BK virus replication following kidney transplant: Does the choice of immunosuppressive regimen influence outcomes?

The increasing prevalence of BK virus nephropathy (BKVN) observed in recent years, with its consequent impact on kidney allograft survival rates, has focused attention on the relationship between immunosuppression regimens and risk of BK virus reactivation. The adoption of more potent immunosuppressive regimens over the last two decades, notably tacrolimus with mycophenolic acid and corticosteroids, appears to be associated with higher rates of BK activation. There is also evidence of a specific increase in risk for tacrolimus-based immunosuppression vs. cyclosporine, which in vitro data suggest may be at least partly due to differences in antiviral activity. Early concerns that mammalian target of rapamycin (mTOR) inhibitor use was associated with development of BKVN do not appear to have been borne out. Protocol-driven BK virus screening is recommended to facilitate early diagnosis and intervention, which primarily comprises the controlled reduction or discontinuation of immunosuppressive drugs. Although a consensus on the optimal strategy for immunosuppression modification is still lacking, early diagnosis of BK reactivation and pre-emptive modification of immunosuppression has resulted in a marked improvement in graft outcomes. Typically, intervention consists of reducing calcineurin inhibitor exposure before or after antimetabolite dose reduction, withdrawal of one agent from a triple therapy regimen, or switching between agents within a therapeutic class. A benefit for antiviral therapy is not yet confirmed. While more data are required, the current evidence base is adequate to justify routine screening with early modification of the intensity and nature of the immunosuppression regimen to reduce the toll of BKVN in the kidney transplant population.