Torque Teno Virus in Kidney Transplant Recipients: Perspectives on Its Role as a Complementary Marker in Monitoring Net Immunosuppression

Monitoring immunosuppression in kidney transplant recipients remains challenging, as conventional therapeutic drug monitoring (TDM) reflects pharmacokinetic exposure rather than the overall functional immune state. Torque teno virus (TTV), a non-pathogenic virus, has emerged as a potential complementary biomarker of the net state of immunosuppression. This review evaluates the current evidence regarding the utility of TTV load in this context, focusing on its correlation with standard pharmacokinetic markers, the analytical performance of quantitative PCR assays, its role as an integrated marker of immunosuppression, and its predictive value for clinical outcomes. Available data indicate that TTV load shows weak and inconsistent correlations with individual drug levels, such as tacrolimus trough concentrations, supporting its role as a complementary rather than substitutive tool. qPCR-based assays demonstrate generally good sensitivity and reproducibility, although inter-assay variability and lack of standardization remain important limitations. Clinically, higher TTV levels have been associated with an increased risk of opportunistic infections, whereas lower levels have been linked to acute rejection, suggesting a potential association between TTV viremia and immune status. TTV monitoring may represent a promising complementary approach for a more individualized assessment of immunosuppression. However, further prospective and interventional studies are required to validate standardized thresholds and determine whether TTV-guided strategies improve transplant outcomes compared with conventional monitoring.