CD28 family of receptors on T cells in chronic HBV infection: Expression characteristics, clinical significance and correlations with PD-1 blockade

Immune checkpoint inhibitors and SARS-CoV2 infection

Infection with severe acute respiratory syndrome coronavirus 2 (SARS‑CoV‑2) triggers coronavirus disease 2019 (COVID-19), which predominantly targets the respiratory tract. SARS-CoV-2 infection, especially severe COVID-19, is associated with dysregulated immune responses against the virus, including exaggerated inflammatory responses known as the cytokine storm, together with lymphocyte and NK cell dysfunction known as immune cell exhaustion. Overexpression of negative immune checkpoints such as PD-1 and CTLA-4 plays a considerable role in the dysfunction of immune cells upon SARS-CoV-2 infection. Blockade of these checkpoints has been suggested to improve the clinical outcome of COVID-19 patients by promoting potent immune responses against the virus. In the current review, we provide an overview of the potential of checkpoint inhibitors to induce potent immune responses against SARS-CoV-2 and improving the clinical outcome of severe COVID-19 patients.

Circulating Th2-biased T follicular helper cells impede antiviral humoral responses during chronic hepatitis B infection through upregulating CTLA4

Failure in curing chronic hepatitis B (CHB) caused by hepatitis B virus (HBV) can lead to functional impairment of B cells. Cytotoxic T-lymphocyte associated antigen 4 (CTLA4) regulates B cell and T follicular helper (Tfh) cell differentiation. In addition, Tfh cells play a critical role in helping B cells generate antibodies upon pathogen exposure. Here, we analyzed the global and HBsAg-specific B cells and circulating Tfh (cTfh) cells using samples from treatment-naïve and Peg-IFN-α-treated CHB patients and healthy subjects. Compared to healthy subjects, CTLA4 expression was significantly increased in cTfh cells, from CHB patients. The frequency of CTLA4⁺cTfh2 cells was negatively correlated with that of HBsAg-specific resting memory B cells. Importantly, inhibition of CTLA4 restored HBsAb secretion and promoted plasma cell differentiation. In addition, CTLA4⁺cTfh2 cells from CHB patients were ineffective in providing B cell help. Both expression of CTLA4 in cTfh and cTfh2 cells and ratios of CLTA4⁺cTfh and CTLA4⁺cTfh2 cells were significantly decreased in Peg-IFN-α-treated CHB patients who showed complete responses. Thus, our results highlighted that cTh2-biased T follicular helper cells could impede antiviral humoral responses during chronic HBV infection by upregulating CTLA4, suggesting that further optimizing potent Tfh cell responses may promote functional cure of CHB.

Focus on T cell exhaustion: new advances in traditional Chinese medicine in infection and cancer

In chronic infections and cancers, T lymphocytes (T cells) are exposed to persistent antigen or inflammatory signals. The condition is often associated with a decline in T-cell function: a state called "exhaustion". T cell exhaustion is a state of T cell dysfunction characterized by increased expression of a series of inhibitory receptors (IRs), decreased effector function, and decreased cytokine secretion, accompanied by transcriptional and epigenetic changes and metabolic defects. The rise of immunotherapy, particularly the use of immune checkpoint inhibitors (ICIs), has dramatically changed the clinical treatment paradigm for patients. However, its low response rate, single target and high immunotoxicity limit its clinical application. The multiple immunomodulatory potential of traditional Chinese medicine (TCM) provides a new direction for improving the treatment of T cell exhaustion. Here, we review recent advances that have provided a clearer molecular understanding of T cell exhaustion, revealing the characteristics and causes of T cell exhaustion in persistent infections and cancers. In addition, this paper summarizes recent advances in improving T cell exhaustion in infectious diseases and cancer with the aim of providing a comprehensive and valuable source of information on TCM as an experimental study and their role in collaboration with ICIs therapy.

