Conversion of tumor-specific CD4+ T-cell tolerance to T-cell priming through in vivo ligation of CD40

Immunotherapy of cancer in 2012

The immunotherapy of cancer has made significant strides in the past few years due to improved understanding of the underlying principles of tumor biology and immunology. These principles have been critical in the development of immunotherapy in the laboratory and in the implementation of immunotherapy in the clinic. This improved understanding of immunotherapy, enhanced by increased insights into the mechanism of tumor immune response and its evasion by tumors, now permits manipulation of this interaction and elucidates the therapeutic role of immunity in cancer. Also important, this improved understanding of immunotherapy and the mechanisms underlying immunity in cancer has fueled an expanding array of new therapeutic agents for a variety of cancers. Pegylated interferon-α2b as an adjuvant therapy and ipilimumab as therapy for advanced disease, both of which were approved by the United States Food and Drug Administration for melanoma in March 2011, are 2 prime examples of how an increased understanding of the principles of tumor biology and immunology have been translated successfully from the laboratory to the clinical setting. Principles that guide the development and application of immunotherapy include antibodies, cytokines, vaccines, and cellular therapies. The identification and further elucidation of the role of immunotherapy in different tumor types, and the development of strategies for combining immunotherapy with cytotoxic and molecularly targeted agents for future multimodal therapy for cancer will enable even greater progress and ultimately lead to improved outcomes for patients receiving cancer immunotherapy.

NFAT1 supports tumor-induced anergy of CD4(+) T cells

Cancer cells express antigens that elicit T cell-mediated responses, but these responses are limited during malignant progression by the development of immunosuppressive mechanisms in the tumor microenvironment that drive immune escape. T-cell hyporesponsiveness can be caused by clonal anergy or adaptive tolerance, but the pathophysiological roles of these processes in specific tumor contexts has yet to be understood. In CD4+ T cells, clonal anergy occurs when the T-cell receptor is activated in the absence of a costimulatory signal. Here we report that the key T-cell transcription factor NFAT mediates expression of anergy-associated genes in the context of cancer. Specifically, in a murine model of melanoma, we found that cancer cells induced anergy in antigen-specific CD4+ T-cell populations, resulting in defective production of several key effector cytokines. NFAT1 deficiency blunted the induction of anergy in tumor antigen-specific CD4+ T cells, enhancing antitumor responses. These investigations identified tumor-induced T-cell hyporesponsiveness as a form of clonal anergy, and they supported an important role for CD4+ T-cell anergy in driving immune escape. By illustrating the dependence of tumor-induced CD4+ T-cell anergy on NFAT1, our findings open the possibility of targeting this transcription factor to improve the efficacy of cancer immunotherapy or immunochemotherapy.

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.

Intratumor OX40 stimulation inhibits IRF1 expression and IL-10 production by Treg cells while enhancing CD40L expression by effector memory T cells

Treg cells maintain the tumor microenvironment in an immunosuppressive state preventing an effective anti-tumor immune response. A possible strategy to overcome Treg-cell suppression focuses on OX40, a costimulatory molecule expressed constitutively by Treg cells while being induced in activated effector T cells. OX40 stimulation, by the agonist mAb OX86, inhibits Treg-cell suppression and boosts effector T-cell activation. Here we uncover the mechanisms underlying the therapeutic activity of OX86 treatment dissecting its distinct effects on Treg and on effector memory T (Tem) cells, the most abundant CD4+ populations strongly expressing OX40 at the tumor site. In response to OX86, tumor-infiltrating Treg cells produced significantly less interleukin 10 (IL-10), possibly in relation to a decrease in the transcription factor interferon regulatory factor 1 (IRF1). Tem cells responded to OX86 by upregulating surface CD40L expression, providing a licensing signal to DCs. The CD40L/CD40 axis was required for Tem-cell-mediated in vitro DC maturation and in vivo DC migration. Accordingly, OX86 treatment was no longer therapeutic in CD40 KO mice. In conclusion, following OX40 stimulation, blockade of Treg-cell suppression and enhancement of the Tem-cell adjuvant effect both concurred to free DCs from immunosuppression and activate the immune response against the tumor.

Cellular and molecular requirements for rejection of B16 melanoma in the setting of regulatory T cell depletion and homeostatic proliferation

We have recently demonstrated that adoptive transfer of regulatory T cell-depleted polyclonal T cells into lymphopenic mice leads to rejection of B16 melanoma, which generated an opportunity to study host requirements for tumor rejection when it effectively occurred. CD8(+) T cell priming and tumor rejection required tumor Ag cross-presentation, as evidenced by tumor outgrowth in Kb(-/-) bone marrow chimeric or B71/2(-/-) mice. CD4(+) T cells were additionally required for optimal tumor control, although not through classical CD4 "help," as the frequency of primed CD8(+) T cells was similar in the absence of CD4(+) T cells, and tumor rejection did not depend upon CD40-CD40L interactions or on IL-2 production by CD4(+) T cells. Rather, CD4(+) T cells appeared to act at the effector phase of tumor rejection and responded to B16-derived Ags in vitro. At the effector phase, IFN-γ production by transferred T cells, but not host cells, was necessary. IFN-γ acted either on host or tumor cells and was associated with reduced tumor vascularity. Finally, tumor rejection occurred after transfer of TNF-α, perforin, or FasL-deficient T cells. However, perforin/FasL double-knockout T cells failed to reject, arguing that the killing of B16 melanoma cells could occur either via the cytotoxic granule or Fas pathways. Collectively, these results support a model in which host tumor Ag cross-presentation primes adoptively transferred T cells, which remain functional in the setting of homeostatic proliferation and regulatory T cell depletion, and which promote tumor rejection via IFN-γ and lysis via cytotoxic granules and/or FasL.

Cytotoxic chemotherapy and CD4+ effector T cells: an emerging alliance for durable antitumor effects

Standard cytotoxic chemotherapy can initially achieve high response rates, but relapses often occur in patients and represent a severe clinical problem. As increasing numbers of chemotherapeutic agents are found to have immunostimulatory effects, there is a growing interest to combine chemotherapy and immunotherapy for synergistic antitumor effects and improved clinical benefits. Findings from recent studies suggest that highly activated, polyfunctional CD4+ effector T cells have tremendous potential in strengthening and sustaining the overall host antitumor immunity in the postchemotherapy window. This review focuses on the latest progresses regarding the impact of chemotherapy on CD4+ T-cell phenotype and function and discusses the prospect of exploiting CD4+ T cells to control tumor progression and prevent relapse after chemotherapy.

Nuclear receptors as modulators of the tumor microenvironment

Over the past several decades of cancer research, the inherent complexity of tumors has become increasingly appreciated. In addition to acquired cell-intrinsic properties, tumor initiation and growth is supported by an abundance of parenchymal, inflammatory, and stromal cell types, which infiltrate and surround the tumor. Accumulating evidence shows that numerous components of this supportive milieu, referred to collectively as the tumor microenvironment, are indeed critical during the process of multistep tumorigenesis. These findings highlight the important interplay between neoplastic cells and tumor-associated cell types, and suggest that therapy should target both neoplastic cells and supportive stromal cells to effectively attenuate tumor growth. The nuclear receptor superfamily encompasses a druggable class of molecules expressed in numerous stromal and parenchymal cell types, whose established physiologic roles suggest their potential as therapeutic and preventive targets in the context of the reactive tumor microenvironment. In this minireview, we discuss recent evidence that tumor-associated inflammation, angiogenesis, and fibrosis can be modulated at the transcriptional level by nuclear receptors and their ligands. As these processes have been widely implicated in cancer initiation, progression, and resistance to current therapy, nuclear receptor ligands targeting the tumor microenvironment may be potent antitumor agents in combination therapies, including for preventing cancer development within high-risk populations.

