TNF superfamily receptor OX40 triggers invariant NKT cell pyroptosis and liver injury.

Tissue-resident immune cells play a key role in local and systemic immune responses. The liver, in particular, hosts a large number of invariant natural killer T (iNKT) cells, which are involved in diverse immune responses. However, the mechanisms that regulate survival and homeostasis of liver iNKT cells are poorly defined. Here we have found that liver iNKT cells constitutively express the costimulatory TNF superfamily receptor OX40 and that OX40 stimulation results in massive pyroptotic death of iNKT cells, characterized by the release of potent proinflammatory cytokines that induce liver injury. This OX40/NKT pyroptosis pathway also plays a key role in concanavalin A-induced murine hepatitis. Mechanistically, we demonstrated that liver iNKT cells express high levels of caspase 1 and that OX40 stimulation activates caspase 1 via TNF receptor-associated factor 6-mediated recruitment of the paracaspase MALT1. We also found that activation of caspase 1 in iNKT cells results in processing of pro-IL-1ß to mature IL-1ß as well as cleavage of the pyroptotic protein gasdermin D, which generates a membrane pore-forming fragment to produce pyroptotic cell death. Thus, our study has identified OX40 as a death receptor for iNKT cells and uncovered a molecular mechanism of pyroptotic cell death. These findings may have important clinical implications in the development of OX40-directed therapies.

Determinants of Human CD134 Essential for Entry of Human Herpesvirus 6B.

We identified two key amino acid residues within human CD134 (hCD134) that are required for its interaction with human herpesvirus 6B (HHV-6B) and for HHV-6B entry into cells. One of the residues (K79) allows access of the HHV-6B ligand to hCD134. Murine CD134 (mCD134) functioned as an HHV-6B receptor when these two amino acid residues were replaced with homologous human residues. This study identifies both the HHV-6B receptor-ligand interaction and the species-specific determinants of hCD134 essential for HHV-6B entry.

Emergence of CD134 cysteine-rich domain 2 (CRD2)-independent strains of feline immunodeficiency virus (FIV) is associated with disease progression in naturally infected cats.

BACKGROUND: Feline immunodeficiency virus (FIV) infection is mediated by sequential interactions with CD134 and CXCR4. Field strains of virus vary in their dependence on cysteine-rich domain 2 (CRD2) of CD134 for infection. FINDINGS: Here, we analyse the receptor usage of viral variants in the blood of 39 naturally infected cats, revealing that CRD2-dependent viral variants dominate in early infection, evolving towards CRD2-independence with disease progression. CONCLUSIONS: These findings are consistent with a shift in CRD2 of CD134 usage with disease progression.

TNF and TNF receptor superfamily members in HIV infection: new cellular targets for therapy?

Tumor necrosis factor (TNF) and TNF receptors (TNFR) superfamily members are engaged in diverse cellular phenomena such as cellular proliferation, morphogenesis, apoptosis, inflammation, and immune regulation. Their role in regulating viral infections has been well documented. Viruses have evolved with numerous strategies to interfere with TNF-mediated signaling indicating the importance of TNF and TNFR superfamily in viral pathogenesis. Recent research reports suggest that TNF and TNFRs play an important role in the pathogenesis of HIV. TNFR signaling modulates HIV replication and HIV proteins interfere with TNF/TNFR pathways. Since immune activation and inflammation are the hallmark of HIV infection, the use of TNF inhibitors can have significant impact on HIV disease progression. In this review, we will describe how HIV infection is modulated by signaling mediated through members of TNF and TNFR superfamily and in turn how these latter could be targeted by HIV proteins. Finally, we will discuss the emerging therapeutics options based on modulation of TNF activity that could ultimately lead to the cure of HIV-infected patients.

T cell costimulation by TNFR superfamily (TNFRSF)4 and TNFRSF25 in the context of vaccination.

