Human polyoma virus-associated interstitial nephritis in the allograft kidney

HLA mismatching increases the risk of BK virus nephropathy in renal transplant recipients

BK virus (BKV) nephropathy is a serious complication in kidney transplant recipients that may lead to irreversible graft failure. We have analyzed the degree of donor/recipient HLA compatibility and HLA antigen association in 40 kidney transplant patients with BKV nephropathy in comparison with a control group of 404 unaffected transplant recipients who were on tacrolimus-based immunosuppression with no induction. HLA compatibility was assessed by determining the number of HLA-A, -B, -DR-mismatched antigens. BK virus nephropathy was diagnosed histologically and confirmed by immunochemistry. Univariate and multiple logistic regression statistical analyses have shown a significant association between BKV nephropathy and HLA mismatching. This analysis showed also that BKV nephritis is associated with a greater number of rejection episodes and a higher incidence of steroid-resistant rejection requiring antilymphocyte treatment. There was no association between BKV nephropathy and any specific HLA allele. We propose that HLA mismatching promotes the development of BKV nephropathy through rejection-related inflammatory processes and heavy immunosuppression which cause virus reactivation and injury of the tubular epithelium.

Polyomavirus infection in pediatric renal transplant recipients: evaluation using a quantitative real-time PCR technique

Polyomavirus infection and related nephropathy is being increasingly recognized as an important cause of allograft dysfunction in adult renal transplant recipients. We prospectively monitored pediatric renal transplant recipients for the presence of BK and JC polyomavirus in urine and blood using a quantitative PCR assay to evaluate the prevalence and clinical relevance of polyomavirus infection in the pediatric renal transplant population. Of 46 pediatric renal recipients who were evaluated, nine (20%) demonstrated isolated BKV viruria, while five (11%) had concomitant BKV viremia and viruria. JCV viruria was found in eight (17%) patients. BKV viremia was associated with a significantly higher urinary BKV viral load: median urinary viral load 1.9 x 10(9) copies/mL (range 6.7 x 10(2)-1.8 x 10(11)) for the group with concomitant viremia and viruria vs. 1.8 x 10(3) copies/mL (range 2.5 x 10(2)-4.5 x 10(6)) for the group with isolated viruria (p < 0.0001). In children that were followed prospectively since their transplantation, the BKV urinary viral load increased markedly before viremia became detectable a few weeks later. None of the patients with JCV viruria or isolated BKV viruria had renal dysfunction. Among the five patients with BKV in both urine and blood, two developed biopsy-proven BKV nephropathy associated with deterioration of the renal function. Management of the BKV nephropathy consisted of reduction of immunosuppression alone or in combination with antiviral treatment with cidofovir. This study shows that polyomavirus infection and related interstitial nephritis is a relevant clinical issue in the pediatric renal transplant population. Monitoring the polyomaviral load in the urine and the blood of the patients using a quantitative PCR technique is a useful tool in the diagnosis and subsequent management of this infection. Even before viremia is present, an important rise in the urinary viral load should draw the attention of the transplant clinician and raise the issue of adapting the immunosuppression.

Use of cidofovir in polyomavirus BK viral nephropathy in two renal allograft recipients

Polyomavirus BK viral allograft nephropathy is a potentially reversible cause of deteriorating function of kidney allografts. Initial treatment involves reducing immunosuppressive medications, with low-dose cidofovir an effective alternative in refractory cases. We describe two cases of BK viral allograft nephropathy responding to low-dose cidofovir after a reduction in immunosuppressive medications failed to clear the virus or stabilize the deterioration in renal function. There were no significant side-effects from this treatment in either patient.

Monitoring the progress of BK virus associated nephropathy in renal transplant recipients

BACKGROUND

Nephropathy associated with BK virus (BKVAN) has recently emerged as an important cause of allograft failure following renal transplantation. The aim of this study was to evaluate the effectiveness of laboratory markers in the follow-up of patients with BKVAN.

METHODS

Serial samples from seven renal transplant recipients with biopsy proven BKVAN were studied. The median follow-up time from diagnosis was 76 weeks. Intervention after the diagnosis of BKVAN included immunosuppression dose reduction, alternative immunosuppressive agents and/or antiviral therapy with cidofovir. Serial urine samples (n = 127) were collected for electron microscopy (EM), decoy cell detection and quantitative urine BK viral load using real-time polymerase chain reaction. Serum BK viral load was also measured serially (n = 72).

RESULTS

All patients showed a reduction in serum and urine viral load during the period of follow-up co-incident with the loss of decoy cells and negative urine EM. Urine samples that were negative for decoy cells or polyomavirus by EM had a urine viral load <10(6) copies/ml and a corresponding serum viral load <10(3) copies/ml. In paired serum/urine samples, there was a proportional relationship between serum and urine viral load with each urine viral load approximately 1000-fold higher than the corresponding serum level. Serum and urine viral loads that decreased to <200 and < 10(6) copies/ml, respectively, correlated with histological improvement.

CONCLUSION

Negative EM and absence of decoy cells could be used as broad indicators of a response to intervention. However, measurement of BK virus DNA level provided a wider dynamic range and could be a better choice for determining the extent of viral control.

Dendritic cells pulsed with polyomavirus BK antigen induce ex vivo polyoma BK virus-specific cytotoxic T-cell lines in seropositive healthy individuals and renal transplant recipients

Polyoma BK virus (BKV)-associated interstitial nephritis has emerged as a relevant complication of immunocompromise after kidney transplantation, leading to reduced survival of the renal allograft. The limitations of current antiviral treatment and the high probability of rejection in kidney graft recipients when control of viral replication is attempted by reduction of immunosuppression warrant further efforts to develop alternative therapeutic tools. Cellular immunotherapy has proved to be a successful approach for prevention and/or treatment of other viral complications in the immunocompromised host. For assessing the feasibility of translating this strategy to the prevention of BKV-associated disease, a procedure for ex vivo reactivation of BKV-specific cytotoxic T cells (CTL) was developed from BKV-seropositive healthy donors and allograft recipients through stimulation with dendritic cells pulsed with inactivated BKV. The CTL lines thus obtained showed BKV specificity, as an efficient lysis of BKV-infected targets was accompanied by little or no reactivity against mock-infected autologous or allogeneic targets. In vitro killing of allogeneic BKV-infected targets, likely as a result of populations of TCRgammadelta+/CD3+ displaying MHC class I unrestricted cytotoxicity, was also displayed. Application of this culture system may allow a preemptive therapy approach to BKV-related complications in transplant recipients, based on CTL treatment guided by BKV DNA levels.

