Long-Term Persistence of Exhausted CD8 T Cells in Chronic Infection Is Regulated by MicroRNA-155

Aryl Hydrocarbon Receptor Role in Co-Ordinating SARS-CoV-2 Entry and Symptomatology: Linking Cytotoxicity Changes in COVID-19 and Cancers; Modulation by Racial Discrimination Stress

There is an under-recognized role of the aryl hydrocarbon receptor (AhR) in co-ordinating the entry and pathophysiology of the severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2) that underpins the COVID-19 pandemic. The rise in pro-inflammatory cytokines during the 'cytokine storm' induce indoleamine 2,3-dioxygenase (IDO), leading to an increase in kynurenine that activates the AhR, thereby heightening the initial pro-inflammatory cytokine phase and suppressing the endogenous anti-viral response. Such AhR-driven changes underpin the heightened severity and fatality associated with pre-existent high-risk medical conditions, such as type II diabetes, as well as to how racial discrimination stress contributes to the raised severity/fatality in people from the Black Asian and Minority Ethnic (BAME) communities. The AhR is pivotal in modulating mitochondrial metabolism and co-ordinating specialized, pro-resolving mediators (SPMs), the melatonergic pathways, acetyl-coenzyme A, and the cyclooxygenase (COX) 2-prostaglandin (PG) E2 pathway that underpin 'exhaustion' in the endogenous anti-viral cells, paralleling similar metabolic suppression in cytolytic immune cells that is evident across all cancers. The pro-inflammatory cytokine induced gut permeability/dysbiosis and suppression of pineal melatonin are aspects of the wider pathophysiological underpinnings regulated by the AhR. This has a number of prophylactic and treatment implications for SARS-CoV-2 infection and cancers and future research directions that better investigate the biological underpinnings of social processes and how these may drive health disparities.

Targeting metabolism to reverse T-cell exhaustion in chronic viral infections

CD8 T-cells are an essential component of the adaptive immune response accountable for the clearance of virus-infected cells via cytotoxic effector functions. Maintaining a specific metabolic profile is necessary for these T-cells to sustain their effector functions and clear pathogens. When CD8 T-cells are activated via T-cell receptor recognition of viral antigen, they transition from a naïve to an effector state and eventually to a memory phenotype, and their metabolic profiles shift as the cells differentiate to accomidate different metabolic demands. However, in the context of particular chronic viral infections (CVIs), CD8 T-cells can become metabolically dysfunctional in a state known as T-cell exhaustion. In this state, CD8 T-cells exhibit reduced effector functions and are unable to properly control pathogens. Clearing these chronic infections becomes progressively difficult as increasing numbers of the effector T-cells become exhausted. Hence, reversal of this dysfunctional metabolic phenotype is vital when considering potential treatments of these infections and offers the opportunity for novel strategies for the development of therapies against CVIs. In this review we explore research implicating alteration of the metabolic state as a means to reverse CD8 T-cell exhaustion in CVIs. These findings indicate that strategies targeting dysfunctional CD8 T-cell metabolism could prove to be a promising option for successfully treating CVIs.

The Multiple Roles of Hepatitis B Virus X Protein (HBx) Dysregulated MicroRNA in Hepatitis B Virus-Associated Hepatocellular Carcinoma (HBV-HCC) and Immune Pathways

Currently, the treatment of hepatitis B virus (HBV)-associated hepatocellular carcinoma (HCC) [HBV-HCC] relies on blunt tools that are unable to offer effective therapy for later stage pathogenesis. The potential of miRNA to treat HBV-HCC offer a more targeted approach to managing this lethal carcinoma; however, the complexity of miRNA as an ancillary regulator of the immune system remains poorly understood. This review examines the overlapping roles of HBx-dysregulated miRNA in HBV-HCC and immune pathways and seeks to demonstrate that specific miRNA response in immune cells is not independent of their expression in hepatocytes. This interplay between the two pathways may provide us with the possibility of using candidate miRNA to manipulate this interaction as a potential therapeutic option.

