Biphasic function of TLR3 adjuvant on tumor and spleen dendritic cells promotes tumor T cell infiltration and regression in a vaccine therapy

Revitalizing antitumor immunity: Leveraging nucleic acid sensors as therapeutic targets

Nucleic acid sensors play a critical role in recognizing and responding to pathogenic nucleic acids as danger signals. Upon activation, these sensors initiate downstream signaling cascades that lead to the production and release of pro-inflammatory cytokines, chemokines, and type I interferons. These immune mediators orchestrate diverse effector responses, including the activation of immune cells and the modulation of the tumor microenvironment. However, careful consideration must be given to balancing the activation of nucleic acid sensors to avoid unwanted autoimmune or inflammatory responses. In this review, we provide an overview of nucleic acid sensors and their role in combating cancer through the perception of various aberrant nucleic acids and activation of the immune system. We discuss the connections between different programmed cell death modes and nucleic acid sensors. Finally, we outline the development of nucleic acid sensor agonists, highlighting how their potential as therapeutic targets opens up new avenues for cancer immunotherapy.

Cell-Based Drug Delivery Systems Participate in the Cancer Immunity Cycle for Improved Cancer Immunotherapy

Immunotherapy aims to activate the cancer patient's immune system for cancer therapy. The whole process of the immune system against cancer referred to as the "cancer immunity cycle", gives insight into how drugs can be designed to affect every step of the anticancer immune response. Cancer immunotherapy such as immune checkpoint inhibitor (ICI) therapy, cancer vaccines, as well as small molecule modulators has been applied to fight various cancers. However, the effect of immunotherapy in clinical applications is still unsatisfactory due to the limited response rate and immune-related adverse events. Mounting evidence suggests that cell-based drug delivery systems (DDSs) with low immunogenicity, superior targeting, and prolonged circulation have great potential to improve the efficacy of cancer immunotherapy. Therefore, with the rapid development of cell-based DDSs, understanding their important roles in various stages of the cancer immunity cycle guides the better design of cell-based cancer immunotherapy. Herein, an overview of how cell-based DDSs participate in cancer immunotherapy at various stages is presented and an outlook on possible challenges of clinical translation and application in future development.

Toll-like receptor-targeted anti-tumor therapies: Advances and challenges

Toll-like receptors (TLRs) are pattern recognition receptors, originally discovered to stimulate innate immune reactions against microbial infection. TLRs also play essential roles in bridging the innate and adaptive immune system, playing multiple roles in inflammation, autoimmune diseases, and cancer. Thanks to the immune stimulatory potential of TLRs, TLR-targeted strategies in cancer treatment have proved to be able to regulate the tumor microenvironment towards tumoricidal phenotypes. Quantities of pre-clinical studies and clinical trials using TLR-targeted strategies in treating cancer have been initiated, with some drugs already becoming part of standard care. Here we review the structure, ligand, signaling pathways, and expression of TLRs; we then provide an overview of the pre-clinical studies and an updated clinical trial watch targeting each TLR in cancer treatment; and finally, we discuss the challenges and prospects of TLR-targeted therapy.

E3 Ubiquitin Ligase Riplet Is Expressed in T Cells and Suppresses T Cell-Mediated Antitumor Immune Responses

The E3 ubiquitin ligase Riplet mediates retinoic acid-inducible gene-I polyubiquitination and is essential for viral-induced expression of type I IFNs in dendritic cells and macrophages. The function of Riplet in innate immunity has been well demonstrated; however, its role in adaptive immunity during the antitumor immune response is unclear. In this study, we examined the role of Riplet in the T cell-mediated antitumor immune response. Riplet was expressed in T cells and upregulated in CD8⁺ T cells in response to TCR-mediated stimulation. Furthermore, PR domain containing 1, eomesodermin, and killer cell lectin-like receptor G1 expression was increased in effector CD8⁺ T cells by Riplet knockout in vitro, which suggests that Riplet is involved in the effector function of CD8⁺ T cells. Our results indicated that Riplet deficiency augmented the antitumor response of MO4 (OVA-expressing melanoma)-bearing mice treated with OVA peptide-pulsed dendritic cells. Moreover, both CD4⁺ and CD8⁺ T cells played important roles in Riplet-mediated augmentation of the antitumor immune response. In tumor-draining lymph nodes, the Th1 response was promoted, and the induction of OVA-specific CD8⁺ T cells and IFN-γ production were enhanced by Riplet deficiency. Furthermore, the IFN-γ response and OVA-specific cytotoxicity of CD8⁺ T cells in tumor tissue were augmented by Riplet deficiency. The expression of Cxcl9fluorescence-minus-one and Cxcl10 mRNA was also enhanced in the tumor microenvironment by Riplet knockout, consistent with the augmented recruitment of CTLs. Overall, we clarified a function of Riplet in T cells, which is to suppress the antitumor immune response through modulating Th1 and CTLs.

Emerging role of RNA sensors in tumor microenvironment and immunotherapy

RNA sensors detect foreign and endogenous RNAs to protect the host by initiating innate and adaptive immune response. In tumor microenvironment (TME), activation of RNA sensors induces tumor-inhibitory cytotoxic T lymphocyte responses and inhibits the activity of immunosuppressive cells though stimulating type I IFN signaling pathway. These characteristics allow RNA sensors to be prospective targets in tumor immunotherapy. Therefore, a comprehensive understanding of the roles of RNA sensors in TME could provide new insight into the antitumor immunotherapy. Moreover, RNA sensors could be prominent triggering targets to synergize with immunotherapies. In this review, we highlight the diverse mechanisms of RNA sensors in cancer immunity and their emerging contributions in cancer immunotherapy, including monotherapy with RNA sensor agonists, as well as combination with chemotherapy, radiotherapy, immune checkpoint blockade or cancer vaccine.

