The interface between transcriptional and epigenetic control of effector and memory CD8⁺ T-cell differentiation

BRD7 as key factor in PBAF complex assembly and CD8+ T cell differentiation

Upon infection, naive CD8+ T cells differentiate into cytotoxic effector cells to eliminate the pathogen-infected cells. Although many mechanisms underlying this process have been demonstrated, the regulatory role of chromatin remodeling system in this process remains largely unknown. Here we show that BRD7, a component of the polybromo-associated BAF complex (PBAF), was required for naive CD8+ T cells to differentiate into functional short-lived effector cells (SLECs) in response to acute infections caused by influenza virus or lymphocytic choriomeningitis virus (LCMV). BRD7 deficiency in CD8+ T cells resulted in profound defects in effector population and functions, thereby impairing viral clearance and host recovery. Further mechanical studies indicate that the expression of BRD7 significantly turned to high from naive CD8+ T cells to effector cells, which bridged BRG1 and PBRM1 to the core module of PBAF complex, consequently facilitating the assembly of PBAF complex rather than BAF complex in the effector cells. The PBAF complex changed the chromatin accessibility at the loci of Tbx21 gene and upregulated its expression, leading to the maturation of effector T cells. Our research demonstrates that BRD7 and the PBAF complex are key in CD8+ T cell development and present a significant target for advancing immune therapies.

ER-associated degradation adapter Sel1L is required for CD8+ T cell function and memory formation following acute viral infection

The maintenance of antigen-specific CD8+ T cells underlies the efficacy of vaccines and immunotherapies. Pathways contributing to CD8+ T cell loss are not completely understood. Uncovering the pathways underlying the limited persistence of CD8+ T cells would be of significant benefit for developing novel strategies of promoting T cell persistence. Here, we demonstrate that murine CD8+ T cells experience endoplasmic reticulum (ER) stress following activation and that the ER-associated degradation (ERAD) adapter Sel1L is induced in activated CD8+ T cells. Sel1L loss limits CD8+ T cell function and memory formation following acute viral infection. Mechanistically, Sel1L is required for optimal bioenergetics and c-Myc expression. Finally, we demonstrate that human CD8+ T cells experience ER stress upon activation and that ER stress is negatively associated with improved T cell functionality in T cell-redirecting therapies. Together, these results demonstrate that ER stress and ERAD are important regulators of T cell function and persistence.

Antiviral memory B cells exhibit enhanced innate immune response facilitated by epigenetic memory

The long-lasting humoral immunity induced by viral infections or vaccinations depends on memory B cells with greatly increased affinity to viral antigens, which are evolved from germinal center (GC) responses. However, it is unclear whether antiviral memory B cells represent a distinct subset among the highly heterogeneous memory B cell population. Here, we examined memory B cells induced by a virus-mimicking antigen at both transcriptome and epigenetic levels and found unexpectedly that antiviral memory B cells exhibit an enhanced innate immune response, which appeared to be facilitated by the epigenetic memory that is established through the memory B cell development. In addition, T-bet is associated with the altered chromatin architecture and is required for the formation of the antiviral memory B cells. Thus, antiviral memory B cells are distinct from other GC-derived memory B cells in both physiological functions and epigenetic landmarks.

Evaluation of the relationship between de-novo DSA development and CXCR5+PD-1+CD8+ T cells and PD-1/PD-L1 mRNA expression in kidney transplant recipients

BACKGROUND AND AIMS

The relationship between the Follicular Cytotoxic T cell subgroup and expression levels of PD1/PD-L1 genes and the development of donor specific antibody (DSA) is unknown. In this study, we aimed to examine CD8+CXCR5+PD-1+ follicular cytotoxic T cell levels and expression levels of PD1/PD-L1 genes in peripheral blood lymphocytes in de-novo DSA positive and negative kidney transplant recipients (KTR).

METHODS

In our study, expression of PD-1/ PD-L1 genes by Real-Time Quantitative PCR method and CD8+CXCR5+PD-1+ T cell expression levels by flow cytometric method were obtained from peripheral blood samples. 63 participants were included in the study (de-novo DSA positive recipients (n = 22, group 1), de-novo DSA negative recipients (n = 20, group 2) and healthy control (n = 21, group 3). All patients had negative PRA before kidney transplantation. Expression (%) levels of target cells were evaluated by flow cytometry method. IBM SPSS Statistics for Windows Version 22 and R.3.3.2 software were used to evaluate the data.

RESULTS

The demographic data of the groups were similar. PD-1 mRNA expression was higher in de-novo DSA positive KTR than negative (respectively, 1.03 ± .29/.82 ± .15, p: .001). CD8+CXCR5+PD-1+ T cell expression levels were found to be higher in the de-novo DSA positive group than in the negative group and similar to the healthy group (respectively, 3.06 ± 1.98/.52 ± .40, p:.001, 3.06 ± 1.98/2.78 ± .59, p:.62). The percentage of CD8+CXCR5+PD-1+ expressing T cells was significantly lower in the HLA-Class II+ group than other groups (HLA CI/II/ I+II, respectively, 3.63 ± 2.72/1.65 ± .50/3.68 ± 1.67, p: .04).

CONCLUSIONS

In our study, a significant relationship was found between DSA formation and PD-1 mRNA level and CD8+CXCR5+PD-1+ follicular cytotoxic T cell in KTR.

Ketolysis drives CD8+ T cell effector function through effects on histone acetylation

Environmental nutrient availability influences T cell metabolism, impacting T cell function and shaping immune outcomes. Here, we identified ketone bodies (KBs)-including β-hydroxybutyrate (βOHB) and acetoacetate (AcAc)-as essential fuels supporting CD8+ T cell metabolism and effector function. βOHB directly increased CD8+ T effector (Teff) cell cytokine production and cytolytic activity, and KB oxidation (ketolysis) was required for Teff cell responses to bacterial infection and tumor challenge. CD8+ Teff cells preferentially used KBs over glucose to fuel the tricarboxylic acid (TCA) cycle in vitro and in vivo. KBs directly boosted the respiratory capacity and TCA cycle-dependent metabolic pathways that fuel CD8+ T cell function. Mechanistically, βOHB was a major substrate for acetyl-CoA production in CD8+ T cells and regulated effector responses through effects on histone acetylation. Together, our results identify cell-intrinsic ketolysis as a metabolic and epigenetic driver of optimal CD8+ T cell effector responses.

