CD137 Ligand-CD137 Interaction is Required For Inflammasome-Associated Brain Injury Following Ischemic Stroke.

The CD137L-CD137 axis is a potent co-stimulatory immune checkpoint regulator that forms a bidirectional signaling pathway between the CD137 ligand (CD137L) and CD137 receptor to regulate immunological activities. This study investigated the potential involvement of the CD137L-CD137 axis on inflammasome-associated brain injury and neurological deficits in a mouse model of focal ischemic stroke. Cerebral ischemia was induced in male C57BL/6J wild-type (WT), CD137L-deficient (CD137L KO) and CD137-deficient (CD137 KO) mice by middle cerebral artery occlusion (MCAO; 60 min), followed by reperfusion (6 h and 24 h). Brain infarct volume and neurological deficit scores were significantly lower in both CD137L KO and CD137 KO mice compared to WT controls. Moreover, CD137L-deficient brains had significantly lower levels of the pyroptotic protein, NT-Gasdermin D, while CD137-deficient brains had significantly lower levels of the pro-apoptotic proteins, cleaved caspase-3, pyroptotic protein, NT-Gasdermin D, and of the secondary pyroptotic protein NT-Gasdermin E, following ischemic stroke. This protection by CD137L and CD137 deletion was associated with a significant decrease in inflammasome signaling. In conclusion, our data provide evidence for the first time that the CD137L-CD137 axis contributes to brain injury and neurological deficits by activating the inflammasome signaling pathway following ischemic stroke.

4-1BB Delineates Distinct Activation Status of Exhausted Tumor-Infiltrating CD8+ T Cells in Hepatocellular Carcinoma.

BACKGROUND AND AIMS: Targeting costimulatory receptors with agonistic antibodies is a promising cancer immunotherapy option. We aimed to investigate costimulatory receptor expression, particularly 4-1BB (CD137 or tumor necrosis factor receptor superfamily member 9), on tumor-infiltrating CD8+ T cells (CD8+ tumor-infiltrating lymphocytes [TILs]) and its association with distinct T-cell activation features among exhausted CD8+ TILs in hepatocellular carcinoma (HCC). APPROACH AND RESULTS: Tumor tissues, adjacent nontumor tissues, and peripheral blood were collected from HCC patients undergoing surgical resection (n = 79). Lymphocytes were isolated and used for multicolor flow cytometry, RNA-sequencing, and in vitro functional restoration assays. Among the examined costimulatory receptors, 4-1BB was most prominently expressed on CD8+ TILs. 4-1BB expression was almost exclusively detected on CD8+ T cells in the tumor-especially on programmed death 1 (PD-1)high cells and not PD-1int and PD-1neg cells. Compared to PD-1int and 4-1BBneg PD-1high CD8+ TILs, 4-1BBpos PD-1high CD8+ TILs exhibited higher levels of tumor reactivity and T-cell activation markers and significant enrichment for T-cell activation gene signatures. Per-patient analysis revealed positive correlations between percentages of 4-1BBpos cells among CD8+ TILs and levels of parameters of tumor reactivity and T-cell activation. Among highly exhausted PD-1high CD8+ TILs, 4-1BBpos cells harbored higher proportions of cells with proliferative and reinvigoration potential. Our 4-1BB-related gene signature predicted survival outcomes of HCC patients in the The Cancer Genome Atlas cohort. 4-1BB agonistic antibodies enhanced the function of CD8+ TILs and further enhanced the anti-PD-1-mediated reinvigoration of CD8+ TILs, especially in cases showing high levels of T-cell activation. CONCLUSION: 4-1BB expression on CD8+ TILs represents a distinct activation state among highly exhausted CD8+ T cells in HCC. 4-1BB costimulation with agonistic antibodies may be a promising strategy for treating HCCs exhibiting prominent T-cell activation.

[CD137-CD137L signaling influences the autophagy via JNK pathway in mouse vascular smooth muscle cells].

