The Toll-like receptor 7/8 agonist resiquimod greatly increases the immunostimulatory capacity of human acute myeloid leukemia cells

Combination therapy of acute myeloid leukemia by dual PI3K/mTOR inhibitor BEZ235 and TLR-7/8 agonist R848 in murine model

BACKGROUND

Due to the high relapse rate and toxicity of the common therapies in patients with acute myeloid leukemia (AML), modifications in the treatment strategies are required. The present study was conducted to determine the effects of combinational therapy with a dual PI3K/mTOR inhibitor, BEZ235, and TLR7/8 agonist, R848, on murine AML model.

METHODS

BEZ235 and R848 were administered to AML leukemic mice in either a single or combination treatment. Frequency of T-CD4+, T-CD8+, MDSCs, NK, exhausted T cells and the degranulation levels was measured via flow cytometry. The cytotoxicity and proliferation levels were evaluated by MTT assay. Then, the expression of iNOS, arginase-1, PD-L1, Gal-9, PVR, IFN-γ, TNF-α, IL-4, IL-10, IL-12 and IL-17 was investigated by Real-Time PCR. Organomegaly, body weight and survival rate were also monitored.

RESULTS

Following combinational therapy with BEZ235 and R848, increasing in the frequency of anti-tumor immune cells including T-CD4+ cells and M1 macroghages, and decreasing in pro-tumor immune cells including MDSCs, exhausted T-CD4+ and T-CD8+ cells and also M2 macrophages were observed. The functional defects of immune cells in term of proliferation, cytotoxicity, degranulation, and cytokines expression were improved in leukemic mice after treatment with BEZ235 and R848. Finally, organomegaly, body weight and survival analysis showed significant improvements after treatment with BEZ235 and R848.

CONCLUSION

Taken together, we indicated that the combinational therapy with BEZ235 and R848 could be considered as a potential and powerful therapeutic option for AML patients. Further clinical studies are required to expand our current findings.

CuMV VLPs Containing the RBM from SARS-CoV-2 Spike Protein Drive Dendritic Cell Activation and Th1 Polarization

Dendritic cells (DCs) are the most specialized and proficient antigen-presenting cells. They bridge innate and adaptive immunity and display a powerful capacity to prime antigen-specific T cells. The interaction of DCs with the receptor-binding domain of the spike (S) protein from the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a pivotal step to induce effective immunity against the S protein-based vaccination protocols, as well as the SARS-CoV-2 virus. Herein, we describe the cellular and molecular events triggered by virus-like particles (VLPs) containing the receptor-binding motif from the SARS-CoV-2 spike protein in human monocyte-derived dendritic cells, or, as controls, in the presence of the Toll-like receptors (TLR)3 and TLR7/8 agonists, comprehending the events of dendritic cell maturation and their crosstalk with T cells. The results demonstrated that VLPs boosted the expression of major histocompatibility complex molecules and co-stimulatory receptors of DCs, indicating their maturation. Furthermore, DCs’ interaction with VLPs promoted the activation of the NF-kB pathway, a very important intracellular signalling pathway responsible for triggering the expression and secretion of proinflammatory cytokines. Additionally, co-culture of DCs with T cells triggered CD4+ (mainly CD4+Tbet+) and CD8+ T cell proliferation. Our results suggested that VLPs increase cellular immunity, involving DC maturation and T cell polarization towards a type 1 T cells profile. By providing deeper insight into the mechanisms of activation and regulation of the immune system by DCs, these findings will enable the design of effective vaccines against SARS-CoV-2.

The Role of TRL7/8 Agonists in Cancer Therapy, with Special Emphasis on Hematologic Malignancies

Toll-like receptors (TLR) belong to the pattern recognition receptors (PRR). TLR7 and the closely correlated TLR8 affiliate with toll-like receptors family, are located in endosomes. They recognize single-stranded ribonucleic acid (RNA) molecules and synthetic deoxyribonucleic acid (DNA)/RNA analogs-oligoribonucleotides. TLRs are primarily expressed in hematopoietic cells. There is compiling evidence implying that TLRs also direct the formation of blood cellular components and make a contribution to the pathogenesis of certain hematopoietic malignancies. The latest research shows a positive effect of therapy with TRL agonists on the course of hemato-oncological diseases. Ligands impact activation of antigen-presenting cells which results in production of cytokines, transfer of mentioned cells to the lymphoid tissue and co-stimulatory surface molecules expression required for T-cell activation. Toll-like receptor agonists have already been used in oncology especially in the treatment of dermatological neoplastic lesions. The usage of these substances in the treatment of solid tumors is being investigated. The present review discusses the direct and indirect influence that TLR7/8 agonists, such as imiquimod, imidazoquinolines and resiquimod have on neoplastic cells and their promising role as adjuvants in anticancer vaccines.

Recent Advances in Delivery Systems for Genetic and Other Novel Vaccines

Vaccination is one of the most successful and cost-effective prophylactic measures against diseases, especially infectious diseases including smallpox and polio. However, the development of effective prophylactic or therapeutic vaccines for other diseases such as cancer remains challenging. This is often due to the imprecise control of vaccine activity in vivo which leads to insufficient/inappropriate immune responses or short immune memory. The development of new vaccine types in recent decades has created the potential for improving the protective potency against these diseases. Genetic and subunit vaccines are two major categories of these emerging vaccines. Owing to their nature, they rely heavily on delivery systems with various functions, such as effective cargo protection, immunogenicity enhancement, targeted delivery, sustained release of antigens, selective activation of humoral and/or cellular immune responses against specific antigens, and reduced adverse effects. Therefore, vaccine delivery systems may significantly affect the final outcome of genetic and other novel vaccines and are vital for their development. This review introduces these studies based on their research emphasis on functional design or administration route optimization, presents recent progress, and discusses features of new vaccine delivery systems, providing an overview of this field.

Ivermectin Enhanced Antitumor Activity of Resiquimod in a Co-Loaded Squalene Emulsion

Immunogenic cell death (ICD) plays an important role in sensitizing tumor cells to antigen-presenting cells followed by antitumor immunity. However, a successful antitumor response by ICD requires both apoptotic tumor microenvironments and activated immune systems. Ivermectin (IVM) has been shown to induce cell apoptosis through autophagy which can be a great candidate for ICD therapy. However, a single treatment of IVM-free drug is not an ideal anticancer therapy due to its anti-inflammatory effects and cytotoxicity. In the present study, IVM was shown to enhance the ICD process in addition to the treatment of resiquimod (R848), a TLR7/8 agonist, when co-loaded in a squalene-based nanoemulsion (NE). R848-IVM co-loaded NE was developed and characterized in vitro. Antitumor activity of R848-IVM NE was also evaluated in vitro and in vivo. R848-IVM NE exhibited long-term stability and reduced cytotoxicity by IVM. In vivo studies demonstrated that IVM significantly augments the ICD by upregulating Cd8a and releasing HMGB1 in tumor tissue, which could enhance R848-driven antitumor immunity. R848-IVM NE treatment showed strong antitumor activity with over 80% tumor growth inhibition, suggesting a potential combination therapy of systemic co-delivering IVM with TLR agonists against solid cancer.

miR-196b-TLR7/8 Signaling Axis Regulates Innate Immune Signaling and Myeloid Maturation in DNMT3A-Mutant AML

PURPOSE

DNMT3A mutations confer a poor prognosis in acute myeloid leukemia (AML), but the molecular mechanisms downstream of DNMT3A mutations in disease pathogenesis are not completely understood, limiting targeted therapeutic options. The role of miRNA in DNMT3A-mutant AML pathogenesis is understudied.

