SATB1 Expression Governs Epigenetic Repression of PD-1 in Tumor-Reactive T Cells

Converged Rab37/IL-6 trafficking and STAT3/PD-1 transcription axes elicit an immunosuppressive lung tumor microenvironment

Background: Increased IL-6 level, M2 macrophages and PD-1⁺CD8⁺ T cells in tumor microenvironments (TME) have been identified to correlate with resistance to checkpoint blockade immunotherapy, yet the mechanism remains poorly understood. Rab small GTPase-mediated trafficking of cytokines is critical in immuno-modulation. We have previously reported dysregulation of Rab37 in lung cancer cells, whereas the roles of Rab37 in tumor-infiltrating immune cells and cancer immunotherapy are unclear.

Methods: The tumor growth of the syngeneic mouse allograft in wild type or Rab37 knockout mice was analyzed. Imaging analyses and vesicle isolation were conducted to determine Rab37-mediated IL-6 secretion. STAT3 binding sites at PD-1 promoter in T cells were identified by chromatin immunoprecipitation assay. Multiplex fluorescence immunohistochemistry was performed to detect the protein level of Rab37, IL-6 and PD-1 and localization of the tumor-infiltrating immune cells in allografts from mice or tumor specimens from lung cancer patients.

Results: We revealed that Rab37 regulates the secretion of IL-6 in a GTPase-dependent manner in macrophages to trigger M2 polarization. Macrophage-derived IL-6 promotes STAT3-dependent PD-1 mRNA expression in CD8⁺ T cells. Clinically, tumors with high stromal Rab37 and IL-6 expression coincide with tumor infiltrating M2-macrophages and PD1⁺CD8⁺ T cells that predicts poor prognosis in lung cancer patients. In addition, lung cancer patients with an increase in plasma IL-6 level are found to be associated with immunotherapeutic resistance. Importantly, combined blockade of IL-6 and CTLA-4 improves survival of tumor-bearing mice by reducing infiltration of PD1⁺CD8⁺ T cells and M2 macrophages in TME.

Conclusions: Rab37/IL-6 trafficking pathway links with IL-6/STAT3/PD-1 transcription regulation to foster an immunosuppressive TME and combined IL-6/CTLA-4 blockade therapy exerts potent anti-tumor efficacy.

Human CD8 T-stem cell memory subsets phenotypic and functional characterization are defined by expression of CD122 or CXCR3

Long-lived T-memory stem cells (T_SCM ) are key to both naturally occurring and vaccine-conferred protection against infection. These cells are characterized by the CD45RA⁺ CCR7⁺ CD95⁺ phenotype. Significant heterogeneity within the T_SCM population is recognized, but distinguishing surface markers and functional characterization of potential subsets are lacking. Human CD8 T_SCM subsets were identified in healthy subjects who had been previously exposed to CMV or Influenza (Flu) virus in flow cytometry by expression of CD122 or CXCR3, and then characterized in proliferation, multipotency, self-renewal, and intracellular cytokine production (TNF-α, IL-2, IFN-γ), together with transcriptomic profiles. The T_SCM CD122^hi -expressing subset (versus CD122^lo ) demonstrated greater proliferation, greater multipotency, and enhanced polyfunctionality with higher frequencies of triple positive (TNF-α, IL-2, IFN-γ) cytokine-producing cells upon exposure to recall antigen. The T_SCM CXCR3^lo subpopulation also had increased proliferation and polyfunctional cytokine production. Transcriptomic analysis further showed that the T_SCM CD122^hi population had increased expression of activation and homing molecules, such as Ccr6, Cxcr6, Il12rb, and Il18rap, and downregulated cell proliferation inhibitors, S100A8 and S100A9. These data reveal that the T_SCM CD122^hi phenotype is associated with increased proliferation, enhanced multipotency and polyfunctionality with an activated memory-cell like transcriptional profile, and hence, may be favored for induction by immunization and for adoptive immunotherapy.

Tackling tumor microenvironment through epigenetic tools to improve cancer immunotherapy

BACKGROUND

Epigenetic alterations are known contributors to cancer development and aggressiveness. Additional to alterations in cancer cells, aberrant epigenetic marks are present in cells of the tumor microenvironment, including lymphocytes and tumor-associated macrophages, which are often overlooked but known to be a contributing factor to a favorable environment for tumor growth. Therefore, the main aim of this review is to give an overview of the epigenetic alterations affecting immune cells in the tumor microenvironment to provoke an immunosuppressive function and contribute to cancer development. Moreover, immunotherapy is briefly discussed in the context of epigenetics, describing both its combination with epigenetic drugs and the need for epigenetic biomarkers to predict response to immune checkpoint blockage.

MAIN BODY

Combining both topics, epigenetic machinery plays a central role in generating an immunosuppressive environment for cancer growth, which creates a barrier for immunotherapy to be successful. Furthermore, epigenetic-directed compounds may not only affect cancer cells but also immune cells in the tumor microenvironment, which could be beneficial for the clinical response to immunotherapy.

CONCLUSION

Thus, modulating epigenetics in combination with immunotherapy might be a promising therapeutic option to improve the success of this therapy. Further studies are necessary to (1) understand in depth the impact of the epigenetic machinery in the tumor microenvironment; (2) how the epigenetic machinery can be modulated according to tumor type to increase response to immunotherapy and (3) find reliable biomarkers for a better selection of patients eligible to immunotherapy.

CD45RB Status of CD8+ T Cell Memory Defines T Cell Receptor Affinity and Persistence

The identity of CD45 isoforms on the T cell surface changes following the activation of naive T cells and impacts intracellular signaling. In this study, we find that the anti-viral memory CD8⁺ T pool is unexpectedly comprised of both CD45RB^hi and CD45RB^lo populations. Relative to CD45RB^lo memory T cells, CD45RB^hi memory T cells have lower affinity and display greater clonal diversity, as well as a persistent CD27^hi phenotype. The CD45RB^hi memory population displays a homeostatic survival advantage in vivo relative to CD45RB^lo memory, and long-lived high-affinity cells that persisted long term convert from CD45RB^lo to CD45RB^hi. Human CD45RO⁺ memory is comprised of both CD45RB^hi and CD45RB^lo populations with distinct phenotypes, and antigen-specific memory to two viruses is predominantly CD45RB^hi. These data demonstrate that CD45RB status is distinct from the conventional central/effector T cell memory classification and has potential utility for monitoring and characterizing pathogen-specific CD8⁺ T cell responses.

Hyper-Progressive Disease: The Potential Role and Consequences of T-Regulatory Cells Foiling Anti-PD-1 Cancer Immunotherapy

Antibody-mediated disruption of the programmed cell death protein 1 (PD-1) pathway has brought much success to the fight against cancer. Nevertheless, a significant proportion of patients respond poorly to anti-PD-1 treatment. Cases of accelerated and more aggressive forms of cancer following therapy have also been reported. Termed hyper-progressive disease (HPD), this phenomenon often results in fatality, thus requires urgent attention. Among possible causes of HPD, regulatory T-cells (Tregs) are of suspect due to their high expression of PD-1, which modulates Treg activity. Tregs are a subset of CD4⁺ T-cells that play a non-redundant role in the prevention of autoimmunity and is functionally dependent on the X chromosome-linked transcription factor FoxP3. In cancer, CD4⁺FoxP3⁺ Tregs migrate to tumors to suppress anti-tumor immune responses, allowing cancer cells to persist. Hence, Treg accumulation in tumors is associated with poor prognosis. In mice, the anti-tumor efficacy of anti-PD-1 can be enhanced by depleting Tregs. This suggests Tregs pose resistance to anti-PD-1 therapy. In this article, we review the relevant Treg functions that suppress tumor immunity and the potential effects anti-PD-1 could have on Tregs which are counter-productive to the treatment of cancer, occasionally causing HPD.