T cells as vehicles for cancer vaccination

The success of cancer vaccines is dependent on the delivery of tumor-associated antigens (TAAs) within lymphoid tissue in the context of costimulatory molecules and immune stimulatory cytokines. Dendritic cells (DCs) are commonly utilized to elicit antitumor immune responses due to their attractive costimulatory molecule and cytokine expression profile. However, the efficacy of DC-based vaccines is limited by the poor viability and lymph-node migration of exogenously generated DCs in vivo. Alternatively, adoptively transferred T cells persist for long periods of time in vivo and readily migrate between the lymphoid and vascular compartments. In addition, T cells may be genetically modified to express both TAA and DC-activating molecules, suggesting that T cells may be ideal candidates to serve as cellular vehicles for antigen delivery to lymph node-resident DCs in vivo. This paper discusses the concept of using T cells to induce tumor-specific immunity for vaccination against cancer.

Immune modulation by chemotherapy or immunotherapy to enhance cancer vaccines

Chemotherapy has been a mainstay in cancer treatment for many years. Despite some success, the cure rate with chemotherapy remains unsatisfactory in some types of cancers, and severe side effects from these treatments are a concern. Recently, understanding of the dynamic interplay between the tumor and immune system has led to the development of novel immunotherapies, including cancer vaccines. Cancer vaccines have many advantageous features, but their use has been hampered by poor immunogenicity. Many developments have increased their potency in pre-clinical models, but cancer vaccines continue to have a poor clinical track record. In part, this could be due to an inability to effectively overcome tumor-induced immune suppression. It had been generally assumed that immune-stimulatory cancer vaccines could not be used in combination with immunosuppressive chemotherapies, but recent evidence has challenged this dogma. Chemotherapies could be used to condition the immune system and tumor to create an environment where cancer vaccines have a better chance of success. Other types of immunotherapies could also be used to modulate the immune system. This review will discuss how immune modulation by chemotherapy or immunotherapy could be used to bolster the effects of cancer vaccines and discuss the advantages and disadvantages of these treatments.

Interaction with FcγRIIB is critical for the agonistic activity of anti-CD40 monoclonal antibody

A high activatory/inhibitory FcγR binding ratio is critical for the activity of mAb such as rituximab and alemtuzumab that attack cancer cells directly and eliminate them by recruiting immune effectors. Optimal FcγR binding profiles of other anti-cancer mAb, such as immunostimulatory mAb that stimulate or block immune receptors, are less clear. In this study, we analyzed the importance of isotype and FcγR interactions in controlling the agonistic activity of the anti-mouse CD40 mAb 3/23. Mouse IgG1 (m1) and IgG2a (m2a) variants of the parental 3/23 (rat IgG2a) were engineered and used to promote humoral and cellular responses against OVA. The mouse IgG1 3/23 was highly agonistic and outperformed the parental Ab when promoting Ab (10-100-fold) and T cell (OTI and OTII) responses (2- to >10-fold). In contrast, m2a was almost completely inactive. Studies in FcγR knockout mice demonstrated a critical role for the inhibitory FcγRIIB in 3/23 activity, whereas activatory FcγR (FcγRI, -III, and -IV) was dispensable. In vitro experiments established that the stimulatory effect of FcγRIIB was mediated through Ab cross-linking delivered in trans between neighboring cells and did not require intracellular signaling. Intriguingly, activatory FcγR provided effective cross-linking of 3/23 m2a in vitro, suggesting the critical role of FcγRIIB in vivo reflects its cellular distribution and bioavailability as much as its affinity for a particular Ab isotype. In conclusion, we demonstrate an essential cross-linking role for the inhibitory FcγRIIB in anti-CD40 immunostimulatory activity and suggest that isotype will be an important issue when optimizing reagents for clinical use.

CD40 expression by human melanocytic lesions and melanoma cell lines and direct CD40 targeting with the therapeutic anti-CD40 antibody CP-870,893

Anti-CD40 antibodies are in clinical development in patients with metastatic melanoma, a cancer that has been reported earlier to express CD40. The antitumor activity of anti-CD40 antibodies may be mediated by direct cytotoxic effects on CD40-positive melanoma cells or indirectly through modulation of host cells. In these studies, biopsies of patients with primary and metastatic melanoma, short-term cultures, and established melanoma cell lines were analyzed for CD40 expression using a combination of methods including immunohistochemistry, flow cytometry, and gene expression profiling, and the cytotoxic effects of the anti-CD40 antibody CP-870,893 on melanoma cell lines were tested using cell viability assays. CD40 was expressed at a higher frequency in metastatic melanoma lesions compared with primary melanomas. There was a variable expression of CD40 in synchronous and metachronous melanoma metastases. Expression of CD40 was present in slightly over half of a large panel of short-term primary melanoma cultures, with a wide range of expression levels by flow cytometry. Similar results were obtained in established melanoma cell lines when analyzed at the mRNA level or by surface protein staining. In approximately one-third of cell lines, the expression of CD40 could be up-regulated with a histone deacetylase inhibitor. Treatment with increasing concentrations of CP-870,893 had no antitumor activity against either CD40-positive or negative melanoma cell lines. In conclusion, approximately one-third to one-half of melanomas expresses CD40 at variable levels. Direct exposure to a CD40-activating antibody does not lead to antitumor activity in melanoma cell lines, suggesting that the antitumor effects of these antibodies in the clinic may be indirectly mediated.

Active immunotherapy combined with blockade of a coinhibitory pathway achieves regression of large tumor masses in cancer-prone mice

Vaccines that aim to expand tumor-specific CD8(+) T cells have yielded disappointing results in cancer patients although they showed efficacy in transplantable tumor mouse models. Using a system that more faithfully mimics a progressing cancer and its immunoinhibitory microenvironment, we here show that in transgenic mice, which gradually develop adenocarcinomas due to expression of HPV-16 E7 within their thyroid, a highly immunogenic vaccine expressing E7 only induces low E7-specific CD8(+) T-cell responses, which fail to affect the size of the tumors. In contrast, the same type of vaccine expressing E7 fused to herpes simplex virus (HSV)-1 glycoprotein D (gD), an antagonist of the coinhibitory B- and T-lymphocyte attenuator (BTLA)/CD160-herpes virus entry mediator (HVEM) pathways, stimulates potent E7-specific CD8(+) T-cell responses, which can be augmented by repeated vaccination, resulting in initial regression of even large tumor masses in all mice with sustained regression in more than half of them. These results indicate that active immunization concomitantly with blockade of the immunoinhibitory HVEM-BTLA/CD160 pathways through HSV-1 gD may result in sustained tumor regression.

Induction of potent anti-tumor responses while eliminating systemic side effects via liposome-anchored combinatorial immunotherapy

Immunostimulatory therapies that activate immune response pathways are of great interest for overcoming the immunosuppression present in advanced tumors. Agonistic anti-CD40 antibodies and CpG oligonucleotides have previously demonstrated potent, synergistic anti-tumor effects, but their clinical use even as monotherapies is hampered by dose-limiting inflammatory toxicity provoked upon systemic exposure. We hypothesized that by anchoring immuno-agonist compounds to lipid nanoparticles we could retain the bioactivity of therapeutics in the local tumor tissue and tumor-draining lymph node, but limit systemic exposure to these potent molecules. We prepared PEGylated liposomes bearing surface-conjugated anti-CD40 and CpG and assessed their therapeutic efficacy and systemic toxicity compared to soluble versions of the same immuno-agonists, injected intratumorally in the B16F10 murine model of melanoma. Anti-CD40/CpG-liposomes significantly inhibited tumor growth and induced a survival benefit similar to locally injected soluble anti-CD40 + CpG. Biodistribution analyses following local delivery showed that the liposomal carriers successfully sequestered anti-CD40 and CpG in vivo, reducing leakage into systemic circulation while allowing draining to the tumor-proximal lymph node. Contrary to locally-administered soluble immunotherapy, anti-CD40/CpG-liposomes did not elicit significant increases in serum levels of ALT enzyme, systemic inflammatory cytokines, or overall weight loss, confirming that off-target inflammatory effects had been minimized. The development of a delivery strategy capable of inducing robust anti-tumor responses concurrent with minimal systemic side effects is crucial for the continued progress of potent immunotherapies toward widespread clinical translation.

