Blimp-1 transcription factor is required for the differentiation of effector CD8(+) T cells and memory responses

Med1 Controls Effector CD8+ T Cell Differentiation and Survival through C/EBPβ-Mediated Transcriptional Control of T-bet

Effector CD8+ T cells are crucial players in adaptive immunity for effective protection against invading pathogens. The regulatory mechanisms underlying CD8+ T cell effector differentiation are incompletely understood. In this study, we defined a critical role of mediator complex subunit 1 (Med1) in controlling effector CD8+ T cell differentiation and survival during acute bacterial infection. Mice with Med1-deficient CD8+ T cells exhibited significantly impaired expansion with evidently reduced killer cell lectin-like receptor G1+ terminally differentiated and Ly6c+ effector cell populations. Moreover, Med1 deficiency led to enhanced cell apoptosis and expression of multiple inhibitory receptors (programmed cell death 1, T cell Ig and mucin domain–containing-3, and T cell immunoreceptor with Ig and ITIM domains). RNA-sequencing analysis revealed that T-bet– and Zeb2-mediated transcriptional programs were impaired in Med1-deficient CD8+ T cells. Overexpression of T-bet could rescue the differentiation and survival of Med1-deficient CD8+ effector T cells. Mechanistically, the transcription factor C/EBPβ promoted T-bet expression through interacting with Med1 in effector T cells. Collectively, our findings revealed a novel role of Med1 in regulating effector CD8+ T cell differentiation and survival in response to bacterial infection.

Epigenetic engineering for optimal CAR-T cell therapy

Recent advancements in cancer immunotherapy, such as chimeric antigen receptor (CAR)-engineered T cell therapy and immune checkpoint therapy (ICT), have significantly improved the clinical outcomes of patients with several types of cancer. To broaden its applicability further and induce durable therapeutic efficacy, it is imperative to understand how antitumor T cells elicit cytotoxic functions, survive as memory T cells, or are impaired in their effector functions (exhausted) at the molecular level. T cell properties are regulated by their gene expression profiles, which are further controlled by epigenetic architectures, such as DNA methylation and histone modifications. Multiple studies have elucidated specific epigenetic genes associated with T-cell phenotypic changes. Conversely, exogenous modification of these key epigenetic factors can significantly alter T cell functions by extensively altering the transcription network, which can be applied in cancer immunotherapy by improving T cell persistence or augmenting effector functions. Since CAR-T cell therapy involves a genetic engineering step during the preparation of the infusion products, it would be a feasible strategy to additionally modulate specific epigenetic genes in CAR-T cells to improve their quality. Here, we review recent studies investigating how individual epigenetic factors play a crucial role in T-cell biology. We further discuss future directions to integrate these findings for optimal cancer immunotherapy.

The Immunomodulatory Role of Hypoxic Tumor-Derived Extracellular Vesicles

Tumor-associated immune cells frequently display tumor-supportive phenotypes. These phenotypes, induced by the tumor microenvironment (TME), are described for both the adaptive and the innate arms of the immune system. Furthermore, they occur at all stages of immune cell development, up to effector function. One major factor that contributes to the immunosuppressive nature of the TME is hypoxia. In addition to directly inhibiting immune cell function, hypoxia affects intercellular crosstalk between tumor cells and immune cells. Extracellular vesicles (EVs) play an important role in this intercellular crosstalk, and changes in both the number and content of hypoxic cancer-cell-derived EVs are linked to the transfer of hypoxia tolerance. Here, we review the current knowledge about the role of these hypoxic cancer-cell-derived EVs in immunosuppression. In addition, we provide an overview of hypoxia-induced factors (i.e., miRNA and proteins) in tumor-derived EVs, and their role in immunomodulation.

Adrenergic signaling controls early transcriptional programs during CD8+ T cell responses to viral infection

Norepinephrine is a key sympathetic neurotransmitter, which acts to suppress CD8 + T cell cytokine secretion and lytic activity by signaling through the β2-adrenergic receptor (ADRB2). Although ADRB2 signaling is considered generally immunosuppressive, its role in regulating the differentiation of effector T cells in response to infection has not been investigated. Using an adoptive transfer approach, we compared the expansion and differentiation of wild type (WT) to Adrb2-/- CD8 + T cells throughout the primary response to vesicular stomatitis virus (VSV) infection in vivo. We measured the dynamic changes in transcriptome profiles of antigen-specific CD8 + T cells as they responded to VSV. Within the first 7 days of infection, WT cells out-paced the expansion of Adrb2-/- cells, which correlated with reduced expression of IL-2 and the IL-2Rα in the absence of ADRB2. RNASeq analysis identified over 300 differentially expressed genes that were both temporally regulated following infection and selectively regulated in WT vs Adrb2-/- cells. These genes contributed to major transcriptional pathways including cytokine receptor activation, signaling in cancer, immune deficiency, and neurotransmitter pathways. By parsing genes within groups that were either induced or repressed over time in response to infection, we identified three main branches of genes that were differentially regulated by the ADRB2. These gene sets were predicted to be regulated by specific transcription factors involved in effector T cell development, such as Tbx21 and Eomes. Collectively, these data demonstrate a significant role for ADRB2 signaling in regulating key transcriptional pathways during CD8 + T cells responses to infection that may dramatically impact their functional capabilities and downstream memory cell development.

Protein Kinase CK2 Controls CD8+ T Cell Effector and Memory Function during Infection

Protein kinase CK2 is a serine/threonine kinase composed of two catalytic subunits (CK2α and/or CK2α') and two regulatory subunits (CK2β). CK2 promotes cancer progression by activating the NF-κB, PI3K/AKT/mTOR, and JAK/STAT pathways, and also is critical for immune cell development and function. The potential involvement of CK2 in CD8⁺ T cell function has not been explored. We demonstrate that CK2 protein levels and kinase activity are enhanced upon mouse CD8⁺ T cell activation. CK2α deficiency results in impaired CD8⁺ T cell activation and proliferation upon TCR stimulation. Furthermore, CK2α is involved in CD8⁺ T cell metabolic reprogramming through regulating the AKT/mTOR pathway. Lastly, using a mouse Listeria monocytogenes infection model, we demonstrate that CK2α is required for CD8⁺ T cell expansion, maintenance, and effector function in both primary and memory immune responses. Collectively, our study implicates CK2α as an important regulator of mouse CD8⁺ T cell activation, metabolic reprogramming, and differentiation both in vitro and in vivo.

BCL6-dependent TCF-1+ progenitor cells maintain effector and helper CD4+ T cell responses to persistent antigen

Soon after activation, CD4⁺ T cells are segregated into BCL6⁺ follicular helper (Tfh) and BCL6^- effector (Teff) T cells. Here, we explored how these subsets are maintained during chronic antigen stimulation using the mouse chronic LCMV infection model. Using single cell-transcriptomic and epigenomic analyses, we identified a population of PD-1⁺ TCF-1⁺ CD4⁺ T cells with memory-like features. TCR clonal tracing and adoptive transfer experiments demonstrated that these cells have self-renewal capacity and continue to give rise to both Teff and Tfh cells, thus functioning as progenitor cells. Conditional deletion experiments showed Bcl6-dependent development of these progenitors, which were essential for sustaining antigen-specific CD4⁺ T cell responses to chronic infection. An analogous CD4⁺ T cell population developed in draining lymph nodes in response to tumors. Our study reveals the heterogeneity and plasticity of CD4⁺ T cells during persistent antigen exposure and highlights their population dynamics through a stable, bipotent intermediate state.