The Role of CTLA-4 in T Cell Exhaustion in Chronic Hepatitis B Virus Infection

Patients with chronic hepatitis B (CHB) gradually develop T cell exhaustion, and the inhibitory receptor molecule, cytotoxic T-lymphocyte antigen-4 (CTLA-4), may play a role in this phenomenon. This systematic review investigates the role of CTLA-4 in the development of T cell exhaustion in CHB. A systematic literature search was conducted on PubMed and Embase on 31 March 2023 to identify relevant studies. Fifteen studies were included in this review. A majority of the studies investigating CD8⁺ T cells demonstrated increased expression of CTLA-4 in CHB patients, though one study found this only in HBeAg-positive patients. Three out of four studies investigating the expression of CTLA-4 on CD4⁺ T cells found upregulation of CTLA-4. Several studies showed constitutive expression of CLTA-4 on CD4⁺ regulatory T cells. CTLA-4 blockade resulted in heterogeneous responses for all T cell types, as it resulted in increased T cell proliferation and/or cytokine production in some studies, while other studies found this only when combining blockade of CTLA-4 with other inhibitory receptors. Although mounting evidence supports a role of CTLA-4 in T cell exhaustion, there is still insufficient documentation to describe the expression and exact role of CTLA-4 in T cell exhaustion in CHB.

Immune checkpoints on T and NK cells in the context of HBV infection: Landscape, pathophysiology and therapeutic exploitation

In hepatitis B virus (HBV) infection, the interplay between the virus and the host immune system is crucial in determining the pathogenesis of the disease. Patients who fail to mount a sufficient and sustained anti-viral immune response develop chronic hepatitis B (CHB). T cells and natural killer (NK) cells play decisive role in viral clearance, but they are defective in chronic HBV infection. The activation of immune cells is tightly controlled by a combination of activating and inhibitory receptors, called immune checkpoints (ICs), allowing the maintenance of immune homeostasis. Chronic exposure to viral antigens and the subsequent dysregulation of ICs actively contribute to the exhaustion of effector cells and viral persistence. The present review aims to summarize the function of various ICs and their expression in T lymphocytes and NK cells in the course of HBV infection as well as the use of immunotherapeutic strategies targeting ICs in chronic HBV infection.

Immunomodulatory regulator blockade in a viral exacerbation model of severe asthma

Asthmatics are more susceptible to viral infections than healthy individuals and are known to have impaired innate anti-viral defences. Influenza A virus causes significant morbidity and mortality in this population. Immuno-modulatory regulators (IMRs) such as PD-1 are activated on T cells following viral infection as part of normal T cell activation responses, and then subside, but remain elevated in cases of chronic exposure to virus, indicative of T cell exhaustion rather than activation. There is evidence that checkpoint inhibition can enhance anti-viral responses during acute exposure to virus through enhancement of CD8+T cell function. Although elevated PD-1 expression has been described in pulmonary tissues in other chronic lung diseases, the role of IMRs in asthma has been relatively unexplored as the basis for immune dysfunction. We first assessed IMR expression in the peripheral circulation and then quantified changes in IMR expression in lung tissue in response to ex-vivo influenza infection. We found that the PD-1 family members are not significantly altered in the peripheral circulation in individuals with severe asthma but are elevated in pulmonary tissues following ex-vivo influenza infection. We then applied PD-1 Mab inhibitor treatment to bronchial biopsy tissues infected with influenza virus and found that PD-1 inhibition was ineffective in asthmatics, but actually increased infection rates in healthy controls. This study, therefore, suggests that PD-1 therapy would not produce harmful side-effects when applied in people with severe asthma, but could have important, as yet undescribed, negative effects on anti-viral responses in healthy individuals that warrant further investigation.

Transcriptional switch of hepatocytes initiates macrophage recruitment and T-cell suppression in endotoxemia

BACKGROUND & AIMS

The liver plays crucial roles in the regulation of immune defense during acute systemic infections. However, the roles of liver cellular clusters and intercellular communication in the progression of endotoxemia have not been well-characterized.

METHODS

Single-cell RNA sequencing analysis was performed, and the transcriptomes of 19,795 single liver cells from healthy and endotoxic mice were profiled. The spatial and temporal changes in hepatocytes and non-parenchymal cell types were validated by multiplex immunofluorescence staining, bulk transcriptomic sequencing, or flow cytometry. Furthermore, we used an adeno-associated virus delivery system to confirm the major mechanisms mediating myeloid cell infiltration and T-cell suppression in septic murine liver.

