Dendritic Cells Support Homeostatic Expansion of Foxp3+ Regulatory T Cells in Foxp3.LuciDTR Mice

Abstract

Foxp3+CD4+ regulatory T cells (Tregs) are crucial in maintaining self-tolerance and limiting immune responses to pathogens. Shifting the sensitive balance between Tregs and effector T cells requires extensive knowledge of the homeostatic properties of the different T cell populations. For the investigation of Treg homeostatic expansion, we introduce in this study novel BAC transgenic mice, designated Foxp3.LuciDTR, coexpressing enhanced GFP, luciferase for bioluminescence imaging of Tregs, and the diphtheria toxin receptor (DTR) for specific ablation of Tregs. Of several founder lines, Foxp3.LuciDTR-4 mice displayed ∼95% Treg depletion following injection of DT, resulting in activation of conventional CD4+ T cells, probably due to lack of control by Tregs. In contrast, Foxp3.LuciDTR-3 mice displayed only ∼70% Treg depletion without concomitant activation of CD4+ T cells and represented, therefore, a suitable model to study Treg homeostasis in an environment where other T cell populations were not altered. After depletion, the Treg compartment recovered to its original size in ∼2 wk. This recovery was mediated in a thymus-independent fashion by homeostatic proliferation of the surviving, nondepleted Tregs. The proliferating Tregs acquired an activated phenotype and maintained their suppressive capacity. Studies involving DT-mediated depletion of dendritic cells in CD11c.DOG mice showed that dendritic cells were required for optimal Treg homeostasis. In addition, IL-2 was identified as an essential factor for homeostatic recovery of the Treg compartment. These results show that Treg homeostasis is specifically regulated by the size of the Treg compartment and is independent of proliferation of conventional T cells.

Transforming growth factor beta-activated kinase 1 (TAK1)-dependent checkpoint in the survival of dendritic cells promotes immune homeostasis and function

“…Mechanistically, peripheral DCs have been implicated in promoting homeostatic proliferation and survival of T cells (22)(23)(24) as well as inducing a low-level tonic signaling in naive T cells to program their responsiveness to foreign antigens (25). Moreover, although a direct role for DCs to promote T reg expansion and accumulation has been established by recent elegant studies (17,26), how this effect contributes to immune homeostasis is not fully understood (20,21,27,28). Because many of the previous studies have used nonphysiological approaches to modulate DC survival, how endogenous regulators of DC survival influence immune homeostasis and function remains to be established.…”

Efficient Treg depletion induces T‐cell infiltration and rejection of large tumors

“…Significant therapeutic success was only observed when complex combinatorial approaches were applied such as total body irradiation combined with adoptive T-cell transfer and vaccination [29], and additional treatment with anti-PDL1 antibody [30], but usually mice were treated when tumors were still small (3-4 days after s.c. tumor inoculation). Thus, immunotherapy of large established tumors remains a major challenge.We have recently established several lines of BAC transgenic Foxp3.LuciDTR mice [31] in which Treg express luciferase for non-invasive bioluminescence imaging (BLI) and the human diphtheria toxin receptor (DTR) for Treg depletion by diphtheria toxin (DT). The availability of Foxp3.LuciDTR mouse lines displaying different degrees of Treg depletion provided us with a unique model to investigate the role of Treg in tumor immunity as well as the extent of depletion required for successful therapy.…”

Manipulating DNA damage-response signaling for the treatment of immune-mediated diseases

“…T cells were assessed by restimulation with 5 μg of peptide, MOG , GP [33][34][35][36][37][38][39][40][41] , or GP 61-80 (Synthetic Biomolecules) in the presence of Golgi Plug (BD Biosciences). Cells were permeabilized using a Cytofix/Cytoperm Kit (BD Biosciences) and stained with anti-IFN-γ or anti-IL17a (Biolegend).…”

“…Splenocytes were harvested from P14 TCR transgenic mice, activated in vitro with the cognate peptide (LCMV GP [33][34][35][36][37][38][39][40][41] , 1 μg/mL), and cultured in complete DMEM media for 2 d. Human T cells were enriched from PBMCs of normal healthy donors and stimulated with Con A (5 μg/mL), or whole PBMCs were stimulated with Pepmix CMV IE1 peptide pool (JTP). Activated human or mouse cells were then expanded in vitro with IL-2 (100 U/mL; PeproTech) for 3-5 d, except where noted otherwise.…”

“…Although PPCA therapy appears to spare nonactivated, bystander T cells, we wanted to look more closely at Tregs because they have been reported to be a chronically dividing T-cell population in vivo (33). Additionally, DNA-damaging agents, including cyclophosphamide, are reported to kill these cells (34,35).…”