Risk factors for BK polyomavirus nephritis in renal allograft recipients1

Recurrent episodes of acute rejection (AR) and/or the intense immunosuppression used for their treatment have been proposed as risk factors for BK nephritis (BKN; BK refers to the initials of the first patient from whom this polyomavirus was isolated). To further examine the relationship between AR and BKN, we analyzed all kidney transplants performed at our center between January 1999 and August 2001 (n = 286). After a mean follow-up of 737 +/- 22 d, we identified nine cases of BKN (3.1%). The mean time to diagnosis of BKN was 326 +/- 56 d. No patient with BKN had a prior history of AR. During the same period, 62 patients were diagnosed with AR (22%). The mean time to diagnosis of AR was 197 +/- 40 d (p = 0.01 vs. time to diagnosis of BKN). Despite aggressive therapy with methylprednisolone and, in some cases, anti-lymphocyte antibody, none of these patients with AR developed BKN. We compared the baseline characteristics of patients in both groups and found that BKN patients were more likely to be white people (78 vs. 44%, p = 0.05) and male (89 vs. 53%, p = 0.04). Moreover, the mean tacrolimus (TAC) levels before diagnosis were higher in BKN than in AR patients (11.7 +/- 0.5 vs. 6.5 +/- 0.6 ng/mL, p < 0.001). In summary, our study shows that BKN often occurs in the absence of prior episodes of AR. In addition, our findings suggest that white males exposed to higher TAC levels are at greater risk of developing BKN.

BKV and SV40 infection of human kidney tubular epithelial cells in vitro

The interaction of BKV with its natural target cells, human kidney epithelial cells, has not been studied. In vitro infections of human primary kidney epithelial cells were performed to investigate a BKV infection in its natural host cell. BKV undergoes a lytic replication cycle in this system: high levels of T antigen expression were first detected at 36 h postinfection, while viral DNA replication, capsid protein expression, and progeny virus were observed at 48 h postinfection. It was observed that the related polyomavirus SV40 is incapable of infecting human kidney epithelium except in the presence of the GM1 ganglioside, recently reported to be an SV40 receptor.

Correlates of quantitative measurement of BK polyomavirus (BKV) DNA with clinical course of BKV infection in renal transplant patients

BK virus-allograft nephropathy (BKVAN) is an increasingly recognized complication after kidney transplantation. Quantitative tests have been advocated to monitor patients, but data demonstrating their efficacy are relatively limited. We developed a real-time PCR assay to quantitate BK virus loads in the setting of renal transplantation, and we correlated the BK virus load with clinical course and with the presence of BK virus in renal biopsy specimens. BK virus loads were measured in urine, plasma, and kidney biopsy samples in three clinical settings: (i) patients with asymptomatic BK viruria, (ii) patients with active BKVAN, and (iii) patients with resolved BKVAN. Active BKVAN was associated with BK viremia greater than 5 x 103 copies/ml and with BK viruria greater than 107 copies/ml in all cases. Resolution of nephropathy led to resolution of viremia, decreased viruria levels, and disappearance of viral inclusions, but low-level viral DNA persisted in biopsy specimens even for patients whose viruria was cleared. All but one patient in the resolved BKVAN group carried a urinary viral load below 107 copies/ml. Viral loads in patients with asymptomatic viruria were generally lower but in some cases overlapped with levels more typical of BKVAN. One patient with asymptomatic viruria and with a viral load overlapping values seen in BKVAN had developed nephropathy by the time of follow-up. In conclusion, serial measurement of viral loads by quantitative PCR is a useful tool in monitoring the course of BK virus infection. The results should be interpreted in conjunction with the clinical picture and biopsy findings.

Glomerular changes in BK virus nephropathy

This study seeks to define the glomerular changes that are associated with human BK virus nephropathy (BKVN). It is based on histopathologic review of 124 biopsies showing light-microscopic changes of viral nephropathy. The diagnosis of BKVN was confirmed by immunohistochemistry or by in situ hybridization. Histological lesions were scored by the Banff 97 criteria for renal allograft pathology and were correlated with clinical parameters. Viral cytopathic effect in the parietal Bowman's capsular epithelium was seen in 21/124 (17%) biopsies. Immunohistochemistry showed infection of Bowman's capsular epithelium in an additional 15/124 (12%) biopsies. Crescents were found in 15/124 (12%) samples. Glomerulitis exceeding grade Banff g1 was only occasionally shown (4/124=3% biopsies). Other pathologic lesions documented include mild increase in mesangial matrix in 23% biopsies, aneurysmal dilatation of glomerular capillaries in 28%, ischemic glomerulopathy in 62%, and chronic transplant glomerulopathy graded as mild (cg1) in 62% of biopsies and as moderate (cg2) in 2/124 (1.9%) biopsies. These findings show that infection of the glomerular epithelium cells can occur in a subset of patients with BKVN, most often in biopsies with high viral load in the tubular epithelium. Isolated crescents can occur in BKVN biopsies, but rapidly progressive glomerulonephritis is not observed. Two biopsies showed electron-dense deposits on ultrastructural examination, but a cause and effect relationship to BK virus infection could not be established.

Polyoma nephropathy and progressive multifocal leukoencephalopathy in a renal transplant recipient

Progressive multifocal leukoencephalopathy is a progressive and ultimately fatal white-matter disease of the brain that is associated with polyomavirus infection. It is uncommon in the general population, and even in the immunosuppressed patient, who is inherently at greatest risk for active infection with the virus, it is rare. The causative agent in progressive multifocal leukoencephalopathy, JC virus, has become increasingly important in recent years as its role in nephropathy in the renal transplant recipient has become better understood. We present a young renal transplant patient who developed nephropathy with renal biopsy changes consistent with polyomavirus lesions and then developed mental status changes and was diagnosed with progressive multifocal leukoencephalopathy.

Polyomavirus BK DNA quantification assay to evaluate viral load in renal transplant recipients

BACKGROUND

Several studies have disclosed a correlation between polyomavirus BK (BKV) and interstitial nephritis in renal transplant recipients and its quantification in urine and serum is therefore required to assess the role of BKV infection in nephropathy.

OBJECTIVE

This paper describes a urine and serum BKV-DNA quantification protocol devised to evaluate the viral load.

STUDY DESIGN

Screening of samples containing > or =10(3)/ml viral genome copies by a semi-quantitative polymerase chain reaction (PCR) assay is followed by precise quantification of the samples containing a high number of viral genomes in a quantitative-competitive (QC)-PCR assay. Generation of the competitor construct relied on the different sizes of wild-type and competitor amplicons.

