Constitutively active Stat5b in CD4+ T cells inhibits graft-versus-host disease lethality associated with increased regulatory T-cell potency and decreased T effector cell responses

Abstract

Overexpression of a constitutively active form of Stat5b (Stat5b-CA) increases regulatory T cells (Tregs). We show that IntroductionCytokines regulate survival, proliferation, and differentiation of various immune cells, and those using the ␥ c chain play a major role in lymphocyte homeostasis. Interleukin-2 (IL-2), IL-7, and IL-15 interactions with their receptors are essential for normal B-and T-cell development and peripheral T-cell homeostasis and proliferation. [1][2][3] The major pathways activated on ␥ c receptor activation are Jak/Stat, MAPK, and PI3K. 4 Although these signals lead to changes in cell proliferation, differentiation, and survival in several T-cell lineages, the transcription factor Stat5 is particularly important for CD4 ϩ CD25 ϩ FoxP3 ϩ regulatory T-cell (Treg) development and homeostasis in mice and humans. [5][6][7][8] T-cell specific deficiency in both homologs, Stat5a and Stat5b, resulted in significantly decreased numbers of Tregs, as well as CD8 ϩ , CD4 ϩ , and ␥␦ T-cell numbers in the thymus and in the periphery in mice. 7,9 Conversely, transgenic (TG) expression of a constitutively active form of Stat5b (Stat5b-CA) in T and B cells resulted in an increase in Tregs, CD8 ϩ , CD4 ϩ , ␥␦, and natural killer T-cell numbers. 5 Deletion or overexpression of Stat5 affected CD8 ϩ T cells more than CD4 ϩ T cells, with the exception of Tregs. CD8 ϩ T cells in Stat5b-CA TG mice were increased far more than CD4 ϩ T cells and exhibited a memory phenotype, whereas most CD4 ϩ T cells maintained a naive phenotype. The majority of CD4 ϩ CD25 ϩ T cells from Stat5b-CA TG mice expressed FoxP3 and suppressed wild-type (WT) effector T-cell (Teff) responses in vitro. On T-cell receptor (TCR) stimulation, in vitro proliferation of CD4 ϩ T cells was lower in Stat5b-CA TG versus WT mice, although because Treg-depleted CD4 ϩ T-cell responders were not used, the influence of Stat5b-CA expression on Teffs could not be derived from these studies. Naive CD4 ϩ CD25 Ϫ CD45RB high T cells from Stat5b-CA TG mice showed enhanced homeostatic proliferation when transferred into WT recipients 10 and, in contrast to WT CD4 ϩ CD25 Ϫ CD45RB high T cells, this proliferation was major histocompatibility complex (MHC) class II-and IL-15-independent, suggesting deregulation of homeostatic proliferation by Stat5b-CA in naive CD4 ϩ T cells. 10 Previous studies have not reported the in vivo function of Stat5b-CA TG Tregs. We show that Stat5b-CA TG Tregs suppressed graft-versus-host disease (GVHD) lethality more efficiently than WT Tregs. Surprisingly, Stat5b-CA TG CD4 ϩ CD25 Ϫ Teffs also had a reduced GVHD lethality capacity compared with WT Teffs. Nonetheless, Stat5b-CA TG Teffs retained a graft-versusleukemia (GVL) effect. These results indicate, for the first time, that Stat5 overexpression in CD4 ϩ T cells plays a major role in Treg expansion and potency in vivo. Moreover, we provide the first evidence that Stat5 overexpression in CD4 ϩ T cells regulates Th2 cytokine production in vivo that is associated with a reduction in G...

CCL17-expressing dendritic cells drive atherosclerosis by restraining regulatory T cell homeostasis in mice

“…Accordingly, the increased activation of Stat5 may interfere with IL-2 production and subsequently induce a negative feedback signal in CD4 + T cells with elevated sensitivity to cell death (42)(43)(44)(45)(46). Moreover, a marked expansion of Tregs was observed in mice with constitutive overexpression of active Stat5 (41). Given the importance of IL-2 in STAT5 activation to sustain Foxp3 expression in Tregs, involving STAT5 binding to a highly conserved STAT-binding site located in the first intron of the FOXP3 gene (47), interference with Stat5 may not only constrict T cell proliferation but also diminish conversion into Foxp3 + Tregs and their peripheral maintenance.…”

“…The proliferation of T cells is tightly regulated by Stat5, which is recruited to the TCR in response to stimulation (39). Whereas Stat5 -/-mice display decreased T cell proliferation due to defective expression of the IL-2 receptor α-chain (40), constitutive overexpression of the active form of Stat5 was found to enhance T cell proliferation but also the rate of apoptosis (41). Accordingly, the increased activation of Stat5 may interfere with IL-2 production and subsequently induce a negative feedback signal in CD4 + T cells with elevated sensitivity to cell death (42)(43)(44)(45)(46).…”

Targeted Rho-associated kinase 2 inhibition suppresses murine and human chronic GVHD through a Stat3-dependent mechanism

“…Stat5 activation promotes expression of FoxP3 expression and reduces lethal acute GVHD when constitutively active. 33 We further describe an increase in TFR cells in mice with ROCK2 inhibition compared with vehicle-treated controls ( Figure 2B). TFR cells are important in the regulation of the GC and prevention of autoimmunity.…”

Treg adoptive therapy: is more better?

“…Several approaches are under investigation to enhance Treg efficacy by increasing their potency with pharmacologic inhibition of protein kinase C-u, 3 augmentation of signal transducer and activator of transcription (Stat) 5 signaling, 4 and inhibition of Stat1. 5 Because all-trans retinoic acid has been shown to significantly augment the suppressive effects on xenogenic GVHD 6 and rapamycin has been shown to stabilize infused Treg, 7 the addition of these agents to Treg cultures are being explored.…”