TNFR superfamily (TNFRSF)4 (OX40, CD134) and TNFRSF25 are costimulatory receptors that influence CD4(+) and CD8(+) T cell responses to cognate Ag. Independently, these receptors have been described to stimulate overlapping functions, including enhanced proliferation and activation for both regulatory T cells (CD4(+)Foxp3(+); Tregs) and conventional T cells (CD4(+)Foxp3(-) or CD8(+)Foxp3(-); Tconvs). To determine the relative functionality of TNFRSF4 and TNFRSF25 in T cell immunity, the activity of TNFRSF4 and TNFRS25 agonistic Abs was compared in the context of both traditional protein/adjuvant (OVA/aluminum hydroxide) and CD8(+)-specific heat shock protein-based (gp96-Ig) vaccine approaches. These studies demonstrate that both TNFRSF4 and TNFRSF25 independently and additively costimulate vaccine-induced CD8(+) T cell proliferation following both primary and secondary Ag challenge. In contrast, the activities of TNFRSF4 and TNFRSF25 were observed to be divergent in the costimulation of CD4(+) T cell immunity. TNFRSF4 agonists were potent costimulators of OVA/aluminum hydroxide-induced CD4(+) Tconv proliferation, but they only weakly costimulated Treg proliferation and IgG2a production, whereas TNFRSF25 agonists were strong costimulators of Treg proliferation, producers of IgG1, IgG2a, and IgG2b, and weak costimulators of CD4(+) Tconv proliferation. Interestingly, Ag-specific cellular and humoral responses were uncoupled upon secondary immunization, which was dramatically affected by the presence of TNFRSF4 or TNFRSF25 costimulation. These studies highlight the overlapping but nonredundant activities of TNFRSF4 and TNFRSF25 in T cell immunity, which may guide the application of receptor agonistic agents as vaccine adjuvants for infectious disease and tumor immunity.

OX40 facilitates control of a persistent virus infection.

During acute viral infections, clearance of the pathogen is followed by the contraction of the anti-viral T cell compartment. In contrast, T cell responses need to be maintained over a longer period of time during chronic viral infections in order to control viral replication and to avoid viral spreading. Much is known about inhibitory signals such as through PD-1 that limit T cell activity during chronic viral infection, but little is known about the stimulatory signals that allow maintenance of anti-viral T cells. Here, we show that the co-stimulatory molecule OX40 (CD134) is critically required in the context of persistent LCMV clone 13 infection. Anti-viral T cells express high levels of OX40 in the presence of their cognate antigen and T cells lacking the OX40 receptor fail to accumulate sufficiently. Moreover, the emergence of T cell dependent germinal center responses and LCMV-specific antibodies are severely impaired. Consequently, OX40-deficient mice fail to control LCMV clone 13 infection over time, highlighting the importance of this signaling pathway during persistent viral infection.

Dual anti-OX40/IL-2 therapy augments tumor immunotherapy via IL-2R-mediated regulation of OX40 expression.

The provision of T cell co-stimulation via members of the TNFR super-family, including OX40 (CD134) and 4-1BB (CD137), provides critical signals that promote T cell survival and differentiation. Recent studies have demonstrated that ligation of OX40 can augment T cell-mediated anti-tumor immunity in pre-clinical models and more importantly, OX40 agonists are under clinical development for cancer immunotherapy. OX40 is of particular interest as a therapeutic target as it is not expressed on naïve T cells but rather, is transiently up-regulated following TCR stimulation. Although TCR engagement is necessary for inducing OX40 expression, the downstream signals that regulate OX40 itself remain unclear. In this study, we demonstrate that OX40 expression is regulated through a TCR and common gamma chain cytokine-dependent signaling cascade that requires JAK3-mediated activation of the downstream transcription factors STAT3 and STAT5. Furthermore, combined treatment with an agonist anti-OX40 mAb and IL-2 augmented tumor immunotherapy against multiple tumor types. Dual therapy was also able to restore the function of anergic tumor-reactive CD8 T cells in mice with long-term well-established (>5 wks) tumors, leading to increased survival of the tumor-bearing hosts. Together, these data reveal the ability of TCR/common gamma chain cytokine signaling to regulate OX40 expression and demonstrate a novel means of augmenting cancer immunotherapy by providing dual anti-OX40/common gamma chain cytokine-directed therapy.

New insights on OX40 in the control of T cell immunity and immune tolerance in vivo.

