Eomes broadens the scope of CD8 T-cell memory by inhibiting apoptosis in cells of low affinity

GFI1-driven transcriptional and epigenetic programs maintain CD8+ T cell stemness and persistence

Long-lived memory CD8+ T cells are essential for the control of persistent viral infections. The mechanisms that preserve memory cells are poorly understood. Fate mapping of the transcriptional repressor GFI1 identified that GFI1 was differentially regulated in virus-specific CD8+ T cells and was selectively expressed in stem cell memory and central memory cells. Deletion of GFI1 led to reduced proliferation and progressive loss of memory T cells, which in turn resulted in failure to maintain antigen-specific CD8+ T cell populations following infection with chronic lymphocytic choriomeningitis virus or murine cytomegalovirus. Ablation of GFI1 resulted in downregulation of the transcription factors EOMES and BCL-2 in memory CD8+ T cells. Ectopic expression of EOMES rescued the expression of BCL-2, but the persistence of memory CD8+ T cells was only partially rescued. These findings highlight the critical role of GFI1 in the long-term maintenance of memory CD8+ T cells in persistent infections by sustaining their proliferative potential.

DYNC2H1 mutation as a potential predictive biomarker for immune checkpoint inhibitor efficacy in NSCLC and melanoma

Dynein cytoplasmic 2 heavy chain 1 (DYNC2H1) is reported to play a potential role in cancer immunotherapy. However, the association between DYNC2H1 mutation and the clinical benefit of immunotherapy in non-small cell lung cancer (NSCLC) and melanoma remains to be elucidated. We collected data from three public immune checkpoint inhibitor (ICI)-treated NSCLC cohorts (n = 137 in total) and seven ICI-treated melanoma cohorts (n = 418 in total) to explore the potential of DYNC2H1 mutation as a predictive biomarker. The clinical outcomes, including the objective response rate (ORR) and progression-free survival (PFS), of patients with DYNC2H1 mutations are significantly better than those of patients with wild-type DYNC2H1. Multivariate Cox regression analysis confirmed that DYNC2H1 mutation was an independent predictive factor for ICI efficacy in NSCLC and melanoma. In addition, DYNC2H1 mutation exhibited no prognostic value for NSCLC or melanoma. Tumour mutational burden (TMB) and tumour neoantigen burden (TNB) were significantly higher in patients with DYNC2H1 mutation than in those with wild-type DYNC2H1 in both NSCLC and melanoma cohort. The analysis of immune-related genes and immune cell enrichment revealed an association between DYNC2H1 mutation and increased immune infiltration, revealing a potential mechanism underlying the predictive role of DYNC2H1 mutation in immunotherapy efficacy. In conclusion, DYNC2H1 mutation serves as a predictive biomarker of ICI efficacy in NSCLC and melanoma.

Low-affinity CD8+ T cells provide interclonal help to high-affinity CD8+ T cells to augment alloimmunity

Following solid organ transplantation, small precursor populations of polyclonal CD8+ T cells specific for any graft-expressed antigen preferentially expand their high-affinity clones. This phenomenon, termed "avidity maturation," results in a larger population of CD8+ T cells with increased sensitivity to alloantigen, posing a greater risk for graft rejection. Using a mouse model of minor-mismatched skin transplantation, coupled with the tracking of 2 skin graft-reactive CD8+ T cell receptor-transgenic tracer populations with high and low affinity for the same peptide-major histocompatibility complex, we explored the conventional paradigm that CD8+ T cell avidity maturation occurs through T cell receptor affinity-based competition for cognate antigen. Our data revealed "interclonal CD8-CD8 help," whereby lower/intermediate affinity clones help drive the preferential expansion of their higher affinity counterparts in an interleukin-2/CD25-dependent manner. Consequently, the CD8-helped high-affinity clones exhibit greater expansion and develop augmented effector functions in the presence of their low-affinity counterparts, correlating with more severe graft damage. Finally, interclonal CD8-CD8 help was suppressed by costimulation blockade treatment. Thus, high-affinity CD8+ T cells can leverage help from low-affinity CD8+ T cells of identical specificity to promote graft rejection. Suppressing provision of interclonal CD8-CD8 help may be important to improve transplant outcomes.

