplnt biopsy. Renl biopsy Renl biopsy remins the gold stndrd for the dignosis of N. It is recommended in ptients with high level of (>4 log copies/ml), with or without n elevtion in serum cretinine. The histology of N is chrcterized by tubulr trophy nd fibrosis with n inflmmtory lymphocytic infiltrte tht cn be mistken for cute cellulr rejection. The presence of intrnucler BK virus inclusion bodies which stin positive for the lrge T ntigen is pthognomonic for N. Biopsy findings cn be focl in nture, nd long with the possibility of smpling error, mking dignosis on occsion chllenging. Owing to these chllenges, negtive biopsy cnnot rule out erly N with 100% certinty. A minimum of two cores including some medull is recommended to mke correct dignosis. The prognostic potentil of biopsy findings hs been studied; the degree of fibrosis nd tubulr trophy ppers to be the most predictive of llogrft outcome [45]. At lest three different histologic grding systems exist to clssify the degree of BK-relted injury seen on renl trnsplnt biopsy (Tble 4). The series from the Myo Clinic [48] ws the first to identify the utility of quntifying the number of infected tubulr cross-sections nd incorporting tht dt into the stndrd Bnff criteri for chronic llogrft injury, which 212 D. Swinski nd S. Gorl

5 ssesses interstitil fibrosis, tubulr trophy, rteril fibrous intiml thickening nd hyline rteriolosclerosis. More recently, Drchenberg et l. [46] t the University of Mrylnd hve proposed n lternte schem, which focuses predominntly on the degree of fibrosis nd inflmmtion. Msutni et l. [45] demonstrted tht inflmmtion nd fibrosis re importnt prognostic prmeters in determining the outcome of N, wheres induced tubulr injury nd histologic virl lod re not informtive, suggesting modifiction to the Bnff Working Proposl to incorporte the degree of inflmmtion into the morphologic criteri used for stging this disese. No single grding system hs emerged s predominnt. To dte, only the Bnff grding system hs been tested for introbserver vribility [47]; the Bnff working proposl hs been shown to hve modertely good introbserver greement, with kpp score of 0.47 ( , P < 0.001) [47]. The estblishment nd vlidtion of uniform grding system will be importnt for clinicl cre in order to ssess prognosis nd for clinicl trils of BK tretment to judge response to therpy. CELLULAR IMMUNE RESPONSE TO BK Cellulr dptive immunity is essentil for the control of nd resolution of N. CD4+ nd CD8+ T cells both hve role in BK clernce. T-cell responses re directed ginst both nonstructurl nd BK cpsid proteins nd cn be mesured vi ELISPOT nd tetrmer stining. Monitoring for the development of nti-bk T cells nd their functionlity my provide dditionl prognostic informtion regrding timeline for recovery. Anti-BK T cells cn be found in both helthy volunteers nd kidney trnsplnt recipients. Using tetrmers nd T cells from HLA-A*0201 individuls, Chen et l. [49] were ble to determine whether CD8s from helthy volunteers responded to different VP1 virl epitopes thn CD8 T cells from ptients with N. In trnsplnt recipients, strong CD8 response ws ssocited with lower BK virl lods in blood nd urine, wheres wek responses correlted with high BK titers nd virl persistence [49, 50]. Similr CD8 responses hve been elicited with the lrge T ntigen [51]. Interferon-γ ELISPOT ssys hve demonstrted tht CD4 responses re trgeted towrds the lrge T ntigen, VP1 cpsid protein [52] nd VP3 [53]. In further studies [54], the development of BK-specific cellulr immune responses s mesured by (interferon) IFN-γ ELISPOT correlted with resolution of N. Schchtner et l.