Innate Immunity Modulating Impurities and the Immunotoxicity of Nanobiotechnology-Based Drug Products

Innate immunity can be triggered by the presence of microbial antigens and other contaminants inadvertently introduced during the manufacture and purification of bionanopharmaceutical products. Activation of these innate immune responses, including cytokine secretion, complement, and immune cell activation, can result in unexpected and undesirable host immune responses. These innate modulators can also potentially stimulate the activation of adaptive immune responses, including the formation of anti-drug antibodies which can impact drug effectiveness. To prevent induction of these adverse responses, it is important to detect and quantify levels of these innate immunity modulating impurities (IIMIs) that may be present in drug products. However, while it is universally agreed that removal of IIMIs from drug products is crucial for patient safety and to prevent long-term immunogenicity, there is no single assay capable of directly detecting all potential IIMIs or indirectly quantifying downstream biomarkers. Additionally, there is a lack of agreement as to which of the many analytical assays currently employed should be standardized for general IIMI screening. Herein, we review the available literature to highlight cellular and molecular mechanisms underlying IIMI-mediated inflammation and its relevance to the safety and efficacy of pharmaceutical products. We further discuss methodologies used for direct and indirect IIMI identification and quantification.

The role of RAGE in host pathology and crosstalk between RAGE and TLR4 in innate immune signal transduction pathways

Although the innate immune receptor protein, Receptor for Advanced Glycation End products (RAGE), has been extensively studied, there has been renewed interest in RAGE for its potential role in sepsis, along with a host of other inflammatory diseases of chronic, noninfectious origin. In contrast to other innate immune receptors, for example, Toll-like receptors (TLRs), that recognize ligands derived from pathogenic organisms that are collectively known as "pathogen-associated molecular patterns" (PAMPs) or host-derived "damage-associated molecular patterns" (DAMPs), RAGE has been shown to recognize a broad collection of DAMPs exclusively. Historically, these DAMPs have been shown to be pro-inflammatory in nature. Early studies indicated that the adaptor molecule, MyD88, might be important for this change. More recent studies have explored further the mechanisms underlying this inflammatory change. Overall, the newer results have shown that there is extensive crosstalk between RAGE and TLRs. The three canonical RAGE ligands, Advanced Glycation End products (AGEs), HMGB1, and S100 proteins, have all been shown to activate both TLRs and RAGE to varying degrees in order to induce inflammation in in vitro models. As with any field that delves deeply into innate signaling, obstacles of reagent purity may be a cause of some of the discrepancies in the literature, and we have found that commercial antibodies that have been widely used exhibit a high degree of nonspecificity. Nonetheless, the weight of published evidence has led us to speculate that RAGE may be physically interacting with TLRs on the cell surface to elicit inflammation via MyD88-dependent signaling.

TLR-4 Signaling vs. Immune Checkpoints, miRNAs Molecules, Cancer Stem Cells, and Wingless-Signaling Interplay in Glioblastoma Multiforme-Future Perspectives

Toll-like-receptor (TLR) family members were detected in the central nervous system (CNS). TLR occurrence was noticed and widely described in glioblastomamultiforme (GBM) cells. After ligand attachment, TLR-4 reorients domains and dimerizes, activates an intracellular cascade, and promotes further cytoplasmatic signaling. There is evidence pointing at a strong relation between TLR-4 signaling and micro ribonucleic acid (miRNA) expression. The TLR-4/miRNA interplay changes typical signaling and encourages them to be a target for modern immunotherapy. TLR-4 agonists initiate signaling and promote programmed death ligand-1 (PD-1L) expression. Most of those molecules are intensively expressed in the GBM microenvironment, resulting in the autocrine induction of regional immunosuppression. Another potential target for immunotreatment is connected with limited TLR-4 signaling that promotes Wnt/DKK-3/claudine-5 signaling, resulting in a limitation of GBM invasiveness. Interestingly, TLR-4 expression results in bordering proliferative trends in cancer stem cells (CSC) and GBM. All of these potential targets could bring new hope for patients suffering from this incurable disease. Clinical trials concerning TLR-4 signaling inhibition/promotion in many cancers are recruiting patients. There is still a lot to do in the field of GBM immunotherapy.