Expansion of memory Vδ2 T cells following SARS-CoV-2 vaccination revealed by temporal single-cell transcriptomics

γδ T cells provide rapid cellular immunity against pathogens. Here, we conducted matched single-cell RNA-sequencing and γδ-TCR-sequencing to delineate the molecular changes in γδ T cells during a longitudinal study following mRNA SARS-CoV-2 vaccination. While the first dose of vaccine primes Vδ2 T cells, it is the second administration that significantly boosts their immune response. Specifically, the second vaccination uncovers memory features of Vδ2 T cells, shaped by the induction of AP-1 family transcription factors and characterized by a convergent central memory signature, clonal expansion, and an enhanced effector potential. This temporally distinct effector response of Vδ2 T cells was also confirmed in vitro upon stimulation with SARS-CoV-2 spike-peptides. Indeed, the second challenge triggers a significantly higher production of IFNγ by Vδ2 T cells. Collectively, our findings suggest that mRNA SARS-CoV-2 vaccination might benefit from the establishment of long-lasting central memory Vδ2 T cells to confer protection against SARS-CoV-2 infection.

Preimmunization with Listeria-vectored cervical cancer vaccine candidate strains can establish specific T-cell immune memory and prevent tumorigenesis

BACKGROUND

Although HPV prophylactic vaccines can provide effective immune protection against high-risk HPV infection, studies have shown that the protective effect provided by them would decrease with the increased age of vaccination, and they are not recommended for those who are not in the appropriate age range for vaccination. Therefore, in those people who are not suitable for HPV prophylactic vaccines, it is worth considering establishing memory T-cell immunity to provide long-term immune surveillance and generate a rapid response against lesional cells to prevent tumorigenesis.

METHODS

In this study, healthy mice were preimmunized with LM∆E6E7 and LI∆E6E7, the two Listeria-vectored cervical cancer vaccine candidate strains constructed previously by our laboratory, and then inoculated with tumor cells 40 d later.

RESULTS

The results showed that preimmunization with LM∆E6E7 and LI∆E6E7 could establish protective memory T-cell immunity against tumor antigens in mice, which effectively eliminate tumor cells. 60% of mice preimmunized with vaccines did not develop tumors, and for the remaining mice, tumor growth was significantly inhibited. We found that preimmunization with vaccines may exert antitumor effects by promoting the enrichment of T cells at tumor site to exert specific immune responses, as well as inhibiting intratumoral angiogenesis and cell proliferation.

CONCLUSION

Altogether, this study suggests that preimmunization with LM∆E6E7 and LI∆E6E7 can establish memory T-cell immunity against tumor antigens in vivo, which provides a viable plan for preventing tumorigenesis and inhibiting tumor progression.

Rethinking IL-1 Antagonism in Respiratory Viral Infections: A Role for IL-1 Signaling in the Development of Antiviral T Cell Immunity

IL-1R integrates signals from IL-1α and IL-1β, and it is widely expressed across tissues and immune cell types. While the expression pattern and function of IL-1R within the innate immune system is well studied, its role in adaptive immunity, particularly within the CD8 T cell compartment, remains underexplored. Here, we show that CD8 T cells dynamically upregulate IL-1R1 levels during priming by APCs, which correlates with their proliferation status and the acquisition of an effector phenotype. Notably, this IL-1 sensitivity persists in memory CD8 T cells of both mice and humans, influencing effector cytokine production upon TCR reactivation. Furthermore, our study highlights that antiviral effector and tissue-resident CD8 T cell responses against influenza A virus infection become impaired in the absence of IL-1 signaling. Altogether, these data support the exploitation of IL-1 activity in the context of T cell vaccination strategies and warrant consideration of the impact of clinical IL-1 inhibition on the rollout of T cell immunity.