OX40 is a T cell costimulatory molecule that belongs to the TNFR superfamily. In the absence of immune activation, OX40 is selectively expressed by Foxp3(+) regulatory T cells (Tregs), but not by resting conventional T cells. The exact role of OX40 in Treg homeostasis and function remains incompletely defined. In this study, we demonstrate that OX40 engagement in vivo in naive mice induces initial expansion of Foxp3(+) Tregs, but the expanded Tregs have poor suppressive function and exhibit features of exhaustion. We also show that OX40 enables the activation of the Akt and Stat5 pathways in Tregs, resulting in transient proliferation of Tregs and reduced levels of Foxp3 expression. This creates a state of relative IL-2 deficiency in naive mice that further impacts Tregs. This exhausted Treg phenotype can be prevented by exogenous IL-2, as both OX40 and IL-2 agonists drive further expansion of Tregs in vivo. Importantly, Tregs expanded by both OX40 and IL-2 agonists are potent suppressor cells, and in a heart transplant model, they promote long-term allograft survival. Our data reveal a novel role for OX40 in promoting immune tolerance and may have important clinical implications.

NF-κB­inducing kinase plays an essential T cell­intrinsic role in graft-versus-host disease and lethal autoimmunity in mice.

NF-κB­inducing kinase (NIK) is an essential upstream kinase in noncanonical NF-κB signaling. NIK-dependent NF-κB activation downstream of several TNF receptor family members mediates lymphoid organ development and B cell homeostasis. Peripheral T cell populations are normal in the absence of NIK, but the role of NIK during in vivo T cell responses to antigen has been obscured by other developmental defects in NIK-deficient mice. Here, we have identified a T cell­intrinsic requirement for NIK in graft-versus-host disease (GVHD), wherein NIK-deficient mouse T cells transferred into MHC class II mismatched recipients failed to cause GVHD. Although NIK was not necessary for antigen receptor signaling, it was absolutely required for costimulation through the TNF receptor family member OX40 (also known as CD134). When we conditionally overexpressed NIK in T cells, mice suffered rapid and fatal autoimmunity characterized by hyperactive effector T cells and poorly suppressive Foxp3(+) Tregs. Together, these data illuminate a critical T cell­intrinsic role for NIK during immune responses and suggest that its tight regulation is critical for avoiding autoimmunity.

Activation of OX40 prolongs and exacerbates autoimmune experimental uveitis.

PURPOSE: T cells are essential for the development of autoimmune uveitis. Although the costimulatory molecule OX40 promotes T-cell function and expansion, it is unclear whether OX40 is implicated in ocular inflammation. The purpose of this study was to examine the role of OX40 in uveitis. METHODS: Experimental autoimmune uveitis (EAU) was induced in B10.RIII mice by subcutaneous injection of interphotoreceptor retinoid-binding protein peptide 161-180 (IRBP(161-180)). Some mice received an intravenous administration of OX40-activating antibody on days 0 and 4 after IRBP(161-180) sensitization or on days 10 and 14 of uveitis onset. The severity of EAU was evaluated by histology at different time points. In addition, ocular inflammatory cytokine expression was determined by real time-PCR, and peripheral activated CD4(+)CD44(+)CD62L(-) T cells and IL-7Rα expression were analyzed by flow cytometry. The activated CD4(+)CD44(+) lymphocytes were rechallenged with IRBP(161-180) in vitro to assess their antigen recall response. RESULTS: The authors demonstrated a marked OX40 expression by infiltrating lymphocytes in enucleated human eyes with end-stage inflammation. In addition, the administration of OX40-activating antibody prolonged and exacerbated the disease course of EAU. Moreover, activation of OX40 not only increased CD4(+)CD44(+)CD62L(-) lymphocyte number, it upregulated IL-7Rα expression in the activated T-cell population. Lastly, these cells exhibited a stronger interferon-γ response to IRBP(161-180) restimulation in vitro. CONCLUSIONS: The results reveal a pathogenic role of OX40 in uveitis. Furthermore, the upregulation of IL-7R in CD4(+)CD44(+) lymphocytes suggests that the activation of OX40 promotes the generation or expansion of uveitogenic memory T cells.

OX40 complexes with phosphoinositide 3-kinase and protein kinase B (PKB) to augment TCR-dependent PKB signaling.

