Requirement for CD28 in Effector Regulatory T Cell Differentiation, CCR6 Induction, and Skin Homing.
ABSTRACT: The skin, similar to most nonlymphoid tissues, contains substantial numbers of T cells. Among these, memory T cells serve a sentinel role to protect against pathogens, and regulatory T cells (Tregs) terminate immune responses as a check against unrestrained inflammation. Previously, we created conditional knockout mice with Treg-specific deletion of CD28. Although these mice have normal numbers of Tregs, these cells have lower levels of CTLA-4, PD-1, and CCR6, and the animals develop systemic autoimmunity characterized by prominent skin inflammation. In this study, we have performed a detailed analysis of the skin disease in these mice. Our data show that Treg-expressed CD28 is required for optimal maturation of CD44(lo)CD62L(hi) central Tregs into CD44(hi)CD62L(lo) effector Tregs (eTregs), as well as induction of CCR6 among the cells that do become eTregs. Although CD28-deficient Tregs are able to regulate inflammation normally when injected directly into the skin, they fail to home properly to inflamed skin. Collectively, these results suggest a key role for CD28 costimulation in promoting a central Treg to eTreg transition with appropriate upregulation of chemokine receptors such as CCR6 that are required for tissue homing.
Project description:Regulatory T cells (Tregs), a subset of CD4(+) T cells, dramatically accumulate with age in humans and mice and contribute to age-related immune suppression. Recently, we showed that a majority of accumulating Tregs in aged mice expressed low levels of CD25, and their accrual is associated with declining levels of IL-2 in aged mice. In this study, we further investigated the origin of CD25(lo) Tregs in aged mice. First, aged Tregs had high expression of neuropilin-1 and Helios, and had a broad V? repertoire. Next, we analyzed the gene expression profile of Tregs, naive T cells, and memory T cells in aged mice. We found that the gene expression profile of aged CD25(lo) Tregs were more related to young CD25(lo) Tregs than to either naive or memory T cells. Further, the gene expression profile of aged Tregs was consistent with recently described "effector" Tregs (eTregs). Additional analysis revealed that nearly all Tregs in aged mice were of an effector phenotype (CD44(hi)CD62L(lo)) and could be further characterized by high levels of ICOS and CD69. ICOS contributed to Treg maintenance in aged mice, because in vivo Ab blockade of ICOSL led to a loss of eTregs, and this loss was rescued in Bim-deficient mice. Further, serum levels of IL-6 increased with age and contributed to elevated expression of ICOS on aged Tregs. Finally, Treg accrual was significantly blunted in aged IL-6-deficient mice. Together, our data show a role for IL-6 in promoting eTreg accrual with age likely through maintenance of ICOS expression.
Project description:Resting central Tregs (cTregs) and activated effector Tregs (eTregs) are required for self-tolerance, but the heterogeneity and relationships within and between phenotypically distinct subsets of cTregs and eTregs are poorly understood. By extensive immune profiling and deep sequencing of TCR-? V regions, two subsets of cTregs, based on expression of Ly-6C, and three subsets of eTregs, based on distinctive expression of CD62L, CD69, and CD103, were identified. Ly-6C(+) cTregs exhibited lower basal activation, expressed on average lower affinity TCRs, and less efficiently developed into eTregs when compared with Ly-6C(-) cTregs. The dominant TCR V?s of Ly-6C(+) cTregs were shared by eTregs at a low frequency. A single TCR clonotype was also identified that was largely restricted to Ly-6C(+) cTregs, even under conditions that promoted the development of eTregs. Collectively, these findings indicate that some Ly-6C(+) cTregs may persist as a lymphoid-specific subset, with minimal potential to develop into highly activated eTregs, whereas other cTregs readily develop into eTregs. In contrast, subsets of CD62L(lo) eTregs showed higher clonal expansion and were more highly interrelated than cTreg subsets based on their TCR-? repertoires, but exhibited varied immune profiles. The CD62L(lo) CD69(-) CD103(-) eTreg subset displayed properties of a transitional intermediate between cTregs and more activated eTreg subsets. Thus, eTreg subsets appear to exhibit substantial flexibility, most likely in response to environmental cues, to adopt defined immune profiles that are expected to optimize suppression of autoreactive T cells.
