Vaccination with dendritic cells pulsed with apoptotic tumors in combination with anti-OX40 and anti-4-1BB monoclonal antibodies induces T cell-mediated protective immunity in Her-2/neu transgenic mice

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.

CD137 (4-1BB)-Based Cancer Immunotherapy on Its 25th Anniversary

Twenty-five years ago, we reported that agonist anti-CD137 monoclonal antibodies eradicated transplanted mouse tumors because of enhanced CD8+ T-cell antitumor immunity. Mouse models indicated that anti-CD137 agonist antibodies synergized with various other therapies. In the clinic, the agonist antibody urelumab showed evidence for single-agent activity against melanoma and non-Hodgkin lymphoma but caused severe liver inflammation in a fraction of the patients. CD137's signaling domain is included in approved chimeric antigen receptors conferring persistence and efficacy. A new wave of CD137 agonists targeting tumors, mainly based on bispecific constructs, are in early-phase trials and are showing promising safety and clinical activity.

SIGNIFICANCE

CD137 (4-1BB) is a costimulatory receptor of T and natural killer lymphocytes whose activity can be exploited in cancer immunotherapy strategies as discovered 25 years ago. Following initial attempts that met unacceptable toxicity, new waves of constructs acting agonistically on CD137 are being developed in patients, offering signs of clinical and pharmacodynamic activity with tolerable safety profiles.

Tipping the scales: Immunotherapeutic strategies that disrupt immunosuppression and promote immune activation

Immunotherapy has emerged as an effective therapeutic approach for several cancer types. However, only a subset of patients exhibits a durable response due in part to immunosuppressive mechanisms that allow tumor cells to evade destruction by immune cells. One of the hallmarks of immune suppression is the paucity of tumor-infiltrating lymphocytes (TILs), characterized by low numbers of effector CD4+ and CD8+ T cells in the tumor microenvironment (TME). Additionally, the proper activation and function of lymphocytes that successfully infiltrate the tumor are hampered by the lack of co-stimulatory molecules and the increase in inhibitory factors. These contribute to the imbalance of effector functions by natural killer (NK) and T cells and the immunosuppressive functions by myeloid-derived suppressor cells (MDSCs) and regulatory T cells (Tregs) in the TME, resulting in a dysfunctional anti-tumor immune response. Therefore, therapeutic regimens that elicit immune responses and reverse immune dysfunction are required to counter immune suppression in the TME and allow for the re-establishment of proper immune surveillance. Immuno-oncology (IO) agents, such as immune checkpoint blockade and TGF-β trapping molecules, have been developed to decrease or block suppressive factors to enable the activity of effector cells in the TME. Therapeutic agents that target immunosuppressive cells, either by direct lysis or altering their functions, have also been demonstrated to decrease the barrier to effective immune response. Other therapies, such as tumor antigen-specific vaccines and immunocytokines, have been shown to activate and improve the recruitment of CD4+ and CD8+ T cells to the tumor, resulting in improved T effector to Treg ratio. The preclinical data on these diverse IO agents have led to the development of ongoing phase I and II clinical trials. This review aims to provide an overview of select therapeutic strategies that tip the balance from immunosuppression to immune activity in the TME.

Boosting Antitumor Response by Costimulatory Strategies Driven to 4-1BB and OX40 T-cell Receptors

Immunotherapy explores several strategies to enhance the host immune system’s ability to detect and eliminate cancer cells. The use of antibodies that block immunological checkpoints, such as anti–programed death 1/programed death 1 ligand and cytotoxic T-lymphocyte–associated protein 4, is widely recognized to generate a long-lasting antitumor immune response in several types of cancer. Evidence indicates that the elimination of tumors by T cells is the key for tumor control. It is well known that costimulatory and coinhibitory pathways are critical regulators in the activation of T cells. Besides blocking checkpoints inhibitors, the agonistic signaling on costimulatory molecules also plays an important role in T-cell activation and antitumor response. Therefore, molecules driven to costimulatory pathways constitute promising targets in cancer therapy. The costimulation of tumor necrosis factor superfamily receptors on lymphocytes surface may transduce signals that control the survival, proliferation, differentiation, and effector functions of these immune cells. Among the members of the tumor necrosis factor receptor superfamily, there are 4-1BB and OX40. Several clinical studies have been carried out targeting these molecules, with agonist monoclonal antibodies, and preclinical studies exploring their ligands and other experimental approaches. In this review, we discuss functional aspects of 4-1BB and OX40 costimulation, as well as the progress of its application in immunotherapies.

Blood Levels of Galectin-9, an Immuno-Regulating Molecule, Reflect the Severity for the Acute and Chronic Infectious Diseases

Galectin-9 (Gal-9) is a β-galactoside-binding lectin capable of promoting or suppressing the progression of infectious diseases. This protein is susceptible to cleavage of its linker-peptides by several proteases, and the resulting cleaved forms, N-terminal carbohydrate recognition domain (CRD) and C-terminal CRD, bind to various glycans. It has been suggested that full-length (FL)-Gal-9 and the truncated (Tr)-Gal-9s could exert different functions from one another via their different glycan-binding activities. We propose that FL-Gal-9 regulates the pathogenesis of infectious diseases, including human immunodeficiency virus (HIV) infection, HIV co-infected with opportunistic infection (HIV/OI), dengue, malaria, leptospirosis, and tuberculosis (TB). We also suggest that the blood levels of FL-Gal-9 reflect the severity of dengue, malaria, and HIV/OI, and those of Tr-Gal-9 markedly reflect the severity of HIV/OI. Recently, matrix metallopeptidase-9 (MMP-9) was suggested to be an indicator of respiratory failure from coronavirus disease 2019 (COVID-19) as well as useful for differentiating pulmonary from extrapulmonary TB. The protease cleavage of FL-Gal-9 may lead to uncontrolled hyper-immune activation, including a cytokine storm. In summary, Gal-9 has potential to reflect the disease severity for the acute and chronic infectious diseases.

Tumor Burden and Immunotherapy: Impact on Immune Infiltration and Therapeutic Outcomes

Cancer immunotherapy has revolutionized the treatment landscape in medical oncology, but its efficacy has been variable across patients. Biomarkers to predict such differential response to immunotherapy include cytotoxic T lymphocyte infiltration, tumor mutational burden, and microsatellite instability. A growing number of studies also suggest that baseline tumor burden, or tumor size, predicts response to immunotherapy. In this review, we discuss the changes in immune profile and therapeutic responses that occur with increasing tumor size. We also overview therapeutic approaches to reduce tumor burden and favorably modulate the immune microenvironment of larger tumors.

