Ectopic expression of a T-box transcription factor, eomesodermin, renders CD4+ Th cells cytotoxic by activating both perforin- and FasL-pathways

DNA methylation heterogeneity attributable to a complex tumor immune microenvironment prompts prognostic risk in glioma

Gliomas are malignant tumours of the human nervous system with different World Health Organization (WHO) classifications, glioblastoma (GBM) with higher grade and are more malignant than lower-grade glioma (LGG). To dissect how the DNA methylation heterogeneity in gliomas is influenced by the complex cellular composition of the tumour immune microenvironment, we first compared the DNA methylation profiles of purified human immune cells and bulk glioma tissue, stratifying three tumour immune microenvironmental subtypes for GBM and LGG samples from The Cancer Genome Atlas (TCGA). We found that more intermediate methylation sites were enriched in glioma tumour tissues, and used the Proportion of sites with Intermediate Methylation (PIM) to compare intertumoral DNA methylation heterogeneity. A larger PIM score reflected stronger DNA methylation heterogeneity. Enhanced DNA methylation heterogeneity was associated with stronger immune cell infiltration, better survival rates, and slower tumour progression in glioma patients. We then created a Cell-type-associated DNA Methylation Heterogeneity Contribution (CMHC) score to explore the impact of different immune cell types on heterogeneous CpG site (CpGct) in glioma tissues. We identified eight prognosis-related CpGct to construct a risk score: the Cell-type-associated DNA Methylation Heterogeneity Risk (CMHR) score. CMHR was positively correlated with cytotoxic T-lymphocyte infiltration (CTL), and showed better predictive performance for IDH status (AUC = 0.96) and glioma histological phenotype (AUC = 0.81). Furthermore, DNA methylation alterations of eight CpGct might be related to drug treatments of gliomas. In conclusion, we indicated that DNA methylation heterogeneity is associated with a complex tumour immune microenvironment, glioma phenotype, and patient's prognosis.

Advances and challenges in immunotherapy for locally advanced nasopharyngeal carcinoma

Nasopharyngeal carcinoma (NPC) is a prevalent malignant tumor of the head and neck, with approximately 70 % of patients being diagnosed at a locally advanced stage. Despite the responsiveness to radiotherapy and chemotherapy, the 5-year survival rate of locally advanced NPC (LANPC) remains at approximately 80 %. Hence, there is an urgent need for novel treatment strategies to improve the prognosis of patients with LANPC. Numerous studies have illustrated the efficacy of immune checkpoint inhibitors (ICIs) in recurrent/metastatic NPC. Hence, the potential of immunotherapy for LANPC is under investigation. Using the Web of Clinical Trials, we identified 84 relevant trials exploring immunotherapy for NPC, encompassing 17 trials focusing on ICIs for LANPC. Preliminary findings from several trials suggest that adding ICIs into the primary treatment for LANPC significantly enhances the objective response rate and progression-free survival, with manageable safety profiles. However, the type, dosage, and timing of integration (induction phase, concurrent phase, and adjuvant phase) of ICIs into standard primary treatment of LANPC varies among these trials and further researches are warranted. This review provides an overview of immunotherapy principles in NPC, discusses recent advances and challenges associated with ICIs in the primary treatment for LANPC derived from published and ongoing clinical trials, and outlines the current landscape of other immunotherapies in LANPC, such as adoptive cell therapy, immunomodulatory agents, and tumor vaccines in LANPC. These insights aim to inform clinical practice and guide future researches.

Cytotoxic CD4+ T cells in chronic viral infections and cancer

CD4+ T cells play an important role in immune responses against pathogens and cancer cells. Although their main task is to provide help to other effector immune cells, a growing number of infections and cancer entities have been described in which CD4+ T cells exhibit direct effector functions against infected or transformed cells. The most important cell type in this context are cytotoxic CD4+ T cells (CD4+ CTL). In infectious diseases anti-viral CD4+ CTL are mainly found in chronic viral infections. Here, they often compensate for incomplete or exhausted CD8+ CTL responses. The induction of CD4+ CTL is counter-regulated by Tregs, most likely because they can be dangerous inducers of immunopathology. In viral infections, CD4+ CTL often kill via the Fas/FasL pathway, but they can also facilitate the exocytosis pathway of killing. Thus, they are very important effectors to keep persistent virus in check and guarantee host survival. In contrast to viral infections CD4+ CTL attracted attention as direct anti-tumor effectors in solid cancers only recently. Anti-tumor CD4+ CTL are defined by the expression of cytolytic markers and have been detected within the lymphocyte infiltrates of different human cancers. They kill tumor cells in an antigen-specific MHC class II-restricted manner not only by cytolysis but also by release of IFNγ. Thus, CD4+ CTL are interesting tools for cure approaches in chronic viral infections and cancer, but their potential to induce immunopathology has to be carefully taken into consideration.

Murine cytotoxic CD4+ T cells in the tumor microenvironment are at a hyper-maturation stage of Th1 CD4+ T cells sustained by IL-12

The roles of tumor-infiltrating CD4+Foxp3- T cells are not well characterized due to their plasticity of differentiation, and varying levels of activation or exhaustion. To further clarify this issue, we used a model featuring subcutaneous murine colon cancer and analyzed the dynamic changes of phenotype and function of the tumor-associated CD4+ T-cell response. We found that, even at a late stage of tumor growth, the tumor-infiltrating CD4+Foxp3- T cells still expressed effector molecules, inflammatory cytokines and molecules that are expressed at reduced levels in exhausted cells. We used microarrays to examine the gene-expression profiles of different subsets of CD4+ T cells and revealed that the tumor-infiltrating CD4+Foxp3- T cells expressed not only type 1 helper (Th1) cytokines, but also cytolytic granules such as those encoded by Gzmb and Prf1. In contrast to CD4+ regulatory T cells, these cells exclusively co-expressed natural killer receptor markers and cytolytic molecules as shown by flow-cytometry studies. We used an ex vivo killing assay and proved that they could directly suppress CT26 tumor cells through granzyme B and perforin. Finally, we used pathway analysis and ex vivo stimulation to confirm that the CD4+Foxp3- T cells expressed higher levels of IL12rb1 genes and were activated by the IL-12/IL-27 pathway. In conclusion, this work finds that, in late-stage tumors, the tumor-infiltrating lymphocyte population of CD4+ cells harbored a sustained, hyper-maturated Th1 status with cytotoxic function supported by IL-12.

T cells in health and disease

T cells are crucial for immune functions to maintain health and prevent disease. T cell development occurs in a stepwise process in the thymus and mainly generates CD4+ and CD8+ T cell subsets. Upon antigen stimulation, naïve T cells differentiate into CD4+ helper and CD8+ cytotoxic effector and memory cells, mediating direct killing, diverse immune regulatory function, and long-term protection. In response to acute and chronic infections and tumors, T cells adopt distinct differentiation trajectories and develop into a range of heterogeneous populations with various phenotype, differentiation potential, and functionality under precise and elaborate regulations of transcriptional and epigenetic programs. Abnormal T-cell immunity can initiate and promote the pathogenesis of autoimmune diseases. In this review, we summarize the current understanding of T cell development, CD4+ and CD8+ T cell classification, and differentiation in physiological settings. We further elaborate the heterogeneity, differentiation, functionality, and regulation network of CD4+ and CD8+ T cells in infectious disease, chronic infection and tumor, and autoimmune disease, highlighting the exhausted CD8+ T cell differentiation trajectory, CD4+ T cell helper function, T cell contributions to immunotherapy and autoimmune pathogenesis. We also discuss the development and function of γδ T cells in tissue surveillance, infection, and tumor immunity. Finally, we summarized current T-cell-based immunotherapies in both cancer and autoimmune diseases, with an emphasis on their clinical applications. A better understanding of T cell immunity provides insight into developing novel prophylactic and therapeutic strategies in human diseases.

