Human polyoma virus-associated interstitial nephritis in the allograft kidney

BK virus regulatory region rearrangements in brain and cerebrospinal fluid from a leukemia patient with tubulointerstitial nephritis and meningoencephalitis

BK virus (BKV) was recovered by polymerase chain reaction (PCR) from brain, kidney, lung, urine, and cerebrospinal fluid (CSF) of a fatal case of BKV tubulointerstitial nephritis with dissemination to lung and brain. Viral regulatory regions in PCR-amplified urine and the lung samples were identical to the archetypal structure, WWT. In the brain and CSF, a rearranged sequence predominated, however. A 94-bp deletion preceded a 71-bp tandem duplication because the same 94-bp segment was deleted from both copies. PCR-amplified regulatory region products were cloned and sequenced to define further the extent of the rearranged structures. Two kidney clones were archetypal, whereas two others were rearranged differently from the brain and from each other. In contrast to the brain clones, the kidney rearrangements seemed to involve deletion after duplication. Three of four brain clones sequenced were identical to the rearrangement found to dominate in the PCR product. A fourth clone showed two short deletions without any duplication. The four CSF clones all showed rearrangements identical to that which was amplified by PCR from CSF and brain. This represents the first molecular analysis of a BKV strain obtained from a central nervous system infection, and it reveals regulatory region rearrangements reminiscent of those described in JC virus from brains with progressive multifocal leukoencephalopathy. We suggest that the presence in the CSF of BKV with a dominant rearranged regulatory region may be useful in the diagnosis of BKV meningoencephalitis secondary to BKV nephritis.

Polyomavirus nephropathy in native kidneys of a solitary pancreas transplant recipient

BACKGROUND

Latent polyomavirus (PV) infection of the urinary tract can be reactivated by immunosuppression. When this occurs in the renal allograft, permanent loss of allograft function can occur. Polyomavirus reactivation could potentially affect the native kidneys of nonrenal transplant recipients and cause renal dysfunction.

METHODS

This article describes a case of PV nephropathy in the native kidneys of a solitary-pancreas transplant recipient. This patient had a progressive increase in serum creatinine. Screening urine cytology showed numerous cells with cytopathic changes suggestive of polyomavirus infection.

RESULTS

Biopsy of the native kidneys of this patient showed renal tubular cells with intranuclear inclusions characteristic of PV infection, which was confirmed by immunohistochemistry. Electron microscopy showed intranuclear viral particles. Patchy inflammation and fibrosis also were noted.

CONCLUSION

Polyomavirus reactivation can occur in the native kidneys of nonrenal solid organ transplant recipients. This should be considered in the differential diagnosis of renal impairment in these patients. The effects of PV reactivation on long-term native kidney function are not known.

Successful retransplantation after renal allograft loss to polyoma virus interstitial nephritis

BACKGROUND

Although polyoma virus infection is being increasingly recognized as a cause of renal allograft dysfunction and failure, the risk of polyoma recurrence in a subsequent transplant is unknown. We present the first reported case of successful retransplantation after polyoma virus-induced renal allograft loss.

CASE REPORT

A 40-year-old Caucasian woman received a cadaveric kidney transplant. Baseline immunosuppression included corticosteroids, mycophenolate mofetil, and tacrolimus. Her post-transplant clinical course was complicated by an early acute rejection episode on posttransplant day (PTD) 6, that warranted treatment with OKT3. A biopsy performed on PTD 154 to evaluate a rise in creatinine revealed polyoma virus interstitial nephritis. Despite reduction in immunosuppression, the renal function progressively worsened and dialysis was initiated by PTD 160, followed by transplant nephrectomy on PTD 184. Four months later, she received a living related kidney from her sister. Immunosuppression was initiated with prednisone, azathioprine, and tacrolimus. She had immediate graft function with a decrease in serum creatinine from 12.8 to 1.1 mg/dl. Three and one-half years after her second renal transplant, her allograft functions well, with a serum creatinine of 1 mg/dl. Both quantitative and qualitative assays of blood and urine (by PCR) remain negative for BK virus, indicating the absence of virus reactivation.

CONCLUSION

Judicious retransplantation should be considered as a therapeutic option in the management of polyoma virus induced graft failure. Previous graft loss secondary to polyoma virus infection is not a contraindication to retransplantation.

