Enhanced virus-specific CD8+ T cell responses by Listeria monocytogenes-infected dendritic cells in the context of Tim-3 blockade

Immunotherapy: Reshape the Tumor Immune Microenvironment

Tumor immune microenvironment (TIME) include tumor cells, immune cells, cytokines, etc. The interactions between these components, which are divided into anti-tumor and pro-tumor, determine the trend of anti-tumor immunity. Although the immune system can eliminate tumor through the cancer-immune cycle, tumors appear to eventually evade from immune surveillance by shaping an immunosuppressive microenvironment. Immunotherapy reshapes the TIME and restores the tumor killing ability of anti-tumor immune cells. Herein, we review the function of immune cells within the TIME and discuss the contribution of current mainstream immunotherapeutic approaches to remolding the TIME. Changes in the immune microenvironment in different forms under the intervention of immunotherapy can shed light on better combination treatment strategies.

TIM-3: An update on immunotherapy

T cell immunoglobulin and mucin domain 3 (TIM-3) was originally found to be expressed on the surface of Th1 cells, acting as a negative regulator and binding to the ligand galectin-9 to mediate Th1 cell the apoptosis. Recent studies have shown that TIM-3 is also expressed on other immune cells, such as macrophages, dendritic cells, and monocytes. In addition, TIM-3 ligands also include Psdter, High Mobility Group Box 1 (HMGB1) and Carcinoembryonic antigen associated cell adhesion molecules (Ceacam-1), which have different effects upon biding to different ligands on immune cells. Studies have shown that TIM-3 plays an important role in autoimmune diseases, chronic viral infections and tumors. A large amount of experimental data supports TIM-3 as an immune checkpoint, and targeting TIM-3 is a promising treatment method in current immunotherapy, especially the new combination of other immune checkpoint blockers. In this review, we summarize the role of TIM-3 in different diseases and its possible signaling pathway mechanisms, providing new insights for better breakthrough immunotherapy.

One Stone, Two Birds: The Roles of Tim-3 in Acute Myeloid Leukemia

T cell immunoglobulin and mucin protein 3 (Tim-3) is an immune checkpoint and plays a vital role in immune responses during acute myeloid leukemia (AML). Targeting Tim-3 kills two birds with one stone by balancing the immune system and eliminating leukemia stem cells (LSCs) in AML. These functions make Tim-3 a potential target for curing AML. This review mainly discusses the roles of Tim-3 in the immune system in AML and as an AML LSC marker, which sheds new light on the role of Tim-3 in AML immunotherapy.

SARS-CoV-2-mediated immune system activation and potential application in immunotherapy

Although novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)-mediated pulmonary inflammation has recently attracted great attention, its pathology and pathogenesis are not clear. Notably, due to both its high infective and pathogenicity, SARS-CoV-2 infection may cause a severe sometimes fatal respiratory disease. A specific vaccine, which relies on the analysis of SARS-CoV-2 structural protein-derived antigenic peptides, is indispensable for restraining the spread and reducing the mortality of SARS-CoV-2. SARS-CoV-2 infections activate cytototxic, myeloid-derived suppressor cells, dendritic cells, macrophages, as well as natural killer, B, helper T, and regulatory T cells, thus further stimulating innate and antigen-specific immune responses. Nevertheless, many immune effector cells cause hyperinflammation and pulmonary immunopathology by releasing proinflammatory cytokines and chemokines, including interferon (IFN)-α, IFN-β, IFN-γ, monocyte chemoattractant protein-1, macrophage inflammatory protein (MIP)-1A, MIP1B, interleukin (IL)-1, IL-2, IL-4, IL-6, IL-7, IL-8, IL-9, IL-12, IL-17, and IL-18, platelet-derived growth factor, fibroblast growth factor, tumor necrosis factor-α, and induced protein 10. Interestingly, related products derived from SARS-CoV-2 are likely to trigger immune evasion. Therefore, investigating SARS-CoV-2-specific vaccines, blocking immunopathology, and prohibiting immune evasion are urgently required for treating SARS-CoV-2 infection. In this review, we emphatically illuminated the development of a SARS-CoV-2-specific vaccine based on the analysis of epitopes, also expounding the molecular mechanisms of SARS-CoV-2-mediated cytokine release syndrome. Furthermore, we comprehensively discussed SARS-CoV-2-associated immune evasion and lung immunopathology. Lastly, potential therapeutic strategies against SARS-CoV-2 were explored.