Epigenetic signature of human immune aging in the GESTALT study

Age-associated DNA methylation in blood cells convey information on health status. However, the mechanisms that drive these changes in circulating cells and their relationships to gene regulation are unknown. We identified age-associated DNA methylation sites in six purified blood-borne immune cell types (naive B, naive CD4+ and CD8+ T cells, granulocytes, monocytes, and NK cells) collected from healthy individuals interspersed over a wide age range. Of the thousands of age-associated sites, only 350 sites were differentially methylated in the same direction in all cell types and validated in an independent longitudinal cohort. Genes close to age-associated hypomethylated sites were enriched for collagen biosynthesis and complement cascade pathways, while genes close to hypermethylated sites mapped to neuronal pathways. In silico analyses showed that in most cell types, the age-associated hypo- and hypermethylated sites were enriched for ARNT (HIF1β) and REST transcription factor (TF) motifs, respectively, which are both master regulators of hypoxia response. To conclude, despite spatial heterogeneity, there is a commonality in the putative regulatory role with respect to TF motifs and histone modifications at and around these sites. These features suggest that DNA methylation changes in healthy aging may be adaptive responses to fluctuations of oxygen availability.

Human Granzyme K Is a Feature of Innate T Cells in Blood, Tissues, and Tumors, Responding to Cytokines Rather than TCR Stimulation

NK cells and CD8 T cells use cytotoxic molecules to kill virally infected and tumor cell targets. While perforin and granzyme B (GzmB) are the most commonly studied lytic molecules, less is known about granzyme K (GzmK). However, this granzyme has been recently associated with improved prognosis in solid tumors. In this study, we show that, in humans, GzmK is predominantly expressed by innate-like lymphocytes, as well as a newly identified population of GzmK+CD8+ non- mucosal-associated invariant T cells with innate-like characteristics. We found that GzmK+ T cells are KLRG1+EOMES+IL-7R+CD62L-Tcf7int, suggesting that they are central memory T and effector memory T cells. Furthermore, GzmK+ cells are absent/low in cord blood, suggesting that GzmK is upregulated with immune experience. Surprisingly, GzmK+ cells respond to cytokine stimuli alone, whereas TCR stimulation downregulates GzmK expression, coinciding with GzmB upregulation. GzmK+ cells have reduced IFN-γ production compared with GzmB+ cells in each T cell lineage. Collectively, this suggests that GzmK+ cells are not naive, and they may be an intermediate memory-like or preterminally differentiated population. GzmK+ cells are enriched in nonlymphoid tissues such as the liver and adipose. In colorectal cancer, GzmK+ cells are enriched in the tumor and can produce IFN-γ, but GzmK+ expression is mutually exclusive with IL-17a production. Thus, in humans, GzmK+ cells are innate memory-like cells that respond to cytokine stimulation alone and may be important effector cells in the tumor.

Recent insights into the role of Akt in CD4 T-cell activation and differentiation: alternative splicing and beyond

The activation and differentiation of CD4⁺ T cells is a complex process that is controlled by many factors. A critical component of the signaling pathway triggered following T-cell receptor (TCR) engagement is the serine threonine kinase Akt. Akt is involved in the control of many cellular processes including proliferation, metabolism, and differentiation of specific T_H-cell subsets. Recent work has shown that, depending on the nature or strength of the TCR activation, Akt may activate different sets of substrates which then lead to differential cellular outcomes. Akt plays an important role in controlling the strength of the TCR signal and several recent studies have identified novel mechanisms including control of the expression of negative regulators of TCR signaling, and the influence on regulatory T cells (Treg) and T_H17 differentiation. Many of these functions are mediated via control of the FoxO family of transcription factors, that play an important role in metabolism and Th cell differentiation. A theme that is emerging is that Akt does not function in the same way in all T-cell types. We highlight differences between CD4 and CD8 T cells as well as between Treg, T_H17, and T_FH cells. While Akt activity has been implicated in the control of alternative splicing in tumor cells, recent studies are emerging that indicate that similar functions may exist in CD4 T cells. In this mini review, we highlight some of the recent advances in these areas of Akt function that demonstrate the varied role that Akt plays in the function of CD4 T cells.

Excessive intake of sugar: An accomplice of inflammation

High sugar intake has long been recognized as a potential environmental risk factor for increased incidence of many non-communicable diseases, including obesity, cardiovascular disease, metabolic syndrome, and type 2 diabetes (T2D). Dietary sugars are mainly hexoses, including glucose, fructose, sucrose and High Fructose Corn Syrup (HFCS). These sugars are primarily absorbed in the gut as fructose and glucose. The consumption of high sugar beverages and processed foods has increased significantly over the past 30 years. Here, we summarize the effects of consuming high levels of dietary hexose on rheumatoid arthritis (RA), multiple sclerosis (MS), psoriasis, inflammatory bowel disease (IBD) and low-grade chronic inflammation. Based on these reported findings, we emphasize that dietary sugars and mixed processed foods may be a key factor leading to the occurrence and aggravation of inflammation. We concluded that by revealing the roles that excessive intake of hexose has on the regulation of human inflammatory diseases are fundamental questions that need to be solved urgently. Moreover, close attention should also be paid to the combination of high glucose-mediated immune imbalance and tumor development, and strive to make substantial contributions to reverse tumor immune escape.

The Expanding Arsenal of Cytotoxic T Cells

Cytotoxic T cells (CTLs) are the main cellular mediators of the adaptive immune defenses against intracellular pathogens and malignant cells. Upon recognition of specific antigen on their cellular target, CTLs assemble an immunological synapse where they mobilise their killing machinery that is released into the synaptic cleft to orchestrate the demise of their cell target. The arsenal of CTLs is stored in lysosome-like organelles that undergo exocytosis in response to signals triggered by the T cell antigen receptor following antigen recognition. These organelles include lytic granules carrying a cargo of cytotoxic proteins packed on a proteoglycan scaffold, multivesicular bodies carrying the death receptor ligand FasL, and the recently discovered supramolecular attack particles that carry a core of cytotoxic proteins encased in a non-membranous glycoprotein shell. Here we will briefly review the main features of these killing entities and discuss their interrelationship and interplay in CTL-mediated killing.