DNA sequencing of viral capsid protein VP-1 region in patients with BK virus interstitial nephritis

BACKGROUND

Mutations in the viral capsid protein VP-1 region are associated with increased pathogenicity of polyomavirus in experimental systems. This study sought to determine whether analogous viral genetic changes occur in human BK virus (BKV) interstitial nephritis (ISN).

METHODS

PCR was used to amplify a 94-bp nucleotide sequence of the viral capsid protein VP-1 region (positions 1740-1833, Dun numbering) in 49 biopsies obtained from 24 patients with BKV-ISN. DNA sequencing was performed by the dideoxy method.

RESULT

The VP-1 region was highly polymorphic and 22 "hot spots" of sequence variability were noted. Genotypes I, II, and IV were assigned to 13, 1, and 5 cases, respectively, but 5 cases could not be unambiguously classified due to sequence heterogeneity at sites used to discriminate between genotypes. Even in cases where genotypes could be assigned, only 5 biopsies showed complete sequence identity with published genotype sequences. Sequential biopsies showed temporal changes in one or more nucleotides in all patients with multiple samples. In one patient, the initial biopsy showed viral genotype 1, although subsequent biopsies showed complex genetic patterns, including a biopsy consistent with viral genotype IV.

CONCLUSIONS

Many viral strains associated with BKV-ISN are difficult to classify and possibly distinct from those described in kidney transplant recipients without BKV-ISN. VP-1 sequences undergo continual modification as patients are followed in time. This genetic instability could conceivably have implications for evasion of host immunity and development of resistance to antiviral drugs.

Rapid kidney allograft failure in patients with polyoma virus nephritis with prior treatment with antilymphocyte agents

Interstitial nephritis owing to polyoma virus infection (PVi) mimics acute allograft rejection. The risk factors for graft failure associated with PVi are unknown. This prompted us to analyse the relationship between the use of antilymphocyte agents (ALA) and graft dysfunction in renal transplant recipients with PVi. Renal transplant recipients who were diagnosed to have PVi nephritis at the Medical College of Wisconsin were included in this study. PVi nephritis was confirmed by urine cytology and characteristic renal histological findings in a total of 14 cases. Other viruses were excluded by immunohistochemistry studies. Patients were divided into two groups: Group A (n = 7) received ALA (OKT3/ATGAM) as treatment for presumptive acute rejection and Group B (n = 7) did not receive ALA therapy. The progression of renal function (GFR) was estimated by a 100/ plasma creatinine and an actuarial kidney survival was estimated by the Kaplan-Meier method. The demographics (age, gender, race, retransplant and kidney versus. kidney/pancreas), prior treatment with steroids for presumptive acute rejection, and renal function at the time of PVi diagnosis were similar betwoen groups. The fall in GFR/month was 6 mL/min/month with prior ALA therapy compared with 1 mL/min/month in those who did not receive ALA, p = 0.002. All seven grafts were lost in the ALA group compared with only two of seven grafts in the other group, p = 0.005. The use of ALA was associated with a rapid fall in GFR and graft failure in patients with PVi nephritis. Careful diagnosis of PVi is warranted in renal allograft recipients prior to initiating ALA therapy.

Polyomavirus BK nephropathy: a (re-)emerging complication in renal transplantation

Persisting polyomavirus replication is now widely recognized as a (re-)emerging cause of renal allograft dysfunction. Up to 5% of renal allograft recipients can be affected about 40weeks (range 6-150) post-transplantation. Progression to irreversible failure of the allograft has been observed in up to 45% of all cases. The BK virus strain is involved in the majority of the cases. Risk factors may include treatment of rejection episodes and increasing viral replication under potent immunosuppressive drugs such as tacrolimus, sirolimus or mycophenolate. The diagnosis requires the histological demonstration of nuclear polyomavirus inclusions in affected tubular epithelial cells. Interstitial inflammatory infiltrates and fibrosis become more prominent in the persisting disease and may be difficult to distinguish from (coexisting) rejection. Detection of polyomavirus-inclusion bearing cells ('decoy cells') in the urine and quantification of BK virus DNA in the plasma have been proposed as surrogate markers for polyomavirus replication and allograft disease, respectively. Antiviral treatment is not yet established; however, reports of treatment with cidofovir are encouraging. Current management aims at the judicious modification and/or reduction of immunosuppression which, in view of preceding or concurrent rejection, is not without risk.

