Toll-like receptor 4 engagement drives differentiation of human and murine dendritic cells from a pro- into an anti-inflammatory mode

Exosome-based strategies for diagnosis and therapy of glioma cancer

Glioblastoma belongs to the most aggressive type of cancer with a low survival rate that is characterized by the ability in forming a highly immunosuppressive tumor microenvironment. Intercellular communication are created via exosomes in the tumor microenvironment through the transport of various biomolecules. They are primarily involved in tumor growth, differentiation, metastasis, and chemotherapy or radiation resistance. Recently several studies have highlighted the critical role of tumor-derived exosomes against immune cells. According to the structural and functional properties, exosomes could be essential instruments to gain a better molecular mechanism for tumor understanding. Additionally, they are qualified as diagnostic/prognostic markers and therapeutic tools for specific targeting of invasive tumor cells such as glioblastomas. Due to the strong dependency of exosome features on the original cells and their developmental status, it is essential to review their critical modulating molecules, clinical relevance to glioma, and associated signaling pathways. This review is a non-clinical study, as the possible role of exosomes and exosomal microRNAs in glioma cancer are reported. In addition, their content to overcome cancer resistance and their potential as diagnostic biomarkers are analyzed.

The Efficacy of Dendritic Cell Vaccine for Newly Diagnosed Glioblastoma: A Meta-analysis of Randomized Controlled Studies

ABSTRACT

The efficacy of dendritic cell vaccine for newly diagnosed glioblastoma remains controversial. We conduct a systematic review and meta-analysis to explore the influence of dendritic cell vaccine on treatment efficacy for newly diagnosed glioblastoma. We search PubMed, EMBASE, Web of science, EBSCO, and Cochrane library databases through December 2019 for randomized controlled trials assessing the efficacy and safety of dendritic cell vaccine for newly diagnosed glioblastoma. This meta-analysis is performed using the random effect model. Three randomized controlled trials are included in the meta-analysis. Overall, compared with control group for newly diagnosed glioblastoma, dendritic cell vaccine shows no substantial effect on median overall survival [standard mean difference, 0.11; 95% confidence interval (CI), -0.18 to 0.41; P = 0.45], median progression-free survival (standard mean difference, 0.12; 95% CI, -0.24 to 0.48; P = 0.50), progression-free survival rate [risk ratio (RR), 1.29; 95% CI, 0.82-2.04; P = 0.27], overall survival rate (RR, 1.29; 95% CI, 0.61-2.72; P = 0.50), or nervous system disorders (RR, 0.80; 95% CI, 0.59-1.08; P = 0.14). Dendritic cell vaccine may provide no obvious benefits for the newly diagnosed glioblastoma.

HMOC, a chrysin derivative, induces tolerogenic properties in lipopolysaccharide-stimulated dendritic cells

Although we previously identified a new hydroxymethoxyl chrysin derivative (HMOC) using ionizing radiation, the anti-inflammatory mechanism of HMOC in dendritic cells remains unclear. In this study, we investigate the effects of HMOC on phenotypic and functional changes in activated bone marrow-derived dendritic cells (BMDCs). In lipopolysaccharide (LPS)-stimulated BMDCs, HMOC treatment inhibited pro-inflammatory cytokines (TNF-α, IL-12p70, and IL-1β), surface molecules (CD80, CD86, MHC-I, and MHC-II), and antigen-presentation to MHC-I and II without a decrease in IL-10. Furthermore, HMOC increased indoleamine 2,3-dioxygenase-1 (IDO1) activity via activation of JNK and p38 signaling in the presence of LPS. Interestingly, LPS-stimulated DCs treated with HMOC inhibited the proliferation and activation of CD4+ and CD8+ T cells, as well as differentiation of CD4+ T cells into Th1-, Th2- and Th17 cells. In addition, LPS-stimulated DCs treated with HMOC induced an increase in CD4+CD25+Foxp3+ regulatory T cells (Tregs). Collectively, our results suggest that HMOC confers tolerogenic properties in BMDCs, which are responsible for inducing Th cell differentiation to Tregs. Our findings provide a better understanding of the anti-inflammatory mechanism of HMOC in DCs and may contribute to development of a valuable therapeutic candidate for atopic dermatitis.