The Role of Metabolic Dysfunction in T-Cell Exhaustion During Chronic Viral Infection

T cells are important components of adaptive immunity that protect the host against invading pathogens during infection. Upon recognizing the activation signals, naïve and/or memory T cells will initiate clonal expansion, trigger differentiation into effector populations and traffic to the inflamed sites to eliminate pathogens. However, in chronic viral infections, such as those caused by human immunodeficiency virus (HIV), hepatitis B and C (HBV and HCV), T cells exhibit impaired function and become difficult to clear pathogens in a state known as T-cell exhaustion. The activation and function persistence of T cells demand for dynamic changes in cellular metabolism to meet their bioenergetic and biosynthetic demands, especially the augmentation of aerobic glycolysis, which not only provide efficient energy generation, but also fuel multiple biochemical intermediates that are essential for nucleotide, amino acid, fatty acid synthesis and mitochondria function. Changes in cellular metabolism also affect the function of effectors T cells through modifying epigenetic signatures. It is widely accepted that the dysfunction of T cell metabolism contributes greatly to T-cell exhaustion. Here, we reviewed recent findings on T cells metabolism under chronic viral infection, seeking to reveal the role of metabolic dysfunction played in T-cell exhaustion.

Batf-mediated epigenetic control of effector CD8+ T cell differentiation

The response of naive CD8⁺ T cells to their cognate antigen involves rapid and broad changes to gene expression that are coupled with extensive chromatin remodeling, but the mechanisms governing these changes are not fully understood. Here, we investigated how these changes depend on the basic leucine zipper ATF-like transcription factor Batf, which is essential for the early phases of the process. Through genome scale profiling, we characterized the role of Batf in chromatin organization at several levels, including the accessibility of key regulatory regions, the expression of their nearby genes, and the interactions that these regions form with each other and with key transcription factors. We identified a core network of transcription factors that cooperated with Batf, including Irf4, Runx3, and T-bet, as indicated by their colocalization with Batf and their binding in regions whose accessibility, interactions, and expression of nearby genes depend on Batf. We demonstrated the synergistic activity of this network by overexpressing the different combinations of these genes in fibroblasts. Batf and Irf4, but not Batf alone, were sufficient to increase accessibility and transcription of key loci, normally associated with T cell function. Addition of Runx3 and T-bet further contributed to fine-tuning of these changes and was essential for establishing chromatin loops characteristic of T cells. These data provide a resource for studying the epigenomic and transcriptomic landscape of effector differentiation of cytotoxic T cells and for investigating the interdependency between transcription factors and its effects on the epigenome and transcriptome of primary cells.

Lung dendritic cells migrate to the spleen to prime long-lived TCF1hi memory CD8+ T cell precursors after influenza infection

[Figure: see text].

Post-transcriptional control of T-cell cytokine production: Implications for cancer therapy

As part of the adaptive immune system, T cells are vital for the eradication of infected and malignantly transformed cells. To perform their protective function, T cells produce effector molecules that are either directly cytotoxic, such as granzymes, perforin, interferon-γ and tumour necrosis factor α, or attract and stimulate (immune) cells, such as interleukin-2. As these molecules can also induce immunopathology, tight control of their production is required. Indeed, inflammatory cytokine production is regulated on multiple levels. Firstly, locus accessibility and transcription factor availability and activity determine the amount of mRNA produced. Secondly, post-transcriptional mechanisms, influencing mRNA splicing/codon usage, stability, decay, localization and translation rate subsequently determine the amount of protein that is produced. In the immune suppressive environments of tumours, T cells gradually lose the capacity to produce effector molecules, resulting in tumour immune escape. Recently, the role of post-transcriptional regulation in fine-tuning T-cell effector function has become more appreciated. Furthermore, several groups have shown that exhausted or dysfunctional T cells from cancer patients or murine models possess mRNA for inflammatory mediators, but fail to produce effector molecules, hinting that post-transcriptional events also play a role in hampering tumour-infiltrating lymphocyte effector function. Here, the post-transcriptional regulatory events governing T-cell cytokine production are reviewed, with a specific focus on the importance of post-transcriptional regulation in anti-tumour responses. Furthermore, potential approaches to circumvent tumour-mediated dampening of T-cell effector function through the (dis)engagement of post-transcriptional events are explored, such as CRISPR/Cas9-mediated genome editing or chimeric antigen receptors.

The Route of Early T Cell Development: Crosstalk between Epigenetic and Transcription Factors

Hematopoietic multipotent progenitors seed the thymus and then follow consecutive developmental stages until the formation of mature T cells. During this process, phenotypic changes of T cells entail stage-specific transcriptional programs that underlie the dynamic progression towards mature lymphocytes. Lineage-specific transcription factors are key drivers of T cell specification and act in conjunction with epigenetic regulators that have also been elucidated as crucial players in the establishment of regulatory networks necessary for proper T cell development. In this review, we summarize the activity of transcription factors and epigenetic regulators that together orchestrate the intricacies of early T cell development with a focus on regulation of T cell lineage commitment.

The transcriptional repressor ID2 supports natural killer cell maturation by controlling TCF1 amplitude

Gaining a mechanistic understanding of the expansion and maturation program of natural killer (NK) cells will provide opportunities for harnessing their inflammation-inducing and oncolytic capacity for therapeutic purposes. Here, we demonstrated that ID2, a transcriptional regulatory protein constitutively expressed in NK cells, supports NK cell effector maturation by controlling the amplitude and temporal dynamics of the transcription factor TCF1. TCF1 promotes immature NK cell expansion and restrains differentiation. The increased TCF1 expression in ID2-deficient NK cells arrests their maturation and alters cell surface receptor expression. Moreover, TCF1 limits NK cell functions, such as cytokine-induced IFN-γ production and the ability to clear metastatic melanoma in ID2-deficient NK cells. Our data demonstrate that ID2 sets a threshold for TCF1 during NK cell development, thus controlling the balance of immature and terminally differentiated cells that support future NK cell responses.

Multi-Dimensional Gene Regulation in Innate and Adaptive Lymphocytes: A View From Regulomes

The precise control of cytokine production by innate lymphoid cells (ILCs) and their T cell adaptive system counterparts is critical to mounting a proper host defense immune response without inducing collateral damage and autoimmunity. Unlike T cells that differentiate into functionally divergent subsets upon antigen recognition, ILCs are developmentally programmed to rapidly respond to environmental signals in a polarized manner, without the need of T cell receptor (TCR) signaling. The specification of cytokine production relies on dynamic regulation of cis-regulatory elements that involve multi-dimensional epigenetic mechanisms, including DNA methylation, transcription factor binding, histone modification and DNA-DNA interactions that form chromatin loops. How these different layers of gene regulation coordinate with each other to fine tune cytokine production, and whether ILCs and their T cell analogs utilize the same regulatory strategy, remain largely unknown. Herein, we review the molecular mechanisms that underlie cell identity and functionality of helper T cells and ILCs, focusing on networks of transcription factors and cis-regulatory elements. We discuss how higher-order chromatin architecture orchestrates these components to construct lineage- and state-specific regulomes that support ordered immunoregulation.