Lymphocyte Exhaustion in AML Patients and Impacts of HMA/Venetoclax or Intensive Chemotherapy on Their Biology

Simple Summary

Patients with acute myeloid leukemia (AML) are routinely treated with either intensive chemotherapy or DNA hypomethylating agents (HMA) in combination with the Bcl-2 inhibitor, venetoclax. While both treatment regimens are highly cytotoxic to the aggressive AML tumor cells, they are also toxic to immune cells. Therefore, we sought to establish the detrimental impacts of these therapies on lymphocytes and their recovery over time in AML patients. Even prior to treatment initiation, the patients were found to have exhausted lymphocytes in peripheral blood, and additional signs of exhaustion were noted after treatment with HMA/venetoclax. In fact, the lymphocytes were still suppressed for two to three months after the initiation of induction therapy. Furthermore, T cells in a subset of patients subsequently found to be resistant to venetoclax therapy exhibited a higher expression of perforin and CD39 and more pronounced IFN-γ production.

Abstract

Acute myeloid leukemia (AML) is an aggressive malignancy that requires rapid treatment with chemotherapies to reduce tumor burden. However, these chemotherapies can compromise lymphocyte function, thereby hindering normal anti-tumor immune responses and likely limiting the efficacy of subsequent immunotherapy. To better understand these negative impacts, we assessed the immunological effects of standard-of-care AML therapies on lymphocyte phenotype and function over time. When compared to healthy donors, untreated AML patients showed evidence of lymphocyte activation and exhaustion and had more prevalent CD57⁺NKG2C⁺ adaptive NK cells, which was independent of human cytomegalovirus (HCMV) status. HMA/venetoclax treatment resulted in a greater fraction of T cells with effector memory phenotype, inhibited IFN-γ secretion by CD8⁺ T cells, upregulated perforin expression in NK cells, downregulated PD-1 and 2B4 expression on CD4⁺ T cells, and stimulated Treg proliferation and CTLA-4 expression. Additionally, we showed increased expression of perforin and CD39 and enhanced IFN-γ production by T cells from pre-treatment blood samples of venetoclax-resistant AML patients. Our results provide insight into the lymphocyte status in previously untreated AML patients and the effects of standard-of-care treatments on their biology and functions. We also found novel pre-treatment characteristics of T cells that could potentially predict venetoclax resistance.

New therapeutic strategies based on biasing IL-2 mutants for cancers and autoimmune diseases

Interleukin-2 (IL-2) is an immunomodulatory multifunctional cytokine. High-dose IL-2 was first approved by the U.S. Food and Drug Administration (FDA) in the 1990s for the treatment of metastatic renal cell carcinoma and metastatic melanoma. However, the short half-life of IL-2 and its toxicity caused by high-dose IL-2 limit the clinical use of IL-2. Recently, the development of cell-type-selective engineered IL-2 products become a hot research filed, mainly because IL-2 stimulates both regulatory T cells (Treg) and effector T cells (Teff) in vivo. The selective effect of IL-2 on Treg and Teff can be improved by designing biased IL-2 mutants, which showed reduced toxicity while being more effective in stimulating anti-tumor effector immunity or ameliorating autoimmune diseases. In this review we summarize the biological properties of IL-2 mutants reported so far. The design process and principle of IL-2 mutants, IL-2 mutant antibody complexes and IL-2 fusion proteins were discussed, which provided research basis for the design and application of IL-2 mutants in the future.

Differentiation of Memory CD8 T Cells Unravel Gene Expression Pattern Common to Effector and Memory Precursors

Long-term immunological protection relies on the differentiation and maintenance of memory lymphocytes. Since the knowledge of memory generation has been centered on in vivo models of infection, there are obstacles to deep molecular analysis of differentiating subsets. Here we defined a novel in vitro CD8 T cell activation and culture regimen using low TCR engagement and cytokines to generate differentiated cells consistent with central memory-like cells, as shown by surface phenotype, gene expression profile and lack of cytotoxic function after challenge. Our results showed an effector signature expressed by in vitro memory precursors and their plasticity under specific conditions. Moreover, memory CD8 T cells conferred long-term protection against bacterial infection and slowed in vivo tumor growth more efficiently than effector cells. This model may allow further understanding of CD8 T cell memory molecular differentiation subsets and be suited for generating cells to be used for immunotherapy.

The long noncoding RNA Malat1 regulates CD8+ T cell differentiation by mediating epigenetic repression

During an immune response to microbial infection, CD8+ T cells give rise to short-lived effector cells and memory cells that provide sustained protection. Although the transcriptional programs regulating CD8+ T cell differentiation have been extensively characterized, the role of long noncoding RNAs (lncRNAs) in this process remains poorly understood. Using a functional genetic knockdown screen, we identified the lncRNA Malat1 as a regulator of terminal effector cells and the terminal effector memory (t-TEM) circulating memory subset. Evaluation of chromatin-enriched lncRNAs revealed that Malat1 grouped with trans lncRNAs that exhibit increased RNA interactions at gene promoters and gene bodies. Moreover, we observed that Malat1 was associated with increased H3K27me3 deposition at a number of memory cell-associated genes through a direct interaction with Ezh2, thereby promoting terminal effector and t-TEM cell differentiation. Our findings suggest an important functional role of Malat1 in regulating CD8+ T cell differentiation and broaden the knowledge base of lncRNAs in CD8+ T cell biology.

The perception and response of T cells to a changing environment are based on the law of initial value

αβ T cells are critical components of the adaptive immune system and are capable of inducing sterilizing immunity after pathogen infection and eliminating transformed tumor cells. The development and function of T cells are controlled through the T cell antigen receptor, which recognizes peptides displayed on major histocompatibility complex (MHC) molecules. Here, we review how T cells generate the ability to recognize self-peptide-bound MHC molecules and use signals derived from these interactions to instruct cellular development, activation thresholds, and functional specialization in the steady state and during immune responses. We argue that the basic tenants of T cell development and function follow Weber-Fetcher's law of just noticeable differences and Wilder's law of initial value. Together, these laws argue that the ability of a system to respond and the quality of that response are scalable to the basal state of that system. Manifestation of these laws in T cells generates clone-specific activation thresholds that are based on perceivable differences between homeostasis and pathogen encounter (self versus nonself discrimination), as well as poised states for subsequent differentiation into specific effector cell lineages.

T cell receptor and IL-2 signaling strength control memory CD8+ T cell functional fitness via chromatin remodeling

Cognate antigen signal controls CD8+ T cell priming, expansion size and effector versus memory cell fates, but it is not known if and how it modulates the functional features of memory CD8+ T cells. Here we show that the strength of T cell receptor (TCR) signaling controls the requirement for interleukin-2 (IL-2) signals to form a pool of memory CD8+ T cells that competitively re-expand upon secondary antigen encounter. Combining strong TCR and intact IL-2 signaling during priming synergistically induces genome-wide chromatin accessibility in regions targeting a wide breadth of biological processes, consistent with greater T cell functional fitness. Chromatin accessibility in promoters of genes encoding for stem cell, cell cycle and calcium-related proteins correlates with faster intracellular calcium accumulation, initiation of cell cycle and more robust expansion. High-dimensional flow-cytometry analysis of these T cells also highlights higher diversity of T cell subsets and phenotypes with T cells primed with stronger TCR and IL-2 stimulation than those primed with weaker strengths of TCR and/or IL-2 signals. These results formally show that epitope selection in vaccine design impacts memory CD8+ T cell epigenetic programming and function.

