RORγt-driven TH17 Cell Differentiation Requires Epigenetic Control by the Swi/Snf Chromatin Remodeling Complex

Chromatin remodeling in lymphocytic function and fate: the multifaceted roles of SWI/SNF complex

The Switch/Sucrose Non-Fermentable (SWI/SNF) chromatin remodeling complex comprises 10-15 subunits, which modulate the arrangement, location, or conformation of nucleosomes to upregulate chromatin accessibility. During lymphocytic differentiation and functional development, the SWI/SNF complex exerts its effects by binding to specific transcription factors (TFs) or DNA sequences via its subunits, which are thereafter recruited to the promoter or enhancer regions of target genes, rendering each subunit crucial wherein. The loss of individual subunits during lymphocytic differentiation not only disrupts the targeting of the SWI/SNF complex but also impairs its chromatin remodeling function, ultimately resulting in altered differentiation of immature lymphocytes, dysfunction of mature lymphocytes, and injured immune responses. Therefore, in this paper, we focus on TFs interacting with SWI/SNF complex subunits in lymphocytes, and summarize the effects of the loss of specific subunits of the SWI/SNF complex on lymphocytic differentiation and function, as well as the modification in the expression of key genes. We also summarize the potential clinical treatments and applications targeting the loss of SWI/SNF complex subunits, and focus on the application in Chimeric Antigen Receptor (CAR) technology. In conclusion, the SWI/SNF complex is a key regulatory factor in lymphocytic biology, involved in fundamental cellular processes and closely associated with hematological diseases and immune dysfunction. However, the specific roles of SWI/SNF complex subunits in different lymphocytic subpopulations remain unclear. Future clarification of the specific functions of these subunits in different lymphocytic subsets is expected to promote the development of immunotherapy and personalized therapy.

Epigenetic Regulation of Innate and Adaptive Immune Cells in Salt-Sensitive Hypertension

Access to excess dietary sodium has heightened the risk of cardiovascular diseases, particularly affecting individuals with salt sensitivity of blood pressure. Our research indicates that innate antigen-presenting immune cells contribute to rapid blood pressure increases in response to excess sodium intake. Emerging evidence suggests that epigenetic reprogramming, with subsequent transcriptional and metabolic changes, of innate immune cells allows these cells to have a sustained response to repetitive stimuli. Epigenetic mechanisms also steer T-cell differentiation in response to innate immune signaling. Immune cells respond to environmental and nutritional cues, such as salt, promoting epigenetic regulation changes. This article aims to identify and discuss the role of epigenetic mechanisms in the immune system contributing to salt-sensitive hypertension.

Regulatory Roles of SWI/SNF Chromatin Remodeling Complexes in Immune Response and Inflammatory Diseases

The switch/sucrose non-fermentable (SWI/SNF) chromatin remodeling complexes (also referred to as BAF complexes) are composed of multiple subunits, which regulate the nucleosome translocation and chromatin accessibility. In recent years, significant advancements have been made in understanding mutated genes encoding subunits of the SWI/SNF complexes in cancer biology. Nevertheless, the role of SWI/SNF complexes in immune response and inflammatory diseases continues to attract significant attention. This review presents a summary of the significant functions of SWI/SNF complexes during the overall process from the development to the activation of innate and adaptive immune cells. In addition, the correlation between various SWI/SNF subunits and diverse inflammatory diseases is explored. Further investigations are warranted in terms of the mechanism of SWI/SNF complexes' preference for binding sites and opposite pro-/anti-inflammatory effects. In conclusion, further efforts are needed to evaluate the druggability of targeting SWI/SNF complexes in inflammatory diseases, and we hope this review will inspire the development of novel immune modulators in clinical practice.

Autoimmune disease: a view of epigenetics and therapeutic targeting

Autoimmune diseases comprise a large group of conditions characterized by a complex pathogenesis and significant heterogeneity in their clinical manifestations. Advances in sequencing technology have revealed that in addition to genetic susceptibility, various epigenetic mechanisms including DNA methylation and histone modification play critical roles in disease development. The emerging field of epigenetics has provided new perspectives on the pathogenesis and development of autoimmune diseases. Aberrant epigenetic modifications can be used as biomarkers for disease diagnosis and prognosis. Exploration of human epigenetic profiles revealed that patients with autoimmune diseases exhibit markedly altered DNA methylation profiles compared with healthy individuals. Targeted cutting-edge epigenetic therapies are emerging. For example, DNA methylation inhibitors can rectify methylation dysregulation and relieve patients. Histone deacetylase inhibitors such as vorinostat can affect chromatin accessibility and further regulate gene expression, and have been used in treating hematological malignancies. Epigenetic therapies have opened new avenues for the precise treatment of autoimmune diseases and offer new opportunities for improved therapeutic outcomes. Our review can aid in comprehensively elucidation of the mechanisms of autoimmune diseases and development of new targeted therapies that ultimately benefit patients with these conditions.

