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

Challenges and opportunities in the development of combination immunotherapy with OX40 agonists

INTRODUCTION

Costimulatory members of the tumor necrosis factor receptor family, such as OX40 (CD134), provide essential survival and differentiation signals that enhance T cell function. Specifically, OX40 (CD134) agonists stimulate potent anti-tumor immunity in a variety of preclinical models but their therapeutic impact in patients with advanced malignancies has been limited thus far.

AREAS COVERED

In this review, we discuss the current state of combination immunotherapy with OX40 agonists including preclinical studies and recent clinical trials. We also discuss the strengths and limitations of these approaches and provide insight into alternatives that may help enhance the efficacy of combination OX40 agonist immunotherapy.

EXPERT OPINION

OX40 agonist immunotherapy has not yet demonstrated significant clinical activity as a monotherapy or in combination with immune checkpoint blockade (ICB), likely due to several factors including the timing of administration, drug potency, and selection of agents for combination therapy clinical trials. We believe that careful consideration of the biological mechanisms regulating OX40 expression and function may help inform new approaches, particularly in combination with novel agents, capable of increasing the therapeutic efficacy of this approach.

Lysine Acetylation/Deacetylation Modification of Immune-Related Molecules in Cancer Immunotherapy

As major post-translational modifications (PTMs), acetylation and deacetylation are significant factors in signal transmission and cellular metabolism, and are modulated by a dynamic process via two pivotal categories of enzymes, histone acetyltransferases (HATs) and histone deacetylases (HDACs). In previous studies, dysregulation of lysine acetylation and deacetylation has been reported to be associated with the genesis and development of malignancy. Scientists have recently explored acetylation/deacetylation patterns and prospective cancer therapy techniques, and the FDA has approved four HDAC inhibitors (HDACi) to be used in clinical treatment. In the present review, the most recent developments in the area of lysine acetylation/deacetylation alteration in cancer immunotherapy were investigated. Firstly, a brief explanation of the acetylation/deacetylation process and relevant indispensable enzymes that participate therein is provided. Subsequently, a multitude of specific immune-related molecules involved in the lysine acetylation/deacetylation process are listed in the context of cancer, in addition to several therapeutic strategies associated with lysine acetylation/deacetylation modification in cancer immunotherapy. Finally, a number of prospective research fields related to cancer immunotherapy concepts are offered with detailed analysis. Overall, the present review may provide a reference for researchers in the relevant field of study, with the aim of being instructive and meaningful to further research as well as the selection of potential targets and effective measures for future cancer immunotherapy strategies.

Current Clinical Trial Landscape of OX40 Agonists

PURPOSE OF REVIEW

Despite the efficacy of immune checkpoint blockade (ICB) immunotherapy, most cancer patients still develop progressive disease necessitating additional treatment options. One approach is ligation of the OX40 (CD134) costimulatory receptor which promotes T cell activation, effector function, and the generation of long-lived memory cells.

RECENT FINDINGS

Numerous preclinical studies have demonstrated that OX40 agonists alone or in combination with ICB (e.g., anti-PD-1, anti-PD-L1, and anti-CTLA-4) augment anti-tumor immunity. In this review, we discuss the impact of OX40 agonists on T cell function and the therapeutic potential of OX40 agonists alone or in conjunction with ICB for patients with advanced malignancies.

Enhancing the Generation of Eomeshi CD8+ T Cells Augments the Efficacy of OX40- and CTLA-4-Targeted Immunotherapy

CTLA-4 blockade in combination with an agonist OX40-specific monoclonal antibody synergizes to augment antitumor immunity through enhanced T-cell effector function, leading to increased survival in preclinical cancer models. We have shown previously that anti-OX40/anti-CTLA-4 combination therapy synergistically enhances the expression of Eomesodermin (Eomes) in CD8⁺ T cells. Eomes is a critical transcription factor for the differentiation and memory function of CD8⁺ T cells. We hypothesized that Eomes^hiCD8⁺ T cells were necessary for anti-OX40/anti-CTLA-4 immunotherapy efficacy and that further enhancement of this population would improve tumor-free survival. Indeed, CD8⁺ T cell-specific deletion of Eomes abrogated the efficacy of anti-OX40/anti-CTLA-4 therapy. We also found that anti-OX40/anti-CTLA-4-induced Eomes^hiCD8⁺ T cells expressed lower levels of checkpoint receptors (PD1, Tim-3, and Lag-3) and higher levels of effector cytokines (IFNγ and TNFα) than their Eomes^lo counterparts. Eomes expression is negatively regulated in T cells through interleukin-2-inducible T-cell kinase (ITK) signaling. We investigated the impact of modulating ITK signaling with ibrutinib, an FDA-approved tyrosine kinase inhibitor, and found that anti-OX40/anti-CTLA-4/ibrutinib therapy further enhanced CD8⁺ T cell-specific Eomes expression, leading to enhanced tumor regression and improved survival, both of which were associated with increased T-cell effector function across multiple tumor models. Taken together, these data demonstrate the potential of anti-OX40/anti-CTLA-4/ibrutinib as a triple therapy to improve the efficacy of immunotherapy.

