OX40 Engagement Research Articles

OX40 agonist stimulation increases and sustains humoral and cell-mediated responses to SARS-CoV-2 protein and saRNA vaccines.

To prevent SARS-CoV-2 infections and generate long-lasting immunity, vaccines need to generate strong viral-specific B and T cell responses. Previous results from our lab and others have shown that immunizations in the presence of an OX40 agonist antibody lead to higher antibody titers and increased numbers of long-lived antigen-specific CD4 and CD8 T cells. Using a similar strategy, we explored the effect of OX40 co-stimulation in a prime and boost vaccination scheme using an adjuvanted SARS-CoV-2 spike protein vaccine in C57BL/6 mice. Our results show that OX40 engagement during vaccination significantly increases long-lived antibody responses to the spike protein. In addition, after immunization spike protein-specific proliferation was greatly increased for both CD4 and CD8 T cells, with enhanced, spike-specific secretion of IFN-γ and IL-2. Booster (3rd injection) immunizations combined with an OX40 agonist (7 months post-prime) further increased vaccine-specific antibody and T cell responses. Initial experiments assessing a self-amplifying mRNA (saRNA) vaccine encoding the spike protein antigen show a robust antigen-specific CD8 T cell response. The saRNA spike-specific CD8 T cells express high levels of GrzmB, IFN-γ and TNF-α which was not observed with protein immunization and this response was further increased by the OX40 agonist. Similar to protein immunizations the OX40 agonist also increased vaccine-specific CD4 T cell responses. In summary, this study compares and contrasts the effects and benefits of both protein and saRNA vaccination and the extent to which an OX40 agonist enhances and sustains the immune response against the SARS-CoV-2 spike protein.

OX40 boosts and sustains humoral and cellular immune responses to SARS-CoV2 spike protein and RNA vaccinations

Abstract To prevent SARS-CoV-2 infections and generate long-lasting immunity, vaccines need to generate both, a strong humoral immune response as well as viral-specific CD4 and CD8 T cells. Previous results from our lab have shown that immunization in the presence of an agonist antibody targeting OX40 led to higher antibody titers and increased numbers of antigen-specific CD4 and CD8 T cells. Using the same strategy, we explored the effect of OX40 co-stimulation in the prime and boost together with the SARS-CoV-2 spike protein + adjuvant in C57Bl/6 mice. Our results show that OX40 engagement led to a significant increase in long-lived antibody responses when compared to mice that did not receive additional co-stimulation. In addition, spike protein and peptide-specific proliferation were greatly increased for both CD4 and CD8 T cells, with augmented secretion of IFN-γ, TNF-α and IL-2. Booster immunizations (7 months post prime) did not lead to anergy, but instead further increased the antibody and T cell responses. In initial experiments, the self-amplifying RNA (saRNA) vaccination generated lower antibody titers, independent of OX40 co-stimulation. However, the saRNA vaccine did induce a robust expansion of antigen-specific CD8 T cells, that expressed high levels of GrzmB, which was further increased by OX40 administration. The strong immune responses and the differential effects of the protein and saRNA vaccines suggest that heterologous prime-boost approaches, as currently approved in adults, might be beneficial in boosting different arms of the anti-viral immune response against SARS-CoV2, with OX40 agonists enhancing both approaches. Further studies in animals will aid defining the effects and benefits of this approach.

Abstract CT097: A first-in-human phase I dose escalation study of the OX40 agonist MOXR0916 in patients with refractory solid tumors