Extremely Differentiated T Cell Subsets Contribute to Tissue Deterioration During Aging

There is a dramatic remodeling of the T cell compartment during aging. The most notorious changes are the reduction of the naive T cell pool and the accumulation of memory-like T cells. Memory-like T cells in older people acquire a phenotype of terminally differentiated cells, lose the expression of costimulatory molecules, and acquire properties of senescent cells. In this review, we focus on the different subsets of age-associated T cells that accumulate during aging. These subsets include extremely cytotoxic T cells with natural killer properties, exhausted T cells with altered cytokine production, and regulatory T cells that gain proinflammatory features. Importantly, all of these subsets lose their lymph node homing capacity and migrate preferentially to nonlymphoid tissues, where they contribute to tissue deterioration and inflammaging.

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.

When Helpers Go Above and Beyond: Development and Characterization of Cytotoxic CD4+ T Cells

Once regarded as an experimental artefact, cytotoxic CD4⁺ T cells (CD4 CTL) are presently recognized as a biologically relevant T cell subset with important functions in anti-viral, anti-tumor, and autoimmune responses. Despite the potentially large impact on their micro-environment, the absolute cell counts of CD4 CTL within the peripheral circulation are relatively low. With the rise of single cell analysis techniques, detection of these cells is greatly facilitated. This led to a renewed appraisal of CD4 CTL and an increased insight into their heterogeneous nature and ontogeny. In this review, we summarize the developmental path from naïve CD4⁺ T cells to terminally differentiated CD4 CTL, and present markers that can be used to detect or isolate CD4 CTL and their precursors. Subsets of CD4 CTL and their divergent functionalities are discussed. Finally, the importance of local cues as triggers for CD4 CTL differentiation is debated, posing the question whether CD4 CTL develop in the periphery and migrate to site of inflammation when called for, or that circulating CD4 CTL reflect cells that returned to the circulation following differentiation at the local inflammatory site they previously migrated to. Even though much remains to be learned about this intriguing T cell subset, it is clear that CD4 CTL represent interesting therapeutic targets for several pathologies.

Cytotoxic CD4+ T cells driven by T-cell intrinsic IL-18R/MyD88 signaling predominantly infiltrate Trypanosoma cruzi-infected hearts

Increasing attention has been directed to cytotoxic CD4+ T cells (CD4CTLs) in different pathologies, both in humans and mice. The impact of CD4CTLs in immunity and the mechanisms controlling their generation, however, remain poorly understood. Here, we show that CD4CTLs abundantly differentiate during mouse infection with the intracellular parasite Trypanosoma cruzi. CD4CTLs display parallel kinetics to Th1 cells in the spleen, mediate specific cytotoxicity against cells presenting pathogen-derived antigens and express immunoregulatory and/or exhaustion markers. We demonstrate that CD4CTL absolute numbers and activity are severely reduced in both Myd88-/- and Il18ra-/- mice. Of note, the infection of mixed-bone marrow chimeras revealed that WT but not Myd88-/- cells transcribe the CD4CTL gene signature and that Il18ra-/- and Myd88-/- CD4+ T cells phenocopy each other. Moreover, adoptive transfer of WT CD4+GzB+ T cells to infected Il18ra-/- mice extended their survival. Importantly, cells expressing the CD4CTL phenotype predominate among CD4+ T cells infiltrating the infected mouse cardiac tissue and are increased in the blood of Chagas patients, in which the frequency of CD4CTLs correlates with the severity of cardiomyopathy. Our findings describe CD4CTLs as a major player in immunity to a relevant human pathogen and disclose T-cell intrinsic IL-18R/MyD88 signaling as a key pathway controlling the magnitude of the CD4CTL response.

CD4+ Cytotoxic T cells - Phenotype, Function and Transcriptional Networks Controlling Their Differentiation Pathways

The two major subsets of peripheral T cells are classically divided into the CD4⁺ T helper cells and the cytotoxic CD8⁺ T cell lineage. However, the appearance of some effector CD4⁺ T cell populations displaying cytotoxic activity, in particular during viral infections, has been observed, thus breaking the functional dichotomy of CD4⁺ and CD8⁺ T lymphocytes. The strong association of the appearance of CD4⁺ cytotoxic T lymphocytes (CD4 CTLs) with viral infections suggests an important role of this subset in antiviral immunity by controlling viral replication and infection. Moreover, CD4 CTLs have been linked with anti-tumor activity and might also cause immunopathology in autoimmune diseases. This raises interest into the molecular mechanisms regulating CD4 CTL differentiation, which are poorly understood in comparison to differentiation pathways of other Th subsets. In this review, we provide a brief overview about key features of CD4 CTLs, including their role in viral infections and cancer immunity, and about the link between CD4 CTLs and immune-mediated diseases. Subsequently, we will discuss the current knowledge about transcriptional and epigenetic networks controlling CD4 CTL differentiation and highlight recent data suggesting a role for histone deacetylases in the generation of CD4 CTLs.

Bona Fide Th17 Cells without Th1 Functional Plasticity Protect against Influenza

Optimal transcriptional programming needed for CD4 T cells to protect against influenza A virus (IAV) is unclear. Most IAV-primed CD4 T cells fit Th1 criteria. However, cells deficient for the Th1 "master regulator," T-bet, although marked by reduced Th1 identity, retain robust protective capacity. In this study, we show that T-bet's paralog, Eomesodermin (Eomes), is largely redundant in the presence of T-bet but is essential for the residual Th1 attributes of T-bet-deficient cells. Cells lacking both T-bet and Eomes instead develop concurrent Th17 and Th2 responses driven by specific inflammatory signals in the infected lung. Furthermore, the transfer of T-bet- and Eomes-deficient Th17, but not Th2, effector cells protects mice from lethal IAV infection. Importantly, these polyfunctional Th17 effectors do not display functional plasticity in vivo promoting gain of Th1 attributes seen in wild-type Th17 cells, which has clouded evaluation of the protective nature of Th17 programming in many studies. Finally, we show that primary and heterosubtypic IAV challenge is efficiently cleared in T-bet- and Eomes double-deficient mice without enhanced morbidity despite a strongly Th17-biased inflammatory response. Our studies thus demonstrate unexpectedly potent antiviral capacity of unadulterated Th17 responses against IAV, with important implications for vaccine design.

CMV exposure drives long-term CD57+ CD4 memory T-cell inflation following allogeneic stem cell transplant

Donor and recipient cytomegalovirus (CMV) serostatus correlate with transplant-related mortality that is associated with reduced survival following allogeneic stem cell transplant (SCT). Prior epidemiologic studies have suggested that CMV seronegative recipients (R-) receiving a CMV-seropositive graft (D+) experience inferior outcomes compared with other serostatus combinations, an observation that appears independent of viral reactivation. We therefore investigated the hypothesis that prior donor CMV exposure irreversibly modifies immunologic function after SCT. We identified a CD4+/CD57+/CD27- T-cell subset that was differentially expressed between D+ and D- transplants and validated results with 120 patient samples. This T-cell subset represents an average of 2.9% (D-/R-), 18% (D-/R+), 12% (D+/R-), and 19.6% (D+/R+) (P < .0001) of the total CD4+ T-cell compartment and stably persists for at least several years post-SCT. Even in the absence of CMV reactivation post-SCT, D+/R- transplants displayed a significant enrichment of these cells compared with D-/R- transplants (P = .0078). These are effector memory cells (CCR7-/CD45RA+/-) that express T-bet, Eomesodermin, granzyme B, secrete Th1 cytokines, and are enriched in CMV-specific T cells. These cells are associated with decreased T-cell receptor diversity (P < .0001) and reduced proportions of major histocompatibility class (MHC) II expressing classical monocytes (P < .0001), myeloid (P = .024), and plasmacytoid dendritic cells (P = .0014). These data describe a highly expanded CD4+ T-cell population and putative mechanisms by which prior donor or recipient CMV exposure may create a lasting immunologic imprint following SCT, providing a rationale for using D- grafts for R- transplant recipients.