The efficacy of dendritic cell vaccine for newly diagnosed glioblastoma: A meta-analysis of randomized controlled studies

INTRODUCTION

The efficacy of dendritic cell vaccine to treat glioblastoma remained elusive and therefore we conducted a meta-analysis to explore the influence of dendritic cell vaccine on treatment efficacy of glioblastoma.

METHODS

PubMed, EMbase, Web of science, EBSCO and Cochrane library databases have been searched through October 2020, and we included randomized controlled trials (RCTs) assessing the efficacy of dendritic cell vaccine for glioblastoma.

RESULTS

Four RCTs and 267 patients were included in the meta-analysis. Compared to control group for glioblastoma, dendritic cell vaccine demonstrated no obvious impact on overall survival (HR=0.59; 95% CI=0.34 to 1.04; P=0.07), progression-free survival (PFS, HR=0.72; 95% CI=0.52 to 1.00; P=0.05), nervous system disorders (OR=0.61; 95% CI=0.29 to 1.29; P=0.20), or adverse events (OR=1.44; 95% CI=0.82 to 2.50; P=0.20).

CONCLUSIONS

Dendritic cell vaccine may be not effective to treat glioblastoma.

Cell Type- and Stimulation-Dependent Transcriptional Programs Regulated by Atg16L1 and Its Crohn's Disease Risk Variant T300A

Genome-wide association studies have identified common genetic variants impacting human diseases; however, there are indications that the functional consequences of genetic polymorphisms can be distinct depending on cell type-specific contexts, which produce divergent phenotypic outcomes. Thus, the functional impact of genetic variation and the underlying mechanisms of disease risk are modified by cell type-specific effects of genotype on pathological phenotypes. In this study, we extend these concepts to interrogate the interdependence of cell type- and stimulation-specific programs influenced by the core autophagy gene Atg16L1 and its T300A coding polymorphism identified by genome-wide association studies as linked with increased risk of Crohn's disease. We applied a stimulation-based perturbational profiling approach to define Atg16L1 T300A phenotypes in dendritic cells and T lymphocytes. Accordingly, we identified stimulus-specific transcriptional signatures revealing T300A-dependent functional phenotypes that mechanistically link inflammatory cytokines, IFN response genes, steroid biosynthesis, and lipid metabolism in dendritic cells and iron homeostasis and lysosomal biogenesis in T lymphocytes. Collectively, these studies highlight the combined effects of Atg16L1 genetic variation and stimulatory context on immune function.

Validation of molecular biomarkers for preoperative diagnostics of human papillary thyroid carcinoma in fine needle aspirates

Background

Despite substantial efforts, reliable preoperative diagnostic for human thyroid malignancies in case of cytologically indeterminate nodules is still missing, resulting in high number of unnecessary thyroidectomies. In an attempt to increase precision of existing preoperative diagnostics, we aimed at validating the panel of molecular biomarkers predictive for papillary thyroid carcinoma (PTC) in preoperative fine needle aspirate (FNA) samples.

Methods

In this prospective study conducted in preoperative thyroid FNA from 44 thyroid nodules, expression levels of 11 molecular biomarkers previously validated on the postoperative samples of PTCs were measured by Cell-to-CT and QuantiGene Plex methods and correlated with final diagnosis.

