Autoreactive T cells in healthy individuals.

The presence of autoreactive CD4(+) T cells in the peripheral blood of healthy human subjects was investigated after removal of CD4(+)CD25(+) regulatory T cells (Treg). CD4(+) T cells that were directed against the type 1 diabetes-associated autoantigen glutamic acid decarboxylase 65, the melanocyte differentiation Ag tyrosinase, and the cancer/testis tumor Ag NY-ESO-1 were readily derived from PBMC of healthy individuals. These autoreactive T cells could be visualized, using Ag-specific class II tetramer reagents, in the peripheral blood of most individuals examined. Addition of CD4(+)CD25(+) Treg back to the CD4(+)CD25(-) population suppressed the expansion of the autoreactive T cells. Autoreactive T cells were cloned based on tetramer binding, and expressed characteristic activation markers upon self-Ag stimulation. These results show that autoreactive T cells are present in most healthy individuals and that Treg likely play an important role of keeping these autoreactive T cells in check.