An injectable superior depot of Telratolimod inhibits post-surgical tumor recurrence and distant metastases

The clinical success of Toll-like receptor (TLR) agonists is based on their capacity to efficiently mobilize both innate and adaptive immunity. However, rapid distribution of TLR agonists into the systemic circulation may result in systemic cytokine storms. Telratolimod (Tel) is a TLR 7/8 agonist whose structure has a hydrophobic long chain that helps to prolong its release. Despite this, the phase I study of Tel showed cytokine release syndromes in 3/35 patients. Herein, we designed an injectable phase transition gel (PGE) that served as a superior drug depot for fatty acid-modified drugs. PGE further minimized the systemic drug exposure of Tel and the possible cytokine storms. In vivo studies demonstrated that Tel@PGE facilitated the recruitment of effector CD8⁺ T lymphocytes (T cells) and the polarization of myeloid-derived suppressor cells (MDSCs) and immunosuppressive M2-like macrophages to tumoricidal antigen-presenting cells. The reshaping of the tumor microenvironment (TME) by Tel@PGE elicited systematic immune responses to significantly prevent B16F10 or 4T-1 tumor postoperative recurrence and metastasis. Therefore, this platform of Tel is expected to provide a clinically available option for effective postoperative combined therapy. STATEMENT OF SIGNIFICANCE: A series of prodrugs or conjugates containing hydrophobic blocks were designed to achieve sustained release at the injection site by reducing the water solubility. However, this strategy sometimes failed short of expectations. Thus, we constructed a biocompatible and biodegradable injectable phase transition gel (PGE) with superior release properties that can be injected subcutaneously into the surgery site. In the long-lasting treatment, the melanoma and breast cancer immunotherapeutic effect significantly enhanced and the risk of cancer metastasis and relapse was reduced. Crucially, for some immune agonists, a superior release control can significantly reduce adverse effects which was decisive for the availability of the drugs.

CpG-C ODN M362 as an immunoadjuvant for HBV therapeutic vaccine reverses the systemic tolerance against HBV

Chronic Hepatitis B virus (CHB) infection is a global public health problem. Oligodeoxynucleotides (ODNs) containing class C unmethylated cytosine-guanine dinucleotide (CpG-C) motifs may provide potential adjuvants for the immunotherapeutic strategy against CHB, since CpG-C ODNs stimulate both B cell and dendritic cell (DC) activation. However, the efficacy of CpG-C ODN as an anti-HBV vaccine adjuvant remains unclear. In this study, we demonstrated that CpG M362 (CpG-C ODN) as an adjuvant in anti-HBV vaccine (cHBV-vaccine) successfully and safely eliminated the virus in HBV-carrier mice. The cHBV-vaccine enhanced DC maturation both in vivo and in vitro, overcame immune tolerance, and recovered exhausted T cells in HBV-carrier mice. Furthermore, the cHBV-vaccine elicited robust hepatic HBV-specific CD8⁺ and CD4⁺ T cell responses, with increased cellular proliferation and IFN-γ secretion. Additionally, the cHBV-vaccine invoked a long-lasting follicular CXCR5⁺ CD8⁺ T cell response following HBV re-challenge. Taken together, CpG M362 in combination with rHBVvac cleared persistent HBV and achieved long-term virological control, making it a promising candidate for treating CHB.

TICAM-1/TRIF associates with Act1 and suppresses IL-17 receptor-mediated inflammatory responses

TICAM-1 (also called TRIF) is the sole adaptor of TLR3 that recognizes double-stranded RNA. Here, we report that TICAM-1 is involved not only in TLR3 signaling but also in the cytokine receptor IL-17RA signaling. We found that TICAM-1 bound to IL-17R adaptor Act1 to inhibit the interaction between IL-17RA and Act1. Interestingly, TICAM-1 knockout promoted IL-17RA/Act1 interaction and increased IL-17A-mediated activation of NF-κB and MAP kinases, leading to enhanced expression of inflammatory cytokines and chemokines upon IL-17A stimulation. Moreover, Ticam-1 knockout augmented IL-17A-mediated CXCL1 and CXCL2 expression in vivo, resulting in accumulation of myeloid cells. Furthermore, Ticam-1 knockout enhanced delayed type hypersensitivity and exacerbated experimental autoimmune encephalomyelitis. Ticam-1 knockout promoted accumulation of myeloid and lymphoid cells in the spinal cord of EAE-induced mice. Collectively, these data indicate that TICAM-1 inhibits the interaction between IL-17RA and Act1 and functions as a negative regulator in IL-17A-mediated inflammatory responses.

Heparanase is a regulator of natural killer cell activation and cytotoxicity

Heparanase is the only mammalian enzyme capable of cleaving heparan sulfate, a glycosaminoglycan of the extracellular matrix and cell surfaces. Most immune cells express heparanase that contributes to a range of functions including cell migration and cytokine expression. Heparanase also promotes natural killer (NK) cell migration; however, its role in other NK cell functions remains to be defined. In this study, heparanase-deficient (Hpse^-/- ) mice were used to assess the role of heparanase in NK cell cytotoxicity, activation, and cytokine production. Upon challenge with the immunostimulant polyinosinic:polycytidylic acid (poly(I:C)), NK cells isolated from Hpse^-/- mice displayed impaired cytotoxicity against EO771.LMB cells and reduced levels of activation markers CD69 and NKG2D. However, in vitro cytokine stimulation of wild-type and Hpse^-/- NK cells resulted in similar CD69 and NKG2D expression, suggesting the impaired NK cell activation in Hpse^-/- mice results from elements within the in vivo niche. NK cells are activated in vivo by dendritic cells (DCs) in response to poly(I:C). Poly(I:C)-stimulated Hpse^-/- bone marrow DCs (BMDCs) expressed less IL-12, and when cultured with Hpse^-/- NK cells, less MCP-1 mRNA and protein was detected. Although cell-cell contact is important for DC-mediated NK cell activation, co-cultures of Hpse^-/- BMDCs and NK cells showed similar levels of contact to wild-type cells, suggesting heparanase contributes to NK cell activation independently of cell-cell contact with DCs. These observations define a role for heparanase in NK cell cytotoxicity and activation and have important implications for how heparanase inhibitors currently in clinical trials for metastatic cancer may impact NK cell immunosurveillance.