EXPERIMENTAL DESIGN

DNA methylation and miRNA expression was evaluated in human AML patient samples and in Dnmt3a/Flt3-mutant AML mice. The treatment efficacy and molecular mechanisms of TLR7/8-directed therapies on DNMT3A-mutant AML were evaluated in vitro on human AML patient samples and in Dnmt3a/Flt3-mutant AML mice.

RESULTS

miR-196b is hypomethylated and overexpressed in DNMT3A-mutant AML and is associated with poor patient outcome. miR-196b overexpression in DNMT3A-mutant AML is important to maintain an immature state and leukemic cell survival through repression of TLR signaling. The TLR7/8 agonist resiquimod induces dendritic cell-like differentiation with costimulatory molecule expression in DNMT3A-mutant AML cells and provides a survival benefit to Dnmt3a/Flt3-mutant AML mice. The small molecule bryostatin-1 augments resiquimod-mediated AML growth inhibition and differentiation.

CONCLUSIONS

DNMT3A loss-of-function mutations cause miRNA locus-specific hypomethylation and overexpression important for mutant DNMT3A-mediated pathogenesis and clinical outcomes. Specifically, the overexpression of miR-196b in DNMT3A-mutant AML creates a novel therapeutic vulnerability by controlling sensitivity to TLR7/8-directed therapies.

Therapeutic applications of toll-like receptors (TLRs) agonists in AML

Acute myeloid leukemia (AML) is an aggressive type of blood cancer affecting bone marrow (BM). In AML, hematopoietic precursors are arrested in the early stages of development and are defined as the presence of ≥ 20% blasts (leukemia cells) in the BM. Toll-like receptors (TLR) are major groups of pattern recognition receptors expressed by almost all innate immune cells that enable them to detect a wide range of pathogen-associated molecular patterns and damage-associated molecular patterns to prime immune responses toward adaptive immunity. Because TLRs are commonly expressed on transformed immune system cells (ranging from blasts to memory cells), they can be a potential option for developing efficient clinical alternatives in hematologic tumors. This is because several in vitro and in vivo investigations have demonstrated that TLR signaling increased the immunogenicity of AML cells, making them more vulnerable to T cell-mediated invasion. This study aimed to review the current knowledge in this field and provide some insight into the therapeutic potentials of TLRs in AML.

A Squalene-Based Nanoemulsion for Therapeutic Delivery of Resiquimod

Agonists for toll-like receptors (TLRs) have shown promising activities against cancer. In the present study, a squalene-based nanoemulsion (NE) was loaded with resiquimod, a TLR7/8 agonist for therapeutic delivery. R848 NE was developed and characterized for long-term stability. In vitro and in vivo antitumor immunity of R848 NE were also evaluated in combination with SD-101, a CpG-containing TLR9 agonist. In vitro studies demonstrated strong long-term stability and immune responses to R848 NE. When combined with SD-101, strong antitumor activity was observed in MC38 murine colon carcinoma model with over 80% tumor growth inhibition. The combination treatment showed a 4-fold increase in systemic TNFa production and a 2.6-fold increase in Cd8a expression in tumor tissues, suggesting strong cell-mediated immune responses against the tumor. The treatment not only demonstrated a strong antitumor immunity by TLR7/8 and TLR9 activations but also induced PD-L1 upregulation in tumors, suggesting a potential therapeutic synergy with immune checkpoint inhibitors.

Network pharmacology-based strategy for predicting therapy targets of Tripterygium wilfordii on acute myeloid leukemia

This is a study on the potential therapeutic targets and pharmacological mechanism of Tripterygium wilfordii (TW) in acute myeloid leukemia (AML) based on network pharmacology.Active components of TW were obtained by network pharmacology through oral bioavailability, drug-likeness filtration. Comparative analysis was used to investigate the overlapping genes between active ingredient's targets and AML treatment-related targets. Using STRING database to analyze interactions among overlapping genes. Both KEGG pathway analysis and Gene Ontology enrichment analysis were conducted in DAVID. These genes were analyzed for survival in OncoLnc database.We screened 53 active ingredients; the results of comparative analysis showed that 8 active ingredients had an effect on AML treatment. On the basis of the active ingredients and overlapping genes, we constructed the Drug-Compounds-Genes-Disease Network. Survival analysis of overlapping genes indicated that some targets possessed a significant influence on patients' survival and prognosis. The enrichment analysis showed that the main pathways of targets were Toll-like receptor signaling pathway, NF-kappa B signaling pathway, and HIF-1 signaling pathway.This study, using a network pharmacologic approach, provides another strategy that can help us to understand the mechanisms by which TW treats AML comprehensively.

Therapeutic strategies to remodel immunologically cold tumors

Immune checkpoint inhibitors (ICIs) induce a durable response in a wide range of tumor types, but only a minority of patients outside these ‘responsive’ tumor types respond, with some totally resistant. The primary predictor of intrinsic immune resistance to ICIs is the complete or near‐complete absence of lymphocytes from the tumor, so‐called immunologically cold tumors. Here, we propose two broad approaches to convert ‘cold’ tumors into ‘hot’ tumors. The first is to induce immunogenic tumor cell death, through the use of oncolytic viruses or bacteria, conventional cancer therapies (e.g. chemotherapy or radiation therapy) or small molecule drugs. The second approach is to target the tumor microenvironment, and covers diverse options such as depleting immune suppressive cells; inhibiting transforming growth factor‐beta; remodelling the tumor vasculature or hypoxic environment; strengthening the infiltration and activation of antigen‐presenting cells and/or effector T cells in the tumor microenvironment with immune modulators; and enhancing immunogenicity through personalised cancer vaccines. Strategies that successfully modify cold tumors to overcome their resistance to ICIs represent mechanistically driven approaches that will ultimately result in rational combination therapies to extend the clinical benefits of immunotherapy to a broader cancer cohort.

Conjugation of TLR7 Agonist Combined with Demethylation Treatment Improves Whole-Cell Tumor Vaccine Potency in Acute Myeloid Leukemia

Background: Acute myeloid leukemia (AML) is a malignant hematological disease with high refractory rate. Immune escape of AML cells is one of the underlying mechanisms mediating the relapse of the cancers. Various immunotherapies based on the 'patients' immune response to tumor cells have been developed to targeting the immune escape of AML cells, which lead to the minimal residual disease (MRD) after treatment. But the efficacy of those treatments or the combination of treatments remains unsatisfactory. Methods: A Toll-like receptor (TLR)-7 agonist SZU-106 was chemically synthesized. SZU-106 was conjugated to Decitabine (DAC), a demethylation agent, treated AML cells to construct tumor vaccine. The potency of the newly constructed AML cell vaccine, SZU-106-DAC-AML was tested in vitro and in vivo for the expression of tumor antigens and the activation level of immune responses. Results: Compared to the well characterized TLR7 agonist R848, SZU-106 has a comparable potency to activate TLR7 signaling pathway. SZU-106-DAC-AML, constructed by conjugating SZU-106 to DAC treated tumor cells, exhibited increased expression of tumor antigens, and enhanced the activation of DC cells and T cells in vitro and in vivo. The result of xenograft tumor model showed that SZU-106-DAC-AML tumor vaccine greatly inhibited tumor growth and prolonged animal survival. Conclusions: Conjugation of TLR7 agonist combined with up-regulation of tumor antigen expression improved the effectiveness of whole-cell tumor vaccine in AML.