Activation of T-bet, FOXP3, and EOMES in Target Organs From Piglets Infected With the Virulent PRRSV-1 Lena Strain

Transcription factors (TFs) modulate genes involved in cell-type-specific proliferative and migratory properties, metabolic features, and effector functions. Porcine reproductive and respiratory syndrome virus (PRRSV) is one of the most important pathogen agents in the porcine industry; however, TFs have been poorly studied during the course of this disease. Therefore, we aimed to evaluate the expressions of the TFs T-bet, GATA3, FOXP3, and Eomesodermin (EOMES) in target organs (the lung, tracheobronchial lymph node, and thymus) and those of different effector cytokines (IFNG, TNFA, and IL10) and the Fas ligand (FASL) during the early phase of infection with PRRSV-1 strains of different virulence. Target organs from mock-, virulent Lena-, and low virulent 3249-infected animals humanely euthanized at 1, 3, 6, 8, and 13 days post-infection (dpi) were collected to analyze the PRRSV viral load, histopathological lesions, and relative quantification through reverse transcription quantitative PCR (RT-qPCR) of the TFs and cytokines. Animals belonging to both infected groups, but mainly those infected with the virulent Lena strain, showed upregulation of the TFs T-bet, EOMES, and FOXP3, together with an increase of the cytokine IFN-γ in target organs at the end of the study (approximately 2 weeks post-infection). These results are suggestive of a stronger polarization to Th1 cells and regulatory T cells (Tregs), but also CD4+ cytotoxic T lymphocytes (CTLs), effector CD8+ T cells, and γδT cells in virulent PRRSV-1-infected animals; however, their biological functionality should be the object of further studies.

Small Molecule Inhibitors Targeting Nuclear Factor κB Activation Markedly Reduce Expression of Interleukin-2, but Not Interferon-γ, Induced by Phorbol Esters and Calcium Ionophores

The T-box transcription factor Eomesodermin (Eomes) promotes the expression of interferon-γ (IFN-γ). We recently reported that the small molecule inhibitors, TPCA-1 and IKK-16, which target nuclear factor κB (NF-κB) activation, moderately reduced Eomes-dependent IFN-γ expression in mouse lymphoma BW5147 cells stimulated with phorbol 12-myristate 13-acetate (PMA) and ionomycin (IM). In the present study, we investigated the direct effects of NF-κB on IFN-γ expression in mouse lymphoma EL4 cells and primary effector T cells. Eomes strongly promoted IFN-γ expression and the binding of RelA and NFATc2 to the IFN-γ promoter when EL4 cells were stimulated with PMA and IM. Neither TPCA-1 nor IKK-16 reduced IFN-γ expression; however, they markedly decreased interleukin (IL)-2 expression in Eomes-transfected EL4 cells. Moreover, TPCA-1 markedly inhibited the binding of RelA, but not that of Eomes or NFATc2 to the IFN-γ promoter. In effector CD4⁺ and CD8⁺ T cells activated with anti-CD3 and anti-CD28 antibodies, IFN-γ expression induced by PMA and A23187 was not markedly decreased by TPCA-1 or IKK-16 under conditions where IL-2 expression was markedly reduced. Therefore, the present results revealed that NF-κB is dispensable for IFN-γ expression induced by PMA and calcium ionophores in EL4 cells expressing Eomes and primary effector T cells.

T-Cell Specificity Influences Disease Heterogeneity in Multiple Sclerosis

BACKGROUND AND OBJECTIVES

Encouraged by the enormous progress that the identification of specific autoantigens added to the understanding of neurologic autoimmune diseases, we undertook here an in-depth study of T-cell specificities in the autoimmune disease multiple sclerosis (MS), for which the spectrum of responsible autoantigens is not fully defined yet. The identification of target antigens in MS is crucial for therapeutic strategies aimed to induce antigen-specific tolerance. In addition, knowledge of relevant T-cell targets can improve our understanding of disease heterogeneity, a hallmark of MS that complicates clinical management.

METHODS

The proliferative response and interferon gamma (IFN-γ) release of CSF-infiltrating CD4⁺ T cells from patients with MS against several autoantigens was used to identify patients with different intrathecal T-cell specificities. Fresh CSF-infiltrating and paired circulating lymphocytes in these patients were characterized in depth by ex vivo immunophenotyping and transcriptome analysis of relevant T-cell subsets. Further examination of these patients included CSF markers of inflammation and neurodegeneration and a detailed characterization with respect to demographic, clinical, and MRI features.

RESULTS

By testing CSF-infiltrating CD4⁺ T cells from 105 patients with MS against seven long-known myelin and five recently described GDP-l-fucose synthase peptides, we identified GDP-l-fucose synthase and myelin oligodendrocyte glycoprotein (35-55) responder patients. Immunophenotyping of CSF and paired blood samples in these patients revealed a significant expansion of an effector memory (CCR7^- CD45RA^-) CD27^- Th1 CD4⁺ cell subset in GDP-l-fucose synthase responders. Subsequent transcriptome analysis of this subset demonstrated expression of Th1 and cytotoxicity-associated genes. Patients with different intrathecal T-cell specificities also differ regarding inflammation- and neurodegeneration-associated biomarkers, imaging findings, expression of HLA class II alleles, and seasonal distribution of the time of the lumbar puncture.

DISCUSSION

Our observations reveal an association between autoantigen reactivity and features of disease heterogeneity that strongly supports an important role of T-cell specificity in MS pathogenesis. These data have the potential to improve patient classification in clinical practice and to guide the development of antigen-specific tolerization strategies.

Down-regulation of EOMES drives T-cell exhaustion via abolishing EOMES-mediated repression of inhibitory receptors of T cells in liver cancer

T‐cell exhaustion is one of the hallmarks in cancer, but the mechanisms underlying T‐cell dysregulation remains unclear. Here, we reported that down‐regulation of transcription factor EOMES contributed to increased levels of inhibitory receptors in T cell among the tumour tissues and resulted in the poor prognosis of hepatocellular carcinoma (HCC). By analysing the correlation between EOMES in tumour‐infiltrating T cells and the clinical features, we demonstrated that the EOMES was related to the advanced stage and poor prognosis of HCC. Further mechanistic studies revealed that the EOMES mainly expressed in the CD8⁺ T cells and were down‐regulated in tumour samples. Moreover, we demonstrated that the EOMES directly bound at the transcriptional regulatory regions of the key inhibitory factors including PD‐1, CTAL‐4 and CD39, and lower levels of EOMES contributed to overexpression of these factors in T cells. Together, our studies provide new insight into the transcriptional deregulation of the inhibitory receptors on T cells during the tumorigenesis.

CD4 T Helper Cell Subsets and Related Human Immunological Disorders

The immune system plays a critical role in protecting hosts from the invasion of organisms. CD4 T cells, as a key component of the immune system, are central in orchestrating adaptive immune responses. After decades of investigation, five major CD4 T helper cell (Th) subsets have been identified: Th1, Th2, Th17, Treg (T regulatory), and Tfh (follicular T helper) cells. Th1 cells, defined by the expression of lineage cytokine interferon (IFN)-γ and the master transcription factor T-bet, participate in type 1 immune responses to intracellular pathogens such as mycobacterial species and viruses; Th2 cells, defined by the expression of lineage cytokines interleukin (IL)-4/IL-5/IL-13 and the master transcription factor GAΤA3, participate in type 2 immune responses to larger extracellular pathogens such as helminths; Th17 cells, defined by the expression of lineage cytokines IL-17/IL-22 and the master transcription factor RORγt, participate in type 3 immune responses to extracellular pathogens including some bacteria and fungi; Tfh cells, by producing IL-21 and expressing Bcl6, help B cells produce corresponding antibodies; whereas Foxp3-expressing Treg cells, unlike Th1/Th2/Th17/Tfh exerting their effector functions, regulate immune responses to maintain immune cell homeostasis and prevent immunopathology. Interestingly, innate lymphoid cells (ILCs) have been found to mimic the functions of three major effector CD4 T helper subsets (Th1, Th2, and Th17) and thus can also be divided into three major subsets: ILC1s, ILC2s, and ILC3s. In this review, we will discuss the differentiation and functions of each CD4 T helper cell subset in the context of ILCs and human diseases associated with the dysregulation of these lymphocyte subsets particularly caused by monogenic mutations.

