Modes of action of TLR7 agonists in cancer therapy

A novel oral TLR7 agonist orchestrates immune response and synergizes with PD-L1 blockade via type I IFN pathway in lung cancer

Despite the groundbreaking impact of immune checkpoint blockade (ICB), response rates in non-small cell lung cancer remain modest, particularly in immune-excluded or immune-desert microenvironments. Toll-like receptor 7 (TLR7) emerges as a latent target bridging innate and adaptive immunity, offering a promising avenue for combination therapies to augment ICB efficacy. Here, we explored the anti-tumor activity of the novel oral TLR7 agonist TQ-A3334 and its potential to enhance anti-programmed death ligand 1 (PD-L1) therapy through a combination strategy in a syngeneic murine lung cancer model. Oral administration of TQ-A3334 significantly alleviated tumor burden in C57BL/6J mice, modulated by type I interferon (IFN), and exhibited low toxicity. This therapy elicited activation of both innate and adaptive immune cells in tumor tissue, particularly increasing the abundance of CD8+ TILs through type I IFN pathway and subsequent CXCL10 expression. In vitro examinations validated that IFN-α-stimulated tumor cells exhibited increased secretion of CXCL10, conducive to the promoted trafficking of CD8+ T cells. Furthermore, combining TQ-A3334 with anti-PD-L1 treatment exceeded tumor control, with a further increase in CD8+ TIL frequency compared to monotherapy. These findings suggest that TQ-A3334 can mobilize innate immunity and promote T cell recruitment into the tumor microenvironment; a combination of TQ-A3334 and anti-PD-L1 antibodies can intensify the sensitivity of tumors to anti-PD-L1 therapy, which demonstrates significant potential for treating poorly immune-infiltrated lung cancer.

Biomimetic Dual-Target Theranostic Nanovaccine Enables Magnetic Resonance Imaging and Chemo/Chemodynamic/Immune Therapy of Glioma

Development of theranostic nanomedicines to tackle glioma remains to be challenging. Here, we present an advanced blood-brain barrier (BBB)-crossing nanovaccine based on cancer cell membrane-camouflaged poly(N-vinylcaprolactam) (PVCL) nanogels (NGs) incorporated with MnO2 and doxorubicin (DOX). We show that the disulfide bond-cross-linked redox-responsive PVCL NGs can be functionalized with dermorphin and imiquimod R837 through cell membrane functionalization. The formed functionalized PVCL NGs having a size of 220 nm are stable, can deplete glutathione, and responsively release both Mn2+ and DOX under the simulated tumor microenvironment to exert the chemo/chemodynamic therapy mediated by DOX and Mn2+, respectively. The combined therapy induces tumor immunogenic cell death to maturate dendritic cells (DCs) and activate tumor-killing T cells. Further, the nanovaccine composed of cancer cell membranes as tumor antigens, R837 as an adjuvant with abilities of DC maturation and macrophages M1 repolarization, and MnO2 with Mn2+-mediated stimulator of interferon gene activation of tumor cells can effectively act on both targets of tumor cells and immune cells. With the dermorphin-mediated BBB crossing, cell membrane-mediated homologous tumor targeting, and Mn2+-facilitated magnetic resonance (MR) imaging property, the designed NG-based theranostic nanovaccine enables MR imaging and combination chemo-, chemodynamic-, and imnune therapy of orthotopic glioma with a significantly decreased recurrence rate.

Huang Lian Jie Du Decoction enhances the anti-tumor efficacy of immune checkpoint inhibitors by activating TLR7/8 signalling in melanoma

BACKGROUND

The clinical application of immune checkpoint inhibitors (ICIs) is limited by their drug resistance, necessitating the development of ICI sensitizers to improve cancer immunotherapy outcomes. Huang Lian Jie Du Decoction (HLJD, Oren-gedoku-to in Japanese, Hwangryunhaedok-tang in Korean), a famous traditional Chinese medicinal prescription, has exhibited potential in the field of cancer treatment. This study aims to investigate the impact of HLJD on the efficacy of ICIs in melanoma and elucidate the underlying mechanisms.

METHODS

The potential synergistic effects of HLJD and ICIs were investigated on the tumor-bearing mice model of B16F10 melanoma, and the tumor infiltration of immune cells was tested by flow cytometry. The differential gene expression in tumors between HLJD and ICIs group and ICIs alone group were analyzed by RNA-seq. The effects of HLJD on oxidative stress, TLR7/8, and type I interferons (IFN-Is) signaling were further validated by immunofluorescence, PCR array, and immunochemistry in tumor tissue.

RESULTS

HLJD enhanced the anti-tumor effect of ICIs, significantly inhibited tumor growth, and prolonged the survival duration in melanoma. HLJD increased the tumor infiltration of anti-tumor immune cells, especially DCs, CD4+ T cells and CD8+T cells. Mechanically, HLJD activated the oxidative stress and TLR7/8 signaling pathway and IFN-Is-related genes in tumors.

CONCLUSIONS

HLJD enhanced the therapeutic benefits of ICIs in melanoma, through increasing reactive oxygen species (ROS), promoting the TLR7/8 pathway, and activating IFN-Is signaling, which in turn activated DCs and T cells.

In situ chemoimmunotherapy hydrogel elicits immunogenic cell death and evokes efficient antitumor immune response

BACKGROUND

Chemoimmunotherapy has shown promising advantages of eliciting immunogenic cell death and activating anti-tumor immune responses. However, the systemic toxicity of chemotherapy and tumor immunosuppressive microenvironment limit the clinical application.

METHODS

Here, an injectable sodium alginate hydrogel (ALG) loaded with nanoparticle albumin-bound-paclitaxel (Nab-PTX) and an immunostimulating agent R837 was developed for local administration. Two murine hepatocellular carcinoma and breast cancer models were established. The tumor-bearing mice received the peritumoral injection of R837/Nab-PTX/ALG once a week for two weeks. The antitumor efficacy, the immune response, and the tumor microenvironment were investigated.

RESULTS

This chemoimmunotherapy hydrogel with sustained-release character was proven to have significant effects on killing tumor cells and inhibiting tumor growth. Peritumoral injection of our hydrogel caused little harm to normal organs and triggered a potent antitumor immune response against both hepatocellular carcinoma and breast cancer. In the tumor microenvironment, enhanced immunogenic cell death induced by the combination of Nab-PTX and R837 resulted in 3.30-fold infiltration of effector memory T cells and upregulation of 20 biological processes related to immune responses.

CONCLUSIONS

Our strategy provides a novel insight into the combination of chemotherapy and immunotherapy and has the potential for clinical translation.

Decreased TLR7 expression was associated with airway eosinophilic inflammation and lung function in asthma: evidence from machine learning approaches and experimental validation

BACKGROUND

Asthma is a global public health concern. The underlying pathogenetic mechanisms of asthma were poorly understood. This study aims to explore potential biomarkers associated with asthma and analyze the pathological role of immune cell infiltration in the disease.

METHODS

The gene expression profiles of induced sputum were obtained from Gene Expression Omnibus datasets (GSE76262 and GSE137268) and were combined for analysis. Toll-like receptor 7 (TLR7) was identified as the core gene by the intersection of two different machine learning algorithms, namely, least absolute shrinkage and selector operation (LASSO) regression and support vector machine-recursive feature elimination (SVM-RFE), and the top 10 core networks based on Cytohubba. CIBERSORT algorithm was used to analyze the difference of immune cell infiltration between asthma and healthy control groups. Finally, the expression level of TLR7 was validated in induced sputum samples of patients with asthma.

