FOXP3-expressing regulatory T （Treg） cells, which suppress aberrant immune response against self-antigens, also suppress anti-tumor immune response. Infiltration of a large number of Treg cells into ...tumor tissues is often associ- ated with poor prognosis. There is accumulating evidence that the removal of Treg cells is able to evoke and enhance anti-tumor immune response. However, systemic depletion of Treg cells may concurrently elicit deleterious autoim- munity. One strategy for evoking effective tumor immunity without antoimmunity is to specifically target terminally differentiated effector Treg cells rather than all FOXP3＋ T cells, because effector Treg cells are the predominant cell type in tumor tissues. Various cell surface molecules, including chemokine receptors such as CCR4, that are specifi- cally expressed by effector Treg cells can be the candidates for depleting effector Treg cells by specific cell-depleting monoclonal antibodies. In addition, other immunological characteristics of effector Treg cells, such as their high ex- pression of CTLA-4, active proliferation, and apoptosis-prone tendency, can be exploited to control specifically their functions. For example, anti-CTLA-4 antibody may kill effector Treg ceils or attenuate their suppressive activity. It is hoped that combination of Treg-cell targeting （e.g., by reducing Treg cells or attenuating their suppressive activity in tumor tissues） with the activation of tumor-specific effector T cells （e.g., by cancer vaccine or immune checkpoint blockade） will make the current cancer immunotherapy more effective.
Foxp3‐expressing regulatory T (Treg) cells, which are indispensable for preventing autoimmunity, also suppress effective tumor immunity. Treg cells abundantly infiltrate into tumor tissues, which is ...often associated with poor prognosis in cancer patients. Removal of Treg cells enhances anti‐tumor immune responses but may also elicit autoimmunity. A key issue in devising Treg‐targeting cancer immunotherapy is, therefore, how to specifically deplete Treg cells infiltrating into tumor tissues without affecting tumor‐reactive effector T cells, while suppressing autoimmunity. This can be achieved by differentially controlling Treg and effector T cells by various ways. In this review, we discuss how tumor‐infiltrating Foxp3+ Treg cells hamper effective anti‐tumor immune responses especially in tumor tissues and how they can be specifically targeted for augmenting tumor immunity but not autoimmunity.
Regulatory T (Treg) cells highly infiltrate into various tumor tissues and hinder immune responses against tumor cells by effector T (Teff) cells. To effectively enhance anti‐tumor immunity, it is essential to selectively remove tumor‐infiltrating Treg cells while preserving tumor‐reactive Teff cells.
Naturally arising regulatory CD4
T (Treg) cells, which specifically express the transcription factor FoxP3 in the nucleus and CD25 and CTLA-4 on the cell surface, are a T-cell subpopulation ...specialized for immune suppression, playing a key role in maintaining immunological self-tolerance and homeostasis. FoxP3 is required for Treg function, especially for its suppressive activity. However, FoxP3 expression per se is not necessary for Treg cell lineage commitment in the thymus and insufficient for full Treg-type gene expression in mature Treg cells. It is Treg-specific epigenetic changes such as CpG demethylation and histone modification that can confer a stable and heritable pattern of Treg type gene expression on developing Treg cells in a FoxP3-independent manner. Anomalies in the formation of Treg-specific epigenome, in particular, Treg-specific super-enhancers, which largely include Treg-specific DNA demethylated regions, are indeed able to cause autoimmune diseases in rodents. Furthermore, in humans, single nucleotide polymorphisms in Treg-specific DNA demethylated regions associated with Treg signature genes, such as IL2RA (CD25) and CTLA4, can affect the development and function of naïve Treg cells rather than effector T cells. Such genetic variations are therefore causative of polygenic common autoimmune diseases including type 1 diabetes and rheumatoid arthritis via affecting endogenous natural Treg cells. These findings on the transcription factor network with FoxP3 at a key position as well as Treg-specific epigenetic landscape facilitate our understanding of Treg cell development and function, and can be exploited to prepare functionally stable FoxP3-expressing Treg cells from antigen-specific conventional T cells to treat autoimmune diseases.
