Systemic targeting of CpG-ODN to the tumor microenvironment with anti-neu-CpG hybrid molecule and T regulatory cell depletion induces memory responses in BALB-neuT tolerant mice

Antibody conjugates for targeted delivery of Toll-like receptor 9 agonist to the tumor tissue

Imiquimod, a Toll-like receptor 7 (TLR7) agonist is routinely used for topical administration in basal cell carcinoma and stage zero melanoma. Similarly, the TLR agonist Bacillus Calmette-Guérin is used for the local treatment of bladder cancer and clinical trials showed treatment efficacy of intratumoral injections with TLR9 agonists. However, when administered systemically, endosomal TLR agonists cause adverse responses due to broad immune activation. Hence, strategies for targeted delivery of TLR agonists to the tumor tissue are needed to enable the widespread use of endosomal TLR agonists in the context of tumor immunotherapy. One strategy for targeted delivery of TLR agonist is their conjugation to tumor antigen-specific therapeutic antibodies. Such antibody-TLR agonist conjugates act synergistically by inducing local TLR-mediated innate immune activation which complements the anti-tumor immune mechanisms induced by the therapeutic antibody. In this study, we explored different conjugation strategies for TLR9 agonists to immunoglobulin G (IgG). We evaluated biochemical conjugation of immunostimulatory CpG oligodesoxyribonucleotides (ODN) to the HER2-specific therapeutic antibody Trastuzumab with different cross-linkers comparing stochastic with site-specific conjugation. The physiochemical make-up and biological activities of the generated Trastuzumab-ODN conjugates were characterized in vitro and demonstrated that site-specific conjugation of CpG ODN is crucial for maintaining the antigen-binding capabilities of Trastuzumab. Furthermore, site-specific conjugate was effective in promoting anti-tumor immune responses in vivo in a pseudo-metastasis mouse model with engineered human HER2-transgenic tumor cells. In this in vivo model, co-delivery of Trastuzumab and CpG ODN in form of site-specific conjugates was superior to co-injection of unconjugated Trastuzumab, CpG ODN or stochastic conjugate in promoting T cell activation and expansion. Thereby, this study highlights that site-specific conjugation of CpG ODN to therapeutic antibodies targeting tumor markers is a feasible and more reliable approach for generation of conjugates which retain and combine the functional properties of the adjuvant and the antibody.

Generation of αCD11b-CpG antibody conjugates for the targeted stimulation of myeloid cells

CpG oligonucleotides are short single-stranded synthetic DNA molecules. Upon binding to Toll-like receptor 9 (TLR9), CpG activates immune cells in humans and mice. This results in robust Th1 type immunity potentially resulting in clearance of pathogens, reduction of allergy and anti-tumor immunity. However, the effectiveness of CpG as an adjuvant depends on its administration route, with only strong effects seen when CpG is administered locally. As local administration is not always feasible, we generated conjugates to specifically deliver CpG to myeloid cells often abundantly present in tumors. For this we coupled CpG (3'-Thiol-modified phosphorothioate (PTO) CpG-ODN1826 type B (5'-tccatgacgttcctgacgtt-3')) to monoclonal antibodies (mAbs) directed against the myeloid cell marker CD11b using maleimide-thiol coupling. The CD11b-CpG mAb (αCD11b-CpG) conjugates contained about four CpG molecules/conjugate and displayed binding and internalization characteristics similar to unconjugated CD11b mAbs (αCD11b). The αCD11b-CpG conjugates readily induced maturation of murine dendritic cells (DCs) in a TLR9-dependent manner in vitro. Following intravenous injection, αCD11b-CpG conjugates efficiently targeted CD11b⁺ immune cells in the blood, lymph nodes and spleen. Finally, injection of αCD11b-CpG conjugates, but not untargeted conjugates, induced maturation of CD11b⁺ cell subsets in vivo. In conclusion, conjugating CpG to αCD11b enabled specific targeting and activation of myeloid cells in vivo.

Immunogenicity of rat-neu+ mouse mammary tumours determines the T cell-dependent therapeutic efficacy of anti-neu monoclonal antibody treatment