[55] compred ELISPOT results from three groups of ptients those with N, those with trnsient viremi nd those who were BK seropositive but never viremic. All ptients with N or trnsient hd low or undetectble T-cell responses t the time of BK rectivtion. Ptients who clered the virus (limited viremi) developed nti-bk T-cell responses within 1 month fter dignosis nd the development of nti- BK T-cells coincided with clernce. Ptients with biopsy-proven N required significntly longer time (medin time 5 months) to develop nti-bk cellulr Tble 4. Summry of BK histology grding systems Bnff working proposl (2009) [45] Americn Society of Trnsplnttion (2013) [21] N stge University of Mrylnd (2001) [46] Polyomvirus Interdisciplinry work group (2005) [47] -Virl infection detected -Miniml tubulr epithelil cell lysis -No cute tubulr necrosis -Chronicity score <ci3 nd <ct3 -Virl infection/cytopthic chnges <25% -Interstitil inflmmtion <10% -Tubulr trophy <10% -Interstitil fibrosis <10% -Virl infection/cytopthic chnges <10% -Interstitil inflmmtion <10% -Tubulr trophy <25% -Fibrosis <25% Stge/Clss A -Any degree of virl infection/cytopthic chnges -Any degree of tubulr injury -No inflmmtion -Virl repliction in cortex or medull -Tubulr epithelil cell lysis -Virl cute tubulr necrosis -Chronicity score <ci3 nd <ct3 -Virl infection/cytopthic chnges 11 50% -Interstitil inflmmtion 11 50% (B %, B % nd B3 >50%) -Tubulr trophy <50% -Interstitil fibrosis <50% -Virl infection/cytopthic chnges <10 >50% -Interstitil inflmmtion 26 >50% -Tubulr trophy <25% -Interstitil fibrosis <25% Stge/Clss B -Any degree of virl infection/cytopthic chnges -Any degree tubulr injury -Inflmmtion <25 >50% -Virl repliction in cortex or medull -Chronicity score = ci3 nd ct3 -Vrible virl infection/cytopthic chnges -Vrible inflmmtion -Tubulr trophy >50% -Interstitil fibrosis >50% -Virl infection/cytopthic chnges <10 >50% -Interstitil inflmmtion <10 >50% -Tubulr trophy >50% -Interstitil fibrosis >50% Stge/Clss C -Any degree of virl infection/cytopthic chnges -Any degree of tubulr injury ->50% tubulr trophy or fibrosis BK virus infection 213

6 immunity. T-cell responses to structurl proteins VP1, VP2 nd VP3 were detected erlier thn those ginst the smll t nd lrge T ntigens. Cytokine production by BK-specific T cells is lso informtive. Trydzensky et l. [56] mesured the percentge of polyfunctionl, BK-specific IFN-γ/interleukin-2/tumor necrosis fctor-α producing CD4 T cells in three groups of ptients: those with prolonged high-titer BK rectivtion, those with virl clernce in <3 months nd those with BK seropositivity but no rectivtion. In their nlysis, they found tht ptients with rpid clernce nd those who were seropositive only hd higher frequencies of polyfunctionl, nti-bk CD4 T cells. Assys to ssess BK-directed cellulr immunity nd nti-bk T-cell phenotype my provide dditionl prognostic informtion regrding virl clernce nd ptient recovery, nd re n ctive re of investigtion. TREATMENT Reduction of immunosuppression is the minsty of N tretment. Mngement pproches differ nd cn include discontinution of the nti-metbolite, dose reduction of the clcineurin inhibitor (CNI) by 25 50% trgeting significntly lower levels (tcrolimus 3 