The aim of this observational study is to characterize the urinary replication of BK polyomavirus (BKV) in kidney transplant recipients. Although BKV reactivation after transplantation is well established, the origin of the replicating virus remains uncertain. Current evidence suggests that BKV detected in recipients may originate either from the transplanted kidney (donor-derived) or from viral reactivation in the recipient. The evaluation of new biomarkers to predict BKV replication are needed.
This study seeks to address the following key questions:
* Origin of the replicating virus: Is the BKV detected in the recipient identical to the virus originating from the donor kidney? * Host immune response and viral genotype: Is there an association between the recipient's immune response and the genotype of the replicating BKV? * Differences in immune response according to viral replication profile: Does the immune response differ between patients presenting isolated BKV viruria and those with both viruria and viremia? * Can new biomarkers help predict BKV replication and viremia?
Patients will be grouped according to their BKV replication profile:
Group 1: patients with BKV viruria without viremia Group 2: patients with both BKV viruria and viremia Comparisons between these two groups will help identify whether different viral genotypes or immune responses are associated with systemic dissemination (viremia).
Kidney transplant recipients will be included if they present BKV viruria during their post-transplant follow-up. Additional blood samples will be collected during scheduled follow-up visits at the university hospital. These visits are part of routine clinical care, and no extra visits will be required specifically for the study.
Kidney transplant patients with a first positive BK virus viral load in urine. - BK virus viral load in urine > 3 log copies/mL.
More than 3 months post-transplant and less than 2 years post-transplant.
Men or women aged 18 years and older.
Followed up at Grenoble Alpes University Hospital.
Expected renal graft survival is < 6 months, estimated by an eGFR < 15 mL/min/1.73 m² at the time of BKPyV viruria
Patients who object to the use of their data and/or samples for research purposes
Subjects who are excluded from another study
Subjects under administrative or judicial supervision
Kidney transplant patients with a first positive BK virus viral load in urine during the 2 years after the graft
Cohort
Prospective
Not listed
To describe the prevalence and variability of different BKPyV genotypes and serotypes in a population of kidney transplant patients with BKPyV viruria/viremia.
The primary endpoint will be the classification by genotyping/serotyping of BKPyV obtained during the first viruria and the first viremia, performed using NGS and serotyping using a seroneutralization technique. The search for SNPs (single nucleotide polymorphisms) will also enable the subclassification of genotypes and better identification of patients at risk of BKPyV viremia and therefore BKPyV-induced nephropathy.
Compare the viral genotype at the first viruria/viremia with the donor serotype and with the recipient serotype.
The donor serotype and recipient serotype will be obtained by seroneutralization (from I to IV) and the viral genotype at the first viremia and first viruria will be obtained by a complete sequencing technique (NGS).
Describe the evolution of urinary BKPyV viral load during infection and compare viruria between viruric-only and viremic patients.
The urinary viral load for BKPyV will be obtained by qPCR (R-Gene) and expressed in log IU/mL at the time of inclusion in the two groups and then up to 6 months post-inclusion.
Describe associations between urinary and blood BKPyV viral load and associated genotypes/the presence of a mismatch between the donor serotype and the recipient genotype.
Urinary viral load at inclusion and at the time of viremia (qPCR R-Gene technique in log IU/mL) and serotype mismatch obtained from serological data at the time of transplantation.
Describe the associations between the waiting time until the first viremia and the presence or absence of a serotype mismatch at the time of transplantation, the genotype at the time of the first viruria, the viral load at the time of the first viruria,
The time will be recorded in days between the first post-transplant viruria and viremia.
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