Rapid in vitro generation of bona fide exhausted CD8+ T cells is accompanied by Tcf7 promotor methylation

Exhaustion is a dysfunctional state of cytotoxic CD8+ T cells (CTL) observed in chronic infection and cancer. Current in vivo models of CTL exhaustion using chronic viral infections or cancer yield very few exhausted CTL, limiting the analysis that can be done on these cells. Establishing an in vitro system that rapidly induces CTL exhaustion would therefore greatly facilitate the study of this phenotype, identify the truly exhaustion-associated changes and allow the testing of novel approaches to reverse or prevent exhaustion. Here we show that repeat stimulation of purified TCR transgenic OT-I CTL with their specific peptide induces all the functional (reduced cytokine production and polyfunctionality, decreased in vivo expansion capacity) and phenotypic (increased inhibitory receptors expression and transcription factor changes) characteristics of exhaustion. Importantly, in vitro exhausted cells shared the transcriptomic characteristics of the gold standard of exhaustion, CTL from LCMV cl13 infections. Gene expression of both in vitro and in vivo exhausted CTL was distinct from T cell anergy. Using this system, we show that Tcf7 promoter DNA methylation contributes to TCF1 downregulation in exhausted CTL. Thus this novel in vitro system can be used to identify genes and signaling pathways involved in exhaustion and will facilitate the screening of reagents that prevent/reverse CTL exhaustion.

Non-coding RNAs in CD8 T cell biology

CD8 T cells are among the most vigorous soldiers of the immune system that fight viral infections and cancer. CD8 T cell development, maintenance, activation and differentiation are under the tight control of multiple transcriptional and post-transcriptional networks. Over the last two decades it has become clear that non-coding RNAs (ncRNAs), which consist of microRNAs (miRNAs) and long ncRNAs (lncRNAs), have emerged as global biological regulators. While our understanding of the function of specific miRNAs has increased since the discovery of RNA interference, it is still very limited, and the field of lncRNAs is just starting to blossom. Here we will summarize our knowledge on the role of ncRNAs in CD8 T cell biology, including differentiation into memory and exhausted cells.

miR-155 Overexpression in OT-1 CD8+ T Cells Improves Anti-Tumor Activity against Low-Affinity Tumor Antigen

Therapy by adoptive transfer of ex vivo-expanded tumor-infiltrating or genetically modified T cells may lead to impressive clinical responses. However, there is a need to improve in vivo persistence and functionality of the transferred T cells, in particular, to face the highly immunosuppressive environment of solid tumors. Here, we investigate the potential of miR-155, a microRNA known to play an important role in CD8+ T cell fitness. We show that forced expression of miR-155 in tumor antigen-specific T cells improves the tumor control of B16 tumors expressing a low-affinity antigen ligand. Importantly, miR-155-transduced T cells exhibit increased proliferation and effector functions associated with a higher glycolytic activity independent of exogenous glucose. Altogether, these data suggest that miR-155 may optimize the antitumor activity of adoptively transferred low-affinity tumor-infiltrating lymphocytes (TILs), in particular, by rendering them more resistant to the glucose-deprived environment of solid tumors. Thus, transgenic expression of miR-155 may enable therapeutic targeting of self-antigen-specific T cells in addition to neoantigen-specific ones.

The immune checkpoint receptor associated phosphatases SHP-1 and SHP-2 are not required for γδT17 cell development, activation, or skin inflammation

IL-17-producing gamma delta (γδT17) cells are innate lymphocytes critical for antibacterial protection at barrier surfaces such as the skin but also highly pathogenic during inflammation. It is therefore important to understand the cellular and molecular mechanisms that could counter-balance overt γδT17 cell activation. Immune checkpoint receptors (ICRs) deliver inhibitory signals to activated lymphocytes and have been implicated as negative regulators of mouse γδT17 cells. In this report, we investigated the cytokine signals that induce ICR expression on γδT17 cells and studied the in vivo role of the Src-homology-2 phosphatases 1 and 2 (SHP-1 and SHP-2) in the context of γδT17-induced psoriasis. We found that surface expression of ICRs can be induced by cytokines; however, SHP-1 or SHP-2 could not inhibit γδT17 responses. In this regard, conditional deletion of SHP-1, SHP-2, or both did no impact γδT17 cell development, expansion, cytokine production, or skin pathology.