4 ng/ml nd cyclosporine ng/ml, or even less) or switching from tcrolimus to cyclosporine (Tble 5). Discontinution of the nti-metbolite such s MMF is the most common pproch, but recent study [63] suggests tht both tcrolimus nd cyclosporine cn inhibit nti-bk T- cell responses in vitro, chllenging this prctice. Other tretment lterntives cn include use of leflunomide, cidofovir, ciprofloxcin, rpmycin or intrvenous immunoglobulin (Tble 5). Objective dt regrding BK tretment re limited; met-nlysis [64] of ll published pproches to BK tretment found only 3 rndomized controlled trils, 9 cohort studies nd 29 cse series. Regrdless of the tretment strtegy employed, rpid virl reduction hs been ssocited with stble or improving glomerulr filtrtion rte (GFR) [65]. Screening with subsequent immunosuppression reduction ws shown to be effective in preventing llogrft loss in singlecenter studies. Schub et l. [33] followed 194 renl trnsplnt recipients for 5 yers posttrnsplnt; ptients with detectble hd their CNI dose decresed in stepwise fshion. resolved in 92% of ptients nd no difference ws observed in 1- nd 3-yer llogrft survivl between the BK-viremi group nd the no group. Another single-center report [13] in which both the CNI nd MMF were reduced simultneously showed similr results; declined in most ptients while estimted GFR (egfr) remined stble nd no llogrfts were lost in the group. A longer term follow-up is eqully encourging. Hrdinger et l. [59] demonstrted t 5-yer follow-up of their cohort of 194 ptients similr efficcy nd sfety for immunosuppression reduction s in the shorter term studies. In their study, ptients with or N treted with immunosuppression reduction hd no difference in ptient or llogrft survivl compred with those without. Ptients mintined on tcrolimus-contining regimens were shown to hve lower cute rejection rtes nd higher egfrs despite BK. In their met-nlysis, Johnston et l. [64] did not find n llogrft survivl benefit with the ddition of cidofovir or leflunomide to immunosuppression reduction, nd clinicl studies Tble 5. Summry of tretment strtegies for nd N Tretment Reference Immunosuppression djustment strtegy Immunosuppression reduction Hirsch et l. [8] Vried; CNI minimiztion or switch of gent Almers et l. CNI nd MMF dose reduction [57] simultneously Weiss et l. [58] Withdrwl of CNI or MMF versus dose reduction of both CNI nd MMF Schub et l. [33] CNI minimiztion followed by discontinution of MMF Hrdinger et l. [59] MMF discontinution followed by minimiztion of the CNI Ptients with or N Outcome Adverse events 5 4/5 clered -Three episodes of rejection -No llogrft losses to N 11 8/11 clered -Three episodes of rejection -No llogrft losses to N 35 19/35 retin -CNI withdrwl is ssocited with llogrft superior llogrft survivl compred function with dose reduction strtegy 38 35/38 clered 23 12/23 clered Leflunomide Fguer et l. [60] MMF replced with leflunomide 11 5/11 clered Lec et l. [61] MMF replced with low-dose or 21 11/21 clered high-dose leflunomide Cidofovir Kuypers et l. MMF/CNI reduction with/without 21 6/8 cidofovir [62] djuvnt cidofovir ptients clered -Three episodes of cute rejection -No grft losses due to BK -No difference in ptient or kidney survivl with BK -Five episodes of cute rejection -No grft losses due to BK -Ptient survivl ws inferior in the BK group, but llogrft survivl ws similr -One episode of cute rejection -One grft lost to N -Four grft losses -Two cute rejections in the cidofovir group -No grft losses in the cidofovir group 214 D. Swinski nd S. Gorl

