Alarmin IL-33 acts as an immunoadjuvant to enhance antigen-specific tumor immunity

Interleukin-33 in Tissue Homeostasis, Injury, and Inflammation

Interleukin-33 (IL-33) is a nuclear-associated cytokine of the IL-1 family originally described as a potent inducer of allergic type 2 immunity. IL-33 signals via the receptor ST2, which is highly expressed on group 2 innate lymphoid cells (ILC2s) and T helper 2 (Th2) cells, thus underpinning its association with helminth infection and allergic pathology. Recent studies have revealed ST2 expression on subsets of regulatory T cells, and for a role for IL-33 in tissue homeostasis and repair that suggests previously unrecognized interactions within these cellular networks. IL-33 can participate in pathologic fibrotic reactions, or, in the setting of microbial invasion, can cooperate with inflammatory cytokines to promote responses by cytotoxic NK cells, Th1 cells, and CD8(+) T cells. Here, we highlight the regulation and function of IL-33 and ST2 and review their roles in homeostasis, damage, and inflammation, suggesting a conceptual framework for future studies.

Circulating IL-33 level is associated with the progression of lung cancer

OBJECTIVES

Interleukin (IL)-33 protects against infection and inflammation; however, few studies have explored the relevance of IL-33 in lung cancer patients. We evaluated relation of plasma IL-33 levels with development and progression of lung cancer.

MATERIALS AND METHODS

A total of 160 patients with lung cancer and 160 controls with normal lungs were enrolled. Plasma IL-33 levels were measured using a specific sandwich ELISA; these levels were followed-up in 18 patients who underwent surgery and in 14 patients treated with chemotherapy. Malignant lesions and normal lung tissues from 10 cancer patients were subjected to immunohistochemical staining for IL-33.

RESULTS

IL-33 levels were significantly lower in cancer patients than normal controls (0.08 vs. 0.38 ng/mL, p=0.005). Among cancer patients, IL-33 decreased in a stage-dependent manner from 0.76 ng/mL in stage I patients to 0.25 ng/mL in those with stage II, 0.08 ng/mL in those with stage III, and 0.08 ng/mL in those with stage IV (p=0.002). The levels were higher at stage I (p=0.041) and markedly lower at stages III and IV than those of controls (p=0.005 and p=0.001, respectively). A similar pattern was observed when IL-33 levels were analyzed by T stage; the levels were 0.39 ng/mL at T1/T2 vs. 0.08 ng/mL at T3/T4 (p=0.001). However, no difference was noted when stage N1 levels were compared with N2 and N3 levels (p=0.058), or between stage M0 and M1 levels (p=0.147). IL-33 levels gradually decreased after surgical resection of malignant lesions (from 1.075 to 0.756 ng/mL, p=0.006), but were unchanged after chemotherapy (0.705 vs. 0.829 ng/mL, p=0.875). On immunohistochemical staining, bronchial epithelial and vascular endothelial cells of normal lung tissues mainly expressed IL-33.

CONCLUSIONS

Plasma IL-33 levels are associated inversely with progression of lung cancer. The observed decreases may be attributed to lung volume reduction containing bronchial epithelium and vascular endothelium as the sources of IL-33.

IL-33 released by alum is responsible for early cytokine production and has adjuvant properties

Human vaccines have used aluminium-based adjuvants (alum) for >80 years despite incomplete understanding of how alum enhances the immune response. Alum can induce the release of endogenous danger signals via cellular necrosis which elicits inflammation-associated cytokines resulting in humoral immunity. IL-33 is proposed to be one such danger signal that is released from necrotic cells. Therefore, we investigated whether there is a role for IL-33 in the adjuvant activity of alum. We show that alum-induced cellular necrosis results in elevated levels of IL-33 following injection in vivo. Alum and IL-33 induce similar increases in IL-5, KC, MCP-1, MIP-1α and MIP-1β; many of which are dependent on IL-33 as shown in IL-33 knockout mice or by using an IL-33-neutralizing recombinant ST2 receptor. Furthermore, IL-33 itself functions as an adjuvant that, while only inducing a marginal primary response, facilitates a robust secondary response comparable to that observed with alum. However, IL-33 is not absolutely required for alum-induced antibody responses since alum mediates similar humoral responses in IL-33 knockout and wild-type mice. Our results provide novel insights into the mechanism of action behind alum-induced cytokine responses and show that IL-33 is sufficient to provide a robust secondary antibody response independently of alum.