Therapeutic strategies for the costimulatory molecule OX40 in T-cell-mediated immunity

The T cell co-stimulatory molecule OX40 and its cognate ligand OX40L have attracted broad research interest as a therapeutic target in T cell-mediated diseases. Accumulating preclinical evidence highlights the therapeutic efficacy of both agonist and blockade of the OX40-OX40L interaction. Despite this progress, many questions about the immuno-modulator roles of OX40 on T cell function remain unanswered. In this review we summarize the impact of the OX40-OX40L interaction on T cell subsets, including Th1, Th2, Th9, Th17, Th22, Treg, Tfh, and CD8+ T cells, to gain a comprehensive understanding of anti-OX40 mAb-based therapies. The potential therapeutic application of the OX40-OX40L interaction in autoimmunity diseases and cancer immunotherapy are further discussed; OX40-OX40L blockade may ameliorate autoantigen-specific T cell responses and reduce immune activity in autoimmunity diseases. We also explore the rationale of targeting OX40-OX40L interactions in cancer immunotherapy. Ligation of OX40 with targeted agonist anti-OX40 mAbs conveys activating signals to T cells. When combined with other therapeutic treatments, such as anti-PD-1 or anti-CTLA-4 blockade, cytokines, chemotherapy, or radiotherapy, the anti-tumor activity of agonist anti-OX40 treatment will be further enhanced. These data collectively suggest great potential for OX40-mediated therapies.

Co-Stimulatory Receptors in Cancers and Their Implications for Cancer Immunotherapy

Immune checkpoint inhibitors (ICIs), including anti-PD-1 and anti-CTLA-4 therapeutic agents, are now approved by the Food and Drug Administration for treatment of various types of cancer. However, the therapeutic efficacy of ICIs varies among patients and cancer types. Moreover, most patients do not develop durable antitumor responses after ICI therapy due to an ephemeral reversal of T-cell dysfunction. As co-stimulatory receptors play key roles in regulating the effector functions of T cells, activating co-stimulatory pathways may improve checkpoint inhibition efficacy, and lead to durable antitumor responses. Here, we review recent advances in our understating of co-stimulatory receptors in cancers, providing the necessary groundwork for the rational design of cancer immunotherapy.

Human Herpesvirus 6 Reactivation Evaluated by Digital Polymerase Chain Reaction and Its Association With Dynamics of CD134-Positive T Cells After Allogeneic Hematopoietic Stem Cell Transplantation

Background

Human herpesvirus 6 (HHV-6) causes life-threatening central nervous system disorders after allogeneic hematopoietic stem cell transplantation (allo-HSCT). Recent studies implicated CD134 as a specific receptor of HHV-6B and demonstrated that its expression levels in CD4-positive T cells after allo-HSCT could be related to the reactivation of HHV-6. We prospectively evaluated the relationship between HHV-6 reactivation and CD134+ T cells in the recipients of allo-HSCT.

Methods

HHV-6 viral load in plasma was quantitatively measured weekly after allo-HSCT by digital polymerase chain reaction in 34 patients. The ratio of CD134 in CD4+ T cells (CD134/CD4 ratio) was serially measured by flow cytometry before and after transplantation.

Results

HHV-6 reactivation was detected in 23 patients (68%). The CD134/CD4 ratio before conditioning was significantly higher in patients with HHV-6 reactivation than in those without (median, 3.8% vs 1.5%, P < .01). In multivariate analysis, a higher CD134/CD4 ratio before conditioning was significantly associated with the incidence of HHV-6 reactivation (odds ratio, 10.5 [95% confidence interval, 1.3–85.1], P = .03).

Conclusions

A higher CD134/CD4 ratio before conditioning was associated with a higher risk of HHV-6 reactivation, suggesting that the rate may be a promising marker for predicting HHV-6 reactivation after allo-HSCT.

Late-Stage Tumor Regression after PD-L1 Blockade Plus a Concurrent OX40 Agonist

The protective capability of tumor antigen-specific T cells is regulated by costimulatory and inhibitory signals. Current approaches in cancer immunotherapy seek to restore the function of unresponsive T cells by blocking inhibitory pathways. In contrast, providing exogenous costimulatory signals to T cells also enhances antitumor functionality. By combining these two clinical approaches, we demonstrate the synergy of targeting PD-L1 together with the costimulatory molecule OX40, to enhance antitumor immunity. Concurrently blocking PD-L1 and providing a costimulatory agonist to OX40 increased the presence and functionality of tumor antigen-specific CD8⁺ T cells with simultaneous enhancement of T-helper type 1 (Th1)-skewed CD4⁺ T cells. This shift was functionally supported by increased glucose metabolism of antigen-specific CD8⁺ T cells and the acquisition of granzyme B by regulatory T cells. Together, this mechanism promoted tumor regression of late-stage tumors beyond that achieved by either blockade as monotherapy. These findings indicate that targeting both T-cell intrinsic (OX40) and extrinsic (PD-L1) regulatory molecules increases the bioenergetic potential of T cells, thereby expanding functional and tumor antigen-specific T cells.

