Polyomavirus nephropathy in kidney transplantation

BKV, CMV, and EBV Interactions and their Effect on Graft Function One Year Post-Renal Transplantation: Results from a Large Multi-Centre Study

Background

BK virus (BKV), Cytomegalovirus (CMV) and Epstein-Barr virus (EBV) reactivations are common after kidney transplantation and associated with increased morbidity and mortality. Although CMV might be a risk factor for BKV and EBV, the effects of combined reactivations remain unknown. The purpose of this study is to ascertain the interaction and effects on graft function of these reactivations.

Methods

3715 serum samples from 540 kidney transplant recipients were analysed for viral load by qPCR. Measurements were performed throughout eight visits during the first post-transplantation year. Clinical characteristics, including graft function (GFR), were collected in parallel.

Findings

BKV had the highest prevalence and viral loads. BKV or CMV viral loads over 10,000 copies·mL⁻¹ led to significant GFR impairment. 57 patients had BKV-CMV combined reactivation, both reactivations were significantly associated (p = 0.005). Combined reactivation was associated with a significant GFR reduction one year post-transplantation of 11.7 mL·min⁻¹·1.73 m⁻² (p = 0.02) at relatively low thresholds (BKV > 1000 and CMV > 4000 copies·mL⁻¹). For EBV, a significant association was found with CMV reactivation (p = 0.02), but no GFR reduction was found. Long cold ischaemia times were a further risk factor for high CMV load.

Interpretation

BKV-CMV combined reactivation has a deep impact on renal function one year post-transplantation and therefore most likely on long-term allograft function, even at low viral loads. Frequent viral monitoring and subsequent interventions for low BKV and/or CMV viraemia levels and/or long cold ischaemia time are recommended.

Fund

Investigator Initiated Trial; financial support by German Federal Ministry of Education and Research (BMBF).

Differential T cell response against BK virus regulatory and structural antigens: A viral dynamics modelling approach

BK virus (BKV) associated nephropathy affects 1-10% of kidney transplant recipients, leading to graft failure in about 50% of cases. Immune responses against different BKV antigens have been shown to have a prognostic value for disease development. Data currently suggest that the structural antigens and regulatory antigens of BKV might each trigger a different mode of action of the immune response. To study the influence of different modes of action of the cellular immune response on BKV clearance dynamics, we have analysed the kinetics of BKV plasma load and anti-BKV T cell response (Elispot) in six patients with BKV associated nephropathy using ODE modelling. The results show that only a small number of hypotheses on the mode of action are compatible with the empirical data. The hypothesis with the highest empirical support is that structural antigens trigger blocking of virus production from infected cells, whereas regulatory antigens trigger an acceleration of death of infected cells. These differential modes of action could be important for our understanding of BKV resolution, as according to the hypothesis, only regulatory antigens would trigger a fast and continuous clearance of the viral load. Other hypotheses showed a lower degree of empirical support, but could potentially explain the clearing mechanisms of individual patients. Our results highlight the heterogeneity of the dynamics, including the delay between immune response against structural versus regulatory antigens, and its relevance for BKV clearance. Our modelling approach is the first that studies the process of BKV clearance by bringing together viral and immune kinetics and can provide a framework for personalised hypotheses generation on the interrelations between cellular immunity and viral dynamics.

BK virus-specific immunity kinetics: a predictor of recovery from polyomavirus BK-associated nephropathy

Impaired BKV-specific immunity is associated with development of BKV-associated nephropathy. Suitable immunological parameters to identify patients at risk, however, are still debated. We monitored 18 kidney-transplant recipients through the course of self-limited BKV-reactivation (n = 11) and BKV-associated nephropathy (n = 7). BKV-specific cellular immunity directed to nonstructural small and Large T-antigen, and structural VP1-3 was analyzed in an interferon-γ Elispot assay. BKV-specific IgM and IgG were measured using an enzyme-linked immunosorbent assay simultaneously. BKV-specific cellular immunity directed to five BKV-proteins increased significantly from diagnosis to resolution of BKV-reactivation (p < 0.001). Patients with self-limited BKV-reactivation developed BKV-specific T cells without therapeutic interventions, and cleared BKV-reactivation within a median period of 1 month. Patients with BKV-associated nephropathy, however, showed BKV-specific T cells after a median period of 5 months after therapeutic interventions only, and cleared BKV-reactivation after a median period of 8 months. Anti-structural T cells were detected earlier than anti-nonstructural T cells, which coincided with BKV-clearance. Patients with BKV-associated nephropathy showed the highest frequencies of BKV-specific T cells at recovery, the highest increase in BKV-specific IgG and persistence of increased IgM levels (p < 0.05). Our results suggest prognostic values of BKV-specific immune monitoring to identify those patients at risk of BKV-associated nephropathy and to aid in the management of therapeutic interventions.