Utility of urinary cytology for diagnosing human polyoma virus infection in transplant recipients: a study of 37 cases with electron microscopic analysis

Human polyoma virus (HPOV) infection is associated with hemorrhagic cystitis, tubulointerstitial nephritis, and renal transplant dysfunction/allograft loss. We evaluated the utility of cytologic examination to detect HPOV infection in 37 urinary cytology (UC) samples (3 bladder washings, and 34 voided samples) from 29 transplant patients, compared to electron microscopic studies (EMS). Evidence of viral infection was found in 11 specimens (30%). Five cases were diagnosed as HPOV by both UC and EMS. One was positive for HPOV by EMS only. Two cases diagnosed as HPOV by UC were demonstrated to be adenovirus (AV) with EMS. Two cases diagnosed as cytomegalovirus (CMV) by EMS had negative UC. One was called HPOV by UC; EMS in this case was negative. Compared to EMS, the sensitivity and specificity of UC for detecting HPOV were 83% and 90%, respectively, with a positive predictive value of 63% and a negative predictive value of 96%. We conclude that UC is a relatively sensitive and specific method for detecting active HPOV infection in transplant patients, and is important in light of the clinical significance of HPOV infection in transplant recipients. The sensitivity and accuracy of UC for diagnosing HPOV can be increased by adding EMS.

BK virus in solid organ transplant recipients: an emerging syndrome

BK virus is a human polyomavirus associated with a range of clinical presentations from asymptomatic viruria with pyuria to ureteral ulceration with ureteral stenosis in renal transplant patients or hemorrhagic cystitis in bone marrow transplant recipients. Infection of renal allografts has been associated with diminished graft function in some individuals. Fortunately, however, the majority of patients with BK virus infections are asymptomatic. The type, duration, and intensity of immunosuppression are major contributors to susceptibility to the activation of BK virus infection. Histopathology is required for the demonstration of renal parenchymal involvement; urine cytology and viral polymerase chain reaction methods are useful adjunctive diagnostic tools. Current, treatment of immunosuppressed patients with polyomavirus viruria is largely supportive and directed toward minimizing immunosuppression. Improved diagnostic tools and antiviral therapies are needed for polyomavirus infections.

Molecular characterization and sequence analysis of polyomavirus strains isolated from needle biopsy specimens of kidney allograft recipients

We retrospectively examined 29 renal allograft biopsy specimens from 42 kidney transplant recipients by means of molecular biologic techniques (nested polymerase chain reaction), immunohistochemical analysis (anti-SV40 antibody), and histologic examination to evaluate the presence of polyomaviruses (PVs), viral genotypes, genomic mutations, and their pathologic significance. PV genomes were found in six cases (21%); restriction fragment length polymorphism analysis characterized 4 as JC virus (JCV) and 2 as BK virus (BKV). The latter also were positively stained immunohistochemically and showed histologically typical intranuclear viral inclusions; JCV cases were negative. DNA sequence analysis revealed only minor changes in the 4 JCV cases (3 archetypes and 1 JCV type 3, not associated with a known pathogenic genotype) but identified 2 specific variants in the BKV isolates (AS and WW strains). Given the different histologic findings (mixed inflammatory infiltration in the AS and no inflammation in the WW strain), we speculate that different BKV strains may cause differential damage in transplanted kidneys. Finally, the negative histologic and immunohistochemical JCV results, as well as the absence of viral mutations, indicate that JCV renal infection is latent in transplant recipients.

Polyomavirus BK nephropathy in a kidney transplant recipient: critical issues of diagnosis and management

Diagnosis of polyomavirus BK nephropathy and treatment by low-dose immunosuppression may be optimized by using surrogate markers, such as the detection of viral inclusion bearing cells in the urine and polyomavirus BK DNA in plasma by polymerase chain reaction. These markers were used prospectively in the management of a 44-year-old woman and led to the diagnosis of polyomavirus BK nephropathy at an early stage. The management was complicated by the concurrence of acute allograft rejection. Two treatment steps were initiated: antirejection therapy consisting of methylprednisolone for 3 days followed by lowering of the maintenance immunosuppression. This treatment resulted in a return of the serum creatinine concentration to the baseline of 1.6 mg/L, clearance of polyomavirus BK from plasma, and disappearance of viral inclusion bearing cells from the urine. After 2 months of stable allograft function, a control biopsy confirmed the resolution of polyomavirus BK nephropathy. Histologic signs of acute interstitial rejection were found and preemptively treated by methylprednisolone without altering the baseline regimen. Allograft function remained stable without evidence of recurrent polyomavirus BK nephropathy. This case shows the value of surrogate markers used in a prospective fashion for diagnosis and management of polyomavirus BK nephropathy with concurrent rejection.