Objective: To investigate whether CD137-CD137L signaling can affect the autophagy of mouse vascular smooth muscle cells(VSMCs) through JNK signal pathway. Methods: Primary culture of C57BL/6J mouse thoracic aorta VSMCs was performed by tissue block adherence method. VSMCs between the third to fifth passages were isolated and cultured. VSMCs were divided into 4 groups: control group, CD137 agonist group, JNK inhibition group, and DMSO group. VSMCs in CD137 agonist group were treated with recombinant protein of CD137L (10 µg/ml), VSMCs in JNK inhibition group were treated with JNK inhibitor SP600125 (10 µmol/L) for 30 minutes followed by recombinant protein of CD137L (10 µg/ml) and DMSO group was treated with the same amount of DMSO in JNK inhibition group for 30 minutes, then added recombinant protein of CD137L (10 µg/ml). Western blot was used to detect the protein expression of p-JNK, LCⅡ and p62 in each group. Fluorescence microscopy was used to track the changes of autophagy in cells which was infected with adenovirus expressing tandem mRFP-GFP-LC3. Transmission electron microscope (TEM) was used to observe intracellular autophagosomes and autolysosomes. Results: (1) Compared with the control group, stimulating CD137-CD137L axis by recombinant protein of CD137L significantly upregulated the expression of p-JNK, LCⅡ and p62 (1.15±0.19 vs. 0.72±0.21, P<0.05;1.03±0.13 vs. 0.59±0.15, P<0.05, and 1.10±0.19 vs. 0.76±0.15, P<0.05). These effects could be reduced by JNK inhibitor (0.61±0.21 vs. 1.15±0.19, P<0.05;0.74±0.11 vs. 1.03±0.13, P<0.05, and 0.21±0.12 vs. 1.10±0.19, P<0.05). The expression of these proteins in DMSO group remained unchanged compared with CD137 agonist group (P>0.05). (2) Changes of autophagy in cells of various group: the number of total fluorescent spots and yellow fluorescent spots in CD137 agonist group was significantly increased compared to control group (total fluorescent spots:(93.00±14.11)/cell vs. (52.33±9.61)/cell, P<0.05, and (64.33±6.81)/cell vs. (25.67±3.51)/cell, P<0.05), moreover, the number of yellow fluorescent spots was higher than the red fluorescent spots fluorescent spots in CD137 agonist group. Compared with CD137 agonist group, pretreatment with JNK inhibitor significantly reduced the number of total fluorescent spots and yellow fluorescent spots ((53.00±3.17)/cell vs. (93.00±14.11)/cell, P<0.05,and (15.33±4.51)/cell vs. (64.33±6.81)/cell, P<0.05). The red fluorescent spots were higher than the yellow fluorescent spots in JNK inhibition group. The number of total fluorescent spots and yellow fluorescent spots in CD137 agonist group was not affected by pretreatment with DMSO (P>0.05). (3) The number of intracellular autophagosomes and autolysosomes was significantly higher in CD137 agonist group than in control group((17.67±6.03)/cell vs. (5.67±2.52)/cell, P<0.05), and the number of autophagosomes was higher than that of autolysosomes in CD137 agonist group((14.00±4.00)/cell vs. (3.67±2.08)/cell, P<0.05). The number of intracellular autophagosomes and autolysosomes was significantly lower in JNK inhibition group compared to CD137 agonist group((5.67±4.04)/cell vs. (17.67±6.03)/cell, P<0.05) and the number of autophagosomes was lower than that of autolysosomes in JNK inhibition group((1.33±1.53)/cell vs. (4.33±2.52)/cell, P<0.05). The number of intracellular autophagosomes and autolysosomes was similar between DMSO group and CD137 agonist group (P>0.05). Conclusion: CD137-CD137L signal may influence autophagy of mouse VSMCs via JNK pathway.

4-1BB expression on MAIT cells is associated with enhanced IFN-γ production and depends on IL-2.

The role of MAIT cells in immunity against Mycobacterium tuberculosis infection in humans is still largely unexplored. In this study, we investigated the functional role of 4-1BB on MAIT cells. We found that 4-1BB was highly up-regulated on MAIT cells from tuberculous pleural effusions following Mtb antigen stimulation and its level of expression correlated with IFN-γ and IL-17 production. 4-1BB expression on MAIT cells in response to Mtb antigens was partially dependent on IL-2 and was associated with common γ chain receptor. By transcriptome sequencing, we identified numerous differentially expressed genes between 4-1BB- and 4-1BB+ MAIT cells. GO enrichment and KEGG pathway analysis of differentially expressed genes identified enriched pathways that included T-cell receptor and NF-κB signaling pathways. It is concluded that 4-1BB has the potential to be used as a biomarker to identify MAIT cells with enhanced IFN-γ and IL-17 responses that might be associated with tuberculosis infection control.

