Proinflammatory response of human leukemic cells to dsRNA transfection linked to activation of dendritic cells

Amplifying Immune Responses: Microparticulate Vaccine Approach Against Breast Cancer

Introduction

The study focuses on evaluating the immune responses generated by a novel microparticulate murine breast cancer vaccine.

Methods

The methodology included the use of a co-culture model of dendritic cells (DCs), and T-cells to evaluate the immunotherapeutic responses generated by the vaccine.

Results

The study observed that the dendritic cells expressed significantly higher levels of MHC I, MHC II, CD 40, and CD 80 cell surface markers in the presence of the vaccine microparticles than the controls (p<0.05). This response was potentiated in the presence of an adjuvant, Poly (I:C). The study also demonstrated that the vaccine microparticles do not elicit inflammatory (TNF-alpha, IFN-gamma, IL-2, and IL-12) or immunosuppressive (IL-10) cytokine production when compared to the control.

Discussion

In conclusion, the study established the role of DCs in stimulating the cancer vaccine's adaptive immune responses.

Targeting innate immune pathways for cancer immunotherapy

The innate immune system is critical for inducing durable and protective T cell responses to infection and has been increasingly recognized as a target for cancer immunotherapy. In this review, we present a framework wherein distinct innate immune signaling pathways activate five key dendritic cell activities that are important for T cell-mediated immunity. We discuss molecular pathways that can agonize these activities and highlight that no single pathway can agonize all activities needed for durable immunity. The immunological distinctions between innate immunotherapy administration to the tumor microenvironment versus administration via vaccination are examined, with particular focus on the strategies that enhance dendritic cell migration, interferon expression, and interleukin-1 family cytokine production. In this context, we argue for the importance of appreciating necessity vs. sufficiency when considering the impact of innate immune signaling in inflammation and protective immunity and offer a conceptual guideline for the development of efficacious cancer immunotherapies.

Comprehensive evaluation of biopolymer immune implants for peritoneal metastasis carcinoma therapy

Immunotherapy has been widely used in the treatment of advanced stage cancers with spreading metastases, while the fully activation of immune system often requires sustained and long-acting immune stimulation by immunotherapeutic agents. In previous studies, we designed a biopolymer immune implant by dynamic covalent bonds and achieved sustained release of loaded immunotherapeutic agents, thus stimulated systemic immune activation and elicited immune memory effects. Herein, we further optimized the implants and carried out a comprehensive evaluation of the implants on peritoneal metastasis carcinoma (PMC) therapy. Our results showed that the implants fabricated with 8-arm polyethylene glycol amine (8-arm PEG-NH₂) and 40% oxidation degree dextran (ODEX) exhibited a satisfactory degradation time for activating the antitumor immunity. The drug combination of oxaliplatin (OxP) and resiquimod (R848) could be sustainably released from the implants for 18 days. The implants cured 75% of mice with PMC and elicited immune memory effects to resist tumor re-challenge without obvious side effects observed. Mechanism analysis revealed that the implants could serve as an in-situ vaccine to enhance the infiltration of activated dendritic cells (DCs), T cells and natural killer (NK) cells inside the tumor, as well as increase the serum tumor necrosis factor α (TNF-α), interferon-γ (IFN-γ) and interleukin 12 (IL-12) levels. These results strongly support the clinical translation potential of this sustained released biopolymer immune implants for PMC therapy.

Enhancing anti-tumour innate immunity by targeting the DNA damage response and pattern recognition receptors in combination with radiotherapy

Radiotherapy is one of the most effective and frequently used treatments for a wide range of cancers. In addition to its direct anti-cancer cytotoxic effects, ionising radiation can augment the anti-tumour immune response by triggering pro-inflammatory signals, DNA damage-induced immunogenic cell death and innate immune activation. Anti-tumour innate immunity can result from recruitment and stimulation of dendritic cells (DCs) which leads to tumour-specific adaptive T-cell priming and immunostimulatory cell infiltration. Conversely, radiotherapy can also induce immunosuppressive and anti-inflammatory mediators that can confer radioresistance. Targeting the DNA damage response (DDR) concomitantly with radiotherapy is an attractive strategy for overcoming radioresistance, both by enhancing the radiosensitivity of tumour relative to normal tissues, and tipping the scales in favour of an immunostimulatory tumour microenvironment. This two-pronged approach exploits genomic instability to circumvent immune evasion, targeting both hallmarks of cancer. In this review, we describe targetable DDR proteins (PARP (poly[ADP-ribose] polymerase); ATM/ATR (ataxia-telangiectasia mutated and Rad3-related), DNA-PKcs (DNA-dependent protein kinase, catalytic subunit) and Wee1 (Wee1-like protein kinase) and their potential intersections with druggable immunomodulatory signalling pathways, including nucleic acid-sensing mechanisms (Toll-like receptors (TLR); cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) and retinoic acid-inducible gene-I (RIG-I)-like receptors), and how these might be exploited to enhance radiation therapy. We summarise current preclinical advances, recent and ongoing clinical trials and the challenges of therapeutic combinations with existing treatments such as immune checkpoint inhibitors.

