Human polyoma virus-associated interstitial nephritis in the allograft kidney

BK virus replication in renal transplant recipients: Analysis of potential risk factors may contribute in reactivation

BACKGROUND

Considering the increasing problem of BK virus infection during post renal transplant surveillance, it is necessary to distinguish the main risk factors leading to reactivation of latent BK virus. Up to now, some probable risk factors have been investigated in some studies, but the results have been confusing and contradictory.

OBJECTIVES

The goal of the present study was to determine the frequency and potential risk factors that may play a role in BK polyomavirus reactivation and nephropathy.

STUDY DESIGN

In this cross-sectional study, 110 patients, who underwent consecutive transplantation between 2010 and 2013, were enrolled without preliminary screening. Urine and blood samples were taken, and quantitative Real-time PCR assay was used to detect and measure the viral load. Demographic and clinical characteristics of the patients who had BK viremia and/or viruria were documented.

RESULTS

Among 110 cases of renal transplant recipients, BK viruria and viremia were found in 54 (49%) and 22 people (20%) respectively. The pre-transplant durations of dialysis among patients with BK viruia were found longer in comparison to BK negative patients. Treatment with Tacrolimus (p=0.03) was found to be a risk factor for development of BK viruria. In patients with viruria and viremia the median creatinine levels were 1.45mg/dl and 1.35mg/dl respectively, which were higher than those in the patients with negative results for BK viruria (p=0.002) and viremia (p=0.02). Also, treatment with Cyclosporine could significantly increase the incidence of BK virus shedding in both urine and blood among patients who received it (p=0.01). Significant relation between reactivation of BK virus and other factors such as age, sex, acute rejection and diabetes was not found.

CONCLUSION

Based on our findings, the main potential risk factors for shedding of BK virus into urine in renal transplant recipients were prolonged pre-transplant dialysis and Tacrolimus regimen. Cyclosporine regimens could be considered as risk factor for both BK viruria and viremia. A significant correlation between BK virus replication and elevated creatinine level was seen among our patients.

BK Virus Nephropathy: Histological Evolution by Sequential Pathology

Reactivation of BK virus in renal allografts causes a destructive chronic infection. This single-center retrospective cohort study describes the evolution of BK virus allograft nephropathy (BKVAN) from 63 kidneys (from 61 patients) using sequential histopathology (454 biopsies, averaging 7.8 ± 2.6 per kidney) followed for 60.1 mo. Uninfected protocol biopsies formulated time-matched control Banff scores (n = 975). Interstitial inflammation occurred in 73% at diagnosis, correlating with viral histopathology (r = 0.413, p = 0.008) and amplifying early injury with accelerated interstitial fibrosis and tubular atrophy (IF/TA, p = 0.017) by 3 mo. Prodromal simian virus 40 large T antigen (SV40T)-negative inflammation with viremia preceded the histological diagnosis in 23.8%. Persistent subacute injury from viral cytopathic effect was associated with acute tubular necrosis and ongoing interstitial inflammation, culminating in IF/TA in 86.9%. Overall, cellular interstitial infiltration mitigated the intensity of subsequent tubular injury, SV40T, and tissue viral load, assessed by sequential paired histology (p < 0.001). Graft loss was predicted by high-level viremia (hazard ratio [HR] 4.996, 95% CI 2.19-11.396, p < 0.001), deceased donor (HR 3.201, 95% CI 1.149-8.915, p = 0.026), and late acute rejection (HR 3.124, 95% CI 1.037-9.413, p = 0.043). Transplant failure occurred in 38.1%, with uncontrolled infection (58.3%) and SV40T-negative chronic rejection (41.7%) causing losses. BKVAN is characterized by subacute virus-induced tubular injury, inflammation, and progressive nephron destruction. Effective antiviral therapy remains an unmet clinical need.

BK polyomavirus: a review of the virology, pathogenesis, clinical and laboratory features, and treatment

BK polyomavirus (BKPyV) is a non-enveloped, circular dsDNA virus with a genome of approximately 5100 base pairs. It can be divided into four major genotypes, but the effects of different genotypes on clinical disease are uncertain. Primary BKPyV infection is generally acquired asymptomatically in childhood. It establishes low-level persistence in many tissues, particularly the genitourinary tract. Reactivation can lead to severe disease including BKPyV-associated nephropathy confirmed by renal biopsy, hemorrhagic cystitis and meningoencephalitis. Nucleic acid amplification testing of blood and urine is the main diagnostic and prognostic test for BKPyV infection. The treatment of BKPyV infection has concentrated on reduction in immunosuppressive therapy. Recent studies suggest that antiviral drugs have demonstrated only modest benefit, but adoptive T-cell therapies offer potential advances.

Genitourinary Tract Infections

Similarly to the general population, genitourinary tract infections are common conditions in theimmunocompromised host. They can be furthermore divided into infections of the urinary tract and genital tract infections. Transplant recipients are more likely to have infections of the urinary tract infections while persons with human immunodeficiency virus (HIV) are at higher risk for the second group of infections, especially sexually transmitted infections (STIs). Manifestations of these diseases can be associated with more complications and can be more severe. We provide an overview of manifestations, diagnosis, and management of these disorders.

BK Polyomavirus and the Transplanted Kidney: Immunopathology and Therapeutic Approaches

BK polyomavirus is ubiquitous, with a seropositivity rate of over 75% in the adult population. Primary infection is thought to occur in the respiratory tract, but asymptomatic BK virus latency is established in the urothelium. In immunocompromised host, the virus can reactivate but rarely compromises kidney function except in renal grafts, where it causes a tubulointerstitial inflammatory response similar to acute rejection. Restoring host immunity against the virus is the cornerstone of treatment. This review covers the virus-intrinsic features, the posttransplant microenvironment as well as the host immune factors that underlie the pathophysiology of polyomavirus-associated nephropathy. Current and promising therapeutic approaches to treat or prevent this complication are discussed in relation to the complex immunopathology of this condition.