Infections in recipients of kidney transplants

A review of infections in kidney transplant recipients is presented in this article, beginning with a discussion of the pretransplant infectious diseases evaluation and an overview of the timing of infectious posttransplant, and then focusing on individual types of infection.

Polyoma viral infection in renal transplantation: the role of immunosuppressive therapy

BACKGROUND

Polyoma virus infection in renal transplant recipients has been observed with increasing frequency in recent years. Renal allograft involvement in this condition may occur as a result of primary infection or secondary to reactivation of the latent virus. Interstitial nephritis, ureteric stenosis, rise in serum creatinine and allograft function loss have been attributed to this viral infection.

METHODS

In this study we reviewed our experience with 8 patients who developed polyoma viral infection confirmed by allograft biopsy. All patients were receiving mycophenolate mofetil as part of the immunosuppression and 7 of the 8 patients were on tacrolimus. All patients have biopsy proven polyoma viral infection. The following therapeutic maneuvers were carried out following the diagnosis of polyoma viral infection: 1) stopping mycophenolate and 2) switching tacrolimus to cyclosporine or reducing the tacrolimus dose to adjust it at a lower therapeutic trough level. The clinical course and outcome of our patients were reviewed in relation to manipulation of immunosuppressive medications.

RESULTS

The incidence of this infection in our transplant program in the last 3 yr was 5.3%. Seventy-five percent of the patients had at least one rejection episode and 63% had more than one rejection episode. The main risk factor for the development of polyoma viral infection was related to the intensity of immunosuppression. The use of antirejection therapy after histological diagnosis of polyoma virus infection was not associated with improvement of renal function despite the histological appearance of acute rejection. Thus, the interstitial nephritis associated with polyoma viral infection appears to be an inflammatory response to the virus rather than acute rejection. Six out of the 8 patients stabilized renal function with reduction in immunosuppression.

CONCLUSIONS

Reduction in immunosuppression was associated with the stabilization of renal function when instituted early. However, these patients were left with a degree of allograft dysfunction and their outcome may be significantly compromised. The lack of effective antiviral therapy for polyoma virus may limit the use of newer and more potent immunosuppressive medications.

Bk virus: a clinical review

We present a review of the clinically oriented literature about BK virus, a relative of JC virus, which is the etiologic agent of progressive multifocal leukoencephalopathy (PML). The kidney, lung, eye, liver, and brain have been proposed as sites of BK virus-associated disease, both primary and reactivated. BK virus has also been detected in tissue specimens from a variety of neoplasms. We believe that BK virus is most often permissively present in sites of disease in immunosuppressed patients, rather than being an etiologic agent that causes symptoms or pathologic findings. There is, however, strong evidence for BK virus-associated hemorrhagic cystitis and nephritis, especially in recipients of solid organ or bone marrow transplants. Now that BK virus can be identified by use of specific and sensitive techniques, careful evaluation of the clinical and pathologic presentations of patients with BK virus will allow us to form a clearer picture of viral-associated pathophysiology in many organ systems.

Molecular characterization and sequence analysis of polyomavirus BKV-strain in a renal-allograft recipient

The significance of polyomavirus (PV) infection was investigated in a 53-year-old patient who underwent renal transplantation and was treated with triple immunosuppressive therapy (tacrolimus, prednisone, and azathioprine). A renal biopsy taken because of the suspicion of acute rejection showed focal inflammatory interstitial infiltration, tubulitis, and tubular cell nuclear changes consistent with the hypothesis of viral infection. Both the tubular and decoy cells identified by means of urinalysis positively stained for anti-SV40 antibody. Polymerase chain reaction performed on the DNA extracted from renal tissue and isolated from urine showed the presence of an antigenic variant (AS) of the BKV archetype after sequence analysis of the transcription control region (TCR). On the basis of the diagnosis of BKV infection, immunosuppressive therapy was reduced. The patient's renal function improved and was still stable 8 months later when urinalysis showed only a few decoy cells, which were found to be infected by JC but not BK virus. These data suggest that only the BKV, probably favoured by immunosuppressive therapy (tacrolimus), causes renal damage. It is worth underlining that even small and sporadic viral genome mutations may lead to pathologic effects.