Abstract Background: OX40 is a co-stimulatory receptor that is transiently expressed by T cells upon antigen recognition. In murine models, OX40 engagement by an agonist anti-OX40 antibody can promote durable tumor regression associated with co-stimulation of effector T cells and reduction of regulatory T cells. MOXR0916 is a humanized effector-competent agonist IgG1 monoclonal antibody that targets OX40. Methods: A Phase I, open-label, multicenter study was conducted to evaluate the safety and pharmacokinetics (PK) of MOXR0916 in patients (pts) with locally advanced or metastatic refractory solid tumors that have progressed after available standard therapy. MOXR0916 was administered at fixed doses every 3 weeks (q3w), and treatment beyond RECIST progression was permitted in the absence of clinical deterioration. A 3+3 dose-escalation was conducted in immunotherapy-naïve pts with a 21-day window to evaluate dose-limiting toxicity (DLT). A dedicated expansion cohort enrolled pts who consented to serial tumor biopsies, enabling immune profiling by immunohistochemistry and gene expression methods. In the biopsy cohort, prior immunotherapy with adequate washout was permitted, provided there was no history of Grade (G) ?3 immune-mediated adverse events (AEs). Results: Enrollment in the dose-finding phase of the trial is complete, with 34 pts treated across 10 dose escalation cohorts (dose levels 0.2-1200 mg) and 36 pts treated in the serial biopsy cohort (dose levels 3.2-600 mg). While NSCLC (n = 8), clear cell RCC (n = 6), melanoma (n = 2), and bladder (n = 2) were represented, less immunogenic tumor types predominated. The median number of prior regimens for metastatic disease was 2 (range 0-9); 4 pts had received prior checkpoint inhibitors. As of 11 Jan 2016, no DLTs, G4/5 AEs attributed to study treatment, or AEs leading to treatment discontinuation were reported. The majority of treatment-related AEs were G1 in severity; 4 related G3 events (autoimmune hepatitis responsive to steroids, worsening dyspnea in a pt with malignant pleural effusions, hypertension, and fatigue) were reported. At doses ?40 mg q3w, PK was linear and sustained peripheral blood OX40 receptor saturation was achieved. Tumor pharmacodynamic (PD) biomarker modulation supportive of the mechanism of action was observed in a subset of pts. Eleven of 70 pts (16%) have been treated with MOXR0916 for > 6 months (?9 cycles) with a best response of stable disease per RECIST v1.1. Updated clinical data will be presented. Conclusions: In a heterogeneous, refractory population, MOXR0916 was well-tolerated at all doses evaluated. The recommended dose and schedule based on PK and OX40 receptor saturation is 300 mg q3w. Tumor PD modulation and evidence of prolonged stable disease support the ongoing expansion phase to evaluate anti-tumor activity in select indications and Phase Ib trial in combination with atezolizumab (anti-PD-L1). Citation Format: Aaron R. Hansen, Jeffrey R. Infante, Grant McArthur, Michael S. Gordon, Alexander M. Lesokhin, Ann-Lee Stayner, Todd M. Bauer, Shahneen Sandhu, Frank Tsai, Alexandra Snyder, Deepa S. Subramaniam, Jeong Kim, Eric Stefanich, Chi-Chung Li, Jane Ruppel, Maria Anderson, Houston Gilbert, Bruce McCall, Mahrukh A. Huseni, Ina Rhee, Michael Pishvaian. A first-in-human phase I dose escalation study of the OX40 agonist MOXR0916 in patients with refractory solid tumors. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr CT097.

A phase Ib dose escalation study of the OX40 agonist MOXR0916 and the PD-L1 inhibitor atezolizumab in patients with advanced solid tumors.

101Background: OX40 is a co-stimulatory receptor that is transiently expressed by T cells upon antigen recognition. In murine models, OX40 engagement by an agonist anti-OX40 antibody can promote durable tumor regression associated with co-stimulation of effector T cells and reduction of regulatory T cells. This dual mechanism of action is predicted to complement the activity of PD-L1 blockade. MOXR0916 is a humanized effector-competent agonist IgG1 monoclonal antibody (mAb) that targets OX40 and atezolizumab is an engineered humanized IgG1 mAb that targets PD-L1. Methods: A Phase I, open-label, multicenter study was conducted to evaluate the safety and pharmacokinetics (PK) of MOXR0916 and atezolizumab in patients (pts) with locally advanced or metastatic solid tumors. A 3+3 dose-escalation was conducted with a 21-day window to evaluate dose-limiting toxicity (DLT). Escalating doses of MOXR0916 in combination with a fixed 1200 mg dose of atezolizumab were administered every 3 weeks (q3w). An expansion coh...