Protection against dengue disease by synthetic nucleic acid antibody prophylaxis/immunotherapy

Dengue virus (DENV) is the most important mosquito-borne viral infection in humans. In recent years, the number of cases and outbreaks has dramatically increased worldwide. While vaccines are being developed, none are currently available that provide balanced protection against all DENV serotypes. Advances in human antibody isolation have uncovered DENV neutralizing antibodies (nAbs) that are capable of preventing infection from multiple serotypes. Yet delivering monoclonal antibodies using conventional methods is impractical due to high costs. Engineering novel methods of delivering monoclonal antibodies could tip the scale in the fight against DENV. Here we demonstrate that simple intramuscular delivery by electroporation of synthetic DNA plasmids engineered to express modified human nAbs against multiple DENV serotypes confers protection against DENV disease and prevents antibody-dependent enhancement (ADE) of disease in mice. This synthetic nucleic acid antibody prophylaxis/immunotherapy approach may have important applications in the fight against infectious disease.

Multivalent TB vaccines targeting the esx gene family generate potent and broad cell-mediated immune responses superior to BCG

Development of a broad-spectrum synthetic vaccine against TB would represent an important advance to the limited vaccine armamentarium against TB. It is believed that the esx family of TB antigens may represent important vaccine candidates. However, only 4 esx antigens have been studied as potential vaccine antigens. The challenge remains to develop a vaccine that simultaneously targets all 23 members of the esx family to induce enhanced broad-spectrum cell-mediated immunity. We sought to investigate if broader cellular immune responses could be induced using a multivalent DNA vaccine representing the esx family protein members delivered via electroporation. In this study, 15 designed esx antigens were created to cross target all members of the esx family. They were distributed into groups of 3 self-processing antigens each, resulting in 5 trivalent highly optimized DNA plasmids. Vaccination with all 5 constructs elicited robust antigen-specific IFN-γ responses to all encoded esx antigens and induced multifunctional CD4 Th1 and CD8 T cell responses. Importantly, we show that when all constructs are combined into a cocktail, the RSQ-15 vaccine, elicited substantial broad Ag-specific T cell responses to all esx antigens as compared with vaccination with BCG. Moreover, these vaccine-induced responses were highly cross-reactive with BCG encoded esx family members and were highly immune effective in a BCG DNA prime-boost format. Furthermore, we demonstrate the vaccine potential and immunopotent profile of several novel esx antigens never previously studied. These data highlight the likely importance of these novel immunogens for study as preventative or therapeutic synthetic TB vaccines in combination or as stand alone antigens.

Interleukin-1 is required for cancer eradication mediated by tumor-specific Th1 cells

The role of inflammation in cancer is controversial as both tumor-promoting and tumor-suppressive aspects of inflammation have been reported. In particular, it has been shown that pro-inflammatory cytokines, like interleukin-1α (IL-1α), IL-1β, IL-6, and tumor necrosis factor α (TNFα), may either promote or suppress cancer. However, the cellular and molecular basis underlying these opposing outcomes remains enigmatic. Using mouse models for myeloma and lymphoma, we have recently reported that inflammation driven by tumor-specific T helper 1 (Th1) cells conferred protection against B-cell cancer and that interferon-γ (IFN-γ) was essential for this process. Here, we have investigated the contribution of several inflammatory mediators. Myeloma eradication by Th1 cells was not affected by inhibition of TNF-α, TNF-related weak inducer of apoptosis (TWEAK), or TNF-related apoptosis-inducing ligand (TRAIL). In contrast, cancer elimination by tumor-specific Th1 cells was severely impaired by the in vivo neutralization of both IL-1α and IL-1β (collectively named IL-1) with IL-1 receptor antagonist (IL-1Ra). The antitumor functions of tumor-specific Th1 cells and tumor-infiltrating macrophages were both affected by IL-1 neutralization. Secretion of the Th1-derived cytokines IL-2 and IFN-γ at the incipient tumor site was severely reduced by IL-1 blockade. Moreover, IL-1 was shown to synergize with IFN-γ for induction of tumoricidal activity in tumor-infiltrating macrophages. This synergy between IL-1 and IFN-γ may explain how inflammation, when driven by tumor-specific Th1 cells, represses rather than promotes cancer. Collectively, the data reveal a central role of inflammation, and more specifically of the canonical pro-inflammatory cytokine IL-1, in enhancing Th1-mediated immunity against cancer.