Auranofin and Cold Atmospheric Plasma Synergize to Trigger Distinct Cell Death Mechanisms and Immunogenic Responses in Glioblastoma

Targeting the redox balance of malignant cells via the delivery of high oxidative stress unlocks a potential therapeutic strategy against glioblastoma (GBM). We investigated a novel reactive oxygen species (ROS)-inducing combination treatment strategy, by increasing exogenous ROS via cold atmospheric plasma and inhibiting the endogenous protective antioxidant system via auranofin (AF), a thioredoxin reductase 1 (TrxR) inhibitor. The sequential combination treatment of AF and cold atmospheric plasma-treated PBS (pPBS), or AF and direct plasma application, resulted in a synergistic response in 2D and 3D GBM cell cultures, respectively. Differences in the baseline protein levels related to the antioxidant systems explained the cell-line-dependent sensitivity towards the combination treatment. The highest decrease of TrxR activity and GSH levels was observed after combination treatment of AF and pPBS when compared to AF and pPBS monotherapies. This combination also led to the highest accumulation of intracellular ROS. We confirmed a ROS-mediated response to the combination of AF and pPBS, which was able to induce distinct cell death mechanisms. On the one hand, an increase in caspase-3/7 activity, with an increase in the proportion of annexin V positive cells, indicates the induction of apoptosis in the GBM cells. On the other hand, lipid peroxidation and inhibition of cell death through an iron chelator suggest the involvement of ferroptosis in the GBM cell lines. Both cell death mechanisms induced by the combination of AF and pPBS resulted in a significant increase in danger signals (ecto-calreticulin, ATP and HMGB1) and dendritic cell maturation, indicating a potential increase in immunogenicity, although the phagocytotic capacity of dendritic cells was inhibited by AF. In vivo, sequential combination treatment of AF and cold atmospheric plasma both reduced tumor growth kinetics and prolonged survival in GBM-bearing mice. Thus, our study provides a novel therapeutic strategy for GBM to enhance the efficacy of oxidative stress-inducing therapy through a combination of AF and cold atmospheric plasma.

A COVID-19 Overview and Potential Applications of Cell Therapy

The COVID-19 pandemic has already reaped thousands of lives, although many scientific studies already showed the possibility of this scenario. Currently, further attention is provided to patients depicting comorbidities such as respiratory or immunocompromised diseases, hypertension, and diabetes, as these individuals show a worse prognosis. Cell therapies using stem cells and/or defense cells, combined or not with traditional treatment, could be an outstanding strategy for COVID-19 management since these treatments can act by modulating the immune system, reducing proliferation, and favoring the complete elimination of the virus. In this review, we highlight the main molecular characteristics of this novel coronavirus, as well as the main pathognomonic signs of COVID-19. Furthermore, possible cell therapies are pointed out to show alternative treatments against COVID-19 and its sequels.

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.

Toll-Like Receptor Agonists and Radiation Therapy Combinations: An Untapped Opportunity to Induce Anticancer Immunity and Improve Tumor control