Interferon-γ couples CD8+ T cell avidity and differentiation during infection

Effective responses to intracellular pathogens are characterized by T cell clones with a broad affinity range for their cognate peptide and diverse functional phenotypes. How T cell clones are selected throughout the response to retain a breadth of avidities remains unclear. Here, we demonstrate that direct sensing of the cytokine IFN-γ by CD8+ T cells coordinates avidity and differentiation during infection. IFN-γ promotes the expansion of low-avidity T cells, allowing them to overcome the selective advantage of high-avidity T cells, whilst reinforcing high-avidity T cell entry into the memory pool, thus reducing the average avidity of the primary response and increasing that of the memory response. IFN-γ in this context is mainly provided by virtual memory T cells, an antigen-inexperienced subset with memory features. Overall, we propose that IFN-γ and virtual memory T cells fulfil a critical immunoregulatory role by enabling the coordination of T cell avidity and fate.

Homeostatic PD-1 signaling restrains EOMES-dependent oligoclonal expansion of liver-resident CD8 T cells

The co-inhibitory programmed death (PD)-1 signaling pathway plays a major role in the context of tumor-specific T cell responses. Conversely, it also contributes to the maintenance of peripheral tolerance, as patients receiving anti-PD-1 treatment are prone to developing immune-related adverse events. Yet, the physiological role of the PD-1/PDL-1 axis in T cell homeostasis is still poorly understood. Herein, we show that under steady-state conditions, the absence of PD-1 signaling led to a preferential expansion of CD8+ T cells in the liver. These cells exhibit an oligoclonal T cell receptor (TCR) repertoire and a terminally differentiated exhaustion profile. The transcription factor EOMES is required for the clonal expansion and acquisition of this differentiation program. Finally, single-cell transcriptomics coupled with TCR repertoire analysis support the notion that these cells arise locally from liver-resident memory CD8+ T cells. Overall, we show a role for PD-1 signaling in liver memory T cell homeostasis.

Thanks for the memories: Low-avidity T cells shine against escape variants

T cell responses against foreign antigens are clonally diverse, but the significance of this diversity is unclear. In this issue of Immunity, Straub et al.¹ show that recruitment of low-avidity T cells during primary infection can provide protection against subsequent encounter with escape variants.

Asymmetric cell division safeguards memory CD8 T cell development

The strength of T cell receptor (TCR) stimulation and asymmetric distribution of fate determinants are both implied to affect T cell differentiation. Here, we uncover asymmetric cell division (ACD) as a safeguard mechanism for memory CD8 T cell generation specifically upon strong TCR stimulation. Using live imaging approaches, we find that strong TCR stimulation induces elevated ACD rates, and subsequent single-cell-derived colonies comprise both effector and memory precursor cells. The abundance of memory precursor cells emerging from a single activated T cell positively correlates with first mitosis ACD. Accordingly, preventing ACD by inhibition of protein kinase Cζ (PKCζ) during the first mitosis upon strong TCR stimulation markedly curtails the formation of memory precursor cells. Conversely, no effect of ACD on fate commitment is observed upon weak TCR stimulation. Our data provide relevant mechanistic insights into the role of ACD for CD8 T cell fate regulation upon different activation conditions.

Vaccination provides superior in vivo recall capacity of SARS-CoV-2-specific memory CD8 T cells

Memory CD8 T cells play an important role in the protection against breakthrough infections with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Whether the route of antigen exposure impacts these cells at a functional level is incompletely characterized. Here, we compare the memory CD8 T cell response against a common SARS-CoV-2 epitope after vaccination, infection, or both. CD8 T cells demonstrate comparable functional capacity when restimulated directly ex vivo, independent of the antigenic history. However, analysis of T cell receptor usage shows that vaccination results in a narrower scope than infection alone or in combination with vaccination. Importantly, in an in vivo recall model, memory CD8 T cells from infected individuals show equal proliferation but secrete less tumor necrosis factor (TNF) compared with those from vaccinated people. This difference is negated when infected individuals have also been vaccinated. Our findings shed more light on the differences in susceptibility to re-infection after different routes of SARS-CoV-2 antigen exposure.