Isolation and characterization of porcine monoclonal antibodies revealed two distinct serotype-independent epitopes on VP2 of foot-and-mouth disease virus

Pigs are susceptible to foot-and-mouth disease virus (FMDV), and the humoral immune response plays an essential role in protection against FMDV infection. However, little information is available about FMDV-specific mAbs derived from single B cells of pigs. This study aimed to determine the antigenic features of FMDV that are recognized by antibodies from pigs. Therefore, a panel of pig-derived mAbs against FMDV were developed using fluorescence-based single B cell antibody technology. Western blotting revealed that three of the antibodies (1C6, P2-7E and P2-8G) recognized conserved antigen epitopes on capsid protein VP2, and exhibited broad reactivity against both FMDV serotypes A and O. An alanine-substitution scanning assay and sequence conservation analysis elucidated that these porcine mAbs recognized two conserved epitopes on VP2: a linear epitope (²KKTEETTLL¹⁰) in the N terminus and a conformational epitope involving residues K63, H65, L66, F67, D68 and L81 on two β-sheets (B-sheet and C-sheet) that depended on the integrity of VP2. Random parings of heavy and light chains of the IgGs confirmed that the heavy chain is predominantly involved in binding to antigen. The light chain of porcine IgG contributes to the binding affinity toward an antigen and may function as a support platform for antibody stability. In summary, this study is the first to reveal the conserved antigenic profile of FMDV recognized by porcine B cells and provides a novel method for analysing the antibody response against FMDV in its natural hosts (i.e. pigs) at the clonal level.

Therapeutic vaccination targeting CD40 and TLR3 controls melanoma growth through existing intratumoral CD8 T cells without new T cell infiltration

Dendritic cells are potently activated by the synergistic action of CD40 stimulation in conjunction with signaling through toll like receptors, subsequently priming T cells. Cancer vaccines targeting the activation of dendritic cells in this manner show promise in murine models and are being developed for human patients. While the efficacy of vaccines based on CD40 and toll like receptor stimulation has been established, further investigation is needed to understand the mechanism of tumor control and how vaccination alters tumor infiltrating immune cells. In this study we vaccinated mice bearing established murine melanoma tumors with agonistic anti-CD40, polyI:C, and tumor antigen. Vaccination led to increased intratumoral T cell numbers and delayed tumor growth, yet did not require trafficking of T cells from the periphery. Pre-existing intratumoral T cells exhibited an acute burst in proliferation but became less functional in response to vaccination. However, the increased intratumoral T cell numbers yielded increased numbers of effector T cells per tumor. Together, our data indicate that the existing T cell response and intratumoral dendritic cells are critical for vaccination efficacy. It also suggests that circulating T cells responding to vaccination may not be an appropriate biomarker for vaccine efficacy.

Targeting Toll-like receptor 3 in dendritic cells for cancer immunotherapy

INTRODUCTION

Activation of innate immune system is a key step to develop anti-tumor immunity. Antigen-presenting dendritic cells (DCs) cross-present tumor-associated antigens to cytotoxic CD8⁺ T cells (CTLs). Signaling from pattern-recognition receptors (PRRs) in DCs is required to induce tumor-specific CTLs.

AREAS COVERED

This review summarizes the properties of PRRs expressed by antigen-presenting DCs, especially TLR3, and provides the recent knowledge of their function in anti-tumor immunity. We also summarize the characteristics of newly-developed TLR3-specific agonist, ARNAX, which efficiently primes DCs to induce anti-tumor immunity without systemic inflammation in mice.

EXPERT OPINION

In cancer immunotherapy, the induction of tumor-specific CTLs is significant for tumor regression and to augment the efficacy of PD-1/PD-L1 blockade. Non-inflammatory TLR3 adjuvant ARNAX that can induce tumor-specific CTLs without inducing inflammation benefits cancer immunotherapy. Development of appropriate protocols for ARNAX vaccine therapy would be useful to overcome the PD-1/PD-L1 blockade resistance.

Dendritic cells transduced with glioma-expressed antigen 2 recombinant adenovirus induces specific cytotoxic lymphocyte response and anti-tumor effect in mice

Introduction

Glioma is an aggressive common cancer with high mortality worldwide. Up to date, the effective medical therapeutical strategy is limited. Numerous previous studies have indicated that glioma-expressed antigen 2 (GLEA2) might be an attractive prognostic glioma biomarker.

Methods

In this experiment, dendritic cells (DCs) transduced with GLEA2 recombinant adenovirus were utilized to generate cytotoxic lymphocytes (CTLs) in vitro. Additionally, trimera mice were immunized with the transduced DCs to generate CTLs in vivo.

Results

The data demonstrated that GLEA2 transduced DCs could effectively generate specific CTL response against glioma without lysing autologous lymphocytes. Moreover, GLEA2 transduced DCs significantly attenuated the tumor growth and prolonged the life span of tumor bearing mice.

Conclusions

These findings suggested that DCs transduced with GLEA2 recombinant adenovirus could generate effective CTL mediated anti-tumor response, and might represent insight in glioma therapy.

Poly I:C-based rHBVvac therapeutic vaccine eliminates HBV via generation of HBV-specific CD8+ effector memory T cells

OBJECTIVE

Chronic hepatitis B (CHB) virus infection is a global health problem. Finding a cure for CHB remains a challenging task.

DESIGN

In this study, poly I:C was employed as an adjuvant for HBV therapeutic vaccine (referred to as pHBV-vaccine) and the feasibility and efficiency of pHBV-vaccine in CHB treatment were evaluated in HBV-carrier mice.