Tacrolimus Blood Level Fluctuation Predisposes to Coexisting BK Virus Nephropathy and Acute Allograft Rejection

BK virus nephropathy (BKVN) and allograft rejection are two distinct disease entities which occur at opposite ends of the immune spectrum. However, they coexist in renal transplant recipients. Predisposing factors for this coexistence remain elusive. We identified nine biopsy-proven BKVN patients with coexisting acute rejection, and 21 patients with BKVN alone. We retrospectively analyzed the dosage and blood concentrations of immunosuppressants during the 3-month period prior to the renal biopsy between the two patient groups. Compared to the BKVN alone group, renal function was noticeably worse in the coexistence group (p = 0.030). Regarding the dose and average drug level of immunosuppressants, there was no difference between the two groups. Interestingly, the coefficient of variance of tacrolimus trough blood level was noticeably higher during the 3-month period prior to the renal biopsy in the coexistence group (p = 0.010). Our novel findings suggest that a higher variability of tacrolimus trough level may be associated with the coexistence of BKVN and acute rejection. Since the prognosis is poor and the treatment is challenging in patients with coexisting BKVN and acute rejection, transplant clinicians should strive to avoid fluctuations in immunosuppressant drug levels in patients with either one of these two disease entities.

Specific IgG Antibodies React to Mimotopes of BK Polyomavirus, a Small DNA Tumor Virus, in Healthy Adult Sera

BK polyomavirus (BKPyV) was isolated in 1971 from the urine of a kidney transplant patient. Soon after its identification, BKPyV was characterized as a kidney-tropic virus, which is responsible of a significant fraction of the rejection of transplant kidney in the host. Moreover, in experimental conditions, BKPyV is able to transform different types of animal and human cells and to induce tumors of different histotypes in experimental animals. BKPyV DNA sequences have been detected in healthy individuals and cancer patients using polymerase chain reaction/Shouthern blot hybridization methods. Serum antibodies against this polyomavirus were revealed using immunological techniques, which, however, cross-react with other polyomaviruses such as JC (JCPyV) and Simian Virus 40. These non-specific data indicate the need of novel immunological methods and new investigations to check in a specific manner, BKPyV spread in humans. To this aim, mimotopes from BKPyV structural capsid protein 1 (VP1) were employed for specific immunological reactions to IgG antibodies of human serum samples. An indirect enzyme-linked immunosorbent assay with synthetic peptides mimicking immunogenic epitopes of BKPyV VP1 was set up and employed to test sera of healthy adult subjects. Data from this innovative immunological assay indicate that serum antibodies against BKPyV VP1 mimotopes are detectable in healthy subjects ranging from 18 to 90 years old. The overall prevalence of serum samples that reacted to BKPyV VP1 mimotopes was 72%. The strong points from this investigation are the novelty of the immunological method, its simplicity of the approach, and the specificity of BKPyV antibody reaction to VP1 mimotopes.

Sex differences in transplantation

Sex plays a role in the incidence and progression of a wide variety of diseases and conditions related to transplantation. Additionally, a growing body of clinical and experimental evidence suggests that sex can impact the pharmacokinetics and pharmacodynamics of several commonly used immunosuppressive and anti-infective drugs in transplant recipients. A better understanding of these sex differences will facilitate advances in individualizing treatment for patients and improve outcomes of solid organ transplantation. Here, we provide a review of sex-related differences in transplantation and highlight opportunities for future research directions.

Imperfect Symmetry of Sp1 and Core Promoter Sequences Regulates Early and Late Virus Gene Expression of the Bidirectional BK Polyomavirus Noncoding Control Region

Rearrangements or point mutations in the noncoding control region (NCCR) of BK polyomavirus (BKPyV) have been associated with higher viral loads and more pronounced organ pathology in immunocompromised patients. The respective alterations affect a multitude of transcription factor binding sites (TFBS) but consistently cause increased expression of the early viral gene region (EVGR) at the expense of late viral gene region (LVGR) expression. By mutating TFBS, we identified three phenotypic groups leading to strong, intermediate, or impaired EVGR expression and corresponding BKPyV replication. Unexpectedly, Sp1 TFBS mutants either activated or inhibited EVGR expression when located proximal to the LVGR (sp1-4) or the EVGR (sp1-2), respectively. We now demonstrate that the bidirectional balance of EVGR and LVGR expression is dependent on affinity, strand orientation, and the number of Sp1 sites. Swapping the LVGR-proximal high-affinity SP1-4 with the EVGR-proximal low-affinity SP1-2 in site strand flipping or inserting an additional SP1-2 site caused a rearranged NCCR phenotype of increased EVGR expression and faster BKPyV replication. The 5' rapid amplification of cDNA ends revealed an imperfect symmetry between the EVGR- and LVGR-proximal parts of the NCCR, consisting of TATA and TATA-like elements, initiator elements, and downstream promoter elements. Mutation or deletion of the archetypal LVGR promoter, which is found in activated NCCR variants, abrogated LVGR expression, which could be restored by providing large T antigen (LTag) in trans Thus, whereas Sp1 sites control the initial EVGR-LVGR expression balance, LTag expression can override inactivation of the LVGR promoter and acts as a key driver of LVGR expression independently of the Sp1 sites and core promoter elements.

IMPORTANCE

Polyomaviridae currently comprise more than 70 members, including 13 human polyomaviruses (PyVs), all of which share a bidirectional genome organization mediated by the NCCR, which determines species and host cell specificity, persistence, replication, and virulence. Here, we demonstrate that the BKPyV NCCR is fine-tuned by an imperfect symmetry of core promoter elements centered around TATA and TATA-like sequences close to the EVGR and LVGR, respectively, which are governed by the directionality and affinity of two Sp1 sites. The data indicated that the BKPyV NCCR is poised toward EVGR expression, which can be readily unlatched by a simple switch affecting Sp1 binding. The resulting LTag, which is the major EVGR protein, drives viral genome replication, renders subsequent LVGR expression independently of archetypal promoter elements, and can overcome enhancer/promoter mutations and deletions. The data are pivotal for understanding how human PyV NCCRs mediate secondary host cell specificity, reactivation, and virulence in their natural hosts.

Unraveling the Role of Allo-Antibodies and Transplant Injury

Alloimmunity driving rejection in the context of solid organ transplantation can be grossly divided into mechanisms predominantly driven by either T cell-mediated rejection (TCMR) and antibody-mediated rejection (ABMR), though the co-existence of both types of rejections can be seen in a variable number of sampled grafts. Acute TCMR can generally be well controlled by the establishment of effective immunosuppression (1, 2). Acute ABMR is a low frequency finding in the current era of blood group and HLA donor/recipient matching and the avoidance of engraftment in the context of high-titer, preformed donor-specific antibodies. However, chronic ABMR remains a major complication resulting in the untimely loss of transplanted organs (3-10). The close relationship between donor-specific antibodies and ABMR has been revealed by the highly sensitive detection of human leukocyte antigen (HLA) antibodies (7, 11-15). Injury to transplanted organs by activation of humoral immune reaction in the context of HLA identical transplants and the absence of donor specific antibodies (17-24), strongly suggest the participation of non-HLA (nHLA) antibodies in ABMR (25). In this review, we discuss the genesis of ABMR in the context of HLA and nHLA antibodies and summarize strategies for ABMR management.