Results

The QuantiGene Plex resulted in reliable gene expression measurements for FNA and core-needle biopsy (CNB) samples, however this method was less sensitive than pre-amplification based Cell-to-CT. Measurements conducted on the same samples by the two methods significantly correlated for most of the genes. Expression levels of TIMP1, c-MET and ARNTL were upregulated in PTC nodules as compared to benign counterparts, supporting previous post-operative studies. Strong correlation was observed between these biomarker alterations in the same samples. Within the sub-group of 15 indeterminate nodules (Bethesda II-V), TIMP1 had 100% specificity and 83% sensitivity for PTC cases.

Conclusions

Assessment of TIMP1, c-MET and core-clock gene ARNTL expression levels by QuantiGene Plex assay in FNA samples holds promise as an ancillary method to the cytological preoperative diagnostics.

Spheroid glioblastoma culture conditions as antigen source for dendritic cell-based immunotherapy: spheroid proteins are survival-relevant targets but can impair immunogenic interferon γ production

BACKGROUND

Glioblastoma is the most aggressive type of brain cancer. Dendritic cell (DC)-based immunotherapy against glioblastoma depends on the effectiveness of loaded antigens. Sphere-inducing culture conditions are being studied by many as a potential antigen source. Here, we investigated two different in vitro conditions (spheroid culture versus adherent culture) in relation to DC immunotherapy: (1) We studied the specific spheroid-culture proteome and assessed the clinical importance of spheroid proteins. (2) We evaluated the immunogenicity of spheroid lysate - both compared to adherent conditions.

METHODS

We used seven spheroid culture systems, three of them patient-derived. Stemness-related markers were studied in those three via immunofluorescence. Spheroid-specific protein expression was measured via quantitative proteomics. The Cancer Genome Atlas (TCGA) survival data was used to investigate the clinical impact of spheroid proteins. Immunogenicity of spheroid versus adherent cell lysate was explored in autologous ELISPOT systems (DCs and T cells from the three patients).

RESULTS

(1) The differential proteome of spheroid versus adherent glioblastoma culture conditions could successfully be established. The top 10 identified spheroid-specific proteins were associated with significantly decreased overall survival (TCGA MIT/Harvard cohort; n = 350, P = 0.014). (2) In exploratory experiments, immunogenicity of spheroid lysate vis-á-vis interferon (IFN)γ production was lower than that of adherent cell lysate (IFNγ ELISPOT; P = 0.034).

CONCLUSIONS

Spheroid culture proteins seem to represent survival-relevant targets, supporting the use of spheroid culture conditions as an antigen source for DC immunotherapy. However, immunogenicity enhancement should be considered for future research. Transferability of our findings in terms of clinical impact and regarding different spheroid-generation techniques needs further validation.

Regulatory perspective on in vitro potency assays for human dendritic cells used in anti-tumor immunotherapy

Dendritic cells (DCs) are key connectors between the innate and adaptive immune system and have an important role in modulating other immune cells. Therefore, their therapeutic application to steer immune responses is considered in various disorders, including cancer. Due to differences in the cell source and manufacturing process, each DC medicinal product is unique. Consequently, release tests to ensure consistent quality need to be product-specific. Although general guidance concerning quality control testing of cell-based therapies is available, cell type-specific regulation is still limited. Especially guidance related to potency testing is needed, because developing an in vitro assay measuring cell properties relevant for in vivo functionality is challenging. In this review, we provide DC-specific guidance for development of in vitro potency assays for characterisation and release. We present a broad overview of in vitro potency assays suggested for DC products to determine their anti-tumor functionality. Several advantages and limitations of these assays are discussed. Also, we provide some points to consider for selection and design of a potency test. The ideal functionality assay for anti-tumor products evaluates the capacity of DCs to stimulate antigen-specific T cells. Because this approach may not be feasible for release, use of surrogate potency markers could be considered, provided that these markers are sufficiently linked to the in vivo DC biological activity and clinical response. Further elucidation of the involvement of specific DC subsets in anti-tumor responses will result in improved manufacturing processes for DC-based products and should be considered during potency assay development.

