Immune Monitoring Goes Viral – Torque Teno Virus for Immunologic Risk Stratification After Kidney Transplantation

Using biomarkers to tailor immunosuppressive therapy after kidney transplantation was proposed to improve clinical care. Timely and individual adaptions of immunosuppression could reduce therapy-related side effects, such as infections, cardiovascular morbidity and malignancy, and further lower the risk of allograft rejection. Despite promising preliminary studies, evidence for implementing such a biomarker in clinical care is insufficient. Prominent candidates for immunologic monitoring after kidney transplantation include donor human leukocyte antigen-specific antibodies, donor-derived cell-free DNA, urinary chemokines and peripheral transcriptomics. In addition, the quantification of Torque Teno virus, a highly prevalent and non-pathogenic virus that was shown to associate with outcomes linked to immunocompetence, has been proposed for immunologic monitoring. This review summarises the prospects and limitations of Torque Teno virus for immunologic risk stratification after kidney transplantation in the context of current state-of-the-art. It will focus on cut-off values of plasma Torque Teno virus load that might be useful to guide immunosuppression in the clinical care of kidney transplant recipients, and highlights recently proposed indications of Torque Teno virus-guided immunosuppression.