BK Polyomavirus

This is a pilot study using cytotoxic T lymphocytes (CTLs) manufactured with the Miltenyi CliniMACS Prodigy Gamma-capture system will be effective in decreasing specific viral load in patients with BK virus viremia and BK virus-associated symptoms post-allogeneic hematopoietic stem cell transplantation (HSCT), renal transplantation, and chemotherapy.

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.

The human pathogen BK polyomavirus (BKPyV) is a ubiquitous, small, non-enveloped DNA virus that infects over 90% of people, typically in childhood with mild or no symptoms. Following primary infection, BKPyV establishes latency predominantly in the reno-urinary tract, and can occasionally be detected in the urine without any concomitant clinical symptoms. However, among kidney transplant recipients (KTR), due to impaired cellular and humoral immunity, uncontrolled viral replication in renal tubular epithelial cells (RPTE) can occur, leading to high-level BKPyV DNAemia and significant damage to the reno-urinary system (ie polyomavirus-associated nephropathy). In the absence of any effective antiviral drug, the mainstay of therapy for significant BKPyV replication among KTR is reducing immunosuppressive drugs, despite the subsequent of risk of graft rejection. Current efforts to identify new monitoring and therapeutical strategies need to be supported by a better understanding of the dynamics of BKPyV-specific immune responses following transplantation. Although adaptive cellular and humoral immune responses play a crucial role in the control of BKPyV reactivation among healthy individuals, immunosuppression and transplantation disrupt immune homeostasis and reshape the immune response landscape both in terms of function and fitness to new stimuli. Consequently, pre-transplant prediction of patients who will be able to control post-transplant BKPyV reactivation or who will develop BKPyV-related complications remains challenging. This knowledge gap stems from insufficient studies on the comprehensive analysis of immune responses during BKPyV reactivation. In particular, most studies to date have not investigated the role of NK cells in this context, despite their potent antiviral activity, heterogenous repertoire in each patient and their recently uncovered adaptive properties. The hypothesis is that among KTR with de novo BKPyV DNAemia, the comprehensive analysis of anti-BKPyV immune responses (including both the description of NK cell repertoire and adaptive immune), could allow * A better stratification of KTR at-risk for BKPyV-related complications using accessible immune biomarkers. * The identification of the most efficient strategies of immunosuppression management for the control of BKPyV DNAemia, that could be further evaluated in a prospective cohort. * The identification of immunological correlates for the control of BKPyV DNAemia, which aim at providing a foundation for the development of future immunotherapeutic strategies.