The effects of interleukin-2 on immune response regulation

The immune system has many adaptive and dynamic components that are regulated to ensure appropriate, precise and rapid response to a foreign pathogen. A delayed or inadequate immune response can lead to prolonged disease, while an excessive or under-regulated response can lead to autoimmunity. The cytokine, interleukin-2 (IL-2) and its receptor IL-2R play an important role in maintaining this balance.The IL-2 receptor transduces pSTAT5 signal through both the intermediate and high affinity receptors, which differ from each other by the presence of CD25 chain in IL-2 receptor. We present experimental data on the kinetics of pSTAT5 signalling through both of the receptors and develop a model that captures this kinetics. We then use this model to parameterize key aspects of two additional models in which we propose and study two different mechanisms by which IL-2 receptor can transduce distinct signals leading to either an activated or a non-activated cell state. We speculate that this initial state differentiation, perhaps enhanced by downstream feedbacks, may eventually lead to differential cell fates.Our result shows that non-linear dynamical models can suggest resolution of a puzzling array of seemingly contradictory experimental results on IL-2 effect on proliferation and differentiation of T-cells.

Stimulating T Cells Against Cancer With Agonist Immunostimulatory Monoclonal Antibodies

Elimination of cancer cells through antitumor immunity has been a long-sought after goal since Sir F. Macfarlane Burnet postulated the theory of immune surveillance against tumors in the 1950s. Finally, the use of immunotherapeutics against established cancer is becoming a reality in the past 5years. Most notable are the monoclonal antibodies (mAbs) directed against inhibitory T-cell receptors cytotoxic T lymphocyte antigen-4 and programmed death-1. The next generation of mAbs targeting T cells is designed to stimulate costimulatory receptors on T cells. Here we review the recent progress on these immunostimulatory agonist antibodies against the costimulatory receptors CD137, GITR, OX40, and CD27.

Critical role of OX40 in the expansion and survival of CD4 T-cell-derived double-negative T cells

CD4⁺ T-cell-converted CD4⁻CD8⁻ double negative (cDNT) have strong suppressive activity in the maintenance of immune tolerance, whereas IL-2 promotes cDNT proliferation and enhances cDNT resistance to apoptosis. However, the intrinsic mechanisms that regulate the survival of cDNT are still unknown. Here we demonstrate that the OX40 molecule was highly expressed on cDNT. The expression of OX40 was necessary to promote proliferation and inhibit apoptosis of cDNT in vivo and in vitro. OX40 promoted the survival of cDNT by regulating the expression of Bcl-2, Bcl-xL, Survivin, and BCL2L11. Canonical NF-κB cell signaling played an important role in the transmission of essential division and survival signals through OX40 in cDNT. IL-2 promoted the survival of cDNT in part via elevating the expression of the OX40 molecule. IL-2 promoted OX40 expression via downregulating the PPARα expression. In conclusion, we elucidated that OX40 is a key molecule that regulates cDNT proliferation and survival. IL-2 promoted OX40 expression by downregulating the PPARα binding to the OX40 promoter, leading to the elevated expression of Bcl-2, Bcl-xL, and Survivin in cDNT, which finally resulted in the promoted proliferation and decreased apoptosis of cDNT.

Immunomodulatory effects of OX40Ig gene-modified adipose tissue-derived mesenchymal stem cells on rat kidney transplantation

Recent studies have suggested that adipose tissue-derived mesenchymal stem cell (ADSC) therapy and OX40 costimulation blockade are two immunomodulatory strategies used to suppress the immune response to alloantigens. However, relatively little has been reported regarding the immunomodulatory potential of the abilityof these two strategies to synergize. Thus, in the present study, we aimed to investigate OX40-Ig fusion protein (OX40Ig) expression in ADSCs and to validate their more potent immunosuppressive activity in preventing renal allograft rejection. For this purpose, ADSCs from Lewis rats were transfected with the recombinant plasmid, pcDNA3.1(-)OX40Ig, by nucleofection. The ADSCs transduced with the plasmid (termed ADSCsOX40Ig) or untransduced ADSCs (termed ADSCsnative) were added to allostimulated mixed lymphocyte reaction (MLR) in vitro. In vivo, ADSCsOX40Ig, ADSCsnative, or PBS were administered to an allogeneic renal transplantation model, and the therapeutic effects, as well as the underlying mechanisms were examined. The results revealed that both the ADSCsnative and ADSCsOX40Ig significantly suppressed T cell proliferation and increased the percentage of CD4+CD25+ regulatory T cells in allogeneic MLR assays, with the ADSCsOX40Ig being more effective. Furthermore, the results from our in vivo experiments revealed that compared with the ADSCsnative or PBS group, the administration of autologous ADSCsOX40Ig markedly prolonged the mean survival time of renal grafts, reduced allograft rejection, and significantly downregulated the mRNA expression of intragraft interferon-γ (IFN-γ) , and upregulated the mRNA expression of interleukin (IL)‑10, transforming growth factor-β (TGF-β) and forkhead box protein 3 (Foxp3). The findings of our study indicate that the use of ADSCsOX40Ig is a promising strategy for preventing renal allograft rejection. This strategy provides the synergistic benefits of ADSC immune modulation and OX40-OX40L pathway blockade, and may therefore have therapeutic potential in clinical renal transplantation.