RESULTS

We found that pHBV-vaccine decreased HBsAg and HBV DNA efficiently and safely in HBV-carrier mice. Further investigation showed that pHBV-vaccine promoted maturation and antigen presentation ability of dendritic cells in vivo and in vitro. This vaccine successfully restored the exhaustion of antigen-specific CD8⁺ T cells and partly broke the immune tolerance established in HBV-carrier mice. pHBV-vaccine also enhanced the proliferation and polyfunctionality of HBV-specific CD11a^hi CD8α^lo cells. Importantly, we observed that T cell activation molecule KLRG1 was only expressed on HBV specific CD11a^hi CD8α^lo cells. Furthermore, pHBV-vaccine reduced the expression of Eomes and increased the serum IL-12 levels, which in turn promoted the generation of effector memory short-lived effector cells (SLECs) to exhibit a critical role in HBV clearance. SLECs induced by pHBV-vaccine might play a crucial role in protecting from HBV reinfection.

CONCLUSIONS

Findings from this study provide a new basis for the development of therapeutic pHBV-vaccine, which might be a potential candidate for clinical CHB therapy.

Effective cancer immunotherapy by natural mouse conventional type-1 dendritic cells bearing dead tumor antigen

Background

The manipulation of dendritic cells (DCs) for cancer vaccination has not reached its full potential, despite the revolution in cancer immunotherapy. DCs are fundamental for CD8+ T cell activation, which relies on cross-presentation of exogenous antigen on MHC-I and can be fostered by immunogenic cancer cell death. Translational and clinical research has focused on in vitro-generated monocyte-derived DCs, while the vaccination efficacy of natural conventional type 1 DCs (cDC1s), which are associated with improved anti-tumor immunity and specialize on antigen cross-presentation, remains unknown.

Methods

We isolated primary spleen mouse cDC1s and established a protocol for fast ex vivo activation and antigen-loading with lysates of tumor cells that underwent immunogenic cell death by UV irradiation. Natural tumor antigen-loaded cDC1s were transferred and their potential for induction of endogenous CD8+ and CD4+ T cell responses in vivo, cancer prevention and therapy were assessed in three grafted cancer models. Further, we tested the efficacy of natural cDC1 vaccination in combination and comparison with anti-PD-1 treatment in two “wildtype” tumor models not expressing exogenous antigens.

Results

Herein, we reveal that primary mouse cDC1s ex vivo loaded with dead tumor cell-derived antigen are activated and induce strong CD8+ T cell responses from the endogenous repertoire upon adoptive transfer in vivo through tumor antigen cross-presentation. Notably, cDC1-based vaccines enhance tumor infiltration by cancer-reactive CD8+ and CD4+ T cells and halt progression of engrafted cancer models, including tumors that are refractory to anti-PD-1 treatment. Moreover, combined tumor antigen-loaded primary cDC1 and anti-PD-1 therapy had strong synergistic effects in a PD-1 checkpoint inhibition susceptible cancer model.

Conclusions

This preclinical proof-of-principle study is first to support the therapeutic efficacy of cancer immunotherapy with syngeneic dead tumor cell antigen-loaded mouse cDC1s, the equivalents of the human dendritic cell subset that correlates with beneficial prognosis of cancer patients. Our data pave the way for translation of cDC1-based cancer treatments into the clinic when isolation of natural human cDC1s becomes feasible.

Electronic supplementary material

The online version of this article (10.1186/s40425-019-0565-5) contains supplementary material, which is available to authorized users.

Vaccine adjuvant ARNAX promotes mucosal IgA production in influenza HA vaccination

Adjuvant stimulates pattern-recognition receptors (PRRs) expressed by dendritic cells, which causes immune-enhancing of T lymphocytes. Adjuvant also induces innate immune response in whole-body cells via PRRs to evoke cytokinemia. A cytokine-mediated immune response is important for the systemic protection of a host from microbial infections. Using an influenza subcomponent vaccine in a mouse model, we intranasally administered a TLR3-specific adjuvant ARNAX + HA split vaccine to mice. ARNAX efficiently induced mucosal IgA and systemic IgG production by nasal drop. Moreover, ARNAX + HA simultaneously induced CD8 and CD4 T cell activation. We have previously shown that ARNAX does not induce harmful systemic cytokine production. Thus, our findings indicate that the ARNAX + HA vaccine is a harmless prophylactic vaccine for flu that induces HA-specific T cell activation and IgA/IgG production. These results suggested that ARNAX + antigen enhanced the immune response without inducing inflammatory toxicity for vaccination against infectious diseases.

Engineering DNA vaccines against infectious diseases

Engineering vaccine-based therapeutics for infectious diseases is highly challenging, as trial formulations are often found to be nonspecific, ineffective, thermally or hydrolytically unstable, and/or toxic. Vaccines have greatly improved the therapeutic landscape for treating infectious diseases and have significantly reduced the threat by therapeutic and preventative approaches. Furthermore, the advent of recombinant technologies has greatly facilitated growth within the vaccine realm by mitigating risks such as virulence reversion despite making the production processes more cumbersome. In addition, seroconversion can also be enhanced by recombinant technology through kinetic and nonkinetic approaches, which are discussed herein. Recombinant technologies have greatly improved both amino acid-based vaccines and DNA-based vaccines. A plateau of interest has been reached between 2001 and 2010 for the scientific community with regard to DNA vaccine endeavors. The decrease in interest may likely be attributed to difficulties in improving immunogenic properties associated with DNA vaccines, although there has been research demonstrating improvement and optimization to this end. Despite improvement, to the extent of our knowledge, there are currently no regulatory body-approved DNA vaccines for human use (four vaccines approved for animal use). This article discusses engineering DNA vaccines against infectious diseases while discussing advantages and disadvantages of each, with an emphasis on applications of these DNA vaccines.