Management of Opportunistic Infections in Solid-Organ Transplantation

Solid-organ transplantation is often the last alternative in many patients with end-stage organ disease. Although advances in immunosuppressive regimens, surgical techniques, organ preservation, and overall management of transplant recipients have improved graft and patient survival, infectious complications remain problematic. Bacterial, fungal, viral, and parasitic infections are implicated after transplantation depending on numerous factors, such as degree of immunosuppression, type of organ transplant, host factors, and period after transplantation. Proper prophylactic and treatment strategies are imperative in the face of chronic immunosuppression, nosocomial and community pathogens, emerging drug resistance, drug-drug interactions, and medication toxicities. This review summarizes the pathophysiology, incidence, prevention, and treatment strategies of common post-transplant infections.

Polyomavirus Nephropathy in Kidney Transplantation

Polyomavirus nephropathy has become an important complication in kidney transplantation, with a prevalence of 1% to 8%. Unfortunately, the risk factors for polyomavirus nephropathy and renal allograft loss are not well defined. The definitive diagnosis is made through assessment of a kidney transplant biopsy. Recently, noninvasive urine and serum markers have been used to assist in polyomavirus nephropathy diagnosis and monitoring. Primary treatment is immunosuppression reduction, but must be balanced with the risks of rejection. No antiviral treatments for polyomavirus nephropathy have been approved by the Food and Drug Administration. Although cidofovir has shown in vitro activity against murine polyomaviruses, and has been effective in some patients, it is associated with significant nephrotoxicity. Graft loss due to polyomavirus nephropathy should not be a contraindication to retransplantation; however, experience is limited. This review presents potential risk factors, screening, diagnostic and monitoring methods, therapeutic management, and retransplantation experience for polyomavirus nephropathy.

Risk Factors for BK Polyoma Virus Treatment and Association of Treatment With Kidney Transplant Failure: Insights From a Paired Kidney Analysis

BACKGROUND

Identification of risk factors for BK polyoma virus (BKPyV) without confounding by donor factors and era effects in paired analysis may inform strategies to prevent BKPyV.

METHODS

In this analysis of 21,575 mate kidney pairs in the Scientific Registry of Transplant Recipients between 2004 and 2010, the presence of a treatment code for BKPyV virus in follow-up forms was used to identify pairs in which 1 of 2 mate kidneys was treated (discordant treatment) or both mate kidneys were treated (concordant treatment).

RESULTS

Among 1975 discordant pairs, younger than 18 years or 60 years or older, male sex, HLA mismatch or 4 greater, acute rejection, and depleting antibody induction had a higher odds of treatment, whereas diabetes and sirolimus had a lower odds of treatment, and treatment was associated with a higher risk of allograft failure (hazards ratio, 2.01; 95% confidence interval, 1.63-2.48). The rate of concordant treatment (0.81%) was 2.8 times higher than expected. Concordant treatment was associated with nonwhite donor ethnicity, donation after circulatory death, transplantation after 2008, and transplantation of mate kidneys in the same center.

CONCLUSIONS

This analysis of kidneys from the same donor in which only 1 transplant was treated for BKPyV identifies specific risk factors (age <18 or ≥ 60 years, male sex, depleting antibody, HLA mismatch ≥ 4) for BKPyV and provides an estimate of the BKPyV-associated risk of allograft failure (hazards ratio = 2.01) without confounding by donor factors or era effects. The higher than expected rate of concordant treatment suggests the importance of donor factors in BKPyV pathogenesis and warrants further study.

Polyomavirus Persistence

Mammalian polyomaviruses are characterized by establishing persistent infections in healthy hosts and generally causing clinical disease only in hosts whose immune systems are compromised. Despite the fact that these viruses were discovered decades ago, our knowledge of the mechanisms that govern viral persistence and reactivation is limited. Whereas mouse polyomavirus has been studied in a fair amount of detail, our understanding of the human viruses in particular is mostly inferred from experiments aimed at addressing other questions. In this review, we summarize the state of our current knowledge, draw conclusions when possible, and suggest areas that are in need of further study.

BK Virus Infection in Kidney Transplantation: A Case for Early Intervention

The prognosis for renal allograft survival in a patient with BK virus–associated nephropathy is distressing because nearly 50% of affected grafts are lost. With these statistics in mind, attempting clinical intervention before BK virus disease develops seems appropriate. Noninvasive screening tools such as tests to detect decoy cells in urine can enable diagnosis of BK viral infection in its early stages. Although it is not entirely clear which patients with BK infection will have BK disease develop, it may be possible to intervene in this early warning period to prevent the further development of BK virus–associated nephropathy. We present a case of a 50-year-old man in whom asymptomatic BK viruria developed 6 weeks after he received a non-HLA matched kidney from a deceased donor. This BK viruria was accompanied, subsequently, by an unexplained increase in serum creatinine level 2 months after transplantation. Following a change in his immunosuppressive regimen as therapy for presumed renal allograft dysfunction associated with BK viral infection, the decoy cells in his urine disappeared and his creatinine levels stabilized.

Risk Factors for the Development of BK Virus Nephropathy in Renal Transplant Recipients

The BK polyoma virus has, in recent years, become a significant cause of renal allograft dysfunction and failure. Among 260 adult kidney transplant recipients, those with biopsy-proven BK virus nephropathy (BKVN) were compared with those without BKVN with regard to gender, age, race, rejection episodes, time on dialysis, number of organs transplanted, HLA match, live donor versus deceased donor, cold ischemia time, delayed graft function, cytomegalovirus (CMV) serostatus of donor and recipient, induction therapy, and maintenance immunosuppression. Episodes of rejection (35.7% of patients with BKVN vs 8.5% of patients without BKVN; P = .01), transplantation of >1 organ (35.7% of patients with BKVN vs 9.0% of patients without BKVN; P = .01), positive CMV serology in both donor and recipient (71.4% of patients with BKVN vs 41.1% of patients without BKVN; P = .03), and a greater cumulative dose of daclizumab use at the time of induction (2.24 ± 0.05 mg/kg in patients with BKVN vs 2.03 ± 0.14 mg/kg in patients without BKVN; P = .04) were statistically significant risk factors for the development of BKVN. Those who developed BKVN received a higher mean cumulative dose of rabbit antithymoglobulin for induction therapy, but that difference failed to achieve statistical significance (P = .07).