PD-L1/PD-1 Axis in Glioblastoma Multiforme

Glioblastoma (GBM) is the most popular primary central nervous system cancer and has an extremely expansive course. Aggressive tumor growth correlates with short median overall survival (OS) oscillating between 14 and 17 months. The survival rate of patients in a three-year follow up oscillates around 10%. The interaction of the proteins programmed death-1 (PD-1) and programmed cell death ligand (PD-L1) creates an immunoregulatory axis promoting invasion of glioblastoma multiforme cells in the brain tissue. The PD-1 pathway maintains immunological homeostasis and protects against autoimmunity. PD-L1 expression on glioblastoma surface promotes PD-1 receptor activation in microglia, resulting in the negative regulation of T cell responses. Glioblastoma multiforme cells induce PD-L1 secretion by activation of various receptors such as toll like receptor (TLR), epidermal growth factor receptor (EGFR), interferon alpha receptor (IFNAR), interferon-gamma receptor (IFNGR). Binding of the PD-1 ligand to the PD-1 receptor activates the protein tyrosine phosphatase SHP-2, which dephosphorylates Zap 70, and this inhibits T cell proliferation and downregulates lymphocyte cytotoxic activity. Relevant studies demonstrated that the expression of PD-L1 in glioma correlates with WHO grading and could be considered as a tumor biomarker. Studies in preclinical GBM mouse models confirmed the safety and efficiency of monoclonal antibodies targeting the PD-1/PD-L1 axis. Satisfactory results such as significant regression of tumor mass and longer animal survival time were observed. Monoclonal antibodies inhibiting PD-1 and PD-L1 are being tested in clinical trials concerning patients with recurrent glioblastoma multiforme.

Type I interferon licenses enhanced innate recognition and transcriptional responses to Franciscella tularensis live vaccine strain

The innate inflammatory response to Francisella tularensis (Ft) in macrophages is significantly governed by the expression of type I interferon (IFN). Previously, the proteolytic processing and maturation of pro-IL-1β protein was shown to depend upon type I IFN expression. We show in this report that paracrine type I IFN can profoundly enhance innate recognition and TLR-dependent transcriptional responses to Ft infection upstream of its role in inflammasome regulation in both primary human monocyte-derived macrophages and primary murine peritoneal macrophages but not murine bone marrow-derived macrophages. This type I IFN-enhanced response is synergistic with TLR2 transcriptional responses, partially TLR2-independent, but strictly MyD88-dependent.

TLR2 promoter hypermethylation creates innate immune dysbiosis

Periodontitis is a common chronic inflammatory disease that is initiated by a complex microbial biofilm that poses significant health and financial burdens globally. Porphyromonas gingivalis is a predominant pathogen that maintains chronic inflammatory periodontitis. Toll-like receptors (TLRs) play an important role in periodontitis by recognizing pathogens and maintaining tissue homeostasis. Deficiencies in TLR expression and downstream signaling may reduce the host's innate defenses against pathogens, leading to bacterial persistence and exacerbated inflammation, which are now being better appreciated in disease pathologies. In the case of periodontitis, gingival epithelial cells form the first line of defense against pathogens. Innate immune dysregulation in these cells relates to severe disease pathology. We recently identified a blunted TLR2 expression in certain gingival epithelial cells expressing diminished cytokine signaling upon P. gingivalis stimulation. Upon detailed analysis of the TLR2 promoter CpG Island, we noted higher CpG methylation in this dysregulated cell type. When these cells were treated with DNA methyltransferase inhibitor, TLR2 mRNA and cytokine expression were significantly increased. If TLR2 expression plasmid was ectopically expressed in dysfunctional cells prior to P. gingivalis stimulation, the cytokine expression was increased, confirming the requirement of TLR2 in the P. gingivalis-mediated inflammatory response. We designed a chronic in vitro infection model to test if P. gingivalis can induce DNA methylation in normal gingival epithelial cells that express higher TLR2 upon agonist stimulation. Chronic treatment of normal epithelial cells with P. gingivalis introduced de novo DNA methylation within the cells. In addition, increased DNA methylation was observed in the gingiva of mice infected with P. gingivalis in a periodontitis oral gavage model. Moreover, tissues obtained from periodontitis patients also exhibited differential TLR2 promoter methylation, as revealed by bisulfite DNA sequencing. Taken together, DNA methylation of TLR2 can modulate host innate defense mechanisms that may confer increased disease susceptibility.