Statement of Significance

This review paper summarizes the state of the engineered/recombinant DNA vaccine field, with a scope entailing “Engineering DNA vaccines against infectious diseases”. We endeavor to emphasize recent advances, recapitulating the current state of the field. In addition to discussing DNA therapeutics that have already been clinically translated, this review also examines current research developments, and the challenges thwarting further progression. Our review covers: recombinant DNA-based subunit vaccines; internalization and processing; enhancing immune protection via adjuvants; manufacturing and engineering DNA; the safety, stability and delivery of DNA vaccines or plasmids; controlling gene expression using plasmid engineering and gene circuits; overcoming immunogenic issues; and commercial successes. We hope that this review will inspire further research in DNA vaccine development.

Trial Watch: Toll-like receptor agonists in cancer immunotherapy

Toll-like receptor (TLR) agonists demonstrate therapeutic promise as immunological adjuvants for anticancer immunotherapy. To date, three TLR agonists have been approved by US regulatory agencies for use in cancer patients. Additionally, the potential of hitherto experimental TLR ligands to mediate clinically useful immunostimulatory effects has been extensively investigated over the past few years. Here, we summarize recent preclinical and clinical advances in the development of TLR agonists for cancer therapy.

The heat shock protein 47 as a potential biomarker and a therapeutic agent in cancer research

Heat shock protein 47 (HSP47) is an important chaperone required for the correct folding and secretion of collagen. Several studies revealed that HSP47 has a role in numerous steps of collagen synthesis, preventing procollagen aggregation and inducing hydroxylation of proline and lysine residues. HSP47 is encoded by the SERPINH1 gene, which is located on chromosome 11q13.5, one of the most frequently amplified regions in human cancer. The altered expression levels of HSP47 have been correlated with several types of cancer, such as cervical, breast, pancreatic and gastric cancers. Studies have shown that HSP47 promotes tumor angiogenesis, growth, migration and metastatic capacity. In this review, we highlight the fundamental aspects of the interaction between HSP47 and collagen and the recent discoveries of the role of this chaperone in different types of malignant neoplasias. We also discuss recent treatments using HSP47 as a therapeutic target, and present evidences that HSP47 is an essential protein for cancer biology and a potential molecular target for chemotherapy.

Activation of TLR3 and its adaptor TICAM-1 increases miR-21 levels in extracellular vesicles released from human cells

Pattern-recognition receptors (PRRs) recognizes viral RNAs and trigger the innate immune responses. Toll-like receptor 3 (TLR3), a PRR, recognizes viral double-stranded RNA (dsRNA) in endolysosomes, whereas cytoplasmic dsRNA is sensed by another PRR, MDA5. TLR3 and MDA5 utilize TICAM-1 and MAVS, respectively, to trigger the signal for inducing innate immune responses. Extracellular vesicles (EVs) include the exosomes and microvesicles; an accumulating body of evidence has shown that EVs delivers functional RNA, such as microRNAs (miRNAs), to other cells and thus mediate intercellular communications. Therefore, EVs carrying miRNAs affect innate immune responses in macrophages and dendritic cells. However, the mechanism underlying the regulation of miRNA levels in EVs remains unclear. To elucidate the mechanism, we sought to reveal the pathway that control miRNA expression levels in EVs. Here, we found that TLR3 stimulation increased miR-21 levels in EVs released from various types of human cells. Ectopic expression of the TLR3 adaptor, TICAM-1, increased miR-21 levels in EVs but not intracellular miR-21 levels, suggesting that TICAM-1 augmented sorting of miR-21 to EVs. In contrast, the MDA5 adaptor, MAVS, did not increase miR-21 levels in EVs. The siRNA for TICAM-1 reduced EV miR-21 levels after stimulation of TLR3. Collectively, our data indicate a novel role of the TLR3-TICAM-1 pathway in controlling miR-21 levels in EVs.

Dendritic cell activation enhances anti-PD-1 mediated immunotherapy against glioblastoma

Introduction

The glioblastoma (GBM) immune microenvironment is highly suppressive as it targets and hinders multiple components of the immune system. Checkpoint blockade (CB) is being evaluated for GBM patients. However, biomarker analyses suggest that CB monotherapy may be effective only in a small fraction of GBM patients. We hypothesized that activation of antigen presentation would increase the therapeutic response to PD-1 blockade.

Results

We show that activating DCs through TLR3 agonists enhances the anti-tumor immune response to CB and increases survival in GBM. Mice treated with TLR3 agonist poly(I:C) and anti-PD-1 demonstrated increased DC activation and increased T cell proliferation in tumor draining lymph nodes. We show that DCs are necessary for the improved anti-tumor immune response.

Conclusions

This study suggests that augmenting antigen presentation is an effective multimodal immunotherapy strategy that intensifies anti-tumor responses in GBM. Specifically, these data represent an expanded role for TLR3 agonists as adjuvants to CB.

Methods

Using a preclinical model of GBM, we tested the efficacy of combinatorial immunotherapy with anti-PD-1 and TLR3 agonist, poly(I:C). Characterization of the immune response in tumor infiltrating immune cells and in secondary lymphoid organs was performed. Additionally, dendritic cell (DC) depletion experiments were performed.