T lymphocyte activation requires signal 1 from the TCR and signal 2 from costimulatory receptors. For long-lasting immunity, growth and survival signals imparted through the Akt/protein kinase B (PKB) pathway in activated or effector T cells are important, and these can be strongly influenced by signaling from OX40 (CD134), a member of the TNFR superfamily. In the absence of OX40, T cells do not expand efficiently to Ag, and memory formation is impaired. How most costimulatory receptors integrate their signals with those from Ag through the TCR is not clear, including whether OX40 directly recruits PKB or molecules that regulate PKB. We show that OX40 after ligation by OX40L assembled a signaling complex that contained the adapter TNFR-associated factor 2 as well as PKB and its upstream activator phosphoinositide 3-kinase (PI3K). Recruitment of PKB and PI3K were dependent on TNFR-associated factor 2 and on translocation of OX40 into detergent-insoluble membrane lipid microdomains but independent of TCR engagement. However, OX40 only resulted in strong phosphorylation and functional activation of the PI3K-PKB pathway when Ag was recognized. Therefore, OX40 primarily functions to augment PKB signaling in T cells by enhancing the amount of PI3K and PKB available to the TCR. This highlights a quantitative role of this TNFR family second signal to supplement signal 1.

Activation of OX40 augments Th17 cytokine expression and antigen-specific uveitis.

Uveitis is a major and common cause of visual disability. Recent studies have shown that Th17 cells are implicated in the pathogenesis of this serious intraocular disorder. Activated T cells express an inducible costimulatory molecule called OX40, and OX40 in turn promotes the activation and proliferation of these lymphocytes. Nevertheless, it is unclear whether OX40 plays a vital role in enhancing the effector function of Th17 cells as well as the severity of uveitis. In this study, we demonstrated an increase of OX40 transcription in ovalbumin-induced uveitis, whereas anti-OX40L antibody substantially inhibited the antigen-specific ocular inflammation. Next, results from flow cytometry showed that activated Th17 cells expressed OX40, and OX40-activating antibody significantly augmented the production of Th17 cytokines in vitro. To validate the impact of OX40 in vivo, we stimulated ovalbumin-specific T cells with the OX40-activating antibody. Compared to donor cells without OX40 activation, adoptive transfer of OX40-stimulated lymphocytes elicited more severe ocular inflammation. Furthermore, an interleukin-17-neutralizing antibody attenuated OX40-mediated uveitis. In conclusion, our findings suggest that activation of OX40 augments Th17 cell function and thereby contributes to ocular inflammation. This study thus enhances our knowledge of costimulatory molecule-mediated immunopathological mechanisms of uveitis and suggests a future therapeutic strategy to treat uveitis by the targeting of OX40.

The cytolytic molecules Fas ligand and TRAIL are required for murine thymic graft-versus-host disease.

Thymic graft-versus-host disease (tGVHD) can contribute to profound T cell deficiency and repertoire restriction after allogeneic BM transplantation (allo-BMT). However, the cellular mechanisms of tGVHD and interactions between donor alloreactive T cells and thymic tissues remain poorly defined. Using clinically relevant murine allo-BMT models, we show here that even minimal numbers of donor alloreactive T cells, which caused mild nonlethal systemic graft-versus-host disease, were sufficient to damage the thymus, delay T lineage reconstitution, and compromise donor peripheral T cell function. Furthermore, to mediate tGVHD, donor alloreactive T cells required trafficking molecules, including CCR9, L selectin, P selectin glycoprotein ligand-1, the integrin subunits alphaE and beta7, CCR2, and CXCR3, and costimulatory/inhibitory molecules, including Ox40 and carcinoembryonic antigen-associated cell adhesion molecule 1. We found that radiation in BMT conditioning regimens upregulated expression of the death receptors Fas and death receptor 5 (DR5) on thymic stromal cells (especially epithelium), while decreasing expression of the antiapoptotic regulator cellular caspase-8-like inhibitory protein. Donor alloreactive T cells used the cognate proteins FasL and TNF-related apoptosis-inducing ligand (TRAIL) (but not TNF or perforin) to mediate tGVHD, thereby damaging thymic stromal cells, cytoarchitecture, and function. Strategies that interfere with Fas/FasL and TRAIL/DR5 interactions may therefore represent a means to attenuate tGVHD and improve T cell reconstitution in allo-BMT recipients.

Pathogenic roles of CD14, galectin-3, and OX40 during experimental cerebral malaria in mice.

