CD28-CD80 interactions control regulatory T cell motility and immunological synapse formation

Role of Regulatory T Cells in Intracerebral Hemorrhage

Intracerebral hemorrhage (ICH) is a common cerebrovascular disease that can lead to severe neurological dysfunction in surviving patients, resulting in a heavy burden on patients and their families. When ICH occurs, the blood‒brain barrier is disrupted, thereby promoting immune cell migration into damaged brain tissue. As important immunosuppressive T cells, regulatory T (Treg) cells are involved in the maintenance of immune homeostasis and the suppression of immune responses after ICH. Treg cells mitigate brain tissue damage after ICH in a variety of ways, such as inhibiting the neuroinflammatory response, protecting against blood‒brain barrier damage, reducing oxidative stress damage and promoting nerve repair. In this review, we discuss the changes in Treg cells in ICH clinical patients and experimental animals, the mechanisms by which Treg cells regulate ICH and treatments targeting Treg cells in ICH, aiming to support new therapeutic strategies for clinical treatment.

Immunological synapse formation between T regulatory cells and cancer-associated fibroblasts promotes tumour development

Cancer-associated fibroblasts (CAFs) have emerged as a dominant non-hematopoietic cell population in the tumour microenvironment, serving diverse functions in tumour progression. However, the mechanisms via which CAFs influence the anti-tumour immunity remain poorly understood. Here, using multiple tumour models and biopsies from cancer patients, we report that α-SMA+ CAFs can form immunological synapses with Foxp3+ regulatory T cells (Tregs) in tumours. Notably, α-SMA+ CAFs can phagocytose and process tumour antigens and exhibit a tolerogenic phenotype which instructs movement arrest, activation and proliferation in Tregs in an antigen-specific manner. Moreover, α-SMA+ CAFs display double-membrane structures resembling autophagosomes in their cytoplasm. Single-cell transcriptomic data showed an enrichment in autophagy and antigen processing/presentation pathways in α-SMA-expressing CAF clusters. Conditional knockout of Atg5 in α-SMA+ CAFs promoted inflammatory re-programming in CAFs, reduced Treg cell infiltration and attenuated tumour development. Overall, our findings reveal an immunosuppressive mechanism entailing the formation of synapses between α-SMA+ CAFs and Tregs in an autophagy-dependent manner.

Regulatory T cells suppress the motility of cytotoxic T cells in Friend retrovirus-infected mice

Antiviral immunity often requires CD8+ cytotoxic T lymphocytes (CTLs) that actively migrate and search for virus-infected targets. Regulatory T cells (Tregs) have been shown to suppress CTL responses, but it is not known whether this is also mediated by effects on CTL motility. Here, we used intravital 2-photon microscopy in the Friend retrovirus (FV) mouse model to define the impact of Tregs on CTL motility throughout the course of acute infection. Virus-specific CTLs were very motile and had frequent short contacts with target cells at their peak cytotoxic activity. However, when Tregs were activated and expanded in late-acute FV infection, CTLs became significantly less motile and contacts with target cells were prolonged. This phenotype was associated with development of functional CTL exhaustion. Tregs had direct contacts with CTLs in vivo and, importantly, their experimental depletion restored CTL motility. Our findings identify an effect of Tregs on CTL motility as part of their mechanism of functional impairment in chronic viral infections. Future studies must address the underlying molecular mechanisms.

In silico engineering a CD80 variant with increased affinity to CTLA-4 and decreased affinity to CD28 for optimized cancer immunotherapy