Using CRISPR to enhance T cell effector function for therapeutic applications

T cells are critical to fight pathogenic microbes and combat malignantly transformed cells in the fight against cancer. To exert their effector function, T cells produce effector molecules, such as the pro-inflammatory cytokines IFN-γ, TNF-α and IL-2. Tumors possess many inhibitory mechanisms that dampen T cell effector function, limiting the secretion of cytotoxic molecules. As a result, the control and elimination of tumors is impaired. Through recent advances in genomic editing, T cells can now be successfully modified via CRISPR/Cas9 technology. For instance, engaging (post-)transcriptional mechanisms to enhance T cell cytokine production, the retargeting of T cell antigen specificity or rendering T cells refractive to inhibitory receptor signaling can augment T cell effector function. Therefore, CRISPR/Cas9-mediated genome editing might provide novel strategies for cancer immunotherapy. Recently, the first-in-patient clinical trial was successfully performed with CRISPR/Cas9-modified human T cell therapy. In this review, a brief overview of currently available techniques is provided, and recent advances in T cell genomic engineering for the enhancement of T cell effector function for therapeutic purposes are discussed.

PSGL-1 Immune Checkpoint Inhibition for CD4+ T Cell Cancer Immunotherapy

Immune checkpoint inhibition targeting T cells has shown tremendous promise in the treatment of many cancer types and are now standard therapies for patients. While standard therapies have focused on PD-1 and CTLA-4 blockade, additional immune checkpoints have shown promise in promoting anti-tumor immunity. PSGL-1, primarily known for its role in cellular migration, has also been shown to function as a negative regulator of CD4+ T cells in numerous disease settings including cancer. PSGL-1 is highly expressed on T cells and can engage numerous ligands that impact signaling pathways, which may modulate CD4+ T cell differentiation and function. PSGL-1 engagement in the tumor microenvironment may promote CD4+ T cell exhaustion pathways that favor tumor growth. Here we highlight that blocking the PSGL-1 pathway on CD4+ T cells may represent a new cancer therapy approach to eradicate tumors.

Toll-like receptor-2/7-mediated T cell activation: An innate potential to augment CD8+ T cell cytokine production

CD8⁺ T cells are critical to combat pathogens and eradicate malignantly transformed cells. To exert their effector function and kill target cells, T cells produce copious amounts of effector molecules, including the pro-inflammatory cytokines interferon γ, tumour necrosis factor α and interleukin 2. TCR triggering alone is sufficient to induce cytokine secretion by effector and memory CD8⁺ T cells. However, T cells can also be directly activated by pathogen-derived molecules, such as through the triggering of Toll-like receptors (TLRs). TLR-mediated pathogen sensing by T cells results in the production of only interferon γ. However, in particular when the antigen load on target cells is low, or when TCR affinity to the antigen is limited, antigen-experienced T cells can benefit from costimulatory signals. TLR stimulation can also function in a costimulatory fashion to enhance TCR triggering. Combined TCR and TLR triggering enhances the proliferation, memory formation and effector function of T cells, resulting in enhanced production of interferon γ, tumour necrosis factor α and interleukin 2. Therefore, TLR ligands or the exploitation of TLR signalling could provide novel opportunities for immunotherapy approaches. In fact, CD19 CAR T cells bearing an intracellular TLR2 costimulatory domain were recently employed to treat cancer patients in a clinical trial. Here, the current knowledge regarding TLR2/7 stimulation-induced cytokine production by T cells is reviewed. Specifically, the transcriptional and post-transcriptional pathways engaged upon TLR2/7 sensing and TLR2/7 signalling are discussed. Finally, the potential uses of TLRs to enhance the anti-tumor effector function of T cells are explored.

Running to Stand Still: Naive CD8+ T Cells Actively Maintain a Program of Quiescence

CD8⁺ T cells play a pivotal role in clearing intracellular pathogens and combatting tumours. Upon infection, naïve CD8⁺ T cells differentiate into effector and memory cells, and this program is underscored by large-scale and coordinated changes in the chromatin architecture and gene expression. Importantly, recent evidence demonstrates that the epigenetic mechanisms that regulate the capacity for rapid effector function of memory T cells are shared by innate immune cells such as natural killer (NK) cells. Thus, it appears that the crucial difference between innate and adaptive immunity is the presence of the naïve state. This important distinction raises an intriguing new hypothesis, that the naïve state was evolutionary installed to restrain a default program of effector and memory differentiation in response to antigen recognition. We argue that the hallmark of adaptive T immunity is therefore the naïve program, which actively maintains CD8⁺ T cell quiescence until receipt of appropriate activation signals. In this review, we examine the mechanistic control of naïve CD8⁺ T cell quiescence and summarise the multiple levels of restraint imposed in naïve cells in to limit spontaneous and inappropriate activation. This includes epigenetic mechanisms and transcription factor (TF) regulation of gene expression, in addition to novel inhibitory receptors, abundance of RNA, and protein degradation.

Crystal structure of the giant panda MHC class I complex: First insights into the viral peptide presentation profile in the bear family

The viral cytotoxic T lymphocyte (CTL) epitope peptides presented by classical MHC-I molecules require the assembly of a peptide-MHC-I-β2m (pMHC-I) trimolecular complex for T cell receptor (TCR) recognition, which is the critical activation link for triggering antiviral T cell immunity. Research on T cell immunology in the Ursidae family, especially structural immunology, is still lacking. In this study, the structure of the key trimolecular complex pMHC-I, which binds a peptide from canine distemper virus, was solved for the first time using giant panda as a representative species of Ursidae. The structural characteristics of the giant panda pMHC-I complex (pAime-128), including the unique pockets in the peptide-binding groove (PBG), were analyzed in detail. Comparing the pAime-128 to others in the bear family and extending the comparison to other mammals revealed distinct features. The interaction between MHC-I and β2m, the features of pAime-128 involved in TCR docking and cluster of differentiation 8 (CD8) binding, the anchor sites in the PBG, and the CTL epitopes of potential viruses that infect pandas were clarified. Unique features of pMHC-I viral antigen presentation in the panda were revealed by solving the three-dimensional (3D) structure of pAime-128. The distinct characteristics of pAime-128 indicate an unusual event that emerged during the evolution of the MHC system in the bear family. These results provide a new platform for research on panda CTL immunity and the design of vaccines for application in the bear family.