RESULTS

We identified a proinflammatory hepatocyte (PIH) subpopulation that developed primarily from periportal hepatocytes and to a lesser extent from pericentral hepatocytes and played key immunoregulatory roles in endotoxemia. Multicellular cluster modeling of ligand-receptor interactions revealed that PIHs play a crucial role in the recruitment of macrophages via the CCL2-CCR2 interaction. Recruited macrophages (RMs) released cytokines (e.g., IL6, TNFα, and IL17) to induce the expression of inhibitory ligands, such as PD-L1, on hepatocytes. Subsequently, RM-stimulated hepatocytes led to the suppression of CD4⁺ and memory T-cell subsets partly via the PD-1/PD-L1 interaction in endotoxemia. Furthermore, sinusoidal endothelial cells expressed the highest levels of proapoptotic and inflammatory genes around the periportal zone. This pattern of gene expression facilitated increases in the number of fenestrations and infiltration of immune cells in the periportal zone.

CONCLUSIONS

Our study elucidates unanticipated aspects of the cellular and molecular effects of endotoxemia on liver cells at the single-cell level and provides a conceptual framework for the development of novel therapeutic approaches for acute infection.

LAY SUMMARY

The liver plays a crucial role in the regulation of immune defense during acute systemic infections. We identified a proinflammatory hepatocyte subpopulation and demonstrated that the interactions of this subpopulation with recruited macrophages are pivotal in the immune response during endotoxemia. These novel findings provide a conceptual framework for the discovery of rational therapeutic targets in acute infection.

Age-associated phenotypic imbalance in TCD4 and TCD8 cell subsets: comparison between healthy aged, smokers, COPD patients and young adults

Background

COPD is associated with an abnormal lung immune response that leads to tissue damage and remodeling of the lung, but also to systemic effects that compromise immune responses. Cigarette smoking also impacts on innate and adaptative immune responses, exerting dual, pro- and anti-inflammatory effects. Previously, we showed that COPD patients presented accelerated telomere shortening and decreased telomerase activity, while, paradoxically, cigarette-smokers exhibited preserved telomerase activity and slower rate of telomere shortening.

Results

Here, we evaluated the naive, CM, EM and TEMRA subsets of TCD4 and TCD8 cells according to the expression of CCR7/CD45RA. We compared age-matched COPD patients, cigarette-smokers without clinical-laboratory evidence of pulmonary compromise, and healthy individuals. They were additionally compared with a group of young adults. For each subset we analysed the expression of markers associated with late differentiation, senescence and exhaustion (CD27/CD28/CD57/KLRG1/PD1). We show that COPD patients presented a drastically reduced naive cells pool, and, paradoxically, increased fractions of naive cells expressing late differentiation, senescence or exhaustion markers, likely impacting on their immunocompetence. Pronounced phenotypic alterations were also evidenced in their three memory T-cell subsets compared with the other aged and young groups, suggesting an also dysfunctional memory pool. Surprisingly, our smokers showed a profile closer to the Healthy aged than COPD patients. They exhibited the usual age-associated shift of naive to EM TCD4 and TCD8 cells, but not to CM or TEMRA T-cells. Nonetheless, their naive T-cells phenotypes were in general similar to those of the Youngs and Healthy aged, suggesting a rather phenotypically preserved subset, while the memory T-cells exhibited increased proportions of cells with the late-differentiation or senescence/exhaustion markers as in the Healthy aged.

Conclusion

Our study extends previous findings by showing that COPD patients have cells expressing a full range of late differentiated, senescent or exhausted phenotypes encompassing all TCD4 and TCD8 subsets, consistent with a premature immunosenescence phenotype. Surprisingly, the smokers group’s results suggest that moderate to heavy chronic cigarette smoking did not accelerate the pace of immunosenescence as compared with the Healthy aged.

The Mechanism of Interleukin-35 in Chronic Hepatitis B

Interleukin-35 (IL-35) is a newly identified inhibitory cytokine. It has recently been found to play an extremely important role in chronic hepatitis B disease, which makes it likely to be a target for new therapies for hepatitis B malady. IL-35 modulates a variety of immune mechanisms to cause persistent viral infections, such as affecting the ratio of helper T cells, reducing the activity of cytotoxic T cells, hindering the antigen presentation capacity for dendritic cells, and increasing the transcription level of hepatitis B virus. On the other hand, IL-35 can control the inflammation caused by hepatitis B liver injury. Therefore, to seek a breakthrough in curing hepatitis B disease, the contradictory part of IL-35 in the occurrence and development of this sickness is worthy of further discussion and research. This article will systematically review the biological effects of IL-35 and the specific mechanisms affecting the disease.