RESULTS

A total of 320 differential expression genes between the asthma and healthy control groups were screened, including 184 upregulated genes and 136 downregulated genes. TLR7 was identified as the core gene after combining the results of LASSO regression, SVM-RFE algorithm, and top 10 hub genes. Significant differences were observed in the distribution of 13 out of 22 infiltrating immune cells in asthma. TLR7 was found to be closely related to the level of several infiltrating immune cells. TLR7 mRNA levels were downregulated in asthmatic patients compared with healthy controls (p = 0.0049). The area under the curve of TLR7 for the diagnosis of asthma was 0.7674 (95% CI 0.631-0.904, p = 0.006). Moreover, TLR7 mRNA levels were negatively correlated with exhaled nitric oxide fraction (r = - 0.3268, p = 0.0347) and the percentage of peripheral blood eosinophils (%) (r = - 0.3472, p = 0.041), and positively correlated with forced expiratory volume in the first second (FEV1) (% predicted) (r = 0.3960, p = 0.0071) and FEV1/forced vital capacity (r = 0.3213, p = 0.0314) in asthmatic patients.

CONCLUSIONS

Decreased TLR7 in the induced sputum of eosinophilic asthmatic patients was involved in immune cell infiltration and airway inflammation, which may serve as a new biomarker for the diagnosis of eosinophilic asthma.

Identification and Optimization of Small Molecule Pyrazolopyrimidine TLR7 Agonists for Applications in Immuno-oncology

Small molecule toll-like receptor (TLR) 7 agonists have gathered considerable interest as promising therapeutic agents for applications in cancer immunotherapy. Herein, we describe the development and optimization of a series of novel TLR7 agonists through systematic structure-activity relationship studies focusing on modification of the phenylpiperidine side chain. Additional refinement of ADME properties culminated in the discovery of compound 14, which displayed nanomolar reporter assay activity and favorable drug-like properties. Compound 14 demonstrated excellent in vivo pharmacokinetic/pharmacodynamic profiles and synergistic antitumor activity when administered in combination with aPD1 antibody, suggesting opportunities of employing 14 in immuno-oncology therapies with immune checkpoint blockade agents.

Absence of toll-like receptor 7 ameliorates survival and reduces intestinal injury in mice after Clostridium difficile infection

Clostridioides difficile (CD) is a major cause of antibiotic-associated diarrhea and pseudomembranous enteritis. C. difficile infection (CDI) is increasingly present in the community and represents a significant burden on the healthcare system. Identification of novel immune-based therapeutic targets from a better understanding of their molecular pathogenesis is urgently required. Toll-like receptor 7 (TLR7) is an important pattern recognition receptor and function as an immune sensor that can trigger host defenses against pathogens, but the relationship between TLR7 and CDI remains unknown. Here, we reported that the expression levels of TLR7 increased significantly in patients and mice with CDI. Absence of TLR7 in mice with CDI demonstrated enhanced bacterial clearance of intestinal contents and reduced intestinal inflammation, edema, injury and prolonged the survival. TLR7 loss decreased the concentrations of tumor necrosis factor (TNF)-α, interferon (IFN)-γ and IFN-α1 in the intestine and improved tissue damage and inflammation. Flow cytometry and immunofluorescence results indicated that TLR7 enhanced leukocyte recruitment in the infected intestine. In-vitro results have shown that TLR7 impairs the phagocytosis and killing ability of macrophages to CD, prompts reactive oxygen species (ROS) production and accelerates apoptosis. To our knowledge, our study first identified TLR7 as a critical factor that contributes to the immunopathology of CDI, suggesting that targeting TLR7 might serve as a potential treatment for CDI.

Recent advances in treating female genital human papillomavirus related neoplasms with topical imiquimod

Human papillomavirus (HPV) encompasses a group of viruses that infect the skin and mucous membranes. In the presence of certain factors, persistent infection with high-risk HPVs can trigger a process of neoplastic transformation. Imiquimod is a topical agent that acts as a Toll-like receptor 7/8 agonist, stimulating the innate and adaptive immune system to exert antitumor and antiviral effects. It has been approved for the treatment of various skin conditions, however, its efficacy and safety in the management of HPV-related-neoplasms of the lower genital tract, such as vulvar, vaginal, and cervical neoplasia, are still under investigation. This review summarizes the current evidence on the use of imiquimod for the treatment of HPV-induced lesions of the female lower genital tract, focusing on its indications, mechanisms of action, outcomes, and predictors of response.

The portrayal of macrophages as tools and targets: A paradigm shift in cancer management

Macrophages play a major role in maintaining an organism's physiology, such as development, homeostasis, tissue repair, and immunity. These immune cells are known to be involved in tumor progression and modulation. Monocytes can be polarized to two types of macrophages (M1 macrophages and pro-tumor M2 macrophages). Through this article, we aim to emphasize the potential of targeting macrophages in order to improve current strategies for tumor management. Various strategies that target macrophages as a therapeutic target have been discussed along with ongoing clinical trials. We have discussed the role of macrophages in various stages of tumor progression epithelial-to-mesenchymal transition (EMT), invasion, maintaining the stability of circulating tumor cells (CTCs) in blood, and establishing a premetastatic niche along with the role of various cytokines and chemokines involved in these processes. Intriguingly macrophages can also serve as drug carriers due to their tumor tropism along the chemokine gradient. They surpass currently explored nanotherapeutics in tumor accumulation and circulation half-life. We have emphasized on macrophage-based biomimetic formulations and macrophage-hitchhiking as a strategy to effectively target tumors. We firmly believe that targeting macrophages or utilizing them as an indigenous carrier system could transform cancer management.

DSP-0509, a systemically available TLR7 agonist, exhibits combination effect with immune checkpoint blockade by activating anti-tumor immune effects

TLR7 is an innate immune receptor that recognizes single-stranded RNAs, and its activation leads to anti-tumor immune effects. Although it is the only approved TLR7 agonist in cancer therapy, imiquimod is allowed to be administered with topical formulation. Thus, systemic administrative TLR7 agonist is expected in terms of expanding applicable cancer types. Here, we demonstrated the identification and characterization of DSP-0509 as a novel small-molecule TLR7 agonist. DSP-0509 is designed to have unique physicochemical features that could be administered systemically with a short half-life. DSP-0509 activated bone marrow-derived dendritic cells (BMDCs) and induced inflammatory cytokines including type I interferons. In the LM8 tumor-bearing mouse model, DSP-0509 reduced tumor growth not only in subcutaneous primary lesions but also in lung metastatic lesions. DSP-0509 inhibited tumor growth in several syngeneic tumor-bearing mouse models. We found that the CD8⁺ T cell infiltration of tumor before treatment tended to be positively correlated with anti-tumor efficacy in several mouse tumor models. The combination of DSP-0509 with anti-PD-1 antibody significantly enhanced the tumor growth inhibition compared to each monotherapy in CT26 model mice. In addition, the effector memory T cells were expanded in both the peripheral blood and tumor, and rejection of tumor re-challenge occurred in the combination group. Moreover, synergistic anti-tumor efficacy and effector memory T cell upregulation were also observed for the combination with anti-CTLA-4 antibody. The analysis of the tumor-immune microenvironment by using the nCounter assay revealed that the combination of DSP-0509 with anti-PD-1 antibody enhanced infiltration by multiple immune cells including cytotoxic T cells. In addition, the T cell function pathway and antigen presentation pathway were activated in the combination group. We confirmed that DSP-0509 enhanced the anti-tumor immune effects of anti-PD-1 antibody by inducing type I interferons via activation of dendritic cells and even CTLs. In conclusion, we expect that DSP-0509, a new TLR7 agonist that synergistically induces anti-tumor effector memory T cells with immune checkpoint blockers (ICBs) and can be administered systemically, will be used in the treatment of multiple cancers.

Preclinical Characterization and Phase I Study of an Anti-HER2-TLR7 Immune-Stimulator Antibody Conjugate in Patients with HER2+ Malignancies

Immune-stimulator antibody conjugates (ISAC) combining tumor-targeting monoclonal antibodies with immunostimulatory agents allow targeted delivery of immune activators into tumors. NJH395 is a novel, first-in-class ISAC comprising a Toll-like receptor 7 (TLR7) agonist conjugated to an anti-HER2 antibody via a noncleavable linker payload. Preclinical characterization showed ISAC-mediated activation of myeloid cells in the presence of antigen-expressing cancer cells, with antigen targeting and TLR7 agonism contributing to antitumor activity. Safety, efficacy, immunogenicity, pharmacokinetics, and pharmacodynamics were investigated in a phase I, multicenter, open-label study in patients with HER2+ non-breast advanced malignancies (NCT03696771). Data from 18 patients enrolled in single ascending dose escalation demonstrated delivery of the TLR7-agonist payload in HER2+ tumor cells and induction of type I IFN responses, which correlated with immune modulation in the tumor microenvironment. Cytokine release syndrome was a common, but manageable, drug-related adverse event. Antidrug antibodies and neuroinflammation at high doses represented significant clinical challenges. Data provide proof-of-mechanism and critical insights for novel immunotherapies.