Hyper-Progressive Disease: The Potential Role and Consequences of T-Regulatory Cells Foiling Anti-PD-1 Cancer Immunotherapy

Antibody-mediated disruption of the programmed cell death protein 1 (PD-1) pathway has brought much success to the fight against cancer. Nevertheless, a significant proportion of patients respond poorly to anti-PD-1 treatment. Cases of accelerated and more aggressive forms of cancer following therapy have also been reported. Termed hyper-progressive disease (HPD), this phenomenon often results in fatality, thus requires urgent attention. Among possible causes of HPD, regulatory T-cells (Tregs) are of suspect due to their high expression of PD-1, which modulates Treg activity. Tregs are a subset of CD4+ T-cells that play a non-redundant role in the prevention of autoimmunity and is functionally dependent on the X chromosome-linked transcription factor FoxP3. In cancer, CD4+FoxP3+ Tregs migrate to tumors to suppress anti-tumor immune responses, allowing cancer cells to persist. Hence, Treg accumulation in tumors is associated with poor prognosis. In mice, the anti-tumor efficacy of anti-PD-1 can be enhanced by depleting Tregs. This suggests Tregs pose resistance to anti-PD-1 therapy. In this article, we review the relevant Treg functions that suppress tumor immunity and the potential effects anti-PD-1 could have on Tregs which are counter-productive to the treatment of cancer, occasionally causing HPD.

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.

Two subsets of stem-like CD8+ memory T cell progenitors with distinct fate commitments in humans

T cell memory relies on the generation of antigen-specific progenitors with stem-like properties. However, the identity of these progenitors has remained unclear, precluding a full understanding of the differentiation trajectories that underpin the heterogeneity of antigen-experienced T cells. We used a systematic approach guided by single-cell RNA-sequencing data to map the organizational structure of the human CD8+ memory T cell pool under physiological conditions. We identified two previously unrecognized subsets of clonally, epigenetically, functionally, phenotypically and transcriptionally distinct stem-like CD8+ memory T cells. Progenitors lacking the inhibitory receptors programmed death-1 (PD-1) and T cell immunoreceptor with Ig and ITIM domains (TIGIT) were committed to a functional lineage, whereas progenitors expressing PD-1 and TIGIT were committed to a dysfunctional, exhausted-like lineage. Collectively, these data reveal the existence of parallel differentiation programs in the human CD8+ memory T cell pool, with potentially broad implications for the development of immunotherapies and vaccines.

Metabolic and epigenetic regulation of T-cell exhaustion

Current immunotherapies yield remarkable clinical outcomes by boosting the power of host immunity in cancer cell elimination and viral clearance. However, after prolonged antigen exposure, CD8⁺ T cells differentiate into a special differentiation state known as T-cell exhaustion, which poses one of the major hurdles to antiviral and antitumor immunity during chronic viral infection and tumour development. Growing evidence indicates that exhausted T cells undergo metabolic insufficiency with altered signalling cascades and epigenetic landscapes, which dampen effector immunity and cause poor responsiveness to immune-checkpoint-blockade therapies. How metabolic stress affects T-cell exhaustion remains unclear; therefore, in this Review, we summarize current knowledge of how T-cell exhaustion occurs, and discuss how metabolic insufficiency and prolonged stress responses may affect signalling cascades and epigenetic reprogramming, thus locking T cells into an exhausted state via specialized differentiation programming.

BTN3A1 governs antitumor responses by coordinating αβ and γδ T cells

Gamma delta (γδ) T cells infiltrate most human tumors, but current immunotherapies fail to exploit their in situ major histocompatibility complex-independent tumoricidal potential. Activation of γδ T cells can be elicited by butyrophilin and butyrophilin-like molecules that are structurally similar to the immunosuppressive B7 family members, yet how they regulate and coordinate αβ and γδ T cell responses remains unknown. Here, we report that the butyrophilin BTN3A1 inhibits tumor-reactive αβ T cell receptor activation by preventing segregation of N-glycosylated CD45 from the immune synapse. Notably, CD277-specific antibodies elicit coordinated restoration of αβ T cell effector activity and BTN2A1-dependent γδ lymphocyte cytotoxicity against BTN3A1⁺ cancer cells, abrogating malignant progression. Targeting BTN3A1 therefore orchestrates cooperative killing of established tumors by αβ and γδ T cells and may present a treatment strategy for tumors resistant to existing immunotherapies.

Epigenetics in modulating immune functions of stromal and immune cells in the tumor microenvironment

Epigenetic regulation of gene expression in cancer cells has been extensively studied in recent decades, resulting in the FDA approval of multiple epigenetic agents for treating different cancer types. Recent studies have revealed novel roles of epigenetic dysregulation in altering the phenotypes of immune cells and tumor-associated stromal cells, including fibroblasts and endothelial cells. As a result, epigenetic dysregulation of these cells reshapes the tumor microenvironment (TME), changing it from an antitumor environment to an immunosuppressive environment. Here, we review recent studies demonstrating how specific epigenetic mechanisms drive aspects of stromal and immune cell differentiation with implications for the development of solid tumor therapeutics, focusing on the pancreatic ductal adenocarcinoma (PDA) TME as a representative of solid tumors. Due to their unique ability to reprogram the TME into a more immunopermissive environment, epigenetic agents have great potential for sensitizing cancer immunotherapy to augment the antitumor response, as an immunopermissive TME is a prerequisite for the success of cancer immunotherapy but is often not developed with solid tumors. The idea of combining epigenetic agents with cancer immunotherapy has been tested both in preclinical settings and in multiple clinical trials. In this review, we highlight the basic biological mechanisms underlying the synergy between epigenetic therapy and immunotherapy and discuss current efforts to translate this knowledge into clinical benefits for patients.

Differential SATB1 Expression Reveals Heterogeneity of Cutaneous T-Cell Lymphoma

SATB1 is an important T-cell specific chromatin organizer in cutaneous T-cell lymphoma, whereas its expression and function in mycosis fungoides (MF) remain ambiguous. Our study aimed to investigate the clinicopathological significance of SATB1 in a cohort of 170 patients with MF. SATB1 expression was heterogeneous among the patients with MF in each clinical stage. High SATB1 expression was associated with epidermal hyperplasia, eosinophil infiltration, less large-cell transformation, and favorable prognosis in MF cases. SATB1 and CD30 coexpression distinguished cutaneous CD30⁺ lymphoproliferative disorders from MF large-cell transformation. SATB1 silencing in MF lines showed that SATB1 upregulated the genes involved in eosinophil recruitment, including signal transducer and activator of transcription 3 and IL13, and downregulated the genes in cell-cycle progression, which may explain the inferior prognosis for low SATB1-expressing cases. Moreover, SATB1 was inversely correlated with PD-1 expression, indicating an exhausted status of SATB1-negative malignant T cells. SATB1 was positively correlated with toll-like receptors expression, suggesting innate immune activation in high SATB1-expressing MF cases. Therefore, variable SATB1 expression promotes heterogeneity in pathology and clinical outcome of patients with MF.