The premise that therapies targeting immune checkpoints can enhance radiation therapy (RT)-induced antitumor immunity is being explored rigorously in the preclinical setting, and early clinical trials testing this hypothesis are beginning to report. Although such approaches might prove efficacious in certain settings, it is likely that many tumor types, particularly those that have a deeply immune-suppressed microenvironment with little or no T cell infiltration, will require alternative approaches. Thus, there is now considerable drive to develop novel immune modulatory therapies that target other areas of the cancer immunity cycle. Toll-like receptors (TLRs) are expressed on sentinel immune cells and play a key role in the host defense against invading pathogens. Innate sensing via TLR-mediated detection of pathogen-derived molecular patterns can lead to maturation of antigen-presenting cells and downstream activation of adaptive immunity. After demonstrating promising efficacy in preclinical studies, drugs that stimulate TLR have been approved for use clinically, albeit to a limited extent. There is a growing body of preclinical evidence that novel agonists targeting TLR3, TLR7/8, or TLR9 in combination with RT might lead to enhanced antitumor immunity. Mechanistic studies have revealed that TLR agonists enhance dendritic cell-mediated T cell priming after RT, in some cases leading to the generation of systemic antitumor immunity and immune memory. In this report, we describe results from preclinical studies that advocate the strategy of combining RT with TLR agonists, discuss reported mechanisms of action, and explore the exciting opportunities of how this approach may be successfully translated into clinical practice.

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.

Clinically Relevant Chemotherapeutics Have the Ability to Induce Immunogenic Cell Death in Non-Small Cell Lung Cancer

The concept of immunogenic cell death (ICD) has emerged as a cornerstone of therapy-induced anti-tumor immunity. To this end, the following chemotherapies were evaluated for their ability to induce ICD in non-small cell lung cancer (NSCLC) cell lines: docetaxel, carboplatin, cisplatin, oxaliplatin and mafosfamide. The ICD hallmarks ATP, ecto-calreticulin, HMGB1, phagocytosis and maturation status of dendritic cells (DCs) were assessed in vitro. Furthermore, an in vivo vaccination assay on C57BL/6J mice was performed to validate our in vitro results. Docetaxel and the combination of docetaxel with carboplatin or cisplatin demonstrated the highest levels of ATP, ecto-calreticulin and HMGB1 in three out of four NSCLC cell lines. In addition, these regimens resulted in phagocytosis of treated NSCLC cells and maturation of DCs. Along similar lines, all mice vaccinated with NSCLC cells treated with docetaxel and cisplatin remained tumor-free after challenge. However, this was not the case for docetaxel, despite its induction of the ICD-related molecules in vitro, as it failed to reject tumor growth at the challenge site in 60% of the mice. Moreover, our in vitro and in vivo data show the inability of oxaliplatin to induce ICD in NSCLC cells. Overall with this study we demonstrate that clinically relevant chemotherapeutic regimens in NSCLC patients have the ability to induce ICD.

Cold Atmospheric Plasma-Treated PBS Eliminates Immunosuppressive Pancreatic Stellate Cells and Induces Immunogenic Cell Death of Pancreatic Cancer Cells

Pancreatic ductal adenocarcinoma (PDAC) is one of the most aggressive cancers with a low response to treatment and a five-year survival rate below 5%. The ineffectiveness of treatment is partly because of an immunosuppressive tumor microenvironment, which comprises tumor-supportive pancreatic stellate cells (PSCs). Therefore, new therapeutic strategies are needed to tackle both the immunosuppressive PSC and pancreatic cancer cells (PCCs). Recently, physical cold atmospheric plasma consisting of reactive oxygen and nitrogen species has emerged as a novel treatment option for cancer. In this study, we investigated the cytotoxicity of plasma-treated phosphate-buffered saline (pPBS) using three PSC lines and four PCC lines and examined the immunogenicity of the induced cell death. We observed a decrease in the viability of PSC and PCC after pPBS treatment, with a higher efficacy in the latter. Two PCC lines expressed and released damage-associated molecular patterns characteristic of the induction of immunogenic cell death (ICD). In addition, pPBS-treated PCC were highly phagocytosed by dendritic cells (DCs), resulting in the maturation of DC. This indicates the high potential of pPBS to trigger ICD. In contrast, pPBS induced no ICD in PSC. In general, pPBS treatment of PCCs and PSCs created a more immunostimulatory secretion profile (higher TNF-α and IFN-γ, lower TGF-β) in coculture with DC. Altogether, these data show that plasma treatment via pPBS has the potential to induce ICD in PCCs and to reduce the immunosuppressive tumor microenvironment created by PSCs. Therefore, these data provide a strong experimental basis for further in vivo validation, which might potentially open the way for more successful combination strategies with immunotherapy for PDAC.

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.

