Kidney transplantation represents the treatment standard for end-stage renal disease. Graft rejection due to inadequate immunosuppression is the leading cause for chronic graft dysfunction, and infectious disease due to reduced immune function is a major cause of death. Optimisation of immunosuppressive drugs is crucial to minimising the risk of infection and rejection and thereby prolonging patient and graft survival. The peripheral blood copy number of the prevalent and non-pathogenic Torque Teno virus (TTV) is associated with the grade of the immunosuppression of the host. Non-interventional studies suggest superiority of TTV copy number guided immunosuppression compared to standard strategies. EU-funded TTV GUIDE TX will test safety and preliminary efficacy of TTV-guided immunosuppression within a phase II randomised and controlled clinical trial.