[CD137 induces vascular muscle cells phenotype transformation through activating nuclear factor of activated T-cells 1 signaling].

Objective: To investigate whether CD137 induces primary vascular muscle cells (VSMCs) phenotype transformation through activating nuclear factor of activated T-cells 1(NFATc1) signaling. Methods: VSMCs were obtained from aorta of C57BL/6J mice (8 weeks, male) through tissue-piece inoculating. Cells were divided into control group, CD137 agonist group (treated with CD137L recombinant protein) and anti-CD137 group (treated with anti-CD137 antibody). In si-RNA transfection assay, cells were divided into si-control group and si-NFATc1 group which were transfected with control or si-NFATc1 sequence respectively. The levels of NFATc1 and other phenotype related protein such as α-smooth muscle actin (α-SMA), smooth muscle myosin heavy chain (SM-MHC), vimentin were detected by Q-PCR and Western blot. Nuclear protein expression and activity of NFATc1 were detected by immunofluorescence and Western blot. Transwell assay was performed to measure the migration of VSMCs. Results: According to Western blot, the expression of NFATc1 and vimentin was significantly upregulated (5.07±0.36 vs. 1.00±0.00, P<0.05; 3.23±0.27 vs. 1.00±0.00, P<0.05) while α-SMA and SM-MHC expressions was significantly downregulated (0.73±0.15 vs. 1.00±0.00, P<0.05; 0.45±0.05 vs. 1.00±0.00, P<0.05) in CD137 agonist group compare to control group. Compared with CD137 agonist group, the expression of NFATc1 and vimentin was significantly downregulated (1.56±0.27 vs. 5.07±0.36, P<0.05; 1.21±0.17 vs. 3.23±0.27, P<0.05), but the levels of α-SMA and SM-MHC were significantly upregulated (2.01±0.43 vs. 0.73±0.15, P<0.05; 2.85 ±0.32 vs. 0.45±0.05, P<0.05) in anti-CD137 group. Compared with si-con group, the expression of SM-MHC and α-SMA was significantly upregulated while the expression of vimentin was significantly downregulated in si-NFATc1 group. Transwell assay results demonstrated that migration cell numbers was significantly higher in CD137L group compared with control group(3.85±0.31 vs. 1.00±0.00, P<0.05), this effect was significantly attenuated by inhibiting NFATc1. Conclusion: CD137 could induce VSMC phenotype transformation through activating NFATc1 signaling.

The EGR2 targets LAG-3 and 4-1BB describe and regulate dysfunctional antigen-specific CD8+ T cells in the tumor microenvironment.

Although the presence of tumor-infiltrating lymphocytes (TILs) indicates an endogenous antitumor response, immune regulatory pathways can subvert the effector phase and enable tumor escape. Negative regulatory pathways include extrinsic suppression mechanisms, but also a T cell-intrinsic dysfunctional state. A more detailed study has been hampered by a lack of cell surface markers defining tumor-specific dysfunctional TILs, and PD-1 alone is not sufficient. Recently, we identified the transcription factor Egr2 as a critical component in controlling the anergic state in vitro. In this study, we show that the Egr2-driven cell surface proteins LAG-3 and 4-1BB can identify dysfunctional tumor antigen-specific CD8+ TIL. Co-expression of 4-1BB and LAG-3 was seen on a majority of CD8+ TILs, but not in lymphoid organs. Functional analysis revealed defective IL-2 and TNF production yet retained expression of IFN-γ and regulatory T cell-recruiting chemokines. Transcriptional and phenotypic characterization revealed coexpression of multiple additional co-stimulatory and co-inhibitory receptors. Administration of anti-LAG-3 plus anti-4-1BB mAbs was therapeutic against tumors in vivo, which correlated with phenotypic normalization. Our results indicate that coexpression of LAG-3 and 4-1BB characterize dysfunctional T cells within tumors, and that targeting these receptors has therapeutic utility.

Involvement of Ly6C, 4-1BB, and KLRG1 in the activation of lamina propria lymphocytes in the small intestine of sanroque mice.