A versatile T cell-based assay to assess therapeutic antigen-specific PD-1-targeted approaches

Blockade of programmed cell death protein 1 (PD-1) immune checkpoint receptor signaling is an established standard treatment for many types of cancer and indications are expanding. Successful clinical trials using monoclonal antibodies targeting PD-1 signaling have boosted preclinical research, encouraging development of novel therapeutics. Standardized assays to evaluate their bioactivity, however, remain restricted. The robust bioassays available all lack antigen-specificity. Here, we developed an antigen-specific, short-term and high-throughput T cell assay with versatile readout possibilities. A genetically modified T cell receptor (TCR)-deficient T cell line was stably transduced with PD-1. Transfection with messenger RNA encoding a TCR of interest and subsequent overnight stimulation with antigen-presenting cells, results in eGFP-positive and granzyme B-producing T cells for single cell or bulk analysis. Control antigen-presenting cells induced reproducible high antigen-specific eGFP and granzyme B expression. Upon PD-1 interaction, ligand-positive antigen-presenting immune or tumor cells elicited significantly lower eGFP and granzyme B expression, which could be restored by anti-PD-(L)1 blocking antibodies. This convenient cell-based assay shows a valuable tool for translational and clinical research on antigen-specific checkpoint-targeted therapy approaches.

The progress and current status of immunotherapy in acute myeloid leukemia

Recently, there has been remarkable progress in basic and preclinical studies of acute myeloid leukemia (AML). The improved outcomes of AML can largely be attributed to advances in supportive care and hematopoietic cell transplantation as opposed to conventional chemotherapy. However, as the 5-year survival rate remains low due to a high incidence of relapse, novel and effective treatments are urgently needed. Increasing attention is focusing on identifying suitable immunotherapeutic strategies for AML. Here, we describe the immunological features, mechanisms of immune escape, and recent progress in immunotherapy for AML. Problems encountered in the clinic will also be discussed. Although current outcomes may be limited, ongoing preclinical or clinical efforts are aimed at improving immunotherapy modalities and designing novel therapies, such as vaccines, monoclonal antibody therapy, chimeric antibody receptor-engineered T cells (CAR-T), TCR-engineered T cells (TCR-T), and checkpoint inhibitors, which may provide promising and effective therapies with higher specificity and efficacy for AML.

Immunogenicity of a Fully Synthetic MUC1 Glycopeptide Antitumor Vaccine Enhanced by Poly(I:C) as a TLR3-Activating Adjuvant

Fully synthetic MUC1 glycopeptide antitumor vaccines have a precisely specified structure and induce a targeted immune response without suppression of the immune response when using an immunogenic carrier protein. However, tumor-associated aberrantly glycosylated MUC1 glycopeptides are endogenous structures, "self-antigens", that exhibit only low immunogenicity. To overcome this obstacle, a fully synthetic MUC1 glycopeptide antitumor vaccine was combined with poly(inosinic acid:cytidylic acid), poly(I:C), as a structurally defined Toll-like receptor 3 (TLR3)-activating adjuvant. This vaccine preparation elicited extraordinary titers of IgG antibodies which strongly bound human breast cancer cells expressing tumor-associated MUC1. Beside the humoral response, the poly(I:C) glycopeptide vaccine induced a pro-inflammatory environment, very important to overcome the immune-suppressive mechanisms, and elicited a strong cellular immune response crucial for tumor elimination.

The Role of Toll-Like Receptors in Hematopoietic Malignancies

Toll-like receptors (TLRs) are a family of pattern recognition receptors that shape the innate immune system by identifying pathogen-associated molecular patterns and host-derived damage-associated molecular patterns. TLRs are widely expressed on both immune cells and non-immune cells, including hematopoietic stem and progenitor cells, effector immune cell populations, and endothelial cells. In addition to their well-known role in the innate immune response to acute infection or injury, accumulating evidence supports a role for TLRs in the development of hematopoietic and other malignancies. Several hematopoietic disorders, including lymphoproliferative disorders and myelodysplastic syndromes, which possess a high risk of transformation to leukemia, have been linked to aberrant TLR signaling. Furthermore, activation of TLRs leads to the induction of a number of proinflammatory cytokines and chemokines, which can promote tumorigenesis by driving cell proliferation and migration and providing a favorable microenvironment for tumor cells. Beyond hematopoietic malignancies, the upregulation of a number of TLRs has been linked to promoting tumor cell survival, proliferation, and metastasis in a variety of cancers, including those of the colon, breast, and lung. This review focuses on the contribution of TLRs to hematopoietic malignancies, highlighting the known direct and indirect effects of TLR signaling on tumor cells and their microenvironment. In addition, the utility of TLR agonists and antagonists as potential therapeutics in the treatment of hematopoietic malignancies is discussed.