Checkpoint molecules coordinately restrain hyperactivated effector T cells in the tumor microenvironment

The immune checkpoint blockade (ICB) immunotherapy has prolonged overall survival for cancer patients but the response rates are low. The resistance to ICB is likely due to compensatory upregulation of additional immune inhibitory molecules. In this study, we first systematically examined Tim-3 expression in immune cells in mouse tumors and found that Tim-3 was specifically up-regulated in a large number of Treg, conventional CD4⁺, CD8⁺ T cells, dendritic cell 1 (DC1), and macrophage 1 (M1) in the tumor microenvironment (TME). Interestingly, Tim-3⁺ T cells in the TME were phenotypically effector but not “exhausted” T cells because Tim-3⁺ PD-1⁺ CD8⁺ T cells had a higher number of mitochondria, greater levels of glycolysis, and higher tumor-specific cytolytic activities compared to Tim-3⁻ PD-1⁻ CD8⁺ T cells. The combination treatment with Tim-3 and PD-1 mAbs resulted in a synergistic antitumor activity but also increased the expression of Lag-3 and GITR in TIL, demonstrating cross-regulation between multiple checkpoint molecules. Furthermore, we found that the antitumor efficacy with triple combination of Tim-3, PD-1, and Lag3 mAbs was much greater than any two antibodies. Mechanistically, we demonstrated that simultaneous targeting of Tim-3, PD-1, and Lag-3 cooperatively increased the levels of granzyme B and tumor-specific cytolytic activities of CD8⁺ TIL. Our data indicate that multiple checkpoint molecules are coordinately upregulated to inhibit the function of hyperactivated T cells in the TME and requirement for the simultaneous blockade of PD-1, Tim-3 and Lag3 for cancer treatment.

A suicidal strain of Listeria monocytogenes is effective as a DNA vaccine delivery system for oral administration

In this study we determined the in vivo activity of model ovalbumin vaccines delivered by direct intramuscular delivery of plasmid DNA or oral delivery using a recombinant suicidal Listeria monocytogenes strain (rsΔ2). In a previous report we described how rsΔ2 is capable of delivering luciferase, as protein or DNA, in vitro, into non-dividing intestinal epithelial cells (Kuo et al., 2009). This is achieved by engineering a dual expression shuttle vector, pDuLX-Luc, that replicates in E. coli and rsΔ2 and drives gene expression from the Listeria promoter (Phly) as well as the eukaryotic cytomegalovirus promoter (CMV), thereby delivering both protein and plasmid DNA to the cell cytoplasm. For the current in vivo study rsΔ2 containing pDuLX-OVA was used to deliver both ovalbumin protein and the mammalian expression plasmid by the oral route. Controls were used to investigate the activity of this system versus positive and negative controls, as well as quantifying activity against direct intramuscular injection of expression plasmids. Oral administration of rsΔ2(pDuLX-OVA) produced significant titres of antibody and was effective at inducing targeted T-cell lysis (approximately 30% lysis relative to an experimental positive control, intravenous OVA-coated splenocytes+lipopolysaccharide). Intramuscular injection of plasmids pDuLX-OVA or p3L-OVA (which lacks the prokaryotic promoter) also produced significant CTL-mediated cell lysis. The delivery of the negative control rsΔ2 (pDuLX-Luc) confirmed that the observed activity was induced specifically by the ovalbumin vaccination. The data suggest that the oral activity of rsΔ2(pDuLX-OVA) is explained by delivery of OVA protein, expressed in rsΔ2 from the prokaryotic promoter present in pDuLX-OVA, but transfection of mammalian cells in vivo may also play a role. Antibody titres were also produced by oral delivery (in rsΔ2) of the p3L-OVA plasmid in which does not include a prokaryotic promoter.

Decreased TIM-3 expression of peripheral blood natural killer cells in patients with severe aplastic anemia

Severe aplastic anemia (SAA) is an autoimmune disease characterized by severe pancytopenia and bone marrow failure. In our previous studies, we found natural killer (NK) cells were aberrant in SAA patients. T cell immunoglobulin mucin-3 (TIM-3), an important regulator of immunity, is widely detected on NK cells and may contribute as a marker of activation and maturation of NK cells. In this study, we found that SAA untreated patients had lower TIM-3 expression on NK cells and CD56^dim NK subsets compared with normal controls, and were correlated with the severity of pancytopenia of SAA. After immunosuppressive therapy (IST), TIM-3 expression recovered to normal level. Moreover, the TIM-3 mRNA levels in NK cells significantly increased in SAA remission patients after IST. We inferred that low expression of TIM-3 on NK cells might lead to NK cells dysfunction and involve in the progress of bone marrow failure in SAA.