OX40 signaling activates epigenetic mechanisms to repress Th17 cells and Th17-related autoimmune diseases (LYM5P.708)

Abstract Th17 cells produce copious amount of IL-17, which mediates host antimicrobial responses and autoimmune diseases. The exact mechanisms that control Th17 homeostasis, especially those that inhibit Th17 differentiation, remain incompletely defined. Here, we found that the T cell costimulatory molecule OX40 is a potent repressor of Th17 cells and Th17-mediated autoimmune disease. Under Th17-polarizing conditions in vitro, engagement of OX40 strongly inhibited IL-17 production despite enhanced cell survival and proliferation. Mechanistically, OX40 engagement induced sustained activation of both canonical and non-canonical NF-kB pathways, and it is RelB that mediated dominant suppression of Th17 cells that is independent of p52 and p50. RelB directly recruited H3K9 methyltransferases G9a and Setdb1 upon binding to IL-17 locus, and this resulted in di- and tri-methylation of H3K9, which led to a closed epigenetic configuration of IL-17 locus that prevents RORγt binding to IL-17 locus. Conversely, inhibition of histone methyltransferase activity significantly reversed OX40-mediated suppression of Th17 cells. Importantly, in an EAE model, stimulation of OX40 in vivo inhibited the disease process, while RelB-deficient CD4+ T cells induced exacerbated disease. In conclusion, our study identified a new mechanism in the control of Th17 cells, and this mechanism relies on OX40 induced repressive epigenetic process. This finding may have important therapeutic implications in the clinic.

Identification of Novel Mechanisms of Tolerance Resistance Induced By OX40.

Induction of donor specific tolerance remains an important goal in transplantation and to identify and overcome barriers to tolerance will significantly improve transplant outcomes in the clinic. In the present study, we examined the effector programs that evade tolerance induction by costimulatory blockade in a mouse heart transplant model. Blocking CD40-CD40L costimulation using an anti-CD40L monoclonal antibody (MR1) induced prolonged survival of C57BL/6 heart allografts in BALB/c recipients (MST>60 days). However, we found that MR1 completely failed to prolong survival of heart allografts that express the OX40L transgene (OX40Ltg grafts) (MST=9 days), indicating that OX40 signaling evades tolerance induction by costimulatory blockade. Histologically, rejection of OX40Ltg heart allografts was associated with extensive lymphocyte infiltration, and a significant proportion of graft infiltrating T cells produced IL-9 (40%), while few of them produced IL-4 or IFN-γ, suggesting that OX40 may drive a new mechanism of tolerance resistance. In an in vitro T cell polarization assay, we showed that OX40 engagement inhibited the induction of TH17 cells by TGF-β/IL-6 and that of inducible Treg cells by TGF- β/IL-2. Instead, OX40 diverted CD4+ T cells to IL-9 producing TH9 cells. Mechanistically, OX40 signaling mediated the induction of TH9 cells by triggering noncanonical NF-κB activation in activated T cells. In an in vivo CFSE model in which CD4+ T cells were stimulated by alloantigens, blocking CD40-CD40L costimulation induced TH9 cells only in the presence of OX40 signaling. These data suggest that induction of TH9 cells may constitute a novel mechanism of tolerance resistance. Interestingly, blocking OX40 costimulation induced long-term heart allograft survival (MST>100 days) and markedly reduced transplant vasculopathy (chronic allograft rejection) in CD40L-/- recipient mice. In conclusion, we identified that OX40 dramatically induces the generation of TH9 cells both in vitro and in vivo, and TH9 cells are closely involved in tolerance resistance. These findings may lead to the development of new therapeutics to promote graft tolerance in transplantation.

OX40 engagement depletes intratumoral Tregs via activating FcγRs, leading to antitumor efficacy.