Rewiring Mitochondrial Metabolism for CD8+ T Cell Memory Formation and Effective Cancer Immunotherapy

Memory T cells persist for long term to mediate robust recall response upon rechallenging with previous encountered pathogens. The memory T cell pool is highly heterogeneous based on distinct phenotypic, functional, and locational properties, and contains discrete subsets, which contribute to diverse immune responses. In this mini-review, we will briefly discuss the distinct subsets of memory T cells and then focus on mitochondria-related metabolic and epigenetic regulations of CD8⁺ T cell memory formation. In particular, we discuss many aspects of mitochondrial quality control systems (biogenesis, dynamics, etc.) in regulating CD8⁺ T cell fate decision and antitumor immunity. Importantly, targeting mitochondrial metabolism to boost T cell memory formation and metabolic fitness might represent an attractive strategy to improve cancer immunotherapy including CAR-T therapy.

The histone methyltransferase DOT1L prevents antigen-independent differentiation and safeguards epigenetic identity of CD8+ T cells

Cytotoxic T cell differentiation is guided by epigenome adaptations, but how epigenetic mechanisms control lymphocyte development has not been well defined. Here we show that the histone methyltransferase DOT1L, which marks the nucleosome core on active genes, safeguards normal differentiation of CD8+ T cells. T cell-specific ablation of Dot1L resulted in loss of naïve CD8+ T cells and premature differentiation toward a memory-like state, independent of antigen exposure and in a cell-intrinsic manner. Mechanistically, DOT1L controlled CD8+ T cell differentiation by ensuring normal T cell receptor density and signaling. DOT1L also maintained epigenetic identity, in part by indirectly supporting the repression of developmentally regulated genes. Finally, deletion of Dot1L in T cells resulted in an impaired immune response. Through our study, DOT1L is emerging as a central player in physiology of CD8+ T cells, acting as a barrier to prevent premature differentiation and controlling epigenetic integrity.

Epigenetic Mechanisms of Resistance to Immune Checkpoint Inhibitors

Immune checkpoint inhibitors (ICIs) have demonstrated to be highly efficient in treating solid tumors; however, many patients have limited benefits in terms of response and survival. This rapidly led to the investigation of combination therapies to enhance response rates. Moreover, predictive biomarkers were assessed to better select patients. Although PD-L1 expression remains the only validated marker in clinics, molecular profiling has brought valuable information, showing that the tumor mutation load and microsatellite instability (MSI) status were associated to higher response rates in nearly all cancer types. Moreover, in lung cancer, EGFR and MET mutations, oncogene fusions or STK11 inactivating mutations were associated with low response rates. Cancer progression towards invasive phenotypes that impede immune surveillance relies on complex regulatory networks and cell interactions within the tumor microenvironment. Epigenetic modifications, such as the alteration of histone patterns, chromatin structure, DNA methylation status at specific promoters and changes in microRNA levels, may alter the cell phenotype and reshape the tumor microenvironment, allowing cells to grow and escape from immune surveillance. The objective of this review is to make an update on the identified epigenetic changes that target immune surveillance and, ultimately, ICI responses, such as histone marks, DNA methylation and miR signatures. Translational studies or clinical trials, when available, and potential epigenetic biomarkers will be discussed as perspectives in the context of combination treatment strategies to enhance ICI responses in patients with solid tumors.

The Swing of Lipids at Peroxisomes and Endolysosomes in T Cell Activation

The immune synapse (IS) is a well-known intercellular communication platform, organized at the interphase between the antigen presenting cell (APC) and the T cell. After T cell receptor (TCR) stimulation, signaling from plasma membrane proteins and lipids is amplified by molecules and downstream pathways for full synapse formation and maintenance. This secondary signaling event relies on intracellular reorganization at the IS, involving the cytoskeleton and components of the secretory/recycling machinery, such as the Golgi apparatus and the endolysosomal system (ELS). T cell activation triggers a metabolic reprogramming that involves the synthesis of lipids, which act as signaling mediators, and an increase of mitochondrial activity. Then, this mitochondrial activity results in elevated reactive oxygen species (ROS) production that may lead to cytotoxicity. The regulation of ROS levels requires the concerted action of mitochondria and peroxisomes. In this review, we analyze this reprogramming and the signaling implications of endolysosomal, mitochondrial, peroxisomal, and lipidic systems in T cell activation.

Chemical individuality in T cells: A Garrodian view of immunometabolism

Metabolically quiescent T cells circulate throughout the body in search of antigen. Following engagement of their cognate receptors, T cells undergo metabolic reprogramming to support their activation, differentiation, and ultimately function. In the spirit of Sir Archibald Garrod, this metabolic reprogramming actually imparts a chemical individuality which confers advantage, while in others confers vulnerability, depending upon the milieu. Studying T cell immunometabolism in the context of inborn errors of metabolism allows one to define essential pathways of intermediary metabolism as well metabolic vulnerabilities and plasticity. Inborn errors of metabolism, a class of diseases first named by Garrod, have a long history of being informative for common physiologic and pathologic processes. This endeavor may be accomplished through the study of patients, animal models, and in vitro models of inborn errors of metabolism. In this review, the basics of intermediary metabolism and core metabolic pathways will be discussed, along with their relationship to T cell immunometabolism. Due to their pleiotropic nature, the reader will be specifically directed toward various inborn errors of metabolism which may be helpful for answering important questions about the role of metabolism in T cells.

Checkpoint inhibitor blockade and epigenetic reprogrammability in CD8+ T-cell activation and exhaustion

CD8⁺ T-cell exhaustion is a dysfunctional state that is regulated through the expression of inhibitory checkpoint receptor genes including the cytotoxic T-lymphocyte–associated antigen 4, programmed death 1, and DNA methylation of effector genes interferon-γ, perforin, and granzyme B. Different strategies have been used to reverse T-cell exhaustion, which is an adverse event of checkpoint inhibitor blockade. Here, we present the mechanisms by which DNA methyltransferase inhibitors and Simian virus 40 large T antigen through viral mimicry can promote the reversion of exhausted CD8⁺ T cells. We examine how these pharmacological strategies can work together to improve the clinical efficacy of immunotherapies.