sCD28, sCD80, sCTLA-4, and sBTLA Are Promising Markers in Diagnostic and Therapeutic Approaches for Aseptic Loosening and Periprosthetic Joint Infection

Aseptic prosthetic loosening and periprosthetic joint infections (PJI) are among the most frequent complications after total knee/hip joint arthroplasty (TJA). Current research efforts focus on understanding the involvement of the immune system in these frequent complications. Different immune cell types have already been implicated in aseptic prosthetic loosening and PJI. The aim of this study was to systematically analyze aspirates from knee and hip joints, evaluating the qualitative and quantitative composition of soluble immunoregulatory markers, with a focus on co-inhibitory and co-stimulatory markers. It has been shown that these molecules play important roles in immune regulation in cancer and chronic infectious diseases, but they have not been investigated in the context of joint replacement. For this purpose, aspirates from control joints (i.e., native joints without implanted prostheses), joints with TJA (no signs of infection or aseptic loosening), joints with aseptic implant failure (AIF; i.e., aseptic loosening), and joints with PJI were collected. Fourteen soluble immunoregulatory markers were assessed using bead-based multiplex assays. In this study, it could be shown that the concentrations of the analyzed immunoregulatory molecules vary between control, TJA, AIF, and PJI joints. Comparing TJA patients to CO patients, sCD80 was significantly elevated. The marker sBTLA was significantly elevated in AIF joints compared to TJA joints. In addition, a significant difference for eight markers could be shown when comparing the AIF and CO groups (sCD27, sCTLA-4, sCD137, sCD80, sCD28, sTIM-3, sPD-1, sBTLA). A significant difference was also reached for nine soluble markers when the PJI and CO groups were compared (sLAG-3, sCTLA-4, sCD27, sCD80, sCD28, sTIM-3, sPD-1, IDO, sBTLA). In summary, the analyzed immunoregulatory markers could be useful for diagnostic purposes as well as to develop new therapeutic approaches for AIF and PJI.

A proportion of CD4+ T cells from patients with chronic Chagas disease undergo a dysfunctional process, which is partially reversed by benznidazole treatment

Background

Signs of senescence and the late stages of differentiation associated with the more severe forms of Chagas disease have been described in the Trypanosoma cruzi antigen-specific CD4⁺ T-cell population. However, the mechanisms involved in these functions are not fully known. To date, little is known about the possible impact of benznidazole treatment on the T. cruzi-specific functional response of CD4⁺ T cells.

Methodology/Principal findings

The functional capacity of CD4⁺ T cells was analyzed by cytometric assays in chronic Chagas disease patients, with indeterminate form (IND) and cardiac alterations (CCC) (25 and 15, respectively) before and after benznidazole treatment. An increase in the multifunctional capacity (expression of IFN-γ, IL-2, TNF-α, perforin and/or granzyme B) of the antigen-specific CD4⁺ T cells was observed in indeterminate versus cardiac patients, which was associated with the reduced coexpression of inhibitory receptors (2B4, CD160, CTLA-4, PD-1 and/or TIM-3). The functional profile of these cells shows statistically significant differences between IND and CCC (p<0.001), with a higher proportion of CD4⁺ T cells coexpressing 2 and 3 molecules in IND (54.4% versus 23.1% and 4.1% versus 2.4%, respectively). A significant decrease in the frequencies of CD4⁺ T cells that coexpress 2, 3 and 4 inhibitory receptors was observed in IND after 24–48 months of treatment (p<0.05, p<0.01 and p<0.05, respectively), which was associated with an increase in antigen-specific multifunctional activity. The IND group showed, at 9–12 months after treatment, an increase in the CD4⁺ T cell subset coproducing three molecules, which were mainly granzyme B⁺, perforin⁺ and IFN-γ⁺ (1.4% versus 4.5%).

Conclusions/Significance

A CD4⁺ T cell dysfunctional process was detected in chronic Chagas disease patients, being more exacerbated in those patients with cardiac symptoms. After short-term benznidazole treatment (9–12 months), indeterminate patients showed a significant increase in the frequency of multifunctional antigen-specific CD4⁺ T cells.