Audencel Immunotherapy Based on Dendritic Cells Has No Effect on Overall and Progression-Free Survival in Newly Diagnosed Glioblastoma: A Phase II Randomized Trial

Dendritic cells (DCs) are antigen-presenting cells that are capable of priming anti-tumor immune responses, thus serving as attractive tools to generate tumor vaccines. In this multicentric randomized open-label phase II study, we investigated the efficacy of vaccination with tumor lysate-charged autologous DCs (Audencel) in newly diagnosed glioblastoma multiforme (GBM). Patients aged 18 to 70 years with histologically proven primary GBM and resection of at least 70% were randomized 1:1 to standard of care (SOC) or SOC plus vaccination (weekly intranodal application in weeks seven to 10, followed by monthly intervals). The primary endpoint was progression-free survival at 12 months. Secondary endpoints were overall survival, safety, and toxicity. Seventy-six adult patients were analyzed in this study. Vaccinations were given for seven (3⁻20) months on average. No severe toxicity was attributable to vaccination. Seven patients showed flu-like symptoms, and six patients developed local skin reactions. Progression-free survival at 12 months did not differ significantly between the control and vaccine groups (28.4% versus 24.5%, p = 0.9975). Median overall survival was similar with 18.3 months (vaccine: 564 days, 95% CI: 436⁻671 versus control: 568 days, 95% CI: 349⁻680; p = 0.89, harzard ratio (HR) 0.99). Hence, in this trial, the clinical outcomes of patients with primary GBM could not be improved by the addition of Audencel to SOC.

Tumor lysate-loaded Bacterial Ghosts as a tool for optimized production of therapeutic dendritic cell-based cancer vaccines

Cancer immunotherapy with dendritic cell (DC)-based vaccines has been used to treat various malignancies for more than two decades, however generally showed a limited clinical success. Among various factors responsible for their modest clinical activity is the lack of universally applied, standardized protocols for the generation of clinical-grade DC vaccines, capable of inducing effective anti-tumor immune responses. We investigated Bacterial Ghosts (BGs) - empty envelopes of Gram-negative bacteria - as a tool for optimized production of DC vaccines. BGs possess various intact cell surface structures, exhibiting strong adjuvant properties required for the induction of DC maturation, whereas their empty internal space can be easily filled with a source tumor antigens, e.g. tumor lysate. Hence BGs emerge as an excellent platform for both the induction of immunogenic DC maturation and loading with tumor antigens in a single-step procedure. We compared the phenotype, cytokine secretion profile, functional activity and ability to induce immunogenic T-cell responses in vitro of human monocyte-derived DCs generated using BG platform and DCs matured with widely used lipopolysaccharide (LPS) plus interferon-γ cocktail and loaded with tumor lysate. Both approaches induced DC maturation, however BG-based protocol was superior to LPS-based protocol in terms of the ability to induce DCs with a lower tolerogenic potential, resulting in a more robust CD8⁺ T cell activation and their functional activity as well as significantly lower induction of regulatory T cells. These superior parameters are attributed, at least in part, to the ability of BG-matured DCs to resist potential immunosuppressive and pro-tolerogenic activity of various tumor cell lysates, including melanoma, renal carcinoma and glioblastoma.

Dendritic Cells and Their Multiple Roles during Malaria Infection

Dendritic cells (DCs) play a central role in the initiation of adaptive immune responses, efficiently presenting antigens to T cells. This ability relies on the presence of numerous surface and intracellular receptors capable of sensing microbial components as well as inflammation and on a very efficient machinery for antigen presentation. In this way, DCs sense the presence of a myriad of pathogens, including Plasmodium spp., the causative agent of malaria. Despite many efforts to control this infection, malaria is still responsible for high rates of morbidity and mortality. Different groups have shown that DCs act during Plasmodium infection, and data suggest that the phenotypically distinct DCs subsets are key factors in the regulation of immunity during infection. In this review, we will discuss the importance of DCs for the induction of immunity against the different stages of Plasmodium, the outcomes of DCs activation, and also what is currently known about Plasmodium components that trigger such activation.