Combined adjuvants of poly(I:C) plus LAG-3-Ig improve antitumor effects of tumor-specific T cells, preventing their exhaustion

Therapeutic cancer vaccines are designed to treat cancer by boosting the endogenous immune system to fight against the cancer. In the development of clinically effective cancer vaccines, one of the most practical objectives is to identify adjuvants that are capable of optimizing the vaccine effects. In this study, we explored the potential of polyinosinic-polycytidylic acid (poly(I:C)) and LAG-3-Ig (soluble recombinant protein of lymphocyte activation gene-3 [LAG-3] extracellular domain fused with human IgG Fc region) as adjuvants for P1A tumor antigen peptide vaccine in a pre-established P815 mouse tumor model with a transfer of tumor-specific T cells. Whereas the use of poly(I:C) or LAG-3-Ig as a signal adjuvant induced a slight enhancement of P1A vaccine effects compared to incomplete Freund's adjuvant, combined treatment with poly(I:C) plus LAG-3-Ig remarkably potentiated antitumor effects, leading to complete rejection of pre-established tumor and long-term survival of mice. The potent adjuvant effects of poly(I:C) plus LAG-3-Ig were associated with an enhanced infiltration of T cells in the tumor tissues, and an increased proliferation and Th1-type cytokine production of tumor-reactive T cells. Importantly, the combined adjuvant of poly(I:C) plus LAG-3-Ig downregulated expressions of PD-1, LAG-3, and TIGIT on P1A-specific T cells, indicating prevention of T cell exhaustion. Taken together, the results of the current study show that the combined adjuvants of poly(I:C) plus LAG-3-Ig with tumor peptide vaccine induce profound antitumor effects by activating tumor-specific T cells.

Generation and Cryopreservation of Clinical Grade Wilms' Tumor 1 mRNA-Loaded Dendritic Cell Vaccines for Cancer Immunotherapy

First described in the 1970s, dendritic cells (DC) are currently subjects of intense investigation to exploit their unique antigen-presenting and immunoregulatory capacities. In cancer, DC show promise to elicit or amplify immune responses directed against cancer cells by activating natural killer (NK) cells and tumor antigen-specific T cells. Wilms' tumor 1 (WT1) protein is a tumor-associated antigen that is expressed in a majority of cancer types and has been designated as an antigen of major interest to be targeted in clinical cancer immunotherapy trials. In this chapter, we describe the generation, cryopreservation, and thawing of clinical grade autologous monocyte-derived DC vaccines that are loaded with WT1 by messenger RNA (mRNA) electroporation. This in-house-developed transfection method gives rise to presentation of multiple antigen epitopes and can be used for all patients without restriction of human leukocyte antigen (HLA) type.

TLR-3 stimulation improves anti-tumor immunity elicited by dendritic cell exosome-based vaccines in a murine model of melanoma

Dendritic cell (DC)-derived exosomes (Dexo) contain the machinery necessary to activate potent antigen-specific immune responses. As promising cell-free immunogens, Dexo have been tested in previous clinical trials for cancer vaccine immunotherapy, yet resulted in limited therapeutic benefit. Here, we explore a novel Dexo vaccine formulation composed of Dexo purified from DCs loaded with antigens and matured with either the TLR-3 ligand poly(I:C), the TLR-4 ligand LPS or the TLR-9 ligand CpG-B. When poly(I:C) was used to produce exosomes together with ovalbumin (OVA), the resulting Dexo vaccine strongly stimulated OVA-specific CD8⁺ and CD4⁺ T cells to proliferate and acquire effector functions. When a B16F10 melanoma cell lysate was used to load DCs with tumor antigens during exosome production together with poly(I:C), we obtained a Dexo vaccine capable of inducing robust activation of melanoma-specific CD8⁺ T cells and the recruitment of cytotoxic CD8⁺ T cells, NK and NK-T cells to the tumor site, resulting in significantly reduced tumor growth and enhanced survival as compared to a Dexo vaccine formulation similar to the one previously tested on human patients. Our results indicate that poly(I:C) is a particularly favorable TLR agonist for DC maturation during antigen loading and exosome production for cancer immunotherapy.

