Everolimus reduces BK polyomavirus infection by suppressing its replication and spread of infection

BK polyomavirus-associated nephropathy is one of serious complications in transplant recipients. Everolimus–a mammalian target of rapamycin inhibitor–has been shown to reduce the incidence of BK polyomavirus infection in transplant recipients. In this study, the effects of everolimus were examined on viral replication and the spread of infection in BK polyomavirus-infected cultures. BK polyomavirus replicated in renal and pulmonary cells, contrary to that in hepatocytes, and spread as diffusely scattered patterns of infected cells, unlike plaque formation through the cell-to-cell mode. BK polyomavirus is stable to heat up to 65 °C with a particle per infectivity ratio of 5000, and the replication cycle was for approximately 34 h. Everolimus administration remarkably reduced the viral replication to 20% in cells treated with 0.1–10 ng/mL, the concentration at which everolimus reached the serum of transplant recipients. In addition, it reduced the amount of viral capsid protein 1 at 5 ng/mL without reducing the ratio of viral capsid protein 1 versus β-actin, and it also retained the pattern of viral capsid protein 1 localization in the nuclei. Everolimus suppressed the number of infected cells to 32.8% during a 14-day treatment, indicating the reduction of BK polyomavirus-infected cell mass to 18.8% of untreated cultures by modifying cellular functions. The reduction in the total number of BK polyomavirus infected cells by everolimus indicates that everolimus alleviates BK polyomavirus infection, including nephropathy in transplant recipients.