Pathogen-Associated Molecular Patterns Induced Crosstalk between Dendritic Cells, T Helper Cells, and Natural Killer Helper Cells Can Improve Dendritic Cell Vaccination

A coordinated cellular interplay is of crucial importance in both host defense against pathogens and malignantly transformed cells. The various interactions of Dendritic Cells (DC), Natural Killer (NK) cells, and T helper (Th) cells can be influenced by a variety of pathogen-associated molecular patterns (PAMPs) and will lead to enhanced CD8⁺ effector T cell responses. Specific Pattern Recognition Receptor (PRR) triggering during maturation enables DC to enhance Th1 as well as NK helper cell responses. This effect is correlated with the amount of IL-12p70 released by DC. Activated NK cells are able to amplify the proinflammatory cytokine profile of DC via the release of IFN-γ. The knowledge on how PAMP recognition can modulate the DC is of importance for the design and definition of appropriate therapeutic cancer vaccines. In this review we will discuss the potential role of specific PAMP-matured DC in optimizing therapeutic DC-based vaccines, as some of these DC are efficiently activating Th1, NK cells, and cytotoxic T cells. Moreover, to optimize these vaccines, also the inhibitory effects of tumor-derived suppressive factors, for example, on the NK-DC crosstalk, should be taken into account. Finally, the suppressive role of the tumor microenvironment in vaccination efficacy and some proposals to overcome this by using combination therapies will be described.

Potency of Both Human Th1 and NK Helper Cell Activation is Determined by IL-12p70-Producing PAMP-Matured DCs

Besides T helper (Th) cells, natural killer (NK) cells have also been described to participate in the shaping of dendritic cell (DC)-mediated adaptive immune responses. At present, it remains unclear to what extent the induction of these NK helper cell immune mechanisms is coupled with Th responses and whether both helper immune responses are induced by the same DC upon specific pathogen recognition receptor (PRR) stimulation. In this study, we demonstrate that maturation of DCs with a cocktail containing FMKp (membrane fragments of Klebsiella pneumoniae) mounts both Th cell and NK cell helper responses in a PRR-triggered dose-dependent manner as determined by the capacity of the helper cells to produce IFN-γ. Furthermore, by triggering an additional PRR pathway [FMKp in combination with poly(I:C) lyovec], we reveal that both approaches modulate the amount of DC-derived IL-12p70 and that this cytokine is the key determinant of the DC-induced Th1 and NK cell helper responses. Moreover, all PRR triggers able to induce IL-12-producing mature DCs are sufficient to induce these helper responses. We propose the existence of a single program used by DCs to induce potent cellular immune responses by stimulating both T helper and NK cell helper processes. This knowledge can help to select the proper PRR triggers in preventive and therapeutic vaccine design.

The Mycobacterium avium subsp. Paratuberculosis protein MAP1305 modulates dendritic cell-mediated T cell proliferation through Toll-like receptor-4

In this study, we show that Mycobacterium avium subsp. paratuberculosis MAP1305 induces the maturation of bone marrow-derived dendritic cells (BMDCs), a representative antigen presenting cell (APC). MAP1305 protein induces DC maturation and the production of pro-inflammatory cytokines (Interleukin (IL)-6), tumor necrosis factor (TNF)-α, and IL-1β) through Toll like receptor-4 (TLR-4) signaling by directly binding with TLR4. MAP1305 activates the phosphorylation of MAPKs, such as ERK, p38MAPK, and JNK, which is essential for DC maturation. Furthermore, MAP1305-treated DCs transform naïve T cells to polarized CD4(+) and CD8(+) T cells, thus indicating a key role for this protein in the Th1 polarization of the resulting immune response. Taken together, M. avium subsp. paratuberculosis MAP1305 is important for the regulation of innate immune response through DC-mediated proliferation of CD4(+) and CD8(+) T cells.