Unraveling exhaustion in adaptive and conventional NK cells

Immune exhaustion in T cells significantly impacts their ability to control malignancies and infections, and its discovery has led to revolutionary therapies for cancer in the form of checkpoint blockade. NK cells, like T cells, are lymphocytes that recognize virally infected and malignantly transformed cells. However, it remains unclear if NK cells are similarly susceptible to exhaustion. In this review, the aims are to summarize what is currently known and to identify key areas of variability that skew the scientific literature on NK cell exhaustion. A lack of consensus on the defining features of NK cell dysfunctional states such as senescence, suppression, and exhaustion has made a comparison between studies difficult. There are also significant differences in the biology of NK cell subsets with long-lived, adaptive NK cells sharing an epigenetic signature closer to memory CD8⁺  T cells than to conventional NK cells. Very different checkpoint receptor expression and effector functions have been shown in adaptive versus conventional NK cells chronically exposed to activating signals. Adaptive NK cells develop in individuals with cytomegalovirus (CMV) infection and well over half of the human population worldwide is CMV seropositive by adulthood. Despite this high prevalence, most studies do not account or control for this population. This may contribute to some of the variability reported in the literature on checkpoint receptor expression on NK cells. In this review, the protective role that exhaustion plays in T cells will also be discussed and the evidence for a similar phenomenon in NK cells will be examined.

Comprehensive Analysis of PD-1 Gene Expression, Immune Characteristics and Prognostic Significance in 1396 Glioma Patients

Background

Programmed cell death protein-1 (PD-1) blockade therapy is one of the most remarkable immunotherapy strategies in many solid tumors, excluding glioma. The PD-1 expression, immune characteristics, and prognosis relevance in glioma remain poorly understood.

Patients and Methods

RNA sequencing (RNA-seq) and mRNA microarray data were obtained for 325 and 301 glioma patients, respectively, from the Chinese Glioma Genome Atlas (CGGA) database. We analyzed the expression profile of PDCD1 (encoding PD-1) according to the different grade, isocitrate dehydrogenase (IDH) mutation status, and molecular subtype of glioblastoma. Gene ontology (GO) analyses were performed to explore biological processes of PD-1-related genes. Survival analysis was conducted using the Kaplan–Meier method. The findings were validated using The Cancer Genome Atlas (TCGA) RNA-seq data from 697 glioma samples. We also confirmed the PDCD1 gene expression feature and survival relevance in our own cohort of 73 glioma patients. R language was used for statistical analysis and generating figures.

Results

PDCD1 was enriched in glioblastoma (WHO, grade IV), IDH wild-type glioma and mesenchymal glioblastoma in CGGA and TCGA datasets; similar results were validated in our own patient cohort. GO analysis revealed that PDCD1-related genes were involved in inflammation immune responses and T cell-mediated immune responses in glioma. Circos plots indicated that PDCD1 was positively associated with CD28, ICOS, and the inhibitory checkpoint molecules CTLA4, HAVCR2, TIGIT, and LAG3. Patients with PDCD1 upregulation had much shorter overall survival.

Conclusion

PDCD1 upregulation was found in more malignant phenotypes of glioma and indicated a worse prognosis. Immunotherapy of targeting PD-1 or combined with other checkpoint molecules (eg, TIM-3, LAG-3, or TIGIT) blockade may represent a promising treatment strategy for glioma.

Special AT-rich Sequence Binding-Protein 1 (SATB1) Correlates with Immune Infiltration in Breast, Head and Neck, and Prostate Cancer

BACKGROUND SATB1 is essential in gene regulation and associates with T cell development. Aberrant SATB1 expression has been reported in various neoplasms. However, correlations between SATB1 and tumor immune infiltration and prognosis in malignancies still remains unclear. MATERIAL AND METHODS We used Oncomine and the Tumor Immune Estimation Resource database to explore the expression of SATB1 in cancers. In addition, Kaplan-Meier plotter, PrognoScan, and Gene Expression Profiling Interactive Analysis were also used to assess the effects of SATB1 on clinical prognosis. Furthermore, correlations between cancer immune infiltration and SATB1 were analyzed via Tumor Immune Estimation Resource. RESULTS The results demonstrated that SATB1 correlates with prognosis in different types of cancers, such as breast invasive carcinoma (BRAC), head and neck cancer (HNSC), and prostate adenocarcinoma (PRAD). Decreased expression of SATB1 was associated with poor overall and progression-free survival of BRAC patients with positive estrogen receptor (ER) as well as mutated TP53. In addition, B cells, CD8+ T cells, CD4+ T cells, macrophages, neutrophils, and dendritic cells infiltration in BRAC, HNSC, and PRAD were also correlated with SATB1 expression level. Moreover, we found strong correlations between SATB1 and various immune markers for BRAC, HNSC, and PRAD. CONCLUSIONS In BRAC, HNSC, and PRAD patients, SATB1 has potential to serve as a prognostic indicator for predicting tumor immune infiltration and prognosis.

Independent Prognostic Value of Intratumoral Heterogeneity and Immune Response Features by Automated Digital Immunohistochemistry Analysis in Early Hormone Receptor-Positive Breast Carcinoma

Immunohistochemistry (IHC) for ER, PR, HER2, and Ki67 is used to predict outcome and therapy response in breast cancer patients. The current IHC assessment, visual or digital, is based mostly on global biomarker expression levels in the tissue sample. In our study, we explored the prognostic value of digital image analysis of conventional breast cancer IHC biomarkers supplemented with their intratumoral heterogeneity and tissue immune response indicators. Surgically excised tumor samples from 101 female patients with hormone receptor-positive breast cancer (HRBC) were stained for ER, PR, HER2, Ki67, SATB1, CD8, and scanned at 20x. Digital image analysis was performed using the HALO™ platform. Subsequently, hexagonal tiling was used to compute intratumoral heterogeneity indicators for ER, PR and Ki67 expression. Multiple Cox regression analysis revealed three independent predictors of the patient's overall survival: Haralick's texture entropy of PR (HR = 0.19, p = 0.0005), Ki67 Ashman's D bimodality (HR = 3.0, p = 0.01), and CD8+SATB1+ cell density in tumor tissue (HR = 0.32, p = 0.02). Remarkably, the PR and Ki67 intratumoral heterogeneity indicators were prognostically more informative than the rates of their expression. In particular, a distinct non-linear relationship between the rate of PR expression and its intratumoral heterogeneity was observed and revealed a non-linear prognostic effect of PR expression. The independent prognostic significance of CD8+SATB1+ cells infiltrating the tumor could indicate their role in anti-tumor immunity. In conclusion, we suggest that prognostic modeling, based entirely on the computational image-based IHC biomarkers, is possible in HRBC patients. The intratumoral heterogeneity and immune response indicators outperformed both conventional breast cancer IHC and clinicopathological variables while markedly increasing the power of the model.

Humoral immune responses: Unsung heroes of the war on cancer

Solid cancers progress from primordial lesions through complex interactions between tumor-promoting and anti-tumor immune cell types, ultimately leading to the orchestration of humoral and T cell adaptive immune responses, albeit in an immunosuppressive environment. B cells infiltrating most established tumors have been associated with a dual role: Some studies have associated antibodies produced by tumor-associated B cells with the promotion of regulatory activities on myeloid cells, and also with direct immunosuppression through the production of IL-10, IL-35 or TGF-β. In contrast, recent studies in multiple human malignancies identify B cell responses with delayed malignant progression and coordinated T cell protective responses. This includes the elusive role of Tertiary Lymphoid Structures identified in many human tumors, where the function of B cells remains unknown. Here, we discuss emerging data on the dual role of B cell responses in the pathophysiology of human cancer, providing a perspective on future directions and possible novel interventions to restore the coordinated action of both branches of the adaptive immune response, with the goal of maximizing immunotherapeutic effectiveness.