Contribution of Aberrant Toll Like Receptor Signaling to the Pathogenesis of Myelodysplastic Syndromes

Toll like receptors (TLRs) are a family of pattern recognition receptors that play a central role in the innate immune response. These receptors are expressed on a wide variety of immune and non-immune cells, and they help shape the immune response to infection and injury through the recognition of pathogen-associated molecular patterns (PAMPs) as well as endogenous damage-associated molecular patterns (DAMPs). Accumulating evidence suggests that, in addition to regulating mature effector immune cells, TLRs can influence the immune response from the level of the hematopoietic stem cell (HSC). HSCs express TLRs, and exposure to TLR ligands influences the cycling, differentiation, and function of HSCs, with chronic TLR stimulation leading to impairment of normal HSC repopulating activity. Moreover, enhanced TLR expression and signaling is associated with myelodysplastic syndromes (MDS), a heterogenous group of HSC disorders characterized by ineffective hematopoiesis and a high risk of transformation to acute leukemias. In this review, we will discuss the role of TLR signaling in the pathogenesis of MDS, focusing on the known direct and indirect effects of this type of signaling on HSCs, the mechanisms of TLR signaling upregulation in MDS, the changes in TLR expression with disease progression, and the therapeutic implications for modulating TLR signaling in the treatment of MDS.

Mimetic Heat Shock Protein Mediated Immune Process to Enhance Cancer Immunotherapy

Inspired by heat shock proteins (HSPs), a self-assembly nanochaperone (nChap) is developed as a novel nanovaccine for boosting antitumor immune responses. Taking advantage of HSP-like microdomains and surface-decorated mannose, this nChap can efficiently capture antigens and ferry them into the dendritic cells (DCs). Subsequently, the nChap can blast lysosomes by transforming the structure and property of surface microdomains, thereby promoting antigen escape and enhancing their cross-presentation in cytoplasm. As a result, the nChap-based nanovaccine can elicit both CD4+ and CD8+ T cell-based immune responses and shows an excellent preventive effect on melanoma. Further combination of the nanovaccine with antiprogrammed death-1 (anti-PD-1) checkpoint blockade offers effective inhibition on the growth of already-established melanoma. Therefore, this nC ap-based nanovaccine provides a simple and robust strategy in mimicking HSPs to realize structure-assisted antigen capture, surface-receptor-mediated DC internalization, and both activation of humoral immunity and cellular immunity, promising for efficient cancer immunotherapy.

Agonist and antagonist ligands of toll-like receptors 7 and 8: Ingenious tools for therapeutic purposes

The discovery of the TLRs family and more precisely its functions opened a variety of gates to modulate immunological host responses. TLRs 7/8 are located in the endosomal compartment and activate a specific signaling pathway in a MyD88-dependant manner. According to their involvement into various autoimmune, inflammatory and malignant diseases, researchers have designed diverse TLRs 7/8 ligands able to boost or block the inherent signal transduction. These modulators are often small synthetic compounds and most act as agonists and to a much lesser extent as antagonists. Some of them have reached preclinical and clinical trials, and only one has been approved by the FDA and EMA, imiquimod. The key to the success of these modulators probably lies in their combination with other therapies as recently demonstrated. We gather in this review more than 360 scientific publications, reviews and patents, relating the extensive work carried out by researchers on the design of TLRs 7/8 modulators, which are classified firstly by their biological activities (agonist or antagonist) and then by their chemical structures, which total syntheses are not discussed here. This review also reports about 90 clinical cases, thereby showing the biological interest of these modulators in multiple pathologies.

Identification of prognostic genes in the acute myeloid leukemia immune microenvironment based on TCGA data analysis

Acute myeloid leukemia (AML) is a common and lethal hematopoietic malignancy that is highly dependent on the bone marrow (BM) microenvironment. Infiltrating immune and stromal cells are important components of the BM microenvironment and significantly influence the progression of AML. This study aimed to elucidate the value of immune/stromal cell-associated genes for AML prognosis by integrated bioinformatics analysis. We obtained expression profiles from The Cancer Genome Atlas (TCGA) database and used the ESTIMATE algorithm to calculate immune scores and stromal scores; we then identified differentially expressed genes (DEGs) based on these scores. Overall survival analysis was applied to reveal common DEGs of prognostic value. Subsequently, we conducted a functional enrichment analysis, generated a protein-protein interaction (PPI) network and performed an interrelation analysis of immune system processes, showing that these genes are mainly associated with the immune/inflammatory response. Finally, eight genes (CD163, CYP27A1, KCNA5, PPM1J, FOLR1, IL1R2, MYOF, VSIG2) were verified to be significantly associated with AML prognosis in the Gene Expression Omnibus (GEO) database. In summary, we identified key microenvironment-related genes that affect the outcomes of AML patients and might serve as therapeutic targets.

NDRG2 and TLR7 as novel DNA methylation prognostic signatures for acute myelocytic leukemia

Acute myelocytic leukemia (AML) is an aggressive malignant tumor and typically fatal without treatment. Identification and development of novel biomarkers could be beneficial for the diagnosis and prognosis of AML patients. Here, we aimed to identify the accurate DNA methylation prognostic signatures for AML patients. The DNA methylation data of AML patients and corresponding clinical information were retrieved from The Cancer Genome Atlas database. CPG sites that correlates closely with the survival of the AML patients were identified and further combined into CPG sites pairs to screen the survival-related pairs. The prognostic signatures were identified by the C-index and forward search algorithms and validated by the verification group. Finally, the functional enrichment analysis was performed on these CPG sites. As a result, a total of 498 CPG sites associated with the overall survival of AML patients was obtained. A prognostic signature composed of 10 CPG sites pairs was obtained and validated. The functional enrichment analysis showed prognostic genes were mainly enriched in tumor protein processing, cell differentiation, blood leukocyte immunity, and platelet growth factor pathways. In summary, we identified two accurate prognostic methylation signatures (NDRG2 and TLR7), which would be served as a novel therapy target for AML.

Functional Toll-Like Receptors (TLRs) Are Expressed by a Majority of Primary Human Acute Myeloid Leukemia Cells and Inducibility of the TLR Signaling Pathway Is Associated with a More Favorable Phenotype

Acute myeloid leukemia (AML) is a highly heterogeneous disease with regard to biological characteristics and receptor expression. Toll-like receptors (TLRs) are upstream to the transcription factor NFκB and part of the innate immune system. They are differentially expressed on AML blasts, and during normal hematopoiesis they initiate myeloid differentiation. In this study, we investigated the response upon TLR stimulation in an AML cohort (n = 83) by measuring the increase of NFκB-mediated cytokine secretion. We observed that TLR4 is readily induced in most patients, while TLR1/2 response was more restricted. General response to TLR stimulation correlated with presence of nucleophosmin gene mutations, increased mRNA expression of proteins, which are part of the TLR signaling pathway and reduced expression of transcription-related proteins. Furthermore, signaling via TLR1/2 appeared to be linked with prolonged patient survival. In conclusion, response upon TLR stimulation, and especially TLR1/2 induction, seems to be part of a more favorable phenotype, which also is characterized by higher basal cytokine secretion and a more mature blast population.

