This case highlights the complexities of post-transplant management in a patient with BK viremia following a second kidney transplant while maintaining a functioning pancreas graft. The management of BKVN requires close viral load surveillance and careful immunosuppressive adjustments to balance the risk of viral progression and rejection.

A key clinical challenge is balancing immunosuppression—over-immunosuppression can exacerbate BK virus replication. At the same time, under-immunosuppression increases the risk of graft rejection, particularly in pancreas transplant recipients, who have higher rejection rates.

Tutivia™ played an important role in guiding patient-specific immunosuppressive decisions. The patient’s low Tutivia™ score of 3 reassured clinicians that the risk of rejection was low, supporting the decision to maintain or cautiously lower immunosuppression or change therapeutic option. This approach allowed for BK infection management while preserving graft function.

A high-risk Tutivia result indicates a nearly sixfold increase in the probability of acute rejection versus a low-risk result (Bestard O, et al. 2024). This underscores the value of Tutivia™ in providing objective, data-driven risk assessment, enabling more precise and confident treatment decisions.

Epidemiology of BK Virus in Transplant Recipients

BK virus is a common opportunistic infection in kidney and pancreas transplant recipients, with reactivation primarily driven by immunosuppression. Studies estimate that up to 30% of KTRs develop BK viremia (Kant S, et al, 2022), and 1–10% progress to BKVN, which can lead to graft dysfunction and loss (Kant S, et al, 2022). Of patients who develop BK viremia, 50% do so by 3 months after kidney transplantation, and 95% of BKVN occurs in the first 2 years after kidney transplantation (KDIGO, 2009). Early detection through BK virus PCR screening and careful immunosuppressive modulation is critical to reducing the risk of BKVN and preserving long-term graft function (Hardinger KL, et al, 2010).

Pathophysiology and Risk Factors for BKVN

BK virus is a polyomavirus that remains latent in the urothelium and renal tubular epithelium of most individuals but can reactivate in the setting of immunosuppression, particularly after kidney transplantation (Hirsch HH and Steiger J, 2003). Viral reactivation leads to replication in renal tubular cells, causing cell lysis, tubular injury, interstitial inflammation, and eventual fibrosis, characteristic of BKVN (Hirsch HH and Steiger J, 2003). The resulting tubular damage and interstitial nephritis can lead to progressive graft dysfunction and, in severe cases, graft loss if untreated (Hirsch HH and Steiger J, 2003).

Risk factors for BK virus reactivation include (Hirsch HH and Steiger J, 2003)

- potent immunosuppressive regimens

- prior rejection episodes

Diagnostic Approaches: BK Virus PCR, Biopsy, and Biomarkers

The primary diagnostic tool is BK virus PCR (Hirsch HH and Steiger J, 2003), which quantifies viral load in plasma and urine. Persistent viremia (>10 000 copies/mL) is highly suggestive of active infection, warranting further evaluation (Hirsch HH and Steiger J, 2003).

A kidney biopsy remains the gold standard for confirming BKVN, distinguishing it from AR. Histopathologic findings include intranuclear viral inclusions (decoy cells), tubulitis, interstitial inflammation, and fibrosis (Baker et al., 2017).

Emerging biomarkers, such as dd-cfDNA, urinary CXCL10, and Tutivia™ scores, are being explored for their ability to differentiate between BKVN and rejection. While dd-cfDNA is often limited in multiorgan transplant recipients, Tutivia™ provides a non-invasive immune risk assessment, aiding in immunosuppressive decision-making alongside traditional diagnostics (Bestard O, et al. 2024).

The Role of Tutivia™ in Post-Transplant Risk Assessment

Tutivia™ is a non-invasive, immune risk assessment tool designed to aid in monitoring transplant recipients, helping differentiate between low and high rejection risk (Bestard O, et al, 2024). By analyzing immune activity at the molecular level, Tutivia™ provides a quantitative score that guides immunosuppressive management without requiring an invasive biopsy.

In patients with BK viremia or nephropathy, a low Tutivia™ score suggests minimal rejection risk, supporting immunosuppression reduction to curb viral replication while minimizing rejection risk. Conversely, a high-risk Tutivia™ result significantly increases the likelihood of AR, with studies showing an odds ratio of 5.74 compared to low-risk results (Bestard O, et al, 2024).

Tutivia™ may be particularly valuable in multiorgan transplant recipients, where traditional markers like dd-cfDNA may be less reliable due to difficulty in distinguishing between different grafts. By integrating Tutivia™ scores with BK virus PCR, biopsy, and routine laboratory monitoring, clinicians can make data-driven, personalized treatment decisions to optimize long-term transplant outcomes.

Management Strategies: Immunosuppression Adjustment and Antiviral Considerations

The management of BK virus reactivation in transplant recipients requires a careful balance between reducing viral replication and maintaining sufficient immunosuppression to prevent graft rejection. The primary strategy involves immunosuppression modulation, as there are no US Food and Drug Administration-approved antiviral therapies for BK virus (Imlay H, et al, 2022).

Immunosuppression adjustments typically include reducing CNIs such as tacrolimus or cyclosporine and/or discontinuing antiproliferative agents like mycophenolate mofetil while maintaining corticosteroids. In high-risk cases, switching to mTOR inhibitors (eg sirolimus or everolimus) may be considered due to their potential antiviral properties.

Regular monitoring with BK virus PCR, kidney function tests, and Tutivia™ scores is essential to guide ongoing management. In cases of severe BKVN, a biopsy may be warranted to assess the extent of injury and determine the need for further intervention.