*Purpose: Non-invasive monitoring strategies are insufficient to detect patients at risk for subclinical graft rejection after kidney transplantation. The highly prevalent and non-pathogenic Torque Teno virus (TTV) reflects the immunosuppression of its host: high level viraemia indicates strong and low level viraemia weak immunosuppression, respectively. Thus TTV replication might serve as a candidate for immunologic monitoring. This sudy was designed to analyse the association between TTV level in the peripheral blood and subclinical kidney graft rejection,

*Methods: To analyze the association between TTV and rejection, an interim analysis of the prospective observational “TTV POET” cohort study (DRKS00012335) was performed including data available until 31/01/2019. All consecutive kidney allograft recipients transplanted at the Medical University Vienna, Austria since 01/12/2016 (n=308) with a protocol biopsies 12 month after transplantation (n=47; median 12.4 months post-transplantation) and stable graft function were included. Biopsy results according to current BANFF classification were analyzed in the context of peripheral blood TTV levels quantified by rt-PCR.

*Results: Graft function of the 47 included patients was excellent (median eGFR MDRD: 57 ml/min/1.73m², urinary PKR: 92 mg/g). Twenty recipients (43%) had subclinical rejection (borderline TCMR, n=16; ABMR, n=3; TCMR type I, n=1). TTV level quantified at the date of biopsy was lower in recipients with rejection compared to recipients without rejection. The risk for rejection increased by 11% with each log level decrease in TTV copies/mL (RR 0.89, 95% CI 0.85-0.93; p<.001). Differences in TTV levels were evident not only at the date of biopsy, but already 6 weeks earlier. Biopsies showing chronic histologic changes, suggesting ongoing allo-reactivity, were associated with increased time spans of TTV levels <1x10⁶ copies/mL.

*Conclusions: Our data suggests an association between TTV level and subclinical graft rejection at 12 months after kidney transplantation. Future clinical trials are necessary to test the potential of TTV guided immunosuppression reducing subclinical rejection.

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