Immunotherapy for melanoma

PURPOSE OF REVIEW

Melanoma therapy has recently seen significant progress, with several new drugs in phase II/III trials showing promising results. In this review, we discuss the most promising immunotherapies either already established or being developed, concentrating on agents for which there are high-level data to support or refute their role in treating this disease. This topic is timely, given the lengthy list of immune checkpoint inhibitors and vaccine formulations in development for melanoma.

RECENT FINDINGS

The discovery of immune checkpoint proteins like CTLA-4, PD-1 and CD40 and the development of antibodies and small molecules that either inhibit or promote their activity has lent a huge impetus to the immunotherapy of melanoma. The development of vaccines that include agonists of various immune signaling like the MAGE-3 ASCI has also revived the field of cancer vaccines. Melanoma is the 'poster child' for immunotherapy of cancer, since a recent randomized phase III trial showed a survival benefit for immunotherapy.

SUMMARY

The burgeoning field of immunotherapy for melanoma has important implications for clinicians, and for the novel paradigms of treatment and response assessment that immunotherapies will promote. The unique side-effect profile for immune checkpoint inhibitors will be a challenge but new skills for dealing with them in community based practice will be learned. The concept that physicians might see late regression, or progression followed by regression will cause a sea-change in the way patients are treated, since treating beyond progression may be suitable in some cases using immunotherapy.

CD40 agonists alter tumor stroma and show efficacy against pancreatic carcinoma in mice and humans

Immunosuppressive tumor microenvironments can restrain antitumor immunity, particularly in pancreatic ductal adenocarcinoma (PDA). Because CD40 activation can reverse immune suppression and drive antitumor T cell responses, we tested the combination of an agonist CD40 antibody with gemcitabine chemotherapy in a small cohort of patients with surgically incurable PDA and observed tumor regressions in some patients. We reproduced this treatment effect in a genetically engineered mouse model of PDA and found unexpectedly that tumor regression required macrophages but not T cells or gemcitabine. CD40-activated macrophages rapidly infiltrated tumors, became tumoricidal, and facilitated the depletion of tumor stroma. Thus, cancer immune surveillance does not necessarily depend on therapy-induced T cells; rather, our findings demonstrate a CD40-dependent mechanism for targeting tumor stroma in the treatment of cancer.

Immune modulation with weekly dosing of an agonist CD40 antibody in a phase I study of patients with advanced solid tumors

BACKGROUND

Single-dose infusion of the agonistic anti-CD40 monoclonal antibody (mAb) CP-870,893 accomplishes immune activation and clinical responses in patients with advanced cancers, but repeat dosing of this agent has not been reported.

RESULTS

Twenty-seven patients were enrolled. The most common adverse event was transient, infusion-related cytokine release syndrome (CRS). Dose-limiting toxicities included grade 3 CRS and grade 3 urticaria; the maximum tolerated dose (MTD) was estimated to be 0.2 mg/kg. Seven patients (26%) had stable disease as the best clinical response; no partial or complete responses were observed. At the MTD, patient B lymphocytes exhibited persistently increased expression of costimulatory and adhesion molecules without resetting to baseline between doses. In 4 of 8 patients (50%) evaluated at the MTD, there were marked declines in total CD3(+) T lymphocytes, as well as CD4(+) and CD8(+) subsets.

PATIENTS AND METHODS

Patients with advanced solid tumor malignancies received weekly intravenous infusions of CP-870,893 in four dose level cohorts. Safety and immune pharmacodynamics were assessed.

CONCLUSIONS

Weekly infusions of the agonist CD40 antibody CP-870,893 were well-tolerated, but there was little clinical activity in advanced cancer patients. Correlative studies demonstrate chronic B cell activation and in some patients, T cell depletion. Longer dosing intervals may be desirable for optimal immune pharmacodynamics.

Production and characterization of agonistic monoclonal antibodies against chicken CD40

CD40 is mainly expressed by professional antigen-presenting cells (APCs). Its ligand, CD40L, is transiently expressed on activated CD4(+) T-cells. CD40-CD40L interactions mediate T-cell help to APCs and provide crucial signals for affinity maturation and B-cell class switching. In mammals, agonistic monoclonal anti-CD40 antibodies (mAbs) mimic the effects of CD40L on APCs, leading to enhanced T-cell priming and expansion, increased antibody production and class switching. In this study, we describe agonistic anti-chicken CD40 mAb 2C5. This mAb detected CD40 on primary chicken B-cells and macrophages, DT40 B-cells, and HD11 macrophages, induced NO synthesis in HD11 macrophages, and stimulated DT40 B-cell proliferation. These observations demonstrated at least partial functional equivalence of 2C5 to chicken CD154. This mAb may therefore constitute a new tool to study the role of CD40 in the chicken immune system, and its agonistic effects suggest that it could also be used as an adjuvant.

Ethylenecarbodiimide-treated splenocytes carrying male CD4 epitopes confer histocompatibility Y chromosome antigen transplant protection by inhibiting CD154 upregulation

In humans and certain strains of laboratory mice, male tissue is recognized as nonself and destroyed by the female immune system via recognition of histocompatibility Y chromosome Ag (Hya). Male tissue destruction is thought to be accomplished by CTLs in a helper-dependent manner. We show that graft protection induced with the immunodominant Hya-encoded CD4 epitope (Dby) attached to female splenic leukocytes (Dby-SPs) with the chemical cross-linker ethylenecarbodiimide significantly, and often indefinitely, prolongs the survival of male skin graft transplants in an Ag-specific manner. In contrast, treatments with the Hya CD8 epitopes (Uty-/Smcy-SPs) failed to prolong graft survival. Dby-SP-tolerized CD4(+) T cells fail to proliferate, secrete IFN-gamma, or effectively prime a CD8 response in recipients of male grafts. Ag-coupled splenocyte treatment is associated with defective CD40-CD40L interactions as demonstrated by the observation that CD4 cells from treated animals exhibit a defect in CD40L upregulation following in vitro Ag challenge. Furthermore, treatment with an agonistic anti-CD40 Ab at the time of transplantation abrogates protection from graft rejection. Interestingly, anti-CD40 treatment completely restores the function of Dby-specific CD4 cells but not Uty- or Smcy-specific CD8 cells.

Immune regulatory antibodies: are they the next advance?