Trypanosoma cruzi infection triggers several immune mechanisms in the host that do not result in a total clearance of the parasite, the persistence of which leads to the chronicity of Chagas disease. The mechanisms by which some chronic patients remain asymptomatic or become symptomatic are not entirely clear. The aim of the present manuscript is to study the CD4⁺ T cell population and its functional capacity in patients with different forms of chronic disease. The obtained results indicate that cells from indeterminate patients have an enhanced multifunctional profile, which is associated with the reduced expression of inhibitory molecules. CD4⁺ T cells from chronic patients with cardiac alterations show lower functional activity against specific antigens of the parasite and increased coexpression of inhibitory molecules. After benznidazole treatment, antigen-specific CD4⁺ T cells, especially those from indeterminate patients, are more likely to show a multifunctional profile and a decline in the coexpression of inhibitory receptors. These results allow us to make progress in clarifying the mechanisms that may influence disease progression and to realize the importance of antiparasitic treatment for the enhancement of the activity of the immune system.

Combination of pegylated interferon-alpha and nucleos(t)ide analogue treatment enhances the activity of natural killer cells in nucleos(t)ide analogue experienced chronic hepatitis B patients

A combination of pegylated interferon-alpha (peg-IFN-α) and nucleos(t)ides analogue (NA) therapy can effectively reduce hepatitis B surface antigen (HBsAg), especially in NA-experienced chronic hepatitis B (CHB) patients. However, the immune mechanism of this therapy is unclear. Forty NA-experienced CHB patients were enrolled into this study. The frequencies of peripheral blood natural killer (NK) cells, dendritic cells (DCs), CD4⁺ T cells, CD8⁺ T cells, T helper (Th) cells, regulatory T cells (T_reg ), B cells and follicular T helper (Tfh) cells were evaluated by flow cytometry. Seven of the 40 patients converted to peg-IFN-α combined with NA treatment, while the other 33 continued to NA therapy. The decrease in HBsAg was more pronounced in the combination treatment group, and only patients receiving combination treatment achieved HBsAg loss. The frequency and absolute number of CD56^bright NK cells in the combination treatment group increased significantly compared with the NA treatment group, whereas the CD56^dim NK cells were decreased. In the NA treatment group, the proportions of CD4⁺ T_N , CD8⁺ T_N , CD19⁺ B and cytotoxic T lymphocyte antigen-4 (CTLA-4)⁺ CD4⁺ T cells were increased, while the proportions of CD4⁺ T_EM , CD8⁺ T_EM , CD25⁺ CD4⁺ T_reg , CD25^high CD4⁺ T_reg , CD127^low CD25⁺ T_reg , programmed cell death 1 (PD-1)⁺ CD4⁺ T, PD-1⁺ CD8⁺ T, CTLA-4⁺ CD8⁺ T, CCR4⁺ CD25⁺ T_reg and CCR4⁺ CD25^high T_reg cells were decreased after therapy. For NA-experienced CHB patients who achieved low HBsAg levels, combination treatment is more likely to result in HBsAg decline and HBsAg clearance by increasing the activity of CD56^bright NK cells.

Checkpoint inhibitors for the treatment of JC virus-related progressive multifocal leukoencephalopathy

Progressive multifocal leukoencephalopathy (PML) is a frequently fatal brain infection caused by the JC polyomavirus (JCV). PML occurs in people with impaired cellular immunity, and the only effective treatment is restoration of immune function. Infection in immunocompromised hosts is often associated with immune exhaustion, which is mediated by inhibitory cell surface receptors known as immune checkpoints, leading to loss of T cell effector function. Blockade of immune checkpoints can reinvigorate host responses to fight infection. Recently, there have been several reports of checkpoint blockade to treat PML in patients in whom immune reconstitution is otherwise not possible, with some evidence for positive response. Larger studies are needed to better understand efficacy of checkpoint blockade in PML and factors that determine response.

The Role of PD-1 in Acute and Chronic Infection

PD-1 as an immune checkpoint molecule down-regulates T cell activity during immune responses in order to prevent autoimmune tissue damage. In chronic infections or tumors, lasting antigen-exposure leads to permanent PD-1 expression that can limit immune-mediated clearance of pathogens or degenerated cells. Blocking PD-1 can enhance T cell function; in cancer treatment PD-1 blockade is already used as a successful therapy. However, the role of PD-1 expression and blocking in the context of acute and chronic infections is less defined. Building on its success in cancer therapy leads to the hypothesis that blocking PD-1 in infectious diseases is also beneficial in acute or chronic infections. This review will focus on the role of PD-1 expression in acute and chronic infections with virus, bacteria, and parasites, with a particular focus on recent studies regarding PD-1 blockade in infectious diseases.

