CD137-CD137 Ligand Interactions in Inflammation

TNFSF9 Is Associated with Favorable Tumor Immune Microenvironment in Patients with Renal Cell Carcinoma Who Are Treated with the Combination Therapy of Nivolumab and Ipilimumab

Combination therapy of nivolumab and ipilimumab (NIVO + IPI) for metastatic renal cell carcinoma (mRCC) has shown efficacy, but approximately 20% of patients experience disease progression in the early stages of treatment. No useful biomarkers have been reported to date. Therefore, it is desirable to identify biomarkers to predict treatment responses in advance. We examined the tumor microenvironment (TME)-related gene expression in mRCC patients treated with NIVO + IPI, between the response and non-response groups, using tumor tissues, before administering NIVO + IPI. In TME-related genes, TNFSF9 expression was identified as a candidate for the predictive biomarker. Its expression discriminated between the response and non-response groups with 88.89% sensitivity and 87.50% specificity (AUC = 0.9444). We further analyzed the roles of TNFSF9 in TME using bioinformatics from The Cancer Genome Atlas (TCGA) cohort. An adaptive immune response was activated in the TNFSF9-high-expression tumors. Indeed, T follicular helper cells, plasma B cells, and tumor-infiltrating CD8+ T cells were increased in the tumors, which indicates the promotion of humoral immunity due to enhanced T-B interactions. However, as the number of regulatory T cells (Treg) increased in the tumors, the percentage of dysfunctional T cells also increased. This suggests that not only PD-1 but also CTLA-4 inhibition may have suppressed Treg activation and improved the therapeutic effect in the TNFSF9 high-expression tumors. Therefore, TNFSF9 may predict the therapeutic efficacy of NIVO + IPI for mRCC and allow more appropriate patient selection.

Intestinal epithelial cells of Japanese flounder (Paralichthys olivaceus) as an in vitro model for studying intestine immune function based on transcriptome analysis

Japanese flounder (Paralichthys olivaceus) is an economically crucial marine species, but diseases like hemorrhagic septicemia caused by Edwardsiella tarda have resulted in significant economic losses. E. tarda infects various hosts, and its pathogenicity in fish is not fully understood. Lipopolysaccharides (LPS) are components of the outer membrane of Gram-negative bacteria and are representative of typical PAMP molecules that cause activation of the immune system. The PoIEC cell line is a newly established intestinal epithelial cell line from P. olivaceus. In order to investigate whether it can be used as an in vitro model for studying the pathogenesis of E. tarda and LPS stimulation, we conducted RNA-seq experiments for the PoIECs model of E. tarda infection and LPS stimulation. In this study, transcriptome sequencing was carried out in the PoIEC cell line after treatment with LPS and E. tarda. A total of 62.52G of high-quality data from transcriptome sequencing results were obtained in nine libraries, of which an average of 87.96% data could be aligned to the P. olivaceus genome. Data analysis showed that 283 and 414 differentially expressed genes (DEGs) in the LPS versus Control (LPS-vs-Con) and E. tarda versus Control groups (Et-vs-Con), respectively, of which 60 DEGs were shared in two comparation groups. The GO terms were predominantly enriched in the extracellular space, inflammatory response, and cytokine activity in the LPS-vs-Con group, whereas GO terms were predominantly enriched in nucleus and positive regulation of transcription by RNA polymerase II in the Et-vs-Con group. KEGG analysis revealed that three immune-related pathways were co-enriched in both comparison groups, including the Toll-like receptor signaling pathway, C-type lectin receptor signaling pathway, and Cytokine-cytokine receptor interaction. Five genes were randomly screened to confirm the validity and accuracy of the transcriptome data. These results suggest that PoIEC cell line can be an ideal in vitro model for studies of marine fish gut immunity and pathogenesis of Edwardsiellosis.