Roquin is an E3 ligase that regulates mRNA stability. Mice with a mutation in the Rc3h1 gene and Roquin protein, referred to as Roquinsan/san or sanroque mice, develop broad-spectrum chronic inflammatory conditions and autoimmune pathologies. Our laboratory recently reported that sanroque mice also develop extensive inflammation that is localized in the small intestine but is rare in the colon. Here, we demonstrate that small intestinal intraepithelial lymphocytes (IELs) are present in the epithelium of sanroque mice but that cell recoverability is low using standard extraction techniques even though lamina propria lymphocytes (LPLs) can be recovered in normal numbers. In studies aimed at characterizing T cell costimulatory markers and activation molecules on LPLs in sanroque mice, we identified Ly6C and 4-1BB (CD137) as being expressed at elevated levels on sanroque small intestinal LPLs, and we show that both of those subsets, in conjunction with cells expressing the KLRG1 T cell activation molecule, are sources of IL-17A, IFN-γ, and TNFα. TNFα was primarily produced by 4-1BB+, KLRG1-cells, but was also made by some 4-1BB-, KLRG1-cells, and 4-1BB-, KLRG1+ cells. These findings collectively suggest that the small intestinal inflammatory response in sanroque mice is driven, at least in part, by LPL activation through Ly6C and 4-1BB signaling, and they provide further evidence in support of using the sanroque mouse as an animal model of chronic small intestinal inflammation.

[CD137 signaling promotes the formation of plaque calcification via inhibiting the fusion of autophagy and lysosomal in Apo E(-/-) mice].

Objective: To investigate whether CD137 signaling promoted the formation of atherosclerotic plaque calcification by inhibiting the fusion of autophagosome and lysosome. Methods: (1) In vivo, CD137 agonist antibody and anti-CD137 antibody were used to stimulate and inhibit the CD137 signaling, respectively. Fifteen Apo E(-/-) mice were randomly divided into three groups: control group (intraperitoneal injection of IgG2b 200 µg) , CD137 agonist group (intraperitoneal injection of CD137 agonist antibody 200 µg) , anti-CD137 group (pretreatment with 200 µg anti-CD137 antibody for 24 hours, then injection of CD137 agonist antibody) . (2) In vitro, primary culture of mouse aortic VSMCs obtained through adherence methods for tissues explants. The cells was divided into three groups: control group, agonist-CD137 group (CD137 agonist antibody 10 µg/ml) , and anti-CD137 group (pretreatment with 10 µg/ml anti-CD137 antibody for 60 minutes, then incubated with 10 µg/ml CD137 agonist antibody) . Von kossa staining was used to detect the calcification in the cell and plaque. Immunohistochemical staining was used to observe the expression of LC3B, Beclin 1 and p62 which are associated with autophagy. The levels of autophagy related protein (LC3) , Beclin 1, p62, and the expression of Runx2 and bone morphogenetic protein 2, which is associated with osteogenic differentiation in the VSMCs, were determined by Western blot. The autophagy flow of each group was detected by fluorescence microscopy. The autophagy was observed by transmission electron microscope in vivo and in vitro. Results: (1) In vivo, the calcified plaque area in CD137 agonist group was significantly larger than that in the control group (3.01%±0.45% vs. 0.27%±0.06%, P<0.01) , and calcified plaque area in anti-CD137 group was significantly smaller compared with that in the CD137 agonist group (1.23%±0.39% vs. 3.01%±0.45%, P<0.05) . Immunohistochemical staining showed that the expression of early autophagy marker protein LC3B and Beclin 1 were significantly upregulated in CD137 agonist group and anti-CD137 group than in control group, and the highest expression was observed in CD137 agonist group (P<0.05) . The expression of advanced autophagy marker protein p62 was higher in the CD137 agonist group than in the anti-CD137 group (P<0.05) . (2) In vitro, the ratio of autophagy related protein LC3 Ⅱ/Ⅰ and p62 protein expression were significantly higher in CD137 agonist group and anti-CD137 group than in control group (P<0.01) , while the expression of p62 protein was significantly higher in CD137 agonist group than that in anti-CD137 group (P<0.05) . In the cell calcification inducing experiment, the expression of BMP-2 and Runx2 protein was significantly higher in CD137 agonist group than that in control group (P<0.01) , but the levels of BMP-2 and Runx2 protein were lower in anti-CD137 group than in CD137 agonist group (P<0.05) . Conclusion: Our results indicate that activation of CD137 signaling can promote the formation of atherosclerotic plaque calcification by inhibiting the fusion of autophagosome and lysosome.

CD137 Regulates NFATc1 Expression in Mouse VSMCs through TRAF6/NF-κB p65 Signaling Pathway.