The use of Trastuzumab (Herceptin), a monoclonal antibody (mAb) targeting HER2/neu, results in an increased median survival in Her2⁺ breast cancer patients. The tumour mutational burden and the presence of tumour infiltrating lymphocytes (TILs) clearly correlate with response to trastuzumab. Here, we investigated if the immunogenicity of the transplantable rat-neu⁺ tumour cell line (TUBO) derived from a BALB/c-NeuT primary tumour is associated with the response to anti-neu mAb therapy. We compared the TUBO tumour outgrowth and tumour infiltrating T cells in isogenic (BALB/c-NeuT) and non-isogenic (WT BALB/c) recipient mice. Furthermore, therapeutic efficacy of anti-neu mAb and the contribution of T cells were examined in both mouse strains. The outgrowth of untreated tumours was significantly better in BALB/c-NeuT than WT BALB/c mice. Moreover, tumour infiltrating T cells were more abundantly present in WT BALB/c than BALB/c-NeuT mice, showing that the TUBO tumour was more immunogenic in WT BALB/c mice. In TUBO tumour bearing WT BALB/c mice, anti-neu mAb therapy resulted in an increase of tumour infiltrating T cells and long-term survival. When T cells were depleted, this strong anti-tumour effect was reduced to an outgrowth delay. In contrast, in TUBO tumour bearing BALB/c-NeuT mice, treatment with anti-neu mAb resulted only in tumour outgrowth delay, both in the presence and absence of T cells. We concluded that in immunogenic tumours the response to anti-neu mAb therapy is enhanced by additional T cell involvement compared to the response to anti-neu mAb in non-immunogenic tumours.

Engineering Targeting Materials for Therapeutic Cancer Vaccines

Therapeutic cancer vaccines constitute a valuable tool to educate the immune system to fight tumors and prevent cancer relapse. Nevertheless, the number of cancer vaccines in the clinic remains very limited to date, highlighting the need for further technology development. Recently, cancer vaccines have been improved by the use of materials, which can strongly enhance their intrinsic properties and biodistribution profile. Moreover, vaccine efficacy and safety can be substantially modulated through selection of the site at which they are delivered, which fosters the engineering of materials capable of targeting cancer vaccines to specific relevant sites, such as within the tumor or within lymphoid organs, to further optimize their immunotherapeutic effects. In this review, we aim to give the reader an overview of principles and current strategies to engineer therapeutic cancer vaccines, with a particular focus on the use of site-specific targeting materials. We will first recall the goal of therapeutic cancer vaccination and the type of immune responses sought upon vaccination, before detailing key components of cancer vaccines. We will then present how materials can be engineered to enhance the vaccine's pharmacokinetic and pharmacodynamic properties. Finally, we will discuss the rationale for site-specific targeting of cancer vaccines and provide examples of current targeting technologies.

Intratumoral CpG-B Promotes Antitumoral Neutrophil, cDC, and T-cell Cooperation without Reprograming Tolerogenic pDC

Cancer immunotherapies utilize distinct mechanisms to harness the power of the immune system to eradicate cancer cells. Therapeutic vaccines, aimed at inducing active immune responses against an existing cancer, are highly dependent on the immunological microenvironment, where many immune cell types display high levels of plasticity and, depending on the context, promote very different immunologic outcomes. Among them, plasmacytoid dendritic cells (pDC), known to be highly immunogenic upon inflammation, are maintained in a tolerogenic state by the tumor microenvironment. Here, we report that intratumoral (i.t.) injection of established solid tumors with CpG oligonucleotides-B (CpG-B) inhibits tumor growth. Interestingly, control of tumor growth was independent of tumor-associated pDC, which remained refractory to CpG-B stimulation and whose depletion did not alter the efficacy of the treatment. Instead, tumor growth inhibition subsequent to i.t. CpG-B injection depended on the recruitment of neutrophils into the milieu, resulting in the activation of conventional dendritic cells, subsequent increased antitumor T-cell priming in draining lymph nodes, and enhanced effector T-cell infiltration in the tumor microenvironment. These results reinforce the concept that i.t. delivery of TLR9 agonists alters the tumor microenvironment by improving the antitumor activity of both innate and adaptive immune cells.Significance: Intratumoral delivery of CpG-B disrupts the tolerogenic tumor microenvironment and inhibits tumor growth. Cancer Res; 78(12); 3280-92. ©2018 AACR.

Radiation-enhanced delivery of systemically administered amphiphilic-CpG oligodeoxynucleotide

Along with vaccines and checkpoint blockade, immune adjuvants may have an important role in tumor immunotherapy. Oligodeoxynucleotides containing unmethylated cytidyl guanosyl dinucleotide motifs (CpG ODN) are TLR9 ligands with attractive immunostimulatory properties, but intratumoral administration has been required to induce an effective anti-tumor immune response. Following on recent studies with radiation-targeted delivery of nanoparticles, we examined enhanced tumor-specific delivery of amphiphile-CpG, an albumin-binding analog of CpG ODN, following systemic administration 3days after tumor irradiation. The combination of radiation and CpG displayed superior tumor control over either treatment alone. Intravital imaging of fluorescently labeled amphiphilic-CpG revealed increased accumulation in irradiated tumors along with decreased off-target accumulation in visceral organs. Within 48h after amphiphile-CpG administration, immune activation could be detected by increased Granzyme B and Interferon gamma activity in the tumor as well as in circulating monocytes and activated CD8⁺ T cells. Using radiotherapy to enhance the targeting of CpG to tumors may help advance this once promising therapy to clinical relevance.