Monitoring the initiation and kinetics of human dendritic cell-induced polarization of autologous naive CD4+ T cells

A crucial step in generating de novo immune responses is the polarization of naive cognate CD4+ T cells by pathogen-triggered dendritic cells (DC). In the human setting, standardized DC-dependent systems are lacking to study molecular events during the initiation of a naive CD4+ T cell response. We developed a TCR-restricted assay to compare different pathogen-triggered human DC for their capacities to instruct functional differentiation of autologous, naive CD4+ T cells. We demonstrated that this methodology can be applied to compare differently matured DC in terms of kinetics, direction, and magnitude of the naive CD4+ T cell response. Furthermore, we showed the applicability of this assay to study the T cell polarizing capacity of low-frequency blood-derived DC populations directly isolated ex vivo. This methodology for addressing APC-dependent instruction of naive CD4+ T cells in a human autologous setting will provide researchers with a valuable tool to gain more insight into molecular mechanisms occurring in the early phase of T cell polarization. In addition, it may also allow the study of pharmacological agents on DC-dependent T cell polarization in the human system.

Dendritic cell-secreted lipocalin2 induces CD8+ T-cell apoptosis, contributes to T-cell priming and leads to a TH1 phenotype

Lipocalin 2 (LCN2), which is highly expressed by dendritic cells (DCs) when treated with dexamethasone (Dex) and lipopolysaccharide (LPS), plays a key role in the defence against bacteria and is also involved in the autocrine apoptosis of T-cells. However, the function of LCN2 when secreted by DCs is unknown: this is a critical gap in our understanding of the regulation of innate and adaptive immune systems. Tolerance, stimulation and suppression are functions of DCs that facilitate the fine-tuning of the immune responses and which are possibly influenced by LCN2 secretion. We therefore examined the role of LCN2 in DC/T-cell interaction. WT or Lcn2^−/− bone marrow-derived DCs were stimulated with LPS or LPS+IFN-γ with and without Dex and subsequently co-cultured with T-cells from ovalbumin-specific TCR transgenic (OT-I and OT-II) mice. We found that CD8⁺ T-cell apoptosis was highly reduced when Lcn2^−/− DCs were compared with WT. An in vivo CTL assay, using LPS-treated DCs, showed diminished killing ability in mice that had received Lcn2^−/− DCs compared with WT DCs. As a consequence, we analysed T-cell proliferation and found that LCN2 participates in T-cell-priming in a dose-dependent manner and promotes a T_H1 microenvironment. DC-secreted LCN2, whose function has previously been unknown, may in fact have an important role in regulating the balance between T_H1 and T_H2. Our results yield insights into DC-secreted LCN2 activity, which could play a pivotal role in cellular immune therapy and in regulating immune responses.

Induction of antigen-specific cytotoxic T lymphocytes by fusion cells generated from allogeneic plasmacytoid dendritic and tumor cells

Previous work has demonstrated that fusion cells generated from autologous monocyte-derived dendritic cells (MoDCs) and whole tumor cells induce efficient antigen-specific cytotoxic T lymphocytes. A major limitation to the use of this strategy is the availability of adequate amounts of autologous tumor cells. Moreover, MoDCs from cancer patients are often defective in their antigen-processing and presentation machinery. In this study, two types of allogeneic cells, a leukemia plasmacytoid dendritic cell (pDC) line (PMDC05) and pancreatic cancer cell lines (PANC-1 or MIA PaCa-2), were fused instead of autologous MoDCs and tumor cells. We created four types of pDC/tumor fusion cells by alternating fusion partners and treating with lipopolysaccharide (LPS): i) PMDC05 fused with PANC-1 (pDC/PANC-1), ii) PMDC05 fused with MIA PaCa-2 (pDC/MIA PaCa-2), iii) LPS-stimulated pDC/PANC-1 (LPS-pDC/PANC-1) and iv) LPS-stimulated pDC/MIA PaCa-2 (LPS-pDC/MIA PaCa-2) and examined their antitumor immune responses. The LPS-pDC/tumor cell fusions were the most active, as demonstrated by their: i) upregulated expression of HLA-DR and CD86 on a per-fusion-cell basis, ii) increased production of IL-12p70, iii) generation of a higher percentage of IFN-γ-producing CD4⁺ and CD8⁺ T cells and iv) augmented induction of MUC1-specific CD8⁺ T cells that lyse target tumor cells. This study provides the first evidence for an in vitro induction of antigen-specific cytotoxic T lymphocytes by LPS-stimulated fusion cells generated from leukemia plasmacytoid DCs and tumor cells and suggests that this strategy has potential applicability to the field of adoptive immunotherapy.