Targeting IL-33 in autoimmunity and inflammation

Interleukin-33 (IL-33) belongs to the IL-1 family of cytokines. Whereas IL-1 is processed and released by live immune cells in response to infection or other triggers, IL-33 is mostly released as a danger signal ("alarmin") from damaged cells. IL-33 may also be processed and released from activated mast cells (MCs) with subsequent autocrine and paracrine actions. IL-33 augments the stimulatory effects of IgE and substance P on MCs but can also trigger release of cytokines from MCs on its own. Blood IL-33 levels are increased in asthma, atopic dermatitis, multiple sclerosis, rheumatoid arthritis, and Sjögren's syndrome. However, prolonged elevation of IL-33 downregulates FcεRI and may be protective in atherosclerosis, suggesting different roles in immune-regulated diseases. Even though neutralizing IL-33, knocking-down its receptor, or using its soluble "decoy" receptor has resulted in anti-inflammatory effects, there appear to be different outcomes in different tissues. Hence, selective regulation of IL-33 synthesis, release, and signaling may be required to provide effective treatment options.

Ubiquitin-like Molecule ISG15 Acts as an Immune Adjuvant to Enhance Antigen-specific CD8 T-cell Tumor Immunity

ISG15 is an ubiquitin-like protein induced by type I interferon associated with antiviral activity. ISG15 is also secreted and known to function as an immunomodulatory molecule. However, ISG15's role in influencing the adaptive CD8 T-cell responses has not been studied. Here, we demonstrate the efficacy of ISG15 as a vaccine adjuvant, inducing human papilloma virus (HPV) E7-specific IFNγ responses as well as the percentage of polyfunctional, cytolytic, and effector CD8 T-cell responses. Vaccination with ISG15 conferred remarkable control and/or regression of established HPV-associated tumor-bearing mice. T-cell depletion coupled with adoptive transfer experiments revealed that ISG15 protective efficacy was CD8 T-cell mediated. Importantly, we demonstrate that ISG15 vaccine-induced responses could be generated independent of ISGylation, suggesting that responses were mostly influenced by free ISG15. Our results provide more insight into the immunomodulatory properties of ISG15 and its potential to serve as an effective immune adjuvant in a therapeutic tumor or infectious disease setting.

Tumor-infiltrating, interleukin-33-producing effector-memory CD8(+) T cells in resected hepatocellular carcinoma prolong patient survival

Interleukin-33 (IL-33), a cytokine with pleiotropic functions, is elevated in serum of patients with hepatocellular carcinoma (HCC). This study investigated the effects of local IL-33 expression in resected HCC on patient survival and on the immunological and molecular tumor microenvironment. Tissue of resected HCCs was stained for hematoxylin and eosin, Masson trichrome, alpha-smooth muscle actin, IL-33, CD8, and IL-13 and analyzed by flow cytometry. Besides histomorphologic evaluation, the immunohistochemical stainings were analyzed for the respective cell numbers separately for tumor area, infiltrative margin, and distant liver stroma. These findings were correlated with clinical data and patient outcome. Further, gene expression of different HCC risk groups was compared using microarrays. In multivariable analysis, infiltration of HCCs by IL-33(+) cells (P = 0.032) and CD8(+) cells (P = 0.014) independently was associated with prolonged patient survival. Flow cytometry demonstrated that cytotoxically active subpopulations of CD8(+) cells, in particular CD8(+) CD62L(-) KLRG1(+) CD107a(+) effector-memory cells, are the main producers of IL-33 in these HCC patients. Using infiltration by IL-33(+) and CD8(+) cells as two separate factors, an HCC immune score was designed and evaluated that stratified patient survival (P = 0.0004). This HCC immune score identified high- and low-risk patients who differ in gene expression profiles (P < 0.001).