JC virus infection in allograft kidneys: analysis by polymerase chain reaction and immunohistochemistry

BACKGROUND

Polyoma virus nephropathy after transplantation is believed to be primarily due to the BK virus. We hypothesized that some cases may be associated with the JC polyoma virus (JCV), which is also known to be latent in the kidney.

METHODS

We sought polymerase chain reaction evidence of JCV infection in needle biopsy specimens with and without viral nephropathy. Cases positive by polymerase chain reaction were studied by immunohistochemistry for VP-1 antigen expression.

RESULTS

JCV DNA was found in 7 (36.8%) of 19 allograft kidney biopsy specimens with viral nephropathy and 0 (0%) of 19 native or allograft biopsy specimens without viral nephropathy. Immunohistochemistry localized JCV to the nuclei of tubular epithelial cells in one case.

CONCLUSIONS

JCV is detectable in a subset of renal allograft kidneys with polyoma virus nephropathy. The tubular epithelium is identified as a site capable of supporting JCV viral capsid protein VP-1 expression, and hence viral replication.

A regulatory region rearranged BK virus is associated with tubulointerstitial nephritis in a rejected renal allograft

A renal allograft transplant patient with high serum creatinine presented clinical symptoms of rejection. Sections of renal biopsy tissue showed mononuclear leukocyte infiltration in the tubulointerstitium and nuclear enlargement with inclusions in the tubular epithelium. The morphological characteristics resembled polyomavirus-induced interstitial nephritis. Electron microscopy of the nuclear inclusions showed paracrystalline arrays of naked viral particles with a diameter of 45 nm. Molecular studies revealed that a new variant of BK virus (BKV) with rearrangement at the regulatory region was involved in the nephritis. The BKV regulatory region contained a tandem repeat from the P-block to the Q-block causing duplication of several important transcriptional elements or transcriptional factor binding motifs. This is the first report to show a naturally occurring BKV variant with regulatory region rearrangement associated with tubulointerstitial nephritis.

POLYOMA VIRUS INFECTION AFTER RENAL TRANSPLANTATION1

BACKGROUND

Polyoma virus infection is characterized by lymphocytic interstitial infiltrate in the kidney, and it mimics acute rejection. The purpose of this study is to estimate renal allograft outcome with this infection and characterize the lymphocytic infiltrates in polyoma virus-infected renal allografts.

METHODS

Patients who had polyoma virus inclusions in renal allograft biopsies were identified. Other viral inclusions were excluded by immunohistochemistry. The lymphocytic infiltrates of six cases of polyoma virus infection were compared with six cases of definite acute rejection by immunostaining for T and B cells.

RESULTS

There were 10 cases of polyoma virus infections in renal transplant recipients. Immunosuppressants consisted of mycophenolate mofetil with tacrolimus in eight cases and mycophenolate mofetil with cyclosporine in two. The median time of diagnosis of polyoma virus infection after transplantation was 9.5 months, and the time to graft failure after the diagnosis was 4 months. Reduced allograft survival was seen in patients who had polyoma virus infection. Immunostaining for T and B cells revealed marked increase in the B cells (CD20) in renal allografts with polyoma virus infection of 21% (range, 5-40%) compared with 6% (range, 0-10%) in those with acute rejection (P=0.039). Reduced cytotoxic T cells (TIA-1: median, 7%; range, 2-15%) were seen in polyoma virus-infected allografts compared with 24% (range, 15-30%) in those patients who had acute rejection (P=0.0159).

CONCLUSION

Irreversible graft failure is more prevalent with polyoma virus infection. Enhanced immunosuppressants with mycophenolate mofetil with tacrolimus may play a role in the development of this infection. An increase in CD20 and a decrease in cytotoxic T cells in allografts is characteristic of polyoma virus infection.