Our previous study proved that CD137-CD137L interaction can regulate the expression of NFATc1. Here, we investigated whether CD137 signaling regulates the expression of NFATc1 in mice VSMCs through TRAF6/NF-κB p65 pathway. Data shows that the CD137 expression can be stimulated by TNF-α in a time-dependent manner in mouse VSMCs. Knockdown of TRAF6 by siTRAF6 significantly attenuated agonist-CD137mAb induced increase of NF-κB p65 and NFATc1 in VSMCs. Pretreatment with a NF-κB inhibitor PDTC for 30 min inhibited the expression of p-p65 in both cytoplasm and nucleus in VSMCs. Thus, the protein level of NFATc1 can be suppressed through inhibition of p-p65. Finally, we also show that the levels of IL-2 and IL-6 can be increased by agonist-CD137 stimulation and decreased when NFATc1 was suppressed. Our data suggest that activated CD137 signaling regulates the expression of NFATc1 and its downstream factors through TRAF6/NF-κB p65 pathways in VSMCs. These findings provide a novel target for treatment of atherosclerosis.

Dengue virus disrupts Daxx and NF-κB interaction to induce CD137-mediated apoptosis.

Dengue virus (DENV) is a positive-strand RNA virus of the Flavivirus family with 4 different serotypes. Clinical manifestations of DENV infection include dengue fever, dengue hemorrhagic fever, and dengue shock syndrome. Following DENV infection, apoptosis of hepatic cells is observed both in vitro and in vivo. However, the molecular mechanisms revealing how viral components affect cellular apoptosis remain unclear. In the present study, the role of death domain-associated protein 6 (Daxx) in DENV-mediated apoptosis was characterized by RNA interference and overexpression studies, and the anti-apoptotic function of Daxx during DENV infection was identified. Furthermore, the viral component, DENV capsid protein (DENV C), interacted with Daxx to disrupt interaction between Daxx and NF-κB. The liberated NF-κB activated the promoter of CD137, which is a member of the TNF family, and is previously shown to induce apoptosis during DENV infection. In summary, DENV C disrupts Daxx and NF-κB interaction to induce CD137-mediated apoptosis during DENV infection.

T-cell costimulatory blockade in organ transplantation.

Before it became possible to derive T-cell lines and clones, initial experimentation on the activation requirements of T lymphocytes was performed on transformed cell lines, such as Jurkat. These studies, although technically correct, proved misleading as most transformed T cells can be activated by stimulation of the clonotypic T-cell receptor (TCR) alone. In contrast, once it became possible to study nontransformed T cells, it quickly became clear that TCR stimulation by itself is insufficient for optimal activation of naïve T cells, but in fact, induces a state of anergy. It then became clear that functional activation of T cells requires not only recognition of major histocompatibility complex (MHC) and peptide by the TCR, but also requires ligation of costimulatory receptors expressed on the cell surface.

Enhanced antitumor activity mediated by human 4-1BB-engineered T cells.

4-1BB (CD137) is a costimulatory molecule transiently expressed on the T-cell surface after TCR engagement, whereas its ligand 4-1BBL can be found on professional antigen-presenting cells, but more importantly, also on tumor cells. As the role of the 4-1BB/4-1BBL pathway has emerged central to CD8(+) T-cell responses and survival, we sought to test its relevance in the context of genetically modified human T cells. To that end, T cells purified from healthy donors and from vaccinated-melanoma patients were transduced to express high levels of constitutive 4-1BB. 4-1BB-transduced T cells were cocultured with melanoma tumor lines and exhibited enhanced cytokine secretion, upregulation of activation markers as well as increased cytotoxicity in a chick-chorioallantoic membrane model of human melanoma tumors. In addition, these cells expanded and proliferated at a higher rate, expressed heightened levels of the antiapoptotic molecule Bcl(XL) and were also relatively insensitive to immunosuppression mediated by transforming growth factor-ß, compared to control cells. We also show that 4-1BBL expression on the target cell is essential to 4-1BB-mediated functional improvement. Overall, we conclude that the modification of human T cells with 4-1BB yields enhanced antitumor function which may have important applications in therapies based on the genetic modification of patient lymphocytes.

Leukocyte-specific protein 1 links TNF receptor-associated factor 1 to survival signaling downstream of 4-1BB in T cells.

