Effect of regulatory T cells on short-term graft outcome in kidney transplant recipients, a prospective observational, single-center study.

Background: Regulatory T cells (Tregs) are important for maintaining immune homeostasis, limiting kidney transplant rejection, and promoting transplant tolerance. Tregs are characterized as CD4 + CD25+ T cells and the transcription factor Foxp3; they constitute 5-10% of all peripheral CD4+ T cells in healthy humans. The reduction in Treg cells after transplantation may be a predictive factor in graft rejection. Therefore, in this study, we investigated the association between Tregs and short-term graft outcomes in renal transplant recipients.

Methods: This prospective observational study included 50 patients of both sexes, aged between 18 and 60 years, with end-stage renal disease (ESRD), and who underwent kidney transplantation at the Nizams Institute of Medical Sciences. Flow cytometry was used to measure the percentage of Tregs (CD4 + CD25+) pre-transplant (baseline) and monthly post-transplant in 50 transplant recipients and 20 healthy controls (HC) over six months. The correlation between Treg percentages and graft outcomes was analyzed.

Results: The percentage of Tregs (Treg%) was significantly lower in ESRD patients before transplantation (baseline) than in the HCs [median 8.5% vs. 14.25%; p < 0.01]. After transplantation, Treg% decreased significantly within a week after grafting compared to the baseline pre-transplant level [median 5.13% vs. 8.5%; p < 0.01]. Moreover, Treg% was lower in the older (> 40 years) than that in the younger age group at one week after transplantation (p > 0.001). Treg% (CD4 + CD25+) was significantly lower in patients with deceased donor renal transplantation (DDRT) than in live renal transplantation (LRT) within the first week of transplantation [median 2.16% vs. 4.6%; p < 0.05] and at the time of graft rejection [median 3.2% vs. 9.2%; p < 0.001]. Induction therapy with anti-IL-2 receptor monoclonal antibody (IL-2RB) lowered Tregs to a greater extent than anti-thymoglobulin (ATG) therapy and no induction therapy [median 3.22% vs. 5.47%, 8.4%, p < 0.05]. In contrast, an increased Treg% was observed in transplant recipients with normal kidney graft function within six months after transplantation compared with the pre-transplant baseline level [median 11.54% vs. 8.5; p < 0.001]. ROC analysis of graft rejection resulted in an area under the curve (AUC) of 0.8 with a p-value <0.05.

Conclusion: Within the first week after transplantation, the percentage of pre-transplant Tregs was significantly decreased compared to that in age- and sex-matched HC. The percentage of Tregs was also lower in patients with advanced age, DDRT, and those who received IL-2RB induction therapy. Patients who experienced graft rejection had lower Treg% compared to their pre-transplant levels. In contrast, patients with normal graft function at six months showed increased Treg%. Together, these results suggest that Treg% measurements are correlated with clinical outcomes.