Overexpression of Chromatin Remodeling Factor SRG3 Down-Regulates IL1β-Expressing M1 Macrophages and IL17-Producing T Cells in Adipose Tissues

The SWItch3-related gene (SRG3) is a core component of ATP-dependent SWI/SNF complexes, which are crucial for regulating immune cell development and function (e.g., macrophages and CD4+ T cells), embryonic development, and non-immune cell differentiation. Notably, SRG3 overexpression has been shown to polarize macrophages in the central nervous system toward an anti-inflammatory M2 phenotype, thereby protecting against the development of experimental autoimmune encephalomyelitis in mice. However, the effect of SRG3 on immune responses in adipose tissues remains unclear. To address this issue, we examined the cellularity and inflammatory status of adipose tissue in B10.PL mice overexpressing the SRG3 gene under the ubiquitous β-actin promoter (SRG3β-actin). Interestingly, SRG3 overexpression significantly reduced adipocyte size in both white and brown adipose tissues, without affecting the overall adipose tissue weight. Such phenotypic effects might be associated with the improved glucose tolerance observed in SRG3β-actin B10.PL mice. Moreover, we found that SRG3 overexpression down-regulates IL1β-expressing M1 macrophages, leading to a significant decrease in the M1/M2 macrophage ratio. Additionally, SRG3β-actin B10.PL mice showed a dramatic reduction in neutrophils as well as IL1β- and IL17-producing T cells in adipose tissues. Taken together, our results indicate that SRG3 plays a vital role in maintaining immune homeostasis within adipose tissues.

SWI/SNF chromatin remodeling factor BAF60b restrains inflammatory diseases by affecting regulatory T cell migration

Regulatory T (Treg) cells play a critical regulatory role in the immune system by suppressing excessive immune responses and maintaining immune balance. The effective migration of Treg cells is crucial for controlling the development and progression of inflammatory diseases. However, the mechanisms responsible for directing Treg cells into the inflammatory tissue remain incompletely elucidated. In this study, we identified BAF60b, a subunit of switch/sucrose nonfermentable (SWI/SNF) chromatin remodeling complexes, as a positive regulator of Treg cell migration that inhibits the progression of inflammation in experimental autoimmune encephalomyelitis (EAE) and colitis animal models. Mechanistically, transcriptome and genome-wide chromatin-landscaped analyses demonstrated that BAF60b interacts with the transcription factor RUNX1 to promote the expression of CCR9 on Treg cells, which in turn affects their ability to migrate to inflammatory tissues. Our work provides insights into the essential role of BAF60b in regulating Treg cell migration and its impact on inflammatory diseases.

Epigenetic reprogramming of T cells: unlocking new avenues for cancer immunotherapy

T cells, a key component of cancer immunotherapy, undergo a variety of histone modifications and DNA methylation changes since their bone marrow progenitor stages before developing into CD8+ and CD4+ T cells. These T cell types can be categorized into distinct subtypes based on their functionality and properties, such as cytotoxic T cells (Tc), helper T cells (Th), and regulatory T cells (Treg) as subtypes for CD8+ and CD4+ T cells. Among these, the CD4+ CD25+ Tregs potentially contribute to cancer development and progression by lowering T effector (Teff) cell activity under the influence of the tumor microenvironment (TME). This contributes to the development of therapeutic resistance in patients with cancer. Subsequently, these individuals become resistant to monoclonal antibody therapy as well as clinically established immunotherapies. In this review, we delineate the different epigenetic mechanisms in cancer immune response and its involvement in therapeutic resistance. Furthermore, the possibility of epi-immunotherapeutic methods based on histone deacetylase inhibitors and histone methyltransferase inhibitors are under investigation. In this review we highlight EZH2 as the principal driver of cancer cell immunoediting and an immune escape regulator. We have addressed in detail how understanding T cell epigenetic regulation might bring unique inventive strategies to overcome drug resistance and increase the efficacy of cancer immunotherapy.