During the past decade, new insights into the mechanisms by which T-cell activation and proliferation are regulated have led to the identification of checkpoint proteins that either up- or down-modulate T-cell reactivity. In the presence of active malignancy, pathophysiologic inhibition of T-cell activity may predominate over stimulation. A number of antibodies have been generated that can block inhibitory checkpoint proteins or promote the activity of activating molecules. In murine models, their use alone or with a vaccine strategy has resulted in regression of poorly immunogenic tumors and cures of established tumors. The prototypical immune regulatory antibodies are those directed against cytotoxic T-lymphocyte antigen-4, a molecule present on activated T cells. In this review, the preclinical rationale and clinical experience with 2 anticytotoxic T-lymphocyte antigen-4 antibodies are extensively discussed, demonstrating that abrogation of an immune inhibitory molecule can result in significant regression of tumors and long-lasting responses. The unique kinetics of antitumor response and the characteristic immune-related side effects of ipilimumab are also discussed. This clinical efficacy of this promising antitumor agent has been evaluated in 2 randomized phase III trials, whose results are eagerly awaited. Programmed death (PD)-1 is another immune inhibitory molecule against which an abrogating human antibody has been prepared. Initial preclinical testing with anti-PD-1 and anti-PD-L1 has shown encouraging results. Stimulatory molecules such as CD40, 41-BB, and OX-40 are also targets for antibody binding and activation, not blockade, and early dose ranging trials with antibodies against all 3 have shown that they can mediate regression of tumors, albeit with their own spectrum of side effects that are different from those that occur with abrogation of immune inhibition.

Immunotherapy for melanoma: current status and perspectives

Immunotherapy is an important modality in the therapy of patients with malignant melanoma. As our knowledge about this disease continues to expand, so does the immunotherapeutic armamentarium. Nevertheless, successful preclinical models do not always translate into clinically meaningful results. The authors give a comprehensive analysis of most recent advances in the immune anti-melanoma therapy, including interleukins, interferons, other cytokines, adoptive immunotherapy, biochemotherapy, as well as the use of different vaccines. We also present the fundamental concepts behind various immune enhancement strategies, passive immunotherapy, as well as the use of immune adjuvants. This review brings into discussion the results of newer and older clinical trials, as well as potential limitations and drawbacks seen with the utilization of various immune therapies in malignant melanoma. Development of novel therapeutic approaches, along with optimization of existing therapies, continues to hold a great promise in the field of melanoma therapy research. Use of anti-CTLA4 and anti-PD1 antibodies, realization of the importance of co-stimulatory signals, which translated into the use of agonist CD40 monoclonal antibodies, as well as activation of innate immunity through enhanced expression of co-stimulatory molecules on the surface of dendritic cells by TLR agonists are only a few items on the list of recent advances in the treatment of melanoma. The need to engineer better immune interactions and to boost positive feedback loops appear crucial for the future of melanoma therapy, which ultimately resides in our understanding of the complexity of immune responses in this disease.

Direct CD4 help provision following interaction of memory CD4 and CD8 T cells with distinct antigen-presenting dendritic cells

Accumulating evidence suggests that CD4 help is needed at the memory stage to mount effective secondary CD8 T cell responses. In this paper, we report that memory CD4 T cells can provide efficient help to memory CD8 T cells after interaction of the two lymphocytes with distinct dendritic cells. Provision of help to CD8 T cells required direct cell-cell contact and involved both IL-2 and CD40 ligation, within a CD4-CD8 T cell synapse. Thus, following antigenic interaction with APCs, activated memory CD4 and CD8 T cells appear to separate from their respective APCs before meeting each other for help provision, regardless of their Ag specificity. CD4 help for memory CD8 T cells therefore appears to be conditioned primarily not by Ag specificity but by activation status.

Activation of tolerogenic dendritic cells in the tumor draining lymph nodes by CD8+ T cells engineered to express CD40 ligand

Tolerogenic dendritic cells in the tumor microenvironment can inhibit the generation and maintenance of robust antitumor T cell responses. In this study, we investigated the effects of local delivery of CD40L by tumor-reactive CD8(+) T cells on dendritic cell activation and antitumor T cell responses in the TRAMP model. To increase the immunostimulatory signal, CD40L was engineered, by deleting the majority of the cytoplasmic domain, to increase its levels of expression and duration on the surface of CD8(+) T cells. Tumor-reactive CD8(+) T cells expressing the truncated form of CD40L stimulated maturation of dendritic cells in vitro and in the prostate draining lymph nodes in vivo. Following dendritic cell maturation, a significantly higher fraction of adoptively transferred, tumor-reactive (reporter) CD8(+) T cells was stimulated to express IFN-gamma and infiltrate the prostate tissue. The antitumor CD8(+) T cell response was further enhanced if TRAMP mice were also immunized with a tumor-specific Ag. These findings demonstrate that augmented T cell responses can be achieved by engineering tumor-reactive T cells to deliver stimulatory signals to dendritic cells in the tumor microenvironment.

Enhancement of humoral and cellular immunity with an anti-glucocorticoid-induced tumour necrosis factor receptor monoclonal antibody

Adjuvants, including antibodies to tumour necrosis factor receptor superfamily members, augment immune responses. One member of this family, glucocorticoid-induced tumour necrosis factor receptor (GITR), is expressed at low levels on naive/resting T cells, B cells and macrophages, but at higher levels on T regulatory cells. The aim of this study was to determine the ability of a rat anti-mouse GITR monoclonal antibody, 2F8, to stimulate murine humoral and cellular immunity in a prime boost model with particular attention to posology and antigen-specific effects. 2F8 enhanced the humoral immune response to ovalbumin and haemagglutinin (HA) compared with controls and this enhancement was equal to or greater than that obtained in mice dosed with standard adjuvants. 2F8 F(ab')(2) fragments were as effective as intact antibody in boosting humoral immunity, indicating that FcR-mediated cross-linking of 2F8 is not required for efficacy. Moreover, the enhanced response was durable and antigen specific. Administration of 2F8 shifted the immune response towards a T helper type 1 response with significant enhancement of immunoglobulin G2a- and G2b-specific anti-HA antibodies, as well as enhanced cellular immunity as measured by ELISPOT. 2F8-treated mice also generated significantly more neutralizing antibodies to HA than control mice. Our findings show that anti-GITR is a robust, versatile adjuvant that, unlike commonly used adjuvants that primarily enhance humoral immunity, enhances both humoral and cellular immunity. These results support the continued development of anti-GITR for such indications as haematological and solid tumours, chronic viral infections, and as a vaccine adjuvant.

Naive tumor-specific CD4(+) T cells differentiated in vivo eradicate established melanoma

In vitro differentiated CD8⁺ T cells have been the primary focus of immunotherapy of cancer with little focus on CD4⁺ T cells. Immunotherapy involving in vitro differentiated T cells given after lymphodepleting regimens significantly augments antitumor immunity in animals and human patients with cancer. However, the mechanisms by which lymphopenia augments adoptive cell therapy and the means of properly differentiating T cells in vitro are still emerging. We demonstrate that naive tumor/self-specific CD4⁺ T cells naturally differentiated into T helper type 1 cytotoxic T cells in vivo and caused the regression of established tumors and depigmentation in lymphopenic hosts. Therapy was independent of vaccination, exogenous cytokine support, CD8⁺, B, natural killer (NK), and NKT cells. Proper activation of CD4⁺ T cells in vivo was important for tumor clearance, as naive tumor-specific CD4⁺ T cells could not completely treat tumor in lymphopenic common gamma chain (γ_c)–deficient hosts. γ_c signaling in the tumor-bearing host was important for survival and proper differentiation of adoptively transferred tumor-specific CD4⁺ T cells. Thus, these data provide a platform for designing immunotherapies that incorporate tumor/self-reactive CD4⁺ T cells.