Cyclosporine A-resistant CAR-T cells mediate antitumour immunity in the presence of allogeneic cells

Chimeric antigen receptor (CAR)-T therapy requires autologous T lymphocytes from cancer patients, a process that is both costly and complex. Universal CAR-T cell treatment from allogeneic sources can overcome this limitation but is impeded by graft-versus-host disease (GvHD) and host versus-graft rejection (HvGR). Here, we introduce a mutated calcineurin subunit A (CNA) and a CD19-specific CAR into the T cell receptor α constant (TRAC) locus to generate cells that are resistant to the widely used immunosuppressant, cyclosporine A (CsA). These immunosuppressant-resistant universal (IRU) CAR-T cells display improved effector function in vitro and anti-tumour efficacy in a leukemia xenograft mouse model in the presence of CsA, compared with CAR-T cells carrying wild-type CNA. Moreover, IRU CAR-T cells retain effector function in vitro and in vivo in the presence of both allogeneic T cells and CsA. Lastly, CsA withdrawal restores HvGR, acting as a safety switch that can eliminate IRU CAR-T cells. These findings demonstrate the efficacy of CsA-resistant CAR-T cells as a universal, 'off-the-shelf' treatment option.

PRRSV-1 induced lung lesion is associated with an imbalance between costimulatory and coinhibitory immune checkpoints

Porcine reproductive and respiratory syndrome virus (PRRSV) induces a dysregulation on the innate and adaptive immune responses. T-cell activation requires a proper interaction and precise balance between costimulatory and coinhibitory molecules, commonly known as immune checkpoints. This study aims to evaluate the expression of immune checkpoints in lung and tracheobronchial lymph node from piglets infected with two PRRSV-1 strains of different virulence during the early stage of infection. Seventy 4-week-old piglets were grouped into three experimental groups: (i) control, (ii) 3249-infected group (low virulent strain), and (iii) Lena-infected group (virulent strain) and were euthanized at 1, 3, 6, 8, and 13 days post-infection (dpi). Lung and tracheobronchial lymph node were collected to evaluate histopathological findings, PRRSV viral load and mRNA expression of costimulatory (CD28, CD226, TNFRSF9, SELL, ICOS, and CD40) and coinhibitory (CTLA4, TIGIT, PD1/PDL1, TIM3, LAG3, and IDO1) molecules through RT-qPCR. Our findings highlight a mild increase of costimulatory molecules together with an earlier and stronger up-regulation of coinhibitory molecules in both organs from PRRSV-1-infected animals, especially in the lung from virulent Lena-infected animals. The simultaneous expression of coinhibitory immune checkpoints could work in synergy to control and limit the inflammation-induced tissue damage. Further studies should be addressed to determine the role of these molecules in later stages of PRRSV infection.

Immune checkpoint molecules in prevention and development of asthma

Allergic asthma is a respiratory disease initiated by type-2 immune responses characterized by secretion of alarmins, interleukin-4 (IL-4), IL-5, and IL-13, eosinophilic inflammation, and airway hyperresponsiveness (AHR). Immune checkpoints (ICPs) are inhibitory or stimulatory molecules expressed on different immune cells, tumor cells, or other cell types that regulate immune system activation and maintain immune homeostasis. Compelling evidence indicates a key role for ICPs in both the progression and prevention of asthma. There is also evidence of asthma development or exacerbation in some cancer patients receiving ICP therapy. The aim of this review is to provide an updated overview of ICPs and their roles in asthma pathogenesis, and to assess their implications as therapeutic targets in asthma.

CD137-CD137L Aggravates Calcification of Vascular Smooth Muscle Cell and Vasculature of ApoE-/- Mice Via Rab7-Mediated Autophagy

Vascular calcification is an independent risk factor for acute cardiovascular events and a predictor of adverse prognosis; the abnormal fusion and degradation of autophagosomes and lysosomes are closely related to the calcification of VSMC and aortic AS plaque in ApoE-/- mice. Rab7 is a member of the Ras protein family and acts as a molecular switch in the fusion between autophagosomes and lysosomes. In this study, we found that the activation of the CD137-CD137L signal promoted calcification by inhibiting the expression and activity of Rab7, which regulates the degradation of autophagic cargo in vascular smooth muscle cells (VSMCs) and aortic atherosclerosis (AS) plaques in ApoE-/- mice. Knockdown of Rab7 impaired its tethering with the downstream molecule FYVE and coiled-coil containing 1 (FYCO1), which transports autophagosomes to lysosomes through microtubule motor kinesins and fuses with lysosomes to degrade the autophagic content. Overexpression of Rab7-alleviated calcification caused by the activation of the CD137 signaling pathway. In addition, FYCO1 knockdown promoted calcification even though the expression and activity of Rab7 were normal. Our results suggest that Rab7 is the target of CD137 signaling; Rab7 cannot interact with its downstream molecule FYCO1 when its activity and expression were inhibited by the activation of CD137 signaling pathway, thus inhibiting the autophagic degradation and promoting calcification.