7 re t best inconclusive. One single-center tril [62] of 21 ptients compred immunosuppression reduction lone versus ddition of cidofovir nd found better llogrft survivl with cidofovir use but no difference in BK clernce. Mny other studies [66, 67] hve filed to find benefit with cidofovir use, nd the risk of renl side effects is significnt. In singlecenter cse series [68], leflunomide ws reported to be n effective tretment for N nd only 5% of ptients treted lost their llogrfts; however, most studies hve not demonstrted benefit with the ddition of this gent. At this time, we do not recommend the use of cidofovir or leflunomide s djuvnt therpy for N. A phse II tril [69] hs looked t the efficcy of FK778 for the tretment of N. FK778 is derivtive of the ctive metbolite of leflunomide nd inhibits pyrimidine biosynthesis to prevent lymphocyte prolifertion. FK778 did decrese nd BK viruri in ptients treted with it, but cute rejection rtes nd incidence of llogrft loss in the FK778 tretment group were much higher thn in the immunosuppression reduction group [69]. No further studies using FK778 re plnned t this time. CONCLUSION BK infection is reltively common nd erly posttrnsplnt compliction fter kidney trnsplnttion. Creful screening cn prevent llogrft loss nd should be employed. Serum BK PCR is the preferred screening method but lterntives exist. Trnsltionl lbortory-bsed ssys re being developed tht my provide dditionl informtion regrding ptient clinicl course in the future. The minsty of tretment remins creful reduction of immunosuppression nd close monitoring for the development of cute rejection. Prospective studies with longer follow-up re still needed to evlute different tretment strtegies while ssessing the possibility of chronic llogrft dysfunction due to systemtic reduction of immunosuppression. CONFLICT OF INTEREST STATEMENT The uthors hve no finncil conflicts of interest to disclose. UPDATE: CLINICAL TRIALS There re currently four BK infection tretment trils open on the NIH clinicl trils website ( [70]; three re ctively recruiting ptients (NCT , NCT nd NCT ) nd the fourth is enrolling by invittion only t this time (NCT ). NCT is rndomized, plcebo controlled tril of ciprofloxcin for the prevention of or N. NCT is rndomized tril compring the efficcy of reduction of immunosuppression versus substitution of tcrolimus for sirolimus for the tretment of or N. NCT is n openlbel tril using combintion of leflunomide nd orotic cid in ptients with high levels of BK viruri. In the fourth tril, NCT , ptients with will be rndomized to either 50% mycophenolte dose reduction or substitution of MMF with everolimus. These trils will hopefully provide new therpeutic options for ptients with nd N. RETRANSPLANTATION Retrnsplnttion fter llogrft loss due to N is resonble option. A recent review of the OPTN dtbse [71] for trnsplnts performed from June 2004 to December 2008 reveled tht 823 llogrfts were lost to N during this time period. Of the 126 retrnsplnts, only one kidney ws lost due to recurrent N. One- nd 3-yer llogrft survivl in the retrnsplnted ptients ws excellent t 98.5 nd 93.6%, respectively [71]. Although kidney trnsplnt loss due to N should not be brrier to retrnsplnttion, pretrnsplnt clernce of BK virl lod is necessry. Trnsplnt nephrectomy