Costimulation Induces CD4 T Cell Antitumor Immunity via an Innate-like Mechanism

Chronic exposure to tumor-associated antigens inactivates cognate T cells, restricting the repertoire of tumor-specific effector T cells. This problem was studied here by transferring TCR transgenic CD4 T cells into recipient mice that constitutively express a cognate self-antigen linked to MHC II on CD11c-bearing cells. Immunotherapeutic agonists to CD134 plus CD137, "dual costimulation," induces specific CD4 T cell expansion and expression of the receptor for the Th2-associated IL-1 family cytokine IL-33. Rather than producing IL-4, however, they express the tumoricidal Th1 cytokine IFNγ when stimulated with IL-33 or IL-36 (a related IL-1 family member) plus IL-12 or IL-2. IL-36, which is induced within B16-F10 melanomas by dual costimulation, reduces tumor growth when injected intratumorally as a monotherapy and boosts the efficacy of tumor-nonspecific dual costimulated CD4 T cells. Dual costimulation thus enables chronic antigen-exposed CD4 T cells, regardless of tumor specificity, to elaborate tumoricidal function in response to tumor-associated cytokines.

Breakthrough concepts in immune-oncology: Cancer vaccines at the bedside

Clinical approval of the immune checkpoint blockade (ICB) agents for multiple cancer types has reinvigorated the long-standing work on cancer vaccines. In the pre-ICB era, clinical efforts focused on the Ag, the adjuvants, the formulation, and the mode of delivery. These translational efforts on therapeutic vaccines range from cell-based (e.g., dendritic cells vaccine Sipuleucel-T) to DNA/RNA-based platforms with various formulations (liposome), vectors (Listeria monocytogenes), or modes of delivery (intratumoral, gene gun, etc.). Despite promising preclinical results, cancer vaccine trials without ICB have historically shown little clinical activity. With the anticipation and expansion of combinatorial immunotherapeutic trials with ICB, the cancer vaccine field has entered the personalized medicine arena with recent advances in immunogenic neoantigen-based vaccines. In this article, we review the literature to organize the different cancer vaccines in the clinical space, and we will discuss their advantages, limits, and recent progress to overcome their challenges. Furthermore, we will also discuss recent preclinical advances and clinical strategies to combine vaccines with checkpoint blockade to improve therapeutic outcome and present a translational perspective on future directions.

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.

Clearance of Chikungunya Virus Infection in Lymphoid Tissues Is Promoted by Treatment with an Agonistic Anti-CD137 Antibody

CD137, a member of the tumor necrosis factor receptor superfamily of cell surface proteins, acts as a costimulatory receptor on T cells, natural killer cells, B cell subsets, and some dendritic cells. Agonistic anti-CD137 monoclonal antibody (MAb) therapy has been combined with other chemotherapeutic agents in human cancer trials. Based on its ability to promote tumor clearance, we hypothesized that anti-CD137 MAb might activate immune responses and resolve chronic viral infections. We evaluated anti-CD137 MAb therapy in a mouse infection model of chikungunya virus (CHIKV), an alphavirus that causes chronic polyarthritis in humans and is associated with reservoirs of CHIKV RNA that are not cleared efficiently by adaptive immune responses. Analysis of viral tropism revealed that CHIKV RNA was present preferentially in splenic B cells and follicular dendritic cells during the persistent phase of infection, and animals lacking B cells did not develop persistent CHIKV infection in lymphoid tissue. Anti-CD137 MAb treatment resulted in T cell-dependent clearance of CHIKV RNA in lymphoid tissue, although this effect was not observed in musculoskeletal tissue. The clearance of CHIKV RNA from lymphoid tissue by anti-CD137 MAb was associated with reductions in the numbers of germinal center B cells and follicular dendritic cells. Similar results were observed with anti-CD137 MAb treatment of mice infected with Mayaro virus, a related arthritogenic alphavirus. Thus, anti-CD137 MAb treatment promotes resolution of chronic alphavirus infection in lymphoid tissues by reducing the numbers of target cells for infection and persistence.IMPORTANCE Although CHIKV causes persistent infection in lymphoid and musculoskeletal tissues in multiple animals, the basis for this is poorly understood, which has hampered pharmacological efforts to promote viral clearance. Here, we evaluated the therapeutic effects on persistent CHIKV infection of an agonistic anti-CD137 MAb that can activate T cell and natural killer cell responses to clear tumors. We show that treatment with anti-CD137 MAb promotes the clearance of persistent alphavirus RNA from lymphoid but not musculoskeletal tissues. This occurs because anti-CD137 MAb-triggered T cells reduce the numbers of target germinal center B cells and follicular dendritic cells, which are the primary reservoirs for CHIKV in the spleen and lymph nodes. Our studies help to elucidate the basis for CHIKV persistence and begin to provide strategies that can clear long-term cellular reservoirs of infection.

A mathematical model of combined CD8 T cell costimulation by 4-1BB (CD137) and OX40 (CD134) receptors

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.

Vaccine Strategies to Improve Anti-cancer Cellular Immune Responses

More than many other fields in medicine, cancer vaccine development has been plagued by a wide gap between the massive amounts of highly encouraging preclinical data on one hand, and the disappointing clinical results on the other. It is clear now that traditional approaches from the infectious diseases' vaccine field cannot be borrowed as such to treat cancer. This review highlights some of the strategies developed to improve vaccine formulations for oncology, including research into more powerful or “smarter” adjuvants to elicit anti-tumoral cellular immune responses. As an illustration of the difficulties in translating smart preclinical strategies into real benefit for the cancer patient, the difficult road of vaccine development in lung cancer is given as example. Finally, an outline is provided of the combinatorial strategies that leverage the increasing knowledge on tumor-associated immune suppressive networks. Indeed, combining with drugs that target the dominant immunosuppressive pathway in a given tumor promises to unlock the true power of cancer vaccines and potentially offer long-term protection from disease relapse.

OX40 triggering concomitant to IL12-engineered cell vaccine hampers the immunoprevention of HER2/neu-driven mammary carcinogenesis

This study evaluated the effects of combining an OX40 agonistic antibody (aOX40) with a cell vaccine targeting HER2/neu, called "Triplex". Such HER2/neu cell vaccine included two biological adjuvants (interleukin 12 (IL12) and allogeneic histocompatibility antigens) and was previously found able to prevent autochthonous HER2/neu-driven mammary carcinogenesis. Timing of aOX40 administration, concomitantly or after cell vaccination, gave opposite results. Unexpectedly, vaccine efficacy was hampered by concomitant OX40 triggering. Such decreased immunoprevention was likely due to a reduced induction of anti-HER2/neu antibodies and to a higher level of Treg activation. On the contrary, aOX40 administration after the completion of vaccination slightly but significantly increased immunopreventive vaccine efficacy, and led to increased production of GM-CSF and IL10. In conclusion, OX40 triggering can either impair or ameliorate immunoprevention of HER2/neu-driven mammary carcinogenesis depending on the schedule of aOX40 administration.