Interplay between epigenetic and genetic alterations in inborn errors of immunity

Inborn errors of immunity (IEIs) comprise a variety of immune conditions leading to infections, autoimmunity, allergy, and cancer. Some IEIs have no identified mutation(s), while others with identical mutations can display heterogeneous presentations. These observations suggest the involvement of epigenetic mechanisms. Epigenetic alterations can arise from downstream activation of cellular pathways through both extracellular stimulation and genetic-associated changes, impacting epigenetic enzymes or their interactors. Therefore, we posit that epigenetic alterations and genetic defects do not exclude each other as a disease-causing etiology. In this opinion, encompassing both basic and clinical viewpoints, we focus on selected IEIs with mutations in transcription factors that interact with epigenetic enzymes. The intricate interplay between these factors offers insights into genetic and epigenetic mechanisms in IEIs.

Lentinula edodes Cultured Extract and Rouxiella badensis subsp. acadiensis (Canan SV-53) Intake Alleviates Immune Deregulation and Inflammation by Modulating Signaling Pathways and Epigenetic Mechanisms

Puberty is a critical developmental period of life characterized by marked physiological changes, including changes in the immune system and gut microbiota development. Exposure to inflammation induced by immune stressors during puberty has been found to stimulate central inflammation and lead to immune disturbance at distant sites from the gut; however, its enduring effects on gut immunity are not well explored. Therefore, in this study, we used a pubertal lipopolysaccharides (LPS)-induced inflammation mouse model to mimic pubertal exposure to inflammation and dysbiosis. We hypothesized that pubertal LPS-induced inflammation may cause long-term dysfunction in gut immunity by enduring dysregulation of inflammatory signaling and epigenetic changes, while prebiotic/probiotic intake may mitigate the gut immune system deregulation later in life. To this end, four-week-old female Balb/c mice were fed prebiotics/probiotics and exposed to LPS in the pubertal window. To better decipher the acute and enduring immunoprotective effects of biotic intake, we addressed the effect of treatment on interleukin (IL)-17 signaling related-cytokines and pathways. In addition, the effect of treatment on gut microbiota and epigenetic alterations, including changes in microRNA (miRNA) expression and DNA methylation, were studied. Our results revealed a significant dysregulation in selected cytokines, proteins, and miRNAs involved in key signaling pathways related to IL-17 production and function, including IL-17A and F, IL-6, IL-1β, transforming growth factor-β (TGF-β), signal transducer and activator of transcription-3 (STAT3), p-STAT3, forkhead box O1 (FOXO1), and miR-145 in the small intestine of adult mice challenged with LPS during puberty. In contrast, dietary interventions mitigated the lasting adverse effects of LPS on gut immune function, partly through epigenetic mechanisms. A DNA methylation analysis demonstrated that enduring changes in gut immunity in adult mice might be linked to differentially methylated genes, including Lpb, Rorc, Runx1, Il17ra, Rac1, Ccl5, and Il10, involved in Th17 cell differentiation and IL-17 production and signaling. In addition, prebiotic administration prevented LPS-induced changes in the gut microbiota in pubertal mice. Together, these results indicate that following a healthy diet rich in prebiotics and probiotics is an optimal strategy for programming immune system function in the critical developmental windows of life and controlling inflammation later in life.

Loss of PBAF promotes expansion and effector differentiation of CD8+ T cells during chronic viral infection and cancer

During chronic viral infection and cancer, it has been established that a subset of progenitor CD8+ T cells continuously gives rise to terminally exhausted cells and cytotoxic effector cells. Although multiple transcriptional programs governing the bifurcated differentiation trajectories have been previously studied, little is known about the chromatin structure changes regulating CD8+ T cell-fate decision. In this study, we demonstrate that the chromatin remodeling complex PBAF restrains expansion and promotes exhaustion of CD8+ T cells during chronic viral infection and cancer. Mechanistically, transcriptomic and epigenomic analyses reveal the role of PBAF in maintaining chromatin accessibility of multiple genetic pathways and transcriptional programs to restrain proliferation and promote T cell exhaustion. Harnessing this knowledge, we demonstrate that perturbation of PBAF complex constrained exhaustion and promoted expansion of tumor-specific CD8+ T cells resulting in antitumor immunity in a preclinical melanoma model, implicating PBAF as an attractive target for cancer immunotherapeutic.

