The Burden of BK Polyomavirus in Pediatric Renal Transplantation: A Belgian Experience

<b>Background/Objectives</b>: To evaluate the outcome of developing BKPyV-DNAemia and presumptive BKPyV-nephropathy (BKPyV-DNAemia ≥ 10⁴ copies/mL for more than 2 weeks) within the first 2 years post-transplant in a Belgian population of renal transplanted children. <b>Methods</b>: All children transplanted between 1 January 2010 and 31 December 2022 at Queen Fabiola Children's University Hospital, Brussels (HUDERF) and at University Hospitals Leuven (UHL) were included in this retrospective study and 86 were followed for at least 2 years post-transplantation. <b>Results</b>: Within the first 2 years, 11/86 (13%) patients developed BKPyV-DNAemia ≥ 10⁴ copies/mL (82% within the first 6 months). Among the 11 patients, 7 underwent a biopsy, of whom 4 were confirmed to have biopsy-proven BKPyV-nephropathy. Of those 11 patients, 4 (36%) developed an acute cellular rejection following immunosuppression reduction. The median eGFR at 2 years post-transplantation was 69 mL/min/1.73 m² (IQR: 59-79) in the seven patients with presumptive BKPyV-nephropathy and 40 mL/min/1.73 m² (IQR: 39-41) in the four with biopsy-proven BKPyV-nephropathy. At last follow-up visit, the median eGFR was 65 mL/min/1.73 m² (IQR: 59-71) in the children with presumptive BKPyV-nephropathy, and 28 mL/min/1.73 m² (IQR: 20-34) in the patients with biopsy-proven BKPyV-nephropathy. No risk factors for developing BKPyV-DNAemia were identified. <b>Conclusions</b>: Our study confirms that while BKPyV-DNAemia monitoring is essential in pediatric kidney transplant recipients, decisions based solely on viral load risk overtreatment and immunological complications. A personalized approach integrating viral, clinical, and immunological markers is urgently needed to balance infection control with graft preservation.