Project description:Regulatory T cells (Tregs) have been shown to be critical in the balance between autoimmunity and tolerance and have been implicated in several human autoimmune diseases. However, the small number of Tregs in peripheral blood limits their therapeutic potential. Therefore, we developed a protocol that would allow for the expansion of Tregs while retaining their suppressive activity. We isolated CD4+CD25 hi cells from human peripheral blood and expanded them in vitro in the presence of anti-CD3 and anti-CD28 magnetic Xcyte Dynabeads and high concentrations of exogenous Interleukin (IL)-2. Tregs were effectively expanded up to 200-fold while maintaining surface expression of CD25 and other markers of Tregs: CD62L, HLA-DR, CCR6, and FOXP3. The expanded Tregs suppressed proliferation and cytokine secretion of responder PBMCs in co-cultures stimulated with anti-CD3 or alloantigen. Treg expansion is a critical first step before consideration of Tregs as a therapeutic intervention in patients with autoimmune or graft-versus-host disease.
Project description:IL-2 plays a critical role in the induction and maintenance of FoxP3-expressing regulatory T cells (FoxP3(+) Tregs). Reduced expression of IL-2 is linked to T-cell-mediated autoimmune diseases such as type 1 diabetes (T1D), in which an imbalance between FoxP3(+) Tregs and pathogenic T effectors exists. We investigated the contribution of IL-2 to dysregulation of FoxP3(+) Tregs by comparing wildtype NOD mice with animals congenic for a C57BL/6-derived disease-resistant Il2 allele and in which T-cell secretion of IL-2 is increased (NOD.B6Idd3). Although NOD mice exhibited a progressive decline in the frequency of CD62L(hi) FoxP3(+) Tregs due to an increase in CD62L(lo) FoxP3(+) Tregs, CD62L(hi) FoxP3(+) Tregs were maintained in the pancreatic lymph nodes and islets of NOD.B6Idd3 mice. Notably, the frequency of proliferating CD62L(hi) FoxP3(+) Tregs was elevated in the islets of NOD.B6Idd3 versus NOD mice. Increasing levels of IL-2 in vivo also resulted in larger numbers of CD62L(hi) FoxP3(+) Tregs in NOD mice. These results demonstrate that IL-2 influences the suppressor activity of the FoxP3(+) Tregs pool by regulating the balance between CD62L(lo) and CD62L(hi) FoxP3(+) Tregs. In NOD mice, reduced IL-2 expression leads to an increase in nonsuppressive CD62L(lo) FoxP3(+) Tregs, which in turn correlates with a pool of CD62L(hi) FoxP3(+) Tregs with limited proliferation.
Project description:PTPN22 gene variation associates with multiple autoimmune diseases, including type 1 diabetes and rheumatoid arthritis. Loss of function studies have demonstrated that PTPN22 impinges on the homeostatic behavior of regulatory T (Treg) cells, a lineage critical for immune tolerance. The frequency and absolute number of Treg cells is increased in Ptpn22-deficient mice, but the mechanism driving this increase is unknown. In this study, we show that Ptpn22 knockdown (KD) promoted the expansion of the Treg cell compartment by upregulating the glucocorticoid-induced TNFR family-related protein (GITR) and increasing GITR signaling. Ptpn22 KD did not accelerate cell division but instead prolonged Treg cell survival, as measured by a decrease in the frequency of apoptotic Treg cells. Loss of Ptpn22 caused a concomitant increase in the proportion of CD44(hi)CD62L(lo) effector Treg cells, at the expense of CD44(lo)CD62L(hi) central Treg cells. The increase in Treg cell numbers, but not their differentiation toward an effector phenotype, was dependent on GITR signaling, because blockade of GITR ligand prevented Treg cell expansion caused by Ptpn22 KD. These findings indicate that GITR plays a key role in regulating the overall size of the Treg cell pool. Our results suggest that the size and composition of the Treg cell compartment are independently controlled and have implications for the design of immunotherapies that seek to improve Treg cell function.
Project description:Regulatory T cells (Tregs) are crucial for the induction and maintenance of self-tolerance and are present in peripheral tissues such as skin and gut under normal, noninflamed conditions. We report isolation and expansion of the Treg population resident in normal human skin. Cutaneous Tregs expressed high levels of CD25, L-selectin, GITR, FOXP3, and intracellular CTLA-4, low levels of CD69, and high levels of the skin-homing addressins CLA, CCR4, and CCR6. Skin Tregs suppressed the proliferation of CD25(lo) T cells from the same skin sample in response to CD3 and CD28 antibodies. Suppression was dependent on cell contact and not affected by neutralizing antibodies to interleukin-10 (IL-10) and transforming growth factor-beta (TGF-beta). Surprisingly, cutaneous Tregs proliferated in an antigen-independent manner when cultured in contact with dermal fibroblasts and IL-15, conditions similar to those found in chronically inflamed skin. We hypothesize that local proliferation of Tregs may occur within inflamed skin and could serve as a brake for cutaneous inflammation as well as a mechanism for the homeostatic proliferation of natural Tregs that has been observed within intact organisms.