BK virus-associated nephropathy in a patient with AIDS

The BK virus is a ubiquitous member of the group of human polyoma viruses that commonly is reactivated in the setting of immunosuppression related to renal transplantation, which results in tubulointerstitial nephritis and allograft dysfunction. BK virus-associated nephropathy occurring in association with human immunodeficiency virus infection and acquired immunodeficiency syndrome (AIDS) was reported only rarely. We describe the case of a 43-year-old man with AIDS presenting with nonoliguric renal failure. The renal biopsy specimen showed tubulointerstitial nephritis and renal tubular cell changes consistent with BK viral inclusions. Results of in situ hybridization for BK viral DNA were positive and showed tubular cell intranuclear inclusions. To our knowledge, this represents the third case of AIDS-associated BK virus-associated nephropathy diagnosed by means of biopsy.

Caveolar endocytosis is critical for BK virus infection of human renal proximal tubular epithelial cells

In recent years, BK virus (BKV) nephritis after renal transplantation has become a severe problem. The exact mechanisms of BKV cell entry and subsequent intracellular trafficking remain unknown. Since human renal proximal tubular epithelial cells (HRPTEC) represent a main natural target of BKV nephritis, analysis of BKV infection of HRPTEC is necessary to obtain additional insights into BKV biology and to develop novel strategies for the treatment of BKV nephritis. We coincubated HRPTEC with BKV and the cholesterol-depleting agents methyl beta cyclodextrin (MBCD) and nystatin (Nys), drugs inhibiting caveolar endocytosis. The percentage of infected cells (detected by immunofluorescence) and the cellular levels of BKV large T antigen expression (detected by Western blot analysis) were significantly decreased in both MBCD- and Nys-treated HPRTEC compared to the level in HRPTEC incubated with BKV alone. HRPTEC infection by BKV was also tested after small interfering RNA (siRNA)-dependent depletion of either the caveolar structural protein caveolin-1 (Cav-1) or clathrin, the major structural protein of clathrin-coated pits. BKV infection was inhibited in HRPTEC transfected with Cav-1 siRNA but not in HRPTEC transfected with clathrin siRNA. The colocalization of labeled BKV particles with either Cav-1 or clathrin was investigated by using fluorescent microscopy and image cross-correlation spectroscopy. The rate of colocalization of BKV with Cav-1 peaked at 4 h after incubation. Colocalization with clathrin was insignificant at all time points. These results suggest that BKV entered into HRPTEC via caveolae, not clathrin-coated pits, and that BKV is maximally associated with caveolae at 4 h after infection, prior to relocation to a different intracellular compartment.

One-year results with extended-release tacrolimus/MMF, tacrolimus/MMF and cyclosporine/MMF in de novo kidney transplant recipients

Once-daily tacrolimus extended-release formulation (Prograf XL, formerly referred to as MR or MR4) was compared with the twice-a-day tacrolimus formulation (TAC) and cyclosporine microemulsion (CsA), all administered in combination with mycophenolate mofetil (MMF), corticosteroids and basiliximab induction, in a phase 3, randomized (1:1:1), open-label trial in 638 de novo kidney transplant recipients. In combination with MMF and corticosteroids, XL had an efficacy profile comparable to TAC and CsA. XL/MMF and TAC/MMF were statistically noninferior at 1-year posttransplantation to CsA/MMF for the primary efficacy endpoint, efficacy failure (death, graft loss, biopsy-confirmed acute rejection (BCAR) or lost to follow-up). One-year patient and graft survival were 98.6% and 96.7% in the XL/MMF group, 95.7% and 92.9% in TAC/MMF group and 97.6% and 95.7% in CsA/MMF group. The safety profile of XL in comparison with CsA was similar to that observed with TAC in this study and consistent with previously published reports of TAC in comparison with CsA. The results support the safety and efficacy of tacrolimus in combination with MMF, corticosteroids and basiliximab induction, as well as XL as a safe and effective once-daily dosing alternative.

Polyomavirus-associated nephropathy: update in diagnosis

The histological diagnosis of BK or JC polyomavirus allograft nephritis (PVAN) requires evaluation of a renal biopsy with demonstration of the polyomavirus cytopathic changes and confirmation with an ancillary technique such as immunohistochemistry. Three histological patterns of PVAN (A, B, and C) are identified in renal biopsies. Pattern A corresponds to the early disease, whereas patterns B and C identify intermediate and very advanced histological changes, respectively. The histological pattern found in the first biopsy correlates with graft outcome. Because PVAN affects the kidney in a random, multifocal manner, a negative biopsy does not rule out the disease. Patients with BK PVAN characteristically have high levels of BK viruria and viremia. Although the cutoff values of viral loads have not been fully determined, there is general agreement that BK viruria of >10(7)/mL and BK viremia of >10(4) are typical of patients with a biopsy showing BK PVAN. Prospective evaluation of viruria with urine cytology (decoy cells) and/or quantitative polymerase chain reaction can aid in the identification of patients at risk for developing PVAN. In addition to histological evaluation, viremia has emerged as the most specific test for the diagnosis of BK PVAN. JC PVAN is very infrequent in comparison with BK PVAN, but is also characterized by large viruria (>10(4)). On the other hand, JC viremia appears to be lower, in the order of 10(3)/mL. The inflammatory changes in PVAN need further characterization. Currently, there are no tools to differentiate acute cellular rejection from viral specific T-cell response.