A novel biologic platform elicits profound T cell costimulatory activity and antitumor immunity in mice

Combination immunotherapies utilizing complementary modalities that target distinct tumor attributes or immunosuppressive mechanisms, or engage different arms of the antitumor immune response, can elicit greater therapeutic efficacy than the component monotherapies. Increasing the number of agents included in a therapeutic cocktail can further increase efficacy, however, this approach poses numerous challenges for clinical translation. Here, a novel platform to simplify combination immunotherapy by covalently linking immunotherapeutic agonists to the costimulatory receptors CD134 and CD137 into a single heterodimeric drug, "OrthomAb", is shown. This reagent not only retains costimulatory T cell activity, but also elicits unique T cell functions that are not programmed by either individual agonist, and preferentially expands effector T cells over Tregs. Finally, in an aggressive melanoma model OrthomAb elicits better therapeutic efficacy compared to the unlinked agonists. This demonstration that two drugs can be combined into one provides a framework for distilling complex combination drug cocktails into simpler delivery platforms.

An Immunotherapeutic CD137 Agonist Releases Eomesodermin from ThPOK Repression in CD4 T Cells

Agonists to the TNF/TNFR costimulatory receptors CD134 (OX40) and CD137 (4-1BB) elicit antitumor immunity. Dual costimulation with anti-CD134 plus anti-CD137 is particularly potent because it programs cytotoxic potential in CD8⁺ and CD4⁺ T cells. Cytotoxicity in dual-costimulated CD4 T cells depends on the T-box transcription factor eomesodermin (Eomes), which we report is induced via a mechanism that does not rely on IL-2, in contrast to CD8⁺ CTL, but rather depends on the CD8 T cell lineage commitment transcription factor Runx3, which supports Eomes expression in mature CD8⁺ CTLs. Further, Eomes and Runx3 were indispensable for dual-costimulated CD4 T cells to mediate antitumor activity in an aggressive melanoma model. Runx3 is also known to be expressed in standard CD4 Th1 cells where it fosters IFN-γ expression; however, the CD4 T cell lineage commitment factor ThPOK represses transcription of Eomes and other CD8 lineage genes, such as Cd8a Hence, CD4 T cells can differentiate into Eomes⁺ cytotoxic CD4⁺CD8⁺ double-positive T cells by terminating ThPOK expression. In contrast, dual-costimulated CD4 T cells express Eomes, despite the continued expression of ThPOK and the absence of CD8α, indicating that Eomes is selectively released from ThPOK repression. Finally, although Eomes was induced by CD137 agonist, but not CD134 agonist, administered individually, CD137 agonist failed to induce CD134^-/- CD4 T cells to express Eomes or Runx3, indicating that both costimulatory pathways are required for cytotoxic Th1 programming, even when only CD137 is intentionally engaged with a therapeutic agonist.

Tumor-targeted costimulation with antibody-fusion proteins improves bispecific antibody-mediated immune response in presence of immunosuppressive factors

Therapeutic strategies aiming for the induction of an effective immune response at the tumor site can be severely hampered by the encounter of an immunosuppressive microenvironment. We investigated here the potential of concerted costimulation by tumor-directed antibody-fusion proteins with B7.1, 4-1BBL and OX40L to enforce bispecific antibody-induced T cell stimulation in presence of recognized immunosuppressive factors including IL-10, TGF-β, indoleamine 2,3-dioxygenase (IDO), PD-L1 and regulatory T cells. The expression and activity of these factors was demonstrated in the HT1080-FAP/PBMC co-culture setting, where individual and combined costimulation were still capable to enhance T cell stimulation, even though the general activation level was reduced. Additional blockade of TGF-ß or PD-1 resulted especially effective in further enhancing the degree of T cell activation. Here, best outcome was achieved by combined costimulation of targeted 4-1BBL and B7.1. Furthermore, their individual impact on the proliferation of naïve, memory and effector CD8⁺ and CD4⁺ T cell subsets, suggest the coverage of a comprehensive T cell response. Thus, our costimulatory antibody-fusion proteins show great potential to support T cell activation in adverse conditions dictated by the tumor microenvironment.

Combination therapy with an OX40L fusion protein and a vaccine targeting the transcription factor twist inhibits metastasis in a murine model of breast cancer

OX40 is a costimulatory receptor that potentiates proliferation, survival, memory formation, and effector function of CD4⁺ and CD8⁺ T-cells, while overcoming the suppressive activity of regulatory T-cells (Tregs). Here, we explored the combination of an OX40L fusion protein (OX40L-FP) with a poxvirus-based cancer vaccine (MVA-Twist-TRICOM) to inhibit tumor metastasis in the 4T1 murine breast cancer model. Contrary to the single agent treatments, the combination therapy significantly decreased the number of metastatic colonies per lung and prolonged survival. Depletion studies demonstrated that these effects were mediated by both CD4⁺ and CD8⁺ T-cells. The combination therapy a) increased the total number of T-cells in the CD4⁺Foxp3^- population and the CD4⁺ central and effector memory subsets within the lung, spleen, and draining lymph node, b) enhanced infiltration of CD4⁺ T-cells into metastatic areas of the lung, and (c) increased the number of functional CD8⁺ T-cells that produced IFNγ and TNFα. The combination therapy also promoted the development of KLRG1^-CD127⁺ memory precursor CD8⁺ T-cells, while reducing those with a KLRG1⁺ terminally differentiated phenotype. Moreover, the combination of OX40L-FP and vaccine induced greater CD4⁺ and CD8⁺ Twist-specific responses. In addition, Tregs isolated from mice receiving the combination were also less immunosuppressive in ex-vivo proliferation assays than those from the OX40L-FP and MVA-Twist-TRICOM monotherapy groups. Such results provide the rationale to combine co-stimulatory agonists with cancer vaccines for the treatment of tumor metastasis.

Cytokines and metabolic factors regulate tumoricidal T-cell function during cancer immunotherapy

Recent advances in cancer biology and genetics have fostered precision therapies targeting tumor-specific attributes. Immune-based therapies that elicit cytolytic T cells (CTL) specific for tumor antigens can provide therapeutic benefit to cancer patients, however, cure rates are typically low. This largely results from immunosuppressive mechanisms operating within the tumor microenvironment, many of which inflict metabolic stresses upon CTL. Conversely, immunotherapies can mitigate specific metabolic stressors. For instance, dual costimulation immunotherapy with CD134 (OX40) plus CD137 (4-1BB) agonists appears to mediate tumor control in part by engaging cytokine networks that enable infiltrating CTL to compete for limiting supplies of glucose. Future efforts combining modalities that endow CTL with complimentary metabolic advantages should improve therapeutic efficacies.

