Suppressor activity of anergic T cells induced by IL‐10‐treated human dendritic cells: association with IL‐2‐ and CTLA‐4‐dependent G₁ arrest of the cell cycle regulated by p27Kip1

We have previously shown that human IL‐10‐treated dendritic cells (DC) induce an antigen‐specific anergy in CD4 + T lymphocytes. These anergic T cells are characterized by an inhibitedproliferation, a reduced production of IL‐2, and additionally display antigen‐specific suppressor activity. In this study we investigated the mechanisms underlying the anergic state and regulatory function of these T cells. We did not observe enhanced rates of programmed cell death of anergic CD4 + suppressor T cells compared to T cells stimulated with mature DC. Cell cycle analysis by DNA staining and Western blot experiments revealed an arrest of anergic CD4 + T suppressor cells in the G 1 phase. High levels of the IL‐2‐dependent cyclin‐dependent kinase (cdk) inhibitor p27 Kip1 were found in anergic CD4 + suppressor T cells resulting in an inhibited activation of retinoblastoma protein and an arrest of cell cycle progression in the G 1 phase. Addition of IL‐2, but not blocking of the CTLA‐4 pathway restored the proliferation of the suppressor T cells. In contrast, both treatments induced a down‐regulation of p27 Kip1 and acomplete inhibition of the antigen‐specific regulatory function as demonstrated by high proliferation and enhanced IFN‐γ production of co‐cultured T cells. Further experiments demonstrated thatp27 Kip ‐expressing regulatory CD4 + CD25 + T cells did not contribute to induction of T cell anergy in this model. Our data show that regulatory function of anergic CD4 + suppressor T cells is associated with an arrest in the G 1 phase of the cell cycle mediated by increased levels of the IL‐2‐ and CTLA‐4‐dependent cdk inhibitor p27 Kip1 .