Formulation and preclinical evaluation of a toll-like receptor 7/8 agonist as an anti-tumoral immunomodulator

The toll-like receptor 7 and 8 (TLR7/8) agonist Resiquimod (R848) has been recognized as a promising immunostimulator for the treatment of cutaneous cancers in multiple clinical trials. However, systemic administration of R848 often results in strong immune-related toxicities while having limited therapeutic effects to the tumor. In the present study, a prodrug-based nanocarrier delivery system was developed that exhibited high therapeutic efficiency. R848 was conjugated to α-tocopherol to constitute an R848-Toco prodrug, followed by formulating with a tocopherol-modified hyaluronic acid (HA-Toco) as a polymeric nano-suspension. In vitro evaluation showed that the delivery system prolonged the release kinetics while maintaining TLR agonist activities. When administered subcutaneously, the nano-suspension formed a depot at the injection site, inducing localized immune responses without systemic expansion. This formulation also suppressed tumor growth and recruited immune cells to the tumor in a murine model of head and neck cancer. In a preclinical canine study of spontaneous mast cell tumors, the treatment led to a 67% response rate (three partial remissions and one complete remission).

Cold Tumors: A Therapeutic Challenge for Immunotherapy

Therapeutic monoclonal antibodies targeting immune checkpoints (ICPs) have changed the treatment landscape of many tumors. However, response rate remains relatively low in most cases. A major factor involved in initial resistance to ICP inhibitors is the lack or paucity of tumor T cell infiltration, characterizing the so-called “cold tumors.” In this review, we describe the main mechanisms involved in the absence of T cell infiltration, including lack of tumor antigens, defect in antigen presentation, absence of T cell activation and deficit of homing into the tumor bed. We discuss then the different therapeutic approaches that could turn cold into hot tumors. In this way, specific therapies are proposed according to their mechanism of action. In addition, ‘‘supra-physiological’’ therapies, such as T cell recruiting bispecific antibodies and Chimeric Antigen Receptor (CAR) T cells, may be active regardless of the mechanism involved, especially in MHC class I negative tumors. The determination of the main factors implicated in the lack of preexisting tumor T cell infiltration is crucial for the development of adapted algorithms of treatments for cold tumors.

TLR-7 Stress Signaling in Differentiating and Mature Eosinophils Is Mediated by the Prolyl Isomerase Pin1

The response of eosinophils (Eos) to respiratory virus has emerged as an important link between pulmonary infection and allergic asthmatic exacerbations. Eos activate innate immune responses through TLR signaling. In this study, using mouse and human Eos and mice lacking the prolyl isomerase Pin1 selectively in Eos, we show that Pin1 is indispensable for eosinophilopoiesis in the bone marrow (BM) and mature cell function in the presence of TLR7 activation. Unbiased in vivo analysis of mouse models of allergic airway inflammation revealed that TLR7 activation in knockout mice resulted in systemic loss of Eos, reduced IFN production, and an inability to clear respiratory viruses. Consistent with this finding, BM mouse Eos progenitors lacking Pin1 showed markedly reduced cell proliferation and survival after TLR7 activation. Mechanistically, unlike wild-type cells, Pin1 null mouse Eos were defective in the activation of the endoplasmic reticulum stress-induced unfolded protein response. We observed significant reductions in the expression of unfolded protein response components and target genes, aberrant TLR7 cleavage and trafficking, and reduced granule protein production in knockout Eos. Our data strongly suggest that Pin1 is required for BM Eos generation and function during concurrent allergen challenge and viral infection.

Enhanced Cancer Vaccination by In Situ Nanomicelle-Generating Dissolving Microneedles

Efficient delivery of tumor antigens and immunostimulatory adjuvants into lymph nodes is crucial for the maturation and activation of antigen-presenting cells (APCs), which subsequently induce adaptive antitumor immunity. A dissolving microneedle (MN) has been considered as an attractive method for transcutaneous immunization due to its superior ability to deliver vaccines through the stratum corneum in a minimally invasive manner. However, because dissolving MNs are mostly prepared using water-soluble sugars or polymers for their rapid dissolution in intradermal fluid after administration, they are often difficult to formulate with poorly water-soluble vaccine components. Here, we develop amphiphilic triblock copolymer-based dissolving MNs in situ that generate nanomicelles (NMCs) upon their dissolution after cutaneous application, which facilitate the efficient encapsulation of poorly water-soluble Toll-like receptor 7/8 agonist (R848) and the delivery of hydrophilic antigens. The sizes of NMCs range from 30 to 40 nm, which is suitable for the efficient delivery of R848 and antigens to lymph nodes and promotion of cellular uptake by APCs, minimizing systemic exposure of the R848. Application of MNs containing tumor model antigen (OVA) and R848 to the skin of EG7-OVA tumor-bearing mice induced a significant level of antigen-specific humoral and cellular immunity, resulting in significant antitumor activity.

Diprovocims: A New and Exceptionally Potent Class of Toll-like Receptor Agonists

A screen conducted with nearly 100000 compounds and a surrogate functional assay for stimulation of an immune response that measured the release of TNF-α from treated human THP-1 myeloid cells differentiated along the macrophage line led to the discovery of the diprovocims. Unique to these efforts and of special interest, the screening leads for this new class of activators of an immune response came from a compound library designed to promote cell-surface receptor dimerization. Subsequent comprehensive structure-activity relationship studies improved the potency 800-fold over that of the screening leads, providing diprovocim-1 and diprovocim-2. The diprovocims act by inducing cell-surface toll-like receptor (TLR)-2 dimerization and activation with TLR1 (TLR1/TLR2 agonist), bear no structural similarity to any known natural or synthetic TLR agonist, and are easy to prepare and synthetically modify, and selected members are active in both human and murine systems. The most potent diprovocim (3, diprovocim-1) elicits full agonist activity at extraordinarily low concentrations (EC₅₀ = 110 pM) in human THP-1 cells, being more potent than the naturally derived TLR1/TLR2 agonist Pam3CSK4 or any other known small molecule TLR agonist.

Toll-like receptors: Important immune checkpoints in the regression of cervical intra-epithelial neoplasia 2

Toll-like receptors (TLRs) are innate immune defenders thought to be critical for the clearance of human papillomavirus (HPV) infections hence preventing the development of HPV-associated high-grade cervical intra-epithelial neoplasia (CIN2 or 3), a potential cervical cancer precursor. However, the role of TLRs in the regression of established cervical lesions, such as CIN2, is hindered by a lack of prospective design studies. Using SYBR green real-time PCR assays, we have examined the gene expression of TLR2, TLR3, TLR7, TLR8 and TLR9, in cytobrush collected endocervical cells of 63 women diagnosed with CIN2 at study entry (baseline) and followed over a 3-year period. Wilcoxon rank-sum test was used to examine the association between TLR expression levels, measured at baseline, and CIN2 outcome (regression vs. persistence/progression) over time. HPV genotyping was performed using Roche Linear Array Assay detecting 37 HPV types. Women with CIN2 regression showed significantly higher baseline levels of TLR2 (p = 0.006) and TLR7 (p = 0.007), as well as a non-significant trend for a higher TLR8 expression (p = 0.053) compared to women with CIN2 persistence/progression. Six women with CIN2 regression, who presented with an HR-HPV DNA-negative CIN2 lesion at study entry, had significantly higher baseline levels of TLR2 (p = 0.005), TLR7 (p = 0.013) and TLR8 (p = 0.012), compared to women with CIN2 persistence/progression, suggesting their role in clearance of HPV prior to clearance of the lesion. Our results confirm a key role of TLRs in regression of CIN2 and support the potential use of TLR-agonists for treatment of these lesions.

