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OX40, a member of the tumor necrosis factor (TNF) receptor superfamily, is expressed on the surface of activated T cells. Upon interaction with its cognate ligand, OX40L, OX40 transmits costimulatory signals to antigen-primed T cells, promoting their activation, differentiation, and survival — processes essential for the establishment of adaptive immunity. Although the OX40-OX40L interaction has been extensively studied in the context of disease treatment, developing a substitute for the naturally expressed membrane-bound OX40L, particularly a multimerized OX40L trimers, that effectively regulates OX40-driven T cell responses remains a significant challenge. In this study, we successfully engineered soluble OX40L-fusion proteins capable of robustly activating OX40 on T cells. This was achieved by incorporating functional multimerization domains into the TNF homology domain of OX40L. These OX40L proteins bound to OX40, subsequently activated NF-κB signaling, and induced cytokine production by T cells in vitro . In vivo , mice treated with one of the OX40L-fusion proteins — comprising a single-chain OX40L trimer linked to the C-terminus of the human IgG1 Fc domain, forming a dimer of trimers — exhibited significantly enhanced clonal expansion of antigen-specific CD4 + T cells during the primary phase of the immune response. A comparable antibody-fusion single-chain TNF protein incorporating 4-1BBL, CD70 (CD27L), or GITRL in place of OX40L elicited similar in vivo T cell responses. Thus, we propose that optimizing the multimerization of OX40L proteins through innovative design strategies may facilitate the development of more effective agonists for targeted immunotherapies.

Immunotherapy is gathering momentum as a primary therapy for cancer patients. However, monotherapies have limited efficacy in improving outcomes and benefit only a subset of patients. Combination therapies targeting multiple pathways can augment an immune response to improve survival further. Here, we demonstrate that dual aOX40 (anti-CD134)/aCTLA-4 (anti–cytotoxic T-lymphocyte–associated protein 4) immunotherapy generated a potent antigen-specific CD8 T-cell response, enhancing expansion, effector function, and memory T-cell persistence. Importantly, OX40 and CTLA-4 expression on CD8 T cells was critical for promoting their maximal expansion following combination therapy. Animals treated with combination therapy and vaccination using anti–DEC-205 (dendritic and epithelial cells, 205 kDa)–HER2 (human epidermal growth factor receptor 2) had significantly improved survival in a mammary carcinoma model. Vaccination with combination therapy uniquely restricted Th2-cytokine production by CD4 cells, relative to combination therapy alone, and enhanced IFNγ production by CD8 and CD4 cells. We observed an increase in MIP-1α (macrophage inflammatory protein-1α)/CCL3 [chemokine (C-C motif) ligand 3], MIP-1β/CCL4, RANTES (regulated on activation, normal T-cell expressed and excreted)/CCL5, and GM-CSF production by CD8 and CD4 T cells following treatment. Furthermore, this therapy was associated with extensive tumor destruction and T-cell infiltration into the tumor. Notably, in a spontaneous model of prostate adenocarcinoma, vaccination with combination therapy reversed anergy and enhanced the expansion and function of CD8 T cells recognizing a tumor-associated antigen. Collectively, these data demonstrate that the addition of a vaccine with combined aOX40/aCTLA-4 immunotherapy augmented antitumor CD8 T-cell function while limiting Th2 polarization in CD4 cells and improved overall survival.

The co-inhibitory receptor Programmed Death-1 (PD-1) curtails immune responses and prevent autoimmunity, however, tumors exploit this pathway to escape from immune destruction. The co-stimulatory receptor OX40 is upregulated on T cells following activation and increases their clonal expansion, survival and cytokine production when engaged. Although antagonistic anti-PD-1 or agonistic anti-OX40 antibodies can promote the rejection of several murine tumors, some poorly immunogenic tumors were refractory to this treatment. In the present study, we evaluated the antitumor effects and mechanisms of combinatorial PD-1 blockade and OX40 triggering in a murine ID8 ovarian cancer model. Although individual anti-PD-1 or OX40 mAb treatment was ineffective in tumor protection against 10-day established ID8 tumor, combined anti-PD-1/OX40 mAb treatment markedly inhibited tumor outgrowth with 60% of mice tumor free 90 days after tumor inoculation. Tumor protection was associated with a systemic immune response with memory and antigen specificity and required CD4(+) cells and CD8(+) T cells. The anti-PD-1/OX40 mAb treatment increased CD4(+) and CD8(+) cells and decreased immunosuppressive CD4(+)FoxP3(+) regulatory T (Treg) cells and CD11b(+)Gr-1(+) myeloid suppressor cells (MDSC), giving rise to significantly higher ratios of both effector CD4(+) and CD8(+) cells to Treg and MDSC in peritoneal cavity; Quantitative RT-PCR data further demonstrated the induction of a local immunostimulatory milieu by anti-PD-1/OX40 mAb treatment. The splenic CD8(+) T cells from combined mAb treated mice produced high levels of IFN-γ upon tumor antigen stimulation and exhibited antigen-specific cytolytic activity. To our knowledge, this is the first study testing the antitumor effects of combined anti-PD-1/OX40 mAb in a murine ovarian cancer model, and our results provide a rationale for clinical trials evaluating ovarian cancer immunotherapy using this combination of mAb.