CD80 or cluster of differentiation 80, also known as B7-1, is a member of the immunoglobulin super family, which binds to CTLA-4 and CD28 T cell receptors and induces inhibitory and inductive signals respectively. Although CTLA-4 and CD28 receptors belong to the same protein family, slight differences in their structures leads to CD80 having a higher binding affinity to CTLA-4 (-14.55 kcal/mol) compared with CD28(-12.51 kcal/mol). In this study, we constructed a variant of CD80 protein with increased binding affinity to CTLA-4 and decreased binding affinity to CD28. This variant has no signaling capability, and can act as a cap for these receptors to protect them from natural CD80 proteins existing in the body. The first step was the evolutionary and alanine scanning analysis of CD80 protein to determine conserved regions in this protein. Next, complex alanine scanning technique was employed to determine CD80 protein hotspots in CD80-CTLA-4 and CD80-CD28 protein complexes. This information was fed into a computational model developed in R for in silico mutagenesis and CD80 variant library construction. The 3D structures of variants were modeled using the Swiss model webserver. After modeling the 3D structures, HADDOCK server was employed to build all protein-protein complexes, which contain CTLA-4-CD80 variant complexes, Wild type CD80-CD28 complexes and CD28-CD80 variant complexes. Protein-protein binding free energy was determined using FoldX and the variant number 316 with mutations at 29, 31, 33 positions showed increased binding affinity to CTLA-4 (-21.43 kcal/mol) and decreased binding affinity to CD28 (- 9.54 kcal/mol). Finally, molecular dynamics (MD) simulations confirmed the stability of variant 316. In conclusion, we designed a new CD80 protein variant with potential immunotherapeutic applications.

Intelligent photothermal dendritic cells restart the cancer immunity cycle through enhanced immunogenic cell death

Dendritic cells (DCs) play a pivotal role in initiating antigen-specific tumor immunity. However, the abnormal function of DCs owing to the immunosuppressive tumor microenvironment (TME) and the insufficient number of tumor infiltrating DCs could promote immune tolerance and tumor immune escape. Thus, there is great potential to employ DCs to induce efficient antitumor immunity. In this paper, we developed intelligent DCs (iDCs), which consist of nanoparticles loaded with photothermal agents (IR-797) and coated with a mature DC membrane. The DC cell membrane on the surface of iDCs preserves the ability to present antigens and prime T cells. The iDCs can also enter the lymph node and stimulate T cells. The activated T cells reduced the expression of heat shock proteins (HSPs) in tumor cells, rendering them more sensitive to heat stress. Subsequently, we used mild photothermal therapy (42-45 °C) to induce immunogenic cell death and contribute to a synergistic antitumor effect. iDCs as a refined and precise system in combination with DC-based immunotherapy and thermal therapy can be stored long-term and on a large scale, so they can be applied in many patients.

Expansion of tumor-associated Treg cells upon disruption of a CTLA-4-dependent feedback loop

Foxp3+ T regulatory (Treg) cells promote immunological tumor tolerance, but how their immune-suppressive function is regulated in the tumor microenvironment (TME) remains unknown. Here, we used intravital microscopy to characterize the cellular interactions that provide tumor-infiltrating Treg cells with critical activation signals. We found that the polyclonal Treg cell repertoire is pre-enriched to recognize antigens presented by tumor-associated conventional dendritic cells (cDCs). Unstable cDC contacts sufficed to sustain Treg cell function, whereas T helper cells were activated during stable interactions. Contact instability resulted from CTLA-4-dependent downregulation of co-stimulatory B7-family proteins on cDCs, mediated by Treg cells themselves. CTLA-4-blockade triggered CD28-dependent Treg cell hyper-proliferation in the TME, and concomitant Treg cell inactivation was required to achieve tumor rejection. Therefore, Treg cells self-regulate through a CTLA-4- and CD28-dependent feedback loop that adjusts their population size to the amount of local co-stimulation. Its disruption through CTLA-4-blockade may off-set therapeutic benefits in cancer patients.