Imiquimod inhibits growth and induces differentiation of myeloid leukemia cell lines

Background

The antitumoral effects of different Toll-like receptor (TLRs) agonists is mediated by activating immune responses to suppress tumors growth, although TLR ligands may also have a direct effect on tumoral cells. Given that TLR signaling induces hematopoietic cell differentiations this may serve as a novel differentiation therapeutic approach for AML.

Methods

We investigated the effects of agonists for the ten human TLRs on the proliferation, apoptosis, cell cycle and differentiation of ten different types of myeloid leukemia cell lines (HL-60, U-937, KG-1, KG-1a, K-562, Kasumi-1, EOL-1, NB4, MOLM-13 and HEL). Proliferation was measured using the CellTiter 96^® Aqueous One Solution Cell Proliferation Assay (Promega). Staining and analysis with a flow cytometer was used to identify cell cycle progression and apoptosis. Differentiation was measured by staining cells with the EuroFlow™ antibody panel for AML and analyzed by flow cytometry. FlowJo software was used to analyze the cytometric data. In all experiments, statistical significance was determined by a two-tailed t test.

Results

The activation of particular TLRs on some cell lines can induce growth inhibition and Imiquimod (a TLR 7 agonist) was the most effective agonist in all leukemic cell lines examined. Imiquimod was able to induce apoptosis, as well as to induce cell cycle alteration and upregulation of myeloid differentiation markers on some of the cell lines tested.

Conclusions

Our results, together with the known efficacy of Imiquimod against many tumor entities, suggest that Imiquimod can be a potential alternative therapy to AML. This drug has a direct cytotoxic effect on leukemic cells, has the potential to induce differentiation, and can also stimulate the activation of cellular immune responses anti-AML.

Structure-Activity Relationship Studies of Pyrimido[5,4-b]indoles as Selective Toll-Like Receptor 4 Ligands

Previous high throughput screening studies led to the discovery of two novel, nonlipid-like chemotypes as Toll-like receptor 4 (TLR4) agonists. One of these chemotypes, the pyrimido[5,4-b]indoles, was explored for structure-activity relationship trends relative to production of TLR4 dependent cytokines/chemokines, resulting in a semioptimized lead (compound 1) that provided a starting point for further optimization studies. In this report, compounds belonging to three areas of structural modification were evaluated for biological activity using murine and human TLR4 reporter cells, primary murine bone marrow derived dendritic cells, and human peripheral blood mononuclear cells. The compounds bearing certain aryl groups at the C8 position, such as phenyl (36) and β-naphthyl (39), had potencies significantly greater than compound 1. Compound 36 displayed human TLR4 agonist activity at submicromolar concentrations. The computational analysis suggests that the improved potency of these C8-aryl derivatives may be the result of additional binding interactions at the interface of the TLR4/myeloid differentiation protein-2 (MD-2) complex.

Mesenchymal Stem Cells in Myeloid Malignancies: A Focus on Immune Escaping and Therapeutic Implications

The importance of the bone marrow microenvironment forming the so-called niche in physiologic hemopoiesis is largely known, and recent evidences support the presence of stromal alterations from the molecular to the cytoarchitectural level in hematologic malignancies. Various alterations in cell adhesion, metabolism, cytokine signaling, autophagy, and methylation patterns of tumor-derived mesenchymal stem cells have been demonstrated, contributing to the genesis of a leukemic permissive niche. This niche allows both the ineffective haematopoiesis typical of myelodysplastic syndromes and the differentiation arrest, proliferation advantage, and clone selection which is the hallmark of acute myeloid leukemia. Furthermore, the immune system, both adaptive and innate, encompassing mesenchymal-derived cells, has been shown to take part to the leukemic niche. Here, we critically review the state of art about mesenchymal stem cell role in myelodysplastic syndromes and acute myeloid leukemia, focusing on immune escaping mechanisms as a target for available and future anticancer therapies.

Anti-tumor Activity of Toll-Like Receptor 7 Agonists

Toll-like receptors (TLRs) are a class of pattern recognition receptors that play a bridging role in innate immunity and adaptive immunity. The activated TLRs not only induce inflammatory responses, but also elicit the development of antigen specific immunity. TLR7, a member of TLR family, is an intracellular receptor expressed on the membrane of endosomes. TLR7 can be triggered not only by ssRNA during viral infections, but also by immune modifiers that share a similar structure to nucleosides. Its powerful immune stimulatory action can be potentially used in the anti-tumor therapy. This article reviewed the anti-tumor activity and mechanism of TLR7 agonists that are frequently applied in preclinical and clinical investigations, and mainly focused on small synthetic molecules, including imiquimod, resiquimod, gardiquimod, and 852A, etc.

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.

Mesenchymal Stem and Progenitor Cells in Normal and Dysplastic Hematopoiesis-Masters of Survival and Clonality?

Myelodysplastic syndromes (MDS) are malignant hematopoietic stem cell disorders that have the capacity to progress to acute myeloid leukemia (AML). Accumulating evidence suggests that the altered bone marrow (BM) microenvironment in general, and in particular the components of the stem cell niche, including mesenchymal stem cells (MSCs) and their progeny, play a pivotal role in the evolution and propagation of MDS. We here present an overview of the role of MSCs in the pathogenesis of MDS, with emphasis on cellular interactions in the BM microenvironment and related stem cell niche concepts. MSCs have potent immunomodulatory capacities and communicate with diverse immune cells, but also interact with various other cellular components of the microenvironment as well as with normal and leukemic stem and progenitor cells. Moreover, compared to normal MSCs, MSCs in MDS and AML often exhibit altered gene expression profiles, an aberrant phenotype, and abnormal functional properties. These alterations supposedly contribute to the “reprogramming” of the stem cell niche into a disease-permissive microenvironment where an altered immune system, abnormal stem cell niche interactions, and an impaired growth control lead to disease progression. The current article also reviews molecular targets that play a role in such cellular interactions and possibilities to interfere with abnormal stem cell niche interactions by using specific targeted drugs.

Discovery and Structure-Activity Relationships of the Neoseptins: A New Class of Toll-like Receptor-4 (TLR4) Agonists

Herein, we report studies leading to the discovery of the neoseptins and a comprehensive examination of the structure-activity relationships (SARs) of this new class of small-molecule mouse Toll-like receptor 4 (mTLR4) agonists. The compounds in this class, which emerged from screening an α-helix mimetic library, stimulate the immune response, act by a well-defined mechanism (mouse TLR4 agonist), are easy to produce and structurally manipulate, exhibit exquisite SARs, are nontoxic, and elicit improved and qualitatively different responses compared to lipopolysaccharide, even though they share the same receptor.

