Expansion of Regulatory T Cells In Vitro and In Vivo by IL-33.

Thymic-derived, regulatory T cells (Treg) represent a subset of CD4(+) T cells that are required for normal immune homeostasis and suppression of unwanted responses against self-antigens (Ags) that prevent autoimmunity. Their role as immune regulators and potent ability to suppress T cell responses has been the focus of intense investigations aimed at utilizing these cells therapeutically, particularly in the settings of autoimmunity and transplantation. Many methods for expanding Treg have been described; however, efforts to generate large numbers of Treg for use in vivo often compromise their suppressor function or rely on the induction of Treg rather than their expansion. Our recent studies have focused on the barrier tissue-derived cytokine IL-33, a recently described IL-1 family member. IL-33 has emerged as a multifunctional protein, with reported roles in driving potent Type 1 and Type 2 immunity, as well as facilitating profound Treg expansion in vitro and in vivo. IL-33-expanded Treg express the IL-33 receptor (R) ST2, and express classical markers associated with Treg phenotype and suppressor function. They suppress both CD4(+) and CD8(+) T cell proliferation and effector functions in vitro, and Treg expressing ST2 have been identified as important regulators of detrimental immune responses in vivo. In the present chapter, we detail methods for expanding significant numbers of Treg using IL-33 both in vitro and in vivo that may potentially be used to promote/maintain organ transplant tolerance or suppress autoimmunity.