A local regulatory T cell feedback circuit maintains immune homeostasis by pruning self-activated T cells

A fraction of mature T cells can be activated by peripheral self-antigens, potentially eliciting host autoimmunity. We investigated homeostatic control of self-activated T cells within unperturbed tissue environments by combining high-resolution multiplexed and volumetric imaging with computational modeling. In lymph nodes, self-activated T cells produced interleukin (IL)-2, which enhanced local regulatory T cell (Treg) proliferation and inhibitory functionality. The resulting micro-domains reciprocally constrained inputs required for damaging effector responses, including CD28 co-stimulation and IL-2 signaling, constituting a negative feedback circuit. Due to these local constraints, self-activated T cells underwent transient clonal expansion, followed by rapid death ("pruning"). Computational simulations and experimental manipulations revealed the feedback machinery's quantitative limits: modest reductions in Treg micro-domain density or functionality produced non-linear breakdowns in control, enabling self-activated T cells to subvert pruning. This fine-tuned, paracrine feedback process not only enforces immune homeostasis but also establishes a sharp boundary between autoimmune and host-protective T cell responses.

B7-1 and GM-CSF enhance the anti-tumor immune effect of DC-tumor fusion vaccine in the treatment of prostate cancer

The treatment of castration-resistant prostate cancer (CRPC) is always a difficulty in the clinic. Most patients with localized tumor eventually develop CRPC, even if hormone therapy is initially effective. Increasing evidence shows immunotherapy has special advantages compared with traditional therapy in cancer treatment. In this study, we constructed the DC-PC-3 fusion vaccine with B7-1- and GM-CSF-specific modification, and studied its ability to stimulate specific immune response and anti-tumor effect in vitro. The results showed that fusion of DC and tumor cells can improve the expression of associated antigens of DCs. DC-tumor fusion vaccine can strongly promote T cell proliferation and IFN-γ secretion and induce a significant tumor-specific cytotoxic T lymphocyte response. In addition, the B7-1/GM-CSF-modified fusion vaccine showed a more significant anti-tumor effect and greater ability to stimulate the immune response than that without specific modification in vitro. Thus, GM-CSF/B7-1-modified fusion vaccine might be used as a potential therapy strategy for prostate cancer.

Treg expansion with trichostatin A ameliorates kidney ischemia/reperfusion injury in mice by suppressing the expression of costimulatory molecules

Innate immune reactions are believed to be associated with ischemia/reperfusion injury (IRI), and IRI might be treatable by expanding regulatory T cells (Tregs), which can suppress the excessive responses of the immune system. Organ IRI is known to be closely involved in the expression of costimulatory molecules. The present study aimed to assess whether Tregs endogenously expanded by the administration of trichostatin A (TsA), a histone deacetylase inhibitor, could reduce renal IRI and to clarify their association with the expression of costimulatory molecules in a murine model. In this study, the wild-type mice used for an IRI model were randomly divided into the following four treatment groups: TsA group, DMSO group (control), DMSO+PC61 group, and TsA + PC61 group. Renal injury in the early phase after IRI was ameliorated in the TsA group (increased Tregs) when compared with the other groups. After renal IRI, both the mRNA and the protein levels of anti-inflammatory cytokines, IL-10 and TGF-β in the kidney and spleen were significantly higher in the TsA group than in the other groups, whereas the IL-6 levels were significantly lower in the TsA group than in the other groups. These results were offset by the administration of PC61, supporting that the renoprotective effect of TsA in this study is Treg dependent. mRNA expression levels of CD80, CD86, and ICAM-1 were lower in the TsA group, consistent with Treg control of injury through costimulatory molecules. Our findings suggest that endogenously expanded Tregs coordinate postischemic immune responses and decrease the expression of costimulatory molecules after renal IRI, and thus, they might ameliorate renal IRI. TsA administration for expanding Tregs is a promising therapeutic strategy for renal IRI.