Human T cells employ conserved AU-rich elements to fine-tune IFN-γ production

Long‐lasting CD8⁺ T cell responses are critical in combatting infections and tumors. The pro‐inflammatory cytokine IFN‐γ is a key effector molecule herein. We recently showed that in murine T cells the production of IFN‐γ is tightly regulated through adenylate uridylate–rich elements (AREs) that are located in the 3′ untranslated region (UTR) of the Ifng mRNA molecule. Loss of AREs resulted in prolonged cytokine production in activated T cells and boosted anti‐tumoral T cell responses. Here, we investigated whether these findings can be translated to primary human T cells. Utilizing CRISPR‐Cas9 technology, we deleted the ARE region from the IFNG 3′ UTR in peripheral blood‐derived human T cells. Loss of AREs stabilized the IFNG mRNA in T cells and supported a higher proportion of IFN‐γ protein‐producing T cells. Importantly, combining MART‐1 T cell receptor engineering with ARE‐Del gene editing showed that this was also true for antigen‐specific activation of T cells. MART‐1‐specific ARE‐Del T cells showed higher percentages of IFN‐γ producing T cells in response to MART‐1 expressing tumor cells. Combined, our study reveals that ARE‐mediated posttranscriptional regulation is conserved between murine and human T cells. Furthermore, generating antigen‐specific ARE‐Del T cells is feasible, a feature that could potentially be used for therapeutical purposes.

A key control point in the T cell response to chronic infection and neoplasia: FOXO1

T cells able to control neoplasia or chronic infections display a signature gene expression profile similar or identical to that of central memory T cells. These cells have qualities of self-renewal and a plasticity that allow them to repeatedly undergo activation (growth, proliferation, and differentiation), followed by quiescence. It is these qualities that define the ability of T cells to establish an equilibrium with chronic infectious agents, and also preserve the ability of T cells to be re-activated (by checkpoint therapy) in response to malignant cancers. Here we describe distinctions between the forms of inhibition mediated by tumors and persistent viruses, we review the properties of T cells associated with long-term immunity, and we identify the transcription factor, FOXO1, as the control point for a program of gene expression that allows CD8⁺ T cells to undergo serial reactivation and self-renewal.

Targeting p53 and histone methyltransferases restores exhausted CD8+ T cells in HCV infection

Hepatitis C virus infection (HCV) represents a unique model to characterize, from early to late stages of infection, the T cell differentiation process leading to exhaustion of human CD8+ T cells. Here we show that in early HCV infection, exhaustion-committed virus-specific CD8+ T cells display a marked upregulation of transcription associated with impaired glycolytic and mitochondrial functions, that are linked to enhanced ataxia-telangiectasia mutated (ATM) and p53 signaling. After evolution to chronic infection, exhaustion of HCV-specific T cell responses is instead characterized by a broad gene downregulation associated with a wide metabolic and anti-viral function impairment, which can be rescued by histone methyltransferase inhibitors. These results have implications not only for treatment of HCV-positive patients not responding to last-generation antivirals, but also for other chronic pathologies associated with T cell dysfunction, including cancer.

CD4+ T cell help creates memory CD8+ T cells with innate and help-independent recall capacities

CD4⁺ T cell help is required for the generation of CD8⁺ cytotoxic T lymphocyte (CTL) memory. Here, we use genome-wide analyses to show how CD4⁺ T cell help delivered during priming promotes memory differentiation of CTLs. Help signals enhance IL-15-dependent maintenance of central memory T (T_CM) cells. More importantly, help signals regulate the size and function of the effector memory T (T_EM) cell pool. Helped T_EM cells produce Granzyme B and IFNγ upon antigen-independent, innate-like recall by IL-12 and IL-18. In addition, helped memory CTLs express the effector program characteristic of helped primary CTLs upon recall with MHC class I-restricted antigens, likely due to epigenetic imprinting and sustained mRNA expression of effector genes. Our data thus indicate that during priming, CD4⁺ T cell help optimizes CTL memory by creating T_EM cells with innate and help-independent antigen-specific recall capacities.

Deciphering host immunity to malaria using systems immunology

A century of conceptual and technological advances in infectious disease research has changed the face of medicine. However, there remains a lack of effective interventions and a poor understanding of host immunity to the most significant and complex pathogens, including malaria. The development of successful interventions against such intractable diseases requires a comprehensive understanding of host-pathogen immune responses. A major advance of the past decade has been a paradigm switch in thinking from the contemporary reductionist (gene-by-gene or protein-by-protein) view to a more holistic (whole organism) view. Also, a recognition that host-pathogen immunity is composed of complex, dynamic interactions of cellular and molecular components and networks that cannot be represented by any individual component in isolation. Systems immunology integrates the field of immunology with omics technologies and computational sciences to comprehensively interrogate the immune response at a systems level. Herein, we describe the system immunology toolkit and report recent studies deploying systems-level approaches in the context of natural exposure to malaria or controlled human malaria infection. We contribute our perspective on the potential of systems immunity for the rational design and development of effective interventions to improve global public health.

WASp Is Essential for Effector-to-Memory conversion and for Maintenance of CD8+T Cell Memory

Wiskott-Aldrich syndrome (WAS) is a rare X-linked primary immunodeficiency characterized by recurrent infections, micro thrombocytopenia, eczema, and a high incidence of autoimmunity and malignancy. A defect in the T cell compartment is thought to be a major cause of immunodeficiency in patients with WAS; However, whether the antigen specific T memory cell is altered has not been extensively studied. Here, we examined the expansion/contraction kinetics of CD8⁺ memory T cells and their maintenance in WASp^−/− mice. The results showed that WAS protein (WASp) is not required for differentiation of CD8⁺ effector T cells; however, CD8⁺ T cells from WASp^−/− mice were hyperactive, resulting in increased cytokine production. The number of CD8⁺ T memory cells decreased as mice aged, and CD8⁺ T cell recall responses and protective immunity were impaired. WASp-deficient CD8⁺ T cells in bone marrow chimeric mice underwent clonal expansion, but the resulting effector cells failed to survive and differentiate into CD8⁺ memory T cells. Taken together, these findings indicate that WASp plays an intrinsic role in differentiation of CD8⁺ memory T cells.