Regulation of PD-1 in T cells for cancer immunotherapy

Study of the molecular mechanisms underlying cancer immune escape is one of the core issues in immuno-oncology research. Cancer cells can evade T cell cytotoxicity by exploiting the upregulation of T cell inhibitory receptors on T cells and their ligands on cancer cells. These upregulated proteins include the inhibitory receptor programmed cell-death protein 1 (PD-1) and its ligand programmed cell death 1 ligand 1 (PD-L1), which can induce T cell exhaustion and reduce T cell activation. Characterizing PD-1 regulation will help to elucidate the molecular mechanisms underlying T cell exhaustion and improve cancer treatment. Recent studies have found that tumor cells regulate PD-1 during gene transcription, post-transcriptional regulation, and post-translational modification and influence the effects of the anticancer immune response by targeting PD-1. In this review,we summarize the mechanisms of PD-1 regulation in T cells.

Current advances in PD-1/PD-L1 axis-related tumour-infiltrating immune cells and therapeutic regimens in glioblastoma

Glioblastoma (GBM) is the most common malignant tumour in the brain, and current treatments are not curative and cannot control recurrence. This limitation indirectly places immunotherapy at the focus of translational GBM research. Many studies on the PD-1/PD-L1 axis in GBM are ongoing, and the immunosuppressive mechanism of PD-1/PD-L1 in GBM is different from that in other solid tumours. This review focuses on the effect of the PD-1/PD-L1 axis on infiltrating immune cells in the suppressive GBM immune microenvironment and summarizes the recent progress in PD-1/PD-L1 axis-related therapies reported in preclinical and clinical GBM studies, providing a reference for the systematic study of PD-1/PD-L1 axis-related anti-GBM immunity.

Microtubule-Driven Stress Granule Dynamics Regulate Inhibitory Immune Checkpoint Expression in T Cells

Despite the clinical success of blocking inhibitory immune checkpoint receptors such as programmed cell death-1 (PD-1) in cancer, the mechanisms controlling the expression of these receptors have not been fully elucidated. Here, we identify a post-transcriptional mechanism regulating PD-1 expression in T cells. Upon activation, the PDCD1 mRNA and ribonucleoprotein complexes coalesce into stress granules that require microtubules and the kinesin 1 molecular motor to proceed to translation. Hence, PD-1 expression is highly sensitive to microtubule or stress granule inhibitors targeting this pathway. Evidence from healthy donors and cancer patients reveals a common regulation for the translation of CTLA4, LAG3, TIM3, TIGIT, and BTLA but not of the stimulatory co-receptors OX40, GITR, and 4-1BB mRNAs. In patients, disproportionality analysis of immune-related adverse events for currently used microtubule drugs unveils a significantly higher risk of autoimmunity. Our findings reveal a fundamental mechanism of immunoregulation with great importance in cancer immunotherapy.

Epigenetic modifiers as new immunomodulatory therapies in solid tumours

Background

Immune therapies have revolutionized cancer treatment over the last few years by allowing improvements in overall survival. However, the majority of patients is still primary or secondary resistant to such therapies, and enhancing sensitivity to immune therapies is therefore crucial to improve patient outcome. Several recent lines of evidence suggest that epigenetic modifiers have intrinsic immunomodulatory properties, which could be of therapeutic interest.

Material and methods

We reviewed preclinical evidence and clinical studies which describe or exploit immunomodulatory properties of epigenetic agents. Experimental approaches, clinical applicability and corresponding ongoing clinical trials are described.

Results

Several epigenetic modifiers, such as histone deacetylase inhibitors, DNA methyl transferase inhibitors, bromodomain inhibitors, lysine-specific histone demethylase 1 inhibitors and enhancer of zeste homolog 2 inhibitors, display intrinsic immunomodulatory properties. The latter can be achieved through the action of these drugs either on cancer cells (e.g. presentation and generation of neoantigens, induction of immunogenic cell death, modulation of cytokine secretion), on immune cells (e.g. linage, differentiation, activation status and antitumor capability), or on components of the microenvironment (e.g. regulatory T cells and macrophages). Several promising combinations, notably with immune checkpoint blockers or adoptive T-cell therapy, can be envisioned. Dedicated clinically relevant approaches for patient selection and trial design will be required to optimally develop such combinations.

Conclusion

In an era where immune therapies are becoming a treatment backbone in many tumour types, epigenetic modifiers could play a crucial role in modulating tumours' immunogenicity and sensitivity to immune agents. Optimal trial design, including window of opportunity trials, will be key in the success of this approach, and clinical evaluation is ongoing.

Exosomes Produced by Mesenchymal Stem Cells Drive Differentiation of Myeloid Cells into Immunosuppressive M2-Polarized Macrophages in Breast Cancer

Tumor-associated macrophages are major contributors to malignant progression and resistance to immunotherapy, but the mechanisms governing their differentiation from immature myeloid precursors remain incompletely understood. In this study, we demonstrate that exosomes secreted by human and mouse tumor-educated mesenchymal stem cells (MSCs) drive accelerated breast cancer progression by inducing differentiation of monocytic myeloid-derived suppressor cells into highly immunosuppressive M2-polarized macrophages at tumor beds. Mechanistically, MSC-derived exosomes but not exosomes from tumor cells contain TGF-β, C1q, and semaphorins, which promote myeloid tolerogenic activity by driving PD-L1 overexpression in both immature myelomonocytic precursors and committed CD206⁺ macrophages and by inducing differentiation of MHC class II⁺ macrophages with enhanced l-Arginase activity and IL-10 secretion at tumor beds. Accordingly, administration of tumor-associated murine MSC-derived exosomes accelerates tumor growth by dampening antitumor immunity, and macrophage depletion eliminates exosome-dependent differences in malignant progression. Our results unveil a new role for MSC-derived exosomes in the differentiation of myeloid-derived suppressor cells into macrophages, which governs malignant growth.

Defining 'T cell exhaustion'

'T cell exhaustion' is a broad term that has been used to describe the response of T cells to chronic antigen stimulation, first in the setting of chronic viral infection but more recently in response to tumours. Understanding the features of and pathways to exhaustion has crucial implications for the success of checkpoint blockade and adoptive T cell transfer therapies. In this Viewpoint article, 18 experts in the field tell us what exhaustion means to them, ranging from complete lack of effector function to altered functionality to prevent immunopathology, with potential differences between cancer and chronic infection. Their responses highlight the dichotomy between terminally differentiated exhausted T cells that are TCF1^- and the self-renewing TCF1⁺ population from which they derive. These TCF1⁺ cells are considered by some to have stem cell-like properties akin to memory T cell populations, but the developmental relationships are unclear at present. Recent studies have also highlighted an important role for the transcriptional regulator TOX in driving the epigenetic enforcement of exhaustion, but key questions remain about the potential to reverse the epigenetic programme of exhaustion and how this might affect the persistence of T cell populations.