HTLV infected individuals have increased B-cell activation and proinflammatory regulatory T-cells

Human T-lymphotropic virus (HTLV) affects the human immune system in many ways, most notably by inducing proliferation of infected CD4 + T cells, but several other cell types are also affected. To characterize the effects of HTLV infection, we analysed blood samples from HTLV-infected individuals by flow cytometry. Samples were collected from visitors at the HIV clinic in Bissau, Guinea-Bissau. These samples were tested for HTLV and HIV, and 199 were analysed by flow cytometry using panels for B cells, T-cell maturation and activation, regulatory T cells (Tregs) and monocytes. CD80+ cell proportions were significantly higher in HTLV infected than in HTLV uninfected in all B cell subsets. Among T cells, there was no change in cell distribution between maturation stages, but a higher CD25+ proportion among Tregs (61.1 % vs 36.3 %, p < 0.001) in HTLV infected than in HTLV uninfected. The level of CD49d on individual cells was also higher (MFI 2734.5 vs 1,041, p < 0.001). In HTLV infected individuals, CD8 + T cells had a lower proportion of CTLA-4+ (2.5 % vs 3.5 %, 0.048) and higher PD1+ proportion on the CD45RO + subset (81.6 % vs 77.1 %, p < 0.001). Together, these findings point toward reduced regulation in HTLV + patients, which leads to immune activation. This study corroborates previous findings and offers new insight into the effects of HTLV by providing a broad flowcytometric analysis of immune cells in HTLV + individuals.

CD28 between tolerance and autoimmunity: the side effects of animal models

Regulation of immune responses is critical for ensuring pathogen clearance and for preventing reaction against self-antigens. Failure or breakdown of immunological tolerance results in autoimmunity. CD28 is an important co-stimulatory receptor expressed on T cells that, upon specific ligand binding, delivers signals essential for full T-cell activation and for the development and homeostasis of suppressive regulatory T cells. Many in vivo mouse models have been used for understanding the role of CD28 in the maintenance of immune homeostasis, thus leading to the development of CD28 signaling modulators that have been approved for the treatment of some autoimmune diseases. Despite all of this progress, a deeper understanding of the differences between the mouse and human receptor is required to allow a safe translation of pre-clinical studies in efficient therapies. In this review, we discuss the role of CD28 in tolerance and autoimmunity and the clinical efficacy of drugs that block or enhance CD28 signaling, by highlighting the success and failure of pre-clinical studies, when translated to humans.

DOCK8 enforces immunological tolerance by promoting IL-2 signaling and immune synapse formation in Tregs

Patients deficient in the guanine nucleotide exchange factor DOCK8 have decreased numbers and impaired in vitro function of Tregs and make autoantibodies, but they seldom develop autoimmunity. We show that, similarly, Dock8-/- mice have decreased numbers and impaired in vitro function of Tregs but do not develop autoimmunity. In contrast, mice with selective DOCK8 deficiency in Tregs develop lymphoproliferation, autoantibodies, and gastrointestinal inflammation, despite a normal percentage and in vitro function of Tregs, suggesting that deficient T effector cell function might protect DOCK8-deficient patients from autoimmunity. We demonstrate that DOCK8 associates with STAT5 and is important for IL-2-driven STAT5 phosphorylation in Tregs. DOCK8 localizes within the lamellar actin ring of the Treg immune synapse (IS). Dock8-/- Tregs have abnormal TCR-driven actin dynamics, decreased adhesiveness, an altered gene expression profile, an unstable IS with decreased recruitment of signaling molecules, and impaired transendocytosis of the costimulatory molecule CD86. These data suggest that DOCK8 enforces immunological tolerance by promoting IL-2 signaling, TCR-driven actin dynamics, and the IS in Tregs.

A Yin and Yang in Epithelial Immunology: The Roles of the αE(CD103)β7 Integrin in T Cells

The proper function(s) of cell-surface receptors is crucial for the regulation of adaptive immune responses. One such receptor is the α_E(CD103)β₇ integrin, whose history in science is closely linked with the evolution of our knowledge of immune regulation. Initially described as a marker of intraepithelial T-lymphocytes, this leukocyte integrin is now seen as a dynamically regulated receptor involved in the functional differentiation of some cytotoxic T cells as well as regulatory T cells, thus presumably contributing to the fine-tuning of immune reactions in epithelial compartments. In this brief overview, we delineate our current view on α_E(CD103)β₇ in T-cell-mediated immune responses.

