CD4(+)CD25(+)FOXP3(+) Treg cells require TCR engagement for suppressive function, thus ensuring that suppression occurs only in the presence of specific antigens; however, to date no studies have addressed the function of self-antigen-specific Treg in humans. These studies were designed to determine whether peripheral generation and function of islet antigen-specific adaptive Treg are defective in human subjects with type 1 diabetes (T1D). Islet antigen-specific adaptive Treg were induced in vitro by activation of CD4(+)FOXP3(-) T cells with glutamic acid decarboxylase and islet-specific glucose-6-phosphate catalytic subunit-related protein peptides in the context of T1D-associated HLA-DRbeta alleles. Antigen-specific Treg were characterized using flow cytometry for FOXP3 and class II tetramer and assessed for the ability to inhibit proliferation. These adaptive Treg were then compared with influenza-specific Treg from the same study population. The function of tetramer(+) cells that expressed FOXP3 was similar for both influenza and islet antigens generated from control and T1D subjects. In fact, the potency of suppression correlated with FOXP3 expression, not antigen specificity. Thus, these data suggest that development of functional adaptive Treg can occur in response to islet antigens and activation of islet-specific Treg may potentially be used as a targeted immunotherapy in T1D.