in ptients with filed grft due to N hs not been found protective fter retrnsplnttion. REFERENCES 1. Grdner SD, Field AM, Colemn DV et l. New humn ppovvirus (BK) isolted from urine fter renl trnsplnttion. Lncet 1971; 1: Purighll R, Shpiro R, McCuley J et l. BK virus infection in kidney llogrft dignosed by needle biopsy. Am J Kidney Dis 1995; 26: Rndhw PS, Finkelsteing S, Scntelbury V et l. Humn polyom virusssocited interstitil nephritis in the llogrft kidney. Trnsplnttion 1999; 67: Tremold S, Akn S, Otte J et l. Rre subtypes of BK virus re vible nd frequently detected in renl trnsplnt recipients with BK virus-ssocited nephropthy. Virology 2010; 404: Tksk T, Goy N, Tokumoto T et l. Subtypes of BK virus prevlent in Jpn nd vrition in their trnscriptionl control region. J Gen Virol 2004; 85: Zhong S, Rndhw PS, Ikegy H et l. Distribution ptterns of BK polyomvirus () subtypes nd subgroups in Americn, Europen, nd Asin popultions suggest co-migrtion of nd the humn rce. J Gen Virol 2009; 90: Stolt A, Ssnusks K, Koskel P et l. Seroepidemiology of the humn polyomviruses. J Gen Virol 2003; 84: Hirsch HH, Knowles W, Dickenmnn M et l. Prospective study of polyomvirus type BK repliction nd nephropthy in renl trnsplnt recipients. N Engl J Med 2002; 347: Brennn DC, Agh I, Schnitzler MA et l. Incidence of BK with tcrolimus versus cyclosporine nd impct of preemptive immunosuppression reduction. Am J Trnsplnt 2005; 5: Koukoulki M, Grispou E, Pistols D et l. Prospective monitoring of BK virus repliction in renl trnsplnt recipients. Trnspl Infect Dis 2009; 11: Almers C, Vetromile F, Grrigue V et l. Monthly screening for BK viremi is n effective strtegy to prevent BK virus nephropthy in renl trnsplnt recipients. Trnspl Infect Dis 2011; 13: Thkur R, Aror S, Nd R et l. Prospective monitoring of BK virus rectivtion in renl trnsplnt recipients in North Indi. Trnspl Infect Dis 2011; 13: Sood P, Sennyke S, Sujeet K et l. Mngement nd outcome of BK viremi in renl trnsplnt Recipients: prospective single center study. Trnsplnttion 2012; 94: Hirsch HH, Vincenti F, Frimn S et l. Polyomvirus BK repliction in denovo kidney trnsplnt ptients receiving tcrolimus or cyclosporine: BK virus infection 215

8 prospective, rndomized, multicenter study. Am J Trnsplnt 2013; 13: Hririn A, Klssen DK. BK virus infection fter nonrenl trnsplnt. Grft 2002; 5: S58 S Brber CE, Hewlett TJ, Geldenhuys L et l. BK virus nephropthy in hert trnsplnt recipients: cse report nd review of the literture. Trnspl Infect Dis 2006; 8: Munoz P, Foged M, Bous E et l. Prevlence of BK virus repliction mong recipients of solid orgn trnsplnts. Clin Infect Dis 2005; 41: Loeches B, Vleri M, Perez M et l. BK virus in liver trnsplnt recipients: prospective study. Trnsplnt Proc 2009; 41: Remund KF, Best M, Egn JJ. Infections relevnt to lung trnsplnttion. Proc Am Thorc Soc 2009; 6: Wisemn AC. Polyomvirus Nephropthy: current perspective nd clinicl considertions. Am J Kidney Dis 2009; 54: Hirsch HH, Rndhw P, nd The AST Infectious Diseses Community of Prctice. BK polyomvirus in solid orgn trnsplnttion. Am J Trnsplnt 2013; 13: Bohl DL, Storch GA, Ryschkewitsch C. et l. Donor origin of BK virus in renl trnsplnttion nd role of HLA C7 in susceptibility to sustined BK viremi. Am J Trnsplnt 2005; 5: Siprksy NF, Kushnir LF, Gllichio MH et l. Ureterl stents: risk fctor for polyomvirus BK viremi in kidney trnsplnt recipients undergoing protocol