Eliciting protective titers of HIV-1 broadly neutralizing antibodies (bnAbs) is a goal of HIV-1 vaccine development, but current vaccine strategies have yet to induce bnAbs in humans. Many bnAbs isolated from HIV-1-infected individuals are encoded by immunoglobulin gene rearrangments with infrequent naive B cell precursors and with unusual genetic features that may be subject to host regulatory control. Here, we administer antibodies targeting immune cell regulatory receptors CTLA-4, PD-1 or OX40 along with HIV envelope (Env) vaccines to rhesus macaques and bnAb immunoglobulin knock-in (KI) mice expressing diverse precursors of CD4 binding site HIV-1 bnAbs. CTLA-4 blockade augments HIV-1 Env antibody responses in macaques, and in a bnAb-precursor mouse model, CTLA-4 blocking or OX40 agonist antibodies increase germinal center B and T follicular helper cells and plasma neutralizing antibodies. Thus, modulation of CTLA-4 or OX40 immune checkpoints during vaccination can promote germinal center activity and enhance HIV-1 Env antibody responses. Elucidation of broadly neutralizing antibodies (bnAb) is a goal in HIV vaccine development. Here, Bradley et al. show that administration of CTLA-4 blocking antibody with vaccine antigens increases HIV-1 envelope antibody responses in macaques and a bnAb precursor mouse model.

Tumour-induced expansion of regulatory T (T Reg ) cells is an obstacle to successful cancer immunotherapy. Does it make more sense to suppress the function of these cells rather than deplete them to improve the efficacy of cancer immunotherapy? Tumour-induced expansion of regulatory T (T Reg ) cells is an obstacle to successful cancer immunotherapy. The potential benefit of T Reg -cell depletion through the interleukin-2 receptor is lost by the concurrent elimination of activated effector lymphocytes and possibly by the de novo induction of T Reg -cell replenishment. In theory, the functional inactivation of T Reg cells will maintain them at high numbers in tumours and avoid their replenishment from the peripheral lymphocyte pool, which has the capacity to further suppress the effector lymphocyte anti-tumour response.

After Mycobacterium tuberculosis (Mtb) infection, many effector T cells traffic to the lungs, but few become activated. Here we use an antigen receptor reporter mouse (Nur77-GFP) to identify recently activated CD4 T cells in the lungs. These Nur77-GFP HI cells contain expanded TCR clonotypes, have elevated expression of co-stimulatory genes such as Tnfrsf4 /OX40, and are functionally more protective than Nur77-GFP LO cells. By contrast, Nur77-GFP LO cells express markers of terminal exhaustion and cytotoxicity, and the trafficking receptor S1pr5 , associated with vascular localization. A short course of immunotherapy targeting OX40 + cells transiently expands CD4 T cell numbers and shifts their phenotype towards parenchymal protective cells. Moreover, OX40 agonist immunotherapy decreases the lung bacterial burden and extends host survival, offering an additive benefit to antibiotics. CD4 T cells from the cerebrospinal fluid of humans with HIV-associated tuberculous meningitis commonly express surface OX40 protein, while CD8 T cells do not. Our data thus propose OX40 as a marker of recently activated CD4 T cells at the infection site and a potential target for immunotherapy in tuberculosis. Marking of recently activated T cells may help further our understanding of immunity against Mycobacterium tuberculosis (Mtb). Here the authors use Nur77-GFP reporter mice infected with Mtb and systems data approaches to implicate OX40 as a marker for recently activated, functionally and transcriptome-wise distinct CD4 T cells, and as a potential target for immunotherapy.

Combined agonist stimulation of the TNFR costimulatory receptors 4-1BB (CD137) and OX40(CD134) has been shown to generate supereffector CD8 T cells that clonally expand to greater levels, survive longer, and produce a greater quantity of cytokines compared to T cells stimulated with an agonist of either costimulatory receptor individually. In order to understand the mechanisms for this effect, we have created a mathematical model for the activation of the CD8 T cell intracellular signaling network by mono- or dual-costimulation. We show that supereffector status is generated via downstream interacting pathways that are activated upon engagement of both receptors, and in silico simulations of the model are supported by published experimental results. The model can thus be used to identify critical molecular targets of T cell dual-costimulation in the context of cancer immunotherapy.