RESULTS AND CONCLUSIONS

Screening by semi-quantitative PCR selects samples with a high number of viral genomes for use in the more labor-intensive and -expensive QC-PCR assay and thus provides a handy means for quantitative DNA analysis of large numbers of samples. The results obtained in BKV-DNA quantification in urine and serum samples from 51 renal transplant recipients (22 on treatment with tacrolimus (FK506) and 29 on cyclosporine A (Cy A)) are interesting: BKV-DNA findings (43.1%) in urine samples are in agreement with the BKV urinary shedding reported in literature (5-45%). With regard to immunosuppressive treatment, the percentage of activation of the infection (revealed by BKV-DNA detection in urine samples) in the two groups of therapy is similar (40.9% vs 44.8%). The observation that the viral load in urine is dissociated with that of serum suggests that both parameters should be investigated in evaluation of the pathogenetic role of BKV reactivation in renal transplant recipients. Moreover, our BKV-DNA quantification protocol could be used to monitor viral load in urine and serum samples from renal transplant recipients so as to detect those at risk of nephropathy and monitor their response to immunosuppression reduction therapy if it occurs.

Retransplantation in patients with graft loss caused by polyoma virus nephropathy

The characteristics and outcome in 10 patients who underwent retransplantation after losing their renal grafts to BK virus-associated nephropathy (BKAN) are described. The patients underwent retransplantation at a mean of 13.3 months after failure of the first graft. Nephroureterectomy of the first graft was performed in seven patients. Maintenance immunosuppression regimens after the first and second grafts were similar, consisting of a combination of a calcineurin inhibitor, mycophenolate mofetil, and prednisone. BKAN recurred in one patient 8 months after retransplantation, but stabilization of graft function was achieved with a decrease in immunosuppression and treatment with low-dose cidofovir. After a mean follow-up of 34.6 months, all patients were found to have good graft function with a mean creatinine of 1.5 mg/dL. From this collective experience from five transplant centers (although the follow-up after retransplantation was not extensive), it can be concluded that patients with graft loss caused by BKAN can safely undergo retransplantation. The risk of recurrence does not seem to be increased in comparison with the first graft.

Retransplantation after kidney graft loss due to polyoma BK virus nephropathy: successful outcome without original allograft nephrectomy

Although polyoma BK virus (BKV)-associated interstitial nephritis has received increasing attention because of its clinical relevance in kidney allograft recipients, data on risk for repeated renal transplantation after BKV-related allograft loss are limited, and the need to perform an original graft nephrectomy is the object of debate. A 15-year-old boy with renal failure secondary to Alport's syndrome underwent renal transplantation. His posttransplantation course was complicated by acute rejection episodes and the presence of circulating anti-glomerular basement membrane antibodies that required aggressive immunosuppressive treatment. Graft failure caused by BKV-associated interstitial nephropathy occurred despite a reduction in immunosuppression and cidofovir treatment. The patient received a second transplant without an original graft nephrectomy, and 15 months after retransplantation, he persists with optimal graft function and is constantly BKV DNA negative in both urine and plasma. Our report indicates that an original allograft nephrectomy may not be mandatory for successful retransplantation after graft loss caused by BKV nephropathy.

Simian virus 40 infection in humans and association with human diseases: results and hypotheses

Simian virus 40 (SV40) is a monkey virus that was introduced in the human population by contaminated poliovaccines, produced in SV40-infected monkey cells, between 1955 and 1963. Epidemiological evidence now suggests that SV40 may be contagiously transmitted in humans by horizontal infection, independent of the earlier administration of SV40-contaminated poliovaccines. This evidence includes detection of SV40 DNA sequences in human tissues and of SV40 antibodies in human sera, as well as rescue of infectious SV40 from a human tumor. Detection of SV40 DNA sequences in blood and sperm and of SV40 virions in sewage points to the hematic, sexual, and orofecal routes as means of virus transmission in humans. The site of latent infection in humans is not known, but the presence of SV40 in urine suggests the kidney as a possible site of latency, as it occurs in the natural monkey host. SV40 in humans is associated with inflammatory kidney diseases and with specific tumor types: mesothelioma, lymphoma, brain, and bone. These human tumors correspond to the neoplasms that are induced by SV40 experimental inoculation in rodents and by generation of transgenic mice with the SV40 early region gene directed by its own early promoter-enhancer. The mechanisms of SV40 tumorigenesis in humans are related to the properties of the two viral oncoproteins, the large T antigen (Tag) and the small t antigen (tag). Tag acts mainly by blocking the functions of p53 and RB tumor suppressor proteins, as well as by inducing chromosomal aberrations in the host cell. These chromosome alterations may hit genes important in oncogenesis and generate genetic instability in tumor cells. The clastogenic activity of Tag, which fixes the chromosome damage in the infected cells, may explain the low viral load in SV40-positive human tumors and the observation that Tag is expressed only in a fraction of tumor cells. "Hit and run" seems the most plausible mechanism to support this situation. The small tag, like large Tag, displays several functions, but its principal role in transformation is to bind the protein phosphatase PP2A. This leads to constitutive activation of the Wnt pathway, resulting in continuous cell proliferation. The possibility that SV40 is implicated as a cofactor in the etiology of some human tumors has stimulated the preparation of a vaccine against the large Tag. Such a vaccine may represent in the future a useful immunoprophylactic and immunotherapeutic intervention against human tumors associated with SV40.

Polyomavirus allograft nephropathy: sequential assessment of histologic viral load, tubulitis, and graft function following changes in immunosuppression

Our initial cases of polyoma virus allograft nephropathy (PVAN) received pulse steroids due to anxiety about concomitant acute rejection triggered by the presence of tubulitis. However, our current policy is to reduce immunosuppression in all cases. The aim of this study was to determine whether clinical follow-up in these patient categories shows any differences in: (a) histologic viral load, (b) grade of tubulitis, and (c) graft function. Reduced viral load assessed within 8 weeks was seen in 4/20 (20.0%) biopsies treated initially by increased immunosuppression, compared to 15/19 (83.3%) biopsies treated with reduced immunosuppression (p = 0.001, Fisher's exact test). Yet, >70% reversal of the rise in serum creatinine occurred in only 3/19 (15.8%) and 1/19 (5.3%) patients, respectively, in these two groups. Improved tubulitis was seen in 11/20 (55%) of biopsies treated with steroids, despite the lack of beneficial effect on serum creatinine in 12/19 (63.1%) instances. In biopsies not treated with any change in immunosuppression, the serum creatinine remained stable in 1/5 (20%) and worsened in 4/5 (80%) biopsies. These data demonstrate that in biopsies with PVAN and tubulitis, reduced immunosuppression is more effective in lowering viral load than steroid therapy. Lack of parallelism between viral load, tubulitis grade, and serum creatinine illustrates a complex interplay of viral and alloimmune factors leading to graft injury.