An in-depth knowledge of the host molecules and biological pathways that contribute towards the pathogenesis of cerebral malaria would help guide the development of novel prognostics and therapeutics. Genome-wide transcriptional profiling of the brain tissue during experimental cerebral malaria (ECM ) caused by Plasmodium berghei ANKA parasites in mice, a well established surrogate of human cerebral malaria, has been useful in predicting the functional classes of genes involved and pathways altered during the course of disease. To further understand the contribution of individual genes to the pathogenesis of ECM, we examined the biological relevance of three molecules -- CD14, galectin-3, and OX40 that were previously shown to be overexpressed during ECM. We find that CD14 plays a predominant role in the induction of ECM and regulation of parasite density; deletion of the CD14 gene not only prevented the onset of disease in a majority of susceptible mice (only 21% of CD14-deficient compared to 80% of wildtype mice developed ECM, p<0.0004) but also had an ameliorating effect on parasitemia (a 2 fold reduction during the cerebral phase). Furthermore, deletion of the galectin-3 gene in susceptible C57BL/6 mice resulted in partial protection from ECM (47% of galectin-3-deficient versus 93% of wildtype mice developed ECM, p<0.0073). Subsequent adherence assays suggest that galectin-3 induced pathogenesis of ECM is not mediated by the recognition and binding of galectin-3 to P. berghei ANKA parasites. A previous study of ECM has demonstrated that brain infiltrating T cells are strongly activated and are CD44(+)CD62L(-) differentiated memory T cells [1]. We find that OX40, a marker of both T cell activation and memory, is selectively upregulated in the brain during ECM and its distribution among CD4(+) and CD8(+) T cells accumulated in the brain vasculature is approximately equal.

Mast cells counteract regulatory T-cell suppression through interleukin-6 and OX40/OX40L axis toward Th17-cell differentiation.

The development of inflammatory diseases implies inactivation of regulatory T (Treg) cells through mechanisms that still are largely unknown. Here we showed that mast cells (MCs), an early source of inflammatory mediators, are able to counteract Treg inhibition over effector T cells. To gain insight into the molecules involved in their interplay, we set up an in vitro system in which all 3 cellular components were put in contact. Reversal of Treg suppression required T cell-derived interleukin-6 (IL-6) and the OX40/OX40L axis. In the presence of activated MCs, concomitant abundance of IL-6 and paucity of Th1/Th2 cytokines skewed Tregs and effector T cells into IL-17-producing T cells (Th17). In vivo analysis of lymph nodes hosting T-cell priming in experimental autoimmune encephalomyelitis revealed activated MCs, Tregs, and Th17 cells displaying tight spatial interactions, further supporting the occurrence of an MC-mediated inhibition of Treg suppression in the establishment of Th17-mediated inflammatory responses.

Synergistic OX40 and CD30 signals sustain CD8+ T cells during antigenic challenge.

Prior to acquiring a memory phenotype, antigen-activated CD8(+) T cells need to expand and then undergo a contraction phase. Utilizing two different antigenic stimuli, we provide evidence that the tumor necrosis factor receptors OX40 and CD30 integrate synergistic signals during the expansion phase to help maintain CD8(+) effectors. Thus, double deficiency in OX40 and CD30 leads to CD8(+) cell loss during expansion after immunization either with OVA or with murine CMV. Following their contraction, OX40- and CD30-deficient CD8(+) T cells persist normally in CMV-infected mice. In contrast, persistence after OVA challenge is dependent on OX40 and CD30. Collectively, our data define the important role of both OX40 and CD30 during CD8(+) T-cell activation, and show that long-term CD8 persistence after contraction is regulated not only by stimulatory receptors but also by the nature of the antigen or how the antigen is presented.

OX40-enhanced tumor rejection and effector T cell differentiation decreases with age.

OX40 agonists have potent immunotherapeutic effects against a variety of murine tumors, yet it is unclear the role that age-related immune senescence plays on their efficacy. We found that middle-aged and elderly tumor-bearing mice (12 and 20 mo old, respectively) treated with anti-OX40 were less responsive compared with young mice 6 mo or less of age. Decreased tumor-free survival was observed in both male and female mice, and was not due to changes in the surface expression of OX40 on T cells in older animals. Enumeration of cytokine-producing effector T cells in tumor-bearing mice revealed a significant decline in these cells in the older mice treated with anti-OX40 compared with their younger counterparts. The decrease of this critical T cell population in middle-aged mice was not a result of inherent T cell deficiencies, but was revealed to be T cell extrinsic. Finally, combining IL-12, an innate cytokine, with anti-OX40 boosted levels of differentiated effector T cells in the older anti-OX40-treated mice and partially restored the defective antitumor responses in the middle-aged mice. Our data show that the anti-OX40-enhancement of tumor immunity and effector T cell numbers is decreased in middle-aged mice and was partially reversed by coadministration of the proinflammatory cytokine IL-12.