screening. Trnsplnt Proc 2011; 43: Thoms A, Dropulic LK, Rhmn MH et l. Ureterl stents: novel risk fctor for polyomvirus nephropthy. Trnsplnttion 2007; 84: Dhrnidhrk VR, Cherikh WS, Abbott KC. An OPTN nlysis of ntionl registry dt on tretment of BK virus llogrft nephropthy in the United Sttes. Trnsplnttion 2009; 87: Cnnon RM, Brock G, Mrvin MR et l. Anlysis of BK virl infection fter lemtuzumb induction for renl trnsplnt. Trnspl Infect Dis 2012; 14: Ison MG, Prker M, Stosor V et l. Development of BK nephropthy in recipients of simultneous pncres-kidney trnsplnttion. Trnsplnttion 2009; 87: Theodoropoulos N, Wnt E, Penugond S et l. BK virus repliction nd nephropthy fter lemtuzumb-inducted kidney trnsplnttion. Am J Trnsplnt 2013; 13: Bohl DL, Brennn DC, Ryschkewitsch C et l. BK virus ntibody titers nd intensity of infections fter renl trnsplnttion. J Clin Virol 2008; 43: Trofe-Clrk J, Swinski D, Sprkes T et l. Single center experience with long-term prospective bk monitoring in renl trnsplnttion. In: Presented t Americn Trnsplnt Congress, Settle, Ksiske BL, Zeier MG, Chpmn JR et l. KDIGO clinicl prctice guideline for the cre of kidney trnsplnt recipients: summry. Kidney Int 2010; 77: Eyileten T, Trofe-Clrk J, Gorl S et l. Single center experience with prospective BK monitoring in renl trnsplnttion. In: Presented t Americn Trnsplnt Congress, Boston, Schub S, Hirsch HH, Dickenmnn M et l. Reducing immunosuppression preserves llogrft function in presumptive nd definitive polyomvirus ssocited nephropthy. Am J Trnsplnt 2010; 10: Bechert CJ, Schndig VJ, Pyne DA et l. Monitoring of BK virl lod in renl llogrft recipients by rel time PCR ssys. Am J Clin Pthol 2010; 133: Singh HK, Andreoni KA, Mden V et l. Presence of urinry Hufen ccurtely predicts polyomvirus nephropthy. J Am Soc Nephrol 2009; 20: Nickeleit V, Klimkit T, Binet IF et l. Testing for polyomvirus type BK DNA in plsm to identify renl llogrft recipients with virl nephropthy. N Engl J Med 2000; 342: Kuppchi S, Thoms B, Kokko KE. BK virus in the kidney trnsplnt ptient. Am J Med Sci 2013; 345: Trofe-Clrk J, Sprkes T, Gentile C et l. BK virus genotype vrince nd discordnt BK viremi PCR ssy results. Am J Trnsplnt 2013; 13: Rndhw P, Knt J, Shpiro R et l. Impct of genomic sequence vribility on quntittive PCR ssys for dignosis of polyomvirus BK infection. J Clin Microbiol 2011; 49: Hoffmn NG, Cook L, Atienz E et l. Mrked vribility of BK virus lod mesurement using quntittive rel time PCR mong commonly used ssys. J Clin Microbiol 2008; 46: Viscount HB, Eid AJ, Espy MJ et l. Polyomvirus polymerse chin rection s surrogte mrker of polyomvirus ssocited nephropthy. Trnsplnttion 2007; 84: Hirsch HH, Brennn DC, Drchenberg CB et l. Polyomvirus ssocited nephropthy in renl trnsplnttion: interdisciplinry nlyses nd recommendtions. Trnsplnttion 2005; 10: Ding R, Medeiros M, Ddhni D et l. Noninvsive dignosis of BK virus nephritis by mesurement of messenger RNA for BK virus VP1 in urine. Trnsplnttion 2002; 74: Ddhni D, Snopkowski C, Ding R et l. Vlidtion of noninvsive dignosis of BK virus nephropthy nd identifiction of prognostic biomrkers. Trnsplnttion 2010; 90: Msutni K, Shpiro R, Bsu A et l. The Bnff 2009 Working Proposl for polyomvirus nephropthy: criticl evlution of its utility s determinnt of clinicl outcome. Am J Trnsplnt 2012; 12: Drchenberg RC, Drchenberg CB, Ppdimitriou JC et l. Morphologicl spectrum of polyom virus