Sustained expression of lipocalin-2 during polymicrobial sepsis

Sepsis is a major healthcare problem and a leading cause of death worldwide. There is no dependable diagnosis, and treatment for this condition remains mainly supportive. The etiology of sepsis is related to an overwhelming inflammatory response. In this regard, the antimicrobial protein lipocalin-2 (Lcn2) has been associated with several inflammatory conditions, but its contribution to polymicrobial sepsis is unclear. Polymicrobial sepsis was induced by cecal ligation and puncture (CLP), and Lcn2 mRNA levels and protein expression were measured in liver and lung tissues. We observed that Lcn2 expression was robustly induced in liver and lung of C57BL/6 J (B6) mice, and remained elevated during the stage of innate immune dysfunction observed in sepsis. This response was different in A/J mice, suggesting a contribution of the genetic background, probably due to differences in IL-10 expression between these two mouse strains. Indeed, IL-10 was found to regulate Lcn2 expression in both primary and J774A.1 macrophages. Thus, Lcn2 expression is highly regulated during CLP-induced sepsis, suggesting that this antimicrobial protein could have a role as a potential biomarker for the diagnosis of sepsis.

Nuclear factor-κB binding motifs specify Toll-like receptor-induced gene repression through an inducible repressosome

Sustained Toll-like receptor (TLR) stimulation continuously activates antimicrobial genes but paradoxically represses inflammatory genes. This phenomenon, termed TLR tolerance, is essential for preventing fatal inflammatory conditions such as sepsis, but its underlying mechanisms are unclear. We report here that NF-κB binding nucleic acids of gene promoters are tolerogenic motifs, which selectively recruit an NcoR-Hdac3-deacetylated-p50 repressosome to inflammatory genes. Genome-wide analyses of TLR4-induced genes revealed that NF-κB motifs were the only regulatory elements significantly enriched in tolerizable genes. Mutating the NF-κB motifs of tolerizable genes converted them into nontolerizable ones, whereas inserting NF-κB binding motifs into nontolerizable genes conferred the tolerance. Although NF-κB p50 was essential for assembling the repressosome, genetic disruption of the NcoR-Hdac3 interaction alone was sufficient to completely abolish TLR4 tolerance and to render mice vulnerable to sepsis. Thus, the specificity of TLR tolerance is dictated by evolutionally conserved nucleic acid motifs that bound by NF-κB and the NcoR repressosome.

Lipopolysaccharide pretreatment of the udder protects against experimental Escherichia coli mastitis

Exposure to pathogen-associated molecular patterns such as LPS can cause an immune refractory state in mammals known as endotoxin tolerance (ET), resulting in a decreased inflammatory response after pathogen contact. This ET concept was used to reduce the severity of an experimentally-induced clinical mastitis. Cows were pretreated with 1 µg LPS per udder quarter and challenged 72 h (group L72EC) or 240 h (group L240EC) later with 500 CFU Escherichia coli. Pretreated animals showed no leukopenia after challenge, no (L72EC), or only slightly (L240EC), elevated body temperature and significantly reduced systemic and local clinical scores compared with cows that were not pretreated. Whereas an increase of milk somatic cell count after the E. coli challenge was abrogated in L72EC animals, it was significantly delayed in the L240EC group. In both pretreated groups the bacterial load in milk was markedly reduced. Based on the expression of inflammation-related genes in lobulo-alveolar mammary tissue, the tolerizing effect of LPS pretreatment is based on the inhibited up-regulation of inflammatory (TNF-α, IL-6, CXCL8, CCL20) and anti-inflammatory genes (IL-10, IRAK-M). These findings indicate that the concept of ET may be usefully applied as mastitis prophylaxis facilitating a rapid response to microbial infection and avoiding dysregulated inflammation.

