Polyomavirus nephropathy in renal transplantation: a clinico-pathological study

The Second International Consensus Guidelines on the Management of BK Polyomavirus in Kidney Transplantation

BK polyomavirus (BKPyV) remains a significant challenge after kidney transplantation. International experts reviewed current evidence and updated recommendations according to Grading of Recommendations, Assessment, Development, and Evaluations (GRADE). Risk factors for BKPyV-DNAemia and biopsy-proven BKPyV-nephropathy include recipient older age, male sex, donor BKPyV-viruria, BKPyV-seropositive donor/-seronegative recipient, tacrolimus, acute rejection, and higher steroid exposure. To facilitate early intervention with limited allograft damage, all kidney transplant recipients should be screened monthly for plasma BKPyV-DNAemia loads until month 9, then every 3 mo until 2 y posttransplant (3 y for children). In resource-limited settings, urine cytology screening at similar time points can exclude BKPyV-nephropathy, and testing for plasma BKPyV-DNAemia when decoy cells are detectable. For patients with BKPyV-DNAemia loads persisting >1000 copies/mL, or exceeding 10 000 copies/mL (or equivalent), or with biopsy-proven BKPyV-nephropathy, immunosuppression should be reduced according to predefined steps targeting antiproliferative drugs, calcineurin inhibitors, or both. In adults without graft dysfunction, kidney allograft biopsy is not required unless the immunological risk is high. For children with persisting BKPyV-DNAemia, allograft biopsy may be considered even without graft dysfunction. Allograft biopsies should be interpreted in the context of all clinical and laboratory findings, including plasma BKPyV-DNAemia. Immunohistochemistry is preferred for diagnosing biopsy-proven BKPyV-nephropathy. Routine screening using the proposed strategies is cost-effective, improves clinical outcomes and quality of life. Kidney retransplantation subsequent to BKPyV-nephropathy is feasible in otherwise eligible recipients if BKPyV-DNAemia is undetectable; routine graft nephrectomy is not recommended. Current studies do not support the usage of leflunomide, cidofovir, quinolones, or IVIGs. Patients considered for experimental treatments (antivirals, vaccines, neutralizing antibodies, and adoptive T cells) should be enrolled in clinical trials.

Immunophenotyping of interstitial infiltrate does not distinguish between BK virus nephropathy and acute cellular rejection

INTRODUCTION

BK virus nephropathy (BKVN) is a significant cause of late renal allograft loss. It is characterized histologically by an interstitial nephritis that can be difficult to distinguish from acute cellular rejection (ACR). We investigated whether immunophenotyping of the infiltrate would aid this distinction.

METHODS

Ten cases of biopsy-proven BKVN, following renal transplantation, were identified from a single transplant centre. The infection was confirmed by renal biopsy and staining for SV-40 T-antigen. Biopsies from 20 consecutive patients with ACR were identified and used as controls. There was no evidence of BK infection serologically or histologically in these patients. Immunohistochemical staining with anti-CD20, perforin and granzyme B was performed on remaining tissue samples.

RESULTS

Clustered B cells were demonstrated in both BKVN and ACR. Hence, the CD20-stained component within the interstitial infiltrate was not useful in distinguishing these biopsies. Perforin-stained slides demonstrated fewer cytotoxic T cells in the biopsies with BK virus (average 2.4 +/- 1.4 cells per 100 lymphocytes per field) compared with those samples with acute rejection (8.6 +/- 5.7 cells per 100 lymphocytes, P < 0.0001). No significant difference in granzyme B staining was detected between ACR and BKVN.

CONCLUSION

Clustered B cells and granzyme B staining did not differentiate between ACR and BKVN. However, ACR cellular infiltrate was rich in perforin positive cells suggesting that perforin staining may be a useful marker to discriminate between these conditions.