Local immunotherapy with the RNA-based immune stimulator CV8102 induces substantial anti-tumor responses and enhances checkpoint inhibitor activity

Immunotherapy has revolutionized cancer treatment in recent years. Although currently approved checkpoint inhibitors (CPIs) yield remarkable anti-tumoral responses in several cancer types, a substantial proportion of patients do not benefit from such therapies. Local activation of innate immune signaling pathways is a promising approach to overcome the immunosuppressive tumor microenvironment, induce anti-tumor immunity, and improve the efficacy of CPI therapies. Here, we assessed the mode of action and efficacy of the RNA-based innate immune stimulator CV8102 for local immunotherapy in preclinical models. Intratumoral (i.t.) administration of CV8102 activated innate immune responses in the tumor microenvironment and draining lymph nodes, resulting in a dose-dependent anti-tumoral response. Combining i.t. CV8102 with systemic anti-programmed death protein 1 (PD-1) treatment further enhanced anti-tumoral responses, inducing tumor infiltration and activation of CD8+ T cells. The resulting memory response prevented tumor growth in rechallenged animals and impaired the growth of non-injected distal tumors. Therefore, i.t. CV8102 delivery is a promising approach for local cancer immunotherapy, especially in combination with CPIs. Clinical testing of CV8102 is ongoing (NCT03291002).

Recent advances in cancer immunotherapy: Modulation of tumor microenvironment by Toll-like receptor ligands

Immunotherapy is considered a promising approach for cancer treatment. An important strategy for cancer immunotherapy is the use of cancer vaccines, which have been widely used for cancer treatment. Despite the great potential of cancer vaccines for cancer treatment, their therapeutic effects in clinical settings have been limited. The main reason behind the lack of significant therapeutic outcomes for cancer vaccines is believed to be the immunosuppressive tumor microenvironment (TME). The TME counteracts the therapeutic effects of immunotherapy and provides a favorable environment for tumor growth and progression. Therefore, overcoming the immunosuppressive TME can potentially augment the therapeutic effects of cancer immunotherapy in general and therapeutic cancer vaccines in particular. Among the strategies developed for overcoming immunosuppression in TME, the use of toll-like receptor (TLR) agonists has been suggested as a promising approach to reverse immunosuppression. In this paper, we will review the application of the four most widely studied TLR agonists including agonists of TLR3, 4, 7, and 9 in cancer immunotherapy.

The antitumoral activity of TLR7 ligands is corrupted by the microenvironment of pancreatic tumors

Toll-like receptors (TLRs) are key players in the innate immune system. Recent studies have suggested that they may affect the growth of pancreatic cancer, a disease with no cure. Among them, TLR7 shows promise for therapy but may also promotes tumor growth. Thus, we aimed to clarify the therapeutic potential of TLR7 ligands in experimental pancreatic cancer models, to open the door for clinical applications. In vitro, we found that TLR7 ligands strongly inhibit the proliferation of both human and murine pancreatic cancer cells, compared with TLR2 agonists. Hence, TLR7 treatment alters cancer cells' cell cycle and induces cell death by apoptosis. In vivo, TLR7 agonist therapy significantly delays the growth of murine pancreatic tumors engrafted in immunodeficient mice. Remarkably, TLR7 ligands administration instead increases tumor growth and accelerates animal death when tumors are engrafted in immunocompetent models. Further investigations revealed that TLR7 agonists modulate the intratumoral content and phenotype of macrophages and that depleting such tumor-associated macrophages strongly hampers TLR7 agonist-induced tumor growth. Collectively, our findings shine a light on the duality of action of TLR7 agonists in experimental cancer models and call into question their use for pancreatic cancer therapy.

Inhibition of estrogen signaling in myeloid cells increases tumor immunity in melanoma

Immune checkpoint blockade (ICB) therapies have significantly prolonged patient survival across multiple tumor types, particularly in melanoma. Interestingly, sex-specific differences in response to ICB have been observed, with males receiving a greater benefit from ICB than females, although the mechanism or mechanisms underlying this difference are unknown. Mining published transcriptomic data sets, we determined that the response to ICBs is influenced by the functionality of intratumoral macrophages. This puts into context our observation that estrogens (E2) working through the estrogen receptor α (ERα) stimulated melanoma growth in murine models by skewing macrophage polarization toward an immune-suppressive state that promoted CD8+ T cell dysfunction and exhaustion and ICB resistance. This activity was not evident in mice harboring macrophage-specific depletion of ERα, confirming a direct role for estrogen signaling within myeloid cells in establishing an immunosuppressed state. Inhibition of ERα using fulvestrant, a selective estrogen receptor downregulator (SERD), decreased tumor growth, stimulated adaptive immunity, and increased the antitumor efficacy of ICBs. Further, a gene signature that determines ER activity in macrophages predicted survival in patients with melanoma treated with ICB. These results highlight the importance of E2/ER signaling as a regulator of intratumoral macrophage polarization, an activity that can be therapeutically targeted to reverse immune suppression and increase ICB efficacy.

Tumor eradicated by combination of imiquimod and OX40 agonist for in situ vaccination

Various cancer vaccines have been developed to generate and amplify antigen‐specific T cell responses against malignancy. Among them, in situ vaccination is one of the most practical types as it can trigger immune responses without previous antigen identification. Here we reported a novel in situ vaccine by intratumoral injection of imiquimod and OX40 agonist. In mice bearing hepatic carcinoma, both the injected tumor and the noninjected tumor in the distant lesion of the same mice were suppressed after vaccination. Further studies found that this in situ vaccine triggered systemic tumor‐specific responses, with one‐fold increase of effector memory T cells properties and stronger toxicity of lymphocytes in spleen. Besides, we found that imiquimod upregulated the expression of OX40 on CD4⁺ T cells and thus enhanced the effectiveness of OX40 agonist. Five immune‐positive‐related pathways were activated after vaccination. This in situ vaccine caused little harm to normal organs and provided long‐term protection against the same syngeneic tumor rechallenge. Due to its effectiveness, feasibility and safety, this strategy could potentially be applied to various types of late‐stage solid tumors and worthy of further clinical research.

A Combined TLR7/TLR9/GATA3 Score Can Predict Prognosis in Biliary Tract Cancer

Biliary tract cancer (BTC) refers to a heterogenous group of epithelial malignancies arising along the biliary tree. The highly aggressive nature combined with its silent presentation contribute to the dismal prognosis of this tumor. Tumor-infiltrating immune cells (TIICs) are frequently present in BTC and there is growing evidence regarding their role as therapeutic targets. In this study, we analyzed the immune cell infiltration in BTC and developed a promising immune signature score to predict prognosis in BTC. Immunohistochemistry (IHC) was carried out on tissue microarray sections from 45 patients with resectable cholangiocarcinoma for the detection of 6-sulfoLacNAc+ monocytes (slanMo), BDCA-2+ plasmacytoid dendritic cells (pDC), CD8+ or CD4+T-lymphocytes, CD103+ cells, GATA3+ cells, Toll-like receptor (TLR) 3, 7 and 9-expressing cells as well as programmed cell death protein 1 and programmed cell death ligand 1 positive cells. Data from the IHC staining were analyzed and correlated with clinicopathological and survival data. High expression of TLR7, TLR9, and GATA3 was associated with improved overall survival (OS, Log-rank p < 0.05). In addition, TLR9 was associated with better disease-free survival (Log-rank p < 0.05). In the multivariate Cox proportional-hazards model for OS, the TLR/TLR9/GATA3 score was found to be an independent prognostic factor for OS (“Score 2” vs. “Score 0”: HR 11.17 95% CI 2.27–54.95, p < 0.01).

