Human Double-Degative Regulatory T Cells Modulate Differentiation and Function of Conventional T Cells By Disrupting mTOR Activity

Regulatory T cells (Treg) play an important role in the maintenance of immune tolerance to self-antigens and are involved in modulating immune responses to promote resolution of inflammation. The subpopulation of TCRαβ+ CD4- CD8- (double-negative, DN) T cells has been described to suppress immune responses in both mice and humans. In murine models infusion and/or activation of DNT cells specifically suppressed alloreactive T cells and prevented development of Graft-versus-Host disease (GvHD) after allogeneic hematopoietic stem cell transplantation (allo-SCT). Moreover, clinical studies in patients after allo-SCT revealed an inverse correlation between the frequency of circulating DNT cells and the severity of GvHD, suggesting a therapeutic potential of human DNT cells. We have recently demonstrated that human DNT cells like their murine counterparts strongly suppress proliferation of both CD4+ and CD8+ T-cells. Here we investigated the impact of human DNT cells on differentiation and function of conventional T cells. Notably, we found that DNT cells blocked proliferation but also modulated the expression of costimulatory/-inhibitory receptors and differentiation markers of conventional T cells. Further analyses demonstrated that the suppressed T cells do not upregulate homing receptors associated with inflammatory processes. In contrast, expression of central memory-cell associated cell surface markers and transcription factors were increased by DNT cells. Moreover, CD4+ T cells failed to produce IL-17 and IFN-γ after coculture with DNT cells whereas IL-2 secretion was enhanced. Given that TCR-induced signal transduction regulate T cell expression profile we further determined the effect of DNT cells on central protein kinases. Notably, DN T cells selectively suppressed the mTOR signaling pathway but not activation of mitogen-activated protein kinases. Enforced activation of the mTOR pathway by a chemical activator rendered conventional T cells unsusceptible to the suppressive activity of DNT cells. Together, our findingsindicate that human DNT cells control not only activation but also migration and functionality of conventional T cells. Further understanding of the mechanisms involved in human DN T-cell suppression may have important implications for using them as a cellular-based therapy to limit alloreactive immune responses.

This work was supported by the Deutsche Forschungsgemeinschaft [DFG-CRC1181 (B04)].