Epigenetic regulation of T cell lineages in skin and blood following hematopoietic stem cell transplantation

Allogeneic hematopoietic stem-cell transplantation (HSCT) seeks to reconstitute the host's immune system from donor stem cells. The success of HSCT is threatened by complications including leukemia relapse or graft-versus-host-disease (GvHD). To investigate the underlying regulatory processes in central and peripheral T cell recovery, we performed sequential multi-omics analysis of T cells of the skin and blood during HSCT. We detected rapid effector T cell reconstitution, while emergence of regulatory T cells was delayed. Epigenetic and gene-regulatory programs were associated with recovering T cells and diverged greatly between skin and blood T cells. The BRG1/BRM-associated factor chromatin remodeling complex and histone deacetylases (HDACs) were epigenetic regulators involved in restoration of T cell homeostasis after transplantation. In isolated T cells of patients after HSCT, we observed class I HDAC-inhibitors to modulate their dysbalance. The present study highlights the importance of epigenetic regulation in the recovery of T cells following HSCT.

Transcriptional and Epigenetic Regulation of Context-Dependent Plasticity in T-Helper Lineages

Th cell lineage determination and functional specialization are tightly linked to the activation of lineage-determining transcription factors (TFs) that bind cis-regulatory elements. These lineage-determining TFs act in concert with multiple layers of transcriptional regulators to alter the epigenetic landscape, including DNA methylation, histone modification and three-dimensional chromosome architecture, in order to facilitate the specific Th gene expression programs that allow for phenotypic diversification. Accumulating evidence indicates that Th cell differentiation is not as rigid as classically held; rather, extensive phenotypic plasticity is an inherent feature of T cell lineages. Recent studies have begun to uncover the epigenetic programs that mechanistically govern T cell subset specification and immunological memory. Advances in next generation sequencing technologies have allowed global transcriptomic and epigenomic interrogation of CD4+ Th cells that extends previous findings focusing on individual loci. In this review, we provide an overview of recent genome-wide insights into the transcriptional and epigenetic regulation of CD4+ T cell-mediated adaptive immunity and discuss the implications for disease as well as immunotherapies.

Promoter methylation status of RORC, IL17A, and TNFA in peripheral blood leukocytes in adolescents with obesity-related asthma

A higher Th17-immune response characterises obesity and obesity-related asthma phenotype. Nevertheless, obesity-related asthma has a more significant Th17-immune response than obesity alone. Retinoid-related orphan receptor C (RORC) is the essential transcription factor for Th17 polarisation. Previous studies have found that adolescents with obesity-related asthma presented upregulation of RORC, IL17A, and TNFA. However, the mechanisms that cause these higher mRNA expression levels in this asthmatic phenotype are poorly understood. Methylation directly regulates gene expression by adding a methyl group to carbon 5 of dinucleotide CpG cytosine. Thus, we evaluated the relationship between RORC, IL17A, and TNFA methylation status and mRNA expression levels to investigate a possible epigenetic regulation. A total of 102 adolescents (11-18 years) were studied in the following four groups: 1) healthy participants (HP), 2) allergic asthmatic participants (AAP), 3) obese participants without asthma (OP), and 4) non-allergic obesity-related asthma participants (OAP). Real-time qPCR assessed the methylation status and gene expression levels in peripheral blood leukocytes. Remarkably, the OAP and AAP groups have lower promoter methylation patterns of RORC, IL17A, and TNFA than the HP group. Notably, the OAP group presents lower RORC promoter methylation status than the OP group. Interestingly, RORC promoter methylation status was moderately negatively associated with gene expression of RORC (r _s = -0.39, p < 0.001) and IL17A (r _s = -0.37, p < 0.01), respectively. Similarly, the promoter methylation pattern of IL17A was moderately negatively correlated with IL17A gene expression (r _s = -0.3, p < 0.01). There is also a moderate inverse relationship between TNFA promoter methylation status and TNFA gene expression (r _s = -0.3, p < 0.01). The present study suggests an association between lower RORC, IL17A, and TNFA gene promoter methylation status with obesity-related asthma and allergic asthma. RORC, IL17A, and TNFA gene promoter methylation patterns are moderately inversely correlated with their respective mRNA expression levels. Therefore, DNA methylation may regulate RORC, IL17A, and TNF gene expression in both asthmatic phenotypes.