Comparative transcriptomes reveal pro-survival and cytotoxic programs of mucosal-associated invariant T cells upon Bacillus Calmette-Guérin stimulation

Mucosal-associated invariant T (MAIT) cells are protective against tuberculous and non-tuberculous mycobacterial infections with poorly understood mechanisms. Despite an innate-like nature, MAIT cell responses remain heterogeneous in bacterial infections. To comprehensively characterize MAIT activation programs responding to different bacteria, we stimulated MAIT cells with E. coli to compare with Bacillus Calmette-Guérin (BCG), which remains the only licensed vaccine and a feasible tool for investigating anti-mycobacterial immunity in humans. Upon sequencing mRNA from the activated and inactivated CD8+ MAIT cells, results demonstrated the altered MAIT cell gene profiles by each bacterium with upregulated expression of activation markers, transcription factors, cytokines, and cytolytic mediators crucial in anti-mycobacterial responses. Compared with E. coli, BCG altered more MAIT cell genes to enhance cell survival and cytolysis. Flow cytometry analyses similarly displayed a more upregulated protein expression of B-cell lymphoma 2 and T-box transcription factor Eomesodermin in BCG compared to E.coli stimulations. Thus, the transcriptomic program and protein expression of MAIT cells together displayed enhanced pro-survival and cytotoxic programs in response to BCG stimulation, supporting BCG induces cell-mediated effector responses of MAIT cells to fight mycobacterial infections.

Chronic lymphocytic leukemia presence impairs antigen-specific CD8+ T-cell responses through epigenetic reprogramming towards short-lived effectors

T-cell dysregulation in chronic lymphocytic leukemia (CLL) associates with low response rates to autologous T cell-based therapies. How CLL affects antigen-specific T-cell responses remains largely unknown. We investigated (epi)genetic and functional consequences of antigen-specific T-cell responses in presence of CLL in vitro and in an adoptive-transfer murine model. Already at steady-state, antigen-experienced patient-derived T cells were skewed towards short-lived effector cells (SLEC) at the expense of memory-precursor effector cells (MPEC). Stimulation of these T cells in vitro showed rapid induction of effector genes and suppression of key memory transcription factors only in presence of CLL cells, indicating epigenetic regulation. This was investigated in vivo by following antigen-specific responses of naïve OT-I CD8⁺ cells to mCMV-OVA in presence/absence of TCL1 B-cell leukemia. Presence of leukemia resulted in increased SLEC formation, with disturbed inflammatory cytokine production. Chromatin and transcriptome profiling revealed strong epigenetic modifications, leading to activation of an effector and silencing of a memory profile through presence of CLL cells. Secondary challenge in vivo confirmed dysfunctional memory responses by antigen-experienced OT-I cells generated in presence of CLL. Altogether, we show that presence of CLL induces a short-lived effector phenotype and impaired memory responses by epigenetic reprogramming during primary responses.

Small intestine and colon tissue-resident memory CD8+ T cells exhibit molecular heterogeneity and differential dependence on Eomes

Tissue-resident memory CD8+ T (TRM) cells are a subset of memory T cells that play a critical role in limiting early pathogen spread and controlling infection. TRM cells exhibit differences across tissues, but their potential heterogeneity among distinct anatomic compartments within the small intestine and colon has not been well recognized. Here, by analyzing TRM cells from the lamina propria and epithelial compartments of the small intestine and colon, we showed that intestinal TRM cells exhibited distinctive patterns of cytokine and granzyme expression along with substantial transcriptional, epigenetic, and functional heterogeneity. The T-box transcription factor Eomes, which represses TRM cell formation in some tissues, exhibited unexpected context-specific regulatory roles in supporting the maintenance of established TRM cells in the small intestine, but not in the colon. Taken together, these data provide previously unappreciated insights into the heterogeneity and differential requirements for the formation vs. maintenance of intestinal TRM cells.