Polyomavirus BK

Polyomavirus hominis 1, better known as BK virus (BKV), infects up to 90% of the general population. However, significant clinical manifestations are rare and limited to individuals with impaired immune functions. BKV has been associated with diverse entities such as haemorrhagic cystitis, ureteric stenosis, vasculopathy, pneumonitis, encephalitis, retinitis, and even multi-organ failure. In addition, BKV has been implicated in autoimmune disease and possibly cancer. Due to high prevalence and frequent reactivation, the role of BKV in some of these pathologies has been difficult to define. Development of BKV diseases is likely to require complementing determinants in the host, the target organ, and possibly the virus, that are subject to modulators such as immunosuppression. These complex aspects are highlighted in polyomavirus-associated nephropathy (PAN), an emerging disease in renal allograft recipients that may jeopardise the progress in renal transplantation accomplished in the past 10 years. Intervention is difficult due to the lack of specific antivirals and relies mostly on improving immune control. Diagnostic strategies using urine cytology and BKV load measurements in plasma have led to earlier diagnosis of PAN, which increased the success rate of intervention. Case series suggest that cidofovir might be effective, especially when combined with reduced immunosuppression.

Population-based study of antibody to the human polyomaviruses BKV and JCV and the simian polyomavirus SV40

Molecular studies suggest that the simian polyomavirus SV40 is present in the human population, possibly introduced in contaminated polio vaccine. However, no recent seroepidemiological data exist in England on SV40 or on the two human polyomaviruses, BKV and JCV. A comparative age seroprevalence study was undertaken on 2,435 residual sera from 1991 by haemagglutination inhibition (HI) for BKV and JCV, and virus neutralisation for SV40. The overall rates of seropositivity for BKV and JCV were 81% and 35%, respectively, and each was significantly related to age (P < 0.001). BKV seroprevalence reached 91% at 5-9 years of age, but JCV seroprevalence reached only 50% by age 60-69 years. There was a highly significant association between BKV antibody titre and age (P < 0.001), titres decreasing linearly at a rate of 8.7% per 10 years (95% CI = 7.4-10% drop). Significantly more males than females had antibody to JCV (P = 0.013). In individuals under 40 years of age there was a significant negative association between the presence of antibody to BKV and JCV (P < 0.001). By contrast, the antibody prevalence to SV40 remained at 1.3-5% throughout all age groups and titres were low. There was a significant positive association between the presence of antibody to SV40 and antibody to both BKV (P < 0.001) and JCV (P = 0.009), and also to the geometric mean titre (GMT) of BKV antibody (P = 0.011). The results indicate that BKV and JCV are transmitted by different routes. There is no serological evidence that SV40 entered the human population during the past 80 years, and the possibility of cross-reaction with BKV or JCV antibody must be considered.

BK virus-associated renal problems--clinical implications

BK virus (BKV), a human polyomavirus, infects most of the human population, but clinically relevant infections are usually limited to individuals who are immunosuppressed. After primary infection, BKV remains latent in the kidneys and can be reactivated in immune deficiency conditions, including transplantation. As primary infection occurs in childhood, BKV may be particularly important in the pediatric transplant population. BKV is associated with tubulointerstitial nephritis and ureteric stenosis in renal transplant recipients and hemorrhagic cystitis in bone marrow transplant recipients. There are increasing reports of BKV causing nephropathy and cystitis in non-renal solid organ transplant recipients and other immunodeficiency diseases. This might be related to the use of more potent immunosuppressive regimens or increasing awareness of BKV as an important pathogen. Diagnosis of BKV disease is by biopsy. Histopathological changes in renal biopsy specimens may mimic rejection or drug toxicity, but BKV nuclear inclusions can be seen. Treatment is by reduction of immunosuppression. Antiviral agents such as cidofovir are showing promise. BKV DNA polymerase chain reaction in blood or biopsy may be helpful in monitoring therapy. The impact of BKV disease in children is not well understood and prospective studies are needed to elucidate this further. This article reviews the current understanding of BKV-associated renal problems.

Influence of surveillance renal allograft biopsy on diagnosis and prognosis of polyomavirus-associated nephropathy

BACKGROUND

Polyomavirus-associated nephropathy (PVAN) is an increasingly prevalent cause of allograft dysfunction.

METHODS

In 18 histologically proven cases of PVAN managed by reduced immunosuppression, monitoring of serum creatinine, and repeated biopsy, graft outcomes were correlated with clinical and histologic indices. Six months postdiagnosis the status of each graft was classified as poor (N = 7) or satisfactory (N = 11). Poor transplant status was defined as graft loss, increased severity of PVAN on repeat biopsy, or serum creatinine>3.0 mg/dL. Diagnosis resulted from either surveillance allograft biopsies (N = 8) or biopsies performed for increased serum creatinine (nonsurveillance, N = 10).

RESULTS

The surveillance biopsy group was more likely than the nonsurveillance group to have satisfactory graft status at 6 months (eight of eight vs. three of ten, P = 0.004) and had significantly lower serum creatinine at diagnosis, 3, and 6 months. Histologic scoring for chronic interstitial and tubular injury was lower in diagnostic surveillance biopsies compared to nonsurveillance biopsies (P = 0.01). Satisfactory transplant status was also associated with reduced or absent virus on repeat biopsy (P = 0.01). Poor transplant status was associated with a higher frequency of recipientneg/donorpos cytomegalovirus (CMV) serology (71% vs. 9%, P = 0.01).

CONCLUSION

Surveillance allograft biopsy provides an important means for earlier detection of PVAN and permits timely alterations to immunosuppression. Early diagnosis is associated with a lesser degree of interstitial fibrosis at diagnosis and lower baseline and subsequent serum creatinine.

Incidence of polyomavirus-nephropathy in renal allografts: influence of modern immunosuppressive drugs

BACKGROUND

In recent years an increasing number of cases with polyomavirus (PV)-nephropathy after renal transplantation were reported from several transplant centres. New, highly potent immunosuppressive drugs like tacrolimus or mycophenolate mofetil were accused as risk factors for this increase. However, data about the incidence of PV-nephropathy in correlation to different immunosuppressive therapy concepts are lacking.

METHODS

All renal transplant biopsies performed at Hannover Medical School between 1999 and 2001 (n=1276) were immunohistochemically screened for the presence of PV-specific proteins. The results were correlated to the different immunosuppressive therapy protocols and patients with PV-nephropathy were compared with a matched control group.

RESULTS

PV-nephropathy was found in <1% of all investigated allograft biopsies (11/1276) and in approximately 1% of all patients (7/638), respectively. All patients being immunohistochemically positive for PV-specific proteins also showed the typical morphological changes of PV-nephropathy. Four out of seven patients with PV-nephropathy were under triple immunosuppression comprising tacrolimus and mycophenolate mofetil. Under this immunosuppressive therapy protocol an eight times higher incidence and a 13 times higher risk (multivariate odds ratio 12.7) of PV-nephropathy was observed in our patients compared with the control group.