Antibodies targeting checkpoint inhibitors or co-stimulatory receptors on T cells have shown significant antitumor efficacy in preclinical and clinical studies. In mouse tumor models, engagement of activating Fcγ receptor (FcγR)-expressing immune cells was recently shown to be required for the tumoricidal activity of antibodies recognizing the tumor necrosis factor superfamily receptor (TNFR) GITR (CD357) and CTLA-4 (CD152). In particular, activating FcγRs facilitated the selective elimination of intratumoral T-cell populations. However, it remains unclear whether FcγRs contribute to the antitumor efficacy of other immunomodulatory antibodies. Here, we explored the mechanism of antitumor activity mediated by an agonistic antibody (clone OX86) to the co-stimulatory TNFR OX40 (CD134). OX40 was highly expressed by intratumoral T cells, particularly those of the FoxP3(+) regulatory T-cell (Treg) lineage. OX86 administration resulted in the depletion of intratumoral regulatory T cells in an activating FcγR-dependent manner, which correlated with tumor regression. Together with previous data from our group and others, these findings support a mechanism whereby antibodies targeting antigens highly expressed by intratumoral T cells can mediate their elimination by FcγR-expressing immune cells, and facilitate subsequent antitumor immunity.

OX40 Is a Potent Immune-Stimulating Target in Late-Stage Cancer Patients

OX40 is a potent costimulatory receptor that can potentiate T-cell receptor signaling on the surface of T lymphocytes, leading to their activation by a specifically recognized antigen. In particular, OX40 engagement by ligands present on dendritic cells dramatically increases the proliferation, effector function, and survival of T cells. Preclinical studies have shown that OX40 agonists increase antitumor immunity and improve tumor-free survival. In this study, we performed a phase I clinical trial using a mouse monoclonal antibody (mAb) that agonizes human OX40 signaling in patients with advanced cancer. Patients treated with one course of the anti-OX40 mAb showed an acceptable toxicity profile and regression of at least one metastatic lesion in 12 of 30 patients. Mechanistically, this treatment increased T and B cell responses to reporter antigen immunizations, led to preferential upregulation of OX40 on CD4(+) FoxP3(+) regulatory T cells in tumor-infiltrating lymphocytes, and increased the antitumor reactivity of T and B cells in patients with melanoma. Our findings clinically validate OX40 as a potent immune-stimulating target for treatment in patients with cancer, providing a generalizable tool to favorably influence the antitumor properties of circulating T cells, B cells, and intratumoral regulatory T cells.

Phase I/II clinical trial of anti-OX40, radiation and cyclophosphamide in patients with prostate cancer: immunological analysis

Meeting abstracts OX40, a member of the Tumor Necrosis Factor Receptor superfamily is a potent co-stimulatory molecule. OX40 engagement increases T cell proliferation, effector function and survival. Pre-clinical studies have shown that OX40 agonist synergizes with radiation and cyclophosphamide to

OX40 engagement promotes potent tumoricidial CD4+ T cells (P2199)

Abstract Several immune-based strategies are currently used to treat melanoma in the clinic; however, very few result in a complete response. CD4+ T cells are potent mediators of anti-tumor immunity and adoptive transfer of specific CD4+ T cells leads to tumor regression. OX40, a costimulatory molecule expressed primarily on activated CD4+ T cells, promotes and enhances anti-tumor immunity with limited success on large tumors in mice. Here we show that OX40 engagement induces a novel CD4+ T cell population characterized by the expression of the master regulator eomesodermin that leads to both terminal differentiation and central memory phenotype, with concomitant secretion of Th1 and Th2 cytokines. This subpopulation of CD4+ T cells eradicates very advanced melanomas in mice, and an analogous population of human tumor-specific CD4+ T cells can kill melanoma in an in vitro system. Interestingly, the combination therapy effectively eliminates tumor escape variants. Our results show that these uniquely programmed effector CD4+ T cells have a distinctive phenotype with increased tumoricidal capability and support the use of immune modulation in reprogramming the phenotype of CD4+ T cells

Induction of tumoricidal function in CD4+ T cells is associated with concomitant memory and terminally differentiated phenotype

Harnessing the adaptive immune response to treat malignancy is now a clinical reality. Several strategies are used to treat melanoma; however, very few result in a complete response. CD4(+) T cells are important and potent mediators of anti-tumor immunity and adoptive transfer of specific CD4(+) T cells can promote tumor regression in mice and patients. OX40, a costimulatory molecule expressed primarily on activated CD4(+) T cells, promotes and enhances anti-tumor immunity with limited success on large tumors in mice. We show that OX40 engagement, in the context of chemotherapy-induced lymphopenia, induces a novel CD4(+) T cell population characterized by the expression of the master regulator eomesodermin that leads to both terminal differentiation and central memory phenotype, with concomitant secretion of Th1 and Th2 cytokines. This subpopulation of CD4(+) T cells eradicates very advanced melanomas in mice, and an analogous population of human tumor-specific CD4(+) T cells can kill melanoma in an in vitro system. The potency of the therapy extends to support a bystander killing effect of antigen loss variants. Our results show that these uniquely programmed effector CD4(+) T cells have a distinctive phenotype with increased tumoricidal capability and support the use of immune modulation in reprogramming the phenotype of CD4(+) T cells.