4-1BB is a member of the TNFR superfamily, which contributes to the activation of signaling pathways required for the survival of activated and memory T cells. We have shown previously that TRAF1, an adaptor protein recruited to 4-1BB, is required for 4-1BB-mediated CD8 T cell survival in vivo. With the use of a proteomics approach in primary T cells, we have identified LSP1 as a novel protein recruited to the 4-1BB signaling complex in a TRAF1-dependent manner. Further characterization of the interaction between TRAF1 and LSP1 revealed that LSP1 requires the TRAF-N domain of TRAF1 for direct association. Similarly to TRAF1(-/-) T cells, LSP1(-/-) T cells exhibit impaired ERK activation following stimulation through 4-1BB and consequently, are unable to down-modulate expression of the proapoptotic Bcl-2 family member Bim. Moreover, we demonstrate that the absence of LSP1 expression leads to defective expansion and survival of T cells in response to 4-1BB stimulation. Thus, we have identified LSP1 as a new mediator involved in 4-1BB signaling and T cell survival. Collectively, our work shows that TRAF1 and LSP1 cooperate downstream of 4-1BB to activate ERK signaling and down-modulate the levels of Bim leading to enhanced T cell survival.

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.

Combined blockade of programmed death-1 and activation of CD137 increase responses of human liver T cells against HBV, but not HCV.

BACKGROUND & AIMS: In patients with chronic hepatitis B virus (HBV) and hepatitis C virus (HCV) infections, antiviral functions of T cells are impaired; these might be increased by blocking T-cell co-inhibitory pathways, such as preventing interaction between the receptor programmed death (PD)-1 and its ligand, PD-L1. We attempted to optimize the restoration of T-cell functions in patients with chronic HBV or HCV infection with a combination of reagents that block PD-1 interaction with PD-L1 and stimulate T-cell signaling via CD137, a member of the tumor necrosis factor-receptor family. METHODS: We assessed the effects of CD137 stimulation (via CD137L), alone or in combination with antibodies that block PD-1 interaction with PD-L1 (anti-PD-L1), on proliferation and production of interferon-γ and interleukin-2 by intrahepatic and peripheral T cells from patients with chronic HBV or HCV infection. We also analyzed expression of different co-stimulatory molecules on virus-specific CD8+ and forkhead box P3+CD4+ cells by flow cytometry. RESULTS: Incubation of intrahepatic T cells with CD137L and anti-PD-L1 increased their responses to HBV, but not HCV. However, HCV-specific T cells isolated from peripheral blood were sensitive to these reagents. Virus-specific T cells from some, but not all patients, had increased responses to anti-PD-L1 when CD137L was added because in some cases the combination of anti-PD-L1 and CD137L overstimulated T cells, leading to their inhibition. Intrahepatic HBV- and HCV-specific CD8+ T cells had different costimulatory profiles; liver cells from patients with chronic HBV infection had a higher proportion of forkhead box P3+ regulatory T cells, with higher levels of PD-1, compared with liver cells from patients with chronic HCV infection. CONCLUSIONS: A combination of reagents that prevent interaction between PD-1 and its ligand and activate CD137 signaling increase responses of intrahepatic HBV-specific T cells and circulating HCV-specific T cells. This strategy might be developed to increase T-cell responses to these viruses in patients with chronic hepatitis B or C, and tailoring the dose of CD137L administered will help optimize results.

Cutting edge: 4-1BB controls regulatory activity in dendritic cells through promoting optimal expression of retinal dehydrogenase.

Dendritic cells (DC) in the gut promote immune tolerance by expressing retinal dehydrogenase (RALDH), an enzyme that promotes retinoic acid, which aids differentiation of Foxp3+ inducible regulatory T cells (iTreg) in the intestinal mucosa. How RALDH expression is regulated is unclear. We found that 4-1BB (CD137), a member of the TNFR family, together with CD103, marked mesenteric lymph node DC with the highest level of RALDH activity, and ligation of 4-1BB maintained RALDH expression in these gut DC. Moreover, 4-1BB signals synergized with those through TLR2 or GM-CSFR to promote RALDH activity in undifferentiated DC. Correspondingly, 4-1BB-deficient mice were impaired in their ability to generate iTreg in the GALT when exposed to oral Ag, and 4-1BB-deficient mesenteric lymph node DC displayed weak RALDH activity and were poor at promoting iTreg development. Thus, our data demonstrate a novel activity of 4-1BB in controlling RALDH expression and the regulatory activity of DC.

4-1BB-mediated signals confer protection against folic acid-induced nephrotoxicity.

