Systems immunology allows a new view on human dendritic cells

Dendritic Cells in Shaping Anti-Tumor T Cell Response

Among professional antigen-presenting cells, dendritic cells (DCs) orchestrate innate and adaptive immunity and play a pivotal role in anti-tumor immunity. DCs are a heterogeneous population with varying functions in the tumor microenvironment (TME). Tumor-associated DCs differentiate developmentally and functionally into three main subsets: conventional DCs (cDCs), plasmacytoid DCs (pDCs), and monocyte-derived DCs (MoDCs). There are two major subsets of cDCs in TME, cDC1 and cDC2. cDC1 is critical for cross-presenting tumor antigens to activate cytotoxic CD8+ T cells and is also required for priming earlier CD4+ T cells in certain solid tumors. cDC2 is vital for priming anti-tumor CD4+ T cells in multiple tumor models. pDC is a unique subset of DCs and produces type I IFN through TLR7 and TLR9. Studies have shown that pDCs are related to immunosuppression in the TME through the secretion of immunosuppressive cytokines and by promoting regulatory T cells. MoDCs differentiate separately from monocytes in response to inflammatory cues and infection. Also, MoDCs can cross-prime CD8+ T cells. In this review, we summarize the subsets and functions of DCs. We also discuss the role of different DC subsets in shaping T cell immunity in TME and targeting DCs for potential immunotherapeutic benefits against cancer.

Personalized dendritic cell vaccination in cancer therapy: An evidence-based research study

Background

Although chemotherapy is considered to be the golden standard, it does not come without a price. Toxicities and resistance are frequently limiting its effectiveness. Immunotherapy has emerged as a safer therapeutic alternative but still has a long way until it has proven to be of equal efficacy. A type of immunotherapy is dendritic cell (DC) vaccination.

Aims and Objectives

We have developed a novel platform for the generation of autologous DCs that have been activated against peptides that are personalized for each patient individually. The aim of the study was to clinically evaluate this platform.

Materials and Methods

Our platform and our algorithm for the determination of the immunogenic peptides has been tested. DC generation was verified both morphologically and by CD80/86 expression. Peptide antigenicity was determined using a number of T-cell epitope prediction algorithms. Response to therapy was evaluated using response evaluation criteria in solid tumors (RECIST) criteria by the doctors involved. Immune status was also evaluated before and after DC vaccination and correlated with circulated tumor cell count.

Results

It was found that DC vaccine increased immune activation while correlated with decreased circulating tumor cell counts. Clinical evaluation by the determination of immune markers may be a superior tool than using RECIST criteria.

Conclusion

Dendritic cell therapies could prove to be a valuable tool in cancer treatment.

Unraveling the Heterogeneity and Ontogeny of Dendritic Cells Using Single-Cell RNA Sequencing

Dendritic cells (DCs) play essential roles in innate and adaptive immunity and show high heterogeneity and intricate ontogeny. Advances in high-throughput sequencing technologies, particularly single-cell RNA sequencing (scRNA-seq), have improved the understanding of DC subsets. In this review, we discuss in detail the remarkable perspectives in DC reclassification and ontogeny as revealed by scRNA-seq. Moreover, the heterogeneity and multifunction of DCs during diseases as determined by scRNA-seq are described. Finally, we provide insights into the challenges and future trends in scRNA-seq technologies and DC research.

Dendritic Cells: Neglected Modulators of Peripheral Immune Responses and Neuroinflammation in Mood Disorders?

Affective disorders (AD) including major depressive disorder (MDD) and bipolar disorder (BD) are common mood disorders associated with increased disability and poor health outcomes. Altered immune responses characterized by increased serum levels of pro-inflammatory cytokines and neuroinflammation are common findings in patients with AD and in corresponding animal models. Dendritic cells (DCs) represent a heterogeneous population of myeloid cells that orchestrate innate and adaptive immune responses and self-tolerance. Upon sensing exogenous and endogenous danger signals, mature DCs secrete proinflammatory factors, acquire migratory and antigen presenting capacities and thus contribute to neuroinflammation in trauma, autoimmunity, and neurodegenerative diseases. However, little is known about the involvement of DCs in the pathogenesis of AD. In this review, we summarize the current knowledge on DCs in peripheral immune responses and neuroinflammation in MDD and BD. In addition, we consider the impact of DCs on neuroinflammation and behavior in animal models of AD. Finally, we will discuss therapeutic perspectives targeting DCs and their effector molecules in mood disorders.