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.

OX40 engagement stabilizes Mxd4 and Mnt protein levels in antigen‐stimulated T cells leading to an increase in cell survival

OX40 engagement on activated T cells leads to increased proliferation, expansion and survival of Ag-specific T cells. Direct ex vivo examination of Ag-stimulated murine T cells show that the Myc antagonists, Mxd4 and Mnt, are transiently upregulated and translocated to the nucleus following OX40 engagement and may be involved in suppressing cell death. Both Mxd4 and Mnt are upregulated following OX40 stimulation through increased protein stability and we identify a critical phosphorylation site in Mxd4 that controls Mxd4 stability. The upregulation of Mxd4 and Mnt contributes to OX40-mediated T-cell survival because siRNA knockdown of Mxd4 and Mnt led to increased cell death. We hypothesize the upregulation of c-Myc following OX40 engagement drives T-cell proliferation and that upregulation of Mxd4 and Mnt suppresses Myc-dependent cell death. Thus, Mxd4 and Mnt upregulation following OX40 engagement most likely increases T-cell survival.

Abstract 2938: A novel OX40 agonist licenses systemic anti-tumor immunity to overcome local immune suppression induced by well-established tumors

Abstract Immune modulating reagents that trigger the T cell costimulatory molecules GITR and OX40 are being evaluated as anti-cancer agents in early-stage clinical trials. However, little pre-clinical information is available regarding the efficacy and mechanism(s) of action for these agents in the setting of advanced, well-established disease. To further characterize the molecular, cellular, and treatment-associated consequences of GITR and OX40 engagement, novel agonistic reagents directed against murine GITR and OX40 (ligand-Fc fusion proteins) were recently constructed and characterized in vitro. We now show that the growth of well-established, day 17 sarcomas is significantly inhibited or ablated by a short course of either treatment, with OX40L-Fc demonstrating superior anti-tumor efficacy over GITRL-Fc at comparable doses. Despite diminished frequencies of CD4+Foxp3+ regulatory T cells (Treg) in the tumor microenvironment (TME) 3 days post-treatment, the presence of myeloid-derived suppressor cells (MDSC) and inhibitory cytokines such as IL-10 and TGFβ appears unaltered and effector T cell production of the Type-1 cytokine IFNγ remains low. Treatment with either GITR or OX40 agonists, however, induces a coordinate increase in CCR7+ dendritic cells in the tumor-draining lymph nodes (TDLN), followed approximately 7 days after treatment by profound expansion of effector T cells expressing the Type-1 chemokine receptor CXCR3. By day 10 post-treatment, particularly with the OX40 agonist, T cells displaying a recently-activated effector phenotype accumulate in the tumor microenvironment and secrete high levels of IFNγ. Collectively, these data suggests a model in which the first level effect of costimulatory treatment is to direct CCR7+ dendritic cells from the TME to the draining lymph nodes. A secondary, systemic response reflects the expansion of highly-reactive CXCR3+ Type-1 T cells in the TDLN and their subsequent trafficking into the TME. The therapeutic efficacy demonstrated in this model by OX40L-Fc, and to a lesser extent GITRL-Fc, strongly supports the translation of such modalities into human clinical trials, while the mechanistic insight gained from these studies suggests that successful immunotherapies will license both local, and perhaps more importantly, systemic Type-1 T cell immunity. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 2938.