disese in renl llogrfts: dignostic ccurcy of urine cytology. Am J Trnsplnt 2001; 1: Sr A, Worwichwong S, Benediktsson H et l. Interobserver greement for polyomvirus nephropthy grding in renl llogrfts using the working proposl from the 10th Bnff Conference on llogrft pthology. Humn Pthol 2011; 42: Buehrig CK, Lger DL, Stegll MD et l. Influence of surveillnce renl llogrft biopsy on dignosis nd prognosis of polyomvirus ssocited nephropthy. Kidney Int 2003; 64: Chen Y, Trofe J, Gordon J et l. Interply of cellulr nd humorl immune responses ginst BK virus in kidney trnsplnt recipients with polyomvirus nephropthy. J Virol 2006; 80: Chen Y, Trofe J, Gordon J et l. nd JCV lrge T ntigen-specific CD*+ T cell responses in HLA A0201+ kidney trnsplnt recipients with polyomvirus nephropthy nd ptients with progressive multifocl leukoencephlopthy. J Clin Virol 2008; 42: Rndhw PS, Popescu I, Mcedo C et l. Detection of CD8+ T cells sensitized to BK virus lrge T ntigen in helthy volunteers nd kidney trnsplnt recipients. Humn Immunol 2006; 67: Binggeli S, Egli A, Schub S et l. Polyomvirus BK specific cellulr immune response to VP1 nd lrge T ntigen in kidney trnsplnt recipients. Am J Trnsplnt 2007; 7: Meuller K, Schchtner T, Sttler A et l. BK-VP3 s new trget of cellulr immunity in BK virus infection. Trnsplnttion 2011; 91: Prosser SE, Orents RJ, Jurgens L et l. Recovery of BK virus lrge T ntigen specific cellulr immune response correltes with resolution of BK virus nephritis. Trnsplnttion 2008; 88: Schchtner T, Muller K, Stein M et l. specific immunity kinetics: predictor of recovery from polyomvirus BK ssocited nephropthy. Am J Trnsplnt 2011; 11: Trydzensky H, Sttler A, Muller K et l. Novel pproch for improved ssessment of phenotypic nd functionl chrcteristics of specific T cell immunity. Trnsplnttion 2011; 92: Almers C, Foulongne V, Grrigue V et l. Does reduction in immunosuppression in viremic ptients prevent BK virus nephropthy in de novo renl trnsplnt recipients? A prospective study. Trnsplnttion 2008; 85: Weiss AS, Grll J, Chn L et l. Aggressive immunosuppression minimiztion reduces grft loss following dignosis of BK virus-ssocited nephropthy: comprison of two reduction strtegies. Clin J Am Soc Nephrol 2008; 3: Hrdinger KL, Koch MJ, Bohl DJ et l. BK virus nd the impct of preemptive immunosuppression reduction: 5 yer results. Am J Trnsplnt 2010; 10: Fguer S, Hirsch HH, Kmr N et l. Leflunomide tretment for polyomvirus BK ssocited nephropthy fter kidney trnsplnttion. Trnsplnt Int 2007; 20: D. Swinski nd S. Gorl

9 61. Lec N, Muczynski KA, Jefferson JA et l. Higher levels of leflunomide re ssocited with hemolysis nd re not superior to lower levels for BK virus clernce in renl trnsplnt ptients. Clin J Am Soc Nephrol 2008; 3: Kuypers DR, Vndooren AK, Lerut E et l. Adjuvnt low dose cidofovir therpy for BK polyomvirus interstitil nephritis in renl trnsplnt recipients. Am J Trnsplnt 2005; 5: Elgi A, Kohli S, Dickenmnn M et l. Inhibition of polyomvirus BK specific T cell responses by immunosuppressive drugs. Trnsplnttion 2009; 88: Johnston O, Jswl D, Gill JS et l. Tretment of polyomvirus infection in kidney trnsplnt recipients: systemtic review. Trnsplnttion 2010; 89: Schwrz A, Linnenweber-Held S, Heim A et l. Fctors influencing virl clering nd renl function during polyomvirus BK-ssocited nephropthy fter renl trnsplnttion. Trnsplnttion 2012; 94: Burgos D, Lopez V, Cbello M