RORγt expression in mature TH17 cells safeguards their lineage specification by inhibiting conversion to TH2 cells

RORγt is the lineage-specific transcription factor for T helper 17 (T_H17) cells and an attractive drug target for treating T_H17-associated diseases. Although the critical role of RORγt in early T_H17 cell differentiation has been well recognized, its function in mature T_H17 cell maintenance remains largely unknown. Here, we show that genetic deletion of Rorc in mature T_H17 cells inhibited their pathogenic functions. Mechanistically, loss of RORγt led to a closed chromatin configuration at key T_H17-specific gene loci, particularly at the "super-enhancer" regions. Unexpectedly, RORγt directly bound and inhibited Il4 transcription, whereas pharmaceutically or genetically targeting RORγt caused spontaneous conversion of T_H17 cells to T_H2-like cells in vitro and in vivo. Our results thus reveal dual crucial functions of RORγt in effector T_H17 cells in maintaining T_H17 cell program and constraining T_H2 cell conversion, offering previously unidenified considerations in therapeutic targeting of RORγt.

Immune hallmarks of rheumatoid arthritis management: A brief review

The purpose of this review was to examine current evidence on immunomodulation mediated by conventional drugs and the use of novel biological agents for the treatment of rheumatoid arthritis (RA). Currently, treatment is focused on maximizing quality of life through sustained clinical remission and/or attenuating disease activity. To do so, disease-modifying antirheumatic drugs, especially methotrexate, are used alone or in combination with other drugs, including leflunomide, biological disease-modifying antirheumatic drugs (bDMARDs) and targeted synthetic disease-modifying antirheumatic drugs (tsDMARDs). The most recent strategies modulate the immune response of the individual RA patient using tsDMARDs such as JAK inhibitors and bDMARDs such as ig-CTLA-4, anti- IL6R, anti-TNF-α and anti-CD20. To better understand current immunopharmacological interventions, we also looked at documented mechanisms of RA-mediated immunomodulation, highlighting perspectives potentially boosting RA treatment.

Pbrm1 intrinsically controls the development and effector differentiation of iNKT cells

Under static condition, the pool size of peripheral invariant natural killer T (iNKT) cells is determined by their homeostatic proliferation, survival and thymic input. However, the underlying mechanism is not fully understood. In the present study, we found that the percentage and number of iNKT cells were significantly reduced in the spleen, but not in the thymus of mice with deletion of polybromo‐1 (Pbrm1) compared to wild type (WT) mice. Pbrm1 deletion did not affect iNKT cell proliferation and survival, instead significantly impaired their development from stage 1 to stage 2. Importantly, loss of Pbrm1 led to a dysfunction of RORγt expression and iNKT17 cell differentiation, but not iNKT1 and iNKT2 proportion. Collectively, our study reveals a novel mechanism of Pbrm1 controlling the peripheral size of iNKT cells through regulating their development and differentiation.

Nuclear receptor RORγ inverse agonists/antagonists display tissue- and gene-context selectivity through distinct activities in altering chromatin accessibility and master regulator SREBP2 occupancy

The nuclear receptor RORγ is a major driver of autoimmune diseases and certain types of cancer due to its aberrant function in T helper 17 (Th17) cell differentiation and tumor cholesterol metabolism, respectively. Compound screening using the classic receptor-coactivator interaction perturbation scheme led to identification of many small-molecule modulators of RORγ(t). We report here that inverse agonists/antagonists of RORγ such as VTP-43742 derivative VTP-23 and TAK828F, which can potently inhibit the inflammatory gene program in Th17 cells, unexpectedly lack high potency in inhibiting the growth of TNBC tumor cells. In contrast, antagonists such as XY018 and GSK805 that strongly suppress tumor cell growth and survival display only modest activities in reducing Th17-related cytokine expression. Unexpectedly, we found that VTP-23 significantly induces the cholesterol biosynthesis program in TNBC cells. Our further mechanistic analyses revealed that VTP-23 enhances the local chromatin accessibility, H3K27ac mark and the cholesterol master regulator SREBP2 recruitment at the RORγ binding sites, whereas XY018 exerts the opposite activities. Yet, they display similar inhibitory effects on circadian rhythm program. Similar distinctions and contrasting activities between TAK828F and SR2211 in their effects on local chromatin structure at Il17 genes were also observed. Together, our study shows for the first-time that structurally distinct RORγ antagonists possess different or even contrasting activities in tissue/cell-specific manner. Our findings also highlight that the activities at natural chromatin are key determinants of RORγ modulators' tissue selectivity.