4-1BB: A promising target for cancer immunotherapy

Immunotherapy, powered by its relative efficacy and safety, has become a prominent therapeutic strategy utilized in the treatment of a wide range of diseases, including cancer. Within this class of therapeutics, there is a variety of drug types such as immune checkpoint blockade therapies, vaccines, and T cell transfer therapies that serve the purpose of harnessing the body’s immune system to combat disease. Of these different types, immune checkpoint blockades that target coinhibitory receptors, which dampen the body’s immune response, have been widely studied and established in clinic. In contrast, however, there remains room for the development and improvement of therapeutics that target costimulatory receptors and enhance the immune response against tumors, one of which being the 4-1BB (CD137/ILA/TNFRSF9) receptor. 4-1BB has been garnering attention as a promising therapeutic target in the setting of cancer, amongst other diseases, due to its broad expression profile and ability to stimulate various signaling pathways involved in the generation of a potent immune response. Since its discovery and demonstration of potential as a clinical target, major progress has been made in the knowledge of 4-1BB and the development of clinical therapeutics that target it. Thus, we seek to summarize and provide a comprehensive update and outlook on those advancements in the context of cancer and immunotherapy.

The long and winding road: From mouse linkage studies to a novel human therapeutic pathway in type 1 diabetes

Autoimmunity involves a loss of immune tolerance to self-proteins due to a combination of genetic susceptibility and environmental provocation, which generates autoreactive T and B cells. Genetic susceptibility affects lymphocyte autoreactivity at the level of central tolerance (e.g., defective, or incomplete MHC-mediated negative selection of self-reactive T cells) and peripheral tolerance (e.g., failure of mechanisms to control circulating self-reactive T cells). T regulatory cell (Treg) mediated suppression is essential for controlling peripheral autoreactive T cells. Understanding the genetic control of Treg development and function and Treg interaction with T effector and other immune cells is thus a key goal of autoimmunity research. Herein, we will review immunogenetic control of tolerance in one of the classic models of autoimmunity, the non-obese diabetic (NOD) mouse model of autoimmune Type 1 diabetes (T1D). We review the long (and still evolving) elucidation of how one susceptibility gene, Cd137, (identified originally via linkage studies) affects both the immune response and its regulation in a highly complex fashion. The CD137 (present in both membrane and soluble forms) and the CD137 ligand (CD137L) both signal into a variety of immune cells (bi-directional signaling). The overall outcome of these multitudinous effects (either tolerance or autoimmunity) depends upon the balance between the regulatory signals (predominantly mediated by soluble CD137 via the CD137L pathway) and the effector signals (mediated by both membrane-bound CD137 and CD137L). This immune balance/homeostasis can be decisively affected by genetic (susceptibility vs. resistant alleles) and environmental factors (stimulation of soluble CD137 production). The discovery of the homeostatic immune effect of soluble CD137 on the CD137-CD137L system makes it a promising candidate for immunotherapy to restore tolerance in autoimmune diseases.

Feedback regulation of antioxidant transcription factor NFE2L1 and immunostimulatory factor 41BBL mediates the crosstalk between oxidative stress and tumor immunity

Targeting the immune checkpoint to inhibit tumor immune escape, which is one of the fundamental causes of cancer, has become an important strategy for cancer treatment. The molecular mechanism of tumor immune escape involved in the process of spontaneous hepatocellular carcinoma after specifically knocking out NFE2L1, the core regulator of redox homeostasis, in the mouse liver is still unclear. Transcriptome data showed that the immunostimulatory TNFSF9/41BBL was significantly reduced in NFE2L1 knockdown hepatocarcinoma HepG2 cells, and this suggests that 41BBL may be an oxidative stress-responsive immune checkpoint. The results of the promoter activity experiment showed that NFE2L1 can promote 41BBL gene transcription activation through the ARE element in the promoter region. In addition, cell biology experiments have found that overexpression of 41BBL can inhibit cell proliferation and promote senescence. Importantly, reactive oxygen species in cells significantly increased after overexpression of 41BBL, whereas NFE2L1 was inhibited, indicating that 41BBL has the effect of feedback regulating oxidative stress in cells. In conclusion, in this study, the transcriptional activation effect of NFE2L1 on 41BBL and the feedback inhibition relationship of 41BBL on NFE2L1 was clarified. The NFE2L1/41BBL axis might be an important pathway that mediates the crosstalk between oxidative stress and the tumor immune response.