Prognostic significance and targeting tumor-associated macrophages in cancer: new insights and future perspectives

Macrophages are phagocytic sentinel cells of the immune system that are central to both innate and adaptive immune responses and serve as the first line of defense against pathogenic insults to tissues. In the tumor microenvironment, tumor-derived factors induce monocyte polarization towards a pro-tumor phenotype. The pro-tumor macrophages regulate key steps in tumorigenicity including tumor growth, angiogenesis, immune suppression, and metastasis. Macrophage infiltration in solid tumors correlates with poor prognosis and resistance to chemotherapy in most cancers. Here in this review, we will shed light on tumor-associated macrophages (TAMs) in regulating tumorigenicity and TAMs as a prognostic biomarker. Also, we will review the recent advances in targeting TAMs to increase the prognosis of cancer patients.

Harnessing immunity for therapy in human papillomavirus driven cancers

In persistent high-risk HPV infection, viral gene expression can trigger some important early changes to immune capabilities which act to protect the lesion from immune attack and subsequently promote its growth and ability for sustained immune escape. This includes immune checkpoint-inhibitor ligand expression (e.g. PD-L1) by tumour or associated immune cells that can block any anti-tumour T-cell effectors. While there are encouraging signs of efficacy for cancer immunotherapies including with immune checkpoint inhibitors, therapeutic vaccines and adoptive cell therapies, overall response and survival rates remain relatively low. HPV oncogene vaccination has shown some useful efficacy in treatment of patients with high-grade lesions but was unable to control later stage cancers. To maximally exploit anti-tumour immune responses, the suppressive factors associated with HPV carcinogenesis must be countered. Importantly, a combination of chemotherapy, reducing immunosuppressive myeloid cells, with therapeutic HPV vaccination significantly improves impact on cancer treatment. Many clinical trials are investigating checkpoint inhibitor treatments in HPV associated cancers but response rates are limited; combination with vaccination is being tested. Further investigation of how chemo- and/or radio-therapy can influence the recovery of effective anti-tumour immunity is warranted. Understanding how to optimally deploy and sequence conventional and immunotherapies is the challenge.

Oral administration of PEGylated TLR7 ligand ameliorates alcohol-associated liver disease via the induction of IL-22

Effective therapies for alcohol-associated liver disease (ALD) are limited; therefore, the discovery of new therapeutic agents is greatly warranted. Toll-like receptor 7 (TLR7) is a pattern recognition receptor for single-stranded RNA, and its activation prevents liver fibrosis. We examined liver and intestinal damage in Tlr7-/- mice to determine the role of TLR7 in ALD pathogenesis. In an alcoholic hepatitis (AH) mouse model, hepatic steatosis, injury, and inflammation were induced by chronic binge ethanol feeding in mice, and Tlr7 deficiency exacerbated these effects. Because these results demonstrated that endogenous TLR7 signaling activation is protective in the AH mouse model, we hypothesized that TLR7 activation may be an effective therapeutic strategy for ALD. Therefore, we investigated the therapeutic effect of TLR7 agonistic agent, 1Z1, in the AH mouse model. Oral administration of 1Z1 was well tolerated and prevented intestinal barrier disruption and bacterial translocation, which thus suppressed ethanol-induced hepatic injury, steatosis, and inflammation. Furthermore, 1Z1 treatment up-regulated the expression of antimicrobial peptides, Reg3b and Reg3g, in the intestinal epithelium, which modulated the microbiome by decreasing and increasing the amount of Bacteroides and Lactobacillus, respectively. Additionally, 1Z1 up-regulated intestinal interleukin (IL)-22 expression. IL-22 deficiency abolished the protective effects of 1Z1 in ethanol-induced liver and intestinal damage, suggesting intestinal IL-22 as a crucial mediator for 1Z1-mediated protection in the AH mouse model. Collectively, our results indicate that TLR7 signaling exerts protective effects in the AH mouse model and that a TLR7 ligand, 1Z1, holds therapeutic potential for the treatment of AH.

Identification of Immune-Related Genes MSR1 and TLR7 in Relation to Macrophage and Type-2 T-Helper Cells in Osteosarcoma Tumor Micro-Environments as Anti-metastasis Signatures

Metastasis of osteosarcoma (OS) is an essential factor affecting the prognosis and survival of patients. The tumor microenvironment, including tumor immune-infiltrating cells (TIIC), is closely related to tumor progression. The purpose of this study was to investigate the differences between metastatic and non-metastatic immune-infiltrating cells in OS and to identify key immune-related genes. The differences in immune infiltration in OS metastasis were calculated based on the ssGSEA algorithm of 28 immuno-infiltrating cells. Weighted gene co-expression network analysis (WGCNA) and intersection analysis were used to screen immune-related modules and hubgenes. Univariate/multivariate/Lasso Cox regressions were used for models construction and signatures screening. The receiver operating characteristic (ROC) and Kaplan-Meier (K-M) curves were constructed to observe the metastases of different groups. Both internal and external data were verified. We found that macrophages and Type-2 T-helper cells were significantly decreased in patients with OS metastases. The high-risk groups obtained from multivariate/Lasso Cox models constructed with 11 immune-related hubgenes almost all underwent distant metastases within 5 years. Interestingly and importantly, two genes, MSR1 and TLR7, appeared in various models and various hubgenes, which play an anti-metastasis role and may prolong overall survival in OS. Our study may help elucidate the impact of TIIC on OS metastasis outcomes and to identify biomarkers and therapeutic targets.

Targeting tumor-associated macrophages: A potential treatment for solid tumors

Tumor-associated macrophages (TAMs) in solid tumors exert protumor activities by releasing cytokines or growth factors into the tumor microenvironment. Increasing studies have also shown that TAMs play a key role in tumor progression, such as tumor angiogenesis, immunosuppression, cell proliferation, migration, invasion, and metastasis. A large body of evidence shows that the abundance of TAMs in solid tumors is correlated with poor disease prognosis and resistance to therapies. Therefore, targeting TAMs in solid tumors is considered to be a promising immunotherapeutic strategy. At present, the therapeutic strategies of targeting macrophages mainly include limiting monocyte recruitment, depletion strategies, promoting macrophage phagocytic activity, and induction of macrophage reprogramming. Additionally, targeting TAMs in combination with conventional therapies has been demonstrated to be a promising therapeutic strategy in solid tumors. In the present review, we summarized various TAMs-targeting therapeutic strategies for treating solid tumors. This review also discusses the challenges for targeting TAMs as tumor treatments, the obstacles in clinical trials, and the perspective for the future development of TAMs-targeting therapies for various cancers.

Reprogramming the tumour microenvironment by radiotherapy: implications for radiotherapy and immunotherapy combinations

Radiotherapy (RT) is a highly effective anti-cancer therapy delivered to around 50-60% of patients. It is part of therapy for around 40% of cancer patients who are cured of their disease. Until recently, the focus of this anti-tumour efficacy has been on the direct tumour cytotoxicity and RT-induced DNA damage. Recently, the immunomodulatory effects of RT on the tumour microenvironment have increasingly been recognized. There is now intense interest in potentially using RT to induce an anti-tumour immune response, which has led to rethinking into how the efficacy of RT could be further enhanced. Following the breakthrough of immune check point inhibitors (ICIs), a new era of immuno-oncology (IO) agents has emerged and established immunotherapy as a routine part of cancer treatment. Despite ICI improving outcomes in many cancer types, overall durable responses occur in only a minority of patients. The immunostimulatory effects of RT make combinations with ICI attractive to potentially amplify anti-tumour immunity resulting in increased tumour responses and improved outcomes. In contrast, tumours with profoundly immunosuppressive tumour microenvironments, dominated by myeloid-derived cell populations, remain a greater clinical challenge and RT may potentially further enhance the immunosuppression. To harness the full potential of RT and IO agent combinations, further insights are required to enhance our understanding of the role these immunosuppressive myeloid populations play, how RT influences these populations and how they may be therapeutically manipulated in combination with RT to improve outcomes further. These are exciting times with increasing numbers of IO targets being discovered and IO agents undergoing clinical evaluation. Multidisciplinary research collaborations will be required to establish the optimal parameters for delivering RT (target volume, dose and fractionation) in combination with IO agents, including scheduling to achieve maximal therapeutic efficacy.