CONCLUSIONS

PV-nephropathy is a rare but serious complication after renal transplantation. A small group of patients under intensive immunosuppression comprising tacrolimus in combination with mycophenolate mofetil has a significantly increased risk of acquiring this deleterious complication.

Renal transplantation and polyomavirus infection: recent clinical facts and controversies

Although many articles have been published on polyomavirus-induced pathologies in transplant recipients, our knowledge regarding their clinical aspects remains relatively limited. In fact, the number of questions and controversies on the subject seems even to be increasing as new publications continue to appear. This article presents some of these controversies through a brief review of recent clinical facts about the three polyomaviruses that infect humans--JC virus, simian virus 40, and BK virus--as they relate to renal transplantation.

Polyomavirus BK infection in pediatric kidney-allograft recipients: a single-center analysis of incidence, risk factors, and novel therapeutic approaches

BACKGROUND

Although a growing body of literature regarding polyoma BK virus (BKV) infection and associated interstitial nephritis in kidney-allograft recipients is becoming available, the impact of BKV infection in the pediatric population has not been fully evaluated.

METHODS

In a retrospective analysis, we performed polymerase chain reaction (PCR) assays for BKV DNA in serum and urine samples from 100 pediatric kidney-allograft recipients referred to our institution in the last 5 years.

RESULTS

BKV viruria was observed in 26 of 100 patients, whereas BKV viremia was demonstrated in 5 patients. Serum creatinine was significantly higher in recipients with positive BK viremia compared with BKV DNA-negative patients (mean 2.66 vs. 1.14 mg/100 mL). Renal biopsy performed in 3 of 5 patients showed graft damage consistent with interstitial nephropathy. In the univariate analysis, negative antibody status of the recipient and the presence of mycophenolate mofetil in baseline immunosuppression were the two factors predictive of active BKV infection.

CONCLUSIONS

Our study shows that BKV-associated nephropathy is a relevant complication in the pediatric kidney transplantation setting also. Identification of patients at risk of developing virus-associated nephropathy, through prospective quantification of viral load, could improve clinical outcome by allowing the use of timely preemptive therapy guided by BKV DNA levels.

Polyomavirus reactivation in native kidneys of pancreas alone allograft recipients

BACKGROUND

Polyomavirus infection is common in childhood, with a seroprevalence of 60% to 100%. These viruses remain latent mostly in the kidney. Impairment in cellular immunity can allow reactivation of the virus. Reactivation can occur in 10% to 45% of renal allografts. A higher intensity of immunosuppression and the allogeneic microenvironment of the graft have been suggested to predispose to reactivation. There are limited data on the status of viral activity in the native kidneys of non-renal solid organ recipients.

METHODS

Thirty-eight recipients of pancreas transplant alone were evaluated for evidence of polyomavirus reactivation by urine cytology. All had received induction therapy and were maintained on tacrolimus, mycophenolate mofetil, and prednisone. The renal function and degree of exposure to immunosuppressive agents of patients shedding polyomavirus-infected renal tubular cells were compared with those of patients with negative urine cytology.

RESULTS

Screening cytology was performed 16 months (mean) after transplantation. Four subjects (11%) had polyomaviruria. The renal function at baseline and time of screening was comparable between the two groups. The 12-hour trough levels of tacrolimus were significantly higher in patients with positive cytology compared with those without viruria. The doses of mycophenolate mofetil and prednisone were not different between the two groups.

CONCLUSION

This study shows that polyomavirus reactivation in native kidneys and urinary tract of pancreas transplant alone patients is not uncommon. In these recipients, viral reactivation was not associated with significant renal functional impairment. The results also suggest that patients who are exposed to higher blood levels of tacrolimus are at higher risk of viral reactivation.

Polyomavirus infection and acute vascular rejection in a kidney allograft: coincidence or mimicry?

During the past decade, polyoma virus (PV) infection has emerged as an important cause of graft dysfunction and failure in kidney transplant recipients. Establishing the correct diagnosis can be difficult, however, because the histologic appearance of PV infection can resemble acute cellular rejection. We report a kidney-pancreas transplant recipient with PV infection, in whom both vascular and cellular rejection were dominant histologic features in a renal biopsy specimen. The patient was successfully managed by tapering immunosuppressive therapy, and continues to have good graft function 3 years after diagnosis of PV infection. This case highlights the spectrum of inflammatory changes associated with PV infection, and the need for caution when such changes are attributed to rejection.

Polyomavirus in kidney and kidney-pancreas transplant recipients

PURPOSE

To report the incidence and clinical characteristics of polyomavirus (PV) nephritis in kidney (KTX) and kidney-pancreas transplant (KPTX) recipients.

METHODS

Single center retrospective analysis of all cases of PV nephritis in KTX and KPTX patients transplanted between 1994 and 1999.

RESULTS

Thirteen (5 KTX and 8 KPTX) patients (2.1%) had PV nephritis diagnosed on multiple biopsies (n = 22) among 504 KTX and 106 KPTX recipients. The incidence of PV nephritis was higher in cadaver donor transplants (2.6% cadaver vs. 0.7% living donors), after KPTX (1% KTX vs. 7.5% KPTX), in males (3.3% male vs. 0.7% female), and in diabetic patients (4.4% diabetic vs. 0.8% nondiabetic). The mean time to diagnosis of PV nephritis was 18 (range 6-48) months after KTX and 17 (range 9-31) months after KPTX. Three KTX patients and 5 KPTX patients had calcineurin inhibitor toxicity on biopsy prior to developing PV nephritis. Reduction in immunosuppression occurred in 100% of KTX and 63% of KPTX patients. Three patients (23%) developed rejection within 3 months of diagnosis of PV, 1 after a reduction in immunosuppression. Despite multiple antiviral treatment regimens, renal allograft failure requiring dialysis occurred in 60% of KTX and 50% of KPTX patients. All KPTX patients remain insulin independent and 2 were successfully retransplanted with living donor kidneys. 2 patients (15%) died but there was no mortality directly related to the virus.

CONCLUSIONS

Polyomavirus nephritis may be increasing in incidence and appears to be unresponsive to either conventional antiviral agents or a reduction in immunosuppression. Most of our cases occurred in male diabetic patients undergoing cadaveric donor transplantation and were preceded by biopsy-proven nephrotoxicity. Further studies are needed to better define the pathogenesis of PV and effective antiviral treatment.