Summary
Naturally occurring regulatory T (nTreg) cells, which specifically express the transcription factor Forkhead box protein P3 (FoxP3), are indispensable for the maintenance of immunological ...self‐tolerance and homeostasis. Recent studies have shown that developing nTreg cells in the thymus acquire a Treg‐specific and stable hypomethylation pattern in a limited number of genes, which encode key molecules including FoxP3, essential for Treg cell function. This epigenetic change is acquired via T‐cell receptor (TCR) stimulation, beginning prior to FoxP3 expression. The Treg‐specific DNA hypomethylated regions generally act as gene enhancers in steady state nTreg cells, contributing to the stable expression of Treg function‐associated key genes including Ctla4, Il2ra, and Ikzf4 in addition to Foxp3. Upon TCR stimulation of mature nTreg cells, FoxP3 strongly represses many genes including Il2, contributing to Treg suppressive activity. Thus, the Treg‐specific epigenome alteration can determine the heritable Treg‐specific gene network including Foxp3 regulation. Considering physiological presence of non‐suppressive FoxP3+ T cells in the immune system and loss of FoxP3 in Treg cells under certain immunological conditions, functional nTreg cells can be more accurately defined as a T‐cell subpopulation possessing the Treg‐type epigenome, rather than FoxP3+ T cells. This epigenome‐based definition of Treg cells would enable better understanding of functional stability, plasticity, and heterogeneity of Treg cells.
Foxp3-expressing CD4
CD25
regulatory T cells (Tregs) constitutively and highly express the immune checkpoint receptor cytotoxic T-lymphocyte-associated antigen-4 (CTLA-4), whose Treg-specific ...deficiency causes severe systemic autoimmunity. As a key mechanism of Treg-mediated suppression, Treg-expressed CTLA-4 down-regulates the expression of CD80/CD86 costimulatory molecules on antigen-presenting cells (APCs). Here, we show that Treg-expressed CTLA-4 facilitated Treg-APC conjugation and immune synapse formation. The immune synapses thus formed provided a stable platform whereby Tregs were able to deplete CD80/CD86 molecules on APCs by extracting them via CTLA-4-dependent trogocytosis. The depletion occurred even with Tregs solely expressing a mutant CTLA-4 form lacking the cytoplasmic portion required for its endocytosis. The CTLA-4-dependent trogocytosis of CD80/CD86 also accelerated in vitro and in vivo passive transfer of other membrane proteins and lipid molecules from APCs to Tregs without their significant reduction on the APC surface. Furthermore, CD80 down-regulation or blockade by Treg-expressed membrane CTLA-4 or soluble CTLA-4-immunoglobulin (CTLA-4-Ig), respectively, disrupted cis-CD80/programmed death ligand-1 (PD-L1) heterodimers and increased free PD-L1 on dendritic cells (DCs), expanding a phenotypically distinct population of CD80
free PD-L1
DCs. Thus, Tregs are able to inhibit the T cell stimulatory activity of APCs by reducing their CD80/CD86 expression via CTLA-4-dependent trogocytosis. This CD80/CD86 reduction on APCs is able to exert dual suppressive effects on T cell immune responses by limiting CD80/CD86 costimulation to naïve T cells and by increasing free PD-L1 available for the inhibition of programmed death-1 (PD-1)-expressing effector T cells. Blockade of CTLA-4 and PD-1/PD-L1 in combination may therefore synergistically hinder Treg-mediated immune suppression, thereby effectively enhancing immune responses, including tumor immunity.
Recent technological advances have enabled massively parallel chromatin profiling with scATAC-seq (single-cell assay for transposase accessible chromatin by sequencing). Here we present ATAC with ...select antigen profiling by sequencing (ASAP-seq), a tool to simultaneously profile accessible chromatin and protein levels. Our approach pairs sparse scATAC-seq data with robust detection of hundreds of cell surface and intracellular protein markers and optional capture of mitochondrial DNA for clonal tracking, capturing three distinct modalities in single cells. ASAP-seq uses a bridging approach that repurposes antibody:oligonucleotide conjugates designed for existing technologies that pair protein measurements with single-cell RNA sequencing. Together with DOGMA-seq, an adaptation of CITE-seq (cellular indexing of transcriptomes and epitopes by sequencing) for measuring gene activity across the central dogma of gene regulation, we demonstrate the utility of systematic multi-omic profiling by revealing coordinated and distinct changes in chromatin, RNA and surface proteins during native hematopoietic differentiation and peripheral blood mononuclear cell stimulation and as a combinatorial decoder and reporter of multiplexed perturbations in primary T cells.