Immunoliposomes: A review on functionalization strategies and targets for drug delivery

Nanoparticles, especially liposomes, have gained prominence in the field of drug delivery for the treatment of human diseases, particularly cancer; they provide several advantages, including controlled drug release, protection of the drug against degradation, improved pharmacokinetics, long circulation, and passive targeting to tumors and inflammatory sites due to the enhanced permeability and retention effect. The functionalization of liposomes with monoclonal antibodies or antibody fragments to generate immunoliposomes has emerged as a promising strategy for targeted delivery to and uptake by cells overexpressing the antigens to these antibodies, with a consequent reduction in side effects. In this review, we address functionalization strategies for the non-covalent and covalent attachment of monoclonal antibodies and their fragments to liposomal surfaces. The main reaction occurs between the sulfhydryl groups of thiolated antibodies and maleimide-containing liposomes. Furthermore, we explore the main targeting possibilities with these ligands for the treatment of a variety of pathologies, including HER2- and EGFR-positive cancers, inflammatory and cardiovascular diseases, infectious diseases, and autoimmune and neurodegenerative diseases, which have not previously been reviewed together. Overall, many studies have shown selective delivery of immunoliposomes to target cells, with promising in vivo results, particularly for cancer treatment. Although clinical trials have been conducted, immunoliposomes have not yet received clinical approval. However, immunoliposomes are promising formulations that are expected to become available for therapeutic use after clinical trials prove their safety and efficacy, and after scaling issues are resolved.

Innate immune mediators in cancer: between defense and resistance

Chronic inflammation in the tumor microenvironment and evasion of the antitumor effector immune response are two of the emerging hallmarks required for oncogenesis and cancer progression. The innate immune system not only plays a critical role in perpetuating these tumor-promoting hallmarks but also in developing antitumor adaptive immune responses. Thus, understanding the dual role of the innate system in cancer immunology is required for the design of combined immunotherapy strategies able to tackle established tumors. Here, we review recent advances in the understanding of the role of cell populations and soluble components of the innate immune system in cancer, with a focus on complement, the adapter molecule Stimulator of Interferon Genes, natural killer cells, myeloid cells, and B cells.

Strategies for designing synthetic immune agonists

Enhancing the immune system is a validated strategy to combat infectious disease, cancer and allergy. Nevertheless, the development of immune adjuvants has been hampered by safety concerns. Agents that can stimulate the immune system often bear structural similarities with pathogen-associated molecular patterns found in bacteria or viruses and are recognized by pattern recognition receptors (PRRs). Activation of these PRRs results in the immediate release of inflammatory cytokines, up-regulation of co-stimulatory molecules, and recruitment of innate immune cells. The distribution and duration of these early inflammatory events are crucial in the development of antigen-specific adaptive immunity in the forms of antibody and/or T cells capable of searching for and destroying the infectious pathogens or cancer cells. However, systemic activation of these PRRs is often poorly tolerated. Hence, different strategies have been employed to modify or deliver immune agonists in an attempt to control the early innate receptor activation through temporal or spatial restriction. These approaches include physicochemical manipulation, covalent conjugation, formulation and conditional activation/deactivation. This review will describe recent examples of discovery and optimization of synthetic immune agonists towards clinical application.

Systemic delivery of chTNT-3/CpG immunoconjugates for immunotherapy in murine solid tumor models

CpG oligodeoxynucleotides (CpG) potently activate the immune system by mimicking microbial DNA. Conjugation of CpG to chTNT-3, an antibody targeting the necrotic centers of tumors, enabled CpG to accumulate in tumors after systemic delivery, where it can activate the immune system in the presence of tumor antigens. CpG chemically conjugated to chTNT-3 (chTNT-3/CpG) were compared to free CpG in their ability to stimulate the immune system in vitro and reduce tumor burden in vivo. In subcutaneous Colon 26 adenocarcinoma and B16-F10 melanoma models in BALB/c and C57BL/6 mice, respectively, chTNT-3/CpG, free CpG, or several different control constructs were administered systemically. Intraperitoneal injections of chTNT-3/CpG delayed tumor growth and improved survival and were comparable to intratumorally administered CpG. Compared to saline-treated mice, chTNT-3/CpG-treated mice had smaller average tumor volumes by as much as 72% in Colon 26-bearing mice and 79% in B16-bearing mice. Systemically delivered free CpG and CpG conjugated to an isotype control antibody did not reduce tumor burden or improve survival. In this study, chTNT-3/CpG retained immunostimulatory activity of the CpG moiety and enabled delivery to tumors. Because systemically administered CpG rapidly clear the body and do not accumulate into tumors, chTNT-3/CpG provide a solution to the limitations observed in preclinical and clinical trials.