VirtualCytometry: a webserver for evaluating immune cell differentiation using single-cell RNA sequencing data

MOTIVATION

The immune system has diverse types of cells that are differentiated or activated via various signaling pathways and transcriptional regulation upon challenging conditions. Immunophenotyping by flow and mass cytometry are the major approaches for identifying key signaling molecules and transcription factors directing the transition between the functional states of immune cells. However, few proteins can be evaluated by flow cytometry in a single experiment, preventing researchers from obtaining a comprehensive picture of the molecular programs involved in immune cell differentiation. Recent advances in single-cell RNA sequencing (scRNA-seq) have enabled unbiased genome-wide quantification of gene expression in individual cells on a large scale, providing a new and versatile analytical pipeline for studying immune cell differentiation.

RESULTS

We present VirtualCytometry, a web-based computational pipeline for evaluating immune cell differentiation by exploiting cell-to-cell variation in gene expression with scRNA-seq data. Differentiating cells often show a continuous spectrum of cellular states rather than distinct populations. VirtualCytometry enables the identification of cellular subsets for different functional states of differentiation based on the expression of marker genes. Case studies have highlighted the usefulness of this subset analysis strategy for discovering signaling molecules and transcription factors for human T-cell exhaustion, a state of T-cell dysfunction, in tumor and mouse dendritic cells activated by pathogens. With more than 226 scRNA-seq datasets precompiled from public repositories covering diverse mouse and human immune cell types in normal and disease tissues, VirtualCytometry is a useful resource for the molecular dissection of immune cell differentiation.

AVAILABILITY AND IMPLEMENTATION

www.grnpedia.org/cytometry.

Transcriptomic analysis of human IL-7 receptor alpha low and high effector memory CD8+ T cells reveals an age-associated signature linked to influenza vaccine response in older adults

Here, we investigated the relationship of the age‐associated expansion of IL‐7 receptor alpha low (IL‐7Rα^low) effector memory (EM) CD8⁺ T cells with the global transcriptomic profile of peripheral blood cells in humans. We found 231 aging signature genes of IL‐7Rα^low EM CD8⁺ T cells that corresponded to 15% of the age‐associated genes (231/1,497) reported by a meta‐analysis study on human peripheral whole blood from approximately 15,000 individuals, having high correlation with chronological age. These aging signature genes were the target genes of several transcription factors including MYC, SATB1, and BATF, which also belonged to the 231 genes, supporting the upstream regulatory role of these transcription factors in altering the gene expression profile of peripheral blood cells with aging. We validated the differential expression of these transcription factors between IL‐7Rα^low and ^high EM CD8⁺ T cells as well as in peripheral blood mononuclear cells (PBMCs) of young and older adults. Finally, we found a significant association with influenza vaccine responses in older adults, suggesting the possible biological significance of the aging signature genes of IL‐7Rα^low EM CD8⁺ T cells. The results of our study support the relationship of the expansion of IL‐7Rα^low EM CD8⁺ T cells with the age‐associated changes in the gene expression profile of peripheral blood cells and its possible biological implications.

Breaking barriers for T cells by targeting the EPHA2/TGF-β/COX-2 axis in pancreatic cancer

Pancreatic ductal adenocarcinoma is projected to become the second leading cause of cancer-related death and is largely resistant to immunotherapies. The tumor microenvironment, largely composed of heterogeneous myeloid cells, creates a physical, metabolic, and immunosuppressive barrier that prevents T cells from infiltrating cancer beds. In this issue of the JCI, Markosyan and colleagues have reported a tumor-intrinsic mechanism that excludes T cells from the vicinity of tumor cells. They showed that a receptor tyrosine kinase, ephrin-A receptor 2 (EPHA2), regulates prostaglandin endoperoxide synthase 2 (PTGS2) (encodes COX-2) expression in a TGF-β signaling-dependent manner. Genetic ablation of Epha2 or Ptgs2 in preclinical models or pharmacological inhibition of COX-2 elicited the transformation of this immunosuppressive microenvironment into a T cell-permissive milieu. Consequent T cell relocation rendered this immunoresistant malignancy responsive to combinations of checkpoint blockers and CD40 agonists. Because the association between T cell infiltration and the EPHA2/TGF-β/COX-2 axis is supported by independent clinical data, these results provide a rationale for ensuing clinical trials aimed at incorporating pancreatic cancer into the range of immunotherapy-responsive tumors.

Epigenetic signature of PD-1+ TCF1+ CD8 T cells that act as resource cells during chronic viral infection and respond to PD-1 blockade

We have recently defined a novel population of PD-1 (programmed cell death 1)+ TCF1 (T cell factor 1)+ virus-specific CD8 T cells that function as resource cells during chronic LCMV infection and provide the proliferative burst seen after PD-1 blockade. Such CD8 T cells have been found in other chronic infections and also in cancer in mice and humans. These CD8 T cells exhibit stem-like properties undergoing self-renewal and also differentiating into the terminally exhausted CD8 T cells. Here we compared the epigenetic signature of stem-like CD8 T cells with exhausted CD8 T cells. ATAC-seq analysis showed that stem-like CD8 T cells had a unique signature implicating activity of HMG (TCF) and RHD (NF-κB) transcription factor family members in contrast to higher accessibility to ETS and RUNX motifs in exhausted CD8 T cells. In addition, regulatory regions of the transcription factors Tcf7 and Id3 were more accessible in stem-like cells whereas Prdm1 and Id2 were more accessible in exhausted CD8 T cells. We also compared the epigenetic signatures of the 2 CD8 T cell subsets from chronically infected mice with effector and memory CD8 T cells generated after an acute LCMV infection. Both CD8 T cell subsets generated during chronic infection were strikingly different from CD8 T cell subsets from acute infection. Interestingly, the stem-like CD8 T cell subset from chronic infection, despite sharing key functional properties with memory CD8 T cells, had a very distinct epigenetic program. These results show that the chronic stem-like CD8 T cell program represents a specific adaptation of the T cell response to persistent antigenic stimulation.

Cholesterol Induces CD8+ T Cell Exhaustion in the Tumor Microenvironment

Tumor-infiltrating T cells often lose their effector function; however, the mechanisms are incompletely understood. We report that cholesterol in the tumor microenvironment induces CD8⁺ T cell expression of immune checkpoints and exhaustion. Tumor tissues enriched with cholesterol and cholesterol content in tumor-infiltrating CD8⁺ T cells were positively and progressively associated with upregulated T cell expression of PD-1, 2B4, TIM-3, and LAG-3. Adoptively transferred CD8⁺ T cells acquired cholesterol, expressed high levels of immune checkpoints, and became exhausted upon entering a tumor. Tumor culture supernatant or cholesterol induced immune checkpoint expression by increasing endoplasmic reticulum (ER) stress in CD8⁺ T cells. Consequently, the ER stress sensor XBP1 was activated and regulated PD-1 and 2B4 transcription. Inhibiting XBP1 or reducing cholesterol in CD8⁺ T cells effectively restored antitumor activity. This study reveals a mechanism underlying T cell exhaustion and suggests a new strategy for restoring T cell function by reducing cholesterol to enhance T cell-based immunotherapy.

