title: Pathology of resolving polyomavirus-associated nephropathy.
abstract: Control of polyomavirus BK (BKV) is achieved by reducing immunosuppression allowing an effective BKV-specific T-cell response. The morphology of resolving BKV-associated nephropathy (PyVAN) has not been systematically investigated. Ninety-nine surveillance biopsies of 35 patients with BKV viremia treated exclusively by immunosuppression reduction were scored according to Banff criteria and grouped relative to BKV viremia as pre-, increasing, decreasing and post-BKV viremia. Thirty-four of 35 patients (97%) cleared BKV viremia after a median of 9 months posttransplantation. The tubulitis score, extent of tubules with intraepithelial lymphocytes, and interstitial inflammation significantly increased from the time of increasing to decreasing viremia. Tubulointerstitial inflammation, to a lower extent, persisted after clearance. The number of SV40+ tubules correlated with the BKV load in plasma, but SV40 immunohistochemistry was frequently negative (60%). During decreasing viremia, 31% of PyVAN cases were plasma cell-rich and 40% showed tubular HLA-DR expression. Compared to baseline 1 month posttransplantation, allograft function remained stable or improved in 29/35 patients (83%) after a median follow-up of 48 months. Within 1 year after clearance of BKV viremia, clinical rejection occurred in 2/35 patients (6%). Our data suggest that resolving PyVAN is typically characterized by a self-limiting acute interstitial nephritis, morphologically indistinguishable from interstitial rejection.
authors.affiliation: Institute for Pathology, University Hospital Basel, Basel, Switzerland.
authors.forename: T
authors.initials: T
authors.lastname: Menter
authors.forename: M
authors.initials: M
authors.lastname: Mayr
authors.forename: S
authors.initials: S
authors.lastname: Schaub
authors.forename: M J
authors.initials: MJ
authors.lastname: Mihatsch
authors.forename: H H
authors.initials: HH
authors.lastname: Hirsch
authors.forename: H
authors.initials: H
authors.lastname: Hopfer
mesh_terms: D000328:Adult; D000368:Aged; D001706:Biopsy; D005260:Female; D005500:Follow-Up Studies; D006084:Graft Rejection / Q000473:pathology* / Q000821:virology; D006801:Humans; D007150:Immunohistochemistry; D007668:Kidney / Q000473:pathology* / Q000821:virology; D007674:Kidney Diseases / Q000473:pathology* / Q000821:virology; D016030:Kidney Transplantation / Q000009:adverse effects*; D008297:Male; D008875:Middle Aged; D011120:Polyomavirus / Q000302:isolation & purification*; D027601:Polyomavirus Infections / Q000473:pathology* / Q000821:virology; D012189:Retrospective Studies; D014184:Transplantation, Homologous; D014412:Tumor Virus Infections / Q000473:pathology* / Q000821:virology; D019562:Viral Load; D055815:Young Adult