Renal allograft loss as the result of polyomavirus interstitial nephritis after simultaneous kidney-pancreas transplantation: results with kidney retransplantation

BACKGROUND

Polyomavirus (PV) infection in kidney transplant patients has been reported to cause interstitial nephritis and subsequent graft loss. The cornerstone of current therapy is a reduction in immunosuppression, which can subsequently lead to kidney allograft rejection. This dilemma becomes even more challenging in the setting of simultaneous kidney-pancreas transplantation, because a reduction in immunosuppression may result in rejection of the pancreas allograft. Antiviral therapy has not been shown to be clinically successful in decreasing the risk of graft loss secondary to PV infection. Furthermore, because of limited experience, the decision to perform retransplantation in patients who lost their primary kidney grafts to PV interstitial nephritis becomes a difficult one.

METHODS

Retrospective review and case studies.

RESULTS

We report two successful living donor kidney retransplants in simultaneous kidney-pancreas transplant patients who lost their first kidney grafts to PV infection. Both patients are receiving rimantadine therapy and performing well, with functioning kidney and pancreas grafts and no evidence of recurrent PV interstitial nephritis 22 and 37 months after retransplantation.

CONCLUSIONS

Although follow-up is limited, our initial experience would indicate that graft loss secondary to PV interstitial nephritis is not an absolute contraindication for kidney retransplantation.

Treatment of refractory BK virus-associated nephropathy with cidofovir

BK virus-associated nephropathy (BKVN) has become recognized as an important cause of allograft dysfunction in renal transplant recipients and despite reduction in immunosuppression, 30-40% of recipients ultimately progress to allograft loss. Cidofovir is an antiviral agent that demonstrates in vitro activity against murine polyomavirus and has been proposed for treatment of BKVN in renal allograft recipients. We describe the clinical course, renal function, serial renal histology and urine and blood viral load measurements in two consecutive patients with refractory BKVN who were treated with low-dose cidofovir (0.25 mg/kg IV). In each case, renal dysfunction and BK viral load progressed despite reduced immunosuppression, and persistent BK virus infection was documented in serial renal allograft biopsy specimens. Administration of low-dose cidofovir was associated with clearance of BK virus DNA from blood and allograft, and stabilization of renal function in both patients, without significant toxicity. These preliminary data suggest that low-dose cidofovir may be tolerated, even among renal transplant recipients with significant renal dysfunction due to BKVN. Prospective, controlled trials are warranted to further define the optimal dose, toxicity and potential role of cidofovir in renal transplant recipients with BK virus nephropathy.

Quantitative viral load monitoring and cidofovir therapy for the management of BK virus-associated nephropathy in children and adults

BACKGROUND

BK virus (BKV)-associated nephropathy (BKVAN) has been increasingly recognized as an important cause of renal transplant dysfunction. We report the role of quantitative viral load monitoring in the management of BKVAN.

METHODS

We developed a real-time quantitative polymerase chain reaction (PCR) assay for BKV detection in urine and plasma. Four renal allograft recipients, including two children, with BKVAN were treated with low-dose cidofovir and followed prospectively.

RESULTS

The PCR assay showed a detection limit of 10 viral copies with an intra-assay coefficient of variation of 19%. All four patients with BKVAN demonstrated intranuclear inclusions on allograft biopsy and a progressive rise in serum creatinine; three patients underwent multiple biopsies before the diagnosis of BKVAN was made. Three of the patients experienced a "viral syndrome" before the onset of renal dysfunction. One child also demonstrated an echogenic renal mass. All of the patients demonstrated strongly positive urinary PCR values (>100,000 copies/microL). BKV DNA was also detected in the plasma of three patients. All the patients were treated with intravenous low-dose cidofovir (0.25-1 mg/kg per dose, every 2-3 weeks, without probenecid). BK viruria resolved within 4 to 12 weeks (after 1-4 doses) of the cidofovir therapy, and all patients remain with stable renal function 6 to 26 months posttherapy.

CONCLUSIONS

Quantitative PCR for BKV is a sensitive and reliable method for following the course of the infection in renal transplant patients. In addition, cidofovir therapy may be useful in the treatment of some of these patients, and its role needs to be investigated further.

Acute Adenoviral Infection of a Graft by Serotype 35 Following Renal Transplantation

Adenoviral infections of immunocompetent patients usually present as self-limiting pharyngitis, gastroenteritis, urocystitis, or conjunctivitis. In immunosuppressed patients, development of the illness can be severe, even life-threatening or fatal, and therapeutical intervention is difficult. Previous case reports of adenoviral infections after kidney transplantation have described a symptomatology of hemorrhagic cystitis, fever, renal dysfunction, and rarely fatal systemic dissemination. Here we report on a 46-year-old female renal transplant recipient suffering from adenoviral serotype 35 nephritis of the donor organ 29 days after transplantation. In this case, the main symptoms of the adenoviral infection were high fever and progressive renal failure of the transplanted organ. At the peak of the clinical symptoms, owing to histological and immunohistochemical evaluations of a kidney biopsy, we were able to establish the diagnosis in time so that adequate therapy could be employed. Immunosuppression was reduced and modified, and a self-limiting course of the infection was observed, followed by significant improvement of graft function. Subsequent to histological diagnosis, adenoviral particles were isolated from urine and identified as adenovirus serotype 35. Adenoviral nephritis of the transplanted organ should be considered in the differential diagnosis of persistent anuria after kidney transplantation. Our case highlights the importance of applying all possible diagnostic techniques, including histological evaluation of renal biopsies.

Lytic JC virus infection in the kidneys of AIDS subjects

Our objective was to investigate the role of the human polyomavirus JC virus as a possible cause of renal damage in AIDS subjects. Histology, immunohistochemistry, and molecular biology were used to evaluate the frequency of viral infection, genotypes, viral status, and the presence of rearrangements or point mutations in specific genomic regions of strains isolated from renal tissue. Formalin-fixed, paraffin-embedded sections of postmortem renal specimens obtained from 111 unselected AIDS patients were stained for routine histology and with anti-SV40 antibody. The immunohistochemically positive specimens were further investigated by means of nested polymerase chain reaction for different polyomavirus genomic regions (large T, transcriptional control region, and viral protein 1). Furthermore, the sequences of transcriptional control region and viral protein 1 were also analyzed. Immunohistochemistry was positive in seven cases (6.3%), four of which showed morphological evidence of viral replication (intranuclear inclusion bodies and/or intratubular cellular casts): in all seven cases, only epithelial tubular cells (with and without inclusion bodies) and cellular casts were stained. The JC virus genome was identified by polymerase chain reaction in five of the seven immunohistochemically positive cases; transcriptional control region and viral protein 1 were amplified in, respectively, three and four cases. Transcriptional control region sequence analysis revealed major rearrangements in all three cases, with duplications of all the transcriptional factor-binding sites, whereas no point mutations were found in the viral protein 1 region, which was characterized as Type 1A in all cases. For the first time in AIDS subjects, this study shows that although rarely, JC virus can replicate in renal tissue. Molecular biology revealed major rearrangements in the transcriptional control region that, together with other unknown factors, could justify the increased pathogenicity of this human polyomavirus.