T-cell exhaustion and stemness in antitumor immunity: Characteristics, mechanisms, and implications

T cells play a crucial role in the regulation of immune response and are integral to the efficacy of cancer immunotherapy. Because immunotherapy has emerged as a promising treatment for cancer, increasing attention has been focused on the differentiation and function of T cells in immune response. In this review, we describe the research progress on T-cell exhaustion and stemness in the field of cancer immunotherapy and summarize advances in potential strategies to intervene and treat chronic infection and cancer by reversing T-cell exhaustion and maintaining and increasing T-cell stemness. Moreover, we discuss therapeutic strategies to overcome T-cell immunodeficiency in the tumor microenvironment and promote continuous breakthroughs in the anticancer activity of T cells.

Combination bezafibrate and nivolumab treatment of patients with advanced non-small cell lung cancer

Despite the success of cancer immunotherapies such as programmed cell death-1 (PD-1) and PD-1 ligand 1 (PD-L1) inhibitors, patients often develop resistance. New combination therapies with PD-1/PD-L1 inhibitors are needed to overcome this issue. Bezafibrate, a ligand of peroxisome proliferator-activated receptor-γ coactivator 1α/peroxisome proliferator-activated receptor complexes, has shown a synergistic antitumor effect with PD-1 blockade in mice that is mediated by activation of mitochondria in T cells. We have therefore now performed a phase 1 trial (UMIN000017854) of bezafibrate with nivolumab in previously treated patients with advanced non-small cell lung cancer. The primary end point was the percentage of patients who experience dose-limiting toxicity, and this combination regimen was found to be well tolerated. Preplanned comprehensive analysis of plasma metabolites and gene expression in peripheral cytotoxic T cells indicated that bezafibrate promoted T cell function through up-regulation of mitochondrial metabolism including fatty acid oxidation and may thereby have prolonged the duration of response. This combination strategy targeting T cell metabolism thus has the potential to maintain antitumor activity of immune checkpoint inhibitors and warrants further validation.

Regulation of CD4 T Cell Responses by the Transcription Factor Eomesodermin

Central to the impacts of CD4 T cells, both positive in settings of infectious disease and cancer and negative in the settings of autoimmunity and allergy, is their ability to differentiate into distinct effector subsets with specialized functions. The programming required to support such responses is largely dictated by lineage-specifying transcription factors, often called ‘master regulators’. However, it is increasingly clear that many aspects of CD4 T cell immunobiology that can determine the outcomes of disease states involve a broader transcriptional network. Eomesodermin (Eomes) is emerging as an important member of this class of transcription factors. While best studied in CD8 T cells and NK cells, an increasing body of work has focused on impacts of Eomes expression in CD4 T cell responses in an array of different settings. Here, we focus on the varied impacts reported in these studies that, together, indicate the potential of targeting Eomes expression in CD4 T cells as a strategy to improve a variety of clinical outcomes.

Divide and Conquer: Phenotypic and Temporal Heterogeneity Within CD8+ T Cell Responses

The advent of technologies that can characterize the phenotypes, functions and fates of individual cells has revealed extensive and often unexpected levels of diversity between cells that are nominally of the same subset. CD8+ T cells, also known as cytotoxic T lymphocytes (CTLs), are no exception. Investigations of individual CD8+ T cells both in vitro and in vivo have highlighted the heterogeneity of cellular responses at the levels of activation, differentiation and function. This review takes a broad perspective on the topic of heterogeneity, outlining different forms of variation that arise during a CD8+ T cell response. Specific attention is paid to the impact of T cell receptor (TCR) stimulation strength on heterogeneity. In particular, this review endeavors to highlight connections between variation at different cellular stages, presenting known mechanisms and key open questions about how variation between cells can arise and propagate.