Diverse Immunomodulatory Effects of Individual IFNα Subtypes on Virus-Specific CD8+ T Cell Responses

Clinical administration of Interferon α (IFNα) resulted in limited therapeutic success against some viral infections. Immune modulation of CD8+ T cell responses during IFNα therapy is believed to play a pivotal role in promoting viral clearance. However, these clinical studies primarily focused on IFNα subtype 2. To date, the immunomodulatory roles of the remaining 10-13 IFNα subtypes remains poorly understood, thereby precluding assessments of their potential for more effective treatments. Here, we report that virus-specific CD8+ T cell responses were influenced to various extents by individual IFNα subtypes. IFNα4, 6, and 9 had the strongest effects on CD8+ T cells, including antiproliferative effects, improved cytokine production and cytotoxicity. Interestingly, augmented cytokine responses were dependent on IFNα subtype stimulation of dendritic cells (DCs), while antiproliferative effects and cytotoxicity were mediated by IFNAR signaling in either CD8+ T cells or DCs. Thus, precise modulation of virus-specific CD8+ T cell responses may be feasible for specific antiviral immunotherapies through careful selection and administration of individual IFNα subtypes.

CD4+ T cell help in cancer immunology and immunotherapy

Cancer immunotherapy aims to promote the activity of cytotoxic T lymphocytes (CTLs) within a tumour, assist the priming of tumour-specific CTLs in lymphoid organs and establish efficient and durable antitumour immunity. During priming, help signals are relayed from CD4⁺ T cells to CD8⁺ T cells by specific dendritic cells to optimize the magnitude and quality of the CTL response. In this Review, we highlight the cellular dynamics and membrane receptors that mediate CD4⁺ T cell help and the molecular mechanisms of the enhanced antitumour activity of CTLs. We outline how deficient CD4⁺ T cell help reduces the response of CTLs and how maximizing CD4⁺ T cell help can improve outcomes in cancer immunotherapy strategies.

Mitochondrial Dysfunction and the Aging Immune System

Mitochondria are ancient organelles that have co-evolved with their cellular hosts, developing a mutually beneficial arrangement. In addition to making energy, mitochondria are multifaceted, being involved in heat production, calcium storage, apoptosis, cell signaling, biosynthesis, and aging. Many of these mitochondrial functions decline with age, and are the basis for many diseases of aging. Despite the vast amount of research dedicated to this subject, the relationship between aging mitochondria and immune function is largely absent from the literature. In this review, three main issues facing the aging immune system are discussed: (1) inflamm-aging; (2) susceptibility to infection and (3) declining T-cell function. These issues are re-evaluated using the lens of mitochondrial dysfunction with aging. With the recent expansion of numerous profiling technologies, there has been a resurgence of interest in the role of metabolism in immunity, with mitochondria taking center stage. Building upon this recent accumulation of knowledge in immunometabolism, this review will advance the hypothesis that the decline in immunity and associated pathologies are partially related to the natural progression of mitochondrial dysfunction with aging.

The Emerging Epigenetic Role of CD8+T Cells in Autoimmune Diseases: A Systematic Review

Autoimmune diseases are usually complex and multifactorial, characterized by aberrant production of autoreactive immune cells and/or autoantibodies against healthy cells and tissues. However, the pathogenesis of autoimmune diseases has not been clearly elucidated. The activation, differentiation, and development of CD8+ T cells can be affected by numerous inflammatory cytokines, transcription factors, and chemokines. In recent years, epigenetic modifications have been shown to play an important role in the fate of CD8+ T cells. The discovery of these modifications that contribute to the activation or suppression of CD8+ cells has been concurrent with the increasing evidence that CD8+ T cells play a role in autoimmunity. These relationships have been studied in various autoimmune diseases, including multiple sclerosis (MS), systemic sclerosis (SSc), type 1 diabetes (T1D), Grave's disease (GD), systemic lupus erythematosus (SLE), aplastic anemia (AA), and vitiligo. In each of these diseases, genes that play a role in the proliferation or activation of CD8+ T cells have been found to be affected by epigenetic modifications. Various cytokines, transcription factors, and other regulatory molecules have been found to be differentially methylated in CD8+ T cells in autoimmune diseases. These genes are involved in T cell regulation, including interferons, interleukin (IL),tumor necrosis factor (TNF), as well as linker for activation of T cells (LAT), cytotoxic T-lymphocyte–associated antigen 4 (CTLA4), and adapter proteins. MiRNAs also play a role in the pathogenesis of these diseases and several known miRNAs that are involved in these diseases have also been shown to play a role in CD8+ regulation.

Antigen receptor control of methionine metabolism in T cells

Immune activated T lymphocytes modulate the activity of key metabolic pathways to support the transcriptional reprograming and reshaping of cell proteomes that permits effector T cell differentiation. The present study uses high resolution mass spectrometry and metabolic labelling to explore how murine T cells control the methionine cycle to produce methyl donors for protein and nucleotide methylations. We show that antigen receptor engagement controls flux through the methionine cycle and RNA and histone methylations. We establish that the main rate limiting step for protein synthesis and the methionine cycle is control of methionine transporter expression. Only T cells that respond to antigen to upregulate and sustain methionine transport are supplied with methyl donors that permit the dynamic nucleotide methylations and epigenetic reprogramming that drives T cell differentiation. These data highlight how the regulation of methionine transport licenses use of methionine for multiple fundamental processes that drive T lymphocyte proliferation and differentiation.

Memory CD8 T cell inflation vs tissue-resident memory T cells: Same patrollers, same controllers?

The induction of long-lived populations of memory T cells residing in peripheral tissues is of considerable interest for T cell-based vaccines, as they can execute immediate effector functions and thus provide protection in case of pathogen encounter at mucosal and barrier sites. Cytomegalovirus (CMV)-based vaccines support the induction and accumulation of a large population of effector memory CD8 T cells in peripheral tissues, in a process called memory inflation. Tissue-resident memory (T_RM ) T cells, induced by various infections and vaccination regimens, constitute another subset of memory cells that take long-term residence in peripheral tissues. Both memory T cell subsets have evoked substantial interest in exploitation for vaccine purposes. However, a direct comparison between these two peripheral tissue-localizing memory T cell subsets with respect to their short- and long-term ability to provide protection against heterologous challenge is pending. Here, we discuss communalities and differences between T_RM and inflationary CD8 T cells with respect to their development, maintenance, function, and protective capacity. In addition, we discuss differences and similarities between the transcriptional profiles of T_RM and inflationary T cells, supporting the notion that they are distinct memory T cell populations.