E3 Ubiquitin Ligase Riplet Is Expressed in T Cells and Suppresses T Cell-Mediated Antitumor Immune Responses

The E3 ubiquitin ligase Riplet mediates retinoic acid-inducible gene-I polyubiquitination and is essential for viral-induced expression of type I IFNs in dendritic cells and macrophages. The function of Riplet in innate immunity has been well demonstrated; however, its role in adaptive immunity during the antitumor immune response is unclear. In this study, we examined the role of Riplet in the T cell-mediated antitumor immune response. Riplet was expressed in T cells and upregulated in CD8⁺ T cells in response to TCR-mediated stimulation. Furthermore, PR domain containing 1, eomesodermin, and killer cell lectin-like receptor G1 expression was increased in effector CD8⁺ T cells by Riplet knockout in vitro, which suggests that Riplet is involved in the effector function of CD8⁺ T cells. Our results indicated that Riplet deficiency augmented the antitumor response of MO4 (OVA-expressing melanoma)-bearing mice treated with OVA peptide-pulsed dendritic cells. Moreover, both CD4⁺ and CD8⁺ T cells played important roles in Riplet-mediated augmentation of the antitumor immune response. In tumor-draining lymph nodes, the Th1 response was promoted, and the induction of OVA-specific CD8⁺ T cells and IFN-γ production were enhanced by Riplet deficiency. Furthermore, the IFN-γ response and OVA-specific cytotoxicity of CD8⁺ T cells in tumor tissue were augmented by Riplet deficiency. The expression of Cxcl9fluorescence-minus-one and Cxcl10 mRNA was also enhanced in the tumor microenvironment by Riplet knockout, consistent with the augmented recruitment of CTLs. Overall, we clarified a function of Riplet in T cells, which is to suppress the antitumor immune response through modulating Th1 and CTLs.

Hobit and Blimp-1 regulate TRM abundance after LCMV infection by suppressing tissue exit pathways of TRM precursors

Tissue‐resident memory T cells (Trm) are retained in peripheral tissues after infection for enhanced protection against secondary encounter with the same pathogen. We have previously shown that the transcription factor Hobit and its homolog Blimp‐1 drive Trm development after viral infection, but how and when these transcription factors mediate Trm formation remains poorly understood. In particular, the major impact of Blimp‐1 in regulating several aspects of effector T‐cell differentiation impairs study of its specific role in Trm development. Here, we used the restricted expression of Hobit in the Trm lineage to develop mice with a conditional deletion of Blimp‐1 in Trm, allowing us to specifically investigate the role of both transcription factors in Trm differentiation. We found that Hobit and Blimp‐1 were required for the upregulation of CD69 and suppression of CCR7 and S1PR1 on virus‐specific Trm precursors after LCMV infection, underlining a role in their retention within tissues. The early impact of Hobit and Blimp‐1 favored Trm formation and prevented the development of circulating memory T cells. Thus, our findings highlight a role of Hobit and Blimp‐1 at the branching point of circulating and resident memory lineages by suppressing tissue egress of Trm precursors early during infection.

Blood Transcriptome Profiling Links Immunity to Disease Severity in Myotonic Dystrophy Type 1 (DM1)

The blood transcriptome was examined in relation to disease severity in type I myotonic dystrophy (DM1) patients who participated in the Observational Prolonged Trial In DM1 to Improve QoL- Standards (OPTIMISTIC) study. This sought to (a) ascertain if transcriptome changes were associated with increasing disease severity, as measured by the muscle impairment rating scale (MIRS), and (b) establish if these changes in mRNA expression and associated biological pathways were also observed in the Dystrophia Myotonica Biomarker Discovery Initiative (DMBDI) microarray dataset in blood (with equivalent MIRS/DMPK repeat length). The changes in gene expression were compared using a number of complementary pathways, gene ontology and upstream regulator analyses, which suggested that symptom severity in DM1 was linked to transcriptomic alterations in innate and adaptive immunity associated with muscle-wasting. Future studies should explore the role of immunity in DM1 in more detail to assess its relevance to DM1.

Engineered Mesenchymal Stem Cells as a Biotherapy Platform for Targeted Photodynamic Immunotherapy of Breast Cancer

Interleukin-12 (IL12) is a pleiotropic cytokine with promising prospects for cancer immunotherapy. Though IL12 gene-based therapy can overcome the fatal hurdle of severe systemic toxicity, targeted delivery and tumor-located expression of IL12 gene remain the challenging issues yet to be solved. Photo-immunotherapy emerging as a novel and precise therapeutic strategy, which elaborately combines immune-activating agents with light-triggered photosensitizers for potentiated anticancer efficacy. Herein, an engineered stem cell-based biotherapy platform (MB/IL12-MSCs) incorporating immune gene plasmid IL12 (pIL12) and photosensitizer methylene blue (MB) is developed to realize tumor-homing delivery of therapeutic agents and photo-immunotherapy efficacy enhancement. The biotherapy platform retained tumor-tropic migration and penetration functions, which improved the intratumoral distribution of therapeutic agents, thereby promoting photodynamic effects and reinforcing immune responses. Importantly, MB/IL12-MSCs restricted the expression and distribution of IL12 at tumor site, which minimized potential toxicity while eliciting sufficient anticancer immunity. In noteworthy, activation of immunity induced by MB/IL12-MSCs established long-term systemic immunologic memory to prevent tumor relapse. The MB/IL12-MSCs outperform their monotherapy counterparts in breast tumor models, and the growth of tumor significantly arrested as well as re-challenging abscopal tumor growth slowdown. Collectively, this work reveals that MSCs-based strategy may advance more efficient, durable, and safer cancer photo-immunotherapy.

Conserved and Unique Functions of Blimp1 in Immune Cells

B-lymphocyte-induced maturation protein-1 (Blimp1), is an evolutionarily conserved transcriptional regulator originally described as a repressor of gene transcription. Blimp1 crucially regulates embryonic development and terminal differentiation in numerous cell lineages, including immune cells. Initial investigations of Blimp1’s role in immunity established its non-redundant role in lymphocytic terminal effector differentiation and function. In B cells, Blimp1 drives plasmablast formation and antibody secretion, whereas in T cells, Blimp1 regulates functional differentiation, including cytokine gene expression. These studies established Blimp1 as an essential transcriptional regulator that promotes efficient and controlled adaptive immunity. Recent studies have also demonstrated important roles for Blimp1 in innate immune cells, specifically myeloid cells, and Blimp1 has been established as an intrinsic regulator of dendritic cell maturation and T cell priming. Emerging studies have determined both conserved and unique functions of Blimp1 in different immune cell subsets, including the unique direct activation of the igh gene transcription in B cells and a conserved antagonism with BCL6 in B cells, T cells, and myeloid cells. Moreover, polymorphisms associated with the gene encoding Blimp1 (PRDM1) have been linked to numerous chronic inflammatory conditions in humans. Blimp1 has been shown to regulate target gene expression by either competing with other transcription factors for binding to the target loci, and/or by recruiting various chromatin-modifying co-factors that promote suppressive chromatin structure, such as histone de-acetylases and methyl-transferases. Further, Blimp1 function has been shown to be essentially dose and context-dependent, which adds to Blimp1’s versatility as a regulator of gene expression. Here, we review Blimp1’s complex roles in immunity and highlight specific gaps in the understanding of the biology of this transcriptional regulator, with a major focus on aspects that could foster the description and understanding of novel pathways regulated by Blimp1 in the immune system.

