Synthetic toll-like receptor 4 agonists stimulate innate resistance to infectious challenge

A synthetic TLR4 agonist significantly increases humoral immune responses and the protective ability of an MDCK-cell-derived inactivated H7N9 vaccine in mice

Antigenically divergent H7N9 viruses pose a potential threat to public health, with the poor immunogenicity of candidate H7N9 vaccines demonstrated in clinical trials underscoring the urgent need for more-effective H7N9 vaccines. In the present study, mice were immunized with various doses of a suspended-MDCK-cell-derived inactivated H7N9 vaccine, which was based on a low-pathogenic H7N9 virus, to assess cross-reactive immunity and cross-protection against antigenically divergent H7N9 viruses. We found that the CRX-527 adjuvant, a synthetic TLR4 agonist, significantly enhanced the humoral immune responses of the suspended-MDCK-cell-derived H7N9 vaccine, with significant antigen-sparing and immune-enhancing effects, including robust virus-specific IgG, hemagglutination-inhibiting (HI), neuraminidase-inhibiting (NI), and virus-neutralizing (VN) antibody responses, which are crucial for protection against influenza virus infection. Moreover, the CRX-527-adjuvanted H7N9 vaccine also elicited cross-protective immunity and cross-protection against a highly pathogenic H7N9 virus with a single vaccination. Notably, NI and VN antibodies might play an important role in cross-protection against lethal influenza virus infections. This study showed that a synthetic TLR4 agonist adjuvant has a potent immunopotentiating effect, which might be considered worth further development as a means of increasing vaccine effectiveness.

Co-Delivery of Novel Synthetic TLR4 and TLR7/8 Ligands Adsorbed to Aluminum Salts Promotes Th1-Mediated Immunity against Poorly Immunogenic SARS-CoV-2 RBD

Despite the availability of effective vaccines against COVID-19, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) continues to spread worldwide, pressing the need for new vaccines with improved breadth and durability. We developed an adjuvanted subunit vaccine against SARS-CoV-2 using the recombinant receptor-binding domain (RBD) of spikes with synthetic adjuvants targeting TLR7/8 (INI-4001) and TLR4 (INI-2002), co-delivered with aluminum hydroxide (AH) or aluminum phosphate (AP). The formulations were characterized for the quantities of RBD, INI-4001, and INI-2002 adsorbed onto the respective aluminum salts. Results indicated that at pH 6, the uncharged RBD (5.73 ± 4.2 mV) did not efficiently adsorb to the positively charged AH (22.68 ± 7.01 mV), whereas it adsorbed efficiently to the negatively charged AP (-31.87 ± 0.33 mV). Alternatively, pre-adsorption of the TLR ligands to AH converted it to a negatively charged particle, allowing for the efficient adsorption of RBD. RBD could also be directly adsorbed to AH at a pH of 8.1, which changed the charge of the RBD to negative. INI-4001 and INI-2002 efficiently to AH. Following vaccination in C57BL/6 mice, both aluminum salts promoted Th2-mediated immunity when used as the sole adjuvant. Co-delivery with TLR4 and/or TLR7/8 ligands efficiently promoted a switch to Th1-mediated immunity instead. Measurements of viral neutralization by serum antibodies demonstrated that the addition of TLR ligands to alum also greatly improved the neutralizing antibody response. These results indicate that the addition of a TLR7/8 and/or TLR4 agonist to a subunit vaccine containing RBD antigen and alum is a promising strategy for driving a Th1 response and neutralizing antibody titers targeting SARS-CoV-2.