Toll-like receptor 3 signal augments radiation-induced tumor growth retardation in a murine model

Radiotherapy induces anti-tumor immunity by induction of tumor antigens and damage-associated molecular patterns (DAMP). DNA, a representative DAMP in radiotherapy, activates the stimulator of interferon genes (STING) pathway which enhances the immune response. However, the immune response does not always parallel the inflammation associated with radiotherapy. This lack of correspondence may, in part, explain the radiation-resistance of tumors. Additive immunotherapy is expected to revive tumor-specific CTL facilitating radiation-resistant tumor shrinkage. Herein pre-administration of the double-stranded RNA, polyinosinic-polycytidylic acid (polyI:C), in conjunction with radiotherapy, was shown to foster tumor suppression in mice bearing radioresistant, ovalbumin-expressing Lewis lung carcinoma (LLC). Extrinsic injection of tumor antigen was not required for tumor suppression. No STING- and CTL-response was induced by radiation in the implant tumor. PolyI:C was more effective for induction of tumor growth retardation at 1 day before radiation than at post-treatment. PolyI:C targeted Toll-like receptor 3 with minimal effect on the mitochondrial antiviral-signaling protein pathway. Likewise, the STING pathway barely contributed to LLC tumor suppression. PolyI:C primed antigen-presenting dendritic cells in draining lymph nodes to induce proliferation of antigen-specific CTL. By combination therapy, CTL efficiently infiltrated into tumors with upregulation of relevant chemokine transcripts. Batf3-positive DC and CD8+ T cells were essential for therapeutic efficacy. Furthermore, polyI:C was shown to stimulate tumor-associated macrophages and release tumor necrosis factor alpha, which acted on tumor cells and increased sensitivity to radiation. Hence, polyI:C treatment prior to radiotherapy potentially induces tumor suppression by boosting CTL-dependent and macrophage-mediated anti-tumor responses. Eventually, polyI:C and radiotherapy in combination would be a promising therapeutic strategy for radiation-resistant tumors.

Type I Interferon-Independent Dendritic Cell Priming and Antitumor T Cell Activation Induced by a Mycoplasma fermentans Lipopeptide

Mycoplasma fermentans-derived diacylated lipoprotein M161Ag (MALP404) is recognized by human/mouse toll-like receptor (TLR) 2/TLR6. Short proteolytic products including macrophage-activating lipopeptide 2 (MALP2) have been utilized as antitumor immune-enhancing adjuvants. We have chemically synthesized a short form of MALP2 named MALP2s (S-[2,3-bis(palmitoyloxy)propyl]-CGNNDE). MALP2 and MALP2s provoke natural killer (NK) cell activation in vitro but only poorly induce tumor regression using in vivo mouse models loading NK-sensitive tumors. Here, we identified the functional mechanism of MALP2s on dendritic cell (DC)-priming and cytotoxic T lymphocyte (CTL)-dependent tumor eradication using CTL-sensitive tumor-implant models EG7 and B16-OVA. Programmed death ligand-1 (PD-L1) blockade therapy in combination with MALP2s + ovalbumin (OVA) showed a significant additive effect on tumor growth suppression. MALP2s increased co-stimulators CD80/86 and CD40, which were totally MyD88-dependent, with no participation of toll-IL-1R homology domain-containing adaptor molecule-1 or type I interferon signaling in DC priming. MALP2s + OVA consequently augmented proliferation of OVA-specific CTLs in the spleen and at tumor sites. Chemokines and cytolytic factors were upregulated in the tumor. Strikingly, longer duration and reinvigoration of CTLs in spleen and tumors were accomplished by the addition of MALP2s + OVA to α-PD-L1 antibody (Ab) therapy compared to α-PD-L1 Ab monotherapy. Then, tumors regressed better in the MALP2s/OVA combination than in the α-PD-L1 Ab monotherapy. Hence, MALP2s/tumor-associated antigens combined with α-PD-L1 Ab is a good therapeutic strategy in some mouse models. Unfortunately, numerous patients are still resistant to PD-1/PD-L1 blockade, and good DC-priming adjuvants are desired. Cytokine toxicity by MALP2s remains to be settled, which should be improved by chemical modification in future studies.

A TLR3-Specific Adjuvant Relieves Innate Resistance to PD-L1 Blockade without Cytokine Toxicity in Tumor Vaccine Immunotherapy

Cancer patients having anti-programmed cell death-1 (PD-1)/PD ligand 1 (L1)-unresponsive tumors may benefit from advanced immunotherapy. Double-stranded RNA triggers dendritic cell (DC) maturation to cross-prime antigen-specific cytotoxic T lymphocytes (CTLs) via Toll-like receptor 3 (TLR3). The TLR3-specific RNA agonist, ARNAX, can induce anti-tumor CTLs without systemic cytokine/interferon (IFN) production. Here, we have developed a safe vaccine adjuvant for cancer that effectively implements anti-PD-L1 therapy. Co-administration of ARNAX with a tumor-associated antigen facilitated tumor regression in mouse models, and in combination with anti-PD-L1 antibody, activated tumor-specific CTLs in lymphoid tissues, enhanced CTL infiltration, and overcame anti-PD-1 resistance without cytokinemia. The TLR3-TICAM-1-interferon regulatory factor (IRF)3-IFN-β axis in DCs exclusively participated in CD8⁺ T cell cross-priming. ARNAX therapy established Th1 immunity in the tumor microenvironment, upregulating genes involved in DC/T cell/natural killer (NK) cell recruitment and functionality. Human ex vivo studies disclosed that ARNAX+antigen induced antigen-specific CTL priming and proliferation in peripheral blood mononuclear cells (PBMCs), supporting the feasibility of ARNAX for potentiating anti-PD-1/PD-L1 therapy in human vaccine immunotherapy.

Interferon-stimulated gene of 20 kDa protein (ISG20) degrades RNA of hepatitis B virus to impede the replication of HBV in vitro and in vivo

Hepatitis B virus (HBV) barely induces host interferon (IFN)-stimulated genes (ISGs), which allows efficient HBV replication in the immortalized mouse hepatocytes as per human hepatocytes. Here we found that transfection of Isg20 plasmid robustly inhibits the HBV replication in HBV-infected hepatocytes irrespective of IRF3 or IFN promoter activation. Transfection of Isg20 is thus effective to eradicate HBV in the infected hepatocytes. Transfection of HBV genome or ε-stem of HBV pgRNA (active pgRNA moiety) failed to induce Isg20 in the hepatocytes, while control polyI:C (a viral dsRNA analogue mimic) activated MAVS pathway leading to production of type I IFN and then ISGsg20 via the IFN-α/β receptor (IFNAR). Consistently, addition of IFN-α induced Isg20 and partially suppressed HBV replication in hepatocytes. Chasing HBV RNA, DNA and proteins by blotting indicated that ISG20 expression decreased HBV RNA and replicative DNA in HBV-transfected cells, which resulted in low HBs antigen production and virus titer. The exonuclease domains of ISG20 mainly participated in HBV-RNA decay. In vivo hydrodynamic injection, ISG20 was crucial for suppressing HBV replication without degrading host RNA in the liver. Taken together, ISG20 acts as an innate anti-HBV effector that selectively degrades HBV RNA and blocks replication of infectious HBV particles. ISG20 would be a critical effector for ameliorating chronic HBV infection in the IFN therapy.