Anion homeostasis is important for non-lytic release of BK polyomavirus from infected cells

BK polyomavirus (BKPyV) is a member of a family of potentially oncogenic viruses, whose reactivation can cause severe pathological conditions in transplant patients, leading to graft rejection. As with many non-enveloped viruses, it is assumed that virus release occurs through lysis of the host cell. We now show the first evidence for a non-lytic release pathway for BKPyV and that this pathway can be blocked by the anion channel inhibitor DIDS. Our data show a dose-dependent effect of DIDS on the release of BKPyV virions. We also observed an accumulation of viral capsids in large LAMP-1-positive acidic organelles within the cytoplasm of cells upon DIDS treatment, suggesting potential late endosome or lysosome-related compartments are involved in non-lytic BKPyV release. These data highlight a novel mechanism by which polyomaviruses can be released from infected cells in an active and non-lytic manner, and that anion homeostasis regulation is important in this pathway.

Distinct BK polyomavirus non-coding control region (NCCR) variants in oral fluids of HIV- associated Salivary Gland Disease patients

HIV-associated Salivary Gland Disease (HIVSGD) is among the most common salivary gland-associated complications in HIV positive individuals and was associated with the small DNA tumorvirus BK polyomavirus (BKPyV). The BKPyV non-coding control region (NCCR) is the main determinant of viral replication and rearranges readily. This study analyzed the BKPyV NCCR architecture and viral loads of 35 immunosuppressed individuals. Throatwash samples from subjects diagnosed with HIVSGD and urine samples from transplant patients were BKPyV positive and yielded BKPyV NCCR sequences. 94.7% of the BKPyV HIVSGD NCCRs carried a rearranged OPQPQQS block arrangement, suggesting a distinct architecture among this sample set. BKPyV from HIV positive individuals without HIVSGD harbored NCCR block sequences that were distinct from OPQPQQS. Cloned HIVSGD BKPyV isolates displayed active promoters and efficient replication capability in human salivary gland cells. The unique HIVSGD NCCR architecture may represent a potentially significant oral-tropic BKPyV substrain.

Characterization of Immunodominant BK Polyomavirus 9mer Epitope T Cell Responses

Uncontrolled BK polyomavirus (BKPyV) replication in kidney transplant recipients (KTRs) causes polyomavirus-associated nephropathy and allograft loss. Reducing immunosuppression is associated with clearing viremia and nephropathy and increasing BKPyV-specific T cell responses in most patients; however, current immunoassays have limited sensitivity, target mostly CD4(+) T cells, and largely fail to predict onset and clearance of BKPyV replication. To characterize BKPyV-specific CD8(+) T cells, bioinformatics were used to predict 9mer epitopes in the early viral gene region (EVGR) presented by 14 common HLAs in Europe and North America. Thirty-nine EVGR epitopes were experimentally confirmed by interferon-γ enzyme-linked immunospot assays in at least 30% of BKPyV IgG-seropositive healthy participants. Most 9mers clustered in domains, and some were presented by more than one HLA class I, as typically seen for immunodominant epitopes. Specific T cell binding using MHC class I streptamers was demonstrated for 21 of 39 (54%) epitopes. In a prospective cohort of 118 pediatric KTRs, 19 patients protected or recovering from BKPyV viremia were experimentally tested, and 13 epitopes were validated. Single HLA mismatches were not associated with viremia, suggesting that failing immune control likely involves multiple factors including maintenance immunosuppression. Combining BKPyV load and T cell assays using immunodominant epitopes may help in evaluating risk and reducing immunosuppression and may lead to safe adoptive T cell transfer.

BK Polyomavirus Replication in Renal Tubular Epithelial Cells Is Inhibited by Sirolimus, but Activated by Tacrolimus Through a Pathway Involving FKBP-12

BK polyomavirus (BKPyV) replication causes nephropathy and premature kidney transplant failure. Insufficient BKPyV-specific T cell control is regarded as a key mechanism, but direct effects of immunosuppressive drugs on BKPyV replication might play an additional role. We compared the effects of mammalian target of rapamycin (mTOR)- and calcineurin-inhibitors on BKPyV replication in primary human renal tubular epithelial cells. Sirolimus impaired BKPyV replication with a 90% inhibitory concentration of 4 ng/mL by interfering with mTOR-SP6-kinase activation. Sirolimus inhibition was rapid and effective up to 24 h postinfection during viral early gene expression, but not thereafter, during viral late gene expression. The mTORC-1 kinase inhibitor torin-1 showed a similar inhibition profile, supporting the notion that early steps of BKPyV replication depend on mTOR activity. Cyclosporine A also inhibited BKPyV replication, while tacrolimus activated BKPyV replication and reversed sirolimus inhibition. FK binding protein 12kda (FKBP-12) siRNA knockdown abrogated sirolimus inhibition and increased BKPyV replication similar to adding tacrolimus. Thus, sirolimus and tacrolimus exert opposite effects on BKPyV replication in renal tubular epithelial cells by a mechanism involving FKBP-12 as common target. Immunosuppressive drugs may therefore contribute directly to the risk of BKPyV replication and nephropathy besides suppressing T cell functions. The data provide rationales for clinical trials aiming at reducing the risk of BKPyV replication and disease in kidney transplantation.

Practical Applications in Immunohistochemistry: Evaluation of Rejection and Infection in Organ Transplantation

CONTEXT

-Immunohistochemical analysis of tissue biopsy specimens is a crucial tool in diagnosis of both rejection and infection in patients with solid organ transplants. In the past 15 years, the concept of antibody-mediated rejection has been refined, and diagnostic criteria have been codified in renal, heart, pancreas, and lung allografts (with studies ongoing in liver, small intestine, and composite grafts), all of which include immunoanalysis for the complement split product C4d.

OBJECTIVES

-To review the general concepts of C4d biology and immunoanalysis, followed by organ-allograft-specific data, and interpretative nuances for kidney, pancreas, and heart, with discussion of early literature for lung and liver biopsies. Additionally, practical applications and limitations of immunostains for infectious organisms (Polyomavirus, Adenoviridae [adenovirus], and the herpes virus family, including Herpes simplex virus, Cytomegalovirus, Human herpes virus 8, and Epstein-Barr virus) are reviewed in the context of transplant recipients.

DATA SOURCES

-Our experience and published primary and review literature.

CONCLUSIONS

-Immunohistochemistry continues to have an important role in transplant pathology, most notably C4d staining in assessment of antibody-mediated rejection and assessment of viral pathogens in tissue. In all facets of transplant pathology, correlation of morphology with special studies and clinical data is critical, as is close communication with the transplant team.