et l. Polyomvirus BK nephropthy: the effect of n erly dignosis on renl function or grft loss. Trnsplnt Proc 2006; 38: Wdei HM, Rule AD, Lewin M et l. Kidney trnsplnt function nd histologicl clernce of virus following dignosis of polyomvirus ssocited nephropthy (PVAN). Am J Trnsplnt 2006; 6: Josephson MA, Gillen D, Jvid B et l. Tretment of renl llogrft polyomvirus BK infection with leflunomide. Trnsplnttion 2006; 81: Gusch A, Roy-Chudhury P, Woodle ES et l. Assessment of efficcy nd sfety of FK778 in comprison with stndrd cre in renl trnsplnt recipients with untreted BK nephropthy. Trnsplnttion 2010; 90: (22 December 2013, dte lst ccessed) 71. Dhrnidhrk VR, Cherikh WS, Neff R et l. Retrnsplnttion: fter BK virus nephropthy in prior kidney trnsplnt: n OPTN dtbse nlysis. Am J Trnsplnt 2010; 10: Received for publiction: ; Accepted in revised form: Nephrol Dil Trnsplnt (2015) 30: doi: /ndt/gfu212 Advnce Access publiction 6 June 2014 Strtegies to increse the donor pool nd ccess to kidney trnsplnttion: n interntionl perspective Umberto Mggiore 1, Riner Oberbuer 2, Julio Pscul 3, Ondrej Viklicky 4, Chris Dudley 5, Klemens Budde 6, Soren Schwrtz Sorensen 7, Mrc Hzzn 8, Mrin Klinger 9 nd Dniel Abrmowicz 10 for the ERA-EDTA-DESCARTES Working Group 1 Deprtment of Nephrology, Aziend Ospedliero-Universitri di Prm, Prm, Itly, 2 KH Elisbethinen Linz nd Deprtment of Nephrology, Medicl University of Vienn, Vienn, Austri, 3 Deprtment of Nephrology, Hospitl del Mr, Brcelon, Spin, 4 Deprtment of Nephrology, Institute for Clinicl nd Experimentl Medicine, Prgue, Czech Republic, 5 Richrd Bright Renl Unit, Bristol, UK, 6 Deprtment of Nephrology, Chrité Medicl University Berlin, Berlin, Germny, 7 Deprtment of Nephrology P, Rigshospitlet, University of Copenhgen, Copenhgen, Denmrk, 8 Service de Néphrologie, Univ Lille Nord de Frnce, Lille, Frnce, 9 Deprtment of Nephrology nd Trnsplnttion Medicine, Wroclw Medicl University, Wroclw, Polnd nd 10 Deprtment of Nephrology, Antwerp University Hospitl, Antwerp, Belgium Correspondence nd offprint requests to: Umberto Mggiore; E-mil: umberto_mggiore@hotmil.com ABSTRACT In this position rticle, DESCARTES (Developing Eduction Science nd Cre for Renl Trnsplnttion in Europen Sttes) bord members describe the current strtegies imed t expnding living nd decesed donor kidney pools. The rticle focuses on the recent progress in desensitiztion nd kidney pired exchnge progrmmes nd on the expnded criteri for The Author Published by Oxford University Press on behlf of ERA- EDTA. This is n Open Access rticle distributed under the terms of the Cretive Commons Attribution Non-Commercil License ( licenses/by-nc/3.0/), which permits non-commercil re-use, distribution, nd reproduction in ny medium, provided the originl work is properly cited. For Downloded from commercil re-use, plese contct journls.permissions@oup.com the use of donor kidneys nd orgns from donors fter circultory deth. It lso highlights differences in policies nd prctices cross different regions with specil regrd to Europen Union countries. Living donor kidney pired exchnge, the decesed donor Acceptble Mismtch Progrmme nd kidneys from donors fter circultory deth re probbly the most promising innovtions for expnding kidney trnsplnttion in Europe over the coming decde. To mximize success, n effort is needed to stndrdize trnsplnt strtegies, policies nd legisltion cross Europen countries. 217