BackgroundPrimary and metastatic brain tumors have a poor prognosis, partly owing to the unique characteristics of the central nervous system (CNS) and tumor immune microenvironment (TIME). One distinct feature of the CNS TIME is the limited infiltration and activation of dendritic cells (DCs). The impact of CNS versus non-CNS TIME can be assessed by injecting tumor cells from the same model, either subcutaneously (peripherally) or into the brain. Subcutaneous tumors drain into the tumor-draining lymph nodes in the skin (TdLN-p), whereas brain tumors drain into the deep cervical TdLN (TdLN-c). We previously showed that CNS tumors that are not responsive to immune checkpoint inhibition become responsive when grown peripherally, and that non-responsiveness correlates with a tolerogenic immune response in the local TIME and TdLN-c.MethodsIn this study, we investigated the immunoregulatory potential of cervical DCs (DC-c) compared with that of peripheral DCs (DC-p) using high-resolution flow cytometry, single-cell RNA sequencing, and ex vivo and in vivo functional characterization of TdLNs from mouse models of glioma and lymphoma.ResultsOur analysis revealed that DC-c promoted regulatory T-cell expansion and poorly cytotoxic CD8+ T cells compared with DC-p. Furthermore, we identified OX40 (Tnfrsf4) as a modulator of immunoregulatory DC-c function and found that its antitumor effect depended on lymphocyte trafficking and the DC transcription factor Batf3. CCR7+OX40+ DCs were efficient in antigen processing and presentation, and OX40 agonists further enhanced DC activation. In TIME, the CCR7+OX40+ DCs expressed OX40L, and blocking it promoted Treg formation ex vivo.ConclusionsOur findings highlight the unique immunoregulatory functions of DC-c in TdLNs and suggest the importance of OX40 signaling through direct effects on CCR7+OX40+ DCs and indirect effects on T cells.

BackgroundImmunotherapies targeting immune checkpoint inhibitors have revolutionized cancer treatment but are limited by incomplete patient responses. Costimulatory agonists like OX40 (CD134), a tumor necrosis factor receptor family member critical for T-cell survival and differentiation, have shown preclinical promise but limited clinical success due to suboptimal receptor activation. Conventional bivalent OX40 agonists fail to induce the trimeric engagement required for optimal downstream signaling. To address this, we developed INBRX-106, a hexavalent OX40 agonist designed to enhance receptor clustering independently of Fc-mediated crosslinking and boost antitumor T-cell responses.MethodsWe assessed INBRX-106’s effects on receptor clustering, signal transduction, and T-cell activation using NF-kß reporter assays, confocal microscopy, flow cytometry, and single-cell RNA sequencing. Therapeutic efficacy was evaluated in murine tumor models and ex vivo human samples. Clinical samples from a phase I/II trial (NCT04198766) were also analyzed for immune activation.ResultsINBRX-106 demonstrated superior receptor clustering and downstream signaling compared with bivalent agonists, leading to robust T-cell activation and proliferation. In murine models, hexavalent OX40 agonism resulted in significant tumor regression, enhanced survival, and increased CD8+ T-cell effector function. Clinical pharmacodynamic analysis in blood samples from patients treated with INBRX-106 showed heightened T-cell activation and proliferation, particularly in central and effector memory subsets, validating our preclinical findings.ConclusionsOur data establish hexavalent INBRX-106 as a differentiated and more potent OX40 agonist, showcasing its ability to overcome the limitations of conventional bivalent therapies by inducing superior receptor clustering and multimeric engagement. This unique clustering mechanism amplifies OX40 signaling, driving robust T-cell activation, proliferation, and effector function in preclinical and clinical settings. These findings highlight the therapeutic potential of INBRX-106 and its capacity to redefine OX40-targeted immunotherapy, providing a compelling rationale for its further clinical development in combination with checkpoint inhibitors.

Vesicular stomatitis virus encoding the IFNβ transgene (VSV-IFNβ) is a mediator of potent oncolytic activity and is undergoing clinical evaluation for the treatment of solid tumors. Emerging preclinical and clinical data suggest treatment of tumors with oncolytic viruses may sensitize tumors to checkpoint inhibitors and increase the anti-tumor immune response. New generations of immuno-oncology molecules including T cell agonists are entering clinical development and could be hypothesized to enhance the activity of oncolytic viruses, including VSV-IFNβ. Here, we show that VSV-IFNβ exhibits multiple mechanisms of action, including direct cell killing, stimulation of an innate immune response, recruitment of CD8 T cells, and depletion of T regulatory cells. Moreover, VSV-IFNβ promotes the establishment of a CD8 T cell response to endogenous tumor antigens. Our data demonstrate a significant enhancement of anti-tumor function for VSV-IFNβ when combined with checkpoint inhibitors, but not OX40 agonists. While the addition of checkpoint inhibitors to VSV-IFNβ generated robust tumor growth inhibition, it resulted in no increase in viral replication, transgene expression, or immunophenotypic changes beyond treatment with VSV-IFNβ alone. We hypothesize that tumor-specific T cells generated by VSV-IFNβ retain activity due to a lack of immune exhaustion when checkpoint inhibitors were used. Replication competent oncolytic viruses are targeted to specifically lyse tumor cells. They have been proposed as additions to immuno-oncology treatment regimens, hypothesized to exhibit complementary mechanisms of action. Durham et al. demonstrate that checkpoint inhibitors, but not a T cell agonist molecule combine with oncolytic VSV-IFNβ to enhance survival.