Nanoparticles Presenting Potent TLR7/8 Agonists Enhance Anti-PD-L1 Immunotherapy in Cancer Treatment

Cancer immunotherapy can be augmented with toll-like receptor agonist (TLRa) adjuvants, which interact with immune cells to elicit potent immune activation. Despite their potential, use of many TLRa compounds has been limited clinically due to their extreme potency and lack of pharmacokinetic control, causing systemic toxicity from unregulated systemic cytokine release. Herein, we overcome these shortcomings by generating poly(ethylene glycol)-poly(lactic acid) (PEG-PLA) nanoparticles (NPs) presenting potent TLR7/8a moieties on their surface. The NP platform allows precise control of TLR7/8a valency and resulting surface presentation through self-assembly using nanoprecipitation. We hypothesize that the pharmacokinetic profile of the NPs minimizes systemic toxicity, localizing TLR7/8a presentation to the tumor bed and tumor-draining lymph nodes. In conjunction with antiprogrammed death-ligand 1 (anti-PD-L1) checkpoint blockade, peritumoral injection of TLR7/8a NPs slows tumor growth, extends survival, and decreases systemic toxicity in comparison to the free TLR7/8a in a murine colon adenocarcinoma model. These NPs constitute a modular platform for controlling pharmacokinetics of immunostimulatory molecules, resulting in increased potency and decreased toxicity.

Trial Watch: experimental TLR7/TLR8 agonists for oncological indications

Resiquimod (R848) and motolimod (VTX-2337) are second-generation experimental derivatives of imiquimod, an imidazoquinoline with immunostimulatory properties originally approved by the US Food and Drug Administration for the topical treatment of actinic keratosis and genital warts more than 20 years ago. Both resiquimod and motolimod operate as agonists of Toll-like receptor 7 (TLR7) and/or TLR8, in thus far delivering adjuvant-like signals to antigen-presenting cells (APCs). In line with such an activity, these compounds are currently investigated as immunostimulatory agents for the treatment of various malignancies, especially in combination with peptide-based, dendritic cell-based, cancer cell lysate-based, or DNA-based vaccines. Here, we summarize preclinical and clinical evidence recently collected to support the development of resiquimod and motolimod and other TLR7/TLR8 agonists as anticancer agents.

Adjuvant Effect of Toll-Like Receptor 9 Activation on Cancer Immunotherapy Using Checkpoint Blockade

Immunotherapy using checkpoint blockade has revolutionized cancer treatment, improving patient survival and quality of life. Nevertheless, the clinical outcomes of such immunotherapy are highly heterogeneous between patients. Depending on the cancer type, the patient response rates to this immunotherapy are limited to 20–30%. Based on the mechanism underlying the antitumor immune response, new therapeutic strategies have been designed with the aim of increasing the effectiveness and specificity of the antitumor immune response elicited by checkpoint blockade agents. The activation of toll-like receptor 9 (TLR9) by its synthetic agonists induces the antitumor response within the innate immunity arm, generating adjuvant effects and priming the adaptive immune response elicited by checkpoint blockade during the effector phase of tumor-cell killing. This review first describes the underlying mechanisms of action and current status of monotherapy using TLR9 agonists and immune checkpoint inhibitors for cancer immunotherapy. The rationale for combining these two agents is discussed, and evidence indicating the current status of such combination therapy as a novel cancer treatment strategy is presented.

Harnessing the immune system to fight cancer with Toll-like receptor and RIG-I-like receptor agonists

Cancer immunotherapy has come of age with the advent of immune checkpoint inhibitors. In this article we review how agonists for receptors of the innate immune system, the Toll-like receptors and the RIG-I-like receptors, impact anticancer immune responses. Treatment with these agonists enhances the activity of anticancer effector cells, such as cytotoxic T cells and NK cells, and at the same time blocks the activity of immunosuppressive cell types such as regulatory T cells and myeloid-derived suppressor cells. These compounds also impact the recruitment of immune cells to the tumor. The phenomena of pattern-recognition receptor tolerance and reprogramming and their implications for immunotherapy are discussed. Finally, novel delivery systems that target the immune-stimulating drugs to the tumor or the tumor-draining lymph nodes to enhance their efficacy and safety are presented.

A TLR7 agonist strengthens T and NK cell function during BRAF-targeted therapy in a preclinical melanoma model

Therapeutic success of targeted therapy with BRAF inhibitors (BRAFi) for melanoma is limited by resistance development. Observations from preclinical mouse models and recent insights into the immunological effects caused by BRAFi give promise for future development of combination therapy for human melanoma. In our study, we used the transplantable D4M melanoma mouse model with the BRAF^V600E mutation and concomitant PTEN loss in order to characterize alterations in tumor‐infiltrating effector immune cells when tumors become resistant to BRAFi. We found that BRAFi‐sensitive tumors displayed a pronounced inflammatory milieu characterized by high levels of cytokines and chemokines accompanied by an infiltration of T and NK cells. The tumor‐infiltrating effector cells were activated and produced high levels of IFN‐γ, TNF‐α and granzyme B. When tumors became resistant and progressively grew, they reverted to a low immunogenic state similar to untreated tumors as reflected by low mRNA levels of proinflammatory cytokines and chemokines and fewer tumor‐infiltrating T and NK cells. Moreover, these T and NK cells were functionally impaired in comparison to their counterparts in BRAFi‐sensitive tumors. Their effector cell function could be restored by additional peritumoral treatment with the TLR7 agonist imiquimod, a clinically approved agent for nonmelanoma skin cancer. Indeed, resistance to BRAFi therapy was delayed and accompanied by high numbers of activated T and NK cells in tumors. Thus, combining BRAFi with an immune stimulating agent such as a TLR ligand could be a promising alternative approach for the treatment of melanoma.

What's new?

While inhibitors targeting mutant BRAF proteins can induce melanoma regression, many tumors become resistant to these agents, possibly owing to immunological effects of BRAF inhibitor therapy. Here, using a preclinical mouse model, the authors show that during the early treatment phase with BRAF inhibitors, melanomas are highly immunogenic, with infiltrating T cells and natural killer cells. When resistance develops, however, tumors regress toward low immunogenicity, similar to untreated tumors. Experiments show that in the BRAF‐sensitive phase, peritumoral injection of the TLR7 ligand imiquimod preserves immunogenicity and delays resistance, thus representing a potentially effective novel therapeutic strategy for melanoma.

Lyophilizable and Multifaceted Toll-like Receptor 7/8 Agonist-Loaded Nanoemulsion for the Reprogramming of Tumor Microenvironments and Enhanced Cancer Immunotherapy

The low therapeutic efficacy of current cancer immunotherapy is related to nonimmunogenic and immunosuppressive tumor microenvironments (TMEs). To overcome these limitations, both the immune priming of antitumoral lymphocytes and the reprogramming of immunosuppressive factors in TMEs are essential. Here, we suggest a nanoemulsion (NE)-based immunotherapeutic platform that can not only modulate tumor-induced suppression but also induce an effective cell-mediated immune response for T cell proliferation. Multifunctional NEs can be fabricated by integrating the efficacy of NEs as delivery systems and the multifaceted immunomodulation characteristics (i.e., immunostimulation and reprogramming of immunosuppression) of small molecule-based Toll-like receptor 7/8 agonists. Local in situ vaccination of melanoma and cervical tumor models with tumor antigens (protein and peptide) adjuvanted with NE loaded with TLR7/8 agonists [NE (TLR7/8a)] induced the recruitment and activation of innate immune cells, infiltration of lymphocytes, and polarization of tumor-associated M2 macrophages, which resulted in inhibition of tumor growth and prolonged survival in both primary and rechallenged tumor models. Antibody-depletion experiments also suggested that macrophages, type I IFN (IFN-α and IFN-β), CD8⁺ T cells, and NK1.1⁺ cells contributed to the antitumor effect of NE (TLR7/8a). The combination of antitumoral lymphocytes and reprogramming of immunosuppressive TMEs induced by NE (TLR7/8a) treatment evoked a synergistic antitumor immune response with immune checkpoint blockade therapy (anti-PD-1 and anti-PD-L1).