CONCLUSION

Infiltration of HCCs by IL-33(+) and CD8(+) cells is independently associated with prolonged patient survival. We suggest that this is due to an induction of highly effective, cytotoxically active CD8(+) CD62L(-) KLRG1(+) CD107a(+) effector-memory cells producing IL-33. Based on these two independent factors, we established an HCC immune score that provides risk stratification for HCC patients and can be used in the clinical setting.

Trial watch: Naked and vectored DNA-based anticancer vaccines

One type of anticancer vaccine relies on the administration of DNA constructs encoding one or multiple tumor-associated antigens (TAAs). The ultimate objective of these preparations, which can be naked or vectored by non-pathogenic viruses, bacteria or yeast cells, is to drive the synthesis of TAAs in the context of an immunostimulatory milieu, resulting in the (re-)elicitation of a tumor-targeting immune response. In spite of encouraging preclinical results, the clinical efficacy of DNA-based vaccines employed as standalone immunotherapeutic interventions in cancer patients appears to be limited. Thus, efforts are currently being devoted to the development of combinatorial regimens that allow DNA-based anticancer vaccines to elicit clinically relevant immune responses. Here, we discuss recent advances in the preclinical and clinical development of this therapeutic paradigm.

Molecular adjuvant IL-33 enhances the potency of a DNA vaccine in a lethal challenge model

Identifying new molecular adjuvants that elicit effective vaccine-induced CD8(+) T cell immunity may be critical for the elimination of many challenging diseases including Tuberculosis, HIV and cancer. Here, we report that co-administration of molecular adjuvant IL-33 during vaccination enhanced the magnitude and function of antigen (Ag)-specific CD8(+) T cells against a model Ag, LCMV NP target protein. These enhanced responses were characterized by higher frequencies of Ag-specific, polyfunctional CD8(+) T cells exhibiting cytotoxic characteristics. Importantly, these cells were capable of robust expansion upon Ag-specific restimulation in vivo and conferred remarkable protection against a high dose lethal LCMV challenge. In addition, we demonstrate the ability of IL-33 to amplifying the frequency of Ag-specific KLRG1(+) effector CD8(+) T cells. These data show that IL-33 is a promising immunoadjuvant at improving T cell immunity in a vaccine setting and suggest further development and understanding of this molecular adjuvant for strategies against many obstinate infectious diseases and cancer.

Critical role of IL-33 receptor ST2 in experimental cerebral malaria development

Cerebral malaria, a severe complication of Plasmodium falciparum infection, can be modeled in murine Plasmodium berghei ANKA (PbA) infection. PbA-induced experimental cerebral malaria (ECM) is CD8(+) T-cell mediated, and influenced by TH 1/TH 2 balance. Here, we show that IL-33 expression is increased in brain undergoing ECM and we address the role of the IL-33/ST2 pathway in ECM development. ST2-deficient mice were resistant to PbA-induced neuropathology. They survived >20 days with no ECM neurological sign and a preserved cerebral microcirculation, while WT mice succumbed within 10 days with ECM, brain vascular leakage, distinct microvascular pathology obstruction, and hemorrhages. Parasitemia and brain parasite load were similar in ST2-deficient and WT mice. Protection was accompanied by reduced brain sequestration of activated CD4(+) T cells and perforin(+) CD8(+) T cells. While IFN-γ and T-cell-attracting chemokines CXCL9 and CXCL10 were not affected in the absence of functional ST2 pathway, the local expression of ICAM-1, CXCR3, and LT-α, crucial for ECM development, was strongly reduced, and this may explain the diminished pathogenic T-cell recruitment and resistance to ECM. Therefore, IL-33 is induced in PbA sporozoite infection, and the pathogenic T-cell responses with local microvascular pathology are dependent on IL-33/ST2 signaling, identifying IL-33 as a new actor in ECM development.