Viral infections after renal transplantation

Viral infections are a leading cause of posttransplantation morbidity and mortality. A number of recent developments have altered our understanding and management of these disorders. The pathogenetic roles of several viruses, including human herpesviruses 6 and 8, have been newly established. Molecular-based diagnostic tests now make more rapid diagnosis possible. The licensing of new potent antiviral agents offers a wider choice of drugs for viral prophylaxis and treatment. The use of more potent immunosuppressive agents is responsible in part for the increasing incidence of some viral infections, but this varies among drugs, and individual viruses differ in their sensitivity to immunosuppressive agents. This review summarizes the natural history, diagnosis, prevention, and treatment of many common viral infections after renal transplantation.

Infections in solid organ transplant recipients

Studies published within the past year have highlighted the potential morbidity associated with polyomaviruses and novel herpesviruses (e.g. human herpesvirus-6, 7 and -8). Although antiviral therapy has not been shown to be effective for polyomaviruses, attempts at management of human herpesvirus-6 and -8 infections with antiviral agents appear anecdotally promising. Bacterial infections remain the most frequently occurring infections in transplant recipients, and the challenges that face the transplant care providers pertain to a striking rise in antimicrobial resistance among these pathogens. Effective prophylaxis and management of invasive mould infections continue to be the focus of clinical studies, but an optimal approach remains elusive.

Testing for polyomavirus type BK DNA in plasma to identify renal-allograft recipients with viral nephropathy

BACKGROUND

Reactivation of polyomavirus type BK (BK virus) is increasingly recognized as a cause of severe renal-allograft dysfunction. Currently, patients at risk for nephropathy due to infection with the BK virus are identified by the presence of cells containing viral inclusion bodies ("decoy cells") in the urine or by biopsy of allograft tissue.

METHODS

In a retrospective analysis, we performed polymerase-chain-reaction assays for BK virus DNA in plasma samples from 9 renal-allograft recipients with BK virus nephropathy; 41 renal-allograft recipients who did not have signs of nephropathy, 16 of whom had decoy cells in the urine; and as immunocompromised controls, 17 patients who had human immunodeficiency virus type 1 (HIV-1) infection (stage C3 according to the classification of the Centers for Disease Control and Prevention) and who had not undergone transplantation.

RESULTS

In all nine patients with BK virus nephropathy, BK virus DNA was detected in the plasma at the time of the initial histologic diagnosis (a mean [+/-SD] of 46+/-28 weeks after transplantation) and during the course of histologically diagnosed, persistent BK virus disease. In three of the six patients with nephropathy who were studied serially after transplantation, BK virus DNA was initially undetectable but was detected 16 to 33 weeks before nephropathy became clinically evident and was confirmed by biopsy. Tests for BK virus DNA in plasma became negative and the nephropathy resolved after the doses of immunosuppressive drugs were decreased in two patients and after removal of the renal allograft in three patients. BK virus DNA was found in the plasma of only 2 of the 41 renal-allograft recipients who had no signs of nephropathy and in none of the patients with HIV-1 infection.

CONCLUSIONS

Testing for BK virus DNA in plasma from renal-allograft recipients with use of the polymerase chain reaction is a sensitive and specific method for identifying viral nephropathy.

BK-virus nephropathy in renal transplants-tubular necrosis, MHC-class II expression and rejection in a puzzling game

We review BK-virus nephropathy (BKN) as a new complication that increasingly affects renal allografts and causes dysfunction. Since starting in 1996, we have seen 11 cases. Currently, the prevalence of BKN is 3% in our graft biopsies. The diagnosis can only be made histologically. The virus affects tubular epithelial cells that show characteristic intranuclear inclusion bodies. The major reason for impaired graft function and a possible way for viral particles to gain access to the blood via peritubular capillaries is necrosis of infected epithelial cells. BK-virus DNA in the plasma, which can be detected by PCR, is closely associated with nephropathy. BK-virus does not stimulate tubular MHC-class II expression as judged by immunofluorescence double labelling. The inflammatory response is inconsistent and the frequency of rejection episodes is not increased during disease. Clinical manifestation of viral nephropathy evolves in several stages. (i) Initial, asymptomatic and reversible activation of the virus, judged by the presence of inclusion bearing cells in the urine. (ii) High dose immunosuppressive drug regimens, often including tacrolimus. (iii) Tubular injury and viraemia as additional promoting conditions. BKN nephropathy was associated with graft loss in 45% of our patients. The remaining patients with persistent viral nephropathy showed renal dysfunction (serum creatinine levels on average 150% above baseline readings). Currently, no established antiviral therapy is available. We discuss attempts to lower immunosuppression as a means to control viral replication. We propose a diagnostic algorithm for screening and monitoring the disease.

