A role for the transcription factor Helios in human CD4(+)CD25(+) regulatory T cells.

Relative upregulation of the Ikaros family transcription factor Helios in natural regulatory T cells (Tregs) has been reported by several groups. However, a role for Helios in regulatory T cells has not yet been described. Here, we show that Helios is upregulated in CD4(+)CD25(+) regulatory T cells. Chromatin-immunoprecipitation (ChIP) experiments indicated that Helios binds to the FoxP3 promoter. These data were further corroborated by experiments showing that knocking-down Helios with siRNA oligonucleotides results in down-regulation of FoxP3. Functionally, we found that suppression of Helios message in CD4(+)CD25(+) T cells significantly attenuates their suppressive function. Taken together, these data suggest that Helios may play an important role in regulatory T cell function and support the concept that Helios may be a novel target to manipulate Treg activity in a clinical setting.

Tc17 CD8 T cells: functional plasticity and subset diversity.

IL-17-secreting CD8 T cells (Tc17) have been described in several settings, but little is known regarding their functional characteristics. While Tc1 cells produced IFN-gamma and efficiently killed targets, Tc17 cells lacked lytic function in vitro. Interestingly, the small numbers of IFN-gamma-positive or IL-17/IFN-gamma-double-positive cells generated under Tc17 conditions also lacked lytic activity and expressed a similar pattern of cell surface proteins to IL-17-producing cells. As is the case for Th17 (CD4) cells, STAT3 is important for Tc17 polarization, both in vitro and in vivo. Adoptive transfer of highly purified, Ag-specific IL-17-secreting Tc17 cells into Ag-bearing hosts resulted in near complete conversion to an IFN-gamma-secreting phenotype and substantial pulmonary pathology, demonstrating functional plasticity. Tc17 also accumulated to a greater extent than did Tc1 cells, suggesting that adoptive transfer of CD8 T cells cultured in Tc17 conditions may have therapeutic potential for diseases in which IFN-gamma-producing cells are desired.

Functionally distinct LAG-3 and PD-1 subsets on activated and chronically stimulated CD8 T cells.

Lymphocyte Activation Gene-3 (LAG-3) is a transmembrane protein that binds MHC class II, enhances regulatory T cell activity, and negatively regulates cellular proliferation, activation, and homeostasis of T cells. Programmed Death 1 (PD-1) also negatively regulates T cell function. LAG-3 and PD-1 are both transiently expressed on CD8 T cells that have been stimulated during acute activation. However, both LAG-3 and PD-1 remain on CD8 T cells at high levels after stimulation within tolerizing environments. Our previous data demonstrated that blockade of either LAG-3 or PD-1 using mAb therapy in combination with vaccination restores the function of tolerized Ag-specific CD8 T cells in models of self and tumor tolerance. It is unclear whether tolerized CD8 T cells coexpress PD-1 and LAG-3 or whether PD-1 and LAG-3 mark functionally distinct populations of CD8 T cells. In this study, we describe three populations of CD8 T cells activated under tolerizing conditions based on LAG-3 and PD-1 staining, each with distinct phenotypic and functional characteristics. From a mechanistic perspective, both Ag concentration and proinflammatory signals control the expression of LAG-3 and PD-1 phenotypes on CD8 T cells under activating and tolerizing conditions. These results imply that signaling through the PD-1 and LAG-3 pathways have distinct functional consequences to CD8 T cells under tolerizing conditions and manipulation of both Ag and cytokine signaling can influence CD8 tolerance through LAG-3 and PD-1.