Antagonism of airway tolerance by endotoxin/lipopolysaccharide through promoting OX40L and suppressing antigen-specific Foxp3+ T regulatory cells.

Respiratory exposure to allergens can lead to airway tolerance. Factors that antagonize tolerance mechanisms in the lung might result in susceptibility to diseases such as asthma. We show that inhalation of endotoxin/LPS with Ag prevented airway tolerance and abolished protection from T cell-driven asthmatic lung inflammation. Under conditions leading to tolerance, adaptive Ag-specific CD4(+)Foxp3(+) T regulatory cells (Treg) were generated following exposure to intranasal Ag and outnumbered IL-4- and IFN-gamma-producing CD4 T cells by 100:1 or greater. Inhaled LPS altered the ratio of Treg to IL-4(+) or IFN-gamma(+) T cells by concomitantly suppressing Treg generation and promoting effector T cell generation. LPS induced OX40L expression on dendritic cells and B cells that resulted in a synergistic activity between TLR4 and OX40 signals, leading to production of IL-4, IFN-gamma, and IL-6, which blocked Treg development. Furthermore, inhibiting OX40/OX40L interactions prevented LPS from suppressing tolerance, and resulted in the generation of greater numbers of adaptive Treg. Thus, cooperation between TLR4 and OX40 controls susceptibility to developing airway disease via modulating the balance between adaptive Treg and IL-4(+) or IFN-gamma(+) T cells. Targeting OX40L then has the potential to improve the efficacy of Ag immunotherapy to promote tolerance.

OX40 costimulatory signals potentiate the memory commitment of effector CD8+ T cells.

A T cell costimulatory molecule, OX40, contributes to T cell expansion, survival, and cytokine production. Although several roles for OX40 in CD8(+) T cell responses to tumors and viral infection have been shown, the precise function of these signals in the generation of memory CD8(+) T cells remains to be elucidated. To address this, we examined the generation and maintenance of memory CD8(+) T cells during infection with Listeria monocytogenes in the presence and absence of OX40 signaling. We used the expression of killer cell lectin-like receptor G1 (KLRG1), a recently reported marker, to distinguish between short-lived effector and memory precursor effector T cells (MPECs). Although OX40 was dispensable for the generation of effector T cells in general, the lack of OX40 signals significantly reduced the number and proportion of KLRG1(low) MPECs, and, subsequently, markedly impaired the generation of memory CD8(+) T cells. Moreover, memory T cells that were generated in the absence of OX40 signals in a host animal did not show self-renewal in a second host, suggesting that OX40 is important for the maintenance of memory T cells. Additional experiments making use of an inhibitory mAb against the OX40 ligand demonstrated that OX40 signals are essential during priming, not only for the survival of KLRG1(low) MPECs, but also for their self-renewing ability, both of which contribute to the homeostasis of memory CD8(+) T cells.

Immune regulation and control of regulatory T cells by OX40 and 4-1BB.

The TNFR family members OX40 (CD134) and 4-1BB (CD137) have been found to play major roles as costimulatory receptors for both CD4 and CD8 T cells. In particular, in many situations, they can control proliferation, survival, and cytokine production, and hence are thought to dictate accumulation of protective T cells during anti-viral and anti-tumor responses and pathogenic T cells during autoimmune reactions. As opposed to simply controlling the activity of naïve, effector, and memory T cells, recent data have suggested that both molecules are also instrumental in controlling the generation and activity of so-called regulatory or suppressor T cells (Treg), perhaps in both positive and negative manners. Part of the action on Treg might function to further promote protective or pathogenic T cells, but alternate activities of OX40 and 4-1BB on Treg are also being described that suggest that there might be control by these molecules at multiple levels that will alter the biological outcome when these receptors are ligated. This review specifically focuses on recent studies of regulatory T cells, and regulatory or suppressive activity, that are modulated by OX40 or 4-1BB.