TNFSF9 Is a Prognostic Biomarker and Correlated with Immune Infiltrates in Pancreatic Cancer

BACKGROUND

TNFSF9 gene has been found to play an anti-tumor role and regulate the function of immune cells. However, the prognostic role of TNFSF9 in pancreatic cancer and its relationship with immune cell infiltration have not been studied.

METHODS

We used Oncomine, UALCAN, and GEPIA databases to analyze the expression of TNFSF9 in pancreatic cancer. We used Kaplan-Meier plotters, GEPIA, and UALCAN to evaluate the effect of TNFSF9 on clinical prognosis. We further used TIMER to study the correlation between TNFSF9 and cancer immune infiltrate cells. In addition, we used GEPIA to analyze the correlation between TNFSF9 expression and gene markers of immune infiltrate cells.

RESULTS

TNFSF9 mRNA expression level was remarkably increased in pancreatic cancer than that in normal tissues (both P < 0.05). In addition, high TNFSF9 expression was significantly related to poor overall survival (OS) and relapse-free survival (RFS) in pancreatic cancer (OS HR = 2.02, P = 0.0012; RFS HR = 2.63, P = 0.022). Moreover, high TNFSF9 expression in pancreatic cancer patients was associated with worse OS in stage 1 to 2 but not stage 3 and stage 4. Specifically, TNFSF9 expression and CD8⁺ T cell infiltration of pancreatic cancer was negatively correlated. TNFSF9 expression showed strong correlations with M1 macrophages in pancreatic cancer.

CONCLUSIONS

Our results suggest that TNFSF9 is associated with prognosis and CD8⁺ T cell infiltration levels in patients with pancreatic cancer. Further, TNFSF9 expression potentially contributes to the modulation of M1 polarization of macrophages. These findings indicate that TNFSF9 can be serves as a prognostic biomarker in determining the prognosis of pancreatic cancer and is associated with different types of phenotypes of immune cell infiltration.

Recombinant CD137-Fc, its synthesis, and applications for improving the immune system functions, such as tumor immunotherapy and to reduce the inflammation due to the novel coronavirus

CD137 (ILA/4-1BB), a member of tumor necrosis factor receptor superfamily, is one of the most important T cell costimulatory molecules. Interaction of this molecule with its ligand transmits a two-way signal that activates both T lymphocyte and antigen presenting cells. The soluble form of CD137 (sCD137) reduces the activity of its membrane isoform and is associated with T lymphocyte activation-induced cell death. Recombinant CD137-Fc may be used to treat cancers, autoimmune disorders and viral infections. It may also be useful for management of coronavirus infection. The 1276 bp DNA sequence encoded CD137-Fc recombinant protein was prepared and subcloned into lentiviral vector and expressed in transduced CHO-K1 eukaryotic cells. The sodium dodecyl sulfate-polyacrylamide gel electrophoresis, Western blot analysis, and enzyme-linked immunosorbent assay analysis results demonstrated that the expression of the 70-kDa CD137-Fc molecule was detectable without any degradation. This study helps to confirm previous research suggesting the use of this recombinant protein as a promising solution for the treatment of virus infections. CD137-Fc fusion protein could also make immunotherapy more effective for some diseases. This product is widely used in novel medical treatments, including cell-based immunotherapy such as dendritic cell, CAR T and CAR NK therapy. Its production and usage in research and treatment is noticeable also in current coronavirus disease 2019 pandemic.

Immuno-comparative screening of adult-derived human liver stem/progenitor cells for immune-inflammatory-associated molecules

OBJECTIVE

One of the main challenges in liver cell therapy is the replacement of damaged cells and the induction of a tolerogenic microenvironment to promote graft acceptance by the recipient. Adult-derived human liver stem/progenitor cells (ADHLSCs) are currently evaluated at the clinical levels as a promising pro-regenerative and immune-modulatory tool. The expression profile of several immunological molecules may influence the local immune-inflammatory response and, therefore, modulate the tissue healing process. To increase the quality and safety of ADHLSCs before transplantation requires an appropriate analysis and characterization of their pattern expression of immune-inflammatory-associated molecules.