Combinatorial immunotherapeutic approaches to restore the function of anergic tumor-reactive cytotoxic CD8+ T cells

Numerous preclinical studies have demonstrated that combination immunotherapy can significantly reduce tumor growth and improve overall survival as compared to monotherapy. Furthermore, dual CTLA-4/PD-1 checkpoint blockade recently received FDA-approval for patients with metastatic melanoma, becoming the first combination immunotherapy to garner this designation in a rapidly evolving field. Despite this progress, the majority of patients do not respond to treatment, underscoring the critical need for more effective therapies. We have been investigating the mechanisms by which combination immunotherapy with an OX40 agonist plus CTLA-4 checkpoint blockade augments effector T cell responses to elicit anti-tumor immunity. Surprisingly, this approach failed to eradicate well-established tumors, in part due to the induction of anergy in cytotoxic CD8⁺ T cells. Further work revealed that anergic CD8⁺ T cells could be rescued by combining a dendritic cell-targeted vaccine with combination immunotherapy. Taken together, these data suggest that novel combinatorial immunotherapeutic strategies incorporating a vaccination strategy may be needed to generate effective anti-tumor responses in the majority of patients with metastatic disease.

Prostate cancer immunotherapy: beyond immunity to curability

Metastatic prostate cancer is the second leading cause of death from cancer in the United States. It is the first prevalent cancer in which overall survival in advanced disease is modestly, but objectively, improved with outpatient delivered dendritic cell-based immunotherapy. More prostate cancer patients have enrolled through Facebook and trusted-site Internet searches in clinical trials for prostate cancer vaccine-based immunotherapy than in immunotherapy trials for lung, breast, colon, pancreas, ovarian, and bladder cancer combined in the past 7 years. Exceptional responses to anti-CTLA-4 treatment have been documented in clinics, and prostate cancer neoantigen characterization and T-cell clonotyping are in their research ascendancy. The prostate is an accessory organ; it is not required for fertility, erectile function, or urinary continence. The true evolutionary advantage of having a prostate for male mammalian physiology is a topic of speculation in seminar rooms and on bar stools, but it remains unknown. Hundreds of prostate lineage-unique proteins (PLUP) exist among the >37,000 normal human prostate lineage-unique open reading frames that can be targeted for immunologic ablation of PLUP(+) prostate cancer cells by prostate-specific autoimmunity. This bioengineered graft-versus-prostate disease is a powerful strategy that can eliminate deaths from prostate cancer. Immunologic tolerance to prostate cancer can be overcome at every clinical stage of presentation. This Cancer Immunology at the Crossroads article aims to present advances in the past two decades of basic, translational, and clinical research in prostate cancer, including bioengineering B-cell and T-cell responses, and ongoing prostate cancer immunotherapy trials.

Combined treatment with dabrafenib and trametinib with immune-stimulating antibodies for BRAF mutant melanoma

The combination of targeted therapy with BRAF and MEK inhibitors has become the standard of care in patients with BRAF^V600E mutant melanoma, but responses are not durable. In addition, the impressive clinical benefits with anti-PD-1 and anti-PD-L1 antibodies (Ab) in patients with heavily pretreated metastatic melanoma and the synergistic effect of dabrafenib, trametinib and anti-PD-1 compared with single therapy alone groups support the idea that combining dabrafenib, trametinib and immunotherapy based on PD-1 blockade could be an interesting approach in the treatment of metastatic melanoma. With our mouse model of syngeneic BRAF^V600E driven melanoma (SM1), we tested whether the addition of an immunostimulatory Ab targeting CD137 (4-1BB) and/or CD134 (OX40) would enhance the antitumor effect of dabrafenib, trametinib and anti-PD-1 or anti-PD-L1 therapy. In vitro studies showed that the combination group of dabrafenib, trametinib and anti-PD-1 increases CD8⁺ tumor infiltrating lymphocytes (TILs), as well as CD4⁺ T cells and tumor-associated macrophages (TAMs). An upregulation of PD-L1 was observed in the combination of dabrafenib, trametinib and anti-PD-1 therapy. Combination of dabrafenib, trametinib and anti-PD-1, with either anti-CD137 or anti-CD134, showed a superior antitumor effect, but the five-agent combination was not superior to the four-agent combinations. In conclusion, the combination of dabrafenib, trametinib, anti-PD1 or anti-PD-L1 therapy results in robust antitumor activity, which is further improved by adding the immune-stimulating Ab anti-CD137 or anti-CD134. Our findings support the testing of these combinations in patients with BRAF^V600E mutant metastatic melanoma.