Cigarette smoke silences innate lymphoid cell function and facilitates an exacerbated type I interleukin-33-dependent response to infection

Cigarette smoking is a major risk factor for chronic obstructive pulmonary disease and is presumed to be central to the altered responsiveness to recurrent infection in these patients. We examined the effects of smoke priming underlying the exacerbated response to viral infection in mice. Lack of interleukin-33 (IL-33) signaling conferred complete protection during exacerbation and prevented enhanced inflammation and exaggerated weight loss. Mechanistically, smoke was required to upregulate epithelial-derived IL-33 and simultaneously alter the distribution of the IL-33 receptor ST2. Specifically, smoke decreased ST2 expression on group 2 innate lymphoid cells (ILC2s) while elevating ST2 expression on macrophages and natural killer (NK) cells, thus altering IL-33 responsiveness within the lung. Consequently, upon infection and release, increased local IL-33 significantly amplified type I proinflammatory responses via synergistic modulation of macrophage and NK cell function. Therefore, in COPD, smoke alters the lung microenvironment to facilitate an alternative IL-33-dependent exaggerated proinflammatory response to infection, exacerbating disease.

IL-33 isoforms: their future as vaccine adjuvants?

The identification and characterization of cytokine isoforms is likely to provide critical important new insight into immunobiology. Cytokine isoforms can provide additional diversity to their complex biological effects that participate in control and protection against different foreign pathogens. Recently, IL-33 has been identified as a proinflammatory cytokine having several different biologically active isoform products. Originally associated with Th2 immunity, new evidence now supports the role of two IL-33 isoforms to facilitate the generation of protective Th1 and CD8 T cell immunity against specific pathogens. Therefore, a better understanding of the IL-33 isoforms will inform us on how to utilize them to facilitate their development as tools as vaccine adjuvants for immune therapy.

Tapping the Potential of DNA Delivery with Electroporation for Cancer Immunotherapy

Cancer is a worldwide leading cause of death, and current conventional therapies are limited. The search for alternative preventive or therapeutic solutions is critical if we are going to improve outcomes for patients. The potential for DNA vaccines in the treatment and prevention of cancer has gained great momentum since initial findings almost 2 decades ago that revealed that genetically engineered DNA can elicit an immune response. The combination of adjuvants and an effective delivery method such as electroporation is overcoming past setbacks for naked plasmid DNA (pDNA) as a potential preventive or therapeutic approach to cancer in large animals and humans. In this chapter, we aim to focus on the novel advances in recent years for DNA cancer vaccines, current preclinical data, and the importance of adjuvants and electroporation with emphasis on prostate, melanoma, and cervical cancer.

Synthetic consensus HIV-1 DNA induces potent cellular immune responses and synthesis of granzyme B, perforin in HIV infected individuals

This study evaluated the safety and immunogenicity of PENNVAX-B in 12 HIV infected individuals. PENNVAX-B is a combination of three optimized synthetic plasmids encoding for multiclade HIV Gag and Pol and a consensus CladeB Env delivered by electroporation. HIV infected individuals whose virus was effectively suppressed using highly active antiretroviral therapy (HAART) received PENNVAX-B DNA followed by electroporation with CELLECTRA-5P at study weeks 0, 4, 8, and 16. Local administration site and systemic reactions to PENNVAX-B were recorded after each treatment along with any adverse events. Pain of the treatment procedure was assessed using a Visual Analog Scale. Whole PBMCs were isolated for use in IFN ELISpot and Flow Cytometric assays. PENNVAX-B was generally safe and well tolerated. Overall, the four dose regimen was not associated with any serious adverse events or severe local or systemic reactions. A rise in antigen-specific SFU was detected in the INFγ ELISpot assay in all 12 participants. T cells from 8/12 participants loaded with both granzyme B and perforin in response to HIV antigen, an immune finding characteristic of long-term nonprogressors (LTNPs) and elite controllers (ECs). Thus administration of PENNVAX-B may prove useful adjunctive therapy to ART for treatment and control of HIV infection.