DExD/H-box helicase 9 intrinsically controls CD8+ T cell-mediated antiviral response through noncanonical mechanisms

Upon virus infection, CD8⁺ T cell accumulation is tightly controlled by simultaneous proliferation and apoptosis. However, it remains unclear how TCR signal coordinates these events to achieve expansion and effector cell differentiation. We found that T cell-specific deletion of nuclear helicase Dhx9 led to impaired CD8⁺ T cell survival, effector differentiation, and viral clearance. Mechanistically, Dhx9 acts as the key regulator to ensure LCK- and CD3ε-mediated ZAP70 phosphorylation and ERK activation to protect CD8⁺ T cells from apoptosis before proliferative burst. Dhx9 directly regulates Id2 transcription to control effector CD8⁺ T cell differentiation. The DSRM and OB_Fold domains are required for LCK binding and Id2 transcription, respectively. Dhx9 expression is predominantly increased in effector CD8⁺ T cells of COVID-19 patients. Therefore, we revealed a previously unknown regulatory mechanism that Dhx9 protects activated CD8⁺ T cells from apoptosis and ensures effector differentiation to promote antiviral immunity independent of nuclear sensor function.

Transcriptional Control of Cell Fate Determination in Antigen-Experienced CD8 T Cells

Robust immunity to intracellular infections is mediated by antigen-specific naive CD8 T cells that become activated and differentiate into phenotypically and functionally diverse subsets of effector cells, some of which terminally differentiate and others that give rise to memory cells that provide long-lived protection. This developmental system is an outstanding model with which to elucidate how regulation of chromatin structure and transcriptional control establish gene expression programs that govern cell fate determination, insights from which are likely to be useful for informing the design of immunotherapeutic approaches to engineer durable immunity to infections and tumors. A unifying framework that describes how naive CD8 T cells develop into memory cells is still outstanding. We propose a model that incorporates a common early linear path followed by divergent paths that slowly lose capacity to interconvert and discuss classical and contemporary observations that support these notions, focusing on insights from transcriptional control and chromatin regulation.

Skin and heart allograft rejection solely by long-lived alloreactive TRM cells in skin of severe combined immunodeficient mice

Whether induced tissue-resident memory T (T_RM) cells in nonlymphoid organs alone can mediate allograft rejection is unknown. By grafting alloskin or heart into severe combined immunodeficient or Rag2KO mice in which a piece of induced CD4⁺ and/or CD8⁺ T_RM cell-containing MHC-matched or syngeneic skin was transplanted in advance, we addressed this issue. The induced CD4⁺ T_RM cells in the skin alone acutely rejected alloskin or heart grafts. RNA-seq analysis showed that induced CD4⁺ T_RM cells in skin favorably differentiated into T_H17-like polarization during the secondary immune response. Inhibition of the key T_H17 signaling molecule RORγt attenuated T_RM cell-mediated graft rejection. Thus, we offer a unique mouse model to specifically study T_RM cell-mediated allograft rejection without the involvement of lymphocytes in lymphoid organs and tissues. Our study provides strong evidence supporting the hypothesis that long-lived alloreactive T_RM cells resident in other organs/tissues substantially contribute to organ allograft rejection.

New Insights into Epigenetic Regulation of T Cell Differentiation

Immature CD4- CD8- thymocytes progress through several developmental steps in the thymus, ultimately emerging as mature CD4+ (helper) or CD8+ (cytotoxic) T cells. Activation of naïve CD4+ and CD8+ T cells in the presence of specific cytokines results in the induction of transcriptional programs that result in their differentiation into effector or memory cells and in the case of CD4+ T cells, the adoption of distinct T-helper fates. Previous studies have shown that histone modification and DNA methylation play important roles in each of these events. More recently, the roles of specific epigenetic regulators in T cell differentiation have been clarified. The identification of the epigenetic modifications and modifiers that control mature T cell differentiation and specification has also provided further insights into how dysregulation of these processes can lead to cancer or autoimmune diseases. In this review, we summarize recent findings that have provided new insights into epigenetic regulation of T cell differentiation in both mice and humans.

Genetic ablation of PRDM1 in antitumor T cells enhances therapeutic efficacy of adoptive immunotherapy

Adoptive cancer immunotherapy can induce objective clinical efficacy in patients with advanced cancer; however, a sustained response is achieved in a minority of cases. The persistence of infused T cells is an essential determinant of a durable therapeutic response. Antitumor T cells undergo a genome-wide remodeling of the epigenetic architecture upon repeated antigen encounters, which inevitably induces progressive T-cell differentiation and the loss of longevity. In this study, we identified PR domain zinc finger protein 1 (PRDM1) i.e., Blimp-1, as a key epigenetic gene associated with terminal T-cell differentiation. The genetic knockout of PRDM1 by clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR associated protein 9 (Cas9) supported the maintenance of an early memory phenotype and polyfunctional cytokine secretion in repeatedly stimulated chimeric antigen receptor (CAR)-engineered T cells. PRDM1 disruption promoted the expansion of less differentiated memory CAR-T cells in vivo, which enhanced T-cell persistence and improved therapeutic efficacy in multiple tumor models. Mechanistically, PRDM1-ablated T cells displayed enhanced chromatin accessibility of the genes that regulate memory formation, thereby leading to the acquisition of gene expression profiles representative of early memory T cells. PRDM1 knockout also facilitated maintaining an early memory phenotype and cytokine polyfunctionality in T-cell receptor-engineered T cells as well as tumor-infiltrating lymphocytes. In other words, targeting PRDM1 enabled the generation of superior antitumor T cells, which is potentially applicable to a wide range of adoptive cancer immunotherapies.

Targeting Wnt Signaling in the Tumor Immune Microenvironment to Enhancing EpCAM CAR T-Cell therapy

Colorectal cancer (CRC) patients are still lacking viable treatments. Chimeric antigen receptor (CAR) T cells have shown promise in hematologic malignancies, but their efficacy in solid tumors has been limited due to the immunosuppressive tumor microenvironment. We found that cancer antigen- EpCAM expression increased in the metastatic stage compared with the primary stage in cancers and the activation of Wnt and TGFβ pathways was positively correlated with EpCAM expression in multiple cancers, including colorectal cancer. We constructed CAR T cells targeting EpCAM that successfully showed selective cytotoxicity in highly EpCAM-expressing cancer cell lines. The combination of EpCAM CAR-T with the Wnt inhibitor-hsBCL9_CT-24 displayed synergetic effect against EpCAM-positive colon cells in vitro and also in vivo. A mechanistic study showed that hsBCL9_CT-24 treatment could modulate the tumor environment and improve infiltration of T cells, while possibly promoting the effector T cells at the early stages and postponing the exhaustion of CAR T cells at advanced stages. Overall, these results demonstrated that the combination of EpCAM CAR T-cell therapy with the Wnt inhibitor can overcome the limitations of CAR T cells in treating solid tumors.