Adjuvant immunotherapy for cancer: both dendritic cell-priming and check-point inhibitor blockade are required for immunotherapy

The immune system eliminates advanced cancer when treated with programmed cell death protein-1 (PD-1) or its ligand (PD-L1) blockade, but PD-1 therapy is effective in only ∼20% of patients with solid cancer. The PD-1 antibody mainly acts on the effector phase of cytotoxic T lymphocytes (CTLs) in tumors but induces no activation of the priming phase of antigen-presenting dendritic cells (DCs). It is reasonable that both DC-priming and PD-1/L1 blocking are mandatory for efficient CTL-mediated tumor cytolysis. For DC-priming, a therapeutic vaccine containing Toll-like receptor (TLR) agonists, namely a priming adjuvant, is a good candidate; however, a means for DC-targeting by TLR adjuvant therapy remains to be developed. TLR adjuvants usually harbor cytokine toxicity, which is a substantial barrier against drug approval. Here, we discuss the functional properties of current TLR adjuvants for cancer immunotherapy and introduce a TLR3-specific adjuvant (ARNAX) that barely induces cytokinemia in mouse models.

Toll-Like Receptor 3 Signal in Dendritic Cells Benefits Cancer Immunotherapy

Pattern recognition receptors (PRRs) play a crucial role in the innate immune system and contribute to host defense against microbial infection. PRR-mediated antimicrobial signals provide robust type-I IFN/cytokine production and trigger inflammation, thereby affecting tumor progression and autoimmune diseases. Accumulating evidence demonstrates that among the PRRs, only the signaling pathway of endosomal toll-like receptor 3 (TLR3) induces no systemic inflammation and mediates cross-priming of antigen-specific CD8⁺ T cells by dendritic cells. Treatment with a newly developed TLR3-specific ligand, ARNAX, along with tumor-associated antigens (TAAs), induces tumor-specific cytotoxic T lymphocytes, modulates the tumor microenvironment to establish Th1-type antitumor immunity, and leads to tumor regression without inflammation in mouse tumor models. Combination therapy using ARNAX/TAA and PD-1/PD-L1 blockade potently enhances antitumor response and overcomes anti-PD-1/PD-L1 resistance. In this review, we will discuss the TLR3-mediated signaling in antitumor immunity and its application to cancer immunotherapy.

The TLR3/TICAM-1 signal constitutively controls spontaneous polyposis through suppression of c-Myc in Apc Min/+ mice

Background

Intestinal tumorigenesis is promoted by myeloid differentiation primary response gene 88 (MyD88) activation in response to the components of microbiota in Apc^Min/+ mice. Microbiota also contains double-stranded RNA (dsRNA), a ligand for TLR3, which activates the toll-like receptor adaptor molecule 1 (TICAM-1, also known as TRIF) pathway.

Methods

We established Apc^Min/+Ticam1^−/− mice and their survival was compared to survival of Apc^Min/+Myd88^−/− and wild-type (WT) mice. The properties of polyps were investigated using immunofluorescence staining and RT-PCR analysis.

Results

We demonstrate that TICAM-1 is essential for suppression of polyp formation in Apc^Min/+ mice. TICAM-1 knockout resulted in shorter survival of mice compared to WT mice or mice with knockout of MyD88 in the Apc^Min/+ background. Polyps were more frequently formed in the distal intestine of Apc^Min/+Ticam1^−/− mice than in Apc^Min/+ mice. Infiltration of immune cells such as CD11b⁺ and CD8α⁺ cells into the polyps was detected histologically. CD11b and CD8α mRNAs were increased in polyps of Apc^Min/+Ticam1^−/− mice compared to Apc^Min/+ mice. Gene expression of inducible nitric oxide synthase (iNOS), interferon (IFN)-γ, CXCL9 and IL-12p40 was increased in polyps of Apc^Min/+Ticam1^−/− mice. mRNA and protein expression of c-Myc, a critical transcription factor for inflammation-associated polyposis, were increased in polyps of Apc^Min/+Ticam1^−/− mice. A Lactobacillus strain producing dsRNA was detected in feces of Apc^Min/+ mice.

Conclusion

These results imply that the TLR3/TICAM-1 pathway inhibits polyposis through suppression of c-Myc expression and supports long survival in Apc^Min/+ mice.

Electronic supplementary material

The online version of this article (10.1186/s12929-017-0387-z) contains supplementary material, which is available to authorized users.