Adoptive transfer of IL-4 reprogrammed Tc17 cells elicits anti-tumour immunity through functional plasticity

Ability of IL-17-producing CD8+ T cells (Tc17) to transform into cytotoxic anti-tumour effectors makes them a promising candidate for immune effector cell (IEC) therapy. However, key factors regulating Tc17 reprogramming remain poorly defined, hindering translation of Tc17-based IEC use from bench to bedside. We probed the effects of multiple cytokines and underlying signalling pathways on Tc17 cells and identified pivotal role for IL-4 and PI3K/AKT in promoting Tc17 transformation into cytotoxic IFN-γ-producing IECs, an effect dependent on Eomes expression. IL-4 not only triggered Tc17 cytotoxicity, but also induced cell expansion, which significantly improved the antitumour potential of Tc17 cells compared to that of IFN-γ-producing CD8+ T cells (Tc1) in a murine model. Furthermore, IL-4/AKT signalling drove the upregulation of the T-cell receptor-associated transmembrane adaptor 1 (Trat1) in Tc17 cells to promote IL-4-induced T-cell receptor stabilization and Tc17 cytotoxicity. Finally, we proposed a possible procedure to expand human Tc17 from peripheral blood of cancer patients, and confirmed the function of IL-4 in Tc17 reprogramming. Collectively, these results document a novel IL-4/AKT/Eomes/Trat1 axis that promotes expansion and transformation of Tc17 cells into cytotoxic effectors with a therapeutic potential. IL-4 priming of Tc17 cells should be further explored as a cell therapy engineering strategy to generate IECs to augment anti-tumour responses.

Hyperglycemia and Not Hyperinsulinemia Mediates Diabetes-Induced Memory CD8 T-Cell Dysfunction

Type 2 diabetes (T2D) causes an increased risk of morbidity and mortality in response to viral infection. T2D is characterized by hyperglycemia and is typically associated with insulin resistance and compensatory hyperinsulinemia. CD8 T cells express the insulin receptor, and previously, we have shown that insulin is able to directly modulate effector CD8 T-cell function. We therefore hypothesized that memory CD8 T-cell responsiveness in the context of T2D is negatively impacted by hyperinsulinemia or hyperglycemia. Using a mouse model for T2D, we could show that memory CD8 T-cell function was significantly reduced in response to rechallenge by viral infection or with melanoma cells. Basal insulin injection of mice increased GLUT-1 expression and glucose uptake in memory CD8 T-cell precursors early after infection, which was prevented when these cells were deficient for the insulin receptor. However, neither insulin injection nor insulin receptor deficiency resulted in a difference in metabolism, memory formation, cytokine production, or recall responses of memory CD8 T cells compared with controls. Importantly, in context of obesity, insulin receptor deficiency on CD8 T cells did not affect the functional capacity of memory CD8 T cells. In contrast, we could show in vitro and in vivo that hyperglycemia significantly impairs the antiviral capacity of memory CD8 T cells. Our findings indicate that obesity impairs the memory CD8 T-cell response against viral infection and cancer through the detrimental effects of hyperglycemia rather than hyperinsulinemia.

Prosurvival IL-7-Stimulated Weak Strength of mTORC1-S6K Controls T Cell Memory via Transcriptional FOXO1-TCF1-Id3 and Metabolic AMPKα1-ULK1-ATG7 Pathways