C-C Chemokine Receptor Type 5 (CCR5)-Mediated Docking of Transferred Tregs Protects Against Early Blood-Brain Barrier Disruption After Stroke

BACKGROUND

Despite recent evidence demonstrating a potent protective effect of adoptively transferred regulatory T cells (Tregs) in ischemic stroke, the mechanism for Treg mobilization and activation in the ischemic brain is, remarkably, unknown. This study determines the role of C-C chemokine receptor type 5 (CCR5) in mediating the docking and activation of transferred Tregs in their protection of early blood-brain barrier disruption after stroke.

METHODS AND RESULTS

Adoptive transfer of CCR5-/- Tregs failed to reduce brain infarct or neurological deficits, indicating an indispensable role of CCR5 in Treg-afforded protection against cerebral ischemia. Two-photon live imaging demonstrated that CCR5 was critical for Treg docking at the injured vessel wall, where they interact with blood-borne neutrophils/macrophages after cerebral ischemic injury. CCR5 deficiency on donor Tregs deprived of their early protection against blood-brain barrier damage. Using flow cytometry, real-time polymerase chain reaction, and immunostaining, we confirmed that the expression of CCL5, a CCR5 ligand, was significantly elevated on the injured endothelium after cerebral ischemia, accompanied by CCR5 upregulation on circulating Tregs. In a Treg-endothelial cell coculture, CCR5 expression was induced on Tregs on their exposure to ischemia-injured endothelial cells. Furthermore, CCR5 induction on Tregs enhanced expression of the inhibitory molecule programmed death ligand 1, which in turn inhibited neutrophil-derived matrix metallopeptidase 9.

CONCLUSIONS

These results suggest that CCR5 is a critical molecule for Treg-mediated blood-brain barrier protection and a potential target to optimize Treg therapy for stroke.

FDA-approved immunosuppressants targeting staphylococcal superantigens: mechanisms and insights

Immunostimulating staphylococcal enterotoxin B (SEB) and related superantigenic toxins cause diseases in human beings and laboratory animals by hyperactivating cells of the immune system. These protein toxins bind to the major histocompatibility complex class II (MHC II) molecules and specific Vβ regions of T-cell receptors (TCRs), resulting in the stimulation of both monocytes/macrophages and T lymphocytes. The bridging of TCR with MHC II molecules by superantigens triggers intracellular signaling cascades, resulting in excessive release of proinflammatory mediators and massive polyclonal T-cell proliferation. The early induction of tumor necrosis factor α, interleukin 1 (IL-1), interleukin 2 (IL-2), interferon gamma (IFNγ), and macrophage chemoattractant protein 1 promotes fever, inflammation, and multiple organ injury. The signal transduction pathways for staphylococcal superantigen-induced toxicity downstream from TCR/major histocompatibility complex (MHC) ligation and interaction of cell surface co-stimulatory molecules include the mitogen-activated protein kinase cascades and cytokine receptor signaling, activating nuclear factor κB (NFκB) and the phosphoinositide 3-kinase/mammalian target of rapamycin pathways. Knowledge of host regulation within these activated pathways and molecules initiated by SEB and other superantigens enables the selection of US Food and Drug Administration (FDA)-approved drugs to interrupt and prevent superantigen-induced shock in animal models. This review focuses on the use of FDA-approved immunosuppressants in targeting the signaling pathways induced by staphylococcal superantigens.