The promise of immunotherapy in head and neck squamous cell carcinoma: combinatorial immunotherapy approaches

The immune system plays a fundamental role in preventing cancer development by recognising and eliminating tumour cells. The recent success in the field of immunotherapy has confirmed the potential to exploit the immune response as a cancer treatment. Head and neck squamous cell carcinoma (HNSCC) is a malignancy characterized by dismal prognosis and high mortality rate; low survival outcomes in combination with significant toxicity of current treatment strategies highlight the necessity for novel therapeutic modalities. HNSCC is a favourable disease for immunotherapy, as immune escape plays a key role in tumour initiation and progression. T-cell checkpoint inhibitors targeting programmed cell death protein-1 have emerged as novel immunotherapy agents showing remarkable efficacy in HNSCC. However, only a minority of patients derive benefit for single-agent immunotherapies. In this regard, combinatorial immunotherapy approaches represent an alternative strategy that might increase the number of patients who respond to immunotherapy. Focusing on HNSCC, this review will summarise novel combinations of immune checkpoint blockade with other immunotherapy treatment modalities.

The importance of correctly timing cancer immunotherapy

INTRODUCTION

The treatment options for cancer-surgery, radiotherapy and chemotherapy-are now supplemented with immunotherapy. Previously underappreciated but now gaining strong interest are the immune modulatory properties of the three conventional modalities. Moreover, there is a better understanding of the needs and potential of the different immune therapeutic platforms. Key to improved treatment will be the combinations of modalities that complete each other's shortcomings. Area covered: Tumor-specific T-cells are required for optimal immunotherapy. In this review, the authors focus on the correct timing of different types of chemotherapeutic agents or immune modulators and immunotherapeutic drugs, not only for the activation and expansion of tumor-specific T-cells but also to support and enhance their anti-tumor efficacy. Expert opinion: At an early phase of disease, clinical success can be obtained using single treatment modalities but at later disease stages, combinations of several modalities are required. The gain in success is determined by a thorough understanding of the direct and indirect immune effects of the modalities used. Profound knowledge of these effects requires optimal tuning of immunomonitoring. This will guide the appropriate combination of treatments and allow for correct sequencing the order and interval of the different therapeutic modalities.

DNA vaccines, electroporation and their applications in cancer treatment

Numerous animal studies and recent clinical studies have shown that electroporation-delivered DNA vaccines can elicit robust Ag-specific CTL responses and reduce disease severity. However, cancer antigens are generally poorly immunogenic, requiring special conditions for immune response induction. To date, many different approaches have been used to elicit Ag-specific CTL and anti-neoplastic responses to DNA vaccines against cancer. In vivo electroporation is one example, whereas others include DNA manipulation, xenogeneic antigen use, immune stimulatory molecule and immune response regulator application, DNA prime-boost immunization strategy use and different DNA delivery methods. These strategies likely increase the immunogenicity of cancer DNA vaccines, thereby contributing to cancer eradication. However, cancer cells are heterogeneous and might become CTL-resistant. Thus, understanding the CTL resistance mechanism(s) employed by cancer cells is critical to develop counter-measures for this immune escape. In this review, the use of electroporation as a DNA delivery method, the strategies used to enhance the immune responses, the cancer antigens that have been tested, and the escape mechanism(s) used by tumor cells are discussed, with a focus on the progress of clinical trials using cancer DNA vaccines.

Enhancing the safety of antibody-based immunomodulatory cancer therapy without compromising therapeutic benefit: Can we have our cake and eat it too?

INTRODUCTION

Monoclonal antibodies (mAbs) targeting checkpoint inhibitors have demonstrated clinical benefit in treating patients with cancer and have paved the way for additional immune-modulating mAbs such as those targeting costimulatory receptors. The full clinical utility of these agents, however, is hampered by immune-related adverse events (irAEs) that can occur during therapy.

AREAS COVERED

We first provide a general overview of tumor immunity, followed by a review of the two major classes of immunomodulatory mAbs being developed as cancer therapeutics: checkpoint inhibitors and costimulatory receptor agonists. We then discuss therapy-associated adverse events. Finally, we describe in detail the mechanisms driving their therapeutic activity, with an emphasis on interactions between antibody fragment crystallizable (Fc) domains and Fc receptors (FcR).

EXPERT OPINION

Given that Fc-FcR interactions appear critical in facilitating the ability of immunomodulatory mAbs to elicit both therapeutically useful as well as adverse effects, the engineering of mAbs that can effectively engage their targets while limiting interaction with FcRs might represent a promising future avenue for developing the next generation of immune-enhancing tumoricidal agents with increased safety and retention of efficacy.

Deciphering CD137 (4-1BB) signaling in T-cell costimulation for translation into successful cancer immunotherapy

CD137 (4-1BB, TNF-receptor superfamily 9) is a surface glycoprotein of the TNFR family which can be induced on a variety of leukocyte subsets. On T and NK cells, CD137 is expressed following activation and, if ligated by its natural ligand (CD137L), conveys polyubiquitination-mediated signals via TNF receptor associated factor 2 that inhibit apoptosis, while enhancing proliferation and effector functions. CD137 thus behaves as a bona fide inducible costimulatory molecule. These functional properties of CD137 can be exploited in cancer immunotherapy by systemic administration of agonist monoclonal antibodies, which increase anticancer CTLs and enhance NK-cell-mediated antibody-dependent cell-mediated cytotoxicity. Reportedly, anti-CD137 mAb and adoptive T-cell therapy strongly synergize, since (i) CD137 expression can be used to select the T cells endowed with the best activities against the tumor, (ii) costimulation of the lymphocyte cultures to be used in adoptive T-cell therapy can be done with CD137 agonist antibodies or CD137L, and (iii) synergistic effects upon coadministration of T cells and antibodies are readily observed in mouse models. Furthermore, the signaling cytoplasmic tail of CD137 is a key component of anti-CD19 chimeric antigen receptors that are used to redirect T cells against leukemia and lymphoma in the clinic. Ongoing phase II clinical trials with agonist antibodies and the presence of CD137 sequence in these successful chimeric antigen receptors highlight the importance of CD137 in oncoimmunology.