Gegen Qinlian Decoction Downregulates the TLR7 Signalling Pathway to Control Influenza A Virus Infection

ETHNOPHARMACOLOGICAL RELEVANCE

In recent years, Gegen Qinlian decoction (GQD) has been applied to treat influenza virus infection, and its clinical effectiveness has been shown. However, the potential mechanism by which GQD acts on influenza A virus (IAV) has not been fully elucidated. Traditional Chinese medicine (TCM) formulas are well known to have multiple targets and effects. Our previous experiments examined the mechanism by which TCM can be used to treat influenza from the perspective of the influenza immune mechanism.

AIM OF THE STUDY

To explore the possible mechanism by which GQD affects mice infected with the FM1 strain of influenza virus.

MATERIALS AND METHODS

Forty-eight C57BL/6 mice were divided randomly into four groups: a normal control (NG) group, an IAV infection (VG) group, an IAV + oseltamivir (30.44 mg/kg) treatment (VO) group, and an IAV + GQD (9.74 g/kg) treatment (VQ) group. We also grouped forty-eight Toll-like receptor 7 knockout (TLR7^-/-) mice in the same manner. The pulmonary mRNA expression of TLR7, myeloid differentiation factor 88 (MyD88), and nuclear factor (NF)-κB p65 was measured by RT-qPCR, and the pulmonary protein expression of TLR7, MyD88, and NF-κB p65 was measured by western blot. The proportions of T helper (Th) 1, Th2, Th17 and regulatory T (Treg) cells were measured by flow cytometry.

RESULTS

IAV infection led to low body weights and high viral load. Compared with those in the NG group, the mRNA expression levels of TLR7, MyD88, and NF-κB p65 in the VG group were upregulated (P < 0.05). However, the mRNA and protein expression levels of TLR7, MyD88, and NF-κB p65 were lower in the VO and VQ groups than in the VG group (P < 0.05). IAV infection led to increased proportions of Th1/Th2 and Th17/Treg cells in the VG group. In the VO and VQ groups, both Th2 and Th1 cell numbers were increased, resulting in a lower Th1/Th2 proportion than that in the VG group.

CONCLUSIONS

GQD downregulated the expression of some key TLR signalling pathway factors. GQD also affected the differentiation of CD4⁺ T cells, thereby exerting a protective systemic effect on influenza virus infection. In conclusion, GQD activated a balanced inflammatory response in the host to limit immune pathological injury and improve clinical and survival outcomes.

TLR7 (Toll-Like Receptor 7) Facilitates Heme Scavenging Through the BTK (Bruton Tyrosine Kinase)-CRT (Calreticulin)-LRP1 (Low-Density Lipoprotein Receptor-Related Protein-1)-Hx (Hemopexin) Pathway in Murine Intracerebral Hemorrhage

Background and Purpose- Heme and iron are considered to be key factors responsible for secondary insults after intracerebral hemorrhage (ICH). Our previous study showed that LRP1 (low-density lipoprotein receptor-related protein-1)-Hx (hemopexin) facilitates removal of heme. The TLR7 (Toll-like receptor 7)-BTK (Bruton tyrosine kinase)-CRT (calreticulin) pathway regulates the expression of LRP1-Hx. This study is designed to clarify whether TLR7 activation facilitates heme scavenging and to establish the potential role of the BTK-CRT-LRP1-Hx signaling pathway in the pathophysiology of ICH. Methods- ICH was induced by stereotactic, intrastriatal injection of type VII collagenase. Mice received TLR7 agonist (imiquimod) via intraperitoneal injection after ICH induction. TLR7 inhibitor (ODN2088), BTK inhibitor (LFM-A13), and CRT agonist (thapsigargin) were given in different groups to further evaluate the underlying pathway. Mice were randomly divided into sham, ICH+vehicle (normal saline), ICH+Imiquimod (2.5, 5, and 10 μg/g), ICH+ODN2088, ICH+LFM-A13, ICH+thapsigargin, and ICH+ODN2088+thapsigargin. Imiquimod was administered twice daily starting at 6 hours after ICH; ODN2088 was administered by intracerebroventricular injection at 30 minutes, and LFM-A13 or thapsigargin was administered by intraperitoneal injection at 3 hours after ICH induction. Neurological scores, cognitive abilities, as well as brain edema, blood-brain barrier permeability, hemoglobin level, brain expression of TLR7/BTK/CRT/LRP1/Hx were analyzed. Results- Low dosage imiquimod significantly attenuated hematoma volume, brain edema, BBB permeability, and neurological deficits after ICH. Imiquimod also increased protein expressions of TLR7, BTK, CRT, LRP1, and Hx; ODN2088 reduced TLR7, BTK, CRT, LRP1, and Hx expressions. Conclusions- TLR7 plays an important role in heme scavenging after ICH by modulating the BTK-CRT-LRP1-Hx pathway. TLR7 may offer protective effects by promoting heme resolution and reduction of brain edema after ICH.

Tuning the Tumor Myeloid Microenvironment to Fight Cancer

The tumor microenvironment (TME) of diverse cancer types is often characterized by high levels of infiltrating myeloid cells including monocytes, macrophages, dendritic cells, and granulocytes. These cells perform a variety of functions in the TME, varying from immune suppressive to immune stimulatory roles. In this review, we summarize the different myeloid cell populations in the TME and the intratumoral myeloid targeting approaches that are being clinically investigated, and discuss strategies that identify new myeloid subpopulations within the TME. The TME therapies include agents that modulate the functional activities of myeloid populations, that impact recruitment and survival of myeloid subpopulations, and that functionally reprogram or activate myeloid populations. We discuss the benefits, limitations and potential side effects of these therapeutic approaches.

Intravenous delivery of the toll-like receptor 7 agonist SC1 confers tumor control by inducing a CD8+ T cell response

TLR7 agonists are considered promising drugs for cancer therapy. The currently available compounds are not well tolerated when administered intravenously and therefore are restricted to disease settings amenable for topical application. Here we present the preclinical characterization of SC1, a novel synthetic agonist with exquisite specificity for TLR7. We found that intravenously administered SC1 mediates systemic release of type I interferon, but not of proinflammatory cytokines such as TNFα and IL6, and results in activation of circulating immune cells. Tumors of SC1-treated mice have brisk immune cell infiltrates and are polarized towards a Th1 type signature. Intratumoral CD8⁺ T cells and CD11b⁺ conventional dendritic cells (cDCs) are significantly increased, plasmacytoid dendritic cells (pDCs) are strongly activated and macrophages are M1 phenotype polarized, whereas myeloid-derived suppressor cells (MDSCs) are decreased. We further show that treatment of mice with SC1 profoundly inhibits the growth of established syngeneic tumors and results in significantly prolonged survival. Mice, which are tumor-free after SC1 treatment are protected from subsequent tumor rechallenge. The antitumor effect of SC1 depends on antigen-specific CD8⁺ T cells, which we found to be strongly enriched in the tumors of SC1-treated mice. In conclusion, this study shows that systemically administered SC1 mobilizes innate and adaptive immunity and is highly potent as single agent in mice and thereby provides a rationale for clinical testing of this compound.