Immunotherapy and tumor microenvironment

Recent exciting progress in cancer immunotherapy has ushered in a new era of cancer treatment. Immunotherapy can elicit unprecedented durable responses in advanced cancer patients that are much greater than conventional chemotherapy. However, such responses only occur in a relatively small fraction of patients. A positive response to immunotherapy usually relies on dynamic interactions between tumor cells and immunomodulators inside the tumor microenvironment (TME). Depending on the context of these interactions, the TME may play important roles to either dampen or enhance immune responses. Understanding the interactions between immunotherapy and the TME is not only critical to dissect the mechanisms of action but also important to provide new approaches in improving the efficiency of current immunotherapies. In this review, we will highlight recent work on how the TME can influence the efficacy of immunotherapy as well as how manipulating the TME can improve current immunotherapy regimens in some cases.

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

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

Activating Fc γ receptors contribute to the antitumor activities of immunoregulatory receptor-targeting antibodies

Antibodies that coengage activating FcγRs expressed by tumor-associated leukocytes facilitate the selective elimination of intratumoral T cells.

Fc γ receptor (FcγR) coengagement can facilitate antibody-mediated receptor activation in target cells. In particular, agonistic antibodies that target tumor necrosis factor receptor (TNFR) family members have shown dependence on expression of the inhibitory FcγR, FcγRIIB. It remains unclear if engagement of FcγRIIB also extends to the activities of antibodies targeting immunoregulatory TNFRs expressed by T cells. We have explored the requirement for activating and inhibitory FcγRs for the antitumor effects of antibodies targeting the TNFR glucocorticoid-induced TNFR-related protein (GITR; TNFRSF18; CD357) expressed on activated and regulatory T cells (T reg cells). We found that although FcγRIIB was dispensable for the in vivo efficacy of anti-GITR antibodies, in contrast, activating FcγRs were essential. Surprisingly, the dependence on activating FcγRs extended to an antibody targeting the non-TNFR receptor CTLA-4 (CD152) that acts as a negative regulator of T cell immunity. We define a common mechanism that correlated with tumor efficacy, whereby antibodies that coengaged activating FcγRs expressed by tumor-associated leukocytes facilitated the selective elimination of intratumoral T cell populations, particularly T reg cells. These findings may have broad implications for antibody engineering efforts aimed at enhancing the therapeutic activity of immunomodulatory antibodies.

Injection site and regulatory T cells influence durable vaccine-induced tumor immunity to an over-expressed self tumor associated antigen

Tumor protein D52 (D52) is constitutively expressed in healthy tissues and overexpressed in multiple cancers, including (but not limited to) breast, prostate and ovarian carcinomas. Although the normal functions of D52 are unknown, it is clear that increased D52 expression levels not only stimulate cell proliferation and metastasis, but also correlate with poor prognosis in a subset of breast cancer patients. The murine orthologs of D52 (mD52) shares 86% identity with its human counterpart (hD52) and mirrors hD52 expression patterns. The forced overexpression of mD52 induces anchorage-independent growth in vitro and promotes tumor formation as well as spontaneous metastasis in vivo. We have previously reported that the intramuscular administration of recombinant mD52 elicits immune responses capable of rejecting a challenge with tumor cells and preventing spontaneous metastasis only in 50% of mice. We hypothesized that mechanisms of peripheral tolerance dampen immune responses against mD52, thus limiting the protective effects of vaccination. To test this hypothesis, mice were depleted of CD25⁺ regulatory T cells (Tregs) and subcutaneously immunized with mD52 prior to a tumor challenge. The subcutaneous immunization failed to induce protective antitumor immunity unless accompanied by Treg depletion, which resulted in a rate of protection of 70% as compared with

T-regulatory cells: key players in tumor immune escape and angiogenesis

T-regulatory cells (Tregs) are found infiltrating tumors in a vast array of tumor types, and tumor-infiltrating Tregs are often associated with a poor clinical outcome. Tregs are potent immunosuppressive cells of the immune system that promote progression of cancer through their ability to limit antitumor immunity and promote angiogenesis. Here, we discuss the ways in which Tregs suppress the antitumor immune response and elaborate on our recent discovery that Tregs make significant direct contributions to tumor angiogenesis. Further, we highlight several current therapies aimed at eliminating Tregs in cancer patients. Given the multifaceted role of Tregs in cancer, a greater understanding of their functions will ultimately strengthen future therapies.