Costimulation Endows Immunotherapeutic CD8 T Cells with IL-36 Responsiveness during Aerobic Glycolysis

CD134- and CD137-primed CD8 T cells mount powerful effector responses upon recall, but even without recall these dual-costimulated T cells respond to signal 3 cytokines such as IL-12. We searched for alternative signal 3 receptor pathways and found the IL-1 family member IL-36R. Although IL-36 alone did not stimulate effector CD8 T cells, in combination with IL-12, or more surprisingly IL-2, it induced striking and rapid TCR-independent IFN-γ synthesis. To understand how signal 3 responses functioned in dual-costimulated T cells we showed that IL-2 induced IL-36R gene expression in a JAK/STAT-dependent manner. These data help delineate a sequential stimulation process where IL-2 conditioning must precede IL-36 for IFN-γ synthesis. Importantly, this responsive state was transient and functioned only in effector T cells capable of aerobic glycolysis. Specifically, as the effector T cells metabolized glucose and consumed O2, they also retained potential to respond through IL-36R. This suggests that T cells use innate receptor pathways such as the IL-36R/axis when programmed for aerobic glycolysis. To explore a function for IL-36R in vivo, we showed that dual costimulation therapy reduced B16 melanoma tumor growth while increasing IL-36R gene expression. In summary, cytokine therapy to eliminate tumors may target effector T cells, even outside of TCR specificity, as long as the effectors are in the correct metabolic state.

Tumor-Unrelated CD4 T Cell Help Augments CD134 plus CD137 Dual Costimulation Tumor Therapy

The ability of immune-based cancer therapies to elicit beneficial CD8(+) CTLs is limited by tolerance pathways that inactivate tumor-specific CD4 Th cells. A strategy to bypass this problem is to engage tumor-unrelated CD4 Th cells. Thus, CD4 T cells, regardless of their specificity per se, can boost CD8(+) CTL priming as long as the cognate epitopes are linked via presentation on the same dendritic cell. In this study, we assessed the therapeutic impact of engaging tumor-unrelated CD4 T cells during dual costimulation with CD134 plus CD137 that provide help via the above-mentioned classical linked pathway, as well as provide nonlinked help that facilitates CTL function in T cells not directly responding to cognate Ag. We found that engagement of tumor-unrelated CD4 Th cells dramatically boosted the ability of dual costimulation to control the growth of established B16 melanomas. Surprisingly, this effect depended upon a CD134-dependent component that was extrinsic to the tumor-unrelated CD4 T cells, suggesting that the dual costimulated helper cells are themselves helped by a CD134(+) cell(s). Nevertheless, the delivery of therapeutic help tracked with an increased frequency of tumor-infiltrating granzyme B(+) effector CD8 T cells and a reciprocal decrease in Foxp3(+)CD4(+) cell frequency. Notably, the tumor-unrelated CD4 Th cells also infiltrated the tumors, and their deletion several days following initial T cell priming negated their therapeutic impact. Taken together, dual costimulation programs tumor-unrelated CD4 T cells to deliver therapeutic help during both the priming and effector stages of the antitumor response.

Immunostimulation by OX40 Ligand Transgenic Ewing Sarcoma Cells

Interleukin-2 (IL-2) transgenic Ewing sarcoma cells can induce tumor specific T and NK cell responses and reduce tumor growth in vivo and in vitro. Nevertheless, the efficiency of this stimulation is not high enough to inhibit tumor growth completely. In addition to recognition of the cognate antigen, optimal T-cell stimulation requires signals from so-called co-stimulatory molecules. Several members of the tumor necrosis factor superfamily have been identified as co-stimulatory molecules that can augment antitumor immune responses. OX40 (CD134) and OX40 ligand (OX40L = CD252; also known as tumor necrosis factor ligand family member 4) is one example of such receptor/ligand pair with co-stimulatory function. In the present investigation, we generated OX40L transgenic Ewing sarcoma cells and tested their immunostimulatory activity in vitro. OX40L transgenic Ewing sarcoma cells showed preserved expression of Ewing sarcoma-associated (anti)gens including lipase member I, cyclin D1 (CCND1), cytochrome P450 family member 26B1 (CYP26B1), and the Ewing sarcoma breakpoint region 1-friend leukemia virus integration 1 (EWSR1-FLI1) oncogene. OX40L-expressing tumor cells showed a trend for enhanced immune stimulation against Ewing sarcoma cells in combination with IL-2 and stimulation of CD137. Our data suggest that inclusion of the OX40/OX40L pathway of co-stimulation might improve immunotherapy strategies for the treatment of Ewing sarcoma.

Relevance of tumor-infiltrating lymphocytes in breast cancer

While breast cancer has not been considered a cancer amenable to immunotherapeutic approaches, recent studies have demonstrated evidence of significant immune cell infiltration via tumor-infiltrating lymphocytes in a subset of patient tumors. In this review we present the current evidence highlighting the clinical relevance and utility of tumor-infiltrating lymphocytes in breast cancer. Retrospective and prospective studies have shown that the presence of tumor-infiltrating lymphocytes is a prognostic marker for higher responses to neoadjuvant chemotherapy and better survival, particularly in triple negative and HER2-positive early breast cancer. Further work is required to determine the immune subsets important in this response and to discover ways of encouraging immune infiltrate in tumor-infiltrating lymphocytes-negative patients.

Therapeutic cancer vaccines

The clinical benefit of therapeutic cancer vaccines has been established. Whereas regression of lesions was shown for premalignant lesions caused by HPV, clinical benefit in cancer patients was mostly noted as prolonged survival. Suboptimal vaccine design and an immunosuppressive cancer microenvironment are the root causes of the lack of cancer eradication. Effective cancer vaccines deliver concentrated antigen to both HLA class I and II molecules of DCs, promoting both CD4 and CD8 T cell responses. Optimal vaccine platforms include DNA and RNA vaccines and synthetic long peptides. Antigens of choice include mutant sequences, selected cancer testis antigens, and viral antigens. Drugs or physical treatments can mitigate the immunosuppressive cancer microenvironment and include chemotherapeutics, radiation, indoleamine 2,3-dioxygenase (IDO) inhibitors, inhibitors of T cell checkpoints, agonists of selected TNF receptor family members, and inhibitors of undesirable cytokines. The specificity of therapeutic vaccination combined with such immunomodulation offers an attractive avenue for the development of future cancer therapies.

Boosting Cancer Immunotherapy with Anti-CD137 Antibody Therapy

In the past 5 years, immunomodulatory antibodies have revolutionized cancer immunotherapy. CD137, a member of the tumor necrosis factor receptor superfamily, represents a promising target for enhancing antitumor immune responses. CD137 helps regulate the activation of many immune cells, including CD4(+) T cells, CD8(+) T cells, dendritic cells, and natural killer cells. Recent studies indicate that the antitumor efficacy of therapeutic tumor-targeting antibodies can be augmented by the addition of agonistic antibodies targeting CD137. As ligation of CD137 provides a costimulatory signal in multiple immune cell subsets, combination therapy of CD137 antibody with therapeutic antibodies and/or vaccination has the potential to improve cancer treatment. Recently, clinical trials of combination therapies with agonistic anti-CD137 mAbs have been launched. In this review, we discuss the recent advances and clinical promise of agonistic anti-CD137 monoclonal antibody therapy.