METHODS

The expression of 27 molecules belonging to T-cell co-stimulatory pathway, CD47 partners, Ikaros family, CD300 family and TNF family were analyzed using flow cytometry. We compared their expression profiles to PBMCs, hepatocytes and ADHLSCs in both expansion and after hepatogenic differentiation culture conditions.

RESULTS

This original immuno-comparative screening revealed that liver cell populations do not constitutively present significant immunological pattern compared to PBMCs. Moreover, our findings highlight that neither the expansion nor the hepatogenic differentiation induces the expression of immune-inflammatory molecules. The detailed expression characteristics (percentage of positive cells and median fluorescence intensity) of each molecule were analyzed and presented.

CONCLUSION

By analyzing 27 relevant molecules, our immuno-comparative screening demonstrates that ADHLSCs keep a non-immunogenic profile independent of their expansion or hepatogenic differentiation state. Accordingly, the immunological profile of ADHLSCs seems to support their safe and efficient use in liver tissue therapeutic repair strategy.

The Costimulatory Pathways and T Regulatory Cells in Ischemia-Reperfusion Injury: A Strong Arm in the Inflammatory Response?

Costimulatory molecules have been identified as crucial regulators in the inflammatory response in various immunologic disease models. These molecules are classified into four different families depending on their structure. Here, we will focus on various ischemia studies that use costimulatory molecules as a target to reduce the inherent inflammatory status. Furthermore, we will discuss the relevant role of T regulatory cells in these inflammatory mechanisms and the costimulatory pathways in which they are involved.

TNFSF9 exerts an inhibitory effect on hepatocellular carcinoma

OBJECTIVE

Tumor necrosis factor superfamily member 9 (TNFSF9), also known as 4-1BBL and CD137L, has been implicated in cancer immunotherapy due to its function as a T-cell co-stimulator. We aimed to investigate the role of TNFSF9 in the cancer pathogenesis in hepatocellular carcinoma (HCC).

METHODS

TNFSF9 expression was examined by immunohistochemistry in 106 pairs of HCC and adjacent non-tumorous tissues, and by quantitative polymerase chain reaction and Western blot in HCC cell lines. The impact of TNFSF9 on the proliferation, migration and invasion of HCC cells was determined using the 3-(4,5-diethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium, inner salt (MTS) and transwell assays in vitro. We also assessed the influence of TNFSF9 on the growth and metastasis of HCC tumors in an orthotopic mouse model of human HCC.

RESULTS

TNFSF9 expression was downregulated in approximately 70% of HCC tissues. A decreased expression of TNFSF9 was also consistently observed in all the four HCC cell lines. Either the overexpression of TNFSF9 or treatment with recombinant TNFSF9 protein could significantly inhibit the proliferation, migration and invasion of Huh7 and SMMC-7721 HCC cells in vitro. The inhibitory effect of TNFSF9 on HCC was further confirmed in vivo. Mice orthotopically transplanted with TNFSF9-overexpressing Huh7 cells developed significantly smaller tumors with less intrahepatic metastasis and distant metastasis compared with the control group.

CONCLUSIONS

TNFSF9 may be a tumor suppressor in HCC. Based on its immune stimulatory aspect and the tumor inhibition property, TNFSF9 may be a promising therapeutic target for HCC.

Targeting the adaptive immune system: new strategies in the treatment of atherosclerosis

Atherosclerosis is a lipid-driven chronic inflammatory disease of the arterial wall. Current treatment of atherosclerosis is focused on limiting its risk factors, such as hyperlipidemia or hypertension. However, treatments that target the inflammatory nature of atherosclerosis are still under development. Discovery of novel targets involved in the inflammation of the arterial wall creates opportunities to design new therapeutics that successfully modulate atherosclerosis. Here, we review drug targets that have proven to play pivotal roles in the adaptive immune system in atherosclerosis, and we discuss their potential as novel therapeutics.