CD8⁺ memory T (T_M) cells play a critical role in immune defense against infection. Two common γ-chain family cytokines, IL-2 and IL-7, although triggering the same mTORC1-S6K pathway, distinctly induce effector T (T_E) cells and T_M cells, respectively, but the underlying mechanism(s) remains elusive. In this study, we generated IL-7R-/and AMPKα1-knockout (KO)/OTI mice. By using genetic and pharmaceutical tools, we demonstrate that IL-7 deficiency represses expression of FOXO1, TCF1, p-AMPKα1 (T₁₇₂), and p-ULK1 (S₅₅₅) and abolishes T cell memory differentiation in IL-7R KO T cells after Listeria monocytogenesis rLmOVA infection. IL-2- and IL-7-stimulated strong and weak S6K (IL-2/S6K^strong and IL-7/S6K^weak) signals control short-lived IL-7R^-CD62L^-KLRG1⁺ T_E and long-term IL-7R⁺CD62L⁺KLRG1^- T_M cell formations, respectively. To assess underlying molecular pathway(s), we performed flow cytometry, Western blotting, confocal microscopy, and Seahorse assay analyses by using the IL-7/S6K^weak-stimulated T_M (IL-7/T_M) and the control IL-2/S6K^strong-stimulated T_E (IL-2/T_E) cells. We determine that the IL-7/S6K^weak signal activates transcriptional FOXO1, TCF1, and Id3 and metabolic p-AMPKα1, p-ULK1, and ATG7 molecules in IL-7/T_M cells. IL-7/T_M cells upregulate IL-7R and CD62L, promote mitochondria biogenesis and fatty acid oxidation metabolism, and show long-term cell survival and functional recall responses. Interestingly, AMPKα1 deficiency abolishes the AMPKα1 but maintains the FOXO1 pathway and induces a metabolic switch from fatty acid oxidation to glycolysis in AMPKα1 KO IL-7/T_M cells, leading to loss of cell survival and recall responses. Taken together, our data demonstrate that IL-7-stimulated weak strength of mTORC1-S6K signaling controls T cell memory via activation of transcriptional FOXO1-TCF1-Id3 and metabolic AMPKα1-ULK1-ATG7 pathways. This (to our knowledge) novel finding provides a new mechanism for a distinct IL-2/IL-7 stimulation model in T cell memory and greatly impacts vaccine development.

Staggered starts in the race to T cell activation

How T lymphocytes tune their responses to different strengths of stimulation is a fundamental question in immunology. Recent work using new optogenetic, single-cell genomic, and live-imaging approaches has revealed that stimulation strength controls the rate of individual cell responses within a population. Moreover, these responses have been found to use shared molecular programs, regardless of stimulation strength. However, additional data indicate that stimulation duration or cytokine feedback can impact later gene expression phenotypes of activated cells. In-depth molecular studies have suggested mechanisms by which stimulation strength might modulate the probability of T cell activation. This emerging model allows activating T cells to achieve a wide range of population responses through probabilistic control within individual cells.

CD8 T Cell Vaccines and a Cytomegalovirus-Based Vector Approach

The twentieth century witnessed a huge expansion in the number of vaccines used with great success in combating diseases, especially the ones caused by viral and bacterial pathogens. Despite this, several major public health threats, such as HIV, tuberculosis, malaria, and cancer, still pose an enormous humanitarian and economic burden. As vaccines based on the induction of protective, neutralizing antibodies have not managed to effectively combat these diseases, in recent decades, the focus has increasingly shifted towards the cellular immune response. There is substantial evidence demonstrating CD8 T cells as key players in the protection not only against many viral and bacterial pathogens, but also in the fight against neoplastic cells. Here, we present arguments for CD8 T cells to be considered as promising candidates for vaccine targeting. We discuss the heterogeneity of CD8 T cell populations and their contribution in the protection of the host. We also outline several strategies of using a common human pathogen, cytomegalovirus, as a vaccine vector since accumulated data strongly suggest it represents a promising approach to the development of novel vaccines against both pathogens and tumors.

Signals for antigen-independent differentiation of memory CD8+ T cells

Conventional CD8+ memory T cells develop upon stimulation with foreign antigen and provide increased protection upon re-challenge. Over the past two decades, new subsets of CD8+ T cells have been identified that acquire memory features independently of antigen exposure. These antigen-inexperienced memory T cells (TAIM) are described under several names including innate memory, virtual memory, and memory phenotype. TAIM cells exhibit characteristics of conventional or true memory cells, including antigen-specific responses. In addition, they show responsiveness to innate stimuli and have been suggested to provide additional levels of protection toward infections and cancer. Here, we discuss the current understanding of TAIM cells, focusing on extrinsic and intrinsic molecular conditions that favor their development, their molecular definitions and immunological properties, as well as their transcriptional and epigenetic regulation.