Role of IL-1 receptor-associated kinase-M (IRAK-M) in priming of immune and inflammatory responses by nitrogen bisphosphonates

Nitrogen bisphosphonates (NBPs) are commonly prescribed for osteoporosis but have also been found to induce inflammatory reactions and to delay the progression of breast cancer. The inflammatory and anticancer effects of the NBPs might be associated with an ability to modulate innate immune signaling. In mice, intraperitoneal NBP administration causes a rapid influx of neutrophils and monocytes that is dependent on the myeloid differentiation primary response gene 88 (MyD88) mediator of Toll-like receptor (TLR) and IL-1 signaling. Bone marrow chimeras demonstrate that this inflammatory response is partially dependent on TLR4 expression by hematopoietic cells and the IL-1 receptor on radioresistant cells. In vitro, NBPs directly stimulate neither murine bone marrow-derived mononuclear cells nor human peripheral blood mononuclear cells, but rather prime them to produce increased amounts of cytokines when exposed to IL-1 or TLR ligands. This potentiation is mediated by a reduction in IL-1 receptor-associated kinase-M, a negative regulator of MyD88-dependent signaling. In vivo, this property renders the NBPs as effective adjuvants that enhance both cellular and antibody responses to antigens.

IFN-γ abrogates endotoxin tolerance by facilitating Toll-like receptor-induced chromatin remodeling

An important mechanism by which IFN-γ primes macrophages for enhanced innate immune responses is abrogation of feedback inhibitory pathways. Accordingly, IFN-γ abrogates endotoxin tolerance, a major negative feedback loop that silences expression of inflammatory cytokine genes in macrophages previously exposed to endotoxin/Toll-like receptor (TLR) ligands. Mechanisms by which IFN-γ inhibits endotoxin tolerance have not been elucidated. Here, we show that pretreatment with IFN-γ prevented tolerization of primary human monocytes and restored TLR4-mediated induction of various proinflammatory cytokines, including IL-6 and TNFα. Surprisingly, IFN-γ did not alter proximal TLR4 signaling defects in tolerized monocytes. Instead, IFN-γ blocked tolerance-associated down-regulation of IL6 and TNF transcription, RNA polymerase II recruitment, and NF-κB and CCAAT/enhancer-binding protein β transcription factor binding to the IL6 and TNF promoters in tolerized monocytes. The mechanism by which IFN-γ restored IL6 expression was by facilitating TLR4-induced recruitment of chromatin remodeling machinery to the IL6 promoter and promoting IL6 locus accessibility in tolerized monocytes. Our results suggest that IFN-γ overcomes endotoxin tolerance by facilitating TLR-induced chromatin remodeling to allow expression of proinflammatory genes. These results identify a mechanism by which IFN-γ promotes activation of macrophages and highlight the importance of chromatin remodeling and transcriptional control in the regulation of inflammatory cytokine production in tolerant and activated macrophages.

Negative regulation of toll-like receptor signaling by NF-kappaB p50 ubiquitination blockade

Toll-like receptors (TLRs) trigger the production of inflammatory cytokines and shape adaptive and innate immunity to pathogens. We report the identification of B cell leukemia (Bcl)-3 as an essential negative regulator of TLR signaling. By blocking ubiquitination of p50, a member of the nuclear factor (NF)-kappaB family, Bcl-3 stabilizes a p50 complex that inhibits gene transcription. As a consequence, Bcl-3-deficient mice and cells were found to be hypersensitive to TLR activation and unable to control responses to lipopolysaccharides. Thus, p50 ubiquitination blockade by Bcl-3 limits the strength of TLR responses and maintains innate immune homeostasis. These findings indicate that the p50 ubiquitination pathway can be selectively targeted to control deleterious inflammatory diseases.