The Promise of Preventive Cancer Vaccines

Years of unsuccessful attempts at fighting established tumors with vaccines have taught us all that they are only able to truly impact patient survival when used in a preventive setting, as would normally be the case for traditional vaccines against infectious diseases. While true primary cancer prevention is still but a long-term goal, secondary and tertiary prevention are already in the clinic and providing encouraging results. A combination of immunopreventive cancer strategies and recently approved checkpoint inhibitors is a further promise of forthcoming successful cancer disease control, but prevention will require a considerable reduction of currently reported toxicities. These considerations summed with the increased understanding of tumor antigens allow space for an optimistic view of the future.

4-1BB Agonists: Multi-Potent Potentiators of Tumor Immunity

Immunotherapy is a rapidly expanding field of oncology aimed at targeting, not the tumor itself, but the immune system combating the cancerous lesion. Of the many approaches currently under study to boost anti-tumor immune responses; modulation of immune co-receptors on lymphocytes in the tumor microenvironment has thus far proven to be the most effective. Antibody blockade of the T cell co-inhibitory receptor cytotoxic T lymphocyte antigen-4 (CTLA-4) has become the first FDA approved immune checkpoint blockade; however, tumor infiltrating lymphocytes express a diverse array of additional stimulatory and inhibitory co-receptors, which can be targeted to boost tumor immunity. Among these, the co-stimulatory receptor 4-1BB (CD137/TNFSF9) possesses an unequaled capacity for both activation and pro-inflammatory polarization of anti-tumor lymphocytes. While functional studies of 4-1BB have focused on its prominent role in augmenting cytotoxic CD8 T cells, 4-1BB can also modulate the activity of CD4 T cells, B cells, natural killer cells, monocytes, macrophages, and dendritic cells. 4-1BB’s expression on both T cells and antigen presenting cells, coupled with its capacity to promote survival, expansion, and enhanced effector function of activated T cells, has made it an alluring target for tumor immunotherapy. In contrast to immune checkpoint blocking antibodies, 4-1BB agonists can both potentiate anti-tumor and anti-viral immunity, while at the same time ameliorating autoimmune disease. Despite this, 4-1BB agonists can trigger high grade liver inflammation which has slowed their clinical development. In this review, we discuss how the underlying immunobiology of 4-1BB activation suggests the potential for therapeutically synergistic combination strategies in which immune adverse events can be minimized.

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.

Betting on improved cancer immunotherapy by doubling down on CD134 and CD137 co-stimulation

The ability of T cells to recognize a vast array of antigens enables them to destroy tumor cells while inflicting minimal collateral damage. Nevertheless, tumor antigens often are a form of self-antigen, and thus tumor immunity can be dampened by tolerance mechanisms that evolved to prevent autoimmunity. Since tolerance can be induced by steady-state antigen-presenting cells that provide insufficient co-stimulation, the exogenous administration of co-stimulatory agonists can favor the expansion and tumoricidal functions of tumor-specific T cells. Agonists of the co-stimulatory tumor necrosis factor receptor (TNFR) family members CD134 and CD137 exert antitumor activity in mice, and as monotherapies have exhibited encouraging results in clinical trials. This review focuses on how the dual administration of CD134 and CD137 agonists synergistically boosts T-cell priming and elaborates a multi-pronged antitumor immune response, as well as how such dual co-stimulation might be translated into effective anticancer therapies.

The anti-lymphoma activities of anti-CD137 monoclonal antibodies are enhanced in FcγRIII(-/-) mice

Agonistic monoclonal antibodies (mAbs) directed against the co-signaling molecule CD137 (4-1BB) elicit potent anti-tumor immunity in mice. This anti-tumor immunity has traditionally been thought to result from the ability of the Fab portion of anti-CD137 to function as an analog for CD137L. Although binding of CD137 by anti-CD137 mAbs has the potential to cross-link the Fc fragments, enabling Fc engagement of low to moderate affinity Fc gamma receptors (FcγR), the relative import of such Fc-FcγR interactions in mediating anti-CD137 associated anti-tumor immunity is unknown. We studied the ability of a rat anti-mouse CD137 mAb (2A) to mediate the anti-tumor response against the EL4E7 lymphoma in WT and FcγR(-/-) strains. 2A-treated FcRγ(-/-) mice had improved anti-tumor immunity against EL4E7, which could be completely recapitulated in FcγRIII(-/-) animals. These improved anti-tumor responses were associated with increased splenic CD8β T cell and dendritic cell (DC) populations. Furthermore, there was an increase in the number of DCs expressing high levels of the CD40, CD80, and CD86 molecules that are associated with more effective antigen presentation. Our results demonstrate an unexpected inhibitory role for FcγRIII in the anti-tumor function of anti-CD137 and underscore the need to consider antibody isotype when engineering therapeutic mAbs.

Apoptosis-regulated low-avidity cancer-specific CD8(+) T cells can be rescued to eliminate HER2/neu-expressing tumors by costimulatory agonists in tolerized mice

A major barrier to vaccines in cancer treatment is their failure to activate and maintain a complete cancer-specific CD8(+) effector T-cell repertoire. Low-avidity T cells are more likely to escape clonal deletion in the thymus when compared with high-avidity T cells, and therefore comprise the major population of effector T cells available for activation in patients with cancer. However, low-avidity T cells fail to traffic into the tumor microenvironment and function in eradicating tumor under optimal vaccination conditions as opposed to high-avidity T cells that escape clonal deletion and function in tumor killing. We used high- and low-avidity T-cell receptor transgenic CD8(+) T cells specific for the immunodominant epitope HER2/neu (RNEU420-429) to identify signaling pathways responsible for the inferior activity of the low-avidity T cells. Adoptive transfer of these cells into tumor-bearing vaccinated mice identified the members of apoptosis pathways that are upregulated in low-avidity T cells. The increased expression of proapoptotic proteins by low-avidity T cells promoted their own cell death and also that of other tumor-specific CD8(+) T cells within their local environment. Importantly, we show that this proapoptotic effect can be overcome by using a strong costimulatory signal that prevents the activation-induced cell death and enables the low-avidity T cells to traffic into the tumor and assist in tumor clearance. These findings identify new therapeutic opportunities for activating the most potent anticancer T-cell responses.