Emergent dynamics of a three-node regulatory network explain phenotypic switching and heterogeneity: a case study of Th1/Th2/Th17 cell differentiation

Naïve helper (CD4+) T-cells can differentiate into distinct functional subsets including Th1, Th2, and Th17 phenotypes. Each of these phenotypes has a 'master regulator' - T-bet (Th1), GATA3 (Th2) and RORγT (Th17) - that inhibits the other two master regulators. Such mutual repression among them at a transcriptional level can enable multistability, giving rise to six experimentally observed phenotypes - Th1, Th2, Th17, hybrid Th/Th2, hybrid Th2/Th17 and hybrid Th1/Th17. However, the dynamics of switching among these phenotypes, particularly in the case of epigenetic influence, remains unclear. Here, through mathematical modeling, we investigated the coupled transcription-epigenetic dynamics in a three-node mutually repressing network to elucidate how epigenetic changes mediated by any 'master regulator' can influence the transition rates among different cellular phenotypes. We show that the degree of plasticity exhibited by one phenotype depends on relative strength and duration of mutual epigenetic repression mediated among the master regulators in a three-node network. Further, our model predictions can offer putative mechanisms underlying relatively higher plasticity of Th17 phenotype as observed in vitro and in vivo. Together, our modeling framework characterizes phenotypic plasticity and heterogeneity as an outcome of emergent dynamics of a three-node regulatory network, such as the one mediated by T-bet/GATA3/RORγT.

Mannan-Binding Lectin Regulates the Th17/Treg Axis Through JAK/STAT and TGF-β/SMAD Signaling Against Candida albicans Infection

Background

Mannan-binding lectin (MBL) is a key molecule in innate immunity and activates the lectin complement pathway, which plays an important role in resisting Candida albicans (C. albicans) infection. However, the underlying mechanism of this resistance to infection remains unclear.

Methods

In this study, we investigated how MBL regulates the differentiation of CD4⁺ T cells into T helper type 17 (Th17) and T regulatory (Treg) cells against C. albicans in mice, as well as the underlying mechanisms. We generated MBL double-knockout (KO) mice and infected them with C. albicans by intraperitoneal injection.

Results

Compared with that in wild-type (WT) mice, the percentage of Th17 cells increased in MBL-null mice, whereas Treg cells decreased, indicating that MBL might regulate the Th17/Treg balance. In addition, in MBL-null mice, the expression levels of interleukin (IL)-17A, IL-21, and the master transcription factor of Th17 cells, RORγt, significantly increased. Conversely, IL-10, IL-2, and the Treg-specific transcription factor, Foxp3, decreased. Moreover, we found that the levels of TGF-β and IL-6 upregulated in MBL-null mice. Mechanistically, we found that MBL regulated the TGF-β/SMAD pathway through the inhibition of p-SMAD2 and promotion of p-SMAD3, and mediated the JAK/STAT pathway through the inhibition of p-JAK2 and p-STAT3 and promotion of p-JAK3 and p-STAT5. MBL double-KO mice showed a more severe inflammatory response and significantly lower survival rates with C. albicans infection.

Conclusion

These results suggest that MBL regulates the Th17/Treg cell balance to inhibit inflammatory responses, possibly via IL-6- and TGF-β-mediated JAK/STAT and TGF-β/SMAD signaling, and play an important role in anti-C. albicans infection.

Epigenetic regulation of T cell adaptive immunity

The conceptualization of adaptive immunity, founded on the observation of immunological memory, has served as the basis for modern vaccination and immunotherapy approaches. This fundamental concept has allowed immunologists to explore mechanisms that enable humoral and cellular lymphocytes to tailor immune response functions to a wide array of environmental insults and remain poised for future pathogenic encounters. Until recently, for T cells it has remained unclear how memory differentiation acquires and sustains a gene expression program that grants a cell with a capacity for a heightened recall response. Recent investigations into this critical question have identified epigenetic programs as a causal molecular mechanism governing T cell subset specification and immunological memory. Here, we outline the studies that have illustrated this concept and posit on how insights into T cell adaptive immunity can be applied to improve upon existing immunotherapies.