BK virus and SV40 co-infection in polyomavirus nephropathy

BACKGROUND

Polyomavirus (PV) nephropathy has been attributed to reactivation of BK virus (BKV) or more rarely JC virus (JCV). The simian virus (SV) 40 is PV that was likely introduced into the human population through contaminated vaccines. The purpose of this study was to identify and characterize the PV that is associated with PV nephropathy.

METHODS

The clinical diagnosis of PV nephropathy (PVN) was made in patients with acute deterioration in renal function whose renal biopsies showed typical viral cytopathic changes in tubular epithelial cells and staining for PV T antigen. Polymerase chain reaction (PCR) amplification of DNA from peripheral blood mononuclear cells (PBMC), urinary cells, and renal biopsy tissue was performed using specific primers for the transcription control regions of BKV, JCV, and SV40, respectively.

RESULTS

Six cases of PV nephropathy were identified in 91 renal transplant recipients (7%). Immunosuppressive therapy was modified in all patients. Renal function stabilized or improved in four patients and deteriorated in two patients, and one patient has lost his allograft, after follow-up from 2 to 25 months. PCR detection demonstrated BKV genome in three of five PBMC samples, six of six urinary cell samples, and two of four renal biopsies. SV40 genome was detected in two of five PBMC samples, one of six urinary cell samples, and two of four renal biopsies. Infectious SV40 and BKV was demonstrated in CV-1 co-cultures using urine from one patient. JCV was not detected in any PVN sample. Co-infection with BKV and SV40 was found in two PVN patients. Urine samples obtained 12 months after transplant from 26 transplant recipients without PVN on simultaneous protocol renal biopsy were analyzed by PCR; BKV genome was demonstrated in 5 of 25 samples, JCV genome was demonstrated in 3 of 25 samples, and SV40 genome was demonstrated in 0 of 25 samples.

CONCLUSION

The authors report molecular evidence that co-infection with BKV and SV40 occurs in renal transplant patients with PVN, suggesting that SV40 may contribute to PVN after renal transplant.

Pathogenesis and management of polyomavirus infection in transplant recipients

Polyomaviruses (JC virus [JCV], BK virus [BKV], and simian virus 40 [SV40]) establish subclinical and persistent infections and share the capacity for reactivation from latency in their host under immunosuppression. JCV establishes latency mainly in the kidney, and its reactivation results in the development of progressive multifocal leukoencephalopathy. BKV causes infection in the kidney and the urinary tract, and its activation causes a number of disorders, including nephropathy and hemorrhagic cystitis. Recent studies have reported SV40 in the allografts of children who received renal transplants and in the urine, blood, and kidneys of adults with focal segmental glomerulosclerosis, which is a cause of end-stage renal disease and an indication for kidney transplantation. Clinical syndromes related to polyomavirus infection are summarized in the present review, and strategies for the management of patients who receive transplants are discussed.

Noninvasive diagnosis of BK virus nephritis by measurement of messenger RNA for BK virus VP1 in urine

BACKGROUND

Polyoma virus type BK (BKV) nephritis has emerged as an important cause of renal allograft dysfunction and graft failure. Its diagnosis is contingent on the invasive procedure of allograft biopsy. A noninvasive diagnostic test for BKV nephritis could improve clinical outcome.

METHODS

We obtained 25 urine specimens from 8 renal allograft recipients with biopsy-confirmed BKV nephritis, 31 samples from 28 recipients in whom BKV nephritis was excluded by allograft biopsy, and 74 specimens from 34 patients with stable allograft function. RNA was isolated from the urinary cells and reverse transcribed to complementary DNA. We designed gene-specific oligonucleotide primers and probes for the measurement of messenger RNA (mRNA) encoding BKV VP1 protein and a constitutively expressed 18S ribosomal RNA (rRNA) by real-time quantitative polymerase chain reaction. We explored the hypothesis that BKV VP1 mRNA levels predict BKV nephritis.

RESULTS

The levels of BKV VP1 mRNA but not the levels of 18S rRNA predicted BKV nephritis. Analysis involving the receiver operating characteristic curve demonstrated that BKV nephritis can be predicted with a sensitivity of 93.8% and a specificity of 93.9% with the use of a cutoff value of 6.5 x 10 BKV VP1 mRNA copy number per nanogram of total RNA ( <0.00001). In the receiver operating characteristic curve analysis, the calculated area under the curve was 0.949 (95% confidence interval, 0.912 to 0.987, <0.00001) for BKV VP1 mRNA levels and 0.562 (95% confidence interval, 0.417 to 0.708, >0.2) for 18S rRNA.

CONCLUSIONS

Measurement of BKV VP1 mRNA in urinary cells offers a noninvasive and accurate means of diagnosing BKV nephritis.

Quantitation of viral DNA in renal allograft tissue from patients with BK virus nephropathy

BACKGROUND

BK virus (BKV) allograft nephropathy (BKVAN) is a complication in renal transplantation recipients. Histopathology is the gold standard for diagnosis. Quantitative polymerase chain reaction (PCR) assay for renal biopsy has not been evaluated as a diagnostic test. Determination of renal BKV load may identify patients at risk for disease before histologic nephropathy.

METHODS

Quantitative PCR assay for BKV DNA was performed in 28 biopsies of patients with BKVAN; 50 biopsies were performed before a diagnosis of BKVAN, and 126 control biopsies were from patients without a history of BKVAN.

RESULTS

BKV DNA was present in 19 of 50 (38%) biopsies performed 1 to 164 weeks before diagnosis of BKVAN. The viral load (mean 216 copies/cell) was lower than in biopsies of patients with BKVAN (mean 6063 viral copies/cell, <0.05). In 10 of 127 (7.8%) control biopsies, a low level of BKV DNA (mean 3.8 copies/cell) was found in three biopsies from chronic allograft nephropathy patients; two biopsies with acute rejection; four biopsies with borderline change; and one biopsy with cytomegalovirus nephritis.

CONCLUSION

BKV load exceeding 59 copies per cell identified all cases of BKVAN. The diagnostic sensitivity, specificity, positive predictive value, and negative predictive value of quantitative PCR were 100%, 92.1%, 73.6%, and 100%, respectively. Lower levels of BKV DNA were identified in biopsies performed before viral nephropathy development. Future research will determine if earlier recognition of at-risk patients allows application of antiviral strategies to improve graft outcome.

