Regulatory T cells (Tregs) are critical mediators of immune homeostasis and hold significant promise in the quest for transplantation tolerance. Progress has now reached a critical threshold as techniques for production of clinical therapies are optimised and Phase I/II clinical trials are in full swing. Initial safety and efficacy data are being reported, with trials assessing a number of different strategies for the introduction of Treg therapy. It is now more crucial than ever to elucidate further the function and behaviour of Tregsin vivoand ensure safe delivery. This review will discuss the current state of the art and future directions in Treg therapy.

3C10 could control acute rejection by its suppressive effect on alloreactive T cells and induction of IL-10-dependent regulatory CD4 T cells.

Physiological effects of cellular hypoxia are sensed by prolyl hydroxylase (PHD) enzymes, which regulate HIFs. Genetic interventions on HIF/PHD pathways have revealed multiple phenotypes that extend the known biology of hypoxia. Recent studies have unexpectedly implicated HIF in aspects of multiple immune and inflammatory pathways. However, such studies are often limited by systemic lethal effects and/or use tissue-specific recombination systems, which are inherently irreversible, unphysiologically restricted, and difficult to time. To study these processes better, we developed recombinant mice that expressed tetracycline-regulated shRNAs broadly targeting the main components of the HIF/PHD pathway, permitting timed bidirectional intervention. We show that stabilization of HIF levels in adult mice through PHD2 enzyme silencing by RNA interference or inducible recombination of floxed alleles results in multilineage leukocytosis and features of autoimmunity. This phenotype was rapidly normalized on reestablishment of the hypoxia-sensing machinery when shRNA expression was discontinued. In both situations, these effects were mediated principally through the Hif2a isoform. Assessment of cells bearing Treg markers from these mice revealed defective function and proinflammatory effects in vivo. We believe our findings reveal a new role for the PHD2/HIF2α pathway in the reversible regulation of T cell and immune activity.