Project description:Transcriptional pathways controlling the development of CD44(hi) memory phenotype (MP) T cells with "innate-like" functions are not well understood. Here we show that the BTB (bric-a-brac, tramtrack, broad complex) domain-containing protein promyelocytic leukemia zinc finger (PLZF) is expressed in CD44(hi), but not in CD44(lo), CD4(+) T cells. Transgenic expression of PLZF during T cell development and in CD4(+) and CD8(+) T cells induced a T cell intrinsic program leading to an increase in peripheral CD44(hi) MP CD4(+) and CD8(+) T cells and a corresponding decrease of naïve CD44(lo) T cells. The MP CD4(+) and CD8(+) T cells produced IFNgamma upon PMA/ionomycin stimulation, thus showing innate-like function. Changes in the naïve versus memory-like subset distribution were already evident in single-positive thymocytes, indicating PLZF-induced T cell developmental alterations. In addition, CD1d-restricted natural killer T cells in PLZF transgenic mice showed impaired development and were severely reduced in the periphery. Finally, after anti-CD3/CD28 stimulation, CD4(+) transgenic T cells showed reduced IL-2 and IFNgamma production but increased IL-4 secretion as a result of enhanced IL-4 production of the CD44(hi)CD62L(+) subset. Our data indicate that PLZF is a novel regulator of the development of CD44(hi) MP T cells with a characteristic partial innate-like phenotype.
Project description:Tregs expressing the transcription factor FOXP3 are critical for immune homeostasis. The costimulatory molecule CD28 is required for optimal activation and function of naive T cells; however, its role in Treg function has been difficult to dissect, as CD28 is required for thymic Treg development, and blockade of CD28-ligand interactions has confounding effects in trans on nonregulatory cells. To address this question, we created Treg-specific Cd28 conditional knockout mice. Despite the presence of normal numbers of FOXP3+ cells, these animals accumulated large numbers of activated T cells, developed severe autoimmunity that primarily affected the skin and lungs, and failed to appropriately resolve induced experimental allergic encephalomyelitis. This in vivo functional impairment was accompanied by dampened expression of CTLA-4, PD-1, and CCR6. Disease occurrence was not due to subversion of Cd28-deficient Tregs into pathogenic cells, as complementation with normal Tregs prevented disease occurrence. Interestingly, in these "competitive" environments, Cd28-deficient Tregs exhibited a pronounced proliferative/survival disadvantage. These data demonstrate clear postmaturational roles for CD28 in FOXP3+ Tregs and provide mechanisms which we believe to be novel to explain how interruption of CD28-ligand interactions may enhance immune responses independent of effects on thymic development or on other cell types.
Project description:Regulatory T cells (Tregs) are required to establish immune tolerance to commensal microbes. Tregs accumulate abruptly in the skin during a defined window of postnatal tissue development. However, the mechanisms mediating Treg migration to neonatal skin are unknown. Here we show that hair follicle (HF) development facilitates the accumulation of Tregs in neonatal skin and that upon skin entry these cells localize to HFs, a primary reservoir for skin commensals. Further, germ-free neonates had reduced skin Tregs indicating that commensal microbes augment Treg accumulation. We identified Ccl20 as a HF-derived, microbiota-dependent chemokine and found its receptor, Ccr6, to be preferentially expressed by Tregs in neonatal skin. The Ccl20-Ccr6 pathway mediated Treg migration in vitro and in vivo. Thus, HF morphogenesis, commensal microbe colonization, and local chemokine production work in concert to recruit Tregs into neonatal skin, thereby establishing this tissue Treg niche early in life.
Project description:The rapid recall of influenza virus-specific CD8(+) T cell effector function is protective, although our understanding of T cell memory remains incomplete. Recent debate has focused particularly on the CD62L lymph node homing receptor. The present analysis shows that although functional memory can be established from both CD62L(hi) and CD62L(lo) CD8(+) T cell subsets soon after initial encounter between naïve precursors and antigen, the optimal precursors are CD8(+)CD44(hi)CD25(lo) immune lymphocytes isolated from draining lymph nodes on day 3.5 after influenza virus infection. Analysis of primed T cells at different times after challenge indicates that the capacity to transfer memory is diminished at the peak of the primary cytotoxic T lymphocyte response, challenging speculations that the transition to memory first requires full differentiation to effector status. It seems that location rather than CD62Lhi/lo phenotype may be the more profitable focus for further dissection of the early establishment of T cell memory.