Immune stimulatory receptor CD40 is required for T-cell suppression and T regulatory cell activation mediated by myeloid-derived suppressor cells in cancer

Immune tolerance to tumors is often associated with accumulation of myeloid-derived suppressor cells (MDSC) and an increase in the number of T-regulatory cells (Treg). In tumor-bearing mice, MDSCs can themselves facilitate the generation of tumor-specific Tregs. In this study, we demonstrate that expression of the immune stimulatory receptor CD40 on MDSCs is required to induce T-cell tolerance and Treg accumulation. In an immune reconstitution model, adoptive transfer of Gr-1+CD115+ monocytic MDSCs derived from CD40-deficient mice failed to recapitulate the ability of wild-type MDSCs to induce tolerance and Treg development in vivo. Agonistic anti-CD40 antibodies phenocopied the effect of CD40 deficiency and also improved the therapeutic efficacy of IL-12 and 4-1BB immunotherapy in the treatment of advanced tumors. Our findings suggest that CD40 is essential not only for MDSC-mediated immune suppression but also for tumor-specific Treg expansion. Blockade of CD40-CD40L interaction between MDSC and Treg may provide a new strategy to ablate tumoral immune suppression and thereby heighten responses to immunotherapy.

Activation of human B cells by the agonist CD40 antibody CP-870,893 and augmentation with simultaneous toll-like receptor 9 stimulation

Background

CD40 activation of antigen presenting cells (APC) such as dendritic cells (DC) and B cells plays an important role in immunological licensing of T cell immunity. Agonist CD40 antibodies have been previously shown in murine models to activate APC and enhance tumor immunity; in humans, CD40-activated DC and B cells induce tumor-specific T cells in vitro. Although clinical translation of these findings for patients with cancer has been previously limited due to the lack of a suitable and available drug, promising clinical results are now emerging from phase I studies of the agonist CD40 monoclonal antibody CP-870,893. The most prominent pharmacodynamic effect of CP-870,893 infusion is peripheral B cell modulation, but direct evidence of CP-870,893-mediated B cell activation and the potential impact on T cell reactivity has not been reported, despite increasing evidence that B cells, like DC, regulate cellular immunity.

Methods

Purified total CD19+ B cells, CD19+ CD27+ memory, or CD19+ CD27^neg subsets from peripheral blood were stimulated in vitro with CP-870,893, in the presence or absence of the toll like receptor 9 (TLR9) ligand CpG oligodeoxynucleotide (ODN). B cell surface molecule expression and cytokine secretion were evaluated using flow cytometry. Activated B cells were used as stimulators in mixed lymphocyte reactions to evaluate their ability to induce allogeneic T cell responses.

Results

Incubation with CP-870,893 activated B cells, including both memory and naïve B cells, as demonstrated by upregulation of CD86, CD70, CD40, and MHC class I and II. CP-870,893-activated B cells induced T cell proliferation and T cell secretion of effector cytokines including IFN-gamma and IL-2. These effects were increased by TLR9 co-stimulation via a CpG ODN identical in sequence to a well-studied clinical grade reagent.

Conclusion

The CD40 mAb CP-870,893 activates both memory and naïve B cells and triggers their T cell stimulatory capacity. Simultaneous TLR9 ligation augments the effect of CP-870,893 alone. These results provide further rationale for combining CD40 and TLR9 activation using available clinical reagents in strategies of novel tumor immunotherapy.

Antitumor immunity and cancer stem cells

Self-renewing cancer stem cells (CSC) capable of spawning more differentiated tumor cell progeny are required for tumorigenesis and neoplastic progression of leukemias and several solid cancers. The mechanisms by which CSC cause tumor initiation and growth are currently unknown. Recent findings that suggest a negative correlation between degrees of host immunocompetence and rates of cancer development raise the possibility that only a restricted minority of malignant cells, namely CSC, may possess the phenotypic and functional characteristics to evade host antitumor immunity. In human malignant melanoma, a highly immunogenic cancer, we recently identified malignant melanoma initiating cells (MMIC), a novel type of CSC, based on selective expression of the chemoresistance mediator ABCB5. Here we present evidence of a relative immune privilege of ABCB5(+) MMIC, suggesting refractoriness to current immunotherapeutic treatment strategies. We discuss our findings in the context of established immunomodulatory functions of physiologic stem cells and in relation to mechanisms responsible for the downregulation of immune responses against tumors. We propose that the MMIC subset might be responsible for melanoma immune evasion and that immunomodulation might represent one mechanism by which CSC advance tumorigenic growth and resistance to immunotherapy. Accordingly, the possibility of an MMIC-driven tumor escape from immune-mediated rejection has important implications for current melanoma immunotherapy.

Nanoparticle-delivered multimeric soluble CD40L DNA combined with Toll-Like Receptor agonists as a treatment for melanoma

Stimulation of CD40 or Toll-Like Receptors (TLR) has potential for tumor immunotherapy. Combinations of CD40 and TLR stimulation can be synergistic, resulting in even stronger dendritic cell (DC) and CD8+ T cell responses. To evaluate such combinations, established B16F10 melanoma tumors were injected every other day X 5 with plasmid DNA encoding a multimeric, soluble form of CD40L (pSP-D-CD40L) either alone or combined with an agonist for TLR1/2 (Pam₃CSK₄ ), TLR2/6 (FSL-1 and MALP2), TLR3 (polyinosinic-polycytidylic acid, poly(I:C)), TLR4 ( monophosphoryl lipid A, MPL), TLR7 (imiquimod), or TLR9 (Class B CpG phosphorothioate oligodeoxynucleotide, CpG). When used by itself, pSP-D-CD40L slowed tumor growth and prolonged survival, but did not lead to cure. Of the TLR agonists, CpG and poly(I:C) also slowed tumor growth, and the combination of these two TLR agonists was more effective than either agent alone. The triple combination of intratumoral pSP-D-CD40L + CpG + poly(I:C) markedly slowed tumor growth and prolonged survival. This treatment was associated with a reduction in intratumoral CD11c+ dendritic cells and an influx of CD8+ T cells. Since intratumoral injection of plasmid DNA does not lead to efficient transgene expression, pSP-D-CD40L was also tested with cationic polymers that form DNA-containing nanoparticles which lead to enhanced intratumoral gene expression. Intratumoral injections of pSP-D-CD40L-containing nanoparticles formed from polyethylenimine (PEI) or C32 (a novel biodegradable poly(B-amino esters) polymer) in combination with CpG + poly(I:C) had dramatic antitumor effects and frequently cured mice of B16F10 tumors. These data confirm and extend previous reports that CD40 and TLR agonists are synergistic and demonstrate that this combination of immunostimulants can significantly suppress tumor growth in mice. In addition, the enhanced effectiveness of nanoparticle formulations of DNA encoding immunostimulatory molecules such as multimeric, soluble CD40L supports the further study of this technology for tumor immunotherapy.

Regression of established AB1 murine mesothelioma induced by peritumoral injections of CpG oligodeoxynucleotide either alone or in combination with poly(I:C) and CD40 ligand plasmid DNA

INTRODUCTION

Stimulation of the CD40 receptor using an agonistic anti-CD40 antibody can slow the growth of AB1 tumors. Stimulation of the GITR receptor may also have antitumor activity by countering the immunosuppressive effects of regulatory CD4 T cells. Similarly, agonists for Toll-Like Receptors (TLR) such as CpG oligodeoxynucleotides (TLR9 agonist) have activity against AB1 tumors. Combinations of CpG with CD40 ligand and polyinosinic-polycytidylic acid (poly(I:C), TLR3 agonist) may be even stronger than CpG alone. The synergistic effects of these combinations have been tested in other tumor types but not in mesothelioma.

METHODS

Established AB1 mesothelioma tumors were injected with either plasmid DNA encoding a novel 4-trimer form of murine CD40 ligand (pSP-D-CD40L), GITR ligand (GITRL), or control plasmid DNA. In addition, CpG with or without poly(I:C) was also injected intratumorally.