An immune relevant signature for predicting prognoses and immunotherapeutic responses in patients with muscle-invasive bladder cancer (MIBC)

Immune checkpoint inhibitors (ICIs) are novel treatments that significantly improve the survival time of MIBC patients, but immunotherapeutic responses are different among MIBC patients. Therefore, it is urgent to find predictive biomarkers that can accurately identify MIBC patients who are sensitive to ICIs. In this study, we computed the relative abundances of 24 immune cells based on the expression profiles of MIBC patients using single‐sample gene set enrichment analysis (ssGSEA). Unsupervised clustering analysis of the 24 immune cells was performed to classify MIBC patients into different immune‐infiltrating groups. Genome (gene mutation and copy number variation), transcriptome (mRNA, lncRNA, and miRNA), and functional enrichment were found to be heterogeneous among different immune‐infiltrating groups. We identified 282 differentially expressed genes (DEGs) associated with immune infiltration by comparing the expression profiles of patients with different immune infiltration profiles, and 20 core prognostic DEGs were identified by univariate Cox regression analysis. An immune‐relevant gene signature (TIM signature) consisting of nine key prognostic DEGs (CCDC80, CD3D, CIITA, FN1, GBP4, GNLY, SPINK1, UBD, and VIM) was constructed using least absolute shrinkage and selection operator (LASSO) Cox regression analysis. Receiver operating characteristic (ROC) curves and subgroup analysis confirmed that the TIM signature was an ideal biomarker for predicting the prognosis of MIBC patients. Its value in predicting immunotherapeutic responses was also validated in The Cancer Genome Atlas (TCGA) cohort (AUC = 0.69, 95% CI = 0.63‐0.74) and the IMvigor210 cohort (AUC = 0.64, 95% = 0.55‐0.74). The TIM signature demonstrates a powerful ability to distinguish MIBC patients with different prognoses and immunotherapeutic responses, but more prospective studies are needed to assess its reliability in the future.

Chronic Lymphocytic Choriomeningitis Infection Causes Susceptibility to Mousepox and Impairs Natural Killer Cell Maturation and Function

Chronic viral infections. like those of humans with cytomegalovirus, human immunodeficiency virus (even when under antiretroviral therapy), and hepatitis C virus or those of mice with lymphocytic choriomeningitis virus (LCMV) clone 13 (CL13), result in immune dysfunction that predisposes the host to severe infections with unrelated pathogens. It is known that C57BL/6 (B6) mice are resistant to mousepox, a lethal disease caused by the orthopoxvirus ectromelia virus (ECTV), and that this resistance requires natural killer (NK) cells and other immune cells. We show that most B6 mice chronically infected with CL13 succumb to mousepox but that most of those that recovered from acute infection with the LCMV Armstrong (Arm) strain survive. We also show that B6 mice chronically infected with CL13 and those that recovered from Arm infection have a reduced frequency and a reduced number of NK cells. However, at steady state, NK cells in mice that have recovered from Arm infection mature normally and, in response to ECTV, get activated, become more mature, proliferate, and increase their cytotoxicity in vivo Conversely, in mice chronically infected with CL13, NK cells are immature and residually activated, and following ECTV infection, they do not mature, proliferate, or increase their cytotoxicity. Given the well-established importance of NK cells in resistance to mousepox, these data suggest that the NK cell dysfunction caused by CL13 persistence may contribute to the susceptibility of CL13-infected mice to mousepox. Whether chronic infections similarly affect NK cells in humans should be explored.IMPORTANCE Infection of adult mice with the clone 13 (CL13) strain of lymphocytic choriomeningitis virus (LCMV) is extensively used as a model of chronic infection. In this paper, we show that mice chronically infected with CL13 succumb to challenge with ectromelia virus (ECTV; the agent of mousepox) and that natural killer (NK) cells in CL13-infected mice are reduced in numbers and have an immature and partially activated phenotype but do respond to ECTV. These data may provide additional clues why humans chronically infected with certain pathogens are less resistant to viral diseases.