Quercetin protects against obesity-induced skeletal muscle inflammation and atrophy

Skeletal muscle inflammation and atrophy are closely associated with metabolic impairment such as insulin resistance. Quercetin, a natural polyphenol flavonoid, is known to elicit anti-inflammatory and antioxidant activities. In this study, we investigated its effect on obesity-induced skeletal muscle inflammation and atrophy in mice. Male C57BL/6 mice were fed a regular diet, a high-fat diet (HFD), and an HFD supplemented with quercetin for nine weeks. Quercetin reduced levels of inflammatory cytokines and macrophage accumulation in the skeletal muscle of the HFD-fed obese mice. It also reduced transcript and protein levels of the specific atrophic factors, Atrogin-1 and MuRF1, in the skeletal muscle of the HFD-fed obese mice, and protected against the reduction of muscle mass and muscle fiber size. In vitro, quercetin markedly diminished transcript levels of inflammatory receptors and activation of their signaling molecules (ERK, p38 MAPK, and NF-κB) in cocultured myotubes/macrophages, and this was accompanied by reduced expression of the atrophic factors. Together, these findings suggest that quercetin reduces obesity-induced skeletal muscle atrophy by inhibiting inflammatory receptors and their signaling pathway. Quercetin may be useful for preventing obesity-induced muscle inflammation and sarcopenia.

Blockade of 4-1BB and 4-1BBL interaction reduces obesity-induced skeletal muscle inflammation

Obesity-induced skeletal muscle inflammation is characterized by increased macrophage infiltration and inflammatory cytokine production. In this study, we investigated whether 4-1BB, a member of the TNF receptor superfamily (TNFRSF9) that provides inflammatory signals, participates in obesity-induced skeletal muscle inflammation. Expression of the 4-1BB gene, accompanied by increased levels of inflammatory cytokines, was markedly upregulated in the skeletal muscle of obese mice fed a high-fat diet, in muscle cells treated with obesity factors, and in cocultured muscle cells/macrophages. In vitro stimulation of 4-1BB with agonistic antibody increased inflammatory cytokine levels in TNFα-pretreated muscle cells, and this effect was absent in cells derived from 4-1BB-deficient mice. Conversely, disruption of the interaction between 4-1BB and its ligand (4-1BBL) with blocking antibody decreased the release of inflammatory cytokines from cocultured muscle cells/macrophages. Moreover, deficiency of 4-1BB markedly reduced macrophage infiltration and inflammatory cytokine production in the skeletal muscle of mice fed a high-fat diet. These findings indicate that 4-1BB mediates the inflammatory responses in obese skeletal muscle by interacting with its ligand 4-1BBL on macrophages. Therefore, 4-1BB and 4-1BBL may be useful targets for prevention of obesity-induced inflammation in skeletal muscle.

Immunology and oxidative stress in multiple sclerosis: clinical and basic approach

Multiple sclerosis (MS) exhibits many of the hallmarks of an inflammatory autoimmune disorder including breakdown of the blood-brain barrier (BBB), the recruitment of lymphocytes, microglia, and macrophages to lesion sites, the presence of multiple lesions, generally being more pronounced in the brain stem and spinal cord, the predominantly perivascular location of lesions, the temporal maturation of lesions from inflammation through demyelination, to gliosis and partial remyelination, and the presence of immunoglobulin in the central nervous system and cerebrospinal fluid. Lymphocytes activated in the periphery infiltrate the central nervous system to trigger a local immune response that ultimately damages myelin and axons. Pro-inflammatory cytokines amplify the inflammatory cascade by compromising the BBB, recruiting immune cells from the periphery, and activating resident microglia. inflammation-associated oxidative burst in activated microglia and macrophages plays an important role in the demyelination and free radical-mediated tissue injury in the pathogenesis of MS. The inflammatory environment in demyelinating lesions leads to the generation of oxygen- and nitrogen-free radicals as well as proinflammatory cytokines which contribute to the development and progression of the disease. Inflammation can lead to oxidative stress and vice versa. Thus, oxidative stress and inflammation are involved in a self-perpetuating cycle.

4-1BB ligand-mediated imbalance of helper 17 T cells and regulatory T cells in patients with allergic asthma

OBJECTIVES

To investigate the presence of 4-1BB ligand (4-1BBL) in the peripheral blood of patients with allergic asthma and evaluate its role in controlling the balance between helper 17 T (T(h)17) and regulatory T (T(reg)) cells.

METHODS

Soluble 4-1BBL (s4-1BBL) was quantified by enzyme-linked immunosorbent assay in plasma from patients with asthma (n = 45) and from healthy control subjects (n = 35). The proportion of monocytes positive for membrane-bound 4-1BBL (m4-1BBL) was determined by flow cytometry. Peripheral blood mononuclear cells from patients with asthma were incubated with anti-4-1BB monoclonal antibody in vitro. Concentrations of interleukin (IL)-17 and transforming growth factor (TGF)-β(1) in the culture supernatant were analysed.

