In kidney transplantation, acute T-cell mediated rejection (aTCMR) is linked with chronic rejection, graft loss, and overall worse outcomes. In this study, peripheral blood samples prior to and post- transplantation were analyzed for expression patterns of regulatory T cell (Treg)-related genes: the forkhead box P3 (FOXP3) and the two CTLA-4 isoforms (full-length and soluble) to forecast acute rejection onset, de novo donor-specific antibodies (DSA) development and renal dysfunction 1 year post-transplantation.

• In peripheral blood of 89 kidney transplant recipients (KTRs), circulating mRNA levels of these biomarkers were profiled within the first post-transplant year and also compared the results with 24 healthy controls.

• A drastic decrease was seen in the three mRNA levels 15 days post-transplantation, with slow recovery evident at 1 year relative to baseline, with very low levels at the time of aTCMR for FOXP3, maybe for the pro-apoptotic role of FOXP3 during inflammation.

• A multivariate Cox regression analysis showed a significant association between aTCMR onset and thymoglobuline induction, everolimus use and an elevated risk from the soluble CTLA-4 (solCTLA-4) expression at 15 days, primarily considering recipients managed with Mycophelolic acid.

• In addition, solCTLA-4 predisposed to graft dysfunction at 1 year.

• Pre-transplant solCTLA-4 concentrations demonstrated a protective link with de novo DSAs development.

• Overall, mRNA levels of Treg-related genes, mainly for solCTLA-4, in peripheral blood could be candidate non-invasive biomarkers of cellular and humoral alloreactivity in clinical transplantation.

• In addition to this, they might aid shaping immunosuppression, tailor monitoring and obtain better long-term results of kidney transplantation in the wake of “precision medicine”.