Functional Impairment of Murine Dendritic Cell Subsets following Infection with Infective Larval Stage 3 of Brugia malayi

Filarial parasites cause functional impairment of host dendritic cells (DCs). However, the effects of early infection on individual DC subsets are not known. In this study, we infected BALB/c mice with infective stage 3 larvae of the lymphatic filarial parasite Brugia malayi (Bm-L3) and studied the effect on fluorescence-activated cell sorter (FACS)-sorted DC subsets. While myeloid DCs (mDCs) accumulated by day 3 postinfection (p.i.), lymphoid DCs (LDCs) and CD8⁺ plasmacytoid DCs (pDCs) peaked at day 7 p.i. in the spleens and mesenteric lymph nodes (mLNs) of infected mice. Increased tumor necrosis factor alpha (TNF-α) but reduced interleukin 12 (IL-12) and Toll-like receptor 4 (TLR4), -6, and -9 and reciprocal secretion of IL-4 and IL-10 were also observed across all DC subsets. Interestingly, Bm-L3 increased the expression of CD80 and CD86 across all DC subsets but decreased that of major histocompatibility complex class II (MHC-II) on mDCs and pDCs, resulting in their impaired antigen uptake and presentation capacities, but maximally attenuated the T-cell proliferation capacity of only mDCs. Furthermore, Bm-L3 increased phosphorylated p38 (p-p38), but not p-ERK, in mDCs and LDCs but downregulated them in pDCs, along with differential modulation of protein tyrosine phosphatases SHP-1, TCPTP, PTEN, and PTP1B across all DC subsets. Taken together, we report hitherto undocumented effects of early Bm-L3 infection on purified host DC subsets that lead to their functional impairment and attenuated host T-cell response.

CD28 Costimulation: From Mechanism to Therapy

Ligation of the CD28 receptor on T cells provides a critical second signal alongside T cell receptor (TCR) ligation for naive T cell activation. Here, we discuss the expression, structure, and biochemistry of CD28 and its ligands. CD28 signals play a key role in many T cell processes, including cytoskeletal remodeling, production of cytokines, survival, and differentiation. CD28 ligation leads to unique epigenetic, transcriptional, and post-translational changes in T cells that cannot be recapitulated by TCR ligation alone. We discuss the function of CD28 and its ligands in both effector and regulatory T cells. CD28 is critical for regulatory T cell survival and the maintenance of immune homeostasis. We outline the roles that CD28 and its family members play in human disease and we review the clinical efficacy of drugs that block CD28 ligands. Despite the centrality of CD28 and its family members and ligands to immune function, many aspects of CD28 biology remain unclear. Translation of a basic understanding of CD28 function into immunomodulatory therapeutics has been uneven, with both successes and failures. Such real-world results might stem from multiple factors, including complex receptor-ligand interactions among CD28 family members, differences between the mouse and human CD28 families, and cell-type specific roles of CD28 family members.

Signaling in T cells - is anything the m(a)TOR with the picture(s)?

The excitement surrounding checkpoint inhibitors in the treatment of patients with cancer exemplifies a triumph of the long-term value of investing in basic science and fundamental questions of T-cell signaling. The pharmaceutical future actively embraces ways of making more patients’ cancers responsive to these inhibitors. Such a process will be aided by elucidation of signaling and regulation. With thousands of articles spread across almost 30 years, this commentary can touch only on portions of the canonical picture of T-cell signaling and provide a few parables from work on mammalian (or mechanistic) target of rapamycin (mTOR) pathways as they link to early and later phases of lymphocyte activation. The piece will turn a critical eye to some issues with models about these pathways in T cells. Many of the best insights lie in the future despite all that is uncovered already, but a contention is that further therapeutic successes will be fostered by dealing with disparities among findings and attention to the temporal, spatial, and stochastic aspects of T-cell responses. Finally, thoughts on some (though not all) items urgently needed for future progress will be mooted.

T regulatory cell chemokine production mediates pathogenic T cell attraction and suppression