Targeting the innate immune system as immunotherapy for acute myeloid leukemia

Because of its disseminated nature and lack of tumor-draining lymph nodes, acute myeloid leukemia (AML) likely employs unique immune evasion strategies as compared to solid malignancies. Targeting these unique mechanisms may result in improved immunotherapeutic approaches. Emerging data suggest that a specific dendritic cell (DC) subset, CD8α DCs, may be responsible for mediating tolerance in AML and thus targeting the innate immune system may be of benefit in this disease. Promising immune targets include the toll-like receptors, calreticulin/CD47, the stimulator of interferon genes pathway, and signal transducer and activator of transcription 3 (STAT3). However, it is becoming clear that compensatory mechanisms may limit the efficacy of these agents alone and thus rationale combinations of immunotherapies are warranted. This review discusses the potential immune evasion strategies in AML, as well as discussion of the promising innate immune targets, both alone and in combination, for this disease.

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.

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.

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.

Poly(I:C)-induced tumour cell death leads to DC maturation and Th1 activation

Dendritic cells (DCs) have the ability to generate peptide epitopes for MHC class I molecules derived from apoptotic tumour cells for direct recognition by cytotoxic T cells. This function has lead to DCs being used in vaccine strategies. In this study, we investigate the effect of inducing apoptosis in tumour cell lines using IFN-γ and poly(I:C), the subsequent maturation of the endocytosing DC and its ability to direct the resulting T cell response. We show that uptake of poly(I:C)-induced apoptotic tumour cells leads to DC maturation and activation with a Th1 cell polarising capacity. In contrast, these effects are not seen by DCs loaded with γ-irradiated apoptotic tumour cells. We propose that the manner in which tumour cells are induced to die can have a profound effect on the endocytosing DC and the resulting T cell response.

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.

Interferon-α in acute myeloid leukemia: an old drug revisited

Interferon-α (IFN-α), a type I IFN, is a well-known antitumoral agent. The investigation of its clinical properties in acute myeloid leukemia (AML) has been prompted by its pleiotropic antiproliferative and immune effects. So far, integration of IFN-α in the therapeutic arsenal against AML has been modest in view of the divergent results of clinical trials. Recent insights into the key pharmacokinetic determinants of the clinical efficacy of IFN along with advances in its pharmaceutical formulation, have sparked renewed interest in its use. This paper reviews the possible applicability of IFN-α in the treatment of AML and provides a rational basis to re-explore its efficacy in clinical trials.

Recent advances in antigen-loaded dendritic cell-based strategies for treatment of minimal residual disease in acute myeloid leukemia

Therapeutic vaccination with dendritic cells (DCs) is recognized as an important experimental therapy for the treatment of minimal residual disease in acute myeloid leukemia. Many sources of leukemia-associated antigens and different methods for antigen loading of DCs have been used in an attempt to optimize anti-tumor responses. For instance, monocyte-derived DCs have been loaded with apoptotic whole-cell suspensions, necrotic cell lysates, tumor-associated peptides, eluted peptides and cellular DNA or RNA. Furthermore, monocyte-derived DCs can be chemically or electrically fused with leukemic blasts, and DCs have been cultured out of leukemic blasts. However, it remains a challenge in cancer immunotherapy to identify which of these methods is the most optimal for antigen loading and activation of DCs. This review discusses recent advances in DC research and the application of this knowledge towards new strategies for antigen loading of DCs in the treatment of minimal residual disease in acute myeloid leukemia.

Targeting Toll-like receptor 7/8 enhances uptake of apoptotic leukemic cells by monocyte-derived dendritic cells but interferes with subsequent cytokine-induced maturation