Modes of action of TLR7 agonists in cancer therapy

From the numerous Toll-like receptor agonists, only TLR7 agonists have been approved for cancer treatment, although they are current restricted to topical application. The main target cells of TLR7 agonists are plasmacytoid dendritic cells, producing IFN-α and thus acting on other immune cells. Thereby dendritic cells acquire enhanced costimulatory and antigen-presenting capacity, priming an adaptive immune response. Besides NK cells, antigen-specific T cells are the main terminal effectors of TLR7 agonists in tumor therapy. This qualifies TLR7 agonists as vaccine adjuvants, which is currently being tested in clinical trials. However, the systemic application of TLR7 agonists shows insufficient efficacy, most likely owing to toxicity-limited dosing. The use of TLR7 agonists in combinational therapy holds the promise of synergistic activity and lower required doses.

Conjugation of toll-like receptor-7 agonist to gastric cancer antigen MG7-Ag exerts antitumor effects

AIM: To investigate the effects of our tumor vaccines on reversing immune tolerance and generating therapeutic response.

METHODS: Vaccines were synthesized by solid phase using an Fmoc strategy, where a small molecule toll-like receptor-7 agonist (T7) was conjugated to a monoclonal gastric cancer 7 antigen mono-epitope (T7-MG1) or tri-epitope (T7-MG3). Cytokines were measured in both mouse bone marrow dendritic cells and mouse spleen lymphocytes after exposed to the vaccines. BALB/c mice were intraperitoneally immunized with the vaccines every 2 wk for a total of three times, and then subcutaneously challenged with Ehrlich ascites carcinoma (EAC) cells. Three weeks later, the mice were killed, and the tumors were surgically removed and weighed. Serum samples were collected from the mice, and antibody titers were determined by ELISA using an alkaline phosphate-conjugated detection antibody for total IgG. Antibody-dependent cell-mediated cytotoxicity was detected by the lactate dehydrogenase method using natural killer cells as effectors and antibody-labeled EAC cells as targets. Cytotoxic T lymphocyte activities were also detected by the lactate dehydrogenase method using lymphocytes as effectors and EAC cells as targets.

RESULTS: Vaccines were successfully synthesized and validated by analytical high performance liquid chromatography and electrospray mass spectrometry, including T7, T7-MG1, and T7-MG3. Rapid inductions of tumor necrosis factor-α and interleukin-12 in bone marrow dendritic cells and interferon γ and interleukin-12 in lymphocytes occurred in vitro after T7, T7-MG1, and T7-MG3 treatment. Immunization with T7-MG3 reduced the EAC tumor burden in BALB/c mice to 62.64% ± 5.55% compared with PBS control (P < 0.01). Six or nine weeks after the first immunization, the monoclonal gastric cancer 7 antigen antibody increased significantly in the T7-MG3 group compared with the PBS control (P < 0.01). As for antibody-dependent cell-mediated cytotoxicity, antisera obtained by immunization with T7-MG3 were able to markedly enhance cell lysis compared to PBS control (31.58% ± 2.94% vs 18.02% ± 2.26%; P < 0.01). As for cytotoxic T lymphocytes, T7-MG3 exhibited obviously greater cytotoxicity compared with PBS control (40.92% ± 4.38% vs 16.29% ± 1.90%; P < 0.01).

CONCLUSION: A successful method is confirmed for the design of gastric cancer vaccines by chemical conjugation of T7 and multi-repeat-epitope of monoclonal gastric cancer 7 antigen.

Augmentation of autologous T cell reactivity with acute myeloid leukemia (AML) blasts by Toll-like receptor (TLR) agonists

This study investigated whether TNF-α, Toll-like receptors (TLRs) 7/8 agonist resiquimod (R848), the TLR4 agonist lipopolysaccharide (LPS) and their combinations can enhance autologous AML-reactive T cell generation in an in vitro culture. AML peripheral blood or bone marrow mononuclear cells were cultured in medium supplemented with GM-CSF/IL-4 to induce dendritic cell (DC) differentiation of AML blasts (AML-DC). The impact of TNF-α, LPS, R848 and their combinations on AML-DC cultures was analyzed. Significantly enhanced CD80, CD40, CD83, CD54, HLA-DR and CD86 expression of AML cells was observed by addition of TNF-α, LPS, R848 alone or combinations. Induced CD80 expression of AML cells was significantly higher through the combination of TNF-α, LPS and R848 (T + L + R) than that by T alone. CTL induced from T + L + R, T + R, T + L, L + R and R, but not T, L alone stimulated cultures showed significantly higher IFN-γ release than the medium control in response to autologous AML cells. IFN-γ release by T + L + R was significantly higher than T or L alone, and T + R was significantly higher than T alone. CTL generated from T + L + R, T + L, T + R, L + R and L alone exerted significantly higher AML cell killing than medium control. AML cell killing by T + L + R and T + R was significantly higher than T or R alone. These results indicate that the combination of T + L + R induces a significantly enhanced antigen presentation effect of AML-DC. We speculate that the complementary effects of reagent combinations may better address the heterogeneity of responses to any single agent in AML cells from different patients.

Poly(I:C) as cancer vaccine adjuvant: knocking on the door of medical breakthroughs

Although cancer vaccination has yielded promising results in patients, the objective response rates are low. The right choice of adjuvant might improve the efficacy. Here, we review the biological rationale, as well as the preclinical and clinical results of polyinosinic:polycytidylic acid and its derivative poly-ICLC as cancer vaccine adjuvants. These synthetic immunological danger signals enhanced vaccine-induced anti-tumor immune responses and contributed to tumor elimination in animal tumor models and patients. Supported by these results, poly-ICLC-containing cancer vaccines are currently extensively studied in the ongoing trials, making it highly plausible that poly-ICLC will be part of the future approved cancer immunotherapies.

RepSox slows decay of CD34+ acute myeloid leukemia cells and decreases T cell immunoglobulin mucin-3 expression

Despite initial response to therapy, most acute myeloid leukemia (AML) patients relapse. To eliminate relapse-causing leukemic stem/progenitor cells (LPCs), patient-specific immune therapies may be required. In vitro cellular engineering may require increasing the "stemness" or immunogenicity of tumor cells and activating or restoring cancer-impaired immune-effector and antigen-presenting cells. Leukapheresis samples provide the cells needed to engineer therapies: LPCs to be targeted, normal hematopoietic stem cells to be spared, and cancer-impaired immune cells to be repaired and activated. This study sought to advance development of LPC-targeted therapies by exploring nongenetic ways to slow the decay and to increase the immunogenicity of primary CD34(+) AML cells. CD34(+) AML cells generally displayed more colony-forming and aldehyde dehydrogenase activity than CD34(-) AML cells. Along with exposure to bone marrow stromal cells and low (1%-5%) oxygen, culture with RepSox (a reprogramming tool and inhibitor of transforming growth factor-β receptor 1) consistently slowed decline of CD34(+) AML and myelodysplastic syndrome (MDS) cells. RepSox-treated AML cells displayed higher CD34, CXCL12, and MYC mRNA levels than dimethyl sulfoxide-treated controls. RepSox also accelerated loss of T cell immunoglobulin mucin-3 (Tim-3), an immune checkpoint receptor that impairs antitumor immunity, from the surface of AML and MDS cells. Our results suggest RepSox may reduce Tim-3 expression by inhibiting transforming growth factor-β signaling and slow decay of CD34(+) AML cells by increasing CXCL12 and MYC, two factors that inhibit AML cell differentiation. By prolonging survival of CD34(+) AML cells and reducing Tim-3, RepSox may promote in vitro immune cell activation and advance development of LPC-targeted therapies.