A prospective study of the efficacy of a combination of autologous dendritic cells, cytokine-induced killer cells, and chemotherapy in advanced non-small cell lung cancer patients

Dendritic cells (DC) play a crucial role in the induction of an effective antitumor immune response. Cytokine-induced killer (CIK) cells, a subset of T lymphocytes, have the capacity to eliminate cancer cells. This study was to evaluate the correlation between the frequency of DC/CIK immunotherapies following regular chemotherapy, the time-to-progression (TTP), and overall survival (OS) of advanced non-small lung cancer patients. Sixty patients with IIIB-IV non-small-cell lung carcinoma (NSCLC) were enrolled from August 2007 to December 2009 and were randomized into two groups. All 60 patients received four courses of navelbine-platinum (NP) chemotherapy. In one group, 30 patients were treated with adoptive autologous DC/CIK cell transfusion twice every 30 days. In the other group, the patients received immunotherapies more than twice every 30 days. The adverse effects, TTP, and OS were evaluated between the two groups. Median survival time of all 60 patients was 13.80 months. The 1-, 2-, and 3-year overall survival rates were 60.0, 21.7, and 15.0 %, respectively. The 1-, 2-, and 3-year overall survival rates of patients receiving more than two immunotherapies were 63.3, 30.0, and 23.3 %, and the rates of those receiving two immunotherapies were 56.7, 13.3, and 6.7 %, respectively. The difference between the two groups was statistically significant (P = 0.037). Compared with patients in the fewer immunotherapies group, TTP in the group receiving more immunotherapies significantly prolonged, with the median improving from 6.2 months (95 % CI, 5.35-9.24) to 7.3 months (95 % CI, 5.45-6.95; P = 0.034). The adverse effects of chemoimmunotherapy were tolerable. Advanced NSCLC patients can benefit from the combination of DC/CIK immunotherapies following conventional chemotherapy. More than two immunotherapies improved TTP and OS of those patients in this study.

CD134/CD137 dual costimulation-elicited IFN-γ maximizes effector T-cell function but limits Treg expansion

T cell tolerance to tumor antigens represents a major hurdle in generating tumor immunity. Combined administration of agonistic monoclonal antibodies to the costimulatory receptors CD134 plus CD137 can program T cells responding to tolerogenic antigen to undergo expansion and effector T cell differentiation, and also elicits tumor immunity. Nevertheless, CD134 and CD137 agonists can also engage inhibitory immune components. To understand how immune stimulatory versus inhibitory components are regulated during CD134 plus CD137 dual costimulation, the current study utilized a model where dual costimulation programs T cells encountering a highly tolerogenic self-antigen to undergo effector differentiation. IFN-γ was found to play a pivotal role in maximizing the function of effector T cells while simultaneously limiting the expansion of CD4⁺CD25⁺Foxp3⁺ Tregs. In antigen-responding effector T cells, IFN-γ operates via a direct cell-intrinsic mechanism to cooperate with IL-2 to program maximal expression of granzyme B. Simultaneously, IFN-γ limits expression of the IL-2 receptor alpha chain (CD25) and IL-2 signaling through a mechanism that does not involve T-bet-mediated repression of IL-2. IFN-γ also limited CD25 and Foxp3 expression on bystanding CD4⁺Foxp3⁺ Tregs, and limited the potential of these Tregs to expand. These effects could not be explained by the ability of IFN-γ to limit IL-2 availability. Taken together, during dual costimulation IFN-γ interacts with IL-2 through distinct mechanisms to program maximal expression of effector molecules in antigen-responding T cells while simultaneously limiting Treg expansion.

Whole cell vaccines--past progress and future strategies

Cancer vaccines have shown success in curing tumors in preclinical models. Accumulating evidence also supports their ability to induce immune responses in patients. In many cases, these responses correlate with improved clinical outcomes. However, cancer vaccines have not yet demonstrated their true potential in clinical trials. This is likely due to the difficulty in mounting a significant anti-tumor response in patients with advanced disease because of pre-existing tolerance mechanisms that are actively turning off immune recognition in cancer patients. This review will examine the recent progress being made in the design and implementation of whole cell cancer vaccines, one vaccine approach that simultaneously targets multiple tumor antigens to activate the immune response. These vaccines have been shown to induce antigen-specific T-cell responses. Preclinical studies evaluating these vaccines given in sequence with other agents and cancer treatment modalities support the use of immunomodulating doses of chemotherapy and radiation, as well as immune-modulating pathway-targeted monoclonal antibodies, to enhance the efficacy of cancer vaccines. Based on emerging preclinical data, clinical trials are currently exploring the use of combinatorial immune-based therapies for the treatment of cancer.

Immunocombination therapy for high-risk neuroblastoma

Neuroblastoma (NBL) is an aggressive malignancy of the sympathetic nervous system. Advanced-stage NBLs prove fatal in approximately 50% of patients within 5 years. Therefore, new treatment modalities are urgently needed. Immunotherapy is a treatment modality that can be combined with established forms of treatment. Administration of monoclonal antibodies or dendritic cell-based therapies alone can lead to favorable clinical outcomes in individual cancer patients; for example patients with melanoma, lymphoma and NBL. However, clinical benefit is still limited to a minority of patients, and further improvements are clearly needed. In this article, we review the most commonly used approaches to treat patients with NBL and highlight the prerequisites and opportunities of cell-based immunotherapy, involving both innate and adaptive immune-effector cells. Furthermore, we discuss the potential of the combined application of immunotherapy and novel tumor-targeted therapies for the treatment of both cancer in general and NBL in particular.

Targeting costimulatory molecules to improve antitumor immunity

The full activation of T cells necessitates the concomitant activation of two signals, the engagement of T-cell receptor by peptide/major histocompatibility complex II and an additional signal delivered by costimulatory molecules. The best characterized costimulatory molecules belong to B7/CD28 and TNF/TNFR families and play crucial roles in the modulation of immune response and improvement of antitumor immunity. Unfortunately, tumors often generate an immunosuppressive microenvironment, where T-cell response is attenuated by the lack of costimulatory molecules on the surface of cancer cells. Thus, targeting costimulatory pathways represent an attractive therapeutic strategy to enhance the antitumor immunity in several human cancers. Here, latest therapeutic approaches targeting costimulatory molecules will be described.

CD134 plus CD137 dual costimulation induces Eomesodermin in CD4 T cells to program cytotoxic Th1 differentiation

Cytotoxic CD4 Th1 cells are emerging as a therapeutically useful T cell lineage that can effectively target tumors, but until now the pathways that govern their differentiation have been poorly understood. We demonstrate that CD134 (OX40) costimulation programs naive self- and virus-reactive CD4 T cells to undergo in vivo differentiation into cytotoxic Th1 effectors. CD137 (4-1BB) costimulation maximized clonal expansion, and IL-2 was necessary for cytotoxic Th1 differentiation. Importantly, the T-box transcription factor Eomesodermin was critical for inducing the cytotoxic marker granzyme B. CD134 plus CD137 dual costimulation also imprinted a cytotoxic phenotype on bystanding CD4 T cells. Thus, to our knowledge, the current study identifies for the first time a specific costimulatory pathway and an intracellular mechanism relying on Eomesodermin that induces both Ag-specific and bystander cytotoxic CD4 Th1 cells. This mechanism might be therapeutically useful because CD134 plus CD137 dual costimulation induced CD4 T cell-dependent tumoricidal function in a mouse melanoma model.