BK polyoma virus infection and renal disease in non-renal solid organ transplantation

BK virus (BKV) is a non-enveloped DNA virus of the polyomaviridae family that causes an interstitial nephritis in immunosuppressed patients. BKV nephropathy is now a leading cause of chronic kidney disease and early allograft failure following kidney transplantation. It is also known to cause renal disease with a progressive decline in kidney function in non-renal solid organ transplant (NRSOT) recipients, although the disease may not be recognized nor its impact appreciated in this patient population. In this report, we review the existing literature to highlight our current understanding of its incidence in NRSOT populations, the approaches to diagnosis and the potential treatment options.

Perception, diagnosis and management of BK polyomavirus replication and disease in paediatric kidney transplant recipients in Europe

BACKGROUND

BK polyomavirus (BKPyV)-associated nephropathy remains a challenge to the success of kidney transplantation, but its impact varies in different transplant programmes.

METHODS

We investigated current practice through a web-based questionnaire made available by the European Society for Paediatric Nephrology (ESPN).

RESULTS

A total of 90 physicians (23% of 391 active members) from 27 countries participated in the study. BKPyV-associated nephropathy is seen in 1-5% of patients annually with treatment success in 30-60%, and graft loss in 10%. Quantitative BKPyV load testing is available to >90% of physicians. Screening is performed in urine alone in 26%, in urine and blood in 37% and in blood alone in 37%. Most physicians (47%) screen at month 1, 2, 3, 6, 9 and 12 post-transplant. For patients with baseline renal function and plasma BKPyV loads of 10 000-1 000 000 copies/mL, 50% report performing renal biopsies prior to intervention. Intervention consists of reducing immunosuppression first with mycophenolate (Myc) in 40%, first with calcineurin inhibitors (CNI) in 29% or with both in 31%. Changing immunosuppressive drugs is considered mainly for biopsy-proven nephropathy consisting of discontinuation of Myc in 75%, and switching from CNI to mTOR inhibitors (52%). Cidofovir, intravenous immunoglobulin G, leflunomide and fluoroquinolones are used in less than one-third of this group. Furthermore, 66% of participants see a need for new antiviral drugs and new immmunosuppressive strategies, and almost 90% are willing to participate in future observational and interventional trials.

CONCLUSION

This ESPN survey suggests that prompt translation of a positive screening test into reducing immunosuppression could improve outcomes.

European perspective on human polyomavirus infection, replication and disease in solid organ transplantation

Human polyomaviruses (HPyVs) are a growing challenge in immunocompromised patients in view of the increasing number of now 12 HPyV species and their diverse disease potential. Currently, histological evidence of disease is available for BKPyV causing nephropathy and haemorrhagic cystitis, JCPyV causing progressive multifocal leukoencephalopathy and occasionally nephropathy, MCPyV causing Merkel cell carcinoma and TSPyV causing trichodysplasia spinulosa, the last two being proliferative skin diseases. Here, the current role of HPyV in solid organ transplantation (SOT) was reviewed and recommendations regarding screening, monitoring and intervention were made. Pre-transplant screening of SOT donor or recipient for serostatus or active replication is currently not recommended for any HPyV. Post-transplant, however, regular clinical search for skin lesions, including those associated with MCPyV or TSPyV, is recommended in all SOT recipients. Also, regular screening for BKPyV replication (e.g. by plasma viral load) is recommended in kidney transplant recipients. For SOT patients with probable or proven HPyV disease, reducing immunosuppression should be considered to permit regaining of immune control. Antivirals would be desirable for treating proven HPyV disease, but are solely considered as adjunct local treatment of trichodysplasia spinulosa, whereas surgical resection and chemotherapy are key in Merkel cell carcinoma. Overall, the quality of the clinical evidence and the strength of most recommendations are presently limited, but are expected to improve in the coming years.

Optimisation and analysis of polymerase chain reaction based DNA sequencing for genotyping polyoma virus in renal transplant patients: a report from South India

PURPOSE

To optimise a polymerase chain reaction (PCR) based DNA sequencing technique for genotyping polyoma virus in clinical specimens obtained from renal transplant patients.

MATERIALS AND METHODS

A hundred and thirty (106 peripheral blood and 24 urine) clinical specimens collected from renal transplant patients were included in the study for detecting the presence of  DNA of BK virus (BKV), JC virus (JCV) by PCR targeting the viral protein 1 (VP1) gene. PCR based DNA sequencing was performed to determine the genotypes of polyoma virus and subjected to bioinformatics analysis to determine the amino acid sequences and screen for mutations in the VP1 gene.

RESULTS

Polyoma virus was detected in 23 (17.69%) specimens of which 19 (82.60%) were positive for BK virus, 3 (13.04%) for JC virus and 1 for both BK and JC virus. PCR based DNA sequencing detected BK virus genotype I in 12 (50%), genotype IV in 8 (33.3%) and JC virus in 4 (16.6%) clinical specimens. BKV genotype I was the predominant genotype (64.2% in peripheral blood and 33.33% in urine) prevalent in south India. Six novel mutations were found--at position 29, 30 to 47 of BKV genotype I; at position 11 and 15 of BKV genotype IV and at position 2 and 30 of JCV.

CONCLUSION

BKV genotype I is the prominent genotype in India and novel mutations detected in the VP1 gene of BKV and JCV are being reported for the first time in literature.

Risk factors for BK virus infection and BK virus-associated nephropathy under the impact of intensive monitoring and pre-emptive immunosuppression reduction

BACKGROUND

BK virus (BKV) nephropathy (BKVN) is an increasingly recognized cause of kidney allograft loss and is thought to be related to the newer, more potent immunosuppressive agents. However, the risk factors for different types of BKV infection under the impact of intensive monitoring and reduction of maintenance immunosuppression are not well understood.

METHODS

Quantitative BKV DNA surveillance in plasma/urine and cytological testing in urine were performed regularly within the first year post-transplantation in 229 kidney recipients. Patients with BK viremia and BKVAN treated with immunosuppression reduction were monitored for BKV every 3-6 months. All the patients were followed up for a minimum of 5 years to exclude later development of BKVAN. Potential variables were compared and analyzed using logistic regression model multivariate analysis to assess and rank the BKV infection-related factors.