Agonists of Co-stimulation in Cancer Immunotherapy Directed Against CD137, OX40, GITR, CD27, CD28, and ICOS

T and natural killer (NK) lymphocytes are considered the main effector players in the immune response against tumors. Full activation of T and NK lymphocytes requires the coordinated participation of several surface receptors that meet their cognate ligands through structured transient cell-to-cell interactions known as immune synapses. In the case of T cells, the main route of stimulation is driven by antigens as recognized in the form of short polypeptides associated with major histocompatibility complex (MHC) antigen-presenting molecules. However, the functional outcome of T-cell stimulation towards clonal expansion and effector function acquisition is contingent on the contact of additional surface receptor-ligand pairs and on the actions of cytokines in the milieu. While some of those interactions are inhibitory, others are activating and are collectively termed co-stimulatory receptors. The best studied belong to either the immunoglobulin superfamily or the tumor necrosis factor-receptor (TNFR) family. Co-stimulatory receptors include surface moieties that are constitutively expressed on resting lymphocytes such as CD28 or CD27 and others whose expression is induced upon recent previous antigen priming, ie, CD137, GITR, OX40, and ICOS. Ligation of these glycoproteins with agonist antibodies actively conveys activating signals to the lymphocyte. Those signals, acting through a potentiation of the cellular immune response, give rise to anti-tumor effects in mouse models. Anti-CD137 antibodies are undergoing clinical trials with evidence of clinical activity and anti-OX40 monoclonal antibodies (mAbs) induce interesting immunomodulation effects in humans. Antibodies anti-CD27 and GITR have recently entered clinical trials. The inherent dangers of these immunomodulation strategies are the precipitation of excessive systemic inflammation or/and invigorating silent autoimmunity. Agonist antibodies, recombinant forms of the natural ligands, and polynucleotide-based aptamers constitute the pharmacologic tools to manipulate such receptors. Preclinical data suggest that the greatest potential of these agents is achieved in combined treatment strategies.

OX40 Agonists and Combination Immunotherapy: Putting the Pedal to the Metal

Recent studies have highlighted the therapeutic efficacy of immunotherapy, a class of cancer treatments that utilize the patient’s own immune system to destroy cancerous cells. Within a tumor the presence of a family of negative regulatory molecules, collectively known as “checkpoint inhibitors,” can inhibit T cell function to suppress anti-tumor immunity. Checkpoint inhibitors, such as CTLA-4 and PD-1, attenuate T cell proliferation and cytokine production. Targeted blockade of CTLA-4 or PD-1 with antagonist monoclonal antibodies (mAbs) releases the “brakes” on T cells to boost anti-tumor immunity. Generating optimal “killer” CD8 T cell responses also requires T cell receptor activation plus co-stimulation, which can be provided through ligation of tumor necrosis factor receptor family members, including OX40 (CD134) and 4-1BB (CD137). OX40 is of particular interest as treatment with an activating (agonist) anti-OX40 mAb augments T cell differentiation and cytolytic function leading to enhanced anti-tumor immunity against a variety of tumors. When used as single agents, these drugs can induce potent clinical and immunologic responses in patients with metastatic disease. However, each of these agents only benefits a subset of patients, highlighting the critical need for more effective combinatorial therapeutic strategies. In this review, we will discuss our current understanding of the cellular and molecular mechanisms by which OX40 agonists synergize with checkpoint inhibitor blockade to augment T cell-mediated anti-tumor immunity and the potential opportunities for clinical translation of combinatorial immunotherapeutic strategies.

The New Era of Cancer Immunotherapy: Manipulating T-Cell Activity to Overcome Malignancy

Using the immune system to control cancer has been investigated for over a century. Yet it is only over the last several years that therapeutic agents acting directly on the immune system have demonstrated improved overall survival for cancer patients in phase III clinical trials. Furthermore, it appears that some patients treated with such agents have been cured of metastatic cancer. This has led to increased interest and acceleration in the rate of progress in cancer immunotherapy. Most of the current immunotherapeutic success in cancer treatment is based on the use of immune-modulating antibodies targeting critical checkpoints (CTLA-4 and PD-1/PD-L1). Several other immune-modulating molecules targeting inhibitory or stimulatory pathways are being developed. The combined use of these medicines is the subject of intense investigation and holds important promise. Combination regimens include those that incorporate targeted therapies that act on growth signaling pathways, as well as standard chemotherapy and radiation therapy. In fact, these standard therapies have intrinsic immune-modulating properties that can support antitumor immunity. In the years ahead, adoptive T-cell therapy will also be an important part of treatment for some cancer patients. Other areas which are regaining interest are the use of oncolytic viruses that immunize patients against their own tumors and the use of vaccines against tumor antigens. Immunotherapy has demonstrated unprecedented durability in controlling multiple types of cancer and we expect its use to continue expanding rapidly.