Diagnosis and management of BK polyomavirus interstitial nephritis in renal transplant recipients

BACKGROUND

Interstitial nephritis caused by BK polyomavirus is a recognized complication of renal transplantation. A study of renal transplant recipients at Duke University Medical Center was undertaken to evaluate diagnostic modalities and assess clinical outcomes in transplant polyomavirus infections.

METHODS

Polyomavirus nephritis was identified in 6 of 240 patients who received renal transplants between January 1996 and June 1998 and an additional patient who underwent transplantation in 1995. The clinical records of these seven patients were reviewed, as were all renal biopsy and nephrectomy specimens. Electron microscopy (EM) was performed on negatively stained urine samples from 6 patients with polyomavirus infection and 23 patients with other diagnoses.

RESULTS

Patients with polyomavirus infection shared several clinical features, including ureteral obstruction (5/7 patients), lymphocele (3/7), bacterial urinary tract infection (3/7), hematuria (3/7), cytomegalovirus infection (3/7), and immunosuppression with mycophenolate mofetil (6/7). All patients experienced elevations in serum creatinine, which stabilized or decreased in four patients with altered or decreased immunosuppression. The diagnosis of polyomavirus infection was established by renal biopsy and EM of urine in five patients, by biopsy alone in one, and by EM alone in one. Sequential examinations of urine by EM were used to monitor the course of infection in six patients.

CONCLUSIONS

Interstitial nephritis due to BK polyomavirus occurred in 2.5% of patients receiving renal transplants at our center since 1996. Polyomavirus infection can cause transplant dysfunction and graft loss, but progression of the infection can frequently be abrogated with alterations in immunosuppressive therapy. Both renal biopsy and EM of urine samples are useful in the diagnosis and monitoring of polyomavirus infections.

Human polyoma virus in renal allograft biopsies: morphological findings and correlation with urine cytology

Human polyoma virus (PV) interstitial nephritis occurs in immunosuppressed patients after reactivation of latent virus in renal epithelium. Currently, there is neither general consensus about the incidence of clinically significant PV infection in renal transplants nor conclusive evidence determining its significance in the long-term graft outcome. We evaluated 601 renal transplant biopsy specimens (from 365 patients) by routine light microscopy and immunoperoxidase stains with antibody against SV40 (which cross reacts with PV). We also examined urine samples from 200 patients (100 obtained concurrently with a renal biopsy in patients presenting with acute graft dysfunction and 100 from patients with stable graft function). Electron microscopic evaluation was performed in 50 renal biopsy specimens and in 23% of all urine samples. PV was identified in 1.8% biopsy specimens (1.9% of patients). PV interstitial nephritis showed the typical viral cytopathic changes in tubular epithelial cells associated with marked tubular damage and a disproportionately mild degree of tubulitis. There was no difference in the incidence of PV in the urine of patients with acutely deteriorating versus stable renal function (18% and 19%, respectively); however, urines with large numbers of infected cells (> 10/cytospin) and inflammatory changes in the sediments corresponded invariably to patients with acute allograft dysfunction (8 of 8), and in most cases to biopsy specimens showing PV interstitial nephritis (7 of 8). Based on these findings, urine samples seem to be the most sensitive and cost-effective screening method for PV infection; only urine samples with inflamed sediments and abundant infected cells correlate with clinically significant disease. In these cases, examination of a renal biopsy is indicated. Immunohistochemical stains are useful to confirm the presence of PV but do not increase the sensitivity of diagnosis of PV if this is not already suspected on routine light microscopy. In our material, immunostains were helpful ruling out the presence of PV in a small number of biopsy specimens (2%) that showed markedly reactive tubular cells resembling PV infection. Most patients with PV interstitial nephritis responded to decreased immunosuppression; however, the decay in graft function (based on creatinine slopes) was significantly more rapid in these patients than in matched controls. Evidence of PV infection should be systematically sought in renal biopsy specimens and urine samples from renal allograft recipients.