Cytotoxic CD4+ T-cells during HIV infection: Targets or weapons?

Classically, CD4⁺ T-cells have been referred as cytokine-producing cells and important players in immune responses by providing soluble factors that potentiate several effector immune functions. However, it is now evident that CD4⁺ T-cells can also elaborate cytotoxic responses, inducing apoptosis of target cells. Cytotoxic CD4⁺ T cells (CD4⁺ CTLs), exhibit cytolytic functions that resemble those of CD8⁺ T-cells; in fact, there is evidence suggesting that they may have a role in the control of viral infections. In this article, we discuss the role of CD4⁺ CTLs during HIV infection, where CD4⁺ CTLs have been associated with viral control and slow disease progression. In addition, we address the implication of CD4⁺ CTLs in the context of antiretroviral therapy and the partial reconstitution of CD8⁺ T-cells effector function.

Role of T-bet, the master regulator of Th1 cells, in the cytotoxicity of murine CD4+ T cells

Although CD4⁺ T cells are generally regarded as helper T cells, some activated CD4⁺ T cells have cytotoxic properties. Given that CD4⁺ cytotoxic T lymphocytes (CTLs) often secrete IFN-γ, CTL activity among CD4⁺ T cells may be attributable to Th1 cells, where a T-box family molecule, T-bet serves as the "master regulator". However, although the essential contribution of T-bet to expression of IFN-γ has been well-documented, it remains unclear whether T-bet is involved in CD4⁺ T cell-mediated cytotoxicity. In this study, to investigate the ability of T-bet to confer cytolytic activity on CD4⁺ T cells, the T-bet gene (Tbx21) was introduced into non-cytocidal CD4⁺ T cell lines and their cytolytic function analyzed. Up-regulation of FasL (CD178), which provided the transfectant with cytotoxicity, was observed in Tbx21transfected CD4⁺ T cells but not in untransfected parental cells. In one cell line, T-bet transduction also induced perforin gene (Prf1) expression and Tbx21 transfectants efficiently killed Fas^- target cells. Although T-bet was found to repress up-regulation of CD40L (CD154), which controls FasL-mediated cytolysis, the extent of CD40L up-regulation on in vitro-differentiated Th1 cells was similar to that on Th2 cells, suggesting the existence of a compensatory mechanism. These results collectively indicate that T-bet may be involved in the expression of genes, such as FasL and Prf1, which confer cytotoxicity on Th1 cells.

Dendritic Cell-Based Immunotherapy for Solid Tumors

As a treatment for solid tumors, dendritic cell (DC)-based immunotherapy has not been as effective as expected. Here, we review the reasons underlying the limitations of DC-based immunotherapy for solid tumors and ask what can be done to improve immune cell-based cancer therapies. Several reports show that, rather than a lack of immune induction, the limited efficacy of DC-based immunotherapy in cases of renal cell carcinoma (RCC) likely results from inhibition of immune responses by tumor-secreted TGF-β and an increase in the number of regulatory T (Treg) cells in and around the solid tumor. Indeed, unlike DC therapy for solid tumors, cytotoxic T lymphocyte (CTL) responses induced by DC therapy inhibit tumor recurrence after surgery; CTL responses also limit tumor metastasis induced by additional tumor-challenge in RCC tumor-bearing mice. Here, we discuss the mechanisms underlying the poor efficacy of DC-based therapy for solid tumors and stress the need for new and improved DC immunotherapies and/or combination therapies with killer cells to treat resistant solid tumors.

The transcription factors Runx3 and ThPOK cross-regulate acquisition of cytotoxic function by human Th1 lymphocytes

Cytotoxic CD4 (CD4_CTX) T cells are emerging as an important component of antiviral and antitumor immunity, but the molecular basis of their development remains poorly understood. In the context of human cytomegalovirus infection, a significant proportion of CD4 T cells displays cytotoxic functions. We observed that the transcriptional program of these cells was enriched in CD8 T cell lineage genes despite the absence of ThPOK downregulation. We further show that establishment of CD4_CTX-specific transcriptional and epigenetic programs occurred in a stepwise fashion along the Th1-differentiation pathway. In vitro, prolonged activation of naive CD4 T cells in presence of Th1 polarizing cytokines led to the acquisition of perforin-dependent cytotoxic activity. This process was dependent on the Th1 transcription factor Runx3 and was limited by the sustained expression of ThPOK. This work elucidates the molecular program of human CD4_CTX T cells and identifies potential targets for immunotherapy against viral infections and cancer.

Many Th Cell Subsets Have Fas Ligand-Dependent Cytotoxic Potential

CD4⁺ Th cells can have cytotoxic activity against cells displaying relevant peptide-MHC class II (p:MHCII) ligands. Cytotoxicity may be a property of Th1 cells and depends on perforin and the Eomes transcription factor. We assessed these assertions for polyclonal p:MHCII-specific CD4⁺ T cells activated in vivo in different contexts. Mice immunized with an immunogenic peptide in adjuvant or infected with lymphocytic choriomeningitis virus or Listeria monocytogenes bacteria induced cytotoxic Th cells that killed B cells displaying relevant p:MHCII complexes. Cytotoxicity was dependent on Fas expression by target cells but was independent of Eomes or perforin expression by T cells. Although the priming regimens induced different proportions of Th1, Th17, regulatory T cells, and T follicular helper cells, the T cells expressed Fas ligand in all cases. Reciprocally, Fas was upregulated on target cells in a p:MHCII-specific manner. These results indicate that many Th subsets have cytotoxic potential that is enhanced by cognate induction of Fas on target cells.

Precursors of human CD4+ cytotoxic T lymphocytes identified by single-cell transcriptome analysis

CD4+ cytotoxic T lymphocytes (CD4-CTLs) have been reported to play a protective role in several viral infections. However, little is known in humans about the biology of CD4-CTL generation, their functional properties, and heterogeneity, especially in relation to other well-described CD4+ memory T cell subsets. We performed single-cell RNA sequencing in more than 9000 cells to unravel CD4-CTL heterogeneity, transcriptional profile, and clonality in humans. Single-cell differential gene expression analysis revealed a spectrum of known transcripts, including several linked to cytotoxic and costimulatory function that are expressed at higher levels in the TEMRA (effector memory T cells expressing CD45RA) subset, which is highly enriched for CD4-CTLs, compared with CD4+ T cells in the central memory (TCM) and effector memory (TEM) subsets. Simultaneous T cell antigen receptor (TCR) analysis in single cells and bulk subsets revealed that CD4-TEMRA cells show marked clonal expansion compared with TCM and TEM cells and that most of CD4-TEMRA were dengue virus (DENV)-specific in donors with previous DENV infection. The profile of CD4-TEMRA was highly heterogeneous across donors, with four distinct clusters identified by the single-cell analysis. We identified distinct clusters of CD4-CTL effector and precursor cells in the TEMRA subset; the precursor cells shared TCR clonotypes with CD4-CTL effectors and were distinguished by high expression of the interleukin-7 receptor. Our identification of a CD4-CTL precursor population may allow further investigation of how CD4-CTLs arise in humans and, thus, could provide insights into the mechanisms that may be used to generate durable and effective CD4-CTL immunity.

Association of increased eomesodermin, BCL6, and granzyme B expression with major clinical manifestations of Hashimoto's thyroiditis - an observational study

PURPOSE

Studies of cytotoxic T cells and their respective lineage master regulators have been limited in Hashimoto's thyroiditis (HT). It is unclear whether their transcriptomes are changed in HT patients and how these changes are associated with the thyroid damage, major clinical manifestations, and disease progression.