Serial OX40 Engagement on CD4+T Cells and Natural Killer T Cells Causes Allergic Airway Inflammation

OX40-OX40 ligand (OX40L) interactions have been proposed to support induction of allergic airway inflammation, which may be attributable to OX40 signaling in CD4(+) helper T cells for adaptive immune responses. However, a possible involvement of natural killer T (NKT) cells in the pathogenesis suggests that the underlying mechanisms are not yet fully elucidated. We aimed to characterize the OX40-modulated cellular contribution to allergic airway inflammation in a mouse model of house dust mite (HDM) allergen exposure. Mice were sensitized to HDM and, 3 weeks later, challenged with HDM on three consecutive days through the airways. Two days after the last exposure, bronchoalveolar lavage fluids and blood samples and lung tissues were evaluated for the airway inflammation. The development of HDM-induced eosinophilic airway inflammation was dependent on OX40 of both CD4(+) T cells and NKT cells; OX40 engagement on CD4(+) T cells in the sensitization led to pulmonary OX40L augmentation after the allergen challenge, which stimulated pulmonary NKT cells through OX40 to provide the pathogenic cytokine milieu. This was ablated by OX40L blockade by inhalation of the neutralizing antibody during the challenge, suggesting the therapeutic potential of targeting pulmonary OX40-OX40L interactions. Moreover, OX40 expression in CD4(+) T cells, but not in NKT cells, was reciprocally regulated by the helper T cell type 1-skewing transcription factor Runx3. OX40 on not only CD4(+) T cells but also NKT cells is involved in allergic airway inflammation. Notably, pulmonary blockade of OX40 ligation on NKT cells has therapeutic implications.

Cutting Edge: OX40 Agonists Can Drive Regulatory T Cell Expansion if the Cytokine Milieu Is Right

We report that OX40 stimulation drives all lineages of CD4 T cell development, including regulatory T cells (Tregs), and the plasticity of the response is dependant on local cytokines. In TGF-beta1-treated cultures, an OX40 agonist increased IFN-gamma and IL-4 production and diverted T cells from the Treg lineage. However, cytokine blockade in the context of OX40 stimulation promoted enhanced Treg accumulation. This observation was evident in naive mice, as OX40 engagement enhanced Treg proliferation and accumulation in vivo. Lastly, OX40 agonist administration influenced experimental autoimmune encephalomyelitis disease severity in opposing directions, depending on the timing of administration. Given during Ag priming, the OX40 agonist drove Treg expansion and inhibited disease, whereas given later it enhanced T cell effector cytokine production in the CNS and exacerbated disease. Hence, OX40 signaling can augment the accumulation of all CD4 T cell lineages; however, its accentuation of immune responses may have vastly different biologic outcomes depending upon the local cytokine milieu.

Ligation of the OX40 co‐stimulatory receptor reverses self‐Ag and tumor‐induced CD8 T‐cell anergy in vivo

AbstractTumor‐specific CD8 T‐cell peripheral tolerance occurs through clonal deletion, suppression, and the induction of anergy and can limit the generation of anti‐tumor immunity. Several groups have demonstrated that prostate cancer can render tumor‐specific CD8 T cells anergic, suggesting reversing tumor‐induced anergy may greatly augment anti‐tumor immunity. Recent work has demonstrated that signaling through the OX40 (CD134) co‐stimulatory receptor, a member of the TNFR super‐family, can augment CD4 and CD8 T‐cell expansion, differentiation, and the generation of memory cells. However, whether OX40 ligation can reverse CD8 T‐cell anergy, and more specifically, tumor‐induced CD8 T‐cell anergy, remains unclear. In the current study, we demonstrate that OX40 ligation can reverse CD8 T‐cell anergy to a prostate‐specific self‐Ag in non‐tumor‐bearing hosts. Furthermore, OX40 engagement reversed tumor‐specific CD8 T‐cell anergy and restored the proliferative capacity of tumor‐reactive CD8 T cells, which attenuated tumor growth and enhanced the survival of tumor‐bearing hosts. These data demonstrate that OX40 ligation can rescue the function of anergic self‐ or tumor‐reactive CD8 T cells in vivo and suggests that OX40‐mediated therapy may provide a novel means of boosting anti‐tumor immunity by restoring the responsiveness of previously anergic tumor‐specific CD8 T cells.