RNA-Binding Protein Expression Alters Upon Differentiation of Human B Cells and T Cells

B cells and T cells are key players in the defence against infections and malignancies. To exert their function, B cells and T cells differentiate into effector and memory cells. Tight regulation of these differentiation processes is key to prevent their malfunction, which can result in life-threatening disease. Lymphocyte differentiation relies on the appropriate timing and dosage of regulatory molecules, and post-transcriptional gene regulation (PTR) is a key player herein. PTR includes the regulation through RNA-binding proteins (RBPs), which control the fate of RNA and its translation into proteins. To date, a comprehensive overview of the RBP expression throughout lymphocyte differentiation is lacking. Using transcriptome and proteome analyses, we here catalogued the RBP expression for human B cells and T cells. We observed that even though the overall RBP expression is conserved, the relative RBP expression is distinct between B cells and T cells. Differentiation into effector and memory cells alters the RBP expression, resulting into preferential expression of different classes of RBPs. For instance, whereas naive T cells express high levels of translation-regulating RBPs, effector T cells preferentially express RBPs that modulate mRNA stability. Lastly, we found that cytotoxic CD8+ and CD4+ T cells express a common RBP repertoire. Combined, our study reveals a cell type-specific and differentiation-dependent RBP expression landscape in human lymphocytes, which will help unravel the role of RBPs in lymphocyte function.

NK and CD8+ T cell phenotypes predict onset and control of CMV viremia after kidney transplant

CMV causes mostly asymptomatic but lifelong infection. Primary infection or reactivation in immunocompromised individuals can be life-threatening. CMV viremia often occurs in solid organ transplant recipients and associates with decreased graft survival and higher mortality. Furthering understanding of impaired immunity that allows CMV reactivation is critical to guiding antiviral therapy and examining the effect of CMV on solid organ transplant outcomes. This study characterized longitudinal immune responses to CMV in 31 kidney transplant recipients with CMV viremia and matched, nonviremic recipients. Recipients were sampled 3 and 12 months after transplant, with additional samples 1 week and 1 month after viremia. PBMCs were stained for NK and T cell markers. PBMC transcriptomes were characterized by RNA-Seq. Plasma proteins were quantified by Luminex. CD8⁺ T cell transcriptomes were characterized by single-cell RNA-Seq. Before viremia, patients had high levels of IL-15 with concurrent expansion of immature CD56^bright NK cells. After viremia, mature CD56^dim NK cells and CD28^–CD8⁺ T cells upregulating inhibitory and NK-associated receptors were expanded. Memory NK cells and NK-like CD28^–CD8⁺ T cells were associated with control of viremia. These findings suggest that signatures of innate activation may be prognostic for CMV reactivation after transplant, while CD8⁺ T cell functionality is critical for effective control of CMV.

PI3Kδ coordinates transcriptional, chromatin, and metabolic changes to promote effector CD8+ T cells at the expense of central memory

Patients with activated phosphatidylinositol 3-kinase delta (PI3Kδ) syndrome (APDS) present with sinopulmonary infections, lymphadenopathy, and cytomegalvirus (CMV) and/or Epstein-Barr virus (EBV) viremia, yet why patients fail to clear certain chronic viral infections remains incompletely understood. Using patient samples and a mouse model (Pik3cdE1020K/+ mice), we demonstrate that, upon activation, Pik3cdE1020K/+ CD8+ T cells exhibit exaggerated features of effector populations both in vitro and after viral infection that are associated with increased Fas-mediated apoptosis due to sustained FoxO1 phosphorylation and Fasl derepression, enhanced mTORC1 and c-Myc signatures, metabolic perturbations, and an altered chromatin landscape. Conversely, Pik3cdE1020K/+ CD8+ cells fail to sustain expression of proteins critical for central memory, including TCF1. Strikingly, activated Pik3cdE1020K/+ CD8+ cells exhibit altered transcriptional and epigenetic circuits characterized by pronounced interleukin-2 (IL-2)/STAT5 signatures and heightened IL-2 responses that prevent differentiation to memory-like cells in IL-15. Our data position PI3Kδ as integrating multiple signaling nodes that promote CD8+ T cell effector differentiation, providing insight into phenotypes of patients with APDS.

The Inhibitory Receptor GPR56 (Adgrg1) Is Specifically Expressed by Tissue-Resident Memory T Cells in Mice But Dispensable for Their Differentiation and Function In Vivo

Tissue-resident memory T (TRM) cells with potent antiviral and antibacterial functions protect the epithelial and mucosal surfaces of our bodies against infection with pathogens. The strong proinflammatory activities of TRM cells suggest requirement for expression of inhibitory molecules to restrain these memory T cells under steady state conditions. We previously identified the adhesion G protein-coupled receptor GPR56 as an inhibitory receptor of human cytotoxic lymphocytes that regulates their cytotoxic effector functions. Here, we explored the expression pattern, expression regulation, and function of GPR56 on pathogen-specific CD8+ T cells using two infection models. We observed that GPR56 is expressed on TRM cells during acute infection and is upregulated by the TRM cell-inducing cytokine TGF-β and the TRM cell-associated transcription factor Hobit. However, GPR56 appeared dispensable for CD8+ T-cell differentiation and function upon acute infection with LCMV as well as Listeria monocytogenes. Thus, TRM cells specifically acquire the inhibitory receptor GPR56, but the impact of this receptor on TRM cells after acute infection does not appear essential to regulate effector functions of TRM cells.

Memory T-Cell Heterogeneity and Terminology

Immunological memory and exhaustion are fundamental features of adaptive immunity. Recent advances reveal increasing heterogeneity and diversity among CD8 T-cell subsets, resulting in new subsets to annotate and understand. Here, we review our current knowledge of differentiation and maintenance of memory and exhausted CD8 T cells, including phenotypic classification, developmental paths, transcriptional and epigenetic features, and cell intrinsic and extrinsic factors. Additionally, we use this outline to discuss the nomenclature of effector, memory, and exhausted CD8 T cells. Finally, we discuss how new findings about these cell types may impact the therapeutic efficacy and development of immunotherapies targeting effector, memory, and/or exhausted CD8 T cells in chronic infections and cancer.

Hobit identifies tissue-resident memory T cell precursors that are regulated by Eomes

Tissue-resident memory CD8⁺ T cells (T_RM) constitute a noncirculating memory T cell subset that provides early protection against reinfection. However, how T_RM arise from antigen-triggered T cells has remained unclear. Exploiting the T_RM-restricted expression of Hobit, we used T_RM reporter/deleter mice to study T_RM differentiation. We found that Hobit was up-regulated in a subset of LCMV-specific CD8⁺ T cells located within peripheral tissues during the effector phase of the immune response. These Hobit⁺ effector T cells were identified as T_RM precursors, given that their depletion substantially decreased T_RM development but not the formation of circulating memory T cells. Adoptive transfer experiments of Hobit⁺ effector T cells corroborated their biased contribution to the T_RM lineage. Transcriptional profiling of Hobit⁺ effector T cells underlined the early establishment of T_RM properties including down-regulation of tissue exit receptors and up-regulation of T_RM-associated molecules. We identified Eomes as a key factor instructing the early bifurcation of circulating and resident lineages. These findings establish that commitment of T_RM occurs early in antigen-driven T cell differentiation and reveal the molecular mechanisms underlying this differentiation pathway.

Bromodomain protein BRD4 directs and sustains CD8 T cell differentiation during infection

In response to infection, pathogen-specific CD8 T cells differentiate into functionally diverse effector and memory T cell populations critical for resolving disease and providing durable immunity. Through small-molecule inhibition, RNAi studies, and induced genetic deletion, we reveal an essential role for the chromatin modifier and BET family member BRD4 in supporting the differentiation and maintenance of terminally fated effector CD8 T cells during infection. BRD4 bound diverse regulatory regions critical to effector T cell differentiation and controlled transcriptional activity of terminal effector-specific super-enhancers in vivo. Consequentially, induced deletion of Brd4 or small molecule-mediated BET inhibition impaired maintenance of a terminal effector T cell phenotype. BRD4 was also required for terminal differentiation of CD8 T cells in the tumor microenvironment in murine models, which we show has implications for immunotherapies. Taken together, these data reveal an unappreciated requirement for BRD4 in coordinating activity of cis regulatory elements to control CD8 T cell fate and lineage stability.

