Transient increase of activated regulatory T cells early after kidney transplantation.

Regulatory T cells (Tregs) are crucial in controlling allospecific immune responses. However, studies in human kidney recipients regarding the contribution of polyspecific Tregs have provided differing results and studies on alloreactive Tregs are missing completely. In this retrospective study, we specifically analyzed activated CD4+CD25highFOXP3+GARP+ Tregs in 17 patients of a living donor kidney transplantation cohort longitudinally over 24 months by flow cytometry (FOXP3: forkhead box protein 3, GARP: glycoprotein A repetitions predominant). We could demonstrate that Tregs of patients with end-stage renal disease (ESRD) are already pre-activated when compared to healthy controls. Furthermore, even though total CD4+CD25highFOXP3+ Treg numbers decreased in the first three months after transplantation, frequency of activated Tregs increased significantly representing up to 40% of all peripheral Tregs. In a cohort of living donor kidney transplantation recipients with stable graft function, frequencies of activated Tregs did not correlate with the occurrence of acute cellular rejection or chronic graft dysfunction. Our results will be important for clinical trials using adoptive Treg therapy after kidney transplantation. Adoptively transferred Tregs could be important to compensate the Treg loss at month 3, while they have to compete within the Treg niche with a large number of activated Tregs.

Isolation of human antigen-specific regulatory T cells with high suppressive function.

Adoptive transfer of regulatory T (Treg) cells could be an alternative to chronic immunosuppression for prevention of allogeneic graft rejection. While polyspecific Treg cells can prevent immune responses under lymphopenic conditions, Ag-specific Treg cells are needed to treat autoimmunity and graft rejection. Yet, reliable markers for Ag-specific Treg cells are missing. We report that latency-associated peptide (LAP) and glycoprotein A repetitions predominant (GARP) can identify human Ag-specific Treg cells. In addition, we show that the depletion of CD154(+) cells from LAP(+) or GARP(+) Treg cells increases the Treg-cell purity to over 90%, as assessed by epigenetic analysis. These Ag-specific Treg cells can be isolated magnetically and might contribute to the development of GMP-based protocols. In addition, Ag-specific Treg cells are functionally far superior to CD4(+) CD25(high) or CD4(+) CD25(high) CD127(low) Treg cells in vitro and in preventing strong alloreactions in humanized mice. They could, therefore, have a high therapeutic potential for the control of alloimmune, autoimmune, and allergic immune responses in patients.