Ligation of the OX40 co‐stimulatory receptor reverses self‐Ag and tumor‐induced CD8 T‐cell anergy in vivo

Tumor-specific CD8 T-cell peripheral tolerance occurs through clonal deletion, suppression, and the induction of anergy and can limit the generation of anti-tumor immunity. Several groups have demonstrated that prostate cancer can render tumor-specific CD8 T cells anergic, suggesting reversing tumor-induced anergy may greatly augment anti-tumor immunity. Recent work has demonstrated that signaling through the OX40 (CD134) co-stimulatory receptor, a member of the TNFR super-family, can augment CD4 and CD8 T-cell expansion, differentiation, and the generation of memory cells. However, whether OX40 ligation can reverse CD8 T-cell anergy, and more specifically, tumor-induced CD8 T-cell anergy, remains unclear. In the current study, we demonstrate that OX40 ligation can reverse CD8 T-cell anergy to a prostate-specific self-Ag in non-tumor-bearing hosts. Furthermore, OX40 engagement reversed tumor-specific CD8 T-cell anergy and restored the proliferative capacity of tumor-reactive CD8 T cells, which attenuated tumor growth and enhanced the survival of tumor-bearing hosts. These data demonstrate that OX40 ligation can rescue the function of anergic self- or tumor-reactive CD8 T cells in vivo and suggests that OX40-mediated therapy may provide a novel means of boosting anti-tumor immunity by restoring the responsiveness of previously anergic tumor-specific CD8 T cells.

OX40 engagement and chemotherapy combination provides potent antitumor immunity with concomitant regulatory T cell apoptosis

Expansion and recruitment of CD4+ Foxp3+ regulatory T (T reg) cells are mechanisms used by growing tumors to evade immune elimination. In addition to expansion of effector T cells, successful therapeutic interventions may require reduction of T reg cells within the tumor microenvironment. We report that the combined use of the alkylating agent cyclophosphamide (CTX) and an agonist antibody targeting the co-stimulatory receptor OX40 (OX86) provides potent antitumor immunity capable of regressing established, poorly immunogenic B16 melanoma tumors. CTX administration resulted in tumor antigen release, which after OX86 treatment significantly enhanced the antitumor T cell response. We demonstrated that T reg cells are an important cellular target of the combination therapy. Paradoxically, the combination therapy led to an expansion of T reg cells in the periphery. In the tumor, however, the combination therapy induced a profound T reg cell depletion that was accompanied by an influx of effector CD8+ T cells leading to a favorable T effector/T reg cell ratio. Closer examination revealed that diminished intratumoral T reg cell levels resulted from hyperactivation and T reg cell–specific apoptosis. Thus, we propose that CTX and OX40 engagement represents a novel and rational chemoimmunotherapy.

The role of Mad, Mnt and c-Myc proteins in OX40 stimulated T cells (33.26)

Abstract We sought to determine the molecular mechanisms by which OX40 mediates T cell function. Gene array analysis of OX40-activated Ag-specific T cells suggested a role for the transcription factor c-Myc and antagonist Mad family proteins. D011.10 T cells were adoptively transferred into BALB/c recipients and immunized with soluble OVA and an agonist anti-OX40 antibody, which enhances Ag-specific T cell proliferation and survival. Western blot analysis of Ag-specific T cells purified ex vivo revealed that Mad4, Mnt and c-Myc proteins were up-regulated after OX40 engagement. Mad4 and Mnt protein levels peaked at days 3-4 and decreased as the cells contracted in size. C-Myc protein levels remained unchanged over time after OX40 stimulation. We hypothesize that the up-regulation of c-Myc in activated T cells drives proliferation and consequently activation-induced cell death, which is counteracted by Mad4 and Mnt proteins after anti-OX40 engagement, allowing T cells to survive the "blast crisis" phase. Indeed, siRNA knockdown of Mad4 and Mnt proteins led to decreased survival of OX40-activated T cells. We also found that OX40 stabilized both Mad4 and Mnt proteins against degradation and we demonstrated the presence of a serine residue in Mad4 that was essential in mediating accelerated protein degradation. These data provide evidence that Mad4 and Mnt play a role to enhance memory T cell survival after OX40 engagement.