Loss of Resistance to Mousepox during Chronic Lymphocytic Choriomeningitis Virus Infection Is Associated with Impaired T-Cell Responses and Can Be Rescued by Immunization

It is well established that chronic viral infections can cause immune suppression, resulting in increased susceptibility to other infectious diseases. However, the effects of chronic viral infection on T-cell responses and vaccination against highly pathogenic viruses are not well understood. We have recently shown that C57BL/6 (B6) mice lose their natural resistance to wild-type (WT) ectromelia virus (ECTV) when chronically infected with lymphocytic choriomeningitis virus (LCMV) clone 13 (CL13). Here we compared the T-cell response to ECTV in previously immunologically naive mice that were chronically infected with CL13 or that were convalescent from acute infection with the Armstrong (Arm) strain of LCMV. Our results show that mice that were chronically infected with CL13 but not those that had recovered from Arm infection have highly defective ECTV-specific CD8⁺ and CD4⁺ T-cell responses to WT ECTV. These defects are at least partly due to the chronic infection environment. In contrast to mice infected with WT ECTV, mice chronically infected with CL13 survived without signs of disease when infected with ECTV-Δ036, a mutant ECTV strain that is highly attenuated. Strikingly, mice chronically infected with CL13 mounted a strong CD8⁺ T-cell response to ECTV-Δ036 and survived without signs of disease after a subsequent challenge with WT ECTV. Our work suggests that enhanced susceptibility to acute viral infections in chronically infected individuals can be partly due to poor T-cell responses but that sufficient T-cell function can be recovered and resistance to acute infection can be restored by immunization with highly attenuated vaccines.IMPORTANCE Chronic viral infections may result in immunosuppression and enhanced susceptibility to infections with other pathogens. For example, we have recently shown that mice chronically infected with lymphocytic choriomeningitis virus (LCMV) clone 13 (CL13) are highly susceptible to mousepox, a disease that is caused by ectromelia virus and that is the mouse homolog of human smallpox. Here we show chronic CL13 infection severely disrupts the expansion, proliferation, activation, and cytotoxicity of T cells in response due at least in part to the suppressive effects of the chronic infection milieu. Notably, despite this profound immunodeficiency, mice chronically infected with CL13 could be protected by vaccination with a highly attenuated variant of ECTV. These results demonstrate that protective vaccination of immunosuppressed individuals is possible, provided that proper immunization tools are used.

MicroRNA-181a regulates IFN-γ expression in effector CD8+ T cell differentiation

CD8⁺ T cells are key players in immunity against intracellular infections and tumors. The main cytokine associated with these protective responses is interferon-γ (IFN-γ), whose production is known to be regulated at the transcriptional level during CD8⁺ T cell differentiation. Here we found that microRNAs constitute a posttranscriptional brake to IFN-γ expression by CD8⁺ T cells, since the genetic interference with the Dicer processing machinery resulted in the overproduction of IFN-γ by both thymic and peripheral CD8⁺ T cells. Using a gene reporter mouse for IFN-γ locus activity, we compared the microRNA repertoires associated with the presence or absence of IFN-γ expression. This allowed us to identify a set of candidates, including miR-181a and miR-451, which were functionally tested in overexpression experiments using synthetic mimics in peripheral CD8⁺ T cell cultures. We found that miR-181a limits IFN-γ production by suppressing the expression of the transcription factor Id2, which in turn promotes the Ifng expression program. Importantly, upon MuHV-4 challenge, miR-181a-deficient mice showed a more vigorous IFN-γ⁺ CD8⁺ T cell response and were able to control viral infection significantly more efficiently than control mice. These data collectively establish a novel role for miR-181a in regulating IFN-γ–mediated effector CD8⁺ T cell responses in vitro and in vivo.

Human and translational immunology in the third millennium: progress, challenges and opportunities

Internationally renowned scientists gathered at the 2nd Human & Translational Immunology Conference in Kos, Greece, to discuss the latest advances in translational immunology, especially vaccinology, infectious diseases and tumor immunotherapy.

TCF-1-Centered Transcriptional Network Drives an Effector versus Exhausted CD8 T Cell-Fate Decision

TCF-1 is a key transcription factor in progenitor exhausted CD8 T cells (Tex). Moreover, this Tex cell subset mediates responses to PD-1 checkpoint pathway blockade. However, the role of the transcription factor TCF-1 in early fate decisions and initial generation of Tex cells is unclear. Single-cell RNA sequencing (scRNA-seq) and lineage tracing identified a TCF-1+Ly108+PD-1+ CD8 T cell population that seeds development of mature Tex cells early during chronic infection. TCF-1 mediated the bifurcation between divergent fates, repressing development of terminal KLRG1Hi effectors while fostering KLRG1Lo Tex precursor cells, and PD-1 stabilized this TCF-1+ Tex precursor cell pool. TCF-1 mediated a T-bet-to-Eomes transcription factor transition in Tex precursors by promoting Eomes expression and drove c-Myb expression that controlled Bcl-2 and survival. These data define a role for TCF-1 in early-fate-bifurcation-driving Tex precursor cells and also identify PD-1 as a protector of this early TCF-1 subset.