T regulatory cells (Tregs) control immune homeostasis by preventing inappropriate responses to self and nonharmful foreign antigens. Tregs use multiple mechanisms to control immune responses, all of which require these cells to be near their targets of suppression; however, it is not known how Treg-to-target proximity is controlled. Here, we found that Tregs attract CD4+ and CD8+ T cells by producing chemokines. Specifically, Tregs produced both CCL3 and CCL4 in response to stimulation, and production of these chemokines was critical for migration of target T cells, as Tregs from Ccl3-/- mice, which are also deficient for CCL4 production, did not promote migration. Moreover, CCR5 expression by target T cells was required for migration of these cells to supernatants conditioned by Tregs. Tregs deficient for expression of CCL3 and CCL4 were impaired in their ability to suppress experimental autoimmune encephalomyelitis or islet allograft rejection in murine models. Moreover, Tregs from subjects with established type 1 diabetes were impaired in their ability to produce CCL3 and CCL4. Together, these results demonstrate a previously unappreciated facet of Treg function and suggest that chemokine secretion by Tregs is a fundamental aspect of their therapeutic effect in autoimmunity and transplantation.

Cell Type-Specific Regulation of Immunological Synapse Dynamics by B7 Ligand Recognition

B7 proteins CD80 (B7-1) and CD86 (B7-2) are expressed on most antigen-presenting cells and provide critical co-stimulatory or inhibitory input to T cells via their T-cell-expressed receptors: CD28 and CTLA-4. CD28 is expressed on effector T cells and regulatory T cells (Tregs), and CD28-dependent signals are required for optimum activation of effector T cell functions. CD28 ligation on effector T cells leads to formation of distinct molecular patterns and induction of cytoskeletal rearrangements at the immunological synapse (IS). CD28 plays a critical role in recruitment of protein kinase C (PKC)-θ to the effector T cell IS. CTLA-4 is constitutively expressed on the surface of Tregs, but it is expressed on effector T cells only after activation. As CTLA-4 binds to B7 proteins with significantly higher affinity than CD28, B7 ligand recognition by cells expressing both receptors leads to displacement of CD28 and PKC-θ from the IS. In Tregs, B7 ligand recognition leads to recruitment of CTLA-4 and PKC-η to the IS. CTLA-4 plays a role in regulation of T effector and Treg IS stability and cell motility. Due to their important roles in regulating T-cell-mediated responses, B7 receptors are emerging as important drug targets in oncology. In this review, we present an integrated summary of current knowledge about the role of B7 family receptor–ligand interactions in the regulation of spatial and temporal IS dynamics in effector and Tregs.

Regulatory T Cells in Autoimmune Diabetes: Mechanisms of Action and Translational Potential

Since the discovery of specialized T cells with regulatory function, harnessing the power of these cells to ameliorate autoimmunity has been a major goal. Here we collate the evidence that regulatory T cells (Treg) can inhibit Type 1 diabetes in animal models and humans. We discuss the anatomical sites and molecular mechanisms of Treg suppressive function in the Type 1 diabetes setting, citing evidence that Treg can function in both the pancreatic lymph nodes and within the pancreatic lesion. Involvement of the CTLA-4 pathway, as well as TGF-β and IL-2 deprivation will be considered. Finally, we summarize current efforts to manipulate Treg therapeutically in individuals with Type 1 diabetes. The translation of this research area from bench to bedside is still in its infancy, but the remarkable therapeutic potential of successfully manipulating Treg populations is clear to see.

Imaging regulatory T cell dynamics and CTLA4-mediated suppression of T cell priming

Foxp3(+) regulatory T cells (Tregs) maintain immune homoeostasis through mechanisms that remain incompletely defined. Here by two-photon (2P) imaging, we examine the cellular dynamics of endogenous Tregs. Tregs are identified as two non-overlapping populations in the T-zone and follicular regions of the lymph node (LN). In the T-zone, Tregs migrate more rapidly than conventional T cells (Tconv), extend longer processes and interact with resident dendritic cells (DC) and Tconv. Tregs intercept immigrant DCs and interact with antigen-induced DC:Tconv clusters, while continuing to form contacts with activated Tconv. During antigen-specific responses, blocking CTLA4-B7 interactions reduces Treg-Tconv interaction times, increases the volume of DC:Tconv clusters and enhances subsequent Tconv proliferation in vivo. Our results demonstrate a role for altered cellular choreography of Tregs through CTLA4-based interactions to limit T-cell priming.