Fueling influenza and the immune response: Implications for metabolic reprogramming during influenza infection and immunometabolism

Recent studies support the notion that glycolysis and oxidative phosphorylation are rheostats in immune cells whose bioenergetics have functional outputs in terms of their biology. Specific intrinsic and extrinsic molecular factors function as molecular potentiometers to adjust and control glycolytic to respiratory power output. In many cases, these potentiometers are used by influenza viruses and immune cells to support pathogenesis and the host immune response, respectively. Influenza virus infects the respiratory tract, providing a specific environmental niche, while immune cells encounter variable nutrient concentrations as they migrate in response to infection. Immune cell subsets have distinct metabolic programs that adjust to meet energetic and biosynthetic requirements to support effector functions, differentiation, and longevity in their ever-changing microenvironments. This review details how influenza coopts the host cell for metabolic reprogramming and describes the overlap of these regulatory controls in immune cells whose function and fate are dictated by metabolism. These details are contextualized with emerging evidence of the consequences of influenza-induced changes in metabolic homeostasis on disease progression.

Global Gene Expression of T Cells Is Differentially Regulated by Peritoneal Dendritic Cell Subsets in an IL-2 Dependent Manner

Dendritic cells (DCs) in peripheral tissues may have a unique role to regulate innate and adaptive immune responses to antigens that enter the tissues. Peritoneal cavity is the body compartment surrounding various tissues and organs and housing diverse immune cells. Here, we investigated the specialized features of classical DC (cDC) subsets following the intraperitoneal injection of a model antigen ovalbumin (OVA). Peritoneal cDC1s were superior to cDC2s in activating OVA-specific CD8 T cells, while both cDCs were similar in stimulating OVA-specific CD4 T cells. Each peritoneal cDC subset differentially regulated the homing properties of CD8 T cells. CD8 T cells stimulated by cDC1s displayed a higher level of lung-homing receptor CCR4, whereas those stimulated by cDC2s prominently expressed various homing receptors including gut-homing molecules CCR9 and α4β7. Also, we found that cDC1s played a dominating role over cDC2s in controlling the overall gene expression of CD8 T cells. Soluble factor(s) emanating from CD8 T cells stimulated by peritoneal cDC1s were responsible for mediating this dominance of cDC1s, and we identified IL-2 as a soluble factor regulating the global gene expression of T cells. Collectively, our study indicates that different peritoneal cDC subsets effectively diversify T cell responses by altering the level of cytokines, such as IL-2, in the milieu.

Resident memory T cells in tumor-distant tissues fortify against metastasis formation

As a critical machinery for rapid pathogen removal, resident memory T cells (T_RMs) are locally generated after the initial encounter. However, their development accompanying tumorigenesis remains elusive. Using a murine breast cancer model, we show that T_RMs develop in the tumor, the contralateral mammary mucosa, and the pre-metastatic lung. Single-cell RNA sequencing of T_RMs reveals two phenotypically distinct populations representing their active versus quiescent phases. These T_RMs in different tissue compartments share the same TCR clonotypes and transcriptomes with a subset of intratumoral effector/effector memory T cells (T_Eff/EMs), indicating their developmental ontogeny. Furthermore, CXCL16 is highly produced by tumor cells and CXCR6^- T_Eff/EMs are the major subset preferentially egressing the tumor to form distant T_RMs. Functionally, releasing CXCR6 retention in the primary tumor amplifies tumor-derived T_RMs in the lung and leads to superior protection against metastases. This immunologic fortification suggests a potential strategy to prevent metastasis in clinical oncology.

PRDM1 decreases sensitivity of human NK cells to IL2-induced cell expansion by directly repressing CD25 (IL2RA)

IL2 receptor signaling is crucial for human NK cell activation and gain of effector functions. The molecular mechanisms involved in termination of IL2 activation are largely unknown in human NK cells. PR/SET domain 1 was previously reported to decrease cell growth and increase apoptosis in an IL2-dependent manner in malignant NK cell lines, suggesting the possibility of down-regulation of IL2 signaling pathway gene(s) through direct transcriptional repression. Using ChIP-Seq, we identified a PRDM1 binding site on the first intron of CD25 (IL2RA), which codes for the IL2 receptor subunit regulating sensitivity to IL2 signaling, in primary NK cells activated with engineered K562 cells or IL2. Ectopic expression of PRDM1 down-regulated CD25 expression at transcript and protein levels in two PRDM1 nonexpressing NK cell lines. shRNA-mediated knockdown of CD25 in two malignant NK cell lines led to progressive depletion of NK cells in low IL2 concentrations. By contrast, ectopic CD25 expression in primary human NK cells led to progressive increase in cell number in CD25-transduced cells in low IL2 concentrations. Altogether these results reveal a pivotal role of PRDM1 in inhibition of IL2-induced NK cell expansion through direct repression of CD25 in activated human NK cells. These observations provide additional support for the role of PRDM1 in attenuation of NK cell activation and growth, with implications on neoplastic transformation or NK cell function when it is deregulated.

T-cell memory in tissues

Immunological memory equips our immune system to respond faster and more effectively against reinfections. This acquired immunity was originally attributed to long-lived, memory T and B cells with body wide access to peripheral and secondary lymphoid tissues. In recent years, it has been realized that both innate and adaptive immunity to a large degree depends on resident immune cells that act locally in barrier tissues including tissue-resident memory T cells (Trm). Here, we will discuss the phenotype of these Trm in mice and humans, the tissues and niches that support them, and their function, plasticity, and transcriptional control. Their unique properties enable Trm to achieve long-lived immunological memory that can be deposited in nearly every organ in response to acute and persistent infection, and in response to cancer. However, Trm may also induce substantial immunopathology in allergic and autoimmune disease if their actions remain unchecked. Therefore, inhibitory and activating stimuli appear to balance the actions of Trm to ensure rapid proinflammatory responses upon infection and to prevent damage to host tissues under steady state conditions.

Cellular networks controlling T cell persistence in adoptive cell therapy

The antitumour activity of endogenous or adoptively transferred tumour-specific T cells is highly dependent on their differentiation status. It is now apparent that less differentiated T cells compared with fully differentiated effector T cells have better antitumour therapeutic effects owing to their enhanced capacity to expand and their long-term persistence. In patients with cancer, the presence of endogenous or adoptively transferred T cells with stem-like memory or precursor phenotype correlates with improved therapeutic outcomes. Advances in our understanding of T cell differentiation states at the epigenetic and transcriptional levels have led to the development of novel methods to generate tumour-specific T cells - namely, chimeric antigen receptor T cells - that are more persistent and resistant to the development of dysfunction. These include the use of novel culture methods before infusion, modulation of transcriptional, metabolic and/or epigenetic programming, and strategies that fine-tune antigen receptor signalling. This Review discusses existing barriers and strategies to overcome them for successful T cell expansion and persistence in the context of adoptive T cell immunotherapy for solid cancers.

