TCRαβ repertoire diversity of human naturally occurring CD4+CD25+ regulatory T cells

We examined the αβ T cell receptor (TCR) repertoire of naturally occurring CD4+CD25+ regulatory T (Treg) cells isolated from healthy human blood. Three-color FACS analysis demonstrated that the usage of variable region segments of TCRβ chains by CD4+CD25+ cells did not differ from those of CD4+CD25− cells. Complementarity-determining region 3 (CDR3) size distribution analyses demonstrated that the repertoire diversity of CDR3β was almost identical between CD4+CD25+ and CD4+CD25− T cell subsets, and that there was no skewing of the CDR3β repertoire of CD4+CD25+ T cells. In contrast, in vitro activated CD4+CD25+ T cells by cytomegalovirus-derived antigens showed a skewed CDR3 size distribution pattern. These findings support the hypothesis that naturally occurring CD4+CD25+ T cell subset in humans is 1argely composed of a T cell lineage positively selected in the thymus as a consequence of the interaction between self-peptides and TCRs and not derived from recent activation by a limited array of antigens.