METHODS

We explored the gene expression patterns of selected transcription factors [eomesodermin (EOMES), BACH2, BCL6, TCF1] and cytolytic molecules [granzyme B (GZMB)] in peripheral blood (PB) T cells of 10 healthy controls and 30 HT patients of various subtypes (hypothyroid, untreated HT; L-thyroxine (T4)-treated HT, and spontaneously euthyroid HT) using real-time quantitative PCR.

RESULTS

EOMES (Mann-Whitney P = 0.044), GZMB (P = 0.028), and BCL6 mRNA (P = 0.001) were overrepresented in PB T cells from HT and showed levels varying by age, thyroid volume and disease severity. BCL6 transcripts were predominantly enriched in severely affected, hypothyroid cases, both on and off LT4. Increased EOMES RNA expression was associated with advancing age, lower thyroid volumes and higher peak adjusted TSH levels over the course of the disease. The body mass-adjusted, steady-state maintenance dose of LT4 increased with GZMB and BCL6 levels in PB T cells of hypothyroid cases, mostly postmenopausal women having long-standing, non-goitrous and atrophic disease form.

CONCLUSIONS

Our exploratory results suggest a role for GZMB, EOMES, and BCL6 in the context of HT, thyroid injury, and aggressive/advanced disease forms. Functions enriched within differentially expressed transcripts could be an important new target in understanding the pathogenesis of HT.

Memory T Cell Proliferation before Hepatitis C Virus Therapy Predicts Antiviral Immune Responses and Treatment Success

The contribution of the host immune system to the efficacy of new anti-hepatitis C virus (HCV) drugs is unclear. We undertook a longitudinal prospective study of 33 individuals with chronic HCV treated with combination pegylated IFN-α, ribavirin, and telaprevir/boceprevir. We characterized innate and adaptive immune cells to determine whether kinetics of the host response could predict sustained virologic response (SVR). We show that characteristics of the host immune system present before treatment were correlated with successful therapy. Augmentation of adaptive immune responses during therapy was more impressive among those achieving SVR. Most importantly, active memory T cell proliferation before therapy predicted SVR and was associated with the magnitude of the HCV-specific responses at week 12 after treatment start. After therapy initiation, the most important correlate of success was minimal monocyte activation, as predicted by previous in vitro work. In addition, subjects achieving SVR had increasing expression of the transcription factor T-bet, a driver of Th1 differentiation and cytotoxic effector cell maturation. These results show that host immune features present before treatment initiation predict SVR and eventual development of a higher frequency of functional virus-specific cells in blood. Such host characteristics may also be required for successful vaccine-mediated protection.

Naive CD4+ T Cells Carrying a TLR2 Agonist Overcome TGF-β-Mediated Tumor Immune Evasion

TLR agonists are effective at treating superficial cancerous lesions, but their use internally for other types of tumors remains challenging because of toxicity. In this article, we report that murine and human naive CD4⁺ T cells that sequester Pam₃Cys₄ (CD4⁺ T^Pam3) become primed for T_h1 differentiation. CD4⁺ T^Pam3 cells encoding the OVA-specific TCR OT2, when transferred into mice bearing established TGF-β-OVA-expressing thymomas, produce high amounts of IFN-γ and sensitize tumors to PD-1/programmed cell death ligand 1 blockade-induced rejection. In contrast, naive OT2 cells without Pam₃Cys₄ cargo are prone to TGF-β-dependent inducible regulatory Foxp3⁺ CD4⁺ T cell conversion and accelerate tumor growth that is largely unaffected by PD-1/programmed cell death ligand 1 blockade. Ex vivo analysis reveals that CD4⁺ T^Pam3 cells are resistant to TGF-β-mediated gene expression through Akt activation controlled by inputs from the TCR and a TLR2-MyD88-dependent PI3K signaling pathway. These data show that CD4⁺ T^Pam3 cells are capable of T_h1 differentiation in the presence of TGF-β, suggesting a novel approach to adoptive cell therapy.

Fas Ligand-mediated cytotoxicity of CD4+ T cells during chronic retrovirus infection

CD4+ helper T cells and cytotoxic CD8+ T cells are key players for adaptive immune responses against acute infections with retroviruses. Similar to textbook knowledge the most important function of CD4+ T cells during an acute retrovirus infection seems to be their helper function for other immune cells. Whereas there was no direct anti-viral activity of CD4+ T cells during acute Friend Virus (FV) infection, they were absolutely required for the control of chronic infection. During chronic FV infection a population of activated FV-specific CD4+ T cells did not express cytotoxic molecules, but Fas Ligand that can induce Fas-induced apoptosis in target cells. Using an MHC II-restricted in vivo CTL assay we demonstrated that FV-specific CD4+ T cells indeed mediated cytotoxic effects against FV epitope peptide loaded targets. CD4 + CTL killing was also detected in FV-infected granzyme B knockout mice confirming that the exocytosis pathway was not involved. However, killing could be blocked by antibodies against FasL, which identified the Fas/FasL pathway as critical cytotoxic mechanism during chronic FV infection. Interestingly, targeting the co-stimulatory receptor CD137 with an agonistic antibody enhanced CD4+ T cell cytotoxicity. This immunotherapy may be an interesting new approach for the treatment of chronic viral infections.

Fighting Viral Infections and Virus-Driven Tumors with Cytotoxic CD4+ T Cells

CD4+ T cells have been and are still largely regarded as the orchestrators of immune responses, being able to differentiate into distinct T helper cell populations based on differentiation signals, transcription factor expression, cytokine secretion, and specific functions. Nonetheless, a growing body of evidence indicates that CD4+ T cells can also exert a direct effector activity, which depends on intrinsic cytotoxic properties acquired and carried out along with the evolution of several pathogenic infections. The relevant role of CD4+ T cell lytic features in the control of such infectious conditions also leads to their exploitation as a new immunotherapeutic approach. This review aims at summarizing currently available data about functional and therapeutic relevance of cytotoxic CD4+ T cells in the context of viral infections and virus-driven tumors.

Cytotoxic CD4 T Cells-Friend or Foe during Viral Infection?

CD4 T cells with cytotoxic function were once thought to be an artifact due to long-term in vitro cultures but have in more recent years become accepted and reported in the literature in response to a number of viral infections. In this review, we focus on cytotoxic CD4 T cells in the context of human viral infections and in some infections that affect mice and non-human primates. We examine the effector mechanisms used by cytotoxic CD4 cells, the phenotypes that describe this population, and the transcription factors and pathways that lead to their induction following infection. We further consider the cells that are the predominant targets of this effector subset and describe the viral infections in which CD4 cytotoxic T lymphocytes have been shown to play a protective or pathologic role. Cytotoxic CD4 T cells are detected in the circulation at much higher levels than previously realized and are now recognized to have an important role in the immune response to viral infections.

Reduced Plasmodium Parasite Burden Associates with CD38+ CD4+ T Cells Displaying Cytolytic Potential and Impaired IFN-γ Production

Using a unique resource of samples from a controlled human malaria infection (CHMI) study, we identified a novel population of CD4+ T cells whose frequency in the peripheral blood was inversely correlated with parasite burden following P. falciparum infection. These CD4+ T cells expressed the multifunctional ectoenzyme CD38 and had unique features that distinguished them from other CD4+ T cells. Specifically, their phenotype was associated with proliferation, activation and cytotoxic potential as well as significantly impaired production of IFN-γ and other cytokines and reduced basal levels of activated STAT1. A CD38+ CD4+ T cell population with similar features was identified in healthy uninfected individuals, at lower frequency. CD38+ CD4+ T cells could be generated in vitro from CD38- CD4+ T cells after antigenic or mitogenic stimulation. This is the first report of a population of CD38+ CD4+ T cells with a cytotoxic phenotype and markedly impaired IFN-γ capacity in humans. The expansion of this CD38+ CD4+ T population following infection and its significant association with reduced blood-stage parasite burden is consistent with an important functional role for these cells in protective immunity to malaria in humans. Their ubiquitous presence in humans suggests that they may have a broad role in host-pathogen defense.