TNF superfamily protein-protein interactions: feasibility of small- molecule modulation

The tumor necrosis factor (TNF) superfamily (TNFSF) contains about thirty structurally related receptors (TNFSFRs) and about twenty protein ligands that bind to one or more of these receptors. Almost all of these cell surface protein-protein interactions (PPIs) represent high-value therapeutic targets for inflammatory or immune modulation in autoimmune diseases, transplant recipients, or cancers, and there are several biologics including antibodies and fusion proteins targeting them that are in various phases of clinical development. Small-molecule inhibitors or activators could represent possible alternatives if the difficulties related to the targeting of protein-protein interactions by small molecules can be addressed. Compounds proving the feasibility of such approaches have been identified through different drug discovery approaches for a number of these TNFSFR-TNFSF type PPIs including CD40-CD40L, BAFFR-BAFF, TRAIL-DR5, and OX40-OX40L. Corresponding structural, signaling, and medicinal chemistry aspects are briefly reviewed here. While none of these small-molecule modulators identified so far seems promising enough to be pursued for clinical development, they provide proof-of-principle evidence that these interactions are susceptible to small-molecule modulation and can serve as starting points toward the identification of more potent and selective candidates.

Common gamma chain (γc) cytokines differentially potentiate TNFR family signaling in antigen-activated CD8(+) T cells

Background

Several members of the common gamma chain (gc) cytokine family are already approved (IL-2) or actively being developed as vaccine adjuvants and cancer immunotherapies. Studies have indicated that co-administration of gc cytokines may enhance the efficacy of immunotherapies that function via direct activation of co-stimulatory T cell receptors. To define the specific influence of gc cytokines on the co-stimulatory capacity of CD8⁺ T cells and identify combinations with synergistic potential, we investigated the direct impact of gc cytokines on the differentiation and transcriptional profile of recently antigen-primed CD8⁺ T cells.

Methods

Naïve CD8⁺ T cells were activated with peptide-pulsed APCs. After 48 hours, CD8⁺ T cells were harvested and re-cultured in media supplemented with IL-2, IL-4, IL-7, IL-15 or IL-21. After 24 hours, cells were analyzed by cytokine bead array, flow cytometry, and mRNA micro-array. Gene networks responsible for specific CD8⁺ T cell functions were constructed through literature-meta review and publicly available annotation databases. Gene expression data from the experimental groups was imported into this network to visualize the impact of each gc cytokine on the functional polarization of recently-activated CD8⁺ T cells.

Results

Among the gc cytokines, IL-2 induced the greatest increase in the expression of co-stimulatory receptors in recently-activated CD8⁺ T cells. IL-2 increased significantly expression of 4-1BB, GITR, ICOS and OX40, at both the transcriptional and protein level. IL-2 also drove the greatest increase in cellular proliferation and the most robust shift towards a pro-survival phenotype, compared with the other gc cytokines. Both IL-4 and IL-21 enhanced expression of cytotoxic effector proteins, but drove distinct phenotypic polarizations, Th2/Tc2 and NK-like, respectively.

Conclusions

Overall, these observations suggest that among gc cytokines, IL-2 may be uniquely capable of synergizing with therapeutic strategies that combine immunization with agonists of co-stimulatory T cell receptors. Previous studies have shown that the timing of IL-2 treatment relative to immunization plays a key role in defining the CD8⁺ T cell response, and the findings from this study indicate that administration of exogenous IL-2 shortly after the initial antigen-priming event has concluded may augment the receptivity of these cells to subsequent TNFR co-stimulation.

The "Trojan Horse" approach to tumor immunotherapy: targeting the tumor microenvironment

Most anticancer therapies including immunotherapies are given systemically; yet therapies given directly into tumors may be more effective, particularly those that overcome natural suppressive factors in the tumor microenvironment. The “Trojan Horse” approach of intratumoural delivery aims to promote immune-mediated destruction by inducing microenvironmental changes within the tumour at the same time as avoiding the systemic toxicity that is often associated with more “full frontal” treatments such as transfer of large numbers of laboratory-expanded tumor-specific cytotoxic T lymphocytes or large intravenous doses of cytokine. Numerous studies have demonstrated that intratumoural therapy has the capacity to minimizing local suppression, inducing sufficient “dangerous” tumor cell death to cross-prime strong immune responses, and rending tumor blood vessels amenable to immune cell traffic to induce effector cell changes in secondary lymphoid organs. However, the key to its success is the design of a sound rational approach based on evidence. There is compelling preclinical data for local immunotherapy approaches in tumor immunology. This review summarises how immune events within a tumour can be modified by local approaches, how this can affect systemic antitumor immunity such that distal sites are attacked, and what approaches have been proven most successful so far in animals and patients.