The architectural design of CD8+ T cell responses in acute and chronic infection: Parallel structures with divergent fates

In response to infection, T cells adopt a range of differentiation states, creating numerous heterogeneous subsets that exhibit different phenotypes, functions, and migration patterns. This T cell heterogeneity is a universal feature of T cell immunity, needed to effectively control pathogens in a context-dependent manner and generate long-lived immunity to those pathogens. Here, we review new insights into differentiation state dynamics and population heterogeneity of CD8+ T cells in acute and chronic viral infections and cancer and highlight the parallels and distinctions between acute and chronic antigen stimulation settings. We focus on transcriptional and epigenetic networks that modulate the plasticity and terminal differentiation of antigen-specific CD8+ T cells and generate functionally diverse T cell subsets with different roles to combat infection and cancer.

Transcriptional and epigenetic regulation of PD-1 expression

Programmed cell death-1 (PD-1) is a co-inhibitory receptor that plays important roles in regulating T cell immunity and peripheral tolerance. PD-1 signaling prevents T cells from overactivation during acute infections, but it maintains T cell exhaustion during chronic infections. Tumor cells can exploit the PD-1 signaling pathway to evade antitumor immune responses. The PD-1 signaling pathway is also essential for maintaining peripheral tolerance and prevention of autoimmunity. PD-1 expression is strictly and differentially regulated by diverse mechanisms in immune cells. It is activated and repressed by distinct transcription factors in different circumstances. Moreover, epigenetic mechanisms are also involved in regulating PD-1 expression. In this review, we summarize the knowledge of the transcriptional and epigenetic regulation of PD-1 expression during different immune responses.

KDM6B-dependent chromatin remodeling underpins effective virus-specific CD8+ T cell differentiation

Naive CD8+ T cell activation results in an autonomous program of cellular proliferation and differentiation. However, the mechanisms that underpin this process are unclear. Here, we profile genome-wide changes in chromatin accessibility, gene transcription, and the deposition of a key chromatin modification (H3K27me3) early after naive CD8+ T cell activation. Rapid upregulation of the histone demethylase KDM6B prior to the first cell division is required for initiating H3K27me3 removal at genes essential for subsequent T cell differentiation and proliferation. Inhibition of KDM6B-dependent H3K27me3 demethylation limits the magnitude of an effective primary virus-specific CD8+ T cell response and the formation of memory CD8+ T cell populations. Accordingly, we define the early spatiotemporal events underpinning early lineage-specific chromatin reprogramming that are necessary for autonomous CD8+ T cell proliferation and differentiation.

Runx proteins and transcriptional mechanisms that govern memory CD8 T cell development

Adaptive immunity to intracellular pathogens and tumors is mediated by antigen-experienced CD8 T cells. Individual naive CD8 T cells have the potential to differentiate into a diverse array of antigen-experienced subsets that exhibit distinct effector functions, life spans, anatomic positioning, and potential for regenerating an entirely new immune response during iterative pathogenic exposures. The developmental process by which activated naive cells undergo diversification involves regulation of chromatin structure and transcription but is not entirely understood. This review examines how alterations in chromatin structure, transcription factor binding, extracellular signals, and single-cell gene expression explain the differential development of distinct effector (T_EFF ) and memory (T_MEM ) CD8 T cell subsets. Special emphasis is placed on how Runx proteins function with additional transcription factors to pioneer changes in chromatin accessibility and drive transcriptional programs that establish the core attributes of cytotoxic T lymphocytes, subdivide circulating and non-circulating T_MEM cell subsets, and govern terminal differentiation. The discussion integrates the roles of specific cytokine signals, transcriptional circuits and how regulation of individual nucleosomes and RNA polymerase II activity can contribute to the process of differentiation. A model that integrates many of these features is discussed to conceptualize how activated CD8 T cells arrive at their fates.

Biomechanics of T Cell Dysfunctions in Chronic Diseases

Understanding the mechanisms behind T cell dysfunctions during chronic diseases is critical in developing effective immunotherapies. As demonstrated by several animal models and human studies, T cell dysfunctions are induced during chronic diseases, spanning from infections to cancer. Although factors governing the onset and the extent of the functional impairment of T cells can differ during infections and cancer, most dysfunctional phenotypes share common phenotypic traits in their immune receptor and biophysical landscape. Through the latest developments in biophysical techniques applied to explore cell membrane and receptor-ligand dynamics, we are able to dissect and gain further insights into the driving mechanisms behind T cell dysfunctions. These insights may prove useful in developing immunotherapies aimed at reinvigorating our immune system to fight off infections and malignancies more effectively. The recent success with checkpoint inhibitors in treating cancer opens new avenues to develop more effective, targeted immunotherapies. Here, we highlight the studies focused on the transformation of the biophysical landscape during infections and cancer, and how T cell biomechanics shaped the immunopathology associated with chronic diseases.

Blimp-1 is essential for allergen-induced asthma and Th2 cell development in the lung

A Th2 immune response is central to allergic airway inflammation, which afflicts millions worldwide. However, the mechanisms that augment GATA3 expression in an antigen-primed developing Th2 cell are not well understood. Here, we describe an unexpected role for Blimp-1, a transcriptional repressor that constrains autoimmunity, as an upstream promoter of GATA3 expression that is critical for Th2 cell development in the lung to inhaled but not systemically delivered allergens but is dispensable for T_FH function and IgE production. Mechanistically, Blimp-1 acts through Bcl6, leading to increased GATA3 expression in lung Th2 cells. Surprisingly, the anti-inflammatory cytokine IL-10, but not the pro-inflammatory cytokines IL-6 or IL-21, is required via STAT3 activation to up-regulate Blimp-1 and promote Th2 cell development. These data reveal a hitherto unappreciated role for an IL-10–STAT3–Blimp-1 circuit as an initiator of an inflammatory Th2 response in the lung to allergens. Thus, Blimp-1 in a context-dependent fashion can drive inflammation by promoting rather than terminating effector T cell responses.

Conversations that count: Cellular interactions that drive T cell fate

The relationship between the extrinsic environment and the internal transcriptional network is circular. Naive T cells first engage with antigen‐presenting cells to set transcriptional differentiation networks in motion. In turn, this regulates specific chemokine receptors that direct migration into distinct lymph node niches. Movement into these regions brings newly activated T cells into contact with accessory cells and cytokines that reinforce the differentiation programming to specify T cell function. We and others have observed similarities in the transcriptional networks that specify both CD4+ T follicular helper (T_FH) cells and CD8+ central memory stem‐like (T_SCM) cells. Here, we compare and contrast the current knowledge for these shared differentiation programs, compared to their effector counterparts, CD4+ T‐helper 1 (T_H1) and CD8+ short‐lived effector (T_SLEC) cells. Understanding the interplay between cellular interactions and transcriptional programming is essential to harness T cell differentiation that is fit for purpose; to stimulate potent T cell effector function for the elimination of chronic infection and cancer; or to amplify the formation of humoral immunity and longevity of cellular memory to prevent infectious diseases.