Synergistic anticancer effects of Pam3CSK4 and Ara-C on B-cell lymphoma cells

PURPOSE

The low immunogenicity of many cancer cells and the immunosuppression by various cancers and anticancer therapies have been an obstacle in the development of efficacious immunotherapies. Our goal was to test whether Toll-like receptor (TLR) agonists and anticancer chemotherapeutic agents synergize in rendering tumor cells more immunogenic.

EXPERIMENTAL DESIGN

We treated B-cell lymphoma cells with the TLR1/2 agonist Pam3CSK4 and the genotoxic anticancer agent 1-β-D-arabinofuranosylcytosine (Ara-C). The effects on the immunogenicity of tumor cells were measured in transfer experiments and in vitro studies.

RESULTS

The treatment of B-cell lymphoma cells with the TLR1/2 agonist Pam3CSK4 enhanced the anticancer effects of the genotoxic agent Ara-C. Mice injected with cotreated tumor cells survived longer than mice challenged with Pam3CSK4 or Ara-C-treated cells. Administration of Pam3CSK4 or Ara-C reduced the tumor load of mice injected with tumor cells. Cotreatment had no effect on the rate of apoptosis or proliferation of Ara-C-treated cells, but upregulated the expression of several immunomodulatory molecules. Consistent with an increased immunogenicity of Pam3CSK4 and Ara-C-treated B-cell lymphoma cells, rejection of cotreated tumor cells required natural killer cells and T cells. We demonstrate that the upregulation of immunomodulatory molecules in response to Pam3CSK4 and Ara-C depended in part on NF-κB.

CONCLUSION

TLR agonists can increase the efficacy of conventional cancer therapies by altering the immunogenicity of B-cell lymphoma cells.

Activation of the TLR1/2 pathway induces the shaping of the immune response status of peripheral blood leukocytes

Toll-like receptors (TLRs) play an essential role in the activation and regulation of the innate and adaptive immune responses through the recognition of specific components of pathogens. TLR1/2 on the cell surface plays an important role in defending against Gram-positive bacteria. The aim of the present study was to examine the expressional variation of immunomodulatory molecules in peripheral blood leukocytes (PBLs) treated with the TLR1/2 agonist, Pam3Cys. The quantitative polymerase chain reaction result showed dramatically increased expression of immune-related factors treated with Pam3Cys. Antibody-chip assays confirmed that activation of TLR1/2 could induce secretion of four important immune factors [interleukin (IL)-6, IL-8, macrophage inflammatory protein-1α and interferon-β). Western-blot analysis indicated the upregulation of three significant signal kinase proteins (phosphorylated signal transducer and activator of transcription 3, extracellular signal-related kinase and c-Jun N-terminal kinase 2). The study demonstrated that there were numerous molecules involved in the immune response of PBLs stimulated by the TLR1/2 ligand. Our future studies will focus on the mechanisms of these molecules in the TLR1/2 agonist-mediated immune response.

Loading of acute myeloid leukemia cells with poly(I:C) by electroporation

In this chapter, we describe the technique of electroporation as an efficient method to load primary leukemic cells with the double-stranded RNA (dsRNA) analogue, polyriboinosinic polyribocytidylic acid (poly(I:C)), and detail on the delicate freezing and thawing procedure of primary leukemic cells.Electroporation is a non-viral gene transfer method by which short-term pores in the membrane of cells are generated by an electrical pulse, allowing molecules to enter the cell. RNA electroporation, a technique developed in our laboratory, is a widely used and versatile transfection method for efficient introduction of both coding RNA (messenger RNA) and non-coding RNA, e.g., dsRNA and small interfering (siRNA), into mammalian cells. Accurate cell processing and storage of patient material is essential for optimal recovery and quality of the cell product for downstream applications.

Identification of substituted pyrimido[5,4-b]indoles as selective Toll-like receptor 4 ligands

A cell-based high-throughput screen to identify small molecular weight stimulators of the innate immune system revealed substituted pyrimido[5,4-b]indoles as potent NFκB activators. The most potent hit compound selectively stimulated Toll-like receptor 4 (TLR4) in human and mouse cells. Synthetic modifications of the pyrimido[5,4-b]indole scaffold at the carboxamide, N-3, and N-5 positions revealed differential TLR4 dependent production of NFκB and type I interferon associated cytokines, IL-6 and interferon γ-induced protein 10 (IP-10) respectively. Specifically, a subset of compounds bearing phenyl and substituted phenyl carboxamides induced lower IL-6 release while maintaining higher IP-10 production, skewing toward the type I interferon pathway. Substitution at N-5 with short alkyl substituents reduced the cytotoxicity of the leading hit compound. Computational studies supported that active compounds appeared to bind primarily to MD-2 in the TLR4/MD-2 complex. These small molecules, which stimulate innate immune cells with minimal toxicity, could potentially be used as adjuvants or immune modulators.

NK cells: key to success of DC-based cancer vaccines?

The cytotoxic and regulatory antitumor functions of natural killer (NK) cells have become attractive targets for immunotherapy. Manipulation of specific NK cell functions and their reciprocal interactions with dendritic cells (DCs) might hold therapeutic promise. In this review, we focus on the engagement of NK cells in DC-based cancer vaccination strategies, providing a comprehensive overview of current in vivo experimental and clinical DC vaccination studies encompassing the monitoring of NK cells. From these studies, it is clear that NK cells play a key regulatory role in the generation of DC-induced antitumor immunity, favoring the concept that targeting both innate and adaptive immune mechanisms may synergistically promote clinical outcome. However, to date, DC vaccination trials are only infrequently accompanied by NK cell monitoring. Here, we discuss different strategies to improve DC vaccine preparations via exploitation of NK cells and provide a summary of relevant NK cell parameters for immune monitoring. We underscore that the design of DC-based cancer vaccines should include the evaluation of their NK cell stimulating potency both in the preclinical phase and in clinical trials.

PD-1 blockade by CT-011, anti-PD-1 antibody, enhances ex vivo T-cell responses to autologous dendritic cell/myeloma fusion vaccine

We have developed a cancer vaccine in which autologous tumor is fused with dendritic cells (DCs) resulting in the presentation of tumor antigens in the context of DC-mediated costimulation. In clinical trials, immunologic responses have been observed, however responses may be muted by inhibitory pathways. The PD1/PDL1 pathway is an important element contributing to tumor-mediated immune suppression. In this study, we demonstrate that myeloma cells and DC/tumor fusions strongly express PD-L1. Compared with a control population of normal volunteers, increased PD-1 expression was observed on T cells isolated from patients with myeloma. It is interesting to note that after autologous transplantation, T-cell expression of PD-1 returned to levels seen in normal controls. We examined the effect of PD-1 blockade on T-cell response to DC/tumor fusions ex vivo. Presence of CT-011, an anti-PD1 antibody, promoted the vaccine-induced T-cell polarization towards an activated phenotype expressing Th1 compared with Th2 cytokines. A concomitant decrease in regulatory T cells and enhanced killing in a cytotoxicity assay was observed. In summary, we demonstrate that PD-1 expression is increased in T cells of patients with active myeloma, and that CT-011 enhances activated T-cell responses after DC/tumor fusion stimulation.