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.

Stem cell-like memory T cells: The generation and application

Stem cell-like memory T cells (Tscm), are a newly defined memory T cell subset with characteristics of long life span, consistent self-renewing, rapid differentiation into effector T cells, and apoptosis resistance. These features indicate that Tscm have great therapeutic or preventive purposes, including being applied in chimeric Ag receptor-engineered T cells, TCR gene-modified T cells, and vaccines. However, the little knowledge about Tscm development restrains their applications. Strength and duration of TCR signaling, cytokines and metabolism in the T cells during activation all influence the Tscm development via regulating transcriptional factors and cell signaling pathways. Here, we summarize the molecular and cellular pathways involving Tscm differentiation, and its clinical application for cancer immunotherapy and prevention.

T-cell dysfunction in chronic lymphocytic leukemia from an epigenetic perspective

Cellular immunotherapeutic approaches such as chimeric antigen receptor (CAR) T-cell therapy in chronic lymphocytic leukemia (CLL) thus far have not met the high expectations. Therefore it is essential to better understand the molecular mechanisms of CLLinduced T-cell dysfunction. Even though a significant number of studies are available on T-cell function and dysfunction in CLL patients, none examine dysfunction at the epigenomic level. In non-malignant T-cell research, epigenomics is widely employed to define the differentiation pathway into T-cell exhaustion. Additionally, metabolic restrictions in the tumor microenvironment that cause T-cell dysfunction are often mediated by epigenetic changes. With this review paper we argue that understanding the epigenetic (dys)regulation in T cells of CLL patients should be leveled to the knowledge we currently have of the neoplastic B cells themselves. This will permit a complete understanding of how these immune cell interactions regulate T- and B-cell function. Here we relate the cellular and phenotypic characteristics of CLL-induced T-cell dysfunction to epigenetic studies of T-cell regulation emerging from chronic viral infection and tumor models. This paper proposes a framework for future studies into the epigenetic regulation of CLL-induced Tcell dysfunction, knowledge that will help to guide improvements in the utility of autologous T-cell based therapies in CLL.

Enhancing the Generation of Eomeshi CD8+ T Cells Augments the Efficacy of OX40- and CTLA-4-Targeted Immunotherapy

CTLA-4 blockade in combination with an agonist OX40-specific monoclonal antibody synergizes to augment antitumor immunity through enhanced T-cell effector function, leading to increased survival in preclinical cancer models. We have shown previously that anti-OX40/anti-CTLA-4 combination therapy synergistically enhances the expression of Eomesodermin (Eomes) in CD8⁺ T cells. Eomes is a critical transcription factor for the differentiation and memory function of CD8⁺ T cells. We hypothesized that Eomes^hiCD8⁺ T cells were necessary for anti-OX40/anti-CTLA-4 immunotherapy efficacy and that further enhancement of this population would improve tumor-free survival. Indeed, CD8⁺ T cell-specific deletion of Eomes abrogated the efficacy of anti-OX40/anti-CTLA-4 therapy. We also found that anti-OX40/anti-CTLA-4-induced Eomes^hiCD8⁺ T cells expressed lower levels of checkpoint receptors (PD1, Tim-3, and Lag-3) and higher levels of effector cytokines (IFNγ and TNFα) than their Eomes^lo counterparts. Eomes expression is negatively regulated in T cells through interleukin-2-inducible T-cell kinase (ITK) signaling. We investigated the impact of modulating ITK signaling with ibrutinib, an FDA-approved tyrosine kinase inhibitor, and found that anti-OX40/anti-CTLA-4/ibrutinib therapy further enhanced CD8⁺ T cell-specific Eomes expression, leading to enhanced tumor regression and improved survival, both of which were associated with increased T-cell effector function across multiple tumor models. Taken together, these data demonstrate the potential of anti-OX40/anti-CTLA-4/ibrutinib as a triple therapy to improve the efficacy of immunotherapy.