Blockade of OX40/OX40 ligand to decrease cytokine messenger RNA expression in acute renal allograft rejection in vitro

AIM

The aim of this study was to investigate cytokine messenger RNA (mRNA) expression by peripheral blood mononuclear cells (PBMCs) from renal recipients experiencing acute rejection by blocking OX40-OX40L interactions with recombinant human OX40-Fc fusion protein (rhOX40Fc) in vitro.

METHODS

PBMCs were isolated from 20 recipients experiencing acute rejection episodes (rejection group) and 20 recipients with stable graft function (stable group). Levels of Th1 (interferon [IFN]-γ) and Th2 (interleukin [IL]-4) mRNA expressions by PBMCs were measured using real-time reverse transcriptase-polymerase chain reactions.

RESULTS

IFN-γ mRNA expression levels were significantly higher in the rejection than the stable group (P < .05). Levels of IL-4 mRNA expression were not significantly different. Among the rejection group, rhOX40Fc reduced significantly the expression of IFN-γ and IL-4 mRNA by anti-CD3-monoclonal antibody stimulated PBMCs (P < .05, and P < .01, respectively).

CONCLUSIONS

Blocking of the interaction between OX40 and OX40L in vitro inhibited production of Thl and Th2 type cytokines.

Targeting tumor-necrosis factor receptor pathways for tumor immunotherapy

With the success of ipilimumab and promise of programmed death-1 pathway-targeted agents, the field of tumor immunotherapy is expanding rapidly. Newer targets for clinical development include select members of the tumor necrosis factor receptor (TNFR) family. Agonist antibodies to these co-stimulatory molecules target both T and B cells, modulating T-cell activation and enhancing immune responses. In vitro and in vivo preclinical data have provided the basis for continued development of 4-1BB, OX40, glucocorticoid-induced TNFR-related gene, herpes virus entry mediator, and CD27 as potential therapies for patients with cancer. In this review, we summarize the immune response to tumors, consider preclinical and early clinical data on select TNFR family members, discuss potential translational challenges and suggest possible combination therapies with the aim of inducing durable antitumor responses.

Combined targeting of costimulatory (OX40) and coinhibitory (CTLA-4) pathways elicits potent effector T cells capable of driving robust antitumor immunity

Ligation of the TNF receptor family costimulatory molecule OX40 (CD134) with an agonist anti-OX40 monoclonal antibody (mAb) enhances antitumor immunity by augmenting T-cell differentiation as well as turning off the suppressive activity of the FoxP3(+)CD4(+) regulatory T cells (Treg). In addition, antibody-mediated blockade of the checkpoint inhibitor CTLA-4 releases the "brakes" on T cells to augment tumor immunotherapy. However, monotherapy with these agents has limited therapeutic benefit particularly against poorly immunogenic murine tumors. Therefore, we examined whether the administration of agonist anti-OX40 therapy in the presence of CTLA-4 blockade would enhance tumor immunotherapy. Combined anti-OX40/anti-CTLA-4 immunotherapy significantly enhanced tumor regression and the survival of tumor-bearing hosts in a CD4 and CD8 T cell-dependent manner. Mechanistic studies revealed that the combination immunotherapy directed the expansion of effector T-bet(high)/Eomes(high) granzyme B(+) CD8 T cells. Dual immunotherapy also induced distinct populations of Th1 [interleukin (IL)-2, IFN-γ], and, surprisingly, Th2 (IL-4, IL-5, and IL-13) CD4 T cells exhibiting increased T-bet and Gata-3 expression. Furthermore, IL-4 blockade inhibited the Th2 response, while maintaining the Th1 CD4 and effector CD8 T cells that enhanced tumor-free survival. These data demonstrate that refining the global T-cell response during combination immunotherapy can further enhance the therapeutic efficacy of these agents.

Agonist antibodies to TNFR molecules that costimulate T and NK cells

Therapy for cancer can be achieved by artificially stimulating antitumor T and natural killer (NK) lymphocytes with agonist monoclonal antibodies (mAb). T and NK cells express several members of the TNF receptor (TNFR) family specialized in delivering a costimulatory signal on their surface. Engagement of these receptors is typically associated with proliferation, elevated effector functions, resistance to apoptosis, and differentiation into memory cells. These receptors lack any intrinsic enzymatic activity and their signal transduction relies on associations with TNFR-associated factor (TRAF) adaptor proteins. Stimulation of CD137 (4-1BB), CD134 (OX40), and glucocorticoid-induced TNFR (GITR; CD357) promotes impressive tumor-rejecting immunity in a variety of murine tumor models. The mechanisms of action depend on a complex interplay of CTL, T-helper cells, regulatory T cells, dendritic cells, and vascular endothelium in tumors. Agonist mAbs specific for CD137 have shown signs of objective clinical activity in patients with metastatic melanoma, whereas anti-OX40 and anti-GITR mAbs have entered clinical trials. Preclinical evidence suggests that engaging TNFR members would be particularly active with conventional cancer therapies and additional immunotherapeutic approaches. Indeed, T-cell responses elicited to tumor antigens by means of immunogenic tumor cell death are amplified by these immunostimulatory agonist mAbs. Furthermore, anti-CD137 mAbs have been shown to enhance NK-mediated cytotoxicity elicited by rituximab and trastuzumab. Combinations with other immunomodulatory mAb that block T-cell checkpoint blockade receptors such as CTLA-4 and PD-1 are also promising.