Combination strategies to enhance antitumor ADCC

The clinical efficacy of monoclonal antibodies as cancer therapeutics is largely dependent upon their ability to target the tumor and induce a functional antitumor immune response. This two-step process of ADCC utilizes the response of innate immune cells to provide antitumor cytotoxicity triggered by the interaction of the Fc portion of the antibody with the Fc receptor on the immune cell. Immunotherapeutics that target NK cells, γδ T cells, macrophages and dendritic cells can, by augmenting the function of the immune response, enhance the antitumor activity of the antibodies. Advantages of such combination strategies include: the application to multiple existing antibodies (even across multiple diseases), the feasibility (from a regulatory perspective) of combining with previously approved agents and the assurance (to physicians and trial participants) that one of the ingredients - the antitumor antibody - has proven efficacy on its own. Here we discuss current strategies, including biologic rationale and clinical results, which enhance ADCC in the following ways: strategies that increase total target-monoclonal antibody-effector binding, strategies that trigger effector cell 'activating' signals and strategies that block effector cell 'inhibitory' signals.

Intratumoral delivery of CpG-conjugated anti-MUC1 antibody enhances NK cell anti-tumor activity

Monoclonal antibodies (mAbs) against tumor-associated antigens are useful anticancer agents. Antibody-dependent cellular cytotoxicity (ADCC) is one of the major mechanisms responsible for initiating natural killer cell (NK)-mediated killing of tumors. However, the regulation of ADCC via NK cells is poorly understood. We have investigated the cytolytic activity of NK cells against pancreatic cancer cells that were coated with an antibody directed against the human tumor antigen, Mucin-1 designated HMFG-2, either alone or conjugated to CpG oligodeoxynucleotide (CpG ODN). Conjugated antibodies were tested for their ability to elicit ADCC in vitro and in vivo against pancreatic cancer cells. NK cells cultured in the presence of immobilized CpG ODN, HMFG-2 Ab, or CpG ODN-conjugated HMFG-2 Ab were able to up-regulate perforin similarly. Interestingly, a significant higher ADCC was observed when CpG ODN-conjugated HMFG-2-coated tumor cells were co-cultured with NK cells compared to unconjugated HMFG-2 Ab or CpG ODN alone. Moreover, MyD88-deficient NK cells can perform ADCC in vitro. Furthermore, intratumoral injections of CpG ODN-conjugated HMFG-2 induced a significant reduction in tumor burden in vivo in an established model of pancreatic tumor in nude mice compared to CpG ODN or the HMFG-2 alone. Depletion of macrophages or NK cells before treatment confirmed that both cells were required for the anti-tumor response in vivo. Results also suggest that CpG ODN and HMFG-2 Ab could be sensed by NK cells on the mAb-coated tumor cells triggering enhanced ADCC in vitro and in vivo.

Targeting and utilizing primary tumors as live vaccines: changing strategies

Tumor metastases and relapse are the major causes of morbidity and mortality in cancer. Although surgery, chemotherapy and/or radiation therapy can typically control primary tumor growth, metastatic and relapsing tumors are often inaccessible or resistant to these treatments. An adaptive immune response can be generated during these conventional treatments of the primary tumor, and presumably both the primary tumor and secondary metastases share many of the same or similar antigenic characteristics recognized by the immune system. Thus, when established, this response should be able to control metastatic growth and tumor relapse. This review summarizes the mechanisms by which antitumor immune responses are generated, and recent findings supporting the hypothesis that many therapies targeting primary tumors can generate antitumor adaptive immune responses to prevent metastases and tumor relapse.

Targeting 4-1BB costimulation to disseminated tumor lesions with bi-specific oligonucleotide aptamers

The paucity of costimulation at the tumor site compromises the ability of tumor-specific T cells to eliminate the tumor. Here, we show that bi-specific oligonucleotide aptamer conjugates can deliver costimulatory ligands to tumor cells in situ and enhance antitumor immunity. In poorly immunogenic subcutaneously implanted tumor and lung metastasis models, systemic delivery of an agonistic 4-1BB aptamer ligand conjugated to a prostate specific membrane antigen (PSMA)-binding tumor-targeting aptamer led to inhibition of tumor growth, was more effective than, and synergized with, vaccination, and exhibited a superior therapeutic index compared to costimulation with 4-1BB antibodies. Tumor inhibition was dependent on homing to PSMA-expressing tumor cells and 4-1BB costimulation. Aptamer targeted costimulation is a broadly applicable and clinically feasible approach to enhance the costimulatory environment of disseminated tumor lesions. This study suggests that potentiating naturally occurring antitumor immunity via tumor-targeted costimulation could be an effective approach to elicit protective immunity to control tumor progression in cancer patients.