Id3 and Bcl6 Promote the Development of Long-Term Immune Memory Induced by Tuberculosis Subunit Vaccine

Long-lived memory cell formation and maintenance are usually regulated by cytokines and transcriptional factors. Adjuvant effects of IL-7 have been studied in the vaccines of influenza and other pathogens. However, few studies investigated the adjuvant effects of cytokines and transcriptional factors in prolonging the immune memory induced by a tuberculosis (TB) subunit vaccine. To address this research gap, mice were treated with the Mycobacterium tuberculosis (M. tuberculosis) subunit vaccine Mtb10.4-HspX (MH) plus ESAT6-Ag85B-MPT64<190-198>-Mtb8.4-Rv2626c (LT70), together with adeno-associated virus-mediated IL-7 or lentivirus-mediated transcriptional factor Id3, Bcl6, Bach2, and Blimp1 at 0, 2, and 4 weeks, respectively. Immune responses induced by the vaccine were examined at 25 weeks after last immunization. The results showed that adeno-associated virus-mediated IL-7 allowed the TB subunit vaccine to induce the formation of long-lived memory T cells. Meanwhile, IL-7 increased the expression of Id3, Bcl6, and bach2-the three key transcription factors for the generation of long-lived memory T cells. The adjuvant effects of transcriptional factors, together with TB fusion protein MH/LT70 vaccination, showed that both Bcl6 and Id3 increased the production of antigen-specific antibodies and long-lived memory T cells, characterized by high proliferative potential of antigen-specific CD4+ and CD8+ T cells, and IFN-γ secretion in CD4+ and CD8+ T cells, respectively, after re-exposure to the same antigen. Overall, our study suggests that IL-7 and transcriptional factors Id3 and Bcl6 help the TB subunit vaccine to induce long-term immune memory, which contributes to providing immune protection against M. tuberculosis infection.

Inhibitory signaling sustains a distinct early memory CD8+ T cell precursor that is resistant to DNA damage

The developmental origins of memory T cells remain incompletely understood. During the expansion phase of acute viral infection, we identified a distinct subset of virus-specific CD8⁺ T cells that possessed distinct characteristics including expression of CD62L, T cell factor 1 (TCF-1), and Eomesodermin; relative quiescence; expression of activation markers; and features of limited effector differentiation. These cells were a quantitatively minor subpopulation of the TCF-1⁺ pool and exhibited self-renewal, heightened DNA damage surveillance activity, and preferential long-term recall capacity. Despite features of memory and somewhat restrained proliferation during the expansion phase, this subset displayed evidence of stronger TCR signaling than other responding CD8⁺ T cells, coupled with elevated expression of multiple inhibitory receptors including programmed cell death 1 (PD-1), lymphocyte activating gene 3 (LAG-3), cytotoxic T-lymphocyte-associated protein 4 (CTLA-4), CD5, and CD160. Genetic ablation of PD-1 and LAG-3 compromised the formation of this CD62L^hi TCF-1⁺ subset and subsequent CD8⁺ T cell memory. Although central memory phenotype CD8⁺ T cells were formed in the absence of these cells, subsequent memory CD8⁺ T cell recall responses were compromised. Together, these results identify an important link between genome integrity maintenance and CD8⁺ T cell memory. Moreover, the data indicate a role for inhibitory receptors in preserving key memory CD8⁺ T cell precursors during initial activation and differentiation. Identification of this rare subpopulation within the memory CD8⁺ T cell precursor pool may help reconcile models of the developmental origin of long-term CD8⁺ T cell memory.

Induction of Progenitor Exhausted Tissue-Resident Memory CD8+ T Cells Upon Salmonella Typhi Porins Adjuvant Immunization Correlates With Melanoma Control and Anti-PD-1 Immunotherapy Cooperation

Immunotherapy has improved the clinical response in melanoma patients, although a relevant percentage of patients still cannot be salvaged. The search for the immune populations that provide the best tumor control and that can be coaxed by immunotherapy strategies is a hot topic in cancer research nowadays. Tumor-infiltrating TCF-1⁺ progenitor exhausted CD8⁺ T cells seem to grant the best melanoma prognosis and also efficiently respond to anti-PD-1 immunotherapy, giving rise to a TIM-3⁺ terminally exhausted population with heightened effector activity. We tested Porins from Salmonella Typhi as a pathogen associated molecular pattern adjuvant of natural or model antigen in prophylactic and therapeutic immunization approaches against murine melanoma. Porins induced protection against melanomas, even upon re-challenging of tumor-free mice. Porins efficiently expanded IFN-γ-producing CD8⁺ T cells and induced central and effector memory in lymph nodes and tissue-resident (Trm) T cells in the skin and tumors. Porins induced TCF-1⁺ PD-1⁺ CD8⁺ Trm T cells in the tumor stroma and the presence of this population correlated with melanoma growth protection in mice. Porins immunization also cooperated with anti-PD-1 immunotherapy to hamper melanoma growth. Importantly, the potentially protective Trm populations induced by Porins in the murine model were also observed in melanoma patients in which their presence also correlated with disease control. Our data support the use of cancer vaccination to sculpt the tumor stroma with efficient and lasting Trm T cells with effector activities, highlighting the use of Porins as an adjuvant. Furthermore, our data place CD8⁺ Trm T cells with a progenitor exhausted phenotype as an important population for melanoma control, either independently or in cooperation with anti-PD-1 immunotherapy.

Area under Immunosurveillance: Dedicated Roles of Memory CD8 T-Cell Subsets

Immunological memory, defined as the ability to respond in an enhanced manner upon secondary encounter with the same pathogen, can provide substantial protection against infectious disease. The improved protection is mediated in part by different populations of memory CD8 T cells that are retained after primary infection. Memory cells persist in the absence of pathogen-derived antigens and enable secondary CD8 T-cell responses with accelerated kinetics and of larger magnitude after reencounter with the same pathogen. At least three subsets of memory T cells have been defined that are referred to as central memory CD8 T cells (Tcm), effector memory CD8 T cells (Tem), and tissue-resident memory CD8 T cells (Trm). Tcm and Tem are circulating memory T cells that mediate bodywide immune surveillance in search of invading pathogens. In contrast, Trm permanently reside in peripheral barrier tissues, where they form a stationary defensive line of sentinels that alert the immune system upon pathogen reencounter. The characterization of these different subsets has been instrumental in our understanding of the strategies that memory T cells employ to counter invading pathogens. It is clear that memory T cells not only have a numerical advantage over naive T cells resulting in improved protection in secondary responses, but also acquire distinct sets of competencies that assist in pathogen clearance. Nevertheless, inherent challenges are associated with the allocation of memory T cells to a limited number of subsets. The classification of memory T cells into Tcm, Tem, and Trm may not take into account the full extent of the heterogeneity that is observed in the memory population. Therefore, in this review, we will revisit the current classification of memory subsets, elaborate on functional and migratory properties attributed to Tcm, Tem, and Trm, and discuss how potential heterogeneity within these populations arises and persists.

Insights Into the Evolution of the prdm1/Blimp1 Gene Family in Teleost Fish

In mammals, Blimp1 (B lymphocyte-induced maturation protein 1) encoded by the prdm1 gene and its homolog Hobit (homolog of Blimp1 in T cells) encoded by znf683, represent key transcriptional factors that control the development and differentiation of both B and T cells. Despite their essential role in the regulation of acquired immunity, this gene family has been largely unexplored in teleosts to date. Until now, one prdm1 gene has been identified in most teleost species, whereas a znf683 homolog has not yet been reported in any of these species. Focusing our analysis on rainbow trout (Oncorhynchus mykiss), an in silico identification and characterization of prdm1-like genes has been undertaken, confirming that prdm1 and znf683 evolved from a common ancestor gene, acquiring three gene copies after the teleost-specific whole genome duplication event (WGD) and six genes after the salmonid-specific WGD. Additional transcriptional studies to study how each of these genes are regulated in homeostasis, in response to a viral infection or in B cells in different differentiation stages, provide novel insights as to how this gene family evolved and how their encoded products might be implicated in the lymphocyte differentiation process in teleosts.