RESULTS

Plasmid injections of pSP-D-CD40L or pSP-D-GITRL, had no significant antitumor effect, possibly reflecting the difficulty of administering DNA injections into this very dense tissue. However, the injection of CpG with or without poly(I:C) strongly suppressed tumor growth and led to long-term tumor-free survival. The response to a triple combination of pSP-D-CD40L + CpG + poly(I:C) was demonstrated by an increase in intratumoral CD8 T cells and a dramatic increase in F4/80 macrophages.

CONCLUSIONS

Intratumoral injections of plasmid DNAs encoding highly active forms of either CD40 ligand or GITR ligand had no significant antitumor effects in this model, although improved DNA delivery techniques could possibly improve this strategy. In contrast, intratumoral CpG injections had significant antitumor effects and there were indications that CpG plus poly(I:C) was even more effective. Taken together, these data confirm previous reports that immune stimulants, especially CpG TLR9 agonists, have potential as a treatment for mesothelioma.

Roadmap to a Better Therapeutic Tumor Vaccine

Cell-based cancer vaccines are a highly attractive alternative to standard cancer therapies. They theoretically have the capability of inciting a multitargeted therapeutic response that functions by reshaping the host-tumor interaction, tipping the balance in favor of tumor rejection. Due to the polyclonal immune response induced, they are less likely to result in therapeutic escape than most cancer treatments in use today. Their immune-based mechanism of action offers a unique approach to management that should not be limited by traditional modes of drug resistance. Their favorable side-effect profile further identifies them as a potential treatment modality of choice. Despite these positive features, a number of hurdles must be overcome in order for cancer vaccines to take their place in the clinic as part of standard cancer therapy. Vaccine protocols must be optimized both to induce a high-quality antitumor T-cell response and to abrogate established mechanisms of immune tolerance that actively function to shut antitumor T cells down. By applying basic knowledge of the molecular features of T-cell biology and immune tolerance to the design of trials that combine tumor vaccines with targeted immunomodulatory drugs, potent strategies for inducing effective antitumor immunity can be developed. The first of these combinatorial trials have already been reported and offer a tantalizing glimpse of the future of cancer immunotherapy.

The Janus faces of CD40 in cancer

CD40 is a TNF receptor family member that is widely recognized for its prominent role in immune regulation and homeostasis. Expression of CD40 is not restricted to normal lymphoid cells but is also evident in the majority of haemopoietic and epithelial malignancies where it has been implicated in oncogenic events. Accumulating evidence, however, suggests that the CD40 pathway can be exploited for cancer therapy by virtue of its ability to stimulate the host anti-tumor immune response, normalize the tumor microenvironment and directly suppress the growth of CD40-positive tumors. Here, we provide an overview of the multifaceted functions of the CD40 pathway in cancer and its emerging role in the treatment of malignancy.

Deficiencies in the CD40 and CD154 receptor-ligand system reduce experimental lung metastasis

It is established that experimental metastasis requires platelet activity. CD154 expressed on and released from activated platelets induces an inflammatory response in endothelial cells and monocytes, including tissue factor production. CD154 has also been shown to activate platelets in vitro and promote thrombus stability in vivo. These CD154 effects may be mediated, at least in part, by CD40 signaling on platelets and vascular endothelial cells. We have previously demonstrated prolonged bleeding and PFA-100 closure times in mice deficient for Cd154 or its receptor Cd40. In the present study, we hypothesized that Cd40 and Cd154 promote lung tumor formation in experimental metastasis in mice. We created mice doubly deficient in Cd40 and Cd154 (Dbl KO) and found them to be both fertile and viable. Injected tumor cells seeded poorly in mice deficient in Cd40 or Cd154, as well as Dbl KO, compared to wild-type mice. We sought to determine whether blood-borne Cd40 versus endothelial Cd40 contribute differentially to reduced experimental lung metastasis, as observed in Cd40 deficient mice. By bone marrow transplantation, we created mice deficient for Cd40 either in the blood compartment but not in the endothelium, or vice versa. We found that mice deficient in blood compartment Cd40 had fewer lung nodules compared to wild-type mice and mice deficient in endothelial Cd40. Our findings suggest an important contribution of the Cd40-Cd154 pathway to experimental lung metastasis. Furthermore, the data points to a selective role for peripheral blood cell Cd40 in this process.

Complete regression of advanced primary and metastatic mouse melanomas following combination chemoimmunotherapy

The development of therapeutic strategies which induce effective cellular antitumor immunity represents an important goal in cancer immunology. Here, we used the unique features of the genetically engineered Hgf-Cdk4(R24C) mouse model to identify a combination chemoimmunotherapy for melanoma. These mice develop primary cutaneous melanomas which grow progressively and metastasize in the absence of immunogenic foreign proteins such as oncogenes or antigens. Primary and metastatic tumors evade innate and adaptive immune defenses, although they naturally express melanocytic antigens which can be recognized by antigen-specific T cells. We found that primary melanomas continued to grow despite infiltration with adoptively transferred, in vivo-activated, tumor-specific CD8(+) T cells. To promote tumor immune defense, we developed a treatment protocol consisting of four complementary components: (a) chemotherapeutic preconditioning prior to (b) adoptive lymphocyte transfer and (c) viral vaccination followed by (d) adjuvant peritumoral injections of immunostimulatory nucleic acids. Lymphocyte ablation and innate antiviral immune stimulation cooperatively enhanced the expansion and the effector cell differentiation of adoptively transferred lymphocytes. The efficacy of the different treatment approaches converged in the tumor microenvironment and induced a strong cytotoxic inflammatory response enabling preferential recognition and destruction of melanoma cells. This combination chemoimmunotherapy caused complete regression of advanced primary melanomas in the skin and metastases in the lung with minimal autoimmune side effects. Our results in a clinically highly relevant experimental model provide a scientific rationale to evaluate similar strategies which unleash the power of innate and adaptive immune defense in future clinical trials.

Molecular mechanism and function of CD40/CD40L engagement in the immune system

SUMMARY

During the generation of a successful adaptive immune response, multiple molecular signals are required. A primary signal is the binding of cognate antigen to an antigen receptor expressed by T and B lymphocytes. Multiple secondary signals involve the engagement of costimulatory molecules expressed by T and B lymphocytes with their respective ligands. Because of its essential role in immunity, one of the best characterized of the costimulatory molecules is the receptor CD40. This receptor, a member of the tumor necrosis factor receptor family, is expressed by B cells, professional antigen-presenting cells, as well as non-immune cells and tumors. CD40 binds its ligand CD40L, which is transiently expressed on T cells and other non-immune cells under inflammatory conditions. A wide spectrum of molecular and cellular processes is regulated by CD40 engagement including the initiation and progression of cellular and humoral adaptive immunity. In this review, we describe the downstream signaling pathways initiated by CD40 and overview how CD40 engagement or antagonism modulates humoral and cellular immunity. Lastly, we discuss the role of CD40 as a target in harnessing anti-tumor immunity. This review underscores the essential role CD40 plays in adaptive immunity.

The biological basis for immunotherapy in patients with chronic myelogenous leukemia

BACKGROUND

Chronic myelogenous leukemia (CML) has long been recognized as an entity responsive to immunotherapeutic interventions. Despite the success of the tyrosine kinase inhibitors (TKIs) in this disease, CML remains incurable. Only allogeneic bone marrow transplantation can provide long-term eradication of CML.

METHODS

This review summarizes the recent advances in the field of immunology in CML, specifically in tumor antigen discovery, that have been incorporated into the design of new clinical trials.

