BK virus infection is one of the causes of renal allograft loss in the current era. Reduction of immunsuppression is the only intervention that prooved to be effective in treating of BK virus in kidney transplant recipient. However, there are evidences from retrospective and prospective studies showed that leflunomide and mTOR inhibitor such as everolimus or sirolimus have positive outcomes in treatment of BK virus in kidney tranplant recipient. The investigators conduct the RCT to compare the efficacy of leflunomide and mTOR inhibitor everolimus, in treatment of BK virus infected patients who do not respond to immunosuppression reduction.