Tumoral expression of IL-33 inhibits tumor growth and modifies the tumor microenvironment through CD8+ T and NK cells

Cancer immunotherapy has shown great promise as a new standard cancer therapeutic modality. However, the response rates are limited for current approach that depends on enhancing spontaneous antitumor immune responses. Therefore, increasing tumor immunogenicity by expressing appropriate cytokines should further improve the current immunotherapy. IL-33 is a member of the IL-1 family of cytokines and is released by necrotic epithelial cells or activated innate immune cells and is thus considered a "danger" signal. The role of IL-33 in promoting type 2 immune responses and tissue inflammation has been well established. However, whether IL-33 drives antitumor immune responses is controversial. Our previous work established that IL-33 promoted the function of CD8(+) T cells. In this study, we showed that the expression of IL-33 in two types of cancer cells potently inhibited tumor growth and metastasis. Mechanistically, IL-33 increased numbers and IFN-γ production by CD8(+) T and NK cells in tumor tissues, thereby inducing a tumor microenvironment favoring tumor eradication. Importantly, IL-33 greatly increased tumor Ag-specific CD8(+) T cells. Furthermore, both NK and CD8(+) T cells were required for the antitumor effect of IL-33. Moreover, depletion of regulatory T cells worked synergistically with IL-33 expression for tumor elimination. Our studies established "alarmin" IL-33 as a promising new cytokine for tumor immunotherapy through promoting cancer-eradicating type 1 immune responses.

Examining IL-33 expression in the cervix of HPV-infected patients: a preliminary study comparing IL-33 levels in different stages of disease and analyzing its potential association with IFN-γ

Research has shown the essential role of interleukin-33 (IL-33) in driving protective anti-viral immunity. IFN-γ has been reported to improve IL-33 expression in cultured epithelial cells. The development of cervical intraepithelial neoplasia (CIN) and carcinogenesis was closely related to human papilloma virus (HPV) infection and defective anti-viral immunity. The aim of this study was to investigate IL-33 expression alternation during the disease progress and its association with IFN-γ in HPV-positive patients. IL-33 was detected in endothelial cells and populations of epithelial cells in cervix. Though there was no statistically significant difference of IL-33 levels in cervical lavage and serum among different stages of disease (P > 0.05), the IL-33 protein and mRNA levels in cervical tissues were significantly lower in severe CIN patients than that of mild CIN or no CIN patients (P < 0.05). In addition, IL-33 protein levels were positively correlated with IFN-γ mRNA levels in all groups except cervical cancer (CA) group (r = 0.546, P < 0.01). In vitro, IFN-γ was also found to upregulate IL-33 expression in human epidermal keratinocytes (NHEKs) in a dose-dependent manner. However, CA tissues did not show further reduced IL-33 protein and mRNA levels compared with severe CIN tissues (P > 0.05). IFN-γ mRNA levels were even higher in CA tissues than in severe CIN tissues (P < 0.05). Therefore, in cervical precancerous tissues, IL-33 levels were lower in more severe lesions and that may be related to diminished local IFN-γ.

Beneficial autoimmunity at body surfaces - immune surveillance and rapid type 2 immunity regulate tissue homeostasis and cancer

Epithelial cells (ECs) line body surface tissues and provide a physicochemical barrier to the external environment. Frequent microbial and non-microbial challenges such as those imposed by mechanical disruption, injury or exposure to noxious environmental substances including chemicals, carcinogens, ultraviolet-irradiation, or toxins cause activation of ECs with release of cytokines and chemokines as well as alterations in the expression of cell-surface ligands. Such display of epithelial stress is rapidly sensed by tissue-resident immunocytes, which can directly interact with self-moieties on ECs and initiate both local and systemic immune responses. ECs are thus key drivers of immune surveillance at body surface tissues. However, ECs have a propensity to drive type 2 immunity (rather than type 1) upon non-invasive challenge or stress – a type of immunity whose regulation and function still remain enigmatic. Here, we review the induction and possible role of type 2 immunity in epithelial tissues and propose that rapid immune surveillance and type 2 immunity are key regulators of tissue homeostasis and carcinogenesis.

Interleukin 33: a switch-hitting cytokine

For many years IL-33 has been widely studied in the context of T helper type 2 (Th2)-driven inflammatory disorders. Interestingly, IL-33 has now emerged as a cytokine with a plethora of pleiotropic properties. Depending on the immune cells targeted by IL-33, it is reported to not only promote Th2 immunity, but also to induce T helper type 1 (Th1) immunity. Furthermore, recent studies have revealed that IL-33 can activate CD8(+) T cells. These new studies provide evidence for its beneficial role in antiviral and antitumor immunity. Here we review the evidence of IL-33 to drive protective T cell immunity plus its potential use as an adjuvant in vaccination and tumor therapy.