Gene Expression-Based Identification of Antigen-Responsive CD8+ T Cells on a Single-Cell Level

CD8⁺ T cells are important effectors of adaptive immunity against pathogens, tumors, and self antigens. Here, we asked how human cognate antigen-responsive CD8⁺ T cells and their receptors could be identified in unselected single-cell gene expression data. Single-cell RNA sequencing and qPCR of dye-labeled antigen-specific cells identified large gene sets that were congruently up- or downregulated in virus-responsive CD8⁺ T cells under different antigen presentation conditions. Combined expression of TNFRSF9, XCL1, XCL2, and CRTAM was the most distinct marker of virus-responsive cells on a single-cell level. Using transcriptomic data, we developed a machine learning-based classifier that provides sensitive and specific detection of virus-responsive CD8⁺ T cells from unselected populations. Gene response profiles of CD8⁺ T cells specific for the autoantigen islet-specific glucose-6-phosphatase catalytic subunit-related protein differed markedly from virus-specific cells. These findings provide single-cell gene expression parameters for comprehensive identification of rare antigen-responsive cells and T cell receptors.

MicroRNA regulation of CD8+ T cell responses

MicroRNAs (miRNAs) are a class of short noncoding RNAs that play critical roles in the regulation of a broad range of biological processes. Like transcription factors, miRNAs exert their effects by modulating the expression of networks of genes that operate in common or convergent pathways. CD8⁺ T cells are critical agents of the adaptive immune system that provide protection from infection and cancer. Here, we review the important roles of miRNAs in the regulation of CD8⁺ T cell biology and provide perspectives on the broader emerging principles of miRNA function.

The PD-1/PD-L1 Axis and Virus Infections: A Delicate Balance

Programmed cell death protein (PD-1) and its ligands play a fundamental role in the evasion of tumor cells from antitumor immunity. Less well appreciated is the fact that the PD-1/PD-L1 axis also regulates antiviral immune responses and is therefore modulated by a number of viruses. Upregulation of PD-1 and its ligands PD-L1 and PD-L2 is observed during acute virus infection and after infection with persistent viruses including important human pathogens such as human immunodeficiency virus (HIV), hepatitis C virus (HCV), and hepatitis B virus (HBV). Experimental evidence suggests that insufficient signaling through the PD-1 pathway promotes immunopathology during acute infection by exaggerating primary T cell responses. If chronic infection is established, however, high levels of PD-1 expression can have unfavorable immunological consequences. Exhaustion and suppression of antiviral immune responses can result in viral immune evasion. The role of the PD-1/PD-L1 axis during viral infections is further complicated by evidence that PD-L1 also mediates inflammatory effects in the acute phase of an immune response. In this review, we discuss the intricate interplay between viruses and the PD-1/PD-L1 axis.

Chimeric antigen receptor T cell persistence and memory cell formation

It is now becoming clear that less differentiated naive and memory T cells are superior to effector T cells in the transfer of immunity for adoptive cell therapy. This review will outline the challenges faced by chimeric antigen receptor (CAR) T cell therapy in the generation of persistence and memory for CAR T cells, and summarize recent strategies to improve CAR T cell persistence, with a focus on memory cell formation. The relevance of enhancing persistence in more differentiated effector T cells is also covered, because genetic and pharmacological interventions may prolong effector T cell activity and lifespan, thereby improving anti-cancer activity. In particular, it may be possible to enforce epigenetic changes in differentiated T cells to enhance memory CAR T cell formation. Optimizing the generation of self-renewing T cell populations (e.g. memory cells), while maintaining differentiated effector T cells through epigenome modification, will help overcome barriers to T cell expansion and survival, thereby improving clinical outcomes in CAR T cell therapy.

miR-155 harnesses Phf19 to potentiate cancer immunotherapy through epigenetic reprogramming of CD8+ T cell fate