RESULTS

Multiple vaccine approaches are currently under clinical investigation. Recent laboratory and clinical data also point to a unique interaction of TKIs with the immune system.

CONCLUSIONS

A better understanding of these interactions combined with advances in the field of immunotherapy will likely lead to incorporation of TKIs in future therapeutic interventions to develop a cure for this disease.

Tumoricidal effects of activated macrophages in a mouse model of chronic lymphocytic leukemia

The Emu-TCL1 transgenic mouse spontaneously develops a CD5(+) B cell lymphoproliferative disorder similar to human chronic lymphocytic leukemia (CLL). Given the ineffectual T cell antitumor responses in this mouse model of CLL, we sought to determine whether combined treatment with anti-CD40 mAb (alphaCD40) and CpG-containing oligodeoxynucleotides (CpG) could exert immunotherapeutic effects. We have previously shown that macrophages activated by sequential ligation of CD40 and TLR9 could become cytotoxic against solid tumor cell lines both in vitro and in vivo. In the current study, we find that alphaCD40 plus CpG-activated macrophages induce tumor B cell apoptosis in vitro and that alphaCD40 plus CpG treatment markedly retards tumor growth in immunodeficient SCID/Beige mice following transplantation of primary tumor B cells. Our results suggest a novel immunotherapeutic strategy for CLL that may be effective even in the face of tumor or chemotherapy-induced T cell immunodeficiency.

Costimulatory and coinhibitory receptors in anti-tumor immunity

SUMMARY

Despite the expression of antigens by tumor cells, spontaneous immune-mediated rejection of cancer seems to be a rare event. T-cell receptor engagement by peptide/major histocompatibility complexes constitutes the main signal for the activation of naive T cells but is not sufficient to initiate a productive generation and maintenance of effector cells. Full activation of T cells requires additional signals driven by costimulatory molecules present on activated antigen-presenting cells but rarely on tumors. Following the discovery of B7-1 (CD80), several other costimulatory molecules have been shown to contribute to T-cell activation and have relevance for improving anti-tumor immunity. Moreover, increasing the understanding of coinhibitory receptors has highlighted key additional pathways that can dominantly inhibit anti-tumor T-cell function. Improving positive costimulation, and interfering with negative regulation, continues to represent an attractive immunotherapeutic approach for the treatment of cancer. This review focuses upon those pathways with the highest potential for clinical application in human cancer patients.

Highlights from the perspectives in melanoma XII conference

The following meeting highlights are from the Perspectives in Melanoma XII conference, held in Scheveningen/The Hague, the Netherlands, on October 2-4, 2008. Selected reviews are included but further discussions of these and other presentations are posted at http://www.MelanomaCare.org.

Antigenic stimulation with cytochrome P450 2J expressed in mouse hepatocellular carcinoma cells regulates host anti-tumour immunity

Cytochrome P450 2J subfamily (CYP2J) enzymes expressed in mouse hepatocellular carcinoma (HCC) cells were identified as an antigen recognized by specific CD4(+) T cells and the structure of its T cell epitope was determined by proteomics-based exploration. The major histocompatibility complex (MHC) class II binding peptides were isolated from I-A(k)/peptide complex of dendritic cells (DCs) loaded or unloaded with MIH-2 mouse HCC cells. MHC class II-binding peptides found in MIH-2-loaded DCs but not in unloaded DCs were determined by tandem mass spectrometric analysis. The peptide, consisting of amino acid 276-290 (DFIDAFLKEMTKYPE) of mouse CYP2J enzymes, was identified as an antigenic peptide presented in the context of MHC class II. Preventive treatment of mice with CYP2J peptide stimulated interferon (IFN)-gamma production of splenocytes and suppressed the growth of implanted CYP2J-positive MIH-2 cells but not CYP2J-negative murine bladder tumour cells. However, continuous treatment of MIH-2-bearing mice with CYP2J peptide significantly suppressed IFN-gamma production of splenocytes and accelerated the growth of implanted MIH-2 tumours in vivo. Increased frequencies of CD4(+)forkhead box P3 regulatory T cells and CD11b(+)Gr-1(+) myeloid suppressor cells were observed in splenocytes from the continuously immunized mice. These results indicate that antigenecity of CYP2J isoforms expressed in HCC cells activate host anti-tumour immunity at an initial stage of HCC, but suppress host anti-tumour immunity with excessive antigenic stimulation at an advanced stage.

Cationic liposome-mediated transfection of CD40 ligand gene inhibits hepatic tumor growth of hepatocellular carcinoma in mice

OBJECTIVE

To evaluate the efficacy of cationic liposome-mediated CD40 ligand (CD40L) gene therapy for hepatocellular carcinoma.

METHODS

1x10(6) of parental H22 cells or H22 cells transfected with the expression vector containing murine CD40L cDNA encoding the entire coding region (pcDNA3.1(+)-mCD40L) were inoculated subcutaneously into the left flanks of syngenic BALB/C mice. The tumor-bearing mice (tumor nodules 10 mm in maximal diameter) received the treatment of the intratumoral injection of pcDNA3.1(+)-mCD40L/Transfectam, pcDNA3.1(+), or phosphate-buffered saline (PBS), or no treatment. The mice were monitored for tumor growth weekly. We examined mCD40L messenger ribonucleic acid (mRNA) expression by reverse transcription polymerase chain reaction (RT-PCR) and the histologic changes in tumors at two weeks after intratumoral injection using immunohistochemical staining of tumor tissues.

RESULTS

All mice inoculated with parental H22 cells developed a tumor subcutaneously, and the tumor size increased progressively within three weeks. However, the mice receiving H22-CD40L cells exhibited complete regression of the tumor two weeks after tumor cell inoculation. The tumor-bearing animals with the treatment of pcDNA3.1(+) or PBS, or without treatment had progressive tumor growth, while those mice treated with pcDNA3.1(+)-mCD40L exhibited a significant inhibition of tumor growth. RT-PCR analysis showed that 783-bp fragments corresponding to the mCD40L mRNA were amplified only from pcDNA3.1(+)-mCD40L treated tumors. The tumor samples from pcDNA3.1(+)-mCD40L-treated mice showed significant lymphocyte infiltration, apoptotic bodies, and confluent necrosis in the tumor tissues.

CONCLUSION

The tumorigenicity of CD40L-expressing cells was abrogated when the cells were implanted subcutaneously. In vivo gene therapy of established liver tumor nodules in mice by the intratumoral injection of pcDNA3.1(+)-mCD40L led to significant tumor inhibition. There was mCD40L mRNA expression in the tissues from pcDNA3.1(+)-mCD40L-treated tumors. The intratumoral injection of pcDNA3.1(+)-mCD40L induced a strong inflammatory, mainly lymphocytic infiltration of the tumor, and increased the necrotic rate of the neoplastic cells.