Correlation of CpG methylation of the Pdcd1 gene with PD-1 expression on CD8+ T cells and medical laboratory indicators in chronic hepatitis B infection

BACKGROUND

The negative signal provided by some co-inhibitory factors such as programmed cell death-1 (PD-1) has been associated with chronic hepatitis B (CHB) infection induced-T cell exhaustion, although the correlation of CpG methylation of the Pdcd1 gene with PD-1 expression and medical laboratory indicators in CHB infection has not yet been elucidated.

METHODS

Blood samples from 20 CHB infection patients and 20 spontaneous clearance (SC) patients were collected. Percentages of PD-1-positive CD8⁺ T cells were analyzed by flow cytometry. The percentage of CpG methylation at the Pdcd1 locus was analyzed by bisulfite sequencing. Student's t test, Pearson and Spearman's correlation, and Mann-Whitney tests were used in the statistical analysis.

RESULTS

Percentages of PD-1-positive CD8⁺ T cells in peripheral blood T cells were significantly higher in CHB patients than in the SC group (p < 0.001). The methylation level of Pdcd1 was significantly lower in CHB patients (p < 0.001) and the methylation level of Pdcd1 was negatively correlated with PD-1 expression level in CD8⁺ T cells (p < 0.001) and hepatitis-B surface antigen (HBsAg) (p < 0.001).

CONCLUSIONS

The results of the present study suggest that Pdcd1 methylation is correlated with PD-1 expression on CD8⁺ T cells and correlated with HBsAg and alanine aminotransferase. The results may provide new ideas regarding anti-PD-1 inhibitors, and epigenetic regulators such as demethylation inhibitors could represent more successful therapeutic strategies in hepatitis B infection patients.

Association of rs10204525 genotype GG and rs2227982 CC combination in programmed cell death 1 with hepatitis B virus infection risk

Single nuclear polymorphism (SNP) of programmed cell death 1 (PD-1) was reported associated with hepatitis B virus (HBV) infection, but the SNP sites studied were limited. Whether the combination of 2 or more SNP sites could better represent the relationship between PD-1 SNP and HBV infection was not studied.Eight hundred ninety-eight HBV-infected patients (222 asymptomatic carriers [AsC], 276 chronic hepatitis B, 105 acute-on-chronic liver failure, and 295 liver cirrhosis) and 364 health controls of South China were enrolled in this study. Four PD-1 SNPs (rs10204525, rs2227982, rs41386349, and rs36084323) were selected and detected by TaqMan probe. The frequency of allele, genotype, and combination of different SNPs were compared between different groups.For allele frequency analysis, G allele of rs10204525 was protective factor (odds ratio (OR) = 0.823, 95% confidence interval (CI) = 0.679-0.997, P = .046) and T allele of rs2227982 was predisposing factor (OR = 1.231, 95% CI = 1.036-1.463, P = .018) in HBV infection. When analyzed in genotype frequency, the genotype GG of rs10204525 and CC of rs2227982 were protective factor of HBV infection. Combination of rs10204525 GG and rs2227982 CC was potent protective factor of HBV infection (OR = 0.552, 95% CI = 0.356-0.857, P = .007) and was also associated with lower HBV load (OR = 0.201, 95% CI = 0.056-0.728, P = .008) in AsC. The 4 SNP sites were not associated with progression of HBV-related liver disease.Rs10204525 and rs2227982 of PD-1 associate with HBV infection and combination of the 2 SNP sites can better predict host susceptibility in HBV infection.

The Inhibitory T Cell Receptors PD1 and 2B4 Are Differentially Regulated on CD4 and CD8 T Cells in a Mouse Model of Non-alcoholic Steatohepatitis