RESULTS

Seventy-eight (34.1%) patients had decoy cells, 99 (43.2%) BK viruria, 38 (16.6%) BK viremia, and 7 (3.1%) BKVAN. Risk for decoy cells, BK viruria, and viremia, and BKVAN in univariate analyses were higher with tacrolimus (Tac) and deceased kidney donation. Multivariate analysis showed that Tac ([HR, 2.7; P = .008], [HR, 2.3; P = .016], [HR, 2.9; P = .032]) and deceased kidney donation ([HR, 2.5; P = .004], [HR, 2.6; P = .002], [HR, 2.1; P = .071]) were risk factors for BK decoy cells, BK viruria, and viremia, respectively. BKVAN was inclined to the patients with the combination of Tac and mycophenolate mofetil and longer BKV clearance time.

CONCLUSIONS

Tac and deceased kidney donation are independent risk factors for BKV infection under the impact of therapeutic drug monitoring.

Polyomavirus BK and prostate cancer: a complex interaction of potential clinical relevance

Several studies associating BK polyomavirus (BKPyV) and prostate cancer (PCa) suggested that this virus may exert its oncogenic activity at early stages of cancer development. The BKPyV oncogene, the large T antigen (LTag), has frequently been detected in areas of proliferative inflammatory atrophy, which is considered a precursor lesion leading to prostatic intraepithelial neoplasia and overt PCa. In a recently updated systematic review, the presence of BKPyV was significantly higher in PCa tissues than in healthy control tissues, providing an indication for a link between BKPyV infection and cancer risk. In addition, recent original investigations highlighted an association between expression of the virus and the clinical course of PCa. For example, by studying immune responses elicited against BKPyV LTag, a significant association between LTag positive cancer lesions and a peculiar regulatory profiling has been observed in PCa patients with evidence of disease recurrence after surgical radical prostatectomy. Lastly, a study carried out in a larger cohort of patients undergoing radical prostatectomy revealed the IgG response against LTag as an independent predictor of disease recurrence. Although a full picture of the mechanisms potentially responsible for the involvement of BKPyV in PCa is not available yet, continuing work on this topic should help to refine the potential role of BKPyV in PCa patients, perhaps revealing unsuspected associations with the clinical course of this disease.

Optimizing JC and BK polyomavirus IgG testing for seroepidemiology and patient counseling

BACKGROUND

Polyomavirus JC (JCPyV) and BK (BKPyV) can cause significant diseases in immunocompromised patients including nephropathy, hemorrhagic cystitis, and leukoencephalopathy. Recently, JCPyV and BKPyV IgG have been explored as risk predictors in multiple sclerosis and transplant patients, but sensitivity, specificity and quantification issues limit current performance.

OBJECTIVE

To improve JCPyV and BKPyV-specific antibody testing.

STUDY DESIGN

Healthy blood donor sera (N=400) were tested at dilutions 1:100, 1:200, and 1:400 for JCPyV- and BKPyV-specific IgG using VP1 virus-like particle (VLP)-based ELISAs normalized to a laboratory reference serum. Normalized optical density 492nm greater or equal 0.1 in all 3 dilutions was regarded as reactive. Sera with discordant reactivity in at least one dilution were retested after VLP preadsorption.

RESULTS

At dilutions 1:100, 1:200, and 1:400, IgG reactivity was 74%, 60% and 53% for JCPyV, and 93%, 86% and 74% for BKPyV, respectively. At these dilutions, JCPyV-VLP preadsorption identified 56, 4 and 0 false-positives and 0, 4 and 27 false-negatives, respectively. Dilution-dependent sensitivity was 100%, 98%, and 89%, and specificity 65, 98%, and 100%, respectively. For sera diluted 100-, 200-, and 400-fold, BKPyV-VLP preadsorption identified 28, 1 and 0 false-positives, and 0, 0 and 46 false-negatives, and sensitivity was 100%, 100%, 86%, and specificity 50%, 98%, 100%, respectively.

CONCLUSION

For seroepidemiology studies, normalized JCPyV and BKPyV IgG ELISA at 1:200 serum dilution provides optimal sensitivity and specificity with the lowest false-positive and false-negative rate. For individual risk assessment, dilutions of 100, 200, and 400 combined with preadsorption for low-reactive sera may be most appropriate.

A revised strategy for monitoring BKV-specific cellular immunity in kidney transplant patients

Reactivation of Polyomavirus BKV is a severe complication in kidney transplant patients. Current treatment requires close monitoring, and modification of immunosuppressive drugs. As an important additional tool, the monitoring of BKV immunity has been based on detection of cytokine-secreting T cells upon BKV-antigen challenge. However, low frequent BKV-specific T cells are often barely detectable and their roles in BKV clearance remain unclear. Here, we analyzed the effects of immunosuppressive agents on BKV-specific T cells in vitro. Significant reductions in expression of several markers, and reduced killing functions upon treatment with calcineurin but not mTOR inhibitors were detected. However, effects of these drugs on expression of surface markers and GranzymeB were substantially less striking than effects on cytokine expression. Consequently, we applied a novel detection strategy for BKV-specific T cells in immunosuppressed kidney transplant patients using these more robust markers, and showed significantly improved sensitivity compared with the conventional IFNγ-based method. Using this strategy and 17-color flow cytometry, we found BKV-specific helper and cytolytic CD4+ T-cell subsets that differed in their memory phenotype, which corresponded with BKV clearance in kidney transplant patients. Thus, our results offer an improved detection strategy for BKV-specific T cells in kidney transplant patients, and shed light on the contributions of these cells to BKV clearance.

Different risk factor profiles distinguish early-onset from late-onset BKV-replication

Two of three reactivations of latent BKV-infection occur within the first 6 months after renal transplantation. However, a clear differentiation between early-onset and late-onset BKV-replication is lacking. Here, we studied all kidney transplant recipients (KTRs) at our single transplant center between 2004 and 2012. A total of 103 of 862 KTRs were diagnosed with BK viremia (11.9%), among which 24 KTRs (2.8%) showed progression to BKV-associated nephropathy (BKVN). Sixty-seven KTRs with early-onset BKV-replication (65%) and 36 KTRs with late-onset BKV-replication (35%) were identified. A control group of 598 KTRs without BKV-replication was used for comparison. Lymphocyte-depleting induction, CMV-reactivation, and acute rejection increased the risk of early-onset BKV-replication (P < 0.05). Presensitized KTRs undergoing renal retransplantation were those at increased risk of late-onset BKV-replication (P < 0.05). Among KTRs with BK viremia, higher doses of mycophenolate increased the risk of progression to BKVN (P = 0.004). KTRs with progression to BKVN showed inferior allograft function (P < 0.05). KTRs with late-onset BK viremia were more likely not to recover to baseline creatinine after BKV-replication (P = 0.018). Our data suggest different risk factors in the pathogenesis of early-onset and late-onset BKV-reactivation. While a more intensified immunosuppression is associated with early-onset BKV-replication, a chronic inflammatory state in presensitized KTRs may contribute to late-onset BKV-replication.