Chronic stimulation drives human NK cell dysfunction and epigenetic reprograming

A population of Natural Killer (NK) cells expressing the activating receptor NKG2C and the maturation marker CD57 expands in response to human cytomegalovirus (HCMV) infection. CD3-CD56dimCD57+NKG2C+ NK cells are similar to CD8+ memory T cells with rapid and robust effector function upon re-stimulation, persistence, and epigenetic remodeling of the IFNG locus. Chronic antigen stimulation drives CD8+ memory T cell proliferation while also inducing genome-wide epigenetic reprograming and dysfunction. We hypothesized that chronic stimulation could similarly induce epigenetic reprograming and dysfunction in NK cells. Here we show that chronic stimulation of adaptive NK cells through NKG2C using plate-bound agonistic antibodies in combination with IL-15 drove robust proliferation and activation of CD3-CD56dimCD57+NKG2C+ NK cells while simultaneously inducing high expression of the checkpoint inhibitory receptors LAG-3 and PD-1. Marked induction of checkpoint inhibitory receptors was also observed on the surface of adaptive NK cells co-cultured with HCMV-infected endothelial cells. Chronically stimulated adaptive NK cells were dysfunctional when challenged with tumor targets. These cells exhibited a pattern of epigenetic reprograming, with genome-wide alterations in DNA methylation. Our study has important implications for cancer immunotherapy and suggest that exhausted NK cells could be targeted with inhibitory checkpoint receptor blockade.

Decreased SATB1 expression promotes AML cell proliferation through NF-κB activation

Background

Special AT-rich sequence-binding protein 1 (SATB1) is a chromatin-remodeling protein that regulates gene expressions in different types of cancer. Up-regulation of SATB1 is linked with progression of tumors. Our previous study showed that SATB1 expression was decreased in T cell leukemia/lymphoma. The contrary roles of SATB1 in solid organ tumors and hematology malignancy may provide hints to study the function of SATB1.

Methods

To characterize SATB1 mRNA and protein expression in acute myeloid leukemia (AML), we performed qRT-PCR and Western blot on bone marrow mononuclear cells from 52 newly diagnosed AML patients. Stable HL-60 cell lines with knockdown of SATB1 by shRNAs sequences (HL-60 SATB1-shRNA1 and HL-60 SATB1-shRNA2) were established. Cell proliferation, cell cycle and cell invasiveness were analyzed. Murine model was established using HL-60 SATB1-shRNAs treated nude mice and tumorigenicity was compared to study the role of SATB1 in vivo. Global gene expression profiles were analyzed in HL-60 cells with SATB1 knockdown to investigate the mechanisms underlying the regulation of AML cell growth by SATB1.

Results

We found that SATB1 expression was significantly decreased in patients with AML compared to normal control, and was increased after complete remission of AML. Knockdown of SATB1 enhanced the proliferation of HL-60 cells and accelerated S phase entry in vitro, and promoted the tumor growth in vivo. Global gene expression profiles were analyzed in HL-60 cells with SATB1 knockdown and the differentially expressed genes were involved in NF-κB, MAPK and PI3 K/Akt signaling pathways. Nuclear NF-κB p65 levels were significantly increased in SATB1 depleted HL-60 cells.

Conclusions

Decreased SATB1 expression promotes AML cell proliferation through NF-κB activation. SATB1 could be a predictor for better response to treatment in AML.

Antagonism between HTRA3 and TGFβ1 Contributes to Metastasis in Non-Small Cell Lung Cancer

High temperature requirement A3 (HTRA3, long and short isoforms) is a member of the HtrA family and has been implicated as a tumor suppressor in cancer progression in multiple cancer types, yet its molecular functions in non-small cell lung cancer (NSCLC) are not well understood. Here, we report that decreased levels of HTRA3 negatively correlate with elevated TGFβ1 in lung tumor tissue with metastasis. Furthermore, high expression of HTRA3 indicated better prognosis independent of TGFβ1 expression. In NSCLC cell lines, exogenous TGFβ1 significantly downregulated the level of HTRA3, especially the long isoform, during induction of epithelial-mesenchymal transition (EMT). Mechanistically, c-Jun, which is elevated by TGFβ1, directly bound the promoter of HTRA3-L and inhibited its transcription. As a negative feedback loop, overexpression of HTRA3-L attenuated TGFβ1-mediated invasion-metastasis cascades via activation of SMAD2/3 and sensitized cells to anti-PD-L1 treatment. Taken together, our findings suggest that in the early stages of cancer, overexpressed HTRA3 acts as a brake on the oncogenic effects of TGFβ1 and inhibits tumor metastasis. In later stages, the role of HTRA3 is weakened and TGFβ1 efficiently promotes EMT in the absence of the HTRA3 brake. SIGNIFICANCE: This study provides new mechanistic insight of the interaction between HTRA3 and TGFβ in lung cancer by illustrating that HTRA3 is a novel mediator acting as a suppressor of TGFβ1-related oncogenic effects.

ER stress-induced mediator C/EBP homologous protein thwarts effector T cell activity in tumors through T-bet repression

Understanding the intrinsic mediators that render CD8⁺ T cells dysfunctional in the tumor microenvironment is a requirement to develop more effective cancer immunotherapies. Here, we report that C/EBP homologous protein (Chop), a downstream sensor of severe endoplasmic reticulum (ER) stress, is a major negative regulator of the effector function of tumor-reactive CD8⁺ T cells. Chop expression is increased in tumor-infiltrating CD8⁺ T cells, which correlates with poor clinical outcome in ovarian cancer patients. Deletion of Chop in T cells improves spontaneous antitumor CD8⁺ T cell immunity and boosts the efficacy of T cell-based immunotherapy. Mechanistically, Chop in CD8⁺ T cells is elevated primarily through the ER stress-associated kinase Perk and a subsequent induction of Atf4; and directly represses the expression of T-bet, a master regulator of effector T cell function. These findings demonstrate the primary role of Chop in tumor-induced CD8⁺ T cell dysfunction and the therapeutic potential of blocking Chop or ER stress to unleash T cell-mediated antitumor immunity.

Divergent SATB1 expression across human life span and tissue compartments

Special AT-rich binding protein-1 (SATB1) is a global chromatin organizer capable of activating or repressing gene transcription in mice and humans. The role of SATB1 is pivotal for T-cell development, with SATB1-knockout mice being neonatally lethal, although the exact mechanism is unknown. Moreover, SATB1 is dysregulated in T-cell lymphoma and proposed to suppress transcription of the Pdcd1 gene, encoding the immune checkpoint programmed cell death protein 1 (PD-1). Thus, SATB1 expression in T-cell subsets across different tissue compartments in humans is of potential importance for targeting PD-1. Here, we comprehensively analyzed SATB1 expression across different human tissues and immune compartments by flow cytometry and correlated this with PD-1 expression. We investigated SATB1 protein levels in pediatric and adult donors and assessed expression dynamics of this chromatin organizer across different immune cell subsets in human organs, as well as in antigen-specific T cells directed against acute and chronic viral infections. Our data demonstrate that SATB1 expression in humans is the highest in T-cell progenitors in the thymus, and then becomes downregulated in mature T cells in the periphery. Importantly, SATB1 expression in peripheral mature T cells is not static and follows fine-tuned expression dynamics, which appear to be tissue- and antigen-dependent. Furthermore, SATB1 expression negatively correlates with PD-1 expression in virus-specific CD8⁺ T cells. Our study has implications for understanding the role of SATB1 in human health and disease and suggests an approach for modulating PD-1 in T cells, highly relevant to human malignancies or chronic viral infections.

