Long-Term Outcomes of BK Viremia in Kidney Transplant Recipients.

BACKGROUND: BK viremia is associated with worse kidney transplant function and de novo donor-specific antibodies (DSA), but mortality and graft survival are not impacted in the short- and intermediate-term. The long-term impact of BK viremia remains unclear.

METHODS: We performed a single-center retrospective study on 1058 consecutive kidney or kidney-pancreas transplant recipients. We classified the cohort based on the presence or absence of BK viremia, BK viral loads, persistence of BK viremia, and pre-existing or de novo DSA. Outcomes included mortality, graft loss, death-censored graft survival (DCGS), estimated glomerular filtration rate, biopsy-proven acute rejection (BPAR), de novo DSA, ureteral stenosis, and genitourinary (GU) malignancies.

RESULTS: Over a median follow-up period of 9.7 years, there was no difference in graft loss (p = 0.08) and mortality (p = 0.56). Time-varying multivariable analysis showed no difference in DCGS [HR 1.02, (0.91-1.16)]. Compared to never BK viremic patients, patients with BK viremia had similar graft function at 5 and 10 years (p = 0.09 and 0.65, respectively), rates of GU malignancies (7.0% vs. 5.2%, p = 0.35) and ureteral stenosis (0.8% vs. 0.4%, p = 0.63). Patients with BK viral loads >10 000 copies/mL had a higher risk of de novo DSA [HR 1.71, (1.08-2.68)] and BPAR [HR 2.11, (1.28-3.47)].

CONCLUSIONS: BK viremia did not impact mortality, graft loss, kidney function, GU malignancies, and ureteral stenosis over long-term follow-up, but BPAR episodes and development of de novo DSA were higher with viral loads >10 000 copies/mL. Strict monitoring protocols and immunosuppression reduction strategies are effective in minimizing the risk associated with BK viremia.