Regulatory T-cell Number in Peripheral Blood at 1 Year Posttransplant as Predictor of Long-term Kidney Graft Survival

Abstract

Background: Regulatory T (Treg) cells play a role in limiting kidney transplant rejection and can potentially promote long-term transplant tolerance. There are no large prospective studies demonstrating the utility of peripheral blood Treg cells as biomarkers for long-term graft outcome in kidney transplantation. The aim of our study was to analyze the influence of the absolute number of peripheral blood Treg cells after transplantation on long-term death-censored graft survival.

Methods: We monitored the absolute numbers of Treg cells by flow cytometry in nonfrozen samples of peripheral blood in 133 kidney transplant recipients, who were prospectively followed up to 2 years after transplantation. Death-censored graft survival was determined retrospectively in January 2017.

Results: The mean time of clinical follow-up was 7.4 ± 2.9 years and 24.1% patients suffered death-censored graft loss (DCGL). Patients with high Treg cells 1 year after transplantation and above the median value (14.57 cells/mm³), showed better death-censored graft survival (5-year survival, 92.5% vs 81.4%, Log-rank P = .030). One-year Treg cells showed a receiver operating characteristic - area under curve of 63.1% (95% confidence interval, 52.9-73.2%, P = 0.026) for predicting DCGL. After multivariate Cox regression analysis, an increased number of peripheral blood Treg cells was a protective factor for DCGL (hazard ratio, 0.961, 95% confidence interval, 0.924-0.998, P = 0.041), irrespectively of 1-year proteinuria and renal function.

Conclusions: Peripheral blood absolute numbers of Treg cells 1 year after kidney transplantation predict a better long-term graft outcome and may be used as prognostic biomarkers.

FIGURE 1

Regulatory T (Treg) cell levels in kidney transplant recipients (KTRs). (A) The comparison of the number of Treg cell/mm³ in peripheral blood of KTRs is depicted and median and interquartile range are shown at different time points (pretransplant, open circles; 6 months posttransplant, open squares; 12 months posttransplant, open triangles; and 24 months posttransplant, open diamonds). Treg cell changes were assessed by the Wilcoxon paired rank test and levels of significance were indicated as **P < .01, ***P < .001, and ****P < .0001.

FIGURE 2

Association of early posttransplant Regulatory T (Treg) cell levels and risk of death-censored graft loss (DCGL). The Treg cell levels before transplant, at 6 and 12 months postkidney transplantation were assessed for risk of DCGL by univariate Cox regression analysis. Treg cell levels were analyzed as a continuous variable.

FIGURE 3

(A) Receiver operational curve analysis of regulatory T (Treg) cell levels at 12 months posttransplant and death-censored graft loss (DCGL). The area under curve (AUC) is 63.1%. A cutoff of 14.57 Treg cells/mm³ in peripheral blood discriminates between DCGL and non-DCGL after kidney transplantation with a sensitivity and a specificity of 51.5% and 75%, respectively. (B) Tertile distribution of Treg cell levels at 12-month postkidney transplantation. Red circles in first tertile and blue circles in third tertile are depicted. White circles represent the second tertile.

FIGURE 4

Regulatory T (Treg) cell level stratification and death-censored graft survival. The kidney transplant recipients (KTRs) were stratified based on tertiles of Treg cell levels at 12 months postkidney transplantation. Above first tertile, high Treg cell levels (19.51 Treg cells/mm³) are shown in red; below third tertile, low Treg cell levels (7.63 Treg cells/mm³) are shown in blue; and second tertile medium Treg cell levels are shown in black. No statistically significant differences were found among the 3 tertiles by the Kaplan-Meier analysis. The lower table shows the number of patients at risk in each group at the given timepoints.