T cell senescence and exhaustion are major barriers to successful cancer immunotherapy. Here we show that miR-155 increases CD8⁺ T cell antitumor function by restraining T cell senescence and functional exhaustion through epigenetic silencing of drivers of terminal differentiation. miR-155 enhances Polycomb repressor complex 2 (PRC2) activity indirectly by promoting the expression of the PRC2-associated factor Phf19 through downregulation of the Akt inhibitor, Ship1. Phf19 orchestrates a transcriptional program extensively shared with miR-155 to restrain T cell senescence and sustain CD8⁺ T cell antitumor responses. These effects rely on Phf19 histone-binding capacity, which is critical for the recruitment of PRC2 to the target chromatin. These findings establish the miR-155–Phf19–PRC2 as a pivotal axis regulating CD8⁺ T cell differentiation, thereby paving new ways for potentiating cancer immunotherapy through epigenetic reprogramming of CD8⁺ T cell fate.

The inability of T cells to properly mount anti-tumour immunity underlies failed cancer immune surveillance or therapy. Here the authors show that a microRNA, miR-155, suppresses Ship1 phosphatase expression to modulate epigenetic reprogramming of CD8 T cell differentiation via the Phf19/PRC2 axis, thereby implicating a novel aspect of cancer immunity regulation.

MicroRNA-155 Expression Is Enhanced by T-cell Receptor Stimulation Strength and Correlates with Improved Tumor Control in Melanoma

microRNAs are short noncoding RNAs that regulate protein expression posttranscriptionally. We previously showed that miR-155 promotes effector CD8⁺ T-cell responses. However, little is known about the regulation of miR-155 expression. Here, we report that antigen affinity and dose determine miR-155 expression in CD8⁺ T cells. In B16 tumors expressing a low-affinity antigen ligand, tumor-specific infiltrating CD8⁺ T cells showed variable miR-155 expression, whereby high miR-155 expression was associated with more cytokine-producing cells and tumor control. Moreover, anti-PD-1 treatment led to both increased miR-155 expression and tumor control by specific CD8⁺ T cells. In addition, miR-155 overexpression enhanced exhausted CD8⁺ T-cell persistence in the LCMV cl13 chronic viral infection model. In agreement with these observations in mouse models, miR-155 expression in human effector memory CD8⁺ T cells positively correlated with their frequencies in tumor-infiltrated lymph nodes of melanoma patients. Low miR-155 target gene signature in tumors was associated with prolonged overall survival in melanoma patients. Altogether, these results raise the possibility that high miR-155 expression in CD8⁺ tumor-infiltrating T cells may be a surrogate marker of the relative potency of in situ antigen-specific CD8⁺ T-cell responses.

CD8+ T cell exhaustion

CD8⁺ T cells are important for the protective immunity against intracellular pathogens and tumor. In the case of chronic infection or cancer, CD8⁺ T cells are exposed to persistent antigen and/or inflammatory signals. This excessive amount of signals often leads CD8⁺ T cells to gradual deterioration of T cell function, a state called "exhaustion." Exhausted T cells are characterized by progressive loss of effector functions (cytokine production and killing function), expression of multiple inhibitory receptors (such as PD-1 and LAG3), dysregulated metabolism, poor memory recall response, and homeostatic proliferation. These altered functions are closely related with altered transcriptional program and epigenetic landscape that clearly distinguish exhausted T cells from normal effector and memory T cells. T cell exhaustion is often associated with inefficient control of persisting infections and cancers, but re-invigoration of exhausted T cells with inhibitory receptor blockade can promote improved immunity and disease outcome. Accumulating evidences support the therapeutic potential of targeting exhausted T cells. However, exhausted T cells comprise heterogenous cell population with distinct responsiveness to intervention. Understanding molecular mechanism of T cell exhaustion is essential to establish rational immunotherapeutic interventions.

MiR155 sensitized B-lymphoma cells to anti-PD-L1 antibody via PD-1/PD-L1-mediated lymphoma cell interaction with CD8+T cells

Background

MicroRNAs (miRs) are involved in lymphoma progression by regulating tumor cell interaction with microenvironment. MiR155 is overexpressed in diffuse large B-cell lymphoma (DLBCL) and its biological effect on tumor microenvironment needs to be futher investigated.

Methods

MiR155 was detected by quantitative real-time PCR in patients with newly diagnosed DLBCL. The mechanism of action of miR155 on lymphoma progression and tumor microenvironment was examined in vitro in B-lymphoma cell lines and in vivo in a murine xenograft model.