The Whole Body as the System in Systems Immunology

The human immune system is comprised of a diverse and interactive network of specialized cells localized in diverse tissues throughout the body, where they mediate protection against pathogens and environmental insults while maintaining tissue homeostasis. Although much of our understanding of human immunology has derived from studies of peripheral blood, recent work utilizing human tissue resources and innovative computational methods have employed a whole-body, systems-based approach, revealing tremendous complexity and heterogeneity of the immune system within individuals and across the population. In this review, we discuss how tissue localization, developmental and age-associated changes, and conditions of health and disease shape the immune response, as well as how improved understanding of interindividual and tissue-specific immunity can be leveraged for developing targeted therapeutics.

Immunological dynamics after subcutaneous immunization with a squalene-based oil-in-water adjuvant

The clinically successful adjuvant MF59 is used in seasonal influenza vaccines, which is proposed to enhance immunity by creating an immune-competent microenvironment in the muscle that allows recruitment of immune cells that drive adaptive immune responses. Here, we examined whether the clinically successful adjuvants MF59/AddaVax could be used for subcutaneous use and how antigen delivery can be synergized with cellular dynamics at the vaccination site. Subcutaneous injection of AddaVax leads to thickening of the skin, characterized by a neutrophil-monocyte recruitment sequence. Skin-infiltrating CCR2⁺Ly6C^high monocytes showed differentiation to CD11b⁺Ly6C⁺MHCII⁺CD11c⁺CD64⁺ monocyte-derived DCs over time in the hypodermal layers of the skin, expressing high levels of CD209a/mDC-SIGN. Surprisingly, skin thickening was accompanied with increased white adipose tissue highly enriched with monocytes. Analysis of the skin-draining lymph nodes revealed early increases in neutrophils and moDCs at 12 hours after injection and later increases in migratory cDC2s. Subcutaneous vaccination with AddaVax enhanced antigen-specific CD8⁺ and CD4⁺ T cell responses, while moDC targeting using antigen-coupled CD209a antibody additionally boosted humoral responses. Hence, oil-in-water emulsions provide an attractive immune modulatory adjuvants aimed at increasing cellular responses, as well as antibody responses when combined with moDC targeting.

Dendritic Cells Currently under the Spotlight; Classification and Subset Based upon New Markers

Dendritic cells (DCs) are considered as a subset of mononuclear phagocytes that composed of multiple subsets with distinct phenotypic features. DCs play crucial roles in the initiation and modulation of immune responses to both allo- and auto-antigens during pathogenic settings, encompassing infectious diseases, cancer, autoimmunity, transplantation, as well as vaccination. DCs play a role in preventing autoimmunity via inducing tolerance to self-antigens. This review focus on the most common subsets of DCs in human. Owing to the low frequencies of DC cells in blood and tissues and also the lack of specific DC markers, studies of DCs have been greatly hindered. Human DCs arise by a dedicated pathway of lympho-myeloid hematopoiesis and give rise into specialized subtypes under the influence of transcription factors that are specific for each linage. In humans, the classification of DCs has been generally separated into the blood and cutaneous subsets, mainly because these parts are more comfortable to examine in humans.

Shaping of Dendritic Cell Function by the Metabolic Micro-Environment

Nutrients are required for growth and survival of all cells, but are also crucially involved in cell fate determination of many cell types, including immune cells. There is a growing appreciation that the metabolic micro-environment also plays a major role in shaping the functional properties of dendritic cells (DCs). Under pathological conditions nutrient availability can range from a very restricted supply, such as seen in a tumor micro-environment, to an overabundance of nutrients found in for example obese adipose tissue. In this review we will discuss what is currently known about the metabolic requirements for DC differentiation and immunogenicity and compare that to how function and fate of DCs under pathological conditions can be affected by alterations in environmental levels of carbohydrates, lipids and amino acids as well as by other metabolic cues, including availability of oxygen, redox homeostasis and lactate levels. Many of these insights have been generated using in vitro model systems, which have revealed highly diverse effects of different metabolic cues on DC function. However, they also stress the importance of shifting toward more physiologically relevant experimental settings to be able to fully delineate the role of the metabolic surroundings in its full complexity in shaping the functional properties of DCs in health and disease.