RESULTS

Plasma s4-1BBL concentrations and the proportion of m4-1BBL-positive monocytes were significantly lower in patients with asthma than in control subjects. The culture supernatant concentration of TGF-β(1) was increased and that of IL-17 was decreased by incubation with anti-4-1BB monoclonal antibody.

CONCLUSIONS

Both soluble and membrane-bound 4-1BBL were reduced in patients with allergic asthma compared with control subjects. 4-1BBL/4-1BB signalling may play an important role in allergic asthma by regulating the T(h)17/T(reg) balance.

4-1BB/4-1BBL interaction promotes obesity-induced adipose inflammation by triggering bidirectional inflammatory signaling in adipocytes/macrophages

Obesity-induced adipose inflammation is characterized by recruitment of macrophages to adipose tissue and release of inflammatory cytokines. 4-1BB, a costimulatory receptor, modulates inflammatory processes through interaction with its ligand 4-1BBL on immune cell surfaces. In this study, we examined whether a 4-1BB/4-1BBL interaction between adipocytes and macrophages participates in obesity-induced adipose inflammation. We found that 4-1BB was expressed on adipocytes and was upregulated by obesity-related factors, which also enhanced 4-1BBL expression on macrophages. 4-1BB and/or 4-1BBL agonists, respectively, activated inflammatory signaling molecules (MAPK/IκBα and MAPK/Akt) in adipocytes and macrophages and enhanced the release of inflammatory cytokines (MCP-1, TNF-α, and IL-6). Moreover, disruption of the 4-1BB/4-1BBL interaction decreased the release of inflammatory cytokines from contact cocultured adipocytes/macrophages. These findings indicate that 4-1BB/4-1BBL-mediated bidirectional signaling in adipocytes/macrophages promotes adipose inflammation. 4-1BB and 4-1BBL may be useful targets for protection against obesity-induced adipose inflammation.

Regulation of Inflammation by Bidirectional Signaling through CD137 and Its Ligand

Although the majority of research on CD137 has been directed to T cells, it is becoming clear that this molecule has distinct functions in other lineages of cells, including non-hematopoietic cells. In particular, emerging evidence suggests that the CD137-its ligand (CD137L) network involving immune cells and non-immune cells, directly or indirectly regulates inflammation in both positive and negative manners. Bidirectional signaling through both CD137 and CD137L is critical in the evolution of inflammation: 1) CD137L signaling plays an indispensible role in the activation and recruitment of neutrophils by inducing the production of proinflammatory cytokines and chemokines in hematopoietic and non-hematopoietic cells such as macrophages, endothelial cells and epithelial cells; 2) CD137 signaling in NK cells and T cells is required for their activation and can influence other cells participating in inflammation via either their production of proinflammatory cytokines or engagement of CD137L by their cell surface CD137: 3) CD137 signaling can suppress inflammation by controlling regulatory activities of dendritic cells and regulatory T cells. As recognition grows of the role of dysregulated CD137 or CD137L stimulation in inflammatory diseases, significant efforts will be needed to develop antagonists to CD137 or CD137L.

Reverse signaling through the co-stimulatory ligand, CD137L, as a critical mediator of sterile inflammation

CD137 (also called 4-1BB and TNFRSF9) has recently received attention as a therapeutic target for cancer and a variety of autoimmune and inflammatory diseases. Stimulating CD137 in vivo enhances CD8(+) T cell-activity and results in strong immunosuppression in some contexts. This paradoxical phenomenon may be partially explained by the ability of CD137-stimulating reagents (usually agonistic monoclonal antibodies against CD137) to overactivate T cells and other CD137-expressing cells. This over-activity is associated with deleting pathogenic T cells and B cells or generating a tolerogenic microenvironment. Recent studies, however, suggest that the biology of CD137 and its ligand (CD137L) are more complex, mainly due to bidirectional signaling between CD137 and CD137L. For example, signaling through CD137L in non-hematopoietic cells such as epithelial cells and endothelial cells has been shown to play an essential role in sterile inflammation by regulating immune cell recruitment. One outstanding, and clinically important, issue is understanding how bidirectional signaling through CD137 and CD137L controls the vicious cycle of sterile inflammation (e.g., ischemia-reperfusion tissue injury and meta-inflammatory diseases).

