Prognosis of BK polyomavirus nephropathy: 10-year analysis of 133 renal transplant recipients at a single center

Background: BK virus-associated nephropathy (BKVN) is an important cause of chronic allograft dysfunction. The objective of our study was to evaluate the prognosis of BKVN. Methods: We retrospectively reviewed the data of 133 renal transplant recipients with BKVN treated at the First Affiliated Hospital of Sun Yat-Sen University between July 2007 and July 2017. BK viral loads, graft function, and pathologic indexes were compared between initial diagnosis and last follow-up. Results: After a mean follow-up period of 14.4 (range, 0.3–109.6) months after diagnosis of BKVN, BK viruria, and BK viremia become negative in 19.5% and 90.2% of patients, respectively. The mean estimated glomerular filtration rate (eGFR) at last follow- up was lower than at diagnosis of BKVN (18.3 ± 9.2 vs. 32.8 ± 20.6 mL·min-1·1.73 m-2, t= 7.426, P < 0.001). Eight (6.0%) patients developed acute rejection after reducing immunosuppression. At last follow-up, the eGFR was significantly lower in patients with subsequent rejection than those without (21.6 ± 9.8 vs. 33.5 ± 20.9 mL·min-1·1.73 m-2, t= 3.034, P= 0.011). In 65 repeat biopsies, SV40-T antigen staining remained positive in 40 patients and became negative in the other 20 patients. The eGFR (42.6 ± 14.3 vs. 26.5 ± 12.3 mL·min-1·1.73 m-2), urine viral loads (median, 1.3 × 105vs. 1.4 × 107 copies/mL), and plasma viral load (median, 0 vs. 0 copies/mL) were all significantly lower in patients with negative SV40-T antigen staining than those with persistent BK involvement (all, P < 0.05). Five (3.8%) recipients lost their graft at diagnosis of BKVN, and 13 (9.8%) lost their graft during the follow-up period. The 1-, 3-, and 5-year graft survival rates after diagnosis of BKVN were 99.2%, 90.7%, and 85.7%, respectively. Higher pathologic stage correlated with lower allograft survival rate (χ2= 6.341, P= 0.042). Conclusion: Secondary rejection and persistent histologic infection in BKVN lead to poor prognosis. Key words: Kidney transplantation; BK virus; Pathology; Rejection; Prognosis