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.

Foxp3-positive macrophages display immunosuppressive properties and promote tumor growth

Regulatory T cells (T reg cells) are characterized by the expression of the forkhead lineage-specific transcription factor Foxp3, and their main function is to suppress T cells. While evaluating T reg cells, we identified a population of Foxp3-positive cells that were CD11b(+)F4/80(+)CD68(+), indicating macrophage origin. These cells were observed in spleen, lymph nodes, bone marrow, thymus, liver, and other tissues of naive animals. To characterize this subpopulation of macrophages, we devised a strategy to purify CD11b(+)F4/80(+)Foxp3(+) macrophages using Foxp3-GFP mice. Analysis of CD11b(+)F4/80(+)Foxp3(+) macrophage function indicated that these cells inhibited the proliferation of T cells, whereas Foxp3(-) macrophages did not. Suppression of T cell proliferation was mediated through soluble factors. Foxp3(-) macrophages acquired Foxp3 expression after activation, which conferred inhibitory properties that were indistinguishable from natural Foxp3(+) macrophages. The cytokine and transcriptional profiles of Foxp3(+) macrophages were distinct from those of Foxp3(-) macrophages, indicating that these cells have different biological functions. Functional in vivo analyses indicated that CD11b(+)F4/80(+)Foxp3(+) macrophages are important in tumor promotion and the induction of T reg cell conversion. For the first time, these studies demonstrate the existence of a distinct subpopulation of naturally occurring macrophage regulatory cells in which expression of Foxp3 correlates with suppressive function.

Antitumor activity mediated by CpG: the route of administration is critical

Unmethylated CpG oligodeoxynucleotides (CpG) are synthetic toll-like receptor 9 agonists that activate innate immune cells and which have been tested as an immune therapy in a number of cancer clinical trials. Although some antitumor immune responses have been reported, so far the majority of studies have failed to show significant clinical responses to CpG. Here we showed that the route of administration is critical to the antitumor activity of CpG. Although intravenous (i.v.) injection of CpG was capable of inducing the activation and expansion of tumor antigen-specific T cells, most of these activated T cells failed to migrate to tumor sites. By contrast, intratumoral (i.t.) injection of CpG led to extensive tumor infiltration of antigen-specific T cells and subsequent tumor suppression. We further showed that very high levels of inflammatory chemokines [regulated upon activation, normal T-cell expressed, and secreted (RANTES), interferon-inducible protein-10 (IP-10), monocyte chemoattractant protein-1, monocyte chemotactic protein (MCP5), macrophage inflammatory proteins (MIP1α, and MIP1β)] were induced in the tumor microenvironment after i.t. CpG injection, compared with administration by the i.v. route. It is interesting to note that, in vivo depletion of plasmacytoid dendritic cells greatly reduced the levels of chemokines induced; also, T-cell accumulation and antitumor effect were impaired. We also showed that i.t. but not i.v. CpG injection induced a broad antigen-specific T-cell response against tumor-derived antigens. Collectively, our data provides evidence that the route of CpG administration is a critical factor in mediating antitumor activity. By inducing localized inflammatory signals at tumor sites, i.t. CpG effectively promotes the migration, activation and function of immune cells, ultimately leading to improved tumor control.

Tumor-infiltrating programmed death receptor-1+ dendritic cells mediate immune suppression in ovarian cancer

Within the ovarian cancer microenvironment, there are several mechanisms that suppress the actions of antitumor immune effectors. Delineating the complex immune microenvironment is an important goal toward developing effective immune-based therapies. A dominant pathway of immune suppression in ovarian cancer involves tumor-associated and dendritic cell (DC)-associated B7-H1. The interaction of B7-H1 with PD-1 on tumor-infiltrating T cells is a widely cited theory of immune suppression involving B7-H1 in ovarian cancer. Recent studies suggest that the B7-H1 ligand, programmed death receptor-1 (PD-1), is also expressed on myeloid cells, complicating interpretations of how B7-H1 regulates DC function in the tumor. In this study, we found that ovarian cancer-infiltrating DCs progressively expressed increased levels of PD-1 over time in addition to B7-H1. These dual-positive PD-1(+) B7-H1(+) DCs have a classical DC phenotype (i.e., CD11c(+)CD11b(+)CD8(-)), but are immature, suppressive, and respond poorly to danger signals. Accumulation of PD-1(+)B7-H1(+) DCs in the tumor was associated with suppression of T cell activity and decreased infiltrating T cells in advancing tumors. T cell suppressor function of these DCs appeared to be mediated by T cell-associated PD-1. In contrast, ligation of PD-1 expressed on the tumor-associated DCs suppressed NF-κB activation, release of immune regulatory cytokines, and upregulation of costimulatory molecules. PD-1 blockade in mice bearing ovarian cancer substantially reduced tumor burden and increased effector Ag-specific T cell responses. Our results reveal a novel role of tumor infiltrating PD-1(+)B7-H1(+) DCs in mediating immune suppression in ovarian cancer.