TRIAL REGISTRATION

ClinicalTrials.gov clinical trial numbers ACTRN12612000814875, ACTRN12613000565741 and ACTRN12613001040752.

Dendritic Cell Immunotherapy Combined with Cytokine-Induced Killer Cells Effectively Suppresses Established Hepatocellular Carcinomas in Mice

BACKGROUND

The response of hepatocellular carcinoma (HCC) to immunotherapy is often disappointing and new strategies are clearly needed. The aim of the present study was to investigate whether cytokine-induced killer (CIK) cells combined with a dendritic cell vaccination enhanced cytotoxicity against hepatocarcinoma tumor cells in an in vivo animal model.

METHODS

CIKs and DCs were prepared from C3H/HeJ mice by conventional methods, the dendritic cell (DC) pulsed with a MH134 cell lysate, DC or CIK alone were used as controls. Cell phenotypes were analyzed by flow cytometry, cytokine secretion levels were determined by enzyme-linked immunosorbent assay (ELISA), and cytotoxicity was assessed by means of an in vitro lactate dehydrogenase (LDH) release assay. A mouse hepatocarcinoma cell MH134-bearing mice model was established to test the in vivo anti-tumor efficacy of the system.

RESULTS

CIK cells combined with DC therapy resulted in significant inhibition of tumor growth compared with the control group, whereas the decrease in tumor growth in mice that had been treated with CIK or DC alone did not reach the level of statistical significance. The combination therapy led to a further increase in the population of cytotoxic T cells (CTLs) in vivo, compared to the CIK or DC alone therapy. In addition, the combination therapy significantly enhanced cytotoxic activity against MH134 cells.

CONCLUSION

Taken together, these results show that a DC + CIK vaccination is more effective than DC or CIK alone therapy for the treatment of hepatocarcinoma cancer.

Expression of T-bet, Eomesodermin and GATA-3 in porcine αβ T cells

The transcription factors GATA-3, T-bet and Eomesodermin play important roles in T-cell development, differentiation and memory formation. However, their expression has not been studied in great detail in porcine T cells. We report on protein expression at the single cell-level of these transcription factors in thymocytes and mature αβ T cells. GATA-3 expression was found in γδ(-) thymocytes, with decreasing expression from the CD4(-)CD8α(-) stage towards single-positive stages. Extra-thymic CD4(+) T cells but not CD8β(+) T cells expressed low levels of GATA-3, which decreased with age. CD4(+) and CD8β(+) T-bet(+) cells mainly displayed a CD8α(+)CD27(-) and perforin(+)CD27(dim/-) phenotype, respectively and had the capacity for IFN-γ production; indicative of an effector/effector memory phenotype. Eomesodermin(+) αβ T cells had mixed phenotypes in regard to CD8α, CD27 and perforin expression. In conclusion, our data so far support the hitherto reported roles for GATA-3 in T-cell development and T-bet for Th1 effector-differentiation, but question the role of Eomesodermin for memory formation of porcine T-cells.

Favorable prognostic influence of T-box transcription factor Eomesodermin in metastatic renal cell cancer patients

T-box transcription factors, T-box expressed in T cells (T-bet) encoded by Tbx21 and Eomesodermin (Eomes), drive the differentiation of effector/memory T cell lineages and NK cells. The aim of the study was to determine the prognostic influence of the expression of these transcription factors in peripheral blood (pB) in a cohort of 41 metastatic (m) RCC patients before receiving sorafenib treatment and to analyze their association with the immunophenotype in pB. In contrast to Tbx21, in the multivariate analysis including clinical features, Eomes mRNA expression was identified as an independent good prognostic factor for progression-free survival (PFS, p = 0.042) and overall survival (OS, p = 0.001) in addition to a favorable ECOG performance status (p = 0.01 and p = 0.008, respectively). Eomes expression correlated positively not only with expression of Tbx21 and TGFβ1 mRNA, but also with mRNA expression of the activation marker ICOS, and with in vivo activated HLA-DR(+) T cells. Eomes expression was negatively associated with TNFα-producing T cells. On protein level, Eomes was mainly expressed by CD56(+)CD3(-) NK cells in pB. In conclusion, we identified a higher Eomes mRNA expression as an independent good prognostic factor for OS and PFS in mRCC patients treated with sorafenib.

Eomesodermin promotes interferon-γ expression and binds to multiple conserved noncoding sequences across the Ifng locus in mouse thymoma cell lines

The T-box transcription factors T-bet and eomesodermin (Eomes) have been shown to regulate the lineage-specific expression of interferon-γ (IFN-γ). However, in contrast to T-bet, the role of Eomes in the expression of IFN-γ remains unclear. In this study, we investigated the Eomes-dependent expression of IFN-γ in the mouse thymoma BW5147 and EL4 cells, which do not express T-bet or Eomes. The ectopic expression of Eomes induced BW5147 and EL4 cells to produce IFN-γ in response to phorbol 12-myristate 13-acetate (PMA) and ionomycin (IM). In BW5147 cells, Eomes augmented luciferase activity driven by the Ifng promoter encoding from -2500 to +113 bp; however, it was not increased by a stimulation with PMA and IM. A chromatin immunoprecipitation assay showed that Eomes bound to the Ifng promoter and conserved noncoding sequence (CNS) -22 kb across the Ifng locus with high efficacy in BW5147 cells. Moreover, Eomes increased permissive histone modifications in the Ifng promoter and multiple CNSs. The stimulation with PMA and IM greatly augmented Eomes binding to CNS-54, CNS-34, CNS+19 and CNS+30, which was inhibited by FK506. These results indicated that Eomes bound to the Ifng promoter and multiple CNSs in stimulation-dependent and stimulation-independent manners.

CRTAM determines the CD4+ cytotoxic T lymphocyte lineage

Naive T cells differentiate into various effector T cells, including CD4(+) helper T cell subsets and CD8(+) cytotoxic T cells (CTL). Although cytotoxic CD4(+) T cells (CD4 +: CTL) also develop from naive T cells, the mechanism of development is elusive. We found that a small fraction of CD4(+) T cells that express class I-restricted T cell-associated molecule (CRTAM) upon activation possesses the characteristics of both CD4(+) and CD8(+) T cells. CRTAM(+) CD4(+) T cells secrete IFN-γ, express CTL-related genes, such as eomesodermin (Eomes), Granzyme B, and perforin, after cultivation, and exhibit cytotoxic function, suggesting that CRTAM(+) T cells are the precursor of CD4(+)CTL. Indeed, ectopic expression of CRTAM in T cells induced the production of IFN-γ, expression of CTL-related genes, and cytotoxic activity. The induction of CD4(+)CTL and IFN-γ production requires CRTAM-mediated intracellular signaling. CRTAM(+) T cells traffic to mucosal tissues and inflammatory sites and developed into CD4(+)CTL, which are involved in mediating protection against infection as well as inducing inflammatory response, depending on the circumstances, through IFN-γ secretion and cytotoxic activity. These results reveal that CRTAM is critical to instruct the differentiation of CD4(+)CTL through the induction of Eomes and CTL-related gene.

Differential dependence on nuclear factor-κB-inducing kinase among natural killer T-cell subsets in their development

Natural killer T cells (NKT cells) are comprised of several subsets. However, the possible differences in their developmental mechanisms have not been fully investigated. To evaluate the dependence of some NKT subpopulations on nuclear factor-κB-inducing kinase (NIK) for their generation, we analysed the differentiation of NKT cells, dividing them into subsets in various tissues of alymphoplasia (aly/aly), a mutant mouse strain that lacks functional NIK. The results indicated that the efficient differentiation of both invariant NKT (iNKT) and non-iNKT cells relied on NIK expression in non-haematopoietic cells; however, the dependence of non-iNKT cells was lower than that of iNKT cells. Especially, the differentiation of CD8(+) non-iNKT cells was markedly resistant to the aly mutation. The proportion of two other NKT cell subsets, NK1.1(+) γδ T cells and NK1.1(-) iNKT cells, was also significantly reduced in aly/aly mice, and this defect in their development was reversed in wild-type host mice given aly/aly bone marrow cells. In exerting effector functions, NIK in NKT-αβ cells appeared dispensable, as NIK-deficient NKT-αβ cells could secrete interleukin-4 or interferon-γ and exhibit cytolytic activity at a level comparable to that of aly/+ NKT-αβ cells. Collectively, these results imply that the NIK in thymic stroma may be critically involved in the differentiation of most NKT cell subsets (although the level of NIK dependence may vary among the subsets), and also that NIK in NKT-αβ cells may be dispensable for their effector function.