Diamino Allose Phosphates: Novel, Potent, and Highly Stable Toll-like Receptor 4 Agonists

Most known synthetic toll-like receptor 4 (TLR4) agonists are carbohydrate-based lipid-A mimetics containing several fatty acyl chains, including a labile 3-O-acyl chain linked to the C-3 position of the non-reducing sugar known to undergo cleavage impacting stability and resulting in loss of activity. To overcome this inherent instability, we rationally designed a new class of chemically more stable synthetic TLR4 ligands that elicit robust innate and adaptive immune responses. This new class utilized a diamino allose phosphate (DAP) scaffold containing a nonhydrolyzable 3-amide bond instead of the classical 3-ester. Accordingly, the DAPs have significantly improved thermostability in aqueous formulations and potency relative to other known natural and synthetic TLR4 ligands. Furthermore, the DAP analogues function as potent vaccine adjuvants to enhance influenza-specific antibodies in mice and provide protection against lethal influenza virus challenges. This novel set of TLR4 ligands show promise as next-generation vaccine adjuvants and stand-alone immunomodulators.

A TLR4 agonist liposome formulation effectively stimulates innate immunity and enhances protection from bacterial infection

Stimulation of innate immunity can protect against infectious insult and could be used in combination with other therapies. Since antibiotic resistance is an increasing concern, strategies to reduce the dose or eliminate the need for these drugs are warranted. Lipo-CRX is a formulation in which the TLR4 agonist CRX-527 is incorporated into lipid membranes in liposomes. Lipo-CRX is less inflammatory than either CRX-527 or LPS, but retains unique capacity to enhance host defense responses. We compared lipo-CRX to other agonists in vitro using mammalian cells and in vivo in mice, and assessed indicators of innate immune responses and protection from bacterial infection. Lipo-CRX is similar to E. coli LPS in its capacity to activate bovine γδ T cells and to recruit neutrophils into mouse lungs, but with less reactivity in the LAL assay. However, lipo-CRX uniquely induced the production of systemic innate immune cytokines. In the mouse model of brucellosis, delivery of lipo-CRX to the lungs reduced the dissemination of B. abortus. While lipo-CRX or the antibiotic ampicillin alone did not alter B. abortus burdens in the lung, the combination had a synergistic beneficial effect. Our data suggest that stimulating the innate immune system with lipo-CRX, either alone or when combined with antibiotics, can enhance bacterial clearance in the mouse model of brucellosis.

Characterization of Dosage Levels for In Ovo Administration of Innate Immune Stimulants for Prevention of Yolk Sac Infection in Chicks

Innate immune stimulants, especially toll-like receptor (TLR) ligands and agonists, are the main players in the initiation of innate immunity and have been widely studied as alternatives to antibiotics to control infection. In the present study, we characterized the dosage levels of various innate immune stimulants, including unmethylated cytosine-phosphate-guanosine dinucleotide -containing oligodeoxynucleotides (CpG ODN), polyinosinic-polycytidylic acid (poly I:C), cyclic polyphosphazene 75B (CPZ75B), avian beta-defensin 2 (ABD2), and combinations of these reagents given in ovo. Data derived from a series of animal experiments demonstrated that the in ovo administration of 10–50 µg CpG ODN/embryo (on embryonic day 18) is an effective formulation for control of yolk sac infection (YSI) due to avian pathogenic Escherichia coli (E. coli) in young chicks. Amongst the different combinations of innate immune stimulants, the in ovo administration of CpG ODN 10 µg in combination with 15 µg of poly I:C was the most effective combination, offering 100% protection from YSI. It is expected that the introduction of these reagents to management practices at the hatchery level may serve as a potential replacement for antibiotics for the reduction of early chick mortality (ECM) due to YSI/colibacillosis.

Toll-Like Receptors (TLRs) as Therapeutic Targets for Treating SARS-CoV-2: An Immunobiological Perspective

INTRODUCTION

Coronavirus disease-19 (COVID-19) caused by SARS-CoV-2 is presently the biggest threat to mankind throughout the globe. Increasing reports on deaths, cases of new infection, and socioeconomic losses are continuously coming from all parts of the world. Developing an efficacious drug and/or vaccine is currently the major goal to the scientific communities. In this context, toll-like receptors (TLRs) could be the useful targets in adopting effective therapeutic approaches.