Clinical development of immunostimulatory monoclonal antibodies and opportunities for combination

Immune system responses are under the control of extracellular biomolecules, which express functions in receptors present on the surface of cells of the immune system, and thus are amenable to be functionally modulated by monoclonal antibodies. Some of these mechanisms are activating and dictate whether the response ensues, while others play the role of powerful repressors. Antagonist antibodies acting on such repressors result in enhanced immune responses, a goal that is also achieved with agonist antibodies acting on the activating receptors. With these simple logics, a series of therapeutic agents are under clinical development and one of them directed at the CTL-associated antigen 4 (CTLA-4) inhibitory receptor (ipilimumab) has been approved for the treatment of metastatic melanoma. The list of antagonist agents acting on repressors under development includes anti-CTLA-4, anti-PD-1, anti-PD-L1 (B7-H1), anti-KIR, and anti-TGF-β. Agonist antibodies currently being investigated in clinical trials target CD40, CD137 (4-1BB), CD134 (OX40), and glucocorticoid-induced TNF receptor (GITR). A blossoming preclinical pipeline suggests that other active targets will also be tested in patients in the near future. All of these antibodies are being developed as conventional monoclonal immunoglobulins, but other engineered antibody formats or RNA aptamers are under preclinical scrutiny. The "dark side" of these immune interventions is that they elicit autoimmune/inflammatory reactions that can be severe in some patients. A critical and, largely, pending subject is to identify reliable predictive biomarkers both for efficacy and immune toxicity. Preclinical and early clinical studies indicate a tremendous potential to further improve efficacy, using combinations from among these new agents that frequently act in a synergistic fashion. Combinations with other more conventional means of treatment such as radiotherapy, chemotherapy, or cancer vaccines also hold much promise.

Targeting of the tumor necrosis factor receptor superfamily for cancer immunotherapy

The tumor necrosis factor (TNF) ligand and cognate TNF receptor superfamilies constitute an important regulatory axis that is pivotal for immune homeostasis and correct execution of immune responses. TNF ligands and receptors are involved in diverse biological processes ranging from the selective induction of cell death in potentially dangerous and superfluous cells to providing costimulatory signals that help mount an effective immune response. This diverse and important regulatory role in immunity has sparked great interest in the development of TNFL/TNFR-targeted cancer immunotherapeutics. In this review, I will discuss the biology of the most prominent proapoptotic and co-stimulatory TNF ligands and review their current status in cancer immunotherapy.

Localized immunotherapy via liposome-anchored Anti-CD137 + IL-2 prevents lethal toxicity and elicits local and systemic antitumor immunity

Immunostimulatory agonists such as anti-CD137 and interleukin (IL)-2 have elicited potent antitumor immune responses in preclinical studies, but their clinical use is limited by inflammatory toxicities that result upon systemic administration. We hypothesized that by rigorously restricting the biodistribution of immunotherapeutic agents to a locally accessible lesion and draining lymph node(s), effective local and systemic antitumor immunity could be achieved in the absence of systemic toxicity. We anchored anti-CD137 and an engineered IL-2Fc fusion protein to the surfaces of PEGylated liposomes, whose physical size permitted dissemination in the tumor parenchyma and tumor-draining lymph nodes but blocked entry into the systemic circulation following intratumoral injection. In the B16F10 melanoma model, intratumoral liposome-coupled anti-CD137 + IL-2Fc therapy cured a majority of established primary tumors while avoiding the lethal inflammatory toxicities caused by equivalent intratumoral doses of soluble immunotherapy. Immunoliposome therapy induced protective antitumor memory and elicited systemic antitumor immunity that significantly inhibited the growth of simultaneously established distal tumors. Tumor inhibition was CD8(+) T-cell-dependent and was associated with increased CD8(+) T-cell infiltration in both treated and distal tumors, enhanced activation of tumor antigen-specific T cells in draining lymph nodes, and a reduction in regulatory T cells in treated tumors. These data suggest that local nanoparticle-anchored delivery of immuno-agonists represents a promising strategy to improve the therapeutic window and clinical applicability of highly potent but otherwise intolerable regimens of cancer immunotherapy. Cancer Res; 73(5); 1547-58. ©2012 AACR.

The confluence of radiotherapy and immunotherapy

Radiotherapy (RT) has been considered a local modality and outcomes have emphasized local and regional control of tumors. Recent data suggests that RT may activate the immune system and the combination of radiation therapy and immune therapies may have the potential to improve both local and distant control of tumor deposits. Below we review principals underlying the concepts of combining both modalities.