Vaccination Produces CD4 T Cells with a Novel CD154-CD40-Dependent Cytolytic Mechanism

The discovery of new vaccines against infectious diseases and cancer requires the development of novel adjuvants with well-defined activities. The TLR4 agonist adjuvant GLA-SE elicits robust Th1 responses to a variety of vaccine Ags and is in clinical development for both infectious diseases and cancer. We demonstrate that immunization with a recombinant protein Ag and GLA-SE also induces granzyme A expression in CD4 T cells and produces cytolytic cells that can be detected in vivo. Surprisingly, these in vivo CTLs were CD4 T cells, not CD8 T cells, and this cytolytic activity was not dependent on granzyme A/B or perforin. Unlike previously reported CD4 CTLs, the transcription factors Tbet and Eomes were not necessary for their development. CTL activity was also independent of the Fas ligand-Fas, TRAIL-DR5, and canonical death pathways, indicating a novel mechanism of CTL activity. Rather, the in vivo CD4 CTL activity induced by vaccination required T cell expression of CD154 (CD40L) and target cell expression of CD40. Thus, vaccination with a TLR4 agonist adjuvant induces CD4 CTLs, which kill through a previously unknown CD154-dependent mechanism.

Cooperativity of HIV-Specific Cytolytic CD4 T Cells and CD8 T Cells in Control of HIV Viremia

CD4+ T cells play a pivotal role in the control of chronic viral infections. Recently, nontraditional CD4+ T cell functions beyond helper effects have been described, and a role for cytolytic CD4+ T cells in the control of HIV infection has been suggested. We define here the transcriptional, phenotypic, and functional profiles of HIV-specific cytolytic CD4+ T cells. Fluidigm BioMark and multiparameter flow cytometric analysis of HIV-specific cytolytic CD4+ T cells revealed a distinct transcriptional signature compared to Th1 CD4+ cells but shared similar features with HIV-specific cytolytic CD8+ T cells. Furthermore, HIV-specific cytolytic CD4+ T cells showed comparable killing activity relative to HIV-specific CD8+ T cells and worked cooperatively in the elimination of virally infected cells. Interestingly, we found that cytolytic CD4+ T cells emerge early during acute HIV infection and tightly follow acute viral load trajectory. This emergence was associated to the early viral set point, suggesting an involvement in early control, in spite of CD4 T cell susceptibility to HIV infection. Our data suggest cytolytic CD4+ T cells as an independent subset distinct from Th1 cells that show combined activity with CD8+ T cells in the long-term control of HIV infection.

IMPORTANCE

The ability of the immune system to control chronic HIV infection is of critical interest to both vaccine design and therapeutic approaches. Much research has focused on the effect of the ability of CD8+ T cells to control the virus, while CD4+ T cells have been overlooked as effectors in HIV control due to the fact that they are preferentially infected. We show here that a subset of HIV-specific CD4+ T cells cooperate in the cytolytic control of HIV replication. Moreover, these cells represent a distinct subset of CD4+ T cells showing significant transcriptional and phenotypic differences compared to HIV-specific Th1 cells but with similarities to CD8+ T cells. These findings are important for our understanding of HIV immunopathology.

Functional heterogeneity in the CD4+ T cell response to murine γ-herpesvirus 68

CD4(+) T cells are critical for the control of virus infections, T cell memory, and immune surveillance. We studied the differentiation and function of murine γ-herpesvirus 68 (MHV-68)-specific CD4(+) T cells using gp150-specific TCR-transgenic mice. This allowed a more detailed study of the characteristics of the CD4(+) T cell response than did previously available approaches for this virus. Most gp150-specific CD4(+) T cells expressed T-bet and produced IFN-γ, indicating that MHV-68 infection triggered differentiation of CD4(+) T cells largely into the Th1 subset, whereas some became follicular Th cells and Foxp3(+) regulatory T cells. These CD4(+) T cells were protective against MHV-68 infection in the absence of CD8(+) T cells and B cells, and protection depended on IFN-γ secretion. Marked heterogeneity was observed in the CD4(+) T cells, based on lymphocyte Ag 6C (Ly6C) expression. Ly6C expression positively correlated with IFN-γ, TNF-α, and granzyme B production; T-bet and KLRG1 expression; proliferation; and CD4(+) T cell-mediated cytotoxicity. Ly6C expression inversely correlated with survival, CCR7 expression, and secondary expansion potential. Ly6C(+) and Ly6C(-) gp150-specific CD4(+) T cells were able to interconvert in a bidirectional manner upon secondary Ag exposure in vivo. These results indicate that Ly6C expression is closely associated with antiviral activity in effector CD4(+) T cells but is inversely correlated with memory potential. Interconversion between Ly6C(+) and Ly6C(-) cells may maintain a balance between the two Ag-specific CD4(+) T cell populations during MHV-68 infection. These findings have significant implications for Ly6C as a surface marker to distinguish functionally distinct CD4(+) T cells during persistent virus infection.

Th17 differentiation and their pro-inflammation function

CD4(+) T helper cells are classical but constantly reinterpreted T-cell subset, playing critical roles in a diverse range of inflammatory responses or diseases. Depending on the cytokines they release and the immune responses they mediate, CD4(+) T cells are classically divided into two major cell populations: Th1 and Th2 cells. However, recent studies challenged this Th1/Th2 paradigm by discovering several T-helper cell subsets with specific differentiation program and functions, including Th17 cells, Treg cells, and Tfh cells. In this chapter, we summarize the current understanding and recent progresses on the Th17 lineage differentiation and its effector impacts on variety of inflammatory responses or disease pathogenesis.

Characterization of T-bet and eomes in peripheral human immune cells

The T-box transcription factors T-bet and Eomesodermin (Eomes) have been well defined as key drivers of immune cell development and cytolytic function. While the majority of studies have defined the roles of these factors in the context of murine T-cells, recent results have revealed that T-bet, and possibly Eomes, are expressed in other immune cell subsets. To date, the expression patterns of these factors in subsets of human peripheral blood mononuclear cells beyond T-cells remain relatively uncharacterized. In this study, we used multiparametric flow cytometry to characterize T-bet and Eomes expression in major human blood cell subsets, including total CD4(+) and CD8(+) T-cells, γδ T-cells, invariant NKT cells, natural killer cells, B-cells, and dendritic cells. Our studies identified novel cell subsets that express T-bet and Eomes and raise implications for their possible functions in the context of other human immune cell subsets besides their well-known roles in T-cells.

Inflammation programs self-reactive CD8+ T cells to acquire T-box-mediated effector function but does not prevent deletional tolerance

CD8(+) T cells must detect foreign antigens and differentiate into effector cells to eliminate infections. But, when self-antigen is recognized instead, mechanisms of peripheral tolerance prevent acquisition of effector function to avoid autoimmunity. These distinct responses are influenced by inflammatory and regulatory clues from the tissue environment, but the mechanism(s) by which naive T cells interpret these signals to generate the appropriate immune response are unclear. The identification of the molecules operative in these cell-fate decisions is crucial for developing new treatment options for patients with cancer or autoimmunity, where manipulation of T cell activity is desired to alter the course of disease. With the use of an in vivo murine model to examine CD8(+) T cell responses to healthy self-tissue, we correlated self-tolerance with a failure to induce the T-box transcription factors T-bet and Eomes. However, inflammation associated with acute microbial infection induced T-bet and Eomes expression and promoted effector differentiation of self-reactive T cells under conditions that normally favor tolerance. In the context of a Listeria infection, these functional responses relied on elevated T-bet expression, independent of Eomes. Alternatively, infection with LCMV induced higher Eomes expression, which was sufficient in the absence of T-bet to promote effector cytokine production. Our results place T-box transcription factors at a molecular crossroads between CD8(+) T cell anergy and effector function upon recognition of peripheral self-antigen, and suggest that inflammation during T cell priming directs these distinct cellular responses.