The potential of nanoparticle vaccines as a treatment for cancer

A complex and multifaceted relationship exists between cancer and the immune system. Advances in our understanding of this relationship have resulted in significant clinical attention in the possibilities of cancer immunotherapy. Harnessing the immune system's potent and selective destructive capability is a major focus of attempts to treat cancer. Despite significant progress in the field, cancer therapy still remains significantly deficient, with cancer being one of the largest contributors to morbidity and mortality in the developed world. It is evident that the design of new treatment regimes is required to exploit cancer immunotherapy. Herein we review the potential for nanotechnology to overcome the challenges that have limited the more widespread implementation of immunotherapy to cancer treatment.

Innate Immune Stimulation in Cancer Therapy

The innate immune system has evolved as a first line of defense against invading pathogens and acts via classes of germline-encoded receptor systems to respond with proinflammatory cytokines. Innate immune cells, predominantly cells of the myeloid compartment, are capable of providing a potent basis for boosting adaptive immunity in malignant diseases. The authors review their current understanding of the molecular mechanisms whereby innate pattern recognition receptors participate in immunosurveillance of cancer cells. They discuss how innate effector mechanisms are currently being targeted pharmacologically and how improved understanding of the biology of these pathways is leading to novel immunotherapies of cancer.

Targeting macrophages: therapeutic approaches in cancer

Infiltration of macrophages in solid tumours is associated with poor prognosis and correlates with chemotherapy resistance in most cancers. In mouse models of cancer, macrophages promote cancer initiation and malignant progression by stimulating angiogenesis, increasing tumour cell migration, invasion and intravasation and suppressing antitumour immunity. At metastatic sites, macrophages promote tumour cell extravasation, survival and subsequent growth. Each of these pro-tumoural activities is promoted by a subpopulation of macrophages that express canonical markers but have unique transcriptional profiles, which makes tumour-associated macrophages (TAMs) good targets for anticancer therapy in humans through either their ablation or their re-differentiation away from pro-tumoural towards antitumoural states. In this Review, we evaluate the state of the art of TAM-targeting strategies, focusing on the limitations and potential side effects of the different therapies such as toxicity, rebound effects and compensatory mechanisms. We provide an extensive overview of the different types of therapy used in the clinic and their limitations in light of known macrophage biology and propose new strategies for targeting TAMs.

CD11c-targeted Delivery of DNA to Dendritic Cells Leads to cGAS- and STING-dependent Maturation

Immunotherapeutic activation of tumor-specific T cells has proven to be an interesting approach in anticancer treatment. Particularly, anti-CTLA-4 and anti-PD-1/PD-L1 treatment looks promising, and conceivably, even better clinical results might be obtained if such treatment could be combined with boosting the existing tumor-specific T-cell response. One way to achieve this could be by increasing the level of maturation of dendritic cells locally and in the draining lymph nodes. When exposed to cancer cells, dendritic cells may spontaneously mature because of danger-associated molecular patterns derived from the tumor cells. Double-stranded DNA play a particularly important role in the activation of the dendritic cells, through engagement of intracellular DNA-sensors, and signaling through the adaptor protein STING. In the present study, we have investigated the maturational response of human monocyte-derived dendritic cells (moDC) and human monocytic THP-1 cells to targeted and untargeted DNA. We used an anti-CD11c antibody conjugated with double-stranded DNA to analyze the maturation status of human moDCs, as well as maturation using a cGAS KO and STING KO THP-1 cell maturation model. We found that dendritic cells can mature after exposure to cytoplasmic double-stranded DNA delivered through CD11c-mediated endocytosis. Moreover, we show that THP-1 cells matured using IL-4, GM-CSF, and ionomycin upregulate DC-maturation markers after CD11c-targeted delivery of double-stranded DNA. This upregulation is completely abrogated in cGAS KO and STING KO cells.

Selective hemangioma cell dysfunction and apoptosis triggered by in vitro treatment with imiquimod

Infantile hemangiomas are the most common benign tumors of infancy, characterized by unregulated angiogenesis and endothelial cells with high mitotic rate. Although spontaneous regression occurs, sometimes treatment is required and alternatives to corticosteroids should be considered to reduce side effects. Imiquimod is an imidazoquinoline, approved for some skin pathologies other than hemangioma. It is proposed that the effectiveness of imiquimod comes from the activation of immune cells at tumor microenvironment. However, the possibility to selectively kill different cell types and to directly impede angiogenesis has been scarcely explored in vitro for endothelial cells. In this work we showed a dramatic cytotoxicity on hemangioma cell, with a significant lower IC50 value in hemangioma compared to normal endothelial cells and melanoma (employed as a non-endothelial tumor cell line). Nuclear morphometric and flow-cytometry assays revealed imiquimod-induced apoptosis on hemangioma and melanoma cells but a small percentage of senescence on normal endothelial cells. At sub-lethal conditions, cell migration, a key step in angiogenesis turned out to be inhibited in a tumor-selective manner along with actin cytoskeleton disorganization on hemangioma cells. Altogether, these findings pointed out the selective cytotoxic effects of imiquimod on transformed endothelial cells, evidencing the potential for imiquimod to be a therapeutic alternative to reduce extensive superficial hemangioma lesions.

Polymer-based nanoparticles loaded with a TLR7 ligand to target the lymph node for immunostimulation

Small-molecule agonists for the Toll-like receptors (TLR) 7 and 8 are effective for the immunotherapy of skin cancer when used as topical agents. Their systemic use has however been largely unsuccessful due to dose-limiting toxicity. We propose a polymer-based nanodelivery system to target resiquimod, a TLR7 ligand, to the lymph node in order to focus the immunostimulatory activity and to prevent a generalized inflammatory response. We demonstrate successful encapsulation of resiquimod in methoxypoly(ethylene glycol)-b-poly(DL-lactic acid) (mPEG-PLA) and mixed poly(DL-lactic-co-glycolic acid) (PLGA)/mPEG-PLA nanoparticles. We show that these particles are taken up mainly by dendritic cells and macrophages, which are the prime initiators of anticancer immune responses. Nanoparticles loaded with resiquimod activate these cells, demonstrating the availability of the immune-stimulating cargo. The unloaded particles are non-inflammatory and do not have cytotoxic activity on immune cells. Following subcutaneous injection in mice, mPEG-PLA and PLGA/mPEG-PLA nanoparticles are detected in dendritic cells and macrophages in the draining lymph nodes, demonstrating the targeting potential of these particles. Thus, polymer-based nanoparticles represent a promising delivery system that allows lymph node targeting for small-molecule TLR7 agonists in the context of systemic cancer immunotherapy.

A TLR7 agonist enhances the antitumor efficacy of obinutuzumab in murine lymphoma models via NK cells and CD4 T cells

Anti-CD20 monoclonal antibodies (mAb) such as rituximab have been proven to be highly effective at improving outcome in B-cell malignancies. However, many patients ultimately relapse and become refractory to treatment. The glycoengineered anti-CD20 mAb obinutuzumab was developed to induce enhanced antibody-dependent cellular cytotoxicity, antibody-dependent phagocytosis and direct cell death and was shown to lead to improved outcomes in a randomized study in B-CLL. We hypothesized that immune stimulation through Toll-like receptor 7 (TLR7) agonism in combination with obinutuzumab would further enhance lymphoma clearance and the generation of long-term antitumor immune responses. Here we demonstrate, in syngeneic human CD20 (hCD20)-expressing models of lymphoma, that systemic administration of a TLR7 agonist (R848) increases responses when administered in combination with obinutuzumab and protects against disease recurrence. Depletion studies demonstrate that primary antitumor activity is dependent on both NK cells and CD4+ T cells but not on CD8+ T cells. However, both CD4+ and CD8+ T cells appear necessary for the generation of protective immunological memory. Importantly, increased tumor-free survival post obinutuzumab and R848 combination therapy was seen in hCD20 transgenic mice, which express hCD20 on normal B cells. These findings provide a rationale for clinical testing of obinutuzumab in combination with systemically administered TLR7 agonists to further improve outcome.