Therapeutic vaccination with dendritic cells (DC) is an emerging investigational therapy for eradication of minimal residual disease in acute myeloid leukemia. Various strategies are being explored in manufacturing DC vaccines ex vivo, e.g., monocyte-derived DC (MoDC) loaded with leukemia-associated antigens (LAA). However, the optimal source of LAA and the choice of DC-activating stimuli are still not well defined. Here, loading with leukemic cell preparations (harboring both unknown and known LAA) was explored in combination with a DC maturation-inducing cytokine cocktail (CC; IL-1β, IL-6, TNF-α, and PGE₂) and Toll-like receptor ligands (TLR-L) to optimize uptake. Since heat shock induced apoptotic blasts were more efficiently taken up than lysates, we focused on uptake of apoptotic leukemic cells. Uptake of apoptotic blast was further enhanced by the TLR7/8-L R848 (20–30%); in contrast, CC-induced maturation inhibited uptake. CC, and to a lesser extent R848, enhanced the ability of MoDC to migrate and stimulate T cells. Furthermore, class II-associated invariant chain peptide expression was down-modulated after R848- or CC-induced maturation, indicating enhanced processing and presentation of antigenic peptides. To improve both uptake and maturation, leukemic cells and MoDC were co-incubated with R848 for 24 h followed by addition of CC. However, this approach interfered with CC-mediated MoDC maturation as indicated by diminished migratory and T cell stimulatory capacity, and the absence of IL-12 production. Taken together, our data demonstrate that even though R848 improved uptake of apoptotic leukemic cells, the sequential use of R848 and CC is counter-indicated due to its adverse effects on MoDC maturation.

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

Immunotherapy for leukemia is a promising targeted strategy to eradicate residual leukemic cells after standard therapy, in order to prevent relapse and to prolong the survival of leukemia patients. However, effective anti-leukemia immune responses are hampered by the weak immunogenicity of leukemic cells. Therefore, much effort is made to identify agents that could increase the immunogenicity of leukemic cells and activate the immune system. Synthetic agonists of Toll-like receptor (TLR)7 and TLR8 are already in use as anticancer treatment, because of their ability to activate several immune pathways simultaneously, resulting in effective antitumor immunity. However, for leukemic cells little is known about the expression of TLR7/8 and the direct effects of their agonists. We hypothesized that TLR7/8 agonist treatment of human acute myeloid leukemia (AML) cells would lead to an increased immunogenicity of AML cells. We observed expression of TLR7 and TLR8 in primary human AML cells and AML cell lines. Passive pulsing of primary AML cells with the TLR7/8 agonist R-848 resulted in increased expression of MHC molecules, production of proinflammatory cytokines, and enhanced allogeneic naïve T cell-stimulatory capacity. These effects were absent or suboptimal if R-848 was administered intracellularly by electroporation. Furthermore, when AML cells were cocultured with allogeneic PBMC in the presence of R-848, interferon (IFN)-gamma was produced by allogeneic NK and NKT cells and AML cells were killed. In conclusion, the immunostimulatory effect of the TLR7/8 agonist R-848 on human AML cells could prove useful for the design of TLR-based immunotherapy for leukemia.

Dendritic cell-based immunotherapy in myeloid leukaemia: translating fundamental mechanisms into clinical applications

Immunotherapy for leukaemia patients, aiming at the generation of anti-leukaemic T cell responses, could provide a new therapeutic approach to eliminate minimal residual disease (MRD) cells in acute myeloid leukaemia (AML). Leukaemic blasts harbour several ways to escape the immune system including deficient MHC class II expression, low levels of co-stimulatory molecules and suppressive cytokines. Therapeutic vaccination with dendritic cells (DC) is now recognized as an important investigational therapy. Due to their unique antigen presenting capacity, immunosuppressive features of the leukaemic blasts can be circumvented. DC can be successfully cultured from leukaemic blasts in 60-70% of patients and show functional potential in vivo. Alternatively, monocyte derived DC obtained at time of complete remission loaded with leukaemia-specific antigens can be used as vaccine. Several sources of leukaemia-associated antigen and different methods of loading antigen onto DC have been used in an attempt to optimize antitumour responses including apoptotic cells, necrotic cell lysates and tumour-associated pep-tides. Currently, the AML-derived cell line MUTZ-3, an immortalized equivalent of CD34(+) DC precursor cells, is under investigation for vaccination purposes. For effective DC vaccination the intrinsic tolerant state of the patient must be overcome. Therefore, the development of efficient and safe adjuvants in antigen specific immunotherapeutic programs should be encouraged.