BACKGROUND: The role of co-stimulatory molecules in renal diseases has been previously examined, however, little is known about the role of 4-1BB in the context of renal diseases resulting from nonimmune-mediated tubulointerstitial fibrosis. Folic acid induced Nephrotoxicity (FAN) in mice was used to explore the role of 4-1BB in this setting. METHODS: CD1 mice were treated with folic acid and kidneys subsequently examined using histochemistry, in addition to defining T cell profiles and evaluating renal function. Increased CD3+ and CD4+ T lymphocytes present in blood and spleen at day 3 suggested immunopathological reactions during the early stages of FAN and decreased CD3+ and CD4+ T lymphocytes on day 14 were characteristic of an immunocompromised state observed during the late stages of FAN. RESULTS: After 14 days of co-treatment with agonistic anti-4-1BB monoclonal antibodies, renal tubulointerstitial lesions were reduced. Renal function was improved, with Bun scores decreasing (p<0.01) and sCr levels decreasing (p<0.01). CD3+ and CD4+ T lymphocytes levels were increased during the early stages of disease in FA treated mice and reduced to the normal level in the 4-1BB-treated mice. CD3+ and CD4+ T lymphocytes levels were decreased in FA treated mice and returned to baseline in the 4-1BB-treated mice during later stages. CONCLUSIONS: Data presented in this report demonstrated that 4-1BB signals had immunoregulatory effects that attenuated early immune-mediated pathology and reversed the immunocompromised state observed during the later stages of disease.

CD137 on inflamed lymphatic endothelial cells enhances CCL21-guided migration of dendritic cells.

CD137/TNFR9/41BB was originally described as a surface molecule present on activated T and NK cells. However, its expression is broader among leukocytes, and it is also detected on hypoxic endothelial cells and inflamed blood vessels, as well as in atherosclerotic lesions. Here, we demonstrate that lymphatic endothelial cells (LECs) up-regulate CD137 expression from undetectable baseline levels on stimulation with TNF-α, LPS, and IL-1ß. CD137 cross-linking with an agonistic mAb results in NF-κB nuclear translocation, followed by up-regulation of VCAM and a 3-fold increase in the production of the chemokine CCL21. Accordingly, there is a 50% increase in CCR7-dependent migration toward conditioned medium from activated LECs on CD137 cross-linking with the agonistic mAb or the natural ligand (CD137L). Such an enhancement of cell migration is also observed with monocyte-derived dendritic cells transmigrating across CD137-activated LEC monolayers. Using explanted human dermal tissue, we found that inflamed skin contains abundant CD137(+) lymphatic vessels and that ex vivo incubation of explanted human dermis with TNF-α induces CD137 expression in lymphatic capillaries. More interestingly, treatment with CD137 agonistic antibody induces CCL21 expression and DC accumulation close to lymphatic vessels. Collectively, our results demonstrate that the inflammatory function of lymphatic vessels can be regulated by CD137.

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.

4-1BB triggering ameliorates experimental autoimmune encephalomyelitis by modulating the balance between Th17 and regulatory T cells.

Agonistic anti-4-1BB Ab is known to ameliorate experimental autoimmune encephalomyelitis. 4-1BB triggering typically leads to the expansion of CD8(+) T cells, which produce abundant IFN-γ, and this in turn results in IDO-dependent suppression of autoimmune responses. However, because neutralization of IFN-γ or depletion of CD8(+) T cell only partially abrogates the effect of 4-1BB triggering, we sought to identify an additional mechanism of 4-1BB-triggered suppression of autoimmune responses using IFN-γ- or IFN-γR-deficient mice. 4-1BB triggering inhibited the generation of Th17 cells that is responsible for experimental autoimmune encephalomyelitis induction and progression, and increased Foxp3(+)CD4(+) regulatory T (Treg) cells, particularly among CD4(+) T cells. This was not due to a direct effect of 4-1BB signaling on CD4(+) T cell differentiation: 4-1BB signaling not only reduced Th17 cells and increased Treg cells in wild-type mice, which could be due to IFN-γ production by the CD8(+) T cells, but also did so in IFN-γ-deficient mice, in that case by downregulating IL-6 production. These results show that although secondary suppressive mechanisms evoked by 4-1BB triggering are usually masked by the strong effects of IFN-γ, 4-1BB signaling seems to modulate autoimmune responses by a number of mechanisms, and modulation of the Th17 versus Treg cell balance is one of those mechanisms.