Ethylenecarbodiimide-coupled allogeneic antigen presenting cells induce human CD4+ regulatory T cells

Adoptive transfer of naturally occurring CD4+CD25+ regulatory T cells can tolerize transplantation alloresponses in animal models. However isolation of these cells in sufficient numbers from humans is cumbersome and prone to contamination with alloreactive CD25+ T cells. Incubation of ethylenecarbodiimide-coupled antigen presenting cells (APC) with naïve T cells and antigen has been shown to induce tolerance in various experimental models. We therefore investigated whether ECDI-coupled allogeneic APC were able to induce an expandable human CD4+ Treg population.CD4+ and CD4+ CD25− cells cultured for 5 days with ECDI-treated human PBMC exhibited potent suppressive capacity in a mixed lymphocyte reaction. Induction of these ECDI-Tregs was associated with up-regulation of Foxp3 mRNA and protein expression and they maintained high expression of CD62L and CD27 as well as low CD127 expression. ECDI-treated APC displayed reduced expression of the co-stimulatory signaling molecules CD40 and CD80, and failed to stimulate proliferation and cytokine secretion in co-cultured CD4+ T cells. Restimulation in the presence of rapamycin and hrIL-2 led to expansion of ECDI-Tregs with increasing Foxp3 levels and suppressive activity significantly higher than expanded naturally occurring CD4+CD25+ Tregs.In summary these findings support the hypothesis that ECDI-coupled APC can convert naïve CD4+ T cells into functional Tregs with different phenotypic characteristics than naturally occurring CD4+CD25+ Tregs. These inducible Tregs could provide a novel approach that might facilitate the translation of ex vivo generated and expanded Tregs into clinical settings.