CD4+ T help promotes influenza virus-specific CD8+ T cell memory by limiting metabolic dysfunction

There is continued interest in developing novel vaccine strategies that induce establish optimal CD8⁺ cytotoxic T lymphocyte (CTL) memory for pathogens like the influenza A viruses (IAVs), where the recall of IAV-specific T cell immunity is able to protect against serologically distinct IAV infection. While it is well established that CD4⁺ T cell help is required for optimal CTL responses and the establishment of memory, when and how CD4⁺ T cell help contributes to determining the ideal memory phenotype remains unclear. We assessed the quality of IAV-specific CD8⁺ T cell memory established in the presence or absence of a concurrent CD4⁺ T cell response. We demonstrate that CD4⁺ T cell help appears to be required at the initial priming phase of infection for the maintenance of IAV-specific CTL memory, with "unhelped" memory CTL exhibiting intrinsic dysfunction. High-throughput RNA-sequencing established that distinct transcriptional signatures characterize the helped vs. unhelped IAV-specific memory CTL phenotype, with the unhelped set showing a more "exhausted T cell" transcriptional profile. Moreover, we identify that unhelped memory CTLs exhibit defects in a variety of energetic pathways, leading to diminished spare respiratory capacity and diminished capacity to engage glycolysis upon reactivation. Hence, CD4⁺ T help at the time of initial priming promotes molecular pathways that limit exhaustion by channeling metabolic processes essential for the rapid recall of memory CD8⁺ T cells.

Satb1 regulates the effector program of encephalitogenic tissue Th17 cells in chronic inflammation

The genome organizer, special AT-rich sequence-binding protein-1 (Satb1), plays a pivotal role in the regulation of global gene networks in a cell type-dependent manner and is indispensable for the development of multiple cell types, including mature CD4+ T, CD8+ T, and Foxp3+ regulatory T cells in the thymus. However, it remains unknown how the differentiation and effector program of the Th subsets in the periphery are regulated by Satb1. Here, we demonstrate that Satb1 differentially regulates gene expression profiles in non-pathogenic and pathogenic Th17 cells and promotes the pathogenic effector program of encephalitogenic Th17 cells by regulating GM-CSF via Bhlhe40 and inhibiting PD-1 expression. However, Satb1 is dispensable for the differentiation and non-pathogenic functions of Th17 cells. These results indicate that Satb1 regulates the specific gene expression and function of effector Th17 cells in tissue inflammation.

T Cell Receptor-Regulated TGF-β Type I Receptor Expression Determines T Cell Quiescence and Activation

It is unclear how quiescence is enforced in naive T cells, but activation by foreign antigens and self-antigens is allowed, despite the presence of inhibitory signals. We showed that active transforming growth factor β (TGF-β) signaling was present in naive T cells, and T cell receptor (TCR) engagement reduced TGF-β signaling during T cell activation by downregulating TGF-β type 1 receptor (TβRI) through activation of caspase recruitment domain-containing protein 11 (CARD11) and nuclear factor κB (NF-κB). TGF-β prevented TCR-mediated TβRI downregulation, but this was abrogated by interleukin-6 (IL-6). Mitigation of TCR-mediated TβRI downregulation through overexpression of TβRI in naive and activated T cells rendered T cells less responsive and suppressed autoimmunity. Naive T cells in autoimmune patients exhibited reduced TβRI expression and increased TCR-driven proliferation compared to healthy subjects. Thus, TCR-mediated regulation of TβRI-TGF-β signaling acts as a crucial criterion to determine T cell quiescence and activation.

FBXO38 mediates PD-1 ubiquitination and regulates anti-tumour immunity of T cells

Dysfunctional T cells in the tumour microenvironment have abnormally high expression of PD-1 and antibody inhibitors against PD-1 or its ligand (PD-L1) have become commonly used drugs to treat various types of cancer^1-4. The clinical success of these inhibitors highlights the need to study the mechanisms by which PD-1 is regulated. Here we report a mechanism of PD-1 degradation and the importance of this mechanism in anti-tumour immunity in preclinical models. We show that surface PD-1 undergoes internalization, subsequent ubiquitination and proteasome degradation in activated T cells. FBXO38 is an E3 ligase of PD-1 that mediates Lys48-linked poly-ubiquitination and subsequent proteasome degradation. Conditional knockout of Fbxo38 in T cells did not affect T cell receptor and CD28 signalling, but led to faster tumour progression in mice owing to higher levels of PD-1 in tumour-infiltrating T cells. Anti-PD-1 therapy normalized the effect of FBXO38 deficiency on tumour growth in mice, which suggests that PD-1 is the primary target of FBXO38 in T cells. In human tumour tissues and a mouse cancer model, transcriptional levels of FBXO38 and Fbxo38, respectively, were downregulated in tumour-infiltrating T cells. However, IL-2 therapy rescued Fbxo38 transcription and therefore downregulated PD-1 levels in PD-1⁺ T cells in mice. These data indicate that FBXO38 regulates PD-1 expression and highlight an alternative method to block the PD-1 pathway.

SATB family chromatin organizers as master regulators of tumor progression

SATB (Special AT-rich binding protein) family proteins have emerged as key regulators that integrate higher-order chromatin organization with the regulation of gene expression. Studies over the past decade have elucidated the specific roles of SATB1 and SATB2, two closely related members of this family, in cancer progression. SATB family chromatin organizers play diverse and important roles in regulating the dynamic equilibrium of apoptosis, cell invasion, metastasis, proliferation, angiogenesis, and immune modulation. This review highlights cellular and molecular events governed by SATB1 influencing the structural organization of chromatin and interacting with several co-activators and co-repressors of transcription towards tumor progression. SATB1 expression across tumor cell types generates cellular and molecular heterogeneity culminating in tumor relapse and metastasis. SATB1 exhibits dynamic expression within intratumoral cell types regulated by the tumor microenvironment, which culminates towards tumor progression. Recent studies suggested that cell-specific expression of SATB1 across tumor recruited dendritic cells (DC), cytotoxic T lymphocytes (CTL), T regulatory cells (Tregs) and tumor epithelial cells along with tumor microenvironment act as primary determinants of tumor progression and tumor inflammation. In contrast, SATB2 is differentially expressed in an array of cancer types and is involved in tumorigenesis. Survival analysis for patients across an array of cancer types correlated with expression of SATB family chromatin organizers suggested tissue-specific expression of SATB1 and SATB2 contributing to disease prognosis. In this context, it is pertinent to understand molecular players, cellular pathways, genetic and epigenetic mechanisms governed by cell types within tumors regulated by SATB proteins. We propose that patient survival analysis based on the expression profile of SATB chromatin organizers would facilitate their unequivocal establishment as prognostic markers and therapeutic targets for cancer therapy.

Engineering CAR-T Cells for Improved Function Against Solid Tumors

Genetic engineering T cells to create clinically applied chimeric antigen receptor (CAR) T cells has led to improved patient outcomes for some forms of hematopoietic malignancies. While this has inspired the biomedical community to develop similar strategies to treat solid tumor patients, challenges such as the immunosuppressive character of the tumor microenvironment, CAR-T cell persistence and trafficking to the tumor seem to limit CAR-T cell efficacy in solid cancers. This review provides an overview of mechanisms that tumors exploit to evade eradication by CAR-T cells as well as emerging approaches that incorporate genetic engineering technologies to improve CAR-T cell activity against solid tumors.