Results

Serum miR155 was significantly elevated, correlated with tumor miR155 expression, and indicated poor disease outcome in DLBCL. MiR155 overexpression was associated with decreased peripheral blood CD8+T cells and inhibition of T-cell receptor signaling. Of note, EBV-positive patients showed higher serum miR155 than EBV-negative patients. In co-culture systems of B-lymphoma cells with immune cells, miR155 induced Fas-mediated apoptosis of CD8+T cells, which could be targeted by anti-PD-1 and anti-PD-L1 antibodies. Moreover, miR155 enhanced lymphoma cell PD-L1 expression, recruited CD8+T cells by PD-1/PD-L1 interaction and inhibited CD8+T cell function via dephosphorylating AKT and ERK. MiR155-induced AKT/ERK inactivation was more obvious in CD8+T cells co-cultured with EBV-infected B-lymphoma cells. In vivo in a murine xenograft model established with subcutaneous injection of A20 cells, PD-L1 blockade particularly retarded miR155-overexpressing tumor growth, consistent with maintenance of CD8+T cells and their function.

Conclusions

As a oncogenic biomarker of B-cell lymphoma, serum miR155 was related to lymphoma progression through modulating PD-1/PD-L1-mediated interaction with CD8+T cells of tumor microenvironment, indicating the sensitivity of B-cell lymphoma to PD-L1 blockade. Also CD8+T cells could be a therapeutic mediator of immune checkpoint inhibitors in treating EBV-associated lymphoid malignancies.

Electronic supplementary material

The online version of this article (10.1186/s12943-019-0977-3) contains supplementary material, which is available to authorized users.

Multifunctional miR-155 Pathway in Avian Oncogenic Virus-Induced Neoplastic Diseases

MicroRNAs (miRNAs) are small noncoding RNAs that fine-tune the responses of the cell by modulating the cell transcriptome and gene expression. MicroRNA 155 (miR-155) is a conserved multifunctional miRNA involved in multiple roles including the modulation of the immune responses. When deregulated, miR-155 can also contribute to cancer as has been demonstrated in several human malignancies such as diffuse large B cell lymphoma, chronic lymphocytic leukemia, as well as in Epstein⁻Barr virus (EBV)-induced B cell transformation. Avian oncogenic viruses such as Marek's disease virus (MDV), avian leukosis virus (ALV), and reticuloendotheliosis virus (REV) that account for more than 90% of cancers in avian species, also make use of the miR-155 pathway during oncogenesis. While oncogenic retroviruses, such as ALV, activate miR-155 by insertional activation, acutely transforming retroviruses use transduced oncogenes such as v-rel to upregulate miR-155 expression. MDV on the other hand, encodes a functional miR-155 ortholog mdv1-miR-M4, similar to the miR-155 ortholog kshv-miR-K11 present in Kaposi's sarcoma-associated herpesvirus (KSHV). We have shown that mdv1-miR-M4 is critical for the induction of MDV-induced lymphomas further demonstrating the oncogenic potential of miR-155 pathway in cancers irrespective of the diverse etiology. In this review, we discuss on our current understanding of miR-155 function in virus-induced lymphomas focusing primarily on avian oncogenic viruses.

CD8 T Cell Exhaustion During Chronic Viral Infection and Cancer

Exhausted CD8 T (Tex) cells are a distinct cell lineage that arise during chronic infections and cancers in animal models and humans. Tex cells are characterized by progressive loss of effector functions, high and sustained inhibitory receptor expression, metabolic dysregulation, poor memory recall and homeostatic self-renewal, and distinct transcriptional and epigenetic programs. The ability to reinvigorate Tex cells through inhibitory receptor blockade, such as αPD-1, highlights the therapeutic potential of targeting this population. Emerging insights into the mechanisms of exhaustion are informing immunotherapies for cancer and chronic infections. However, like other immune cells, Tex cells are heterogeneous and include progenitor and terminal subsets with unique characteristics and responses to checkpoint blockade. Here, we review our current understanding of Tex cell biology, including the developmental paths, transcriptional and epigenetic features, and cell intrinsic and extrinsic factors contributing to exhaustion and how this knowledge may inform therapeutic targeting of Tex cells in chronic infections, autoimmunity, and cancer.