Multipronged CD4(+) T-cell effector and memory responses cooperate to provide potent immunity against respiratory virus

Over the last decade, the known spectrum of CD4(+) T-cell effector subsets has become much broader, and it has become clear that there are multiple dimensions by which subsets with a particular cytokine commitment can be further defined, including their stage of differentiation, their location, and, most importantly, their ability to carry out discrete functions. Here, we focus on our studies that highlight the synergy among discrete subsets, especially those defined by helper and cytotoxic function, in mediating viral protection, and on distinctions between CD4(+) T-cell effectors located in spleen, draining lymph node, and in tissue sites of infection. What emerges is a surprising multiplicity of CD4(+) T-cell functions that indicate a large arsenal of mechanisms by which CD4(+) T cells act to combat viruses.

α4-integrins control viral meningoencephalitis through differential recruitment of T helper cell subsets

Introduction

Natalizumab blocks α4-integrins and is a prototypic agent for a series of anti-inflammatory drugs that impair trafficking of immune cells into the CNS. However, modulation of the access of immune cells to the CNS is associated with impaired immune surveillance and detrimental viral infections of the CNS. Here, we explored the potency of cellular immune responses within the CNS to protect against viral encephalitis in mice with T cell conditional disruption of VLA-4 integrin (α4β1) expression.

Results

While VLA-4 expression in virus specific Th1 cells is non-redundant for their ability to access the CNS, α4-integrin deficient Th17 cells enter the CNS compartment and generate an inflammatory milieu upon intrathecal vaccinia virus (VV) infection. However, in contrast to Th1 cells that can adopt direct cytotoxic properties, Th17 cells fail to clear the virus due to insufficient Eomes induced perforin-1 expression.

Conclusion

The quality of the intrathecal cellular antiviral response under conditions of impaired VLA-4 function jeopardizes host protection. Our functional in vivo data extend our mechanistic understanding of anti-viral immunity in the CNS and help to estimate the risk potential of upcoming therapeutic agents that target the trafficking of immune cells into distinct anatomical compartments.

CD4+ T cells develop antiretroviral cytotoxic activity in the absence of regulatory T cells and CD8+ T cells

Conventional CD4(+) T cells play an important role in viral immunity. In most virus infections, they provide essential help for antiviral B and T cell responses. In chronic infections, including HIV infection, an expansion of regulatory T cells (Tregs) has been demonstrated, which can suppress virus-specific CD4(+) T cell responses in vitro. However, the suppressive activity of Tregs on effector CD4(+) T cells in retroviral infection is less well documented in vivo. We took advantage of a transgenic mouse in which Tregs can be selectively depleted to determine the influence of such cells on retrovirus-specific CD4(+) T cell responses during an ongoing infection. Mice were infected with Friend retrovirus (FV), and Tregs were depleted during the acute phase of the infection. In nondepleted mice, activated CD4(+) T cells produced Th1-type cytokines but did not exhibit any antiviral cytotoxicity as determined in a major histocompatibility complex (MHC) class II-restricted in vivo cytotoxic T lymphocyte (CTL) assay. Depletion of Tregs significantly increased the numbers of virus-specific CD4(+) T cells and improved their cytokine production, whereas it induced only very little CD4(+) T cell cytotoxicity. However, after dual depletion of Tregs and CD8(+) T cells, conventional CD4(+) T cells developed significant cytotoxic activity against FV epitope-labeled target cells in vivo and contributed to the control of virus replication. Thus, both Tregs and CD8(+) T cells influence the cytotoxic activity of conventional CD4(+) T cells during an acute retroviral infection.

Eomesodermin of atlantic salmon: an important regulator of cytolytic gene and interferon gamma expression in spleen lymphocytes

Eomesodermin (Eomes), a T-bet homologue expressed in activated CD8+T cells was recently proposed to act as a master regulator of cytotoxic CD8+ T cell effector function and offers an exciting avenue for future exploration. Here, we have identified and characterized the full-length Atlantic salmon Eomes cDNA (2477 bp). Promoter analysis of the salmon Eomes showed the presence of important putative transcription binding sites like SP1, FOXO, Oct-1, SMAD, STAT, IRF, and Ets-1. The basal core region responsible for the promoter activity was located between base −199 and +59. Quantitative PCR analysis revealed that the Atlantic salmon Eomes was ubiquitously expressed in all the tissues studied but strongly expressed in the ovary, spleen, brain, and the head kidney. Moreover, the involvement of Eomes in Atlantic salmon immune response and its relation with the cytolytic activity was demonstrated by investigating the early time dependent expression profile of Eomes and CD8α followed by high interferon gamma (IFN-γ) and granzyme A expression during challenge with live Aeromonas salmonicida and Infectious Pancreatic Necrosis (IPN) virus. Therefore, we further analyzed the regulated expression and function of this transcription factor in spleen lymphocytes. Overexpression of Eomes induced IFN-γ, and granzyme A expression but not perforin expression, whereas small interfering RNA (siRNA) mediated suppression of Eomes expression led to significantly reduced IFN-γ production. Thus, Eomes may be critical in cytolytic gene expression and function in fish similar to mammals. Furthermore, IFN-α, and mitogens induced Eomes expression. Taken together, this is the first study on the promoter activity and regulatory role of Eomes in fish.

Anti-cancer versus cancer-promoting effects of the interleukin-17-producing T helper cells

Research on T helper 17 (Th17) cells with regard to immunoediting has revealed elusive results. Whereas enhanced Th17 response and related molecules such as interleukin (IL)-17, IL-21, IL-22, IL-23 and STAT3 accompanied tumor induction and progression, finding that tumor growth/stage was negatively correlated with increased infiltration of Th17 cells in the tumor mass has prompted elucidation of various antitumor mechanisms elicited by Th17 and their related molecules. The pro-tumor efficacy of Th17 response included promotion of neutrophilia and induction of angiogenic (e.g. VEGF, MMP2 and MMP9) and anti-apoptotic factors (e.g. Bcl-XL), as well as expansion and activation of myeloid-derived suppressor cells, which facilitate generation of tumor-specific regulatory T cells. Other tumor immunogenic settings revealed anti-tumor pathways including induction of cytotoxic activity, expression of MHC antigens, the ability Th17 cells to reside within the tumor, and to convert into IFN-γ producers. Notably, Th17 cell related molecules exert indirect pro- or anti-tumor effects via inducing viral persistence or mediating protective mechanisms against bacterial and viral infection. Herein, the recent literature revealing such immunoediting events mediated by Th17 cells and their associated molecules as delivered by various experimental regimens and observed in cancer patient are revised, with a focus on some proposed anti-cancer therapies.

Key molecules in the differentiation and commitment program of T helper 17 (Th17) cells up-to-date

The mechanisms underlying autoimmunity and cancer remain elusive. However, perpendicular evidence has been evolved in the past decade that T helper (Th)17 cells and their related molecules are implicated in initiation and induction of various disease settings including both diseases. Meanwhile, extensive research on Th17 cells elucidated various molecules including cytokines and transcription factors as well as signaling pathways involved in the differentiation, maturation, survival and ultimate commitment of Th17 cells. In the current review, we revise the mechanistic underpinnings delivered by recent research on these molecules in the Th17 differentiation/commitment concert. We emphasize on those molecules proposed as targets for attaining potential therapies of various autoimmune disorders and cancer, aiming both at dampening the dark-side of Th17 repertoire and simultaneously potentiating its benefits in the roster of the antimicrobial response.