Stimulation of the glucocorticoid-induced TNF receptor family-related receptor on CD8 T cells induces protective and high-avidity T cell responses to tumor-specific antigens

Treatment of tumor-bearing mice with a stimulatory Ab to glucocorticoid-induced TNFR family-related receptor (GITR) has previously been shown to elicit protective T cell responses against poorly immunogenic tumors. However, the role of GITR stimulation on CD8 T cells and the nature of tumor rejection Ags have yet to be determined. In this study, we show that a stimulatory mAb to GITR (clone DTA-1) acts directly on CD8 T cells, but not on CD4(+)CD25(+) regulatory T (T(reg)) cells, in B16 tumor-bearing mice to induce concomitant immunity against secondary B16 tumors, as well as protective memory following surgical excision of the primary tumor. Melanoma growth itself induced GITR expression on tumor-specific CD8 T cells, providing a mechanism whereby these cells may respond to stimulatory anti-GITR. Unexpectedly, in contrast to T(reg) cell depletion therapy with anti-CD4, GITR stimulation induced very weak CD8 T cell responses to melanocyte differentiation Ags expressed by the tumor, and did not induce autoimmune vitiligo. Accordingly, GITR-stimulated hosts that were primed with B16 melanoma rejected B16, but not the unrelated JBRH melanoma, indicating that tumor rejection Ags are tumor-specific rather than shared. In support of this, we show that GITR stimulation induces CD8 T cell responses to a tumor-specific Ag, and that these responses are of higher functional avidity compared with those induced by T(reg) cell depletion. We conclude that stimulation of GITR on effector CD8 T cells results in high-avidity T cell responses to tumor-specific Ags, thereby inducing potent antitumor immunity in the absence of autoimmunity.

Depletion of regulatory T cells by anti-GITR mAb as a novel mechanism for cancer immunotherapy

In vitro, engagement of GITR on Treg cells by the agonistic anti-GITR mAb, DTA-1, appears to abrogate their suppressive function. The consequence of in vivo engagement of GITR by DTA-1 is, however, less clear. In this study, we show that Treg cells isolated from DTA-1-treated mice were as potent as those from untreated mice in suppressing conventional CD4 T cells in vitro, indicating that in vivo GITR ligation does not disable Treg cells. Treatment of Foxp3/GFP knock-in mice with DTA-1 led to a selective reduction of circulating Treg cells, suggesting that DTA-1 is a depleting mAb which preferentially targets Treg cells. In tumour-bearing mice, DTA-1-mediated depletion of Treg cells was most marked in tumours but not in tumour-draining lymph node. These features were confirmed in an adoptive transfer model using tumour antigen-specific Treg cells. Interestingly, Treg cells detected in tumour tissues expressed much higher levels of GITR than those in tumour-draining lymph nodes, indicating that the efficiency of depletion might be correlated with the level of GITR expression. Finally, in vivo labelling of GITR in naive or tumour-bearing mice demonstrated that Treg cells constitutively expressed higher levels of GITR than conventional T cells, independent of location and activation state, consistent with the preferential in vivo depletion of Tregs by DTA-1. Thus, depletion of Treg cells represents a previously unrecognised in vivo activity of DTA-1 which has important implications for the application of anti-GITR antibodies in cancer immunotherapy.

Intratumoral DNA electroporation induces anti-tumor immunity and tumor regression

In situ expression of a foreign antigen and an immune-modulating cytokine by intratumoral DNA electroporation was tested as a cancer therapy regimen. Transgene expression in the tumors was sustained for 2-3 weeks after intratumoral electroporation with mammalian expression plasmid containing firefly luciferase cDNA. Electroporation with cDNA encoding tetanus toxin fragment C (TetC) induced tetanus toxin-binding antibody, demonstrating immune recognition of the transgene product. Intratumoral electroporation with TetC and IL-12 cDNA after mice were treated with CD25 mAb to remove regulatory T cells induced IFN-gamma producing T-cell response to tumor-associated antigen, heavy inflammatory infiltration, regression of established tumors and immune memory to protect mice from repeated tumor challenge. Intratumoral expression of immune-modulating molecules may be most suitable in the neoadjuvant setting to enhance the therapeutic efficacy and provide long-term protection.

