#6310 ANALYSIS OF THERAPEUTIC ATTITUDES TOWARDS BK VIRUS INFECTION IN RENAL TRANSPLANTATION: A RETROSPECTIVE COHORT STUDY
Authors: Rincón María Muñiz , Salazar Sara Huertas , Cubillo Beatriz Rodríguez , López Esther Culebras , de la Higuera Díaz María Ángeles Moreno , Romero Natividad Calvo , Pérez-Flores Isabel , López Rómulo Katsu Loayza , Meneses Arianne Aiffil , Morales Nancy Daniela Valencia , Fructuoso Ana Sanchez 
Published: June 2023

Abstract

Background and Aims
BK virus infection continues to be one of the most common clinical issues encountered by transplants providers, which can lead to BK virus nephropathy and, ultimately, graft loss. Despite its importance, there are still many uncertainties surrounding effective prevention and treatment strategies. The aim of this study is to evaluate the BK virus prevalence disease in a cohort of kidney transplant patients, examine consequences of immunosuppression regimens readjustments and assess the progression of viremia and viruria.

Method
This study analyzed a cohort of patients who received kidney transplants from January 2011 to January 2020 and had a minimum graft survival of three months. In accordance with our established protocol, viremia was measured on a quarterly basis during the first year after transplantation and annually thereafter. BK virus infection (BKVi) was defined as a plasma viral load, determined by real-time PCR, of 10,000 copies/ml or greater, or a viral load of 5,000 copies/ml or greater if accompanied by viruria of greater than 10 million copies/ml. Out of the 490 patients initially selected, 42 were excluded from the study due to inadequate data.

Results
The maximum levels of viremia during the course of the study were classified as follows: viremia ≥ 10,000 (N = 78; 17.4%), between 5,000-10,000 (N = 11; 2.4%), between 500-1,000 (N = 17; 3.8%) and undetectable (N = 342; 76.3%). The maximum levels of viruria were classified as: viruria ≥ 1 million (N = 98, 21.9%), between 999,999-100,000 (N = 15; 3.3%), between 99,999-10,000 (N = 20, 4.5%) and undetectable (N = 315; 70.3%). In the group diagnosed with BKVi, viremia ≥ 10,000 appeared at a median post-transplant time of 5.8 (2.9-11.7) months. The treatment approach involved replacing tacrolimus or mycophenolate with mTOR inhibitor, based on the patient's immunological risk. In some cases of high immunological risk or intolerance to mTOR inhibitor during the first month, treatment with tacrolimus and mycophenolate was continued. If the previous regimens were not effective, treatment with cyclosporine and mTOR inhibitor was initiated in some cases. The key results are summarized in the Table 1.

Conclusion
The combination of tacrolimus and mTOR inhibitor appears to be an effective option for BK virus infection, while the combination of mTOR inhibitor and mycophenolate has a high discontinuation rate, which can result in subsequent increase in viremia. In cases where there is no favorable response, the combination of cyclosporine and mTOR inhibitor can be effective. The changes in immunosuppression in patients with BKVi did not result in significant differences in renal function at one year or five years after transplantation, although the sample size is limited and more research is needed to confirm this. Keeping tacrolimus and mycophenolate may lead to a longer time until viremia becomes negative, which could have long-term implications for renal function.