Prospective study of polyomavirus type BK replication and nephropathy in renal-transplant recipients

BACKGROUND

Nephropathy associated with the polyomavirus type BK (BKV) nephropathy has emerged as a cause of allograft failure linked to immunosuppressive regimens containing tacrolimus or mycophenolate mofetil. The presence of viral inclusions, known as "decoy cells," in urine and the presence of BKV DNA in plasma have been proposed as markers for the replication of BKV and associated nephropathy, but data from prospective studies have been lacking.

METHODS

In a prospective, single-center study, we followed 78 renal-transplant recipients who were receiving immunosuppressive therapy that included tacrolimus (37 patients) or mycophenolate mofetil (41 patients). Urine was tested for the presence of decoy cells at routine visits. BKV DNA was measured 3, 6, and 12 months after transplantation and whenever decoy cells were detected. The viral load in plasma was quantified with the use of a real-time polymerase-chain-reaction method. Renal biopsy was performed if allograft function deteriorated.

RESULTS

Twenty-three patients had decoy-cell shedding a median of 16 weeks after transplantation (range, 2 to 69), 10 patients had BKV viremia at a median of 23 weeks (range, 4 to 73), and 5 had BKV nephropathy at a median of 28 weeks (range, 8 to 86). Kaplan-Meier estimates of the probability of decoy-cell shedding, viremia, and nephropathy were 30 percent (95 percent confidence interval, 20 to 40 percent), 13 percent (95 percent confidence interval, 5 to 21 percent), and 8 percent (95 percent confidence interval, 1 to 15 percent), respectively. Antirejection treatment, particularly with corticosteroids, was associated with BKV replication and nephropathy. The viral load in plasma was higher in patients with BKV nephropathy than in those without nephropathy (P<0.001 by the Mann-Whitney test). BKV antibodies were detected in 77 percent of the 78 patients before transplantation, including 4 of 5 with BKV nephropathy.

CONCLUSIONS

BKV nephropathy in renal-transplant recipients represents a secondary infection associated with rejection and its treatment in most cases and could be monitored by measuring the viral load in plasma.

BK virus-associated hemorrhagic cystitis in a Human Immunodeficiency Virus-infected patient

BK virus-associated hemorrhagic cystitis is a common clinical problem in bone marrow transplant recipients but is considered rare in other immunosuppressed patient populations. We describe a human immunodeficiency virus-infected patient with non-Hodgkin's lymphoma in whom BK virus-associated hemorrhagic cystitis developed; viruria was quantitated in urine by immunocytochemistry, and the patient showed no response to cidofovir.

Clinical course of polyoma virus nephropathy in 67 renal transplant patients

Polyoma virus (PV) can cause interstitial nephritis and lead to graft failure in renal transplant recipients. The clinical course of patients with polyoma virus nephritis (PVN) is not well understood, partially due to its relatively low incidence. This study is a retrospective analysis of our experience over 4 yr. The specific purpose is to outline the clinical course and outcome of patients with PVN and to study the relationship between immunosuppression and the disease process. Between June 1997 and March 2001, 67 patients with graft dysfunction were found to have biopsy-proven PVN. The diagnosis was made at a mean of 12.8 +/- 9.9 mo posttransplantation. The majority of patients were men (79%) with a mean age of 54 +/- 14 yr (range, 28 to 75). All patients received immunosuppression with a calcineurin inhibitor (tacrolimus in 89% of patients). All patients except two received mycophenolate mofetil and prednisone. After the diagnosis of PVN, maintenance immunosuppression was reduced in 52 patients and remained unchanged in 15 patients. After reduction of immunosuppression, eight patients (15.3%) developed acute rejection and six (11.5%) became negative for PV in biopsy and urine. After a mean observation period of 12.6 mo (mean of 26 mo posttransplantation), 16.4% of patients had lost their grafts (8 of 52 in the reduction group and 3 of 15 in the no change group). In comparison to a case-matched polyoma virus-negative control group, the PVN patients were older (P =.0004) and there was a predominance of men (P = 0.02). Kaplan-Meier analysis demonstrated that patients with PVN had reduced graft survival compared with negative controls (P =.0004). It is concluded that PVN is a serious hazard for renal transplant recipients and contributes directly to graft loss. Antiviral drugs are needed, as the reduction of immunosuppression alone may not significantly improve graft function in patients with already established PVN. Although multiple factors probably play a role in the development of PVN, judicious use of immunosuppressive agents is indicated to minimize the occurrence of this infection.

Morphological spectrum of polyoma virus disease in renal allografts: diagnostic accuracy of urine cytology

The morphological features of polyoma virus disease (PVDz) in 571 concurrent urine and biopsy samples from 413 patients are described. In 54 patients PV was found in both biopsy and urine samples. Histologically, PV presented as: (a) mild, viral cytopathic/cytolytic changes, with absent or minimal inflammation involving isolated tubules; (b) moderate and severe, cytopathic/cytolytic changes associated with patchy or diffuse tubulo-interstitial inflammation and atrophy; (c) advanced, graft sclerosis with rare or absent viral cytopathic changes, indistinguishable from chronic allograft nephropathy. Histological progression from mild to moderate or severe disease was seen in 28 patients. The mean post-transplantation time at diagnosis was similar in patients with mild or moderate-severe renal involvement (1.05 and 1.3 years, respectively). All patients presented with similarly increased values of serum creatinine (mean 1.35 mg/dL). There was strong correlation between the number of PV infected cells in urine and the concurrent biopsies (p = 0.0001). In 13 patients PV was found only in urine; of these, two developed PVDz later. The positive predictive value of a positive urine was 90%, the negative predictive value of a negative urine was 99% and the accuracy of the test was 97%. We conclude that urine cytology is useful to evaluate renal transplant patients with PV reactivation because sloughed tubular cells are found in urine and positive urine samples are a consistent manifestation of PV renal involvement.

Expression and antigenic characterization of the major capsid proteins of human polyomaviruses BK and JC in Saccharomyces cerevisiae

BK and JC viruses are ubiquitous human polyomaviruses that are associated with post-transplant interstitial nephritis (BK virus) and progressive multifocal leucoencephalopathy (JC virus). The use of a yeast system to express the major capsid protein (VP1) of two antigenic variants of BKV (strains SB and AS) and JCV is described. VP1s of AS and JCV expressed in Saccharomyces cerevisiae produced proteins of expected molecular weight as determined by gel electrophoresis whereas that of SB appeared to be lower than anticipated. However, all VP1s self-assembled into virus-like particles (VLP) retaining sialic acid-binding and antigenic properties of native virions. This method is highly efficient for producing recombinant proteins and therefore provides an alternative to the baculovirus system.