Infiltrating CD4 and CD8 T cells have been shown to worsen inflammatory liver damage in non-alcoholic steatohepatitis (NASH). Inhibitory T cell receptors such as the programmed cell death protein 1 (PD1) and the natural killer cell receptor 2B4 regulate the activity of CD4 and CD8 T cells and therefore play an important role in immune tolerance required in the liver. In this study, we investigated the expression profile of inhibitory T cell receptors on CD4 and CD8 T cells in a mouse model of NASH. Male B57BL/6J mice were fed a Western diet for 24 weeks. The expression levels of inhibitory receptors on the surface of intrahepatic and peripheral T cells were measured and correlated with markers of activation (CD107a, CD69, and CD44), metabolic disorder (serum triglycerides, serum cholesterol, γ-glutamyl transferase, hepatic triglycerides), inflammation (serum alanine aminotransferase and aspartate aminotransferase) and hepatic fibrosis (collagen 1A1, α-smooth muscle actin, hydroxyproline). Under Western diet, PD1 is exclusively upregulated on intrahepatic and peripheral CD8⁺ T cells, whereas the expression level on CD4 T cells is unaffected. In contrast, 2B4 is upregulated liver-specifically on both CD4 and CD8 T cells and unchanged on peripheral T cells. Upregulation of PD1 on CD8 T cells is restricted to CD8 effector memory T cells and correlates with lower levels of degranulation. Similarly, the inhibitory function of PD1 on intrahepatic CD4 T cells is shown by a lower CD69 and CD44 expression on PD1-positive CD4 T cells. In murine steatohepatitis, the upregulation of PD1 on CD8 T cells and 2B4 on CD4 and CD8 T cells potentially limits T cell-mediated liver damage. Therefore, these inhibitory T cell receptors could serve as promising targets of immune-modulatory NASH therapy.

Signal Transduction Via Co-stimulatory and Co-inhibitory Receptors

T-cell receptor (TCR)-mediated antigen-specific stimulation is essential for initiating T-cell activation. However, signaling through the TCR alone is not sufficient for inducing an effective response. In addition to TCR-mediated signaling, signaling through antigen-independent co-stimulatory or co-inhibitory receptors is critically important not only for the full activation and functional differentiation of T cells but also for the termination and suppression of T-cell responses. Many studies have investigated the signaling pathways underlying the function of each molecular component. Co-stimulatory and co-inhibitory receptors have no kinase activity, but their cytoplasmic region contains unique functional motifs and potential phosphorylation sites. Engagement of co-stimulatory receptors leads to recruitment of specific binding partners, such as adaptor molecules, kinases, and phosphatases, via recognition of a specific motif. Consequently, each co-stimulatory receptor transduces a unique pattern of signaling pathways. This review focuses on our current understanding of the intracellular signaling pathways provided by co-stimulatory and co-inhibitory molecules, including B7:CD28 family members, immunoglobulin, and members of the tumor necrosis factor receptor superfamily.

Recovery of circulating CD56dim NK cells and the balance of Th17/Treg after nucleoside analog therapy in patients with chronic hepatitis B and low levels of HBsAg

BACKGROUND AND AIMS

Much evidence indicates that the soluble antigens secreted by hepatitis B virus (HBV) inhibit the function of the immune system. The aim of this study is to investigate, after treatment with nucleoside (acid) analogs (NAs) and the inhibition of viral replication, whether the immune systems of patients with a peripheral blood HBV-DNA level <1000 IU/mL, hepatitis B e antigen (HBeAg) disappearance, and a decrease in hepatitis B surface antigen (HBsAg) levels could be reconstructed.

METHODS

The frequency and phenotype of circulating natural killer (NK) cells, dendritic cells (DCs), T-helper (Th) cells, regulatory T (Treg) cells, CD4⁺, CD8⁺ T cells, T follicular helper (Tfh) cells and B cells subtypes were tested by flow cytometry in chronic hepatitis B (CHB) patients and healthy controls (HCs). The levels of HBV-related serum HBsAg, HBeAg, HBV-DNA load, alanine aminotransferase (ALT) and aspartate aminotransferase (AST) were determined.

RESULTS

Regarding the innate immune system, an increased frequency of CD56^dim NK cells was found in the therapeutic response (TR) group compared with that in the immune-active phase (IA) group. Additionally, regarding the adaptive immune system, the Th17/CD4⁺CD25⁺CD127^dimTreg ratio was reduced in the TR group. Additionally, the frequency of CD40L⁺CXCR5⁺CD4⁺T cells and CD40⁺CD19⁺CD27⁺CD38⁺B cells was significantly higher than that of HCs, while that of PDL1⁺CD19⁺ B cells was lower. Furthermore, the frequencies of CTLA4⁺CD4⁺T cells and CTLA4⁺CD8⁺T cells in patients with CHB were significantly higher than those in HCs.