Predictive value of TLR7 polymorphism for cetuximab-based chemotherapy in patients with metastatic colorectal cancer

The TLR7 and TLR9 signalings are implicated in the regulation of the immune system through type-I interferon induction. Preclinical studies have demonstrated the immunomodulatory and antitumor effects of TLR7 and TLR9 agonists in combination with cetuximab. We tested the hypothesis that genetic variations in TLR7 and TLR9 and their downstream molecules IRF5 and IRF7 were associated with outcomes in metastatic colorectal cancer (mCRC) patients receiving cetuximab-based chemotherapy. Six single nucleotide polymorphisms (SNPs) in TLR7, TLR9, IRF5 and IRF7 were tested for the association with RR, PFS, and OS in KRAS-wild type mCRC patients. Patients treated with FOLFIRI + cetuximab or FOLFIRI + bevacizumab in the FIRE-3 trial served as a discovery set (FIRE3-Cet, n = 244) or a control set (FIRE3-Bev, n = 246), respectively. Patients treated with FOLFOX or SOX + cetuximab in the JACCRO-CC05/06 trial served as a validation set (JACCRO, n = 76). Genomic DNA isolated from tumor tissue samples was analyzed by PCR-based direct sequencing. In the discovery cohort, patients with the TLR7 rs3853839 G/G variant showed a trend toward longer PFS than those with any C variants (median 10.0 vs. 11.8 months, HR 1.39, p = 0.092). This preliminary association was confirmed in the validation cohort, and those with the G/G genotype showed a PFS benefit compared with others (univariate: 9.1 vs. 11.6 months, HR 2.04, p = 0.005, multivariate: HR 2.02, 95% CI: 1.14-3.55, p = 0.015). This association was not observed in the control cohort. Our findings suggest that TLR7 rs3853839 predicts the outcome of cetuximab-based chemotherapy in mCRC patients.

Production of Adjuvant-Loaded Biodegradable Particles for Use in Cancer Vaccines

Immune adjuvants, such as ligands for pathogen-associated molecular patterns (PAMPs), have been showing promise in boosting immune responses to tumor associated antigens, and delivering these adjuvants as discrete packages is considered advantageous over delivery in soluble form. Here we describe in detail, methods for independently loading a range of adjuvants into polymer-based biodegradable particles. We also describe the means by which to characterize these particles with respect to adjuvant loading and release kinetics as well as in terms of particle size, shape, and zeta-potential. These adjuvant-loaded particles have the potential to be used in dendritic cell-based uptake experiments performed in vitro or to be used in preclinical cancer vaccine research applications where they can be co-delivered with antigen-loaded particles or some other vaccine component comprising antigenic material.

Turning tumour cells into antigen presenting cells: The next step to improve cancer immunotherapy?

Downregulation/loss of the antigen presentation is a major immune escape mechanism in cancer. It allows tumour cells to become 'invisible' and avoid immune attack by antitumour T cells. In tumour harbouring properties of professional antigen presenting cells (i.e. tumour B cells in lymphoma), downregulation/loss of the antigen presentation may also prevent direct priming of naïve T cells by tumour cells. Here, we review treatments that may induce/restore antigen presentation by the tumour cells. These treatments may increase the generation of antitumour T cells and/or their capacity to recognise and eliminate tumour cells. By forcing tumour cells to present their antigens, these treatments may sensitise patients to T cell-based immunotherapies, including checkpoint inhibitors.

TLR7-based cancer immunotherapy decreases intratumoral myeloid-derived suppressor cells and blocks their immunosuppressive function

Myeloid-derived suppressor cells (MDSC) are a heterogeneous population of immature myeloid cells with the capacity to inhibit immunological responses. During cancer progression, MDSC are recruited to the tumor sites and secondary lymphoid organs, leading to the suppression of the antitumor function of NK and T cells. Here, we show that the TLR7/8 agonist resiquimod (R848) has a direct effect on MDSC populations in tumor-bearing mice. Systemic application of R848 led to a rapid reduction in both intratumoral and circulating MDSC. The subpopulation of monocytic MDSC (m-MDSC) was the most affected by R848 treatment with an up to 5-fold decrease in the tumor. We found that TLR7 stimulation in tumor-bearing mice led to a maturation and differentiation of MDSC with upregulation of the surface molecules CD11c, F4/80, MHC-I, and MHC-II. MDSC treated with R848 lost their immunosuppressive function and acquired instead an antigen-presenting phenotype with the capability to induce specific T-cell proliferation. Importantly, we found that MDSC co-injected s.c. with CT26 tumor cells lost their ability to support tumor growth after pretreatment with R848. Our results demonstrate that treatment of tumor-bearing mice with a TLR7/8 agonist acts directly on MDSC to induce their maturation and leads them to acquire a non-suppressive status. Considering the obstacles posed by MDSC for cancer immunotherapy, targeting these cells by a TLR7/8 agonist may improve immune responses against cancer.

A novel TLR7 agonist reverses NK cell anergy and cures RMA-S lymphoma-bearing mice

Toll-like receptor 7 (TLR7) agonists are potent immune stimulants able to overcome cancer-associated immune suppression. Due to dose-limiting systemic toxicities, only the topically applied TLR7 agonist (imiquimod) has been approved for therapy of skin tumors. There is a need for TLR7-activating compounds with equivalent efficacy but less toxicity. SC1, a novel small molecule agonist for TLR7, is a potent type-1 interferon inducer, comparable to the reference TLR7 agonist resiquimod, yet with lower induction of proinflammatory cytokines. In vivo, SC1 activates NK cells in a TLR7-dependent manner. Mice bearing the NK cell-sensitive lymphoma RMA-S are cured by repeated s. c. administrations of SC1 as efficiently as by the administration of resiquimod. No relevant toxicities were observed. Mechanistically, SC1 reverses NK cell anergy and restores NK cell-mediated tumor cell killing in an IFN-α-dependent manner. TLR7 targeting by SC1-based compounds may form an attractive strategy to activate NK cell responses for cancer therapy.

Targeted delivery of let-7b to reprogramme tumor-associated macrophages and tumor infiltrating dendritic cells for tumor rejection

Both tumor associated macrophages (TAMs) and tumor infiltrating dendritic cells (TIDCs) are important components in the tumor microenvironment that mediate tumor immunosuppression and promote cancer progression. Targeting these cells and altering their phenotypes may become a new strategy to recover their anti-tumor activities and thereby restore the local immune surveillance against tumor. In this study, we constructed a nucleic acid delivery system for the delivery of let-7b, a synthetic microRNA mimic. Our carrier has an affinity for the mannose receptors on TAMs/TIDCs and is responsive to the low-pH tumor microenvironment. The delivery of let-7b could reactivate TAMs/TIDCs by acting as a TLR-7 agonist and suppressing IL-10 production in vitro. In a breast cancer mouse model, let-7b delivered by this system efficiently reprogrammed the functions of TAMs/TIDCs, reversed the suppressive tumor microenvironment, and inhibited tumor growth. Taken together, this strategy, designed based upon TAMs/TIDCs-targeting delivery and the dual biological functions of let-7b (TLR-7 ligand and IL-10 inhibitor), may provide a new approach for cancer immunotherapy.

Potent and Selective Inhibitors of MTH1 Probe Its Role in Cancer Cell Survival

Recent literature has claimed that inhibition of the enzyme MTH1 can eradicate cancer. MTH1 is one of the "housekeeping" enzymes that are responsible for hydrolyzing damaged nucleotides in cells and thus prevent them from being incorporated into DNA. We have developed orthogonal and chemically distinct tool compounds to those published in the literature to allow us to test the hypothesis that inhibition of MTH1 has wide applicability in the treatment of cancer. Here we present the work that led to the discovery of three structurally different series of MTH1 inhibitors with excellent potency, selectivity, and proven target engagement in cells. None of these compounds elicited the reported cellular phenotype, and additional siRNA and CRISPR experiments further support these observations. Critically, the difference between the responses of our highly selective inhibitors and published tool compounds suggests that the effect reported for the latter may be due to off-target cytotoxic effects. As a result, we conclude that the role of MTH1 in carcinogenesis and utility of its inhibition is yet to be established.