Lack of interleukin-6 in the tumor microenvironment augments type-1 immunity and increases the efficacy of cancer immunotherapy

Conquering immunosuppression in tumor microenvironments is crucial for effective cancer immunotherapy. It is well known that interleukin (IL)‐6, a pleiotropic cytokine, is produced in the tumor‐bearing state. In the present study, we investigated the precise effects of IL‐6 on antitumor immunity and the subsequent tumorigenesis in tumor‐bearing hosts. CT26 cells, a murine colon cancer cell line, were intradermally injected into wild‐type and IL‐6‐deficient mice. As a result, we found that tumor growth was decreased significantly in IL‐6‐deficient mice compared with wild‐type mice and the reduction was abrogated by depletion of CD8⁺ T cells. We further evaluated the immune status of tumor microenvironments and confirmed that mature dendritic cells, helper T cells and cytotoxic T cells were highly accumulated in tumor sites under the IL‐6‐deficient condition. In addition, higher numbers of interferon (IFN)‐γ‐producing T cells were present in the tumor tissues of IL‐6‐deficient mice compared with wild‐type mice. Surface expression levels of programmed death‐ligand 1 (PD‐L1) and MHC class I on CT26 cells were enhanced under the IL‐6‐deficient condition in vivo and by IFN‐γ stimulation in vitro. Finally, we confirmed that in vivo injection of an anti‐PD‐L1 antibody or a Toll‐like receptor 3 ligand, polyinosinic‐polycytidylic acid, effectively inhibited tumorigenesis under the IL‐6‐deficient condition. Based on these findings, we speculate that a lack of IL‐6 produced in tumor‐bearing host augments induction of antitumor effector T cells and inhibits tumorigenesis in vivo, suggesting that IL‐6 signaling may be a promising target for the development of effective cancer immunotherapies.

Interleukin-6/STAT3 signaling as a promising target to improve the efficacy of cancer immunotherapy

Overcoming the immunosuppressive state in tumor microenvironments is a critical issue for improving the efficacy of cancer immunotherapy. Interleukin (IL)‐6, a pleiotropic cytokine, is highly produced in the tumor‐bearing host. Previous studies have indicated that IL‐6 suppresses the antigen presentation ability of dendritic cells (DC) through activation of signal transducer and activator of transcription 3 (STAT3). Thus, we focused on the precise effect of the IL‐6/STAT3 signaling cascade on human DC and the subsequent induction of antitumor T cell immune responses. Tumor‐infiltrating CD11b⁺CD11c⁺ cells isolated from colorectal cancer tissues showed strong induction of the IL‐6 gene, downregulated surface expression of human leukocyte antigen (HLA)‐DR, and an attenuated T cell‐stimulating ability compared with those from peripheral blood mononuclear cells, suggesting that the tumor microenvironment suppresses antitumor effector cells. In vitro experiments revealed that IL‐6‐mediated STAT3 activation reduced surface expression of HLA‐DR on CD14⁺ monocyte‐derived DC. Moreover, we confirmed that cyclooxygenase 2, lysosome protease and arginase activities were involved in the IL‐6‐mediated downregulation of the surface expression levels of HLA class II on human DC. These findings suggest that IL‐6‐mediated STAT3 activation in the tumor microenvironment inhibits functional maturation of DC to activate effector T cells, blocking introduction of antitumor immunity in cancers. Therefore, we propose in this review that blockade of the IL‐6/STAT3 signaling pathway and target molecules in DC may be a promising strategy to improve the efficacy of immunotherapies for cancer patients.

The Anti-Oxidant Ergothioneine Augments the Immunomodulatory Function of TLR Agonists by Direct Action on Macrophages

L-Ergothioneine (EGT) is a naturally-occurring amino acid which is characterized by its antioxidant property; yet, the physiological role of EGT has yet to be established. We investigated the immune-enhancing properties of EGT, and found that it acts as a potentiator of toll-like receptor (TLR) signaling. When mouse bone marrow-derived macrophages (BMDMs) were pretreated with EGT, TLR signal-mediated cytokine production was augmented in BMDMs. The results were reproducible with TLR2, 3, 4 and 7 agonists. In particular, IL-6 and IL-12p40 were elevated further by pretreatment with EGT in BMDMs, suggesting the induction of M1 polarization. In co-culture assay with OT-II CD4⁺ T cells and splenic F4/80⁺ macrophages, EGT significantly induced Th17 skewing in CD4⁺ T cells. Thus, EGT is an immune modifier as well as a redox controller under TLR stimulation that induces M1 macrophages and a Th17 shift in inflammation.

Tumoricidal efficacy coincides with CD11c up-regulation in antigen-specific CD8(+) T cells during vaccine immunotherapy

Background

Dendritic cells (DCs) mount tumor-associated antigens (TAAs), and the double-stranded RNA adjuvant Poly(I:C) stimulates Toll-like receptor 3 (TLR3) signal in DC, which in turn induces type I interferon (IFN) and interleukin-12 (IL-12), then cross-primes cytotoxic T lymphocytes (CTLs). Proliferation of CTLs correlates with tumor regression. How these potent cells expand with high quality is crucial to the outcome of CTL therapy. However, good markers reflecting the efficacy of DC-target immunotherapy have not been addressed.

Methods

Using an EG7 (ovalbumin, OVA-positive) tumor-implant mouse model, we examined what is a good marker for active CTL induction in treatment with Poly(I:C)/OVA.

Results

Simultaneous administration of Poly(I:C) and antigen (Ag) OVA significantly increased a minor population of CD8⁺ T cells, that express CD11c in lymphoid and tumor sites. The numbers of the CD11c⁺ CD8⁺ T cells correlated with those of induced Ag-specific CD8⁺ T cells and tumor regression. The CD11c⁺ CD8⁺ T cell moiety was characterized by its high killing activity and IFN-γ-producing ability, which represent an active phenotype of the effector CTLs. Not only a TLR3-specific (TICAM-1-dependent) signal but also TLR2 (MyD88) signal in DC triggered the expansion of CD11c⁺ CD8⁺ T cells in tumor-bearing mice. Notably, human CD11c⁺ CD8⁺ T cells also proliferated in peripheral blood mononuclear cells (PBMC) stimulated with cytomegalovirus (CMV) Ag.

Conclusions

CD11c expression in CD8⁺ T cells reflects anti-tumor CTL activity and would be a marker for immunotherapeutic efficacy in mouse models and probably cancer patients as well.

Electronic supplementary material

The online version of this article (doi:10.1186/s13046-016-0416-x) contains supplementary material, which is available to authorized users.