METHODS

This chapter has been written by incorporating the findings on TLR-based therapies against SARS-CoV-2 demonstrated in the recently published research papers/reviews.

RESULTS

TLRs are the essential components of host immunity and play critical roles in deciding the fate of SARS-CoV-2 by influencing the immunoregulatory circuits governing human immune response to this pathogen. Hitherto, a number of multi-subunit peptide-based vaccines and pharmacological agents developed against SARS-CoV-2 have been found to manipulate TLR function. Therefore, circumventing overt immunopathology of COVID-19 applying TLR-antagonists can effectively reduce the morality caused from "cytokine storm"-induced multiorgan failure. Similarly, pre-administration of TLR- agonists may be used as a prophylaxis to sensitize the immune system of the individuals having risk of infection. A lot of collaborative efforts are required for bench-to-bench transformation of these knowledges.

CONCLUSION

This chapter enlightens the potentials and promises of TLR-guided therapeutic strategies against COVID-19 by reviewing the major findings and achievements depicted in the literatures published till date.

MUC1 Specific Immune Responses Enhanced by Coadministration of Liposomal DDA/MPLA and Lipoglycopeptide

Mucin 1 (MUC1), a well-known tumor-associated antigen and attractive target for tumor immunotherapy, is overexpressed in most human epithelial adenomas with aberrant glycosylation. However, its low immunogenicity impedes the development of MUC1-targeted antitumor vaccines. In this study, we investigated three liposomal adjuvant systems containing toll-like receptor 4 (TLR4) agonist monophosphoryl lipid A (MPLA) and auxiliary lipids of different charges: cationic lipid dimethyldioctadecylammonium (DDA), neutral lipid distearoylglycerophosphocholine (DSPC) or anionic lipid dioleoylphosphatidylglycerol (DOPG), respectively. ELISA assay evidenced that the positively charged DDA/MPLA liposomes are potent immune activators, which induced remarkable levels of anti-MUC1 antibodies and exhibited robust Th1-biased immune responses. Importantly, the antibodies induced by DDA/MPLA liposomes efficiently recognized and killed MUC1-positive tumor cells through complement-mediated cytotoxicity. In addition, antibody titers in mice immunized with P2-MUC1 vaccine were significantly higher than those from mice immunized with P1-MUC1 or MUC1 vaccine, which indicated that the lipid conjugated on MUC1 antigen also played important role for immunomodulation. This study suggested that the liposomal DDA/MPLA with lipid-MUC1 is a promising antitumor vaccine, which can be used for the immunotherapy of various epithelial carcinomas represented by breast cancer.

The clinical role of host and bacterial-derived extracellular vesicles in pneumonia

Pneumonia is among the leading causes of morbidity and mortality worldwide. Due to constant evolution of respiratory bacteria and viruses, development of drug resistance and emerging pathogens, it constitutes a considerable health care threat. To enable development of novel strategies to control pneumonia, a better understanding of the complex mechanisms of interaction between host cells and infecting pathogens is vital. Here, we review the roles of host cell and bacterial-derived extracellular vesicles (EVs) in these interactions. We discuss clinical and experimental as well as pathogen-overarching and pathogen-specific evidence for common viral and bacterial elicitors of community- and hospital-acquired pneumonia. Finally, we highlight the potential of EVs for improved management of pneumonia patients and discuss the translational steps to be taken before they can be safely exploited as novel vaccines, biomarkers, or therapeutics in clinical practice.

TLR4 biased small molecule modulators

Biased pharmacological modulators provide potential therapeutic benefits, including greater pharmacodynamic specificity, increased efficiency and reduced adverse effects. Therefore, the identification of such modulators as drug candidates is highly desirable. Currently, attention was mainly paid to biased signaling modulators targeting G protein-coupled receptors (GPCRs). The biased signaling modulation of non-GPCR receptors has yet to be exploited. Toll-