Anti-CD137 mAb Deletes Both Donor CD4 and CD8 T Cells in Acute Graft-versus-host Disease

We previously demonstrated that in vivo engagement of CD137, a member of TNF receptor superfamily, can delete allorective CD4(+) T cells through the induction of activation-induced cell death (AICD) in chronic graft-versus-host disease (cGVHD) and subsequently reverse established cGVHD. In this study, we further showed that agonistic anti-CD137 mAb was highly effective in triggering AICD of donor CD8(+) T cells as well as donor CD4(+) T cells in the C57BL/6→unirradiated (C57BL/6 × DBA/2)F1 acute GVHD model. Our results suggest that strong allostimulation should facilitate AICD of both alloreactive CD4(+) and CD8(+) T cells induced by CD137 stimulation. Therefore, depletion of pathogenic T cells using agonistic anti-CD137 mAb combined with potent TCR stimulation may be used to block autoimmune or inflammatory diseases mediated by T cells.

Reverse signaling through the costimulatory ligand CD137L in epithelial cells is essential for natural killer cell-mediated acute tissue inflammation

Renal ischemia-reperfusion injury (IRI) after kidney transplantation is a major cause of delayed graft function. Even though IRI is recognized as a highly coordinated and specific process, the pathways and mechanisms through which the innate response is activated are poorly understood. In this study, we used a mouse model of acute kidney IRI to examine whether the interactions of costimulatory receptor CD137 and its ligand (CD137L) are involved in the early phase of acute kidney inflammation caused by IRI. We report here that the specific expressions of CD137 on natural killer cells and of CD137L on tubular epithelial cells (TECs) are required for acute kidney IRI. Reverse signaling through CD137L in TECs results in their production of the chemokine (C-X-C motif) receptor 2 ligands CXCL1 and CXCL2 and the subsequent induction of neutrophil recruitment, resulting in a cascade of proinflammatory events during kidney IRI. Our findings identify an innate pathogenic pathway for renal IRI involving the natural killer cell-TEC-neutrophil axis, whereby CD137-CD137L interactions provide the causal contribution of epithelial cell dysregulation to renal IRI. The CD137L reverse signaling pathway in epithelial cells therefore may represent a good target for blocking the initial stage of inflammatory diseases, including renal IRI.

Recombinant TAT-CD137 Ligand Cytoplasmic Domain Fusion Protein Induces the Production of IL-6 and TNF-α in Peritoneal Macrophages

Background

The ligand for CD137 (CD137L; also called 4-1BBL) is mainly expressed on activated APCs such as dendritic cells, B cells and macrophages. Even though CD137L functions as a trigger of the CD137 signaling pathway for T cell activation and expansion, engagement of CD137L can deliver a signal leading to the production of proinflammatory cytokines in macrophages.

Methods

We generated cell-permeable TAT-CD137L cytoplasmic domain fusion protein (TAT-CD137Lct) and examined its ability to initiate the CD137L reverse signaling pathway.

Results

Treatment of TAT-CD137Lct induced the production of high levels of IL-6 and TNF-α mRNAs and proteins in peritoneal macrophages. TAT-CD137Lct increased phosphorylation of Erk, p38 MAPK and Jnk, and activated transcription factors C/EBP and CREB. However, TAT-CD137Lct did not visibly affect the degradation of the inhibitor of NF-kB (IkBα). We further demonstrated that JNK activation was required for TAT-CD137Lct-induced production of TNF-α, while activation of Erk and p38 MAPK were involved in IL-6 and TNF-α production.

Conclusion

Our results suggest that TAT-CD137Lct is an effective activator for the CD137L reverse signaling pathway.

Intervention with costimulatory pathways as a therapeutic approach for graft-versus-host disease

Graft-versus-host disease (GVHD) is mediated by mature donor T cells contained in the hematopoietic stem cell graft. During the development of GVHD, signaling through a variety of costimulatory receptors plays an important role in allogeneic T cell responses. Even though delivery of costimulatory signals is a prerequisite for full activation of donor T cells in the phase of their interactions with host APCs, their involvement with GVHD might occur over multiple stages. Like many other aspects of GVHD, promise of therapeutic interventions with costimulatory pathways has been gleaned from preclinical models. In this review, I summarize some of the advances in roles of costimulatory molecules in GVHD pathophysiology and discuss preclinical approaches that warrant further exploration in the clinic, focusing on novel strategies to delete pathogenic T cells.