Epigenetic programming of T cells impacts immune reconstitution in hematopoietic stem cell transplant recipients

Immune reconstitution following hematopoietic stem cell transplantation (HSCT) is critical in preventing harmful sequelae in recipients with cytomegalovirus (CMV) infection. To understand the molecular mechanisms underlying immune reconstitution kinetics, we profiled the transcriptome-chromatin accessibility landscape of CMV-specific CD8⁺ T cells from HCST recipients with different immune reconstitution efficiencies. CMV-specific T cells from HSCT recipients with stable antiviral immunity expressed higher levels of interferon/defense response and cell cycle genes in an interconnected network involving PI3KCG, STAT5B, NFAT, RBPJ, and lower HDAC6, increasing chromatin accessibility at the enhancer regions of immune and T-cell receptor signaling pathway genes. By contrast, the transcriptional and epigenomic signatures of CMV-specific T cells from HSCT recipients with unstable immune reconstitution showed commonalities with T-cell responses in other nonresolving chronic infections. These signatures included higher levels of EGR and KLF factors that, along with lower JARID2 expression, maintained higher accessibility at promoter and CpG-rich regions of genes associated with apoptosis. Furthermore, epigenetic targeting via inhibition of HDAC6 or JARID2 enhanced the transcription of genes associated with differential responses, suggesting that drugs targeting epigenomic modifiers may have therapeutic potential for enhancing immune reconstitution in HSCT recipients. Taken together, these analyses demonstrate that transcription factors and chromatin modulators create different chromatin accessibility landscapes in T cells of HSCT recipients that not only affect immediate gene expression but also differentially prime cells for responses to additional signals. Epigenetic therapy may be a promising strategy to promote immune reconstitution in HSCT recipients.

Therapeutic Cancer Vaccines-T Cell Responses and Epigenetic Modulation

There is great interest in developing efficient therapeutic cancer vaccines, as this type of therapy allows targeted killing of tumor cells as well as long-lasting immune protection. High levels of tumor-infiltrating CD8⁺ T cells are associated with better prognosis in many cancers, and it is expected that new generation vaccines will induce effective production of these cells. Epigenetic mechanisms can promote changes in host immune responses, as well as mediate immune evasion by cancer cells. Here, we focus on epigenetic modifications involved in both vaccine-adjuvant-generated T cell immunity and cancer immune escape mechanisms. We propose that vaccine-adjuvant systems may be utilized to induce beneficial epigenetic modifications and discuss how epigenetic interventions could improve vaccine-based therapies. Additionally, we speculate on how, given the unique nature of individual epigenetic landscapes, epigenetic mapping of cancer progression and specific subsequent immune responses, could be harnessed to tailor therapeutic vaccines to each patient.

Aging of Antiviral CD8+ Memory T Cells Fosters Increased Survival, Metabolic Adaptations, and Lymphoid Tissue Homing

Aging of established antiviral T cell memory can foster a series of progressive adaptations that paradoxically improve rather than compromise protective CD8⁺ T cell immunity. We now provide evidence that this gradual evolution, the pace of which is contingent on the precise context of the primary response, also impinges on the molecular mechanisms that regulate CD8⁺ memory T cell (T_M) homeostasis. Over time, CD8⁺ T_M generated in the wake of an acute infection with the natural murine pathogen lymphocytic choriomeningitis virus become more resistant to apoptosis and acquire enhanced cytokine responsiveness without adjusting their homeostatic proliferation rates; concurrent metabolic adaptations promote increased CD8⁺ T_M quiescence and fitness but also impart the reacquisition of a partial effector-like metabolic profile; and a gradual redistribution of aging CD8⁺ T_M from blood and nonlymphoid tissues to lymphatic organs results in CD8⁺ T_M accumulations in bone marrow, splenic white pulp, and, particularly, lymph nodes. Altogether, these data demonstrate how temporal alterations of fundamental homeostatic determinants converge to render aged CD8⁺ T_M poised for greater recall responses.

Neonatal influenza-specific effector CTLs retain elevated CD31 levels at the site of infection and have decreased IFN-γ production

The underlying mechanisms that regulate neonatal immune suppression are poorly characterized. CD31 (PECAM1) is highly expressed on neonatal lymphocytes and is a known modulator of TCR signaling. To further characterize the role of CD31 in the neonatal CTL response, 3-d and 7-d-old murine neonates were infected with influenza virus and compared to adults. The majority of the pulmonary viral-specific CTLs in the 3-d-old murine neonate retain CD31 expression, whereas adult CTLs have decreased CD31 expression. In addition, CD31⁺ neonatal viral-specific CTLs demonstrate decreased IFN-γ production, decreased proliferative capacity, and increased likelihood of death. At the peak of infection, sorted neonatal effector CTLs continue to transcribe CD31, indicating a developmental regulation of expression. To explore potential mechanisms for this reduced function, we compared the expression of the transcription factors Eomesodermin (Eomes) and T-bet; there was a significant increase in Eomes paired with a reduction in T-bet in CD31⁺ neonatal effector CTLs in the lung. Furthermore, in vitro stimulated neonatal CTLs significantly reduce IFN-γ production upon CD31 signaling. Altogether, these data indicate that neonatal CTLs may retain elevated levels of CD31 to maintain peripheral T cell suppression during the bridge to ex utero life.

Fates of CD8+ T cells in Tumor Microenvironment

Studies have reported a positive correlation between elevated CD8+ T cells in the tumor microenvironment (TME) and good prognosis in cancer. However, the mechanisms linking T cell tumor-infiltration and tumor rejection are yet to be fully understood. The cells and factors of the TME facilitate tumor development in various ways. CD8+ T cell function is influenced by a number of factors, including CD8+ T cell trafficking and localization into tumor sites; as well as CD8+ T cell growth and differentiation. This review highlights recent literature as well as currently evolving concepts regarding the fates of CD8+ T cells in the TME from three different aspects CD8+ T cell trafficking, differentiation and function. A thorough understanding of factors contributing to the fates of CD8+ T cells will allow researchers to develop new strategies and improve on already existing strategies to facilitate CD8+ T cell mediated anti-tumor function, impede T cell dysfunction and modulate the TME into a less immunosuppressive TME.