Deceleration of glycometabolism impedes IgG-producing B-cell-mediated tumor elimination by targeting SATB1

B lymphocytes, known as antibody producers, mediate tumor cell destruction in the manner of antibody-dependent cell-mediated cytotoxicity; however, their anti-tumor function seems to be weakened during tumorigenesis, while the underlying mechanisms remain unclear. In this study, we found that IgG mediated anti-tumor effects, but IgG-producing B cells decreased in various tumors. Considering the underlying mechanism, glycometabolism was noteworthy. We found that tumor-infiltrating B cells were glucose-starved and accompanied by a deceleration of glycometabolism. Both inhibition of glycometabolism and deprivation of glucose through tumor cells, or glucose-free treatment, reduced the differentiation of B cells into IgG-producing cells. In this process, special AT-rich sequence-binding protein-1 (SATB1) was significantly silenced in B cells. Down-regulating SATB1 by inhibiting glycometabolism or RNA interference reduced the binding of signal transducer and activator of transcription 6 (STAT6) to the promoter of germline Cγ gene, subsequently resulting in fewer B cells producing IgG. Our findings provide the first evidence that glycometabolic inhibition by tumorigenesis suppresses differentiation of B cells into IgG-producing cells, and altering glycometabolism may be promising in improving the anti-tumor effect of B cells.

Stromal Fibroblasts Mediate Anti-PD-1 Resistance via MMP-9 and Dictate TGFβ Inhibitor Sequencing in Melanoma

Although anti-PD-1 therapy has improved clinical outcomes for select patients with advanced cancer, many patients exhibit either primary or adaptive resistance to checkpoint inhibitor immunotherapy. The role of the tumor stroma in the development of these mechanisms of resistance to checkpoint inhibitors remains unclear. We demonstrated that pharmacologic inhibition of the TGFβ signaling pathway synergistically enhanced the efficacy of anti-CTLA-4 immunotherapy but failed to augment anti-PD-1/PD-L1 responses in an autochthonous model of BRAF^V600E melanoma. Additional mechanistic studies revealed that TGFβ pathway inhibition promoted the proliferative expansion of stromal fibroblasts, thereby facilitating MMP-9-dependent cleavage of PD-L1 surface expression, leading to anti-PD-1 resistance in this model. Further work demonstrated that melanomas escaping anti-PD-1 therapy exhibited a mesenchymal phenotype associated with enhanced TGFβ signaling activity. Delayed TGFβ inhibitor therapy, following anti-PD-1 escape, better served to control further disease progression and was superior to a continuous combination of anti-PD-1 and TGFβ inhibition. This work illustrates that formulating immunotherapy combination regimens to enhance the efficacy of checkpoint blockade requires an in-depth understanding of the impact of these agents on the tumor microenvironment. These data indicated that stromal fibroblast MMP-9 may desensitize tumors to anti-PD-1 and suggests that TGFβ inhibition may generate greater immunologic efficacy when administered following the development of acquired anti-PD-1 resistance.See related Spotlight on p. 1444.

H3K4me3 mediates the NF-κB p50 homodimer binding to the pdcd1 promoter to activate PD-1 transcription in T cells

PD-1 is a co-repressive receptor that curbs T cell activation and thereby serves as a protection mechanism against autoimmunity under physiological conditions. Under pathological conditions, tumor cells express PD-L1 as an adaptive resistant mechanism to suppress PD-1⁺ T cells to evade host immunosurveillance. PD-1 therefore is a key target in cancer immunotherapy. Despite the extensive studies of PD-1 expression regulation, the pdcd1 transcription machinery and regulatory mechanisms are still not fully understood. We report here that the NF-κB p50 homodimer is a transcription regulator of PD-1 in activated T cells. A putative κB sequence exists at the pdcd1 promoter. All five NF-κB Rel subunits are activated in activated T cells. However, only the p50 homodimer directly binds to the κB sequence at the pccd1 promoter in CD4⁺ and CD8⁺ T cells. Deficiency in p50 results in reduced PD-1 expression in both CD4⁺ and CD8⁺ T cells in vitro. Using an in vivo mixed bone marrow chimera mouse model, we show that p50 regulates PD-1 expression in a cell-intrinsic way and p50 deficiency leads to decreased PD-1 expression in both antigen-specific CD4⁺ and CD8⁺ T cells in vivo. The expression levels of H3K4me3-specific histone methyltransferase increased significantly, resulting in a significant increase in H3K4me3 deposition at the pdcd1 promoter in activated CD4⁺ and CD8⁺ T cells. Inhibition of H3K4me3 significantly decreased p50 binding to the pdcd1 promoter and PD-1 expression in a T cell line. Our findings determine that the p50-H3K4me3 axis regulates pdcd1 transcription activation in activated T cells.

TGF-β in T Cell Biology: Implications for Cancer Immunotherapy

Transforming Growth Factor beta (TGF-β) is a pleiotropic cytokine produced in large amounts within cancer microenvironments that will ultimately promote neoplastic progression, notably by suppressing the host’s T-cell immunosurveillance. This effect is mostly due to the well-known inhibitory effect of TGF-β on T cell proliferation, activation, and effector functions. Moreover, TGF-β subverts T cell immunity by favoring regulatory T-cell differentiation, further reinforcing immunosuppression within tumor microenvironments. These findings stimulated the development of many strategies to block TGF-β or its signaling pathways, either as monotherapy or in combination with other therapies, to restore anti-cancer immunity. Paradoxically, recent studies provided evidence that TGF-β can also promote differentiation of certain inflammatory populations of T cells, such as Th17, Th9, and resident-memory T cells (Trm), which have been associated with improved tumor control in several models. Here, we review current advances in our understanding of the many roles of TGF-β in T cell biology in the context of tumor immunity and discuss the possibility to manipulate TGF-β signaling to improve cancer immunotherapy.

TGF-β in T Cell Biology: Implications for Cancer Immunotherapy

Transforming Growth Factor beta (TGF-β) is a pleiotropic cytokine produced in large amounts within cancer microenvironments that will ultimately promote neoplastic progression, notably by suppressing the host’s T-cell immunosurveillance. This effect is mostly due to the well-known inhibitory effect of TGF-β on T cell proliferation, activation, and effector functions. Moreover, TGF-β subverts T cell immunity by favoring regulatory T-cell differentiation, further reinforcing immunosuppression within tumor microenvironments. These findings stimulated the development of many strategies to block TGF-β or its signaling pathways, either as monotherapy or in combination with other therapies, to restore anti-cancer immunity. Paradoxically, recent studies provided evidence that TGF-β can also promote differentiation of certain inflammatory populations of T cells, such as Th17, Th9, and resident-memory T cells (Trm), which have been associated with improved tumor control in several models. Here, we review current advances in our understanding of the many roles of TGF-β in T cell biology in the context of tumor immunity and discuss the possibility to manipulate TGF-β signaling to improve cancer immunotherapy.

Epigenetic control of CD8+ T cell differentiation

Upon stimulation, small numbers of naive CD8+ T cells proliferate and differentiate into a variety of memory and effector cell types. CD8+ T cells can persist for years and kill tumour cells and virally infected cells. The functional and phenotypic changes that occur during CD8+ T cell differentiation are well characterized, but the epigenetic states that underlie these changes are incompletely understood. Here, we review the epigenetic processes that direct CD8+ T cell differentiation and function. We focus on epigenetic modification of DNA and associated histones at genes and their regulatory elements. We also describe structural changes in chromatin organization that affect gene expression. Finally, we examine the translational potential of epigenetic interventions to improve CD8+ T cell function in individuals with chronic infections and cancer.