Infectious complications in renal transplant recipients

Post-kidney transplant infection is the most common life-threatening complication of long-term immunosuppressive therapy. Optimal immunosuppression, in which a balance is maintained between prevention of rejection and avoidance of infection, is the most challenging aspect of posttransplantation care. The study of infectious complications in immunologically compromised recipients is changing rapidly, particularly in the fields of prophylactic and preemptive strategies, molecular diagnostic methods, and antimicrobial agents. In addition, emerging pathogens such as BK polyomavirus and West Nile flavivirus infections and the introduction of newer immunosuppressive agents that constantly change the risk profiles for opportunistic infections has added layers of complexity to this burgeoning field. Although remarkable progress has been made in these disciplines, comprehensive understanding of the clinical manifestations of infections remains limited, and the standardization of prophylaxis, diagnosis, and treatment of most infections is yet inadequately defined. The long-term goal for optimal care of transplant recipients, with respect to infection, is the prevention and/or early recognition and treatment of infections while avoiding drug-related toxicities.

Interplay of cellular and humoral immune responses against BK virus in kidney transplant recipients with polyomavirus nephropathy

Reactivation of the polyomavirus BK (BKV) causes polyomavirus nephropathy (PVN) in kidney transplant (KTx) recipients and may lead to loss of the renal allograft. We have identified two HLA-A*0201-restricted nine-amino-acid cytotoxic T lymphocyte (CTL) epitopes of the BKV major capsid protein VP1, VP1(p44), and VP1(p108). Using tetramer staining assays, we showed that these epitopes were recognized by CTLs in 8 of 10 (VP1(p44)) and 5 of 10 (VP1(p108)) HLA-A*0201+ healthy individuals, while both epitopes elicited a CTL response in 10 of 10 KTx recipients with biopsy-proven PVN, although at variable levels. After in vitro stimulation with the respective peptides, CTLs directed against VP1(p44) were more abundant than against VP1(p108) in most healthy individuals, while the converse was true in KTx recipients with PVN, suggesting a shift in epitope immunodominance in the setting of active BKV infection. A strong CTL response in KTx recipients with PVN appeared to be associated with decreased BK viral load in blood and urine and low anti-BKV antibody titers, while a low or undetectable CTL response correlated with viral persistence and high anti-BKV antibody titers. These results suggest that this cellular immune response is present in most BKV-seropositive healthy individuals and plays an important role in the containment of BKV in KTx recipients with PVN. Interestingly, the BKV CTL epitopes bear striking homology with the recently described CTL epitopes of the other human polyomavirus JC (JCV), JCV VP1(p36) and VP1(p100). A high degree of epitope cross-recognition was present between BKV and corresponding JCV-specific CTLs, which indicates that the same population of cells is functionally effective against these two closely related viruses.

Human polyomaviruses and brain tumors

Polyomaviruses are DNA tumor viruses with small circular genomes. Three polyomaviruses have captured attention with regard to their potential role in the development of human brain tumors: JC virus (JCV), BK virus (BKV), and simian vacuolating virus 40 (SV40). JCV is a neurotropic polyomavirus that is the etiologic agent of progressive multifocal leukoencephalopathy (PML), a fatal demyelinating disease of the central nervous system occurring mainly in AIDS patients. BKV is the causative agent of polyomavirus-associated nephropathy (PVN) which occurs after renal transplantation when BKV reactivates from a latent state during immunosuppressive therapy to cause allograft failure. SV40, originating in rhesus monkeys, gained notoriety when it entered the human population via contaminated polio vaccines. All three viruses are highly oncogenic when injected into the brain of experimental animals. Reports indicate that these viruses, especially JCV, are associated with brain tumors and other cancers in humans as evidenced from the analysis of clinical samples for the presence of viral DNA sequences and expression of viral proteins. Human polyomaviruses encode three non-capsid regulatory proteins: large T-antigen, small t-antigen, and agnoprotein. These proteins interact with a number of cellular target proteins to exert effects that dysregulate pathways involved in the control of various host cell functions including the cell cycle, DNA repair, and others. In this review, we describe the three polyomaviruses, their abilities to cause brain and other tumors in experimental animals, the evidence for an association with human brain tumors, and the latest findings on the molecular mechanisms of their actions.