Signals through 4-1BB inhibit T regulatory cells by blocking IL-9 production enhancing antitumor responses

Previous studies from our laboratory indicate that intratumoral (i.t.) injections of CpG-ODN are the most effective adjuvant strategy to induce an antitumor immune response in tolerant BALB-neuT mice but insufficient for tumor eradication. We evaluated whether this treatment strategy could be enhanced by the presence of anti-OX40 and anti-4-1BB antibodies. Treatment with anti-4-1BB resulted in a greater antitumor response than anti-OX40. The results indicate that anti-4-1BB but not anti-OX40 inhibited the suppressive function of T regulatory cells (Tregs). Through microarray analysis we evaluated the mechanism by which anti-4-1BB inhibits iTregs using the Foxp3-GFP mice. We observed specific transcriptional differences in over 100 genes in iTregs treated with anti-4-1BB, and selected those genes that remained unaffected by exposure to anti-OX40. Interleukin 9 was transcriptionally down-regulated 28-fold by anti-4-1BB treatment, and this was matched by a significant reduction of IL-9 secretion by iTregs. Furthermore, blockade of the common γ-chain receptor resulted in the inhibition of iTreg-suppressive function. More importantly, neutralization of IL-9 plus i.t. injections of CpG-ODN induces tumor rejection in BALB-neuT and MUC-1 tolerant transgenic mice. These results indicate that IL-9 plays a role in iTreg biology during the tumor inflammatory process enhancing/promoting the suppressive function of these cells and that the blockade of IL-9 could serve as a novel strategy to modulate the function of Tregs to enhance the antitumor effect of tumor vaccines.

Integrating costimulatory agonists to optimize immune-based cancer therapies

While immunotherapy for cancer has become increasingly popular, clinical benefits for such approaches remain limited. This is likely due to tumor-associated immune suppression, particularly in the advanced-disease setting. Thus, a major goal of novel immunotherapeutic design has become the coordinate reversal of existing immune dysfunction and promotion of specific tumoricidal T-cell function. Costimulatory members of the TNF-receptor family are important regulators of T-cell-mediated immunity. Notably, agonist ligation of these receptors restores potent antitumor immunity in the tumor-bearing host. Current Phase I/II evaluation of TNF-receptor agonists as single-modality therapies will illuminate their safety, mechanism(s) of action, and best use in prospective combinational immunotherapy approaches capable of yielding superior benefits to cancer patients.

Delivery of immunostimulatory monoclonal antibodies by encapsulated hybridoma cells

Immunostimulatory monoclonal antibodies are immunoglobulins directed toward surface proteins of immune system cells that augment the immune response against cancer in a novel therapeutic fashion. Exogenous administration of the recombinant humanized immunoglobulins is being tested in clinical trials with agents of this kind directed at a variety of immune-controlling molecular targets. In this study, the encapsulation of antibody-producing hybridoma cells was tested in comparison with the systemic administration of monoclonal antibodies. Hybridomas producing anti-CD137 and anti-OX40 mAb were encapsulated in alginate to generate microcapsules containing viable cells that secrete antibody. Immobilized cells in vitro were able to release the rat immunoglobulin produced by the hybridomas into the supernatant. Microcapsules were implanted by injection into the subcutaneous tissue of mice and thereby provided a platform for viable secreting cells, which lasted for more than 1 week. The pharmacokinetic profile of the rat monoclonal antibodies following microcapsule implantation was similar to that attained following an intraperitoneal administration of the purified antibodies. The rat-mouse hybridoma cells did not engraft as tumors in immunocompetent mice, while they lethally xenografted in immunodeficient mice, if not microencapsulated. The antitumor therapeutic activity of the strategy was studied on established CT26 colon carcinomas resulting in complete tumor eradication in an elevated fraction of cases and strong tumor-specific CTL responses with either anti-CD137 or anti-OX40 producing hybridomas, thus offering proof of the concept. This form of administration permitted combinations of more than one immunostimulatory monoclonal antibody to exploit the synergistic effects such as those known to be displayed by anti-CD137 and anti-OX40 mAb.

Anti-tumor immune response induced by dendritic cells transduced with truncated PSMA IRES 4-1BBL recombinant adenoviruses

Up-regulation of receptor-ligand pairs during interaction of a peptide-bound MHC complex on dendritic cells (DCs) with cognate TCR may amplify, sustain, and drive diversity in the ensuing T cell immune response. Members of the TNF ligand superfamily and the TNFR superfamily contribute to this costimulatory molecule signaling. In the present study, we used replication deficient adenoviruses to introduce a tumor-associated Ag (a truncated human prostate-specific membrane antigen (tPSMA)) and the T cell costimulatory molecule 4-1BBL into murine DCs, and observed the ability of these recombinant DCs to elicit tPSMA-directed T-cell responses in vitro and anti-tumor immunity to RM-1-tPSMA in a murine tumor model. Infection of DCs with Ad-tPSMA-IRES-m4-1BBL induced tPSMA-specific proliferative responses and up-regulated CD80 and CD86 s signaling molecules. The cytotoxic T lymphocytes activated by the Ad-tPSMA-IRES-m4-1BBL-transfected DCs showed significantly higher IFN-gamma production and cytotoxicity against the RM-1 cells transfected with tPSMA. Moreover, vaccination of mice with Ad-tPSMA-IRES-m4-1BBL-transfected DCs induced a potent protective and therapeutic anti-tumor immunity to RM-1-tPSMA in a tumor model. These results demonstrated that development of DCs engineered to express tPSMA and 4-1BBL by recombinant adenovirus-mediated gene transfer may offer a new strategy for prostate cancer immunotherapy.

Cancer, aging and immunotherapy: lessons learned from animal models

Aging of the immune system is associated with a dramatic reduction in responsiveness as well as functional dysregulation. This deterioration of immune function with advancing age is associated with an increased incidence of cancer. Although there is a plethora of reports evaluating the effect of immunotherapy in stimulating antitumor immune responses, the majority of these studies do not pay attention to the effect aging has on the immune system. Studies from our group and others indicate that immunotherapies could be effective in the young, are not necessarily effective in the old. To optimally stimulate an antitumor immune response in the old, it is necessary to (1) identify and understand the intrinsic defects of the old immune system and (2) use relevant models that closely reflect those of cancer patients, where self-tolerance and aging are present simultaneously. The present review summarizes some defects found in the old immune system affecting the activation of antitumor immune responses, the strategies used to activate stronger antitumor immune response in the old and the use of a tolerant animal tumor model to target a self-tumor antigen for the optimization of immunotherapeutic interventions in the old.