Overcoming immunologic tolerance to melanoma: targeting CTLA-4 with ipilimumab (MDX-010)

Targeted biologic therapies such as anti-cytotoxic T lymphocyte antigen (CTLA-4) monoclonal antibodies, either as monotherapy or in combination with chemotherapy or vaccines, have shown great promise in late-stage melanoma, which has a very poor prognosis. Melanoma is relatively resistant to both chemotherapy and radiotherapy. Blockade of CTLA-4, which inhibits T-cell proliferation, promotes stimulation of adaptive immunity and T-cell activation, resulting in eradication of tumor cells. Two human monoclonal antibodies are under investigation in melanoma. Phase II and III clinical trials are currently evaluating the efficacy and safety of ipilimumab (MDX-010, Medarex, Inc., Princeton, NJ, and Bristol-Myers Squibb, Princeton, NJ) and tremelimumab (CP-675,206; Pfizer Pharmaceuticals, New York) in melanoma. Data are available on ipilimumab, which has been explored as monotherapy and in combination with vaccines, other immunotherapies such as interleukin-2, and chemotherapies such as dacarbazine. Overall response rates range from 13% with ipilimumab plus vaccine in patients with stage IV disease to 17% and 22% with ipilimumab plus dacarbazine or interleukin-2, respectively, in patients with metastatic disease. Responses have been durable, and among those experiencing grade 3 or 4 autoimmune toxicities, even higher response rates have been seen--up to 36%. While the optimal dose of ipilimumab has yet to be established, studies also indicate that higher doses may be more effective. Importantly, the lack of an initial clinical response may not predict ultimate treatment failure, because the onset of a response may follow progressive disease or stable disease. Pending results from registration studies with ipilimumab and lessons learned from registration studies conducted with tremelimumab will help to define the role of anti-CTLA-4 blockade in the treatment of metastatic melanoma.

Heterospecific CD4 help to rescue CD8 T cell killers

Help from CD4 T cells may be required for optimal generation and maintenance of memory CD8 T cells and also for optimal Ag reactivation. We examined whether the helper cell and the CD8 killer cell need to have the same Ag specificity for help to be effective during interactions of memory T cells with mature APC. This is important because virus and tumor Ag-specific CD4 T cell responses are selectively impaired in several chronic viral infections and malignancies. We performed studies in vitro and in vivo and found that functional memory CD4 T cells generated from a distinct antigenic source (heterospecific helpers) could provide direct and effective help to memory CD8 T cells. Functional heterospecific memory CD4 T cells could also rescue secondary CD8 T cell responses in an experimental tumor model in which homospecific CD4 help was impaired. This could provide a rationale for immunotherapy strategies designed to bypass impaired homospecific help.

Self-antigen prevents CD8 T cell effector differentiation by CD134 and CD137 dual costimulation

We compared how CD4 vs CD8 cells attain the capacity to express the effector cytokine IFN-gamma under both immunogenic and tolerogenic conditions. Although the Ifng gene locus was epigenetically repressed in naive Ag-inexperienced CD4 cells, it had already undergone partial remodeling toward a transcriptionally competent configuration in naive CD8 cells. After TCR stimulation, CD8 cells fully remodeled the Ifng locus and gained the capacity to express high levels of IFN-gamma more rapidly than CD4 cells. Enforced dual costimulation through OX40 and 4-1BB redirected CD8 cells encountering soluble exogenous peptide to expand and differentiate into IFN-gamma and TNF-alpha double-producing effectors rather than becoming tolerant. Despite this and the stronger tendency of CD8 compared with CD4 cells to differentiate into IFN-gamma-expressing effectors, when parenchymal self-Ag was the source of tolerizing Ag, enforced dual costimulation selectively boosted expansion but did not push effector differentiation in CD8 cells while both expansion and effector differentiation were dramatically boosted in CD4 cells. Notably, enforced dual costimulation was able to push effector differentiation in CD8 cells encountering cognate parenchymal self-Ag when CD4 cells were simultaneously engaged. Thus, the ability of enforced OX40 plus 4-1BB dual costimulation to redirect CD8 cells to undergo effector differentiation was unexpectedly influenced by the source of tolerizing Ag and help was selectively required to facilitate CD8 cell effector differentiation when the tolerizing Ag derived from self.

Maleimide conjugation markedly enhances the immunogenicity of both human and murine idiotype-KLH vaccines

The collection of epitopes present within the variable regions of the tumor-specific clonal immunoglobulin expressed by B cell lymphomas (idiotype, Id) can serve as a target for active immunotherapy. Traditionally, tumor-derived Id protein is chemically conjugated to the immunogenic foreign carrier protein keyhole limpet hemocyanin (KLH) using glutaraldehyde to serve as a therapeutic vaccine. While this approach offered promising results for some patients treated in early clinical trials, glutaraldehyde Id-KLH vaccines have failed to induce immune and clinical responses in many vaccinated subjects. We recently described an alternative conjugation method employing maleimide-sulfhydryl chemistry that significantly increased the therapeutic efficacy of Id-KLH vaccines in three different murine B cell lymphoma models, with protection mediated by either CD8(+) T cells or antibodies. We now define in detail the methods and parameters critical for enhancing the in vivo immunogenicity of human as well as murine Id-KLH conjugate vaccines. Optimal conditions for Id sulfhydryl pre-reduction were determined, and maleimide Id-KLH conjugates maintained stability and potency even after prolonged storage. Field flow fractionation analysis of Id-KLH particle size revealed that maleimide conjugates were far more uniform in size than glutaraldehyde conjugates. Under increasingly stringent conditions, maleimide Id-KLH vaccines maintained superior efficacy over glutaraldehyde Id-KLH in treating established, disseminated murine lymphoma. More importantly, human maleimide Id-KLH conjugates were consistently superior to glutaraldehyde Id-KLH conjugates in inducing Id-specific antibody and T cell responses. The described methods should be easily adaptable to the production of clinical grade vaccines for human trials in B cell malignancies.

Potent tumor-specific protection ignited by adoptively transferred CD4+ T cells

Administration of anti-CD25 mAb before an aggressive murine breast tumor inoculation provoked effective antitumor immunity. Compared with CD4(+) T cells purified from anti-CD25 mAb-pretreated mice that did not reject tumor, CD4(+) T cells purified from anti-CD25 mAb-pretreated mice that rejected tumor stimulated by dendritic cells (DCs) produced more IFN-gamma and IL-2, and less IL-17 in vitro, and ignited protective antitumor immunity in vivo in an adoptive transfer model. Tumor Ag-loaded DCs activated naive CD8(+) T cells in the presence of these CD4(+) T cells in vitro. Tumor Ag and adoptively transferred CD4(+) T cells were both required for inducing a long-term tumor-specific IFN-gamma-producing cellular response and potent protective antitumor activity. Although adoptively transferred CD4(+) T cells ignited effective tumor-specific antitumor immunity in wild-type mice, they failed to do so in endogenous NK cell-depleted, Gr-1(+) cell-depleted, CD40(-/-), CD11c(+) DC-depleted, B cell(-/-), CD8(+) T cell-depleted, or IFN-gamma(-/-) mice. Collectively, the data suggest that adoptively transferred CD4(+) T cells orchestrate both endogenous innate and adaptive immunity to generate effective tumor-specific long-term protective antitumor immunity. The data also demonstrate the pivotal role of endogenous DCs in the tumor-specific protection ignited by adoptively transferred CD4(+) T cells. Thus, these findings highlight the importance of adoptively transferred CD4(+) T cells, as well as host immune components, in generating effective tumor-specific long-term antitumor activity.

Linkage of a tumor immune function and cell cycle de-regulation via a gene regulatory network subcircuit

Gene regulatory network (GRN) subcircuits have been described for cell fate progressions in animal development. The hallmark of these subcircuits is the integration of promoters, and positive- and negative-acting promoter binding proteins, such that an alteration in function of any one member of the defined subcircuit, occurring with a change in cell fate, defines a change in status for all other members of the subcircuit. Here we describe a GRN subcircuit that links a tumor immune function with cell cycle de-regulation. All members of this subcircuit have a predictable status change in response to rescue of the growth-controlled phenotype. Given the similarities between the molecular mechanisms underlying cell status changes in tumorigenesis and development, application of GRN paradigms to tumor progression is particularly apt and offers the hope of providing a more concise, reliable, and therapeutically useful series of predictions linking gene regulation and tumor progression.