CONCLUSION

After NA treatment and the inhibition of viral replication, circulating CD56^dim NK cells and the balance of Th17/Treg can be recovered. Restoring circulating CD56^dim NK cells and the Th17/Treg balance may help reduce HBsAg levels in patients.

CTLA‑4 interferes with the HBV‑specific T cell immune response (Review)

Hepatitis B virus (HBV) infection is a major cause of hepatic inflammation. Successful HBV clearance in patients is associated with sustained viral control by effector T cells. Compared with acute hepatitis B, chronic HBV infection is associated with the depletion of T cells, resulting in weak or absent virus-specific T cells reactivity, which is described as 'exhaustion'. This exhaustion is characterized by impaired cytokine production and sustained expression of multiple coinhibitory molecules. Cytotoxic T lymphocyte-associated antigen-4 (CTLA-4) is one of many coinhibitory molecules that can attenuate T cell activation by inhibiting costimulation and transmitting inhibitory signals to T cells. Persistent HBV infection results in the upregulation of CTLA-4 on hepatic CD8⁺ T cells. This prompts CD8⁺ T cell apoptosis, and the activation of cytotoxic T lymphocytes is blocked. Similar to CD8⁺ T cells, CD4⁺ T helper (Th) cell proliferation is hindered following CTLA-4 upregulation. In addition, the differentiation of CD4⁺ Th is polarized toward the Th2/peripherally-inducible T regulatory cell types, increasing the levels of anti-inflammatory cytokines. Conversely, the activation of proinflammatory cells (Th1 and follicular helper T) is blocked, and the levels of proinflammatory cytokines decline. This review summarizes the current literature relevant to T cell exhaustion in patients with HBV-related chronic hepatitis, and discusses the roles of CTLA-4 in T cell exhaustion.

Immune checkpoints in chronic obstructive pulmonary disease

Cell-mediated immune responses are vital to the body's defence against infection and play a key role in tumour immunity. T-cell activation and cytotoxic function is tightly regulated by a series of immune-regulatory receptor-ligand interactions or immune checkpoints. These controls limit immune-mediated damage, particularly in the context of chronic infection. However, prolonged signalling through these axes can lead to progressive loss of T-cell function, termed exhaustion.Understanding of the biology of checkpoints and that exhaustion is reversible has been key to the development of new therapies directed at reversing the dysfunctional status of T-cells, which are dramatically improving outcomes of cancer treatment.Emerging data suggest that immune checkpoint axes are dysregulated in chronic obstructive pulmonary disease (COPD). T-cells from diseased lungs express the key receptor programmed death (PD)1 and demonstrate loss of cytotoxic function. However, the picture is complex with evidence of downregulation of the associated ligand PDL1 on alveolar macrophages. The resulting impact may be excessive T-cell inflammation as a consequence of acute infection, which may contribute to the pattern of exacerbation and lung damage characteristic of COPD. More work is needed to understand these immune controls in COPD before the therapeutic advances seen in lung cancer can be explored.

Immune checkpoints and their inhibition in cancer and infectious diseases

The development of chronic infections and cancer is facilitated by a variety of immune subversion mechanisms, such as the production of anti-inflammatory cytokines, induction of regulatory T (Treg) cells, and expression of immune checkpoint molecules, including CTLA-4 and PD-1. CTLA-4, expressed on T cells, interacts with CD80/CD86, thereby limiting T-cell activation and leading to anergy. PD-1 is predominantly expressed on T cells and its interaction with PD-L1 and PD-L2 expressed on antigen-presenting cells (APCs) and tumors sends a negative signal to T cells, which can lead to T-cell exhaustion. Given their role in suppressing effector T-cell responses, immune checkpoints are being targeted for the treatment of cancer. Indeed, antibodies binding to CTLA-4, PD-1, or PD-L1 have shown remarkable efficacy, especially in combination therapies, for a number of cancers and have been licensed for the treatment of melanoma, nonsmall cell lung cancer, and renal and bladder cancers. Moreover, immune checkpoint inhibitors have been shown to enhance ex vivo effector T-cell responses from patients with chronic viral, bacterial, or parasitic infection, including HIV, tuberculosis, and malaria. Although the data from clinical trials in infectious diseases are still sparse, these inhibitors have great potential for treating chronic infections, especially when combined with therapeutic vaccines.