Observations on the use of cidofovir for BK virus infection in renal transplantation

BACKGROUND

In renal transplantation, BK virus infection can result in significant graft nephropathy and loss. While reduction in immunosuppression (IS) is considered standard therapy, adjunct agents may be warranted. Data are suggestive of a possible role of cidofovir for the management of BK. This study aims to describe the course of BK viremia (BKV) in a large cohort of renal transplant patients receiving adjunct cidofovir.

METHODS

We evaluated kidney and kidney-pancreas recipients who received cidofovir combined with reduced IS for management of high-level BKV or BK virus nephropathy (BKVN). We examined the rate and timing of BKV clearance, and performed a multivariate analysis to identify risk factors associated with long-term (>6 months) viremia.

RESULTS

In total, 75 patients received a median of 13 doses of cidofovir in conjunction with reduced IS; 32 patients (43%) had short-term BKV (≤6 months), and 43 (57%) had long-term BKV. Overall, 53 of 75 patients (71%) eventually cleared BKV at a median of 4.2 months (interquartile range 2.1-9.3 months). Independent factors associated with long-term BKV included older age (odds ratio [OR] 1.1, P = 0.02), delayed graft function (OR 31.4, P = 0.01), and higher peak BKV (OR 12.8, P = 0.02), while BKV reduction by at least 1 log(10) copies/mL at 1 month of treatment was associated with clearance within 6 months (OR 49.3, P < 0.01). Patients with earlier clearance maintained stable graft function and no graft losses, while long-term BKV was associated with a 15% decline in estimated glomerular filtration rate.

CONCLUSIONS

Adjunct cidofovir resulted in preservation of renal function when viral clearance occurred within 6 months of initiation. This retrospective review defines factors predicting response to cidofovir in conjunction with reduced IS for BKVN or high-level BKV. Still, considering cost, frequency of administration, and treatment duration, a randomized trial is necessary to define the exact utility of cidofovir in the setting of BK virus infection.

The kinetics of urinary shedding of BK virus in children with renal disease

Children with renal diseases are typically treated with immunosuppressive drugs, which place them at high risk of reactivation of the BK virus (BKV). Currently, little is known about the impact of immunosuppressive drugs on the kinetics of urinary shedding of BKV and viral reactivation in pediatric patients with renal diseases. Urine samples were collected monthly for 1 year from 20 children (median age, 9 years; range, 4-15 years) with renal diseases and subjected to real-time PCR. Urinary shedding of BKV was detected in 35% (7/20) of the patients, three of these patients having persistent viral DNA excretion (two cases, twelve times; one case, four times) and four having intermittent viral DNA excretion. Thirty-four of the 240 urine samples contained BKV DNA (median copy numbers, 5.66 log copies/mL; range, 2.45-7.69 log copies/mL). In two of the cases with persistent viral shedding, high copy numbers (range, 4.57-7.69 log copies/mL) of BKV DNA were detected in all 12 urine samples collected. In the other case with persistent viral excretion, a range of 2.45-3.98 log copies/mL of BKV DNA was detected in the four urine samples collected between the 9th and 12th sampling time points. Additionally, high copy numbers (range, 3.12-4.36 log copies/mL) of BKV DNA were detected intermittently in the urine samples of the other four cases. No remarkable correlations were found between the kinetics of BKV DNA loads and urinary findings such as proteinuria and hematuria. The present data demonstrate the kinetics of urinary BKV shedding in pediatric patients with renal diseases. Additionally, no pathogenic role for BKV infection was identified.

Ureteral Stent Placement Increases the Risk for Developing BK Viremia after Kidney Transplantation

The placement of ureteral stent (UrSt) at kidney transplantation reduces major urological complications but increases the risk for developing nephropathy from the BK virus. It is unclear whether UrSt placement increases nephropathy risk by increasing risk of precursor viral replication or by other mechanisms. We retrospectively investigated whether UrSt placement increased the risk for developing BK Viremia (BKVM) in adult and pediatric kidney transplants performed at the University of Florida between July 1, 2007, and December 31, 2010. In this period all recipients underwent prospective BKV PCR monitoring and were maintained on similar immunosuppression. Stent placement or not was based on surgeon preference. In 621 transplants, UrSt were placed in 295 (47.5%). BKVM was seen in 22% versus 16% without UrSt (P = 0.05). In multivariate analyses, adjusting for multiple transplant covariates, only UrSt placement remained significantly associated with BKVM (P = 0.04). UrSt placement significantly increased the risk for BKVM. Routine UrSt placement needs to be revaluated, since benefits may be negated by the need for more BK PCR testing and potential for graft survival-affecting nephritis.

Autopsy Renal Pathology

We provide an overview of assessment of the kidneys at autopsy, with special considerations for pediatric versus adult kidneys. We describe the approach to gross examination, tissue allocation when needed for additional studies of potential medical renal disease, the spectrum of congenital abnormalities of the kidneys and urinary tract, and approach to cystic diseases of the kidney. We also discuss common lesions seen at autopsy, including acute tubular injury, ischemic versus toxic contributions to this injury, interstitial nephritis, and common vascular diseases. Infections commonly involve the kidney at autopsy, and the key features and differential diagnoses are also discussed.

Characterization of urinary CD4⁺ and CD8⁺ T cells in kidney transplantation patients with polyomavirus BK infection and allograft rejection

BACKGROUND AND OBJECTIVES

The objective of this study was to characterize CD4(+) and CD8(+) T-cell populations in blood and urine of renal transplant patients with BK virus (BKV) infection or allograft rejection.

MATERIALS AND METHODS

Percentages and absolute numbers of CD4(+) and CD8(+) effector memory T-cell subtype (TEM ) and terminal differentiated T cells (TTD ) in renal transplant patients with BKV infection (n = 14), with an episode of allograft rejection (n = 9), and in uncomplicated renal transplant patients with a stable kidney function (n = 12) were measured and compared using 4-color fluorescence-activated cell sorting. Results were correlated with the number of CD4(+) and CD8(+) T cells in renal biopsies.

RESULTS

In patients with allograft rejection, the number of urinary CD4(+) TEM and CD8(+) TEM cells was significantly increased compared to patients with BKV infection or patients without complications. Positive correlation was found between the number of CD4(+) and CD8(+) cells in the renal biopsies and the number of CD4(+) and CD8(+) cells in urine. In patients with rejection, after 2 months of immunosuppressive therapy, a reduction in urinary CD8(+) TEM cells was found.

