Autocrine Ifn Gamma Controls The Regulatory Function Of Lymphoproliferative Double Negative T Cells

TCR alpha beta(+) CD4(-)CD8(-)NK(-) double negative T cells (DN T cells) can act as regulatory T cells to inhibit allograft rejection and autoimmunity. Their role in graft-versus-host disease and mechanisms of suppression remain elusive. In this study, we demonstrate that DN T cells can inhibit CD4(+) T cell-mediated GVHD in a semi-allogeneic model of bone marrow transplantation. Furthermore, we present evidence of a novel autocrine IFN gamma signaling pathway in Fas-deficient C57BL/6.lpr (B6.lpr) DN T cells. B6.lpr DN T cells lacking IFN gamma or its receptor were impaired in their ability to suppress syngeneic CD4(+) T cells responding to alloantigen stimulation both in vitro and in vivo. Autocrine IFN gamma signaling was required for sustained B6.lpr DN T cell IFN gamma secretion in vivo and for upregulation of surface Fas ligand expression during TCR stimulation. Fas ligand (FasL) expression by B6.lpr DN T cells permitted lysis of activated CD4(+) T cells and was required for suppression of GVHD. Collectively, our data indicate that DN T cells can inhibit GVHD and that IFN gamma plays a critical autocrine role in controlling the regulatory function of B6.lpr DN T cells.