Targeting the tumor microenvironment with anti-neu/anti-CD40 conjugated nanoparticles for the induction of antitumor immune responses

Clinical and preclinical data indicate that immunotherapeutic interventions could induce immune responses capable of controlling or retard the tumor growth. However, immunotherapies need to be further optimized. We hypothesized that a more effective strategy for tumor eradication is to directly target the tumor microenvironment in order to generate a proinflammatory response and induce a localized antitumor immune response capable of eliminating the tumor cells. Nanoparticles have been proven to be an effective delivery system. In these studies we evaluated conjugated anti-RNEU and anti-CD40 antibodies onto PLA-(poly dl-lactic acid)-biodegradable nanoparticles (PLA-NP) for the induction of antitumor immune responses. The anti-neu/anti-CD40-NP were functional in vitro recognizing RNEU(+) tumors and activating dendritic cells. The delivery of anti-neu/anti-CD40-NP but not anti-neu-NP or anti-CD40-NP induced an antitumor response resulting in complete tumor elimination and generation of protective memory responses. The anti-neu/anti-CD40-NP specifically activated an antitumor response against RNEU(+) tumors but not against RNEU(-) tumors. The antitumor immune responses correlate with the induction of a Th1-proinflammatory response, reduction in the number of Tregs within the tumor and activation of a specific cytotoxic response. These results indicate that anti-neu/anti-CD40-NP with immunomodulatory properties are safe and can be used effectively as cancer vaccines strategy for the specific induction of antitumor immune responses.

Targeted liposomal delivery of TLR9 ligands activates spontaneous antitumor immunity in an autochthonous cancer model

Accessibility of tumors for highly effective local treatment represents a major challenge for anticancer therapy. Immunostimulatory oligodeoxynucleotides (ODN) with CpG motifs are ligands of TLR9, which prime spontaneous antitumor immunity, but are less effective when applied systemically. We therefore developed a liposome-based agent for selective delivery of CpG-ODN into the tumor environment. A peptide that specifically targets angiogenic endothelial cells in a transgenic tumor model for islet cell carcinogenesis was engrafted into CpG-ODN containing liposomes. Intravenous injection of these liposomes resulted in specific accumulation around tumor vessels, increased uptake by tumor-resident macrophages, and retention over time. In contrast, nontargeted liposomes did not localize to the tumor vasculature. Consequently, only vascular targeting of CpG-ODN liposomes provoked a marked inflammatory response at vessel walls with enhanced CD8(+) and CD4(+) T cell infiltration and, importantly, activation of spontaneous, tumor-specific cytotoxicity. In a therapeutic setting, 40% of tumor-bearing, transgenic mice survived beyond week 45 after systemic administration of vascular-directed CpG-ODN liposomes. In contrast, control mice survived up to 30 wk. Therapeutic efficacy was further improved by increasing the frequency of tumor-specific effector cells through adoptive transfers. NK cells and CD8(+) T cells were major effectors which induced tumor cell death and acted in conjunction with antivascular effects. Thus, tumor homing with CpG-ODN-loaded liposomes is as potent as direct injection of free CpG-ODN and has the potential to overcome some major limitations of conventional CpG-ODN monotherapy.

Therapeutic immunity by adoptive tumor-primed CD4(+) T-cell transfer in combination with in vivo GITR ligation

Tumor-primed CD4(+) T cells from splenocytes of tumor-rejection mice in combination with in vivo glucocorticoid-induced tumor necrosis factor receptor (GITR) ligation (the combination therapy) elicited effective host CD8(+) T cell-dependent therapeutic immunity against a murine breast tumor. GITR ligation in vitro enhanced tumor-primed CD4(+) T-cell activity and partially abrogated regulatory T cells (Treg) suppressor function. Dendritic cells (DCs) from tumor-draining lymph nodes (TDLNs) of tumor-bearing mice treated by the combination therapy stimulated Ag-specific T cells and produced interleukin (IL)-12 ex vivo. Whereas tumor-primed CD4(+) T cells or in vivo GITR ligation alone induced a tumor-specific interferon (IFN)-gamma-producing cellular response, the combination therapy enhanced and sustained it. Furthermore, the combination therapy in vivo attenuated Treg's ability to suppress IL-12 production by DCs and IFN-gamma production by effectors ex vivo. Importantly, tumor-primed CD4(+) CD25(-) T cells from splenocytes of untreated tumor-bearing mice in combination with in vivo GITR ligation also elicited an effective therapeutic effect in this model. These data suggest that the combination therapy may improve DC function, accentuate tumor-specific T-cell responses, and attenuate Treg suppressor function, thereby eliciting effective therapeutic immunity.