CONCLUSIONS

CD4(+) TEM and CD8(+) TEM cells in urine could be a marker to distinguish allograft rejection from BKV-associated nephropathy and to monitor therapy effectiveness in renal transplant patients with allograft rejection.

Association of interferon gamma gene polymorphisms with BK virus infection among Hispanic renal allograft recipients

BACKGROUND

BK virus nephropathy is one of the most common viral infections that affect up to 10% of renal transplant recipients (RTRs), causing allograft dysfunction and graft loss. Interferon-gamma (IFN-γ) gene polymorphisms have been associated with parvovirus B19, hepatitis C virus, HIV-1/AIDS infection, cytomegalovirus viremia, and disease. IFN-γ is known to have potent inhibitory effects on BK virus gene expression, both at the level of transcription and translation.

METHODS

It was investigated whether IFN-γ polymorphisms are associated with BKV infection. Genotyping of four single-nucleotide polymorphisms located in the IFN-γ gene were performed on DNA collected from a total of 251 RTRs (71 RTRs with BKV infection and 180 without BKV infection).

RESULTS

Analysis of the results showed that IFN-γ (rs12369470) CC genotype was significantly associated with susceptibility to BKV infection (OR: 2.9, 95% CI: 1.29-6.44, P=0.007) while the IFN-γ +874 (rs2435061) TT and (rs2406918) CC genotypes appear to be markers for protection against BKV infection (OR: 0.29, 95% CI: 0.1-0.83, P=0.01 for rs245061; OR: 0.61, 95% CI: 0.4-0.94, P=0.02 for rs24069718). A haplotype analysis using the combination of rs2435061-rs2406918-rs2870953 showed that the A-G-T haplotype was associated with a significantly reduced risk for BKV infection (OR: 0.43, 95% CI: 0.25-0.73, P=0.001).

CONCLUSION

Polymorphisms in the IFN-γ gene may confer certain protection or predisposition for BKV infection.

BK virus infection: an update on diagnosis and treatment

BK virus, first isolated in 1971, is a significant risk factor for renal transplant dysfunction and allograft loss. Unfortunately, treatment options for BK virus infection are limited, and there is no effective prophylaxis. Although overimmunosuppression remains the primary risk factor for BK infection after transplantation, male gender, older recipient age, prior rejection episodes, degree of human leukocyte antigen mismatching, prolonged cold ischemia time, BK serostatus and ureteral stent placement have all been implicated as risk factors. Routine screening for BK has been shown to be effective in preventing allograft loss in patients with BK viruria or viremia. Reduction of immunosuppression remains the mainstay of BK nephropathy treatment and is the best studied intervention. Laboratory-based methods such as ELISPOT assays have provided new insights into the immune response to BK and may help guide therapy in the future. In this review, we will discuss the epidemiology of BK virus infection, screening strategies, treatment options and future research directions.

Efficacy of levofloxacin in the treatment of BK viremia: a multicenter, double-blinded, randomized, placebo-controlled trial

BACKGROUND AND OBJECTIVES

BK virus reactivation in kidney transplant recipients can lead to progressive allograft injury. Reduction of immunosuppression remains the cornerstone of treatment for active BK infection. Fluoroquinolone antibiotics are known to have in vitro antiviral properties, but the evidence for their use in patients with BK viremia is inconclusive. The objective of the study was to determine the efficacy of levofloxacin in the treatment of BK viremia.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Enrollment in this prospective, multicenter, double-blinded, placebo-controlled trial occurred from July 2009 to March 2012. Thirty-nine kidney transplant recipients with BK viremia were randomly assigned to receive levofloxacin, 500 mg daily, or placebo for 30 days. Immunosuppression in all patients was adjusted on the basis of standard clinical practices at each institution. Plasma BK viral load and serum creatinine were measured monthly for 3 months and at 6 months.

RESULTS

At the 3-month follow-up, the percentage reductions in BK viral load were 70.3% and 69.1% in the levofloxacin group and the placebo group, respectively (P=0.93). The percentage reductions in BK viral load were also equivalent at 1 month (58% versus and 67.1%; P=0.47) and 6 months (82.1% versus 90.5%; P=0.38). Linear regression analysis of serum creatinine versus time showed no difference in allograft function between the two study groups during the follow-up period.

CONCLUSIONS

A 30-day course of levofloxacin does not significantly improve BK viral load reduction or allograft function when used in addition to overall reduction of immunosuppression.

Emerging trends in infections among renal transplant recipients

Outcomes following renal and simultaneous kidney-pancreas transplants have improved significantly due to better surgical techniques and improved modalities of antirejection therapy. However, infection remains a significant cause of morbidity and mortality. The use of new modalities of immunosuppression and routine use of antimicrobial prophylaxis has changed the pattern of infections post-transplantation. Cytomegalovirus remains a significant problem and BK virus has emerged as an important pathogen. New antimicrobial agents are now available to treat infection, however, antimicrobial resistance remains a concern.

HLA-A2, HLA-B44 and HLA-DR15 are associated with lower risk of BK viremia

BACKGROUND

Human leucocyte antigens (HLAs) modulate immunity to polyomavirus BK (BKV). Identification of HLAs that alter the course of infection will facilitate risk stratification, and customization of pre-emptive intervention strategies.

METHODS

We performed a retrospective cohort study with 998 kidney transplant patients with BKV infection status confirmed by polymerase chain reaction (PCR). Clinical parameters and donor-recipient matching for specific HLAs were examined in relation to occurrence of viremia. An emphasis was placed on donor-recipient matching rather than the actual frequency of specific HLA-alleles, since a successful immune response requires sharing of HLAs between a virus-infected target cell and the anti-viral effector cell.

RESULTS

Using multivariate statistics, low risk of BK viremia was associated with matching of HLA-A2 [hazard ratio (HR) 0.51, 95% confidence interval (CI) 0.28-0.85], HLA-B44 (HR 0.31, 95% CI 0.076-0.85) and HLA-DR15 (HR 0.35, 95% CI 0.084-0.93) (P < 0.05), whereas high risk of viremia was associated with male gender (HR 2.38, 95% CI 1.46-4.09, P < 0.001).

CONCLUSIONS

HLAs that associated with a lower predisposition to the development of BK viremia have been identified. Evaluation of donor-recipient mismatching for these HLAs could potentially be used to (i) fine tune virus screening strategies for BKV in individual patients and (ii) facilitate discovery of major histocompatibility complex (MHC) class I and II binding peptides that can elicit clinically meaningful BKV-specific immunity.