Toll-like receptors and their role in carcinogenesis and anti-tumor treatment

Toll-like receptors (TLRs) have been described as major components of the innate immune system, recognizing the conserved molecular structures found in the large groups of pathogens called pathogen-associated molecular patterns (PAMPs). TLR expression is ubiquitous, from epithelial to immunocompetent cells. TLR ligation triggers several adapter proteins and downstream kinases, leading to the induction of key pro-inflammatory mediators but also anti-inflammatory and anti-tumor cytokines. The result of this activation goes beyond innate immunity to shape the adaptive responses against pathogens and tumor cells, and maintains host homeostasis via cell debris utilization. TLRs have already become potent targets in infectious disease treatment and vaccine therapy and in neoplastic disease treatment, due to their ability to enhance antigen presentation. However, some studies show the dual effect of TLR stimulation on malignant cells: they can be proapoptotic or promote survival under different conditions. It is therefore crucial to design further studies assessing the biology of these receptors in normal and transformed cells. The established role of TLRs in human disease therapy is based on TLR7 and TLR4 agonists, respectively for the novel treatment of some types of skin cancer and for the anti-hepatitis B virus vaccine. Some clinical trials involving TLR agonists as potent enhancers of the anti-tumor response in solid tumors have begun.

Acute myeloid leukemic cell lines loaded with synthetic dsRNA trigger IFN-gamma secretion by human NK cells

Natural killer (NK) cells are key players of innate immunity. Besides their major cytotoxic function, NK cells can also produce inflammatory cytokines such as interferon (IFN)-gamma. In this way, NK cells can shape adaptive immune responses through activation of dendritic cells (DC), thereby promoting the bidirectional cross-talk between NK cells and DC. Including this helper function of NK cells in cancer vaccination might be important for the induction of effective T cell responses. Here, we explored the capacity of purified human NK cells to produce IFN-gamma upon two-signal stimulation using different types of acute myeloid leukemia (AML) cells and type I IFN. Based on our previous findings that AML cells produce IFN-alpha upon electroporation with the synthetic double-stranded (ds)RNA polyriboinosinic polyribocytidylic acid (poly(I:C)), we hypothesized that dsRNA-loaded tumor cells provide both signals to elicit an NK cell-driven IFN-gamma production. Our results show that in vitro, NK cells become strong IFN-gamma-secreting cells upon stimulation with specific AML cells and IFN-alpha, with a variable responsiveness against different AML cell lines. Importantly, loading of AML cells with poly(I:C) is an elegant method to provide NK cells with both signals, a feature that could have important clinical implications because it obviates the side effects of systemic cytokine administration. Moreover, in addition to our previous findings that DC become activated upon phagocytosis of poly(I:C)-electroporated AML cells, these data strongly encourage future research on the potential of dsRNA-transfected AML cells and their effect to favor NK-DC cross-talk for the design of leukemia vaccines.

Measles virus induces oncolysis of mesothelioma cells and allows dendritic cells to cross-prime tumor-specific CD8 response

Despite conventional medical and surgical treatments, malignant pleural mesothelioma (MPM) remains incurable. Oncovirotherapy (i.e., the use of replication-competent virus for cancer treatment) is currently explored in clinical trials. In this study, we investigated the antineoplastic potential of a new oncolytic viral agent, a live-attenuated measles virus (MV) strain derived from the Edmonston vaccine lineage (Schwarz strain). We evaluated both oncolytic activity and immunoadjuvant properties of the MV vaccine strain on mesothelioma tumor cells. Infectivity, syncytium formation, and cytolytic activity of MV were studied on a panel of mesothelioma cells derived from pleural effusions of MPM patients. We observed that MV infected preferentially MPM cell lines in comparison with nontransformed mesothelial cells, leading to an efficient killing of a significant fraction of tumor cells. A cytoreductive activity was also evidenced through formation of multinuclear cellular aggregates (syncytia). The susceptibility of MPM cell lines to measles infection was assessed by the analysis of cell surface expression of the MV vaccine receptor (CD46). We also evaluated whether MV infection of mesothelioma cells could elicit an autologous antitumor immune response. We showed that MV Schwarz strain induced apoptotic cell death of infected mesothelioma cells, which were efficiently phagocytosed by dendritic cells (DC). Loading of DCs with MV-infected MPM cells induced DC spontaneous maturation, as evidenced by the increased expression of MHC and costimulatory molecules along with the production of proinflammatory cytokines. Priming of autologous T cells by DCs loaded with MV-infected MPM cells led to a significant proliferation of tumor-specific CD8 T cells. Altogether, these data strongly support the potential of oncolytic MV as an efficient therapeutic agent for mesothelioma cancer.