Regulatory dendritic cells for immunotherapy in immunologic diseases

We recognize well the abilities of dendritic cells to activate effector T cell (Teff cell) responses to an array of antigens and think of these cells in this context as pre-eminent antigen-presenting cells, but dendritic cells are also critical to the induction of immunologic tolerance. Herein, we review our knowledge on the different kinds of tolerogenic or regulatory dendritic cells that are present or can be induced in experimental settings and humans, how they operate, and the diseases in which they are effective, from allergic to autoimmune diseases and transplant tolerance. The primary conclusions that arise from these cumulative studies clearly indicate that the agent(s) used to induce the tolerogenic phenotype and the status of the dendritic cell at the time of induction influence not only the phenotype of the dendritic cell, but also that of the regulatory T cell responses that they in turn mobilize. For example, while many, if not most, types of induced regulatory dendritic cells lead CD4⁺ naïve or Teff cells to adopt a CD25⁺Foxp3⁺ Treg phenotype, exposure of Langerhans cells or dermal dendritic cells to vitamin D leads in one case to the downstream induction of CD25⁺Foxp3⁺ regulatory T cell responses, while in the other to Foxp3⁻ type 1 regulatory T cells (Tr1) responses. Similarly, exposure of human immature versus semi-mature dendritic cells to IL-10 leads to distinct regulatory T cell outcomes. Thus, it should be possible to shape our dendritic cell immunotherapy approaches for selective induction of different types of T cell tolerance or to simultaneously induce multiple types of regulatory T cell responses. This may prove to be an important option as we target diseases in different anatomic compartments or with divergent pathologies in the clinic. Finally, we provide an overview of the use and potential use of these cells clinically, highlighting their potential as tools in an array of settings.

Trial Watch: Toll-like receptor agonists for cancer therapy

Toll-like receptors (TLRs) have long been known for their ability to initiate innate immune responses upon exposure to conserved microbial components such as lipopolysaccharide (LPS) and double-stranded RNA. More recently, this family of pattern recognition receptors has been attributed a critical role in the elicitation of anticancer immune responses, raising interest in the development of immunochemotherapeutic regimens based on natural or synthetic TLR agonists. In spite of such an intense wave of preclinical and clinical investigation, only three TLR agonists are currently licensed by FDA for use in cancer patients: bacillus Calmette–Guérin (BCG), an attenuated strain of Mycobacterium bovis that operates as a mixed TLR2/TLR4 agonist; monophosphoryl lipid A (MPL), a derivative of Salmonella minnesota that functions as a potent agonist of TLR4; and imiquimod, a synthetic imidazoquinoline that activates TLR7. One year ago, in the August and September issues of OncoImmunology, we described the main biological features of TLRs and discussed the progress of clinical studies evaluating the safety and therapeutic potential of TLR agonists in cancer patients. Here, we summarize the latest developments in this exciting area of research, focusing on preclinical studies that have been published during the last 13 mo and clinical trials launched in the same period to investigate the antineoplastic activity of TLR agonists.