Quantifying Human Innate Cytokine and Chemokine Responses Ex Vivo via Pattern Recognition Receptor Stimulation

Linkages between human innate immune capacity, the environment in which we live, and the development of clinical tolerance versus a spectrum of disease phenotypes are a major focus of inflammatory disease research. While extensive epidemiologic evidence indicates key roles for the microbiome and other environmental factors, the underlying mechanisms that explain how these stimuli lead to a given clinical phenotype remain speculative. Here we review strategies for characterizing human cytokine production ex vivo in response to innate immune receptor stimulation with defined ligands. Human cytokine and chemokine biomarker data provides a tool to test hypotheses on the relationship between innate immune capacity in vivo and expression of current or future clinical phenotypes. The most important limitations of experimental strategies that have been used to date are reviewed. Detailed experimental protocols are provided for characterization of pattern recognition receptor (PRR)-driven stimulation with a panel of bacterial (TLR4, TLR5) and viral (TLR3, TLR7/8, RIG-I/MDA5) ligands to assess the role played by human pro-inflammatory, anti-inflammatory, Th1-like, and Th2-like responses. The importance of characterizing human innate immune phenotypes extends beyond discovery-based research to development of improved strategies for prevention or inhibition of chronic inflammatory diseases, improved design of immunization programs, and more effective cancer immunotherapy.

Immune effector mechanisms in malaria: An update focusing on human immunity

The past decade has witnessed dramatic decreases in malaria-associated mortality and morbidity around the world. This progress has largely been due to intensified malaria control measures, implementation of rapid diagnostics and establishing a network to anticipate and mitigate antimalarial drug resistance. However, the ultimate tool for malaria prevention is the development and implementation of an effective vaccine. To date, malaria vaccine efforts have focused on determining which of the thousands of antigens expressed by Plasmodium falciparum are instrumental targets of protective immunity. The antigenic variation and antigenic polymorphisms arising in parasite genes under immune selection present a daunting challenge for target antigen selection and prioritization, and is a given caveat when interpreting immune recall responses or results from monovalent vaccine trials. Other immune evasion strategies executed by the parasite highlight the myriad of ways in which it can become a recurrent infection. This review provides an update on immune effector mechanisms in malaria and focuses on our improved ability to interrogate the complexity of human immune system, accelerated by recent methodological advances. Appreciating how the human immune landscape influences the effectiveness and longevity of antimalarial immunity will help explain which conditions are necessary for immune effector mechanisms to prevail.

Modulation of Immune Tolerance via Siglec-Sialic Acid Interactions

One of the key features of the immune system is its extraordinary capacity to discriminate between self and non-self and to respond accordingly. Several molecular interactions allow the induction of acquired immune responses when a foreign antigen is recognized, while others regulate the resolution of inflammation, or the induction of tolerance to self-antigens. Post-translational signatures, such as glycans that are part of proteins (glycoproteins) and lipids (glycolipids) of host cells or pathogens, are increasingly appreciated as key molecules in regulating immunity vs. tolerance. Glycans are sensed by glycan binding receptors expressed on immune cells, such as C-type lectin receptors (CLRs) and Sialic acid binding immunoglobulin type lectins (Siglecs), that respond to specific glycan signatures by triggering tolerogenic or immunogenic signaling pathways. Glycan signatures present on healthy tissue, inflamed and malignant tissue or pathogens provide signals for “self” or “non-self” recognition. In this review we will focus on sialic acids that serve as “self” molecular pattern ligands for Siglecs. We will emphasize on the function of Siglec-expressing mononuclear phagocytes as sensors for sialic acids in tissue homeostasis and describe how the sialic acid-Siglec axis is exploited by tumors and pathogens for the induction of immune tolerance. Furthermore, we highlight how the sialic acid-Siglec axis can be utilized for clinical applications to induce or inhibit immune tolerance.

Tobacco Smoke Induces and Alters Immune Responses in the Lung Triggering Inflammation, Allergy, Asthma and Other Lung Diseases: A Mechanistic Review

Many studies have been undertaken to reveal how tobacco smoke skews immune responses contributing to the development of chronic obstructive pulmonary disease (COPD) and other lung diseases. Recently, environmental tobacco smoke (ETS) has been linked with asthma and allergic diseases in children. This review presents the most actual knowledge on exact molecular mechanisms responsible for the skewed inflammatory profile that aggravates inflammation, promotes infections, induces tissue damage, and may promote the development of allergy in individuals exposed to ETS. We demonstrate how the imbalance between oxidants and antioxidants resulting from exposure to tobacco smoke leads to oxidative stress, increased mucosal inflammation, and increased expression of inflammatory cytokines (such as interleukin (IL)-8, IL-6 and tumor necrosis factor α ([TNF]-α). Direct cellular effects of ETS on epithelial cells results in increased permeability, mucus overproduction, impaired mucociliary clearance, increased release of proinflammatory cytokines and chemokines, enhanced recruitment of macrophages and neutrophils and disturbed lymphocyte balance towards Th2. The plethora of presented phenomena fully justifies a restrictive policy aiming at limiting the domestic and public exposure to ETS.