Latent and Productive Polyomavirus Infections of Renal Allografts

Polyomavirus allograft nephropathy, also termed BK virus nephropathy (BKN) after the main causative agent, the polyoma-BK-virus strain, is a major complication following kidney transplantation. BKN is the most common viral infection affecting the renal allograft with a reported prevalence of 1% up to 10%. It often leads to chronic allograft dysfunction and graft loss. BKN is most likely caused by the reactivation of latent BK viruses which, under sustained and intensive immunosuppression, enter a replicative/productive cycle. Viral disease, i.e., BKN, is typically limited to the kidney transplant. It is histologically defined by the presence of intranuclear viral inclusion bodies in epithelial cells and severe tubular injury. Virally induced tubular damage is the morphological correlate for allograft dysfunction. In this chapter, different variants of polyomavirus intranuclear inclusion bodies [types 1 through 4] and adjunct techniques [immunohistochemistry, in-situ hybridization, electron microscopy and polymerase chain reaction (PCR)] that are used for proper characterization of disease are described. Special emphasis is placed on the clinical and pathophysiological significance of different histological stages of BKN.

Polyomavirus nephropathy in native kidneys and renal allografts: an update on an escalating threat

Polyomavirus nephropathy, also termed BK-virus nephropathy (BKN) after the main causative agent, the polyoma-BK-virus strain, is a significant complication after kidney transplantation. BKN is the most common viral infection that affects renal allografts with a prevalence of 1-9% on average 8-13 months post surgery. It can also occur sporadically in native kidneys. Viral nephropathy is caused by the (re)activation of latent BK viruses that enter into a replicative cycle under sustained and intensive immunosuppression. Pure productive kidney infections with JC- and SV-40 polyomaviruses are exceptionally rare. BKN is morphologically defined by the presence of intranuclear viral inclusion bodies in epithelial cells and tubular injury, which is the morphological correlate for renal dysfunction. Renal disease can progress through different histologic stages (from early BKN stage A to late fibrotic stage C) that carry prognostic significance; disease stages B and C often result in chronic kidney (allograft) dysfunction and end-stage renal disease. The clinical goal is to diagnose viral nephropathy in disease stage A and to limit chronic renal injury. Strategies to recognize, classify, and manage BKN are critically discussed including ancillary techniques for risk assessment and patient monitoring: (i) urine cytology and the search for so-called 'decoy cells'; (ii) PCR analyses for viral load measurements in the plasma and urine; and (iii) negative staining urine electron microscopy to identify viral particles.

Urinary HLA-DR and CD54 expression--indicators for inflammatory activity in decoy cell shedding patients

BACKGROUND

Polyomavirus (PV) nephropathy may coexist with or follow acute renal transplant rejection. The aim of this study was to evaluate whether HLA-DR and CD54 are useful cellular markers for surveillance of acute rejection in PV-infected patients.

METHODS

A prospective study was conducted using 205 renal transplant patients. Urine samples were collected at a regular interval post-transplantation for routine cytology and immunocytochemistry. Urinary levels of tumour necrosis factor alpha, soluble interleukin-2 receptor and interleukin-6 were used as adjunctive markers for acute rejection.

RESULTS

Of the 699 total samples, decoy cells were identified in 100 samples of 50 patients. Patients with decoy cell-positive (DCP) samples had higher serum creatinine levels than decoy cell-negative (DCN) samples (1.55 vs 1.41 mg/dl, respectively; P = 0.006). DCP samples were also more likely to be HLA-DR positive (50.0 vs 32.4%; P = 0.029), as well as CD54 positive (17.4 vs 6.9%; P = 0.038). However, serum creatinine levels did not correlate with HLA-DR or CD54 positivity among DCP samples. Instead, CD54 positivity correlated with decoy cell grades. Immunosuppression decreased in 11 DCP patients, and HLA-DR was negatively converted in three of them. None of the patients developed acute clinical rejection. Urinary cytokine levels did not correlate with serum creatinine levels, nor did they correlate with HLA-DR or CD54 status among DCP patients.

CONCLUSIONS

Urinary tubular HLA-DR and CD54 expression increased in decoy cell shedding patients but did not indicate a concomitant acute rejection. These markers may instead indicate renal inflammatory activity associated with viral reactivation, which has the potential to progress to PV interstitial nephritis.

Polyomavirus interstitial nephritis and concurrent post-transplant lymphoma in a renal allograft: coincidence or more?

We describe a case of an Epstein-Barr virus (EBV)-negative post-transplant large B-cell non-Hodgkin lymphoma located in the renal allograft, spleen, liver and left inguinal lymph node of a renal recipient and accompanied by a simultaneous polyomavirus-associated nephropathy. To our knowledge, this is the first report of a simultaneous polyomavirus infection and post-transplant lymphoproliferative disorder.