Polyoma BK virus-associated nephropathy (BKVN) is a significant cause of premature graft loss in kidney transplant recipients. Transient BK viremia is observed after an induction therapy; however, the natural course and the clinical significance of this phenomenon are unclear.

In this single-center retrospective study, we analyzed 527 patients who received kidney or kidney/pancreas transplantation and were screened for BK virus plasma PCR from Sep. 2008 to Dec. 2011. The patients were induced with T-cell depleting antibody +/- anti-IL2 receptor antibody, and maintained with tacrolimus-based immunosuppression. BK viremia and BKVN were treated initially by reduction of immunosuppressive medication, and in some cases, with leflunomide, ciprofloxacin, or intravenous immunoglobulin.

During the initial 3 mo after transplantation, 131 (24.9%) patients had at least one positive BK viremia. Of these patients, 69.5% continued to shed the virus beyond 3 mo post-TX. The viremic patients during the 3-mo period had a higher incidence of BKVN (6/131, 4.6%) than non-viremic patients (4/396, 1.0%, OR 4.704, p=0.0182). Both the patient survival (92.5% vs. 97.7%) and death-censored graft survival (89.1% vs. 97.4%) were inferior in the viremic patients (p=0.0259 and p=0.0009, respectively) as compared with non-viremic patients.

To further clarify the significance of “transient” viremia after the induction therapy, these 131 patients were divided into 2 subgroups: patients whose BK viremia disappeared after 1 mo until 3 mo (n=40, transient viremia) and patients who had viremia after 1 mo post-Tx (n=91, persistent viremia). None of the transient-viremia patients developed BKVN, whereas 6 persistent-viremia patients developed BKVN. There were no significant differences in patient and graft survival (92.5% vs. 92.6% at 3 years, p=0.9777 and 88.9% vs. 89.4%, p=0.8926) between groups, and they were worse than BK virus-negative patients.

In conclusion, BK viremia is relatively common after T-cell depleting antibody therapies with tacrolimus maintenance. BK viremia during 3 mo post-Tx is a significant risk factor for subsequent BKVN. Although transient BK viremia during 1 mo post-Tx was not associated with BKVN, poor patient and graft survival in this patient group may suggest a negative impact of BK viremia from other mechanisms.

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