Cytotoxic T lymphocyte antigen-4 (CTLA-4) is essential for immunological (self-) tolerance, but due to the early fatality of CTLA-4 KO mice, its specific function in central and peripheral tolerance ...and in different systemic diseases remains to be determined. Here, we further examined the role of CTLA-4 by abrogating CTLA-4 expression in adult mice and compared the resulting autoimmunity that follows with that produced by congenital CTLA-4 deficiency. We found that conditional deletion of CTLA-4 in adult mice resulted in spontaneous lymphoproliferation, hypergammaglobulinemia, and histologically evident pneumonitis, gastritis, insulitis, and sialadenitis, accompanied by organ-specific autoantibodies. However, in contrast to congenital deficiency, this was not fatal. CTLA-4 deletion induced preferential expansion of CD4⁺Foxp3⁺ Treg cells. However, T cells from CTLA-4–deficient inducible KO mice were able to adoptively transfer the diseases into T cell-deficient mice. Notably, cell transfer of thymocytes de novo produced myocarditis, otherwise not observed in donor mice depleted in adulthood. Moreover, CTLA-4 deletion in adult mice had opposing impacts on induced autoimmune models. Thus, although CTLA-4–deficient mice had more severe collagen-induced arthritis (CIA), they were protected against peptide-induced experimental autoimmune encephalomyelitis (EAE); however, onset of protein-induced EAE was only delayed. Collectively, this indicates that CTLA-4 deficiency affects both central and peripheral tolerance and Treg cell-mediated suppression.
Regulatory T cells (Tregs), either natural or induced, suppress a variety of physiological and pathological immune responses. One of the key issues for understanding Treg function is to determine how ...they suppress other lymphocytes at the molecular level in vivo and in vitro. Here we propose that there may be a key suppressive mechanism that is shared by every forkhead box p3 (Foxp3)+ Treg in vivo and in vitro in mice and humans. When this central mechanism is abrogated, it causes a breach in self-tolerance and immune homeostasis. Other suppressive mechanisms may synergistically operate with this common mechanism depending on the environment and the type of an immune response. Further, Treg-mediated suppression is a multi-step process and impairment or augmentation of each step can alter the ultimate effectiveness of Treg-mediated suppression. These findings will help to design effective ways for controlling immune responses by targeting Treg suppressive functions.
Naturally occurring CD4⁺CD25⁺ regulatory T cells (Treg) suppress in vitro the proliferation of other T cells in a cell-contact-dependent manner. Dendritic cells (DCs) appear to be a target of ...Treg-mediated immune suppression. We show here that, in coculture of dye-labeled Treg cells and CD4⁺CD25⁻ naïve T cells in the presence of T cell receptor stimulation, Treg cells, which are more mobile than naïve T cells in vitro, out-compete the latter in aggregating around DCs. Deficiency or blockade of leukocyte function-associated antigen-1 (LFA-1) (CD11a/CD18) abrogates Treg aggregation, whereas that of cytotoxic T lymphocyte-associated antigen 4 (CTLA-4) (CD152) does not. After forming aggregates, Treg cells specifically down-regulate the expression of CD80/86, but not CD40 or class II MHC, on DCs in both a CTLA-4- and LFA-1-dependent manner. Notably, Treg exerts this CD80/86-down-modulating effect even in the presence of strong DC-maturating stimuli, such as GM-CSF, TNF-α, IFN-γ, type I IFN, and lipopolysaccharide. Taken together, as a possible mechanism of in vitro Treg-mediated cell contact-dependent suppression, we propose that antigen-activated Treg cells exert suppression by two distinct steps: initial LFA-1-dependent formation of Treg aggregates on immature DCs and subsequent LFA-1- and CTLA-4-dependent active down-modulation of CD80/86 expression on DCs. Both steps prevent antigen-reactive naïve T cells from being activated by antigen-presenting DCs, resulting in specific immune suppression and tolerance.
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