Role of Tim-3 in hepatitis B virus infection: An overview

Hepatitis B virus (HBV) infection has received increasing public attention. HBV is the prototypical member of hepadnaviruses, which naturally infect only humans and great apes and induce the acute and persistent chronic infection of hepatocytes. A large body of evidence has demonstrated that dysfunction of the host anti-viral immune response is responsible for persistent HBV replication, unresolved inflammation and disease progression. Many regulatory factors are involved in immune dysfunction. Among these, T cell immunoglobulin domain and mucin domain-3 (Tim-3), one of the immune checkpoint proteins, has attracted increasing attention due to its critical role in regulating both adaptive and innate immune cells. In chronic HBV infection, Tim-3 expression is elevated in many types of immune cells, such as T helper cells, cytotoxic T lymphocytes, dendritic cells, macrophages and natural killer cells. Tim-3 over-expression is often accompanied by impaired function of the above-mentioned immunocytes, and Tim-3 inhibition can at least partially rescue impaired immune function and thus promote viral clearance. A better understanding of the regulatory role of Tim-3 in host immunity during HBV infection will shed new light on the mechanisms of HBV-related liver disease and suggest new therapeutic methods for intervention.

MicroRNA-155 regulates interferon-γ production in natural killer cells via Tim-3 signalling in chronic hepatitis C virus infection

Host immune responses must be tightly regulated by an intricate balance between positive and negative signals while fighting pathogens; persistent pathogens may usurp these regulatory mechanisms to dampen host immunity to facilitate survival in vivo. Here we report that Tim-3, a negative signalling molecule expressed on monocytes and T cells, is up-regulated on natural killer (NK) cells in individuals chronically infected with hepatitis C virus (HCV). Additionally, the transcription factor T-bet was also found to be up-regulated and associated with Tim-3 expression in NK cells during chronic HCV infection. MicroRNA-155 (miR-155), an miRNA that inhibits signalling proteins involved in immune responses, was down-regulated in NK cells by HCV infection. This Tim-3/T-bet over-expression and miR-155 inhibition were recapitulated in vitro by incubating primary NK cells or NK92 cell line with Huh-7 hepatocytes expressing HCV. Reconstitution of miR-155 in NK cells from HCV-infected patients led to a decrease in T-bet/Tim-3 expression and an increase in interferon-γ production. Blocking Tim-3 signalling also enhanced interferon-γ production in NK cells by improving signal transducer and activator of transcription-5 phosphorylation. These data indicate that HCV-induced, miR-155-regulated Tim-3 expression regulates NK cell function, suggesting a novel mechanism for balancing immune clearance and immune injury during chronic viral infection.

Hepatitis C virus-induced reduction in miR-181a impairs CD4(+) T-cell responses through overexpression of DUSP6

T cells play a crucial role in viral clearance or persistence; however, the precise mechanisms that control their responses during viral infection remain incompletely understood. MicroRNA (miR) has been implicated as a key regulator controlling diverse biological processes through posttranscriptional repression. Here, we demonstrate that hepatitis C virus (HCV)-mediated decline of miR-181a expression impairs CD4(+) T-cell responses through overexpression of dual specific phosphatase 6 (DUSP6). Specifically, a significant decline of miR-181a expression along with overexpression of DUSP6 was observed in CD4(+) T cells from chronically HCV-infected individuals compared to healthy subjects, and the levels of miR-181a loss were found to be negatively associated with the levels of DUSP6 overexpression in these cells. Importantly, reconstitution of miR-181a or blockade of DUSP6 expression in CD4(+) T cells led to improved T-cell responses including enhanced CD25 and CD69 expression, increased interleukin-2 expression, and improved proliferation of CD4(+) T cells derived from chronically HCV-infected individuals.

CONCLUSION

Since a decline of miR-181a concomitant with DUSP6 overexpression is the signature marker for age-associated T-cell senescence, these findings provide novel mechanistic insights into HCV-mediated premature T-cell aging through miR-181a-regulated DUSP6 signaling and reveal new targets for therapeutic rejuvenation of impaired T-cell responses during chronic viral infection.