The TLR7/8 ligand resiquimod targets monocyte-derived dendritic cell differentiation via TLR8 and augments functional dendritic cell generation

Imidazoquinolone compounds, such as resiquimod are Toll-like receptor (TLR) 7/8 ligands representing novel immune response modifiers undergoing clinical testing. Resiquimod has been reported to modulate conventional human monocyte-derived DC (moDC) differentiation, but the role of TLR7 and TLR8 is unclear. We directly dissected the TLR7- and TLR8-dependency by employing selective TLR7 ligands and resiquimod-coculture experiments with inhibitory oligonucleotides (iODN) suppressing TLR7, TLR7+8 or TLR7+8+9. Selective TLR7 ligands did not affect conventional moDC differentiation as analyzed by CD14/CD1a expression. iODN experiments confirmed that resiquimod's effects during DC differentiation were antagonized only with TLR8 iODNs. Direct comparison of resiquimod DC with TLR7- and control-DC revealed significantly higher T-cell costimulatory molecule and MHC class II expression. Resiquimod DC promoted significantly stronger allogeneic T-cell proliferation and stronger naïve CD4(+) T-cell proliferation. These results indicate the relevance of TLR8 for human monocyte-derived DC differentiation and maturation and may be relevant for clinical trials employing resiquimod.

Poly(I:C) enhances the susceptibility of leukemic cells to NK cell cytotoxicity and phagocytosis by DC

α Active specific immunotherapy aims at stimulating the host's immune system to recognize and eradicate malignant cells. The concomitant activation of dendritic cells (DC) and natural killer (NK) cells is an attractive modality for immune-based therapies. Inducing immunogenic cell death to facilitate tumor cell recognition and phagocytosis by neighbouring immune cells is of utmost importance for guiding the outcome of the immune response. We previously reported that acute myeloid leukemic (AML) cells in response to electroporation with the synthetic dsRNA analogue poly(I:C) exert improved immunogenicity, demonstrated by enhanced DC-activating and NK cell interferon-γ-inducing capacities. To further invigorate the potential of these immunogenic tumor cells, we explored their effect on the phagocytic and cytotoxic capacity of DC and NK cells, respectively. Using single-cell analysis, we assessed these functionalities in two- and three-party cocultures. Following poly(I:C) electroporation AML cells become highly susceptible to NK cell-mediated killing and phagocytosis by DC. Moreover, the enhanced killing and the improved uptake are strongly correlated. Interestingly, tumor cell killing, but not phagocytosis, is further enhanced in three-party cocultures provided that these tumor cells were upfront electroporated with poly(I:C). Altogether, poly(I:C)-electroporated AML cells potently activate DC and NK cell functions and stimulate NK-DC cross-talk in terms of tumor cell killing. These data strongly support the use of poly(I:C) as a cancer vaccine component, providing a way to overcome immune evasion by leukemic cells.

Clinical evaluation of cellular immunotherapy in acute myeloid leukaemia

Immunotherapy is currently under active investigation as an adjuvant therapy to improve the overall survival of patients with acute myeloid leukaemia (AML) by eliminating residual leukaemic cells following standard therapy. The graft-versus-leukaemia effect observed following allogeneic haematopoietic stem cell transplantation has already demonstrated the significant role of immune cells in controlling AML, paving the way to further exploitation of this effect in optimized immunotherapy protocols. In this review, we discuss the current state of cellular immunotherapy as adjuvant therapy for AML, with a particular focus on new strategies and recently published results of preclinical and clinical studies. Therapeutic vaccines that are being tested in AML include whole tumour cells as an autologous source of multiple leukaemia-associated antigens (LAA) and autologous dendritic cells loaded with LAA as effective antigen-presenting cells. Furthermore, adoptive transfer of cytotoxic T cells or natural killer cells is under active investigation. Results from phase I and II trials are promising and support further investigation into the potential of cellular immunotherapeutic strategies to prevent or fight relapse in AML patients.

Toll-like receptor 7/8 agonist resiquimod induces late preconditioning in neonatal cardiac myocytes

AIM

To investigate whether R-848 (resiquimod, toll-like receptor 7/8 agonist) can induce late preconditioning in neonatal cardiac myocytes.

METHODS

The protective effects of R-848 on neonatal myocytes against anoxia-reoxygenation-induced injury were tested, and intracellular reactive oxygen species (ROS) were determined. The protein synthesis inhibitor cyclohexamide (CH) and the ROS scavenger N-acetylcysteine (NAC) were used in this model to test if new protein synthesis and oxidative stress were necessary for their cardioprotective effects. The activation of nuclear factor kappa B (NFκB) and hypoxia inducible factor 1 (HIF1) was investigated by electrophoretic mobility shift assays (EMSA), and inducible nitric oxide synthase (iNOS) was assessed by immunoblotting. After iNOS was down-regulated by small interfering RNA (siRNA) transfection, the cardioprotective effect was reassessed.

RESULTS

ROS were triggered soon after R-848 (0.01-1.0 μg/L) administration, however, the cardioprotective effect of which was induced 24 h later. This protection was abolished by CH or NAC pretreatment. NFκB and HIF1 activation and iNOS up-regulation were involved in this protective mechanism. The cardioprotective effect was also attenuated after iNOS was knocked down.

CONCLUSION

R-848 provided a cardioprotective effect through a late preconditioning mechanism via a ROS/NFκB-HIF1/iNOS-dependent pathway.

Inhibiting the inhibitors: evaluating agents targeting cancer immunosuppression

IMPORTANCE OF THE FIELD

Immunotherapy of cancer has not improved disease-free or overall patient survival. The lack of concordance between immunological and clinical responses in cancer immunotherapy trials is thought to result from the pervasive presence of tumor-driven immune suppression that allows tumor to escape and that has not been adequately targeted by current therapies.

AREAS COVERED IN THIS REVIEW

Because multiple mechanisms of tumor induced suppression have been identified and shown to contribute to tumor escape, the opportunity arises to interfere with these mechanisms. A range of known tumor-derived inhibitors can now be blocked or neutralized by biologic or metabolic agents. Used alone or in combination with each other or with conventional cancer therapies, these agents offer novel therapeutic strategies for the control of tumor escape.

WHAT THE READER WILL GAIN

This review deals with currently available inhibitors for counteracting tumor immune escape. The restoration of effective anti-tumor immunity in patients with cancer will require new approaches aiming at: i) protection of immune cells from adverse effects of myeloid-derived suppressor cells, regulatory T cells or inhibitory factors thus enhancing effector functions; and ii) prolonging survival of central memory T cells, thus ensuring long-term protection.

TAKE HOME MESSAGE

Inhibitors of mechanisms responsible for tumor escape could restore anti-tumor immune responses in patients with cancer.

Immunotherapy prospects for acute myeloid leukaemia

While chemotherapy is successful at inducing remission of acute myeloid leukaemia (AML), the disease has a high probability of relapse. Strategies to prevent relapse involve consolidation chemotherapy, stem cell transplantation and immunotherapy. Evidence for immunosurveillance of AML and susceptibility of leukaemia cells to both T cell and natural killer (NK) cell attack and justifies the application of immune strategies to control residual AML persisting after remission induction. Immune therapy for AML includes allogeneic stem cell transplantation, adoptive transfer of allogeneic or autologous T cells or NK cells, vaccination with leukaemia cells, dendritic cells, cell lysates, peptides and DNA vaccines and treatment with cytokines, antibodies and immunomodulatory agents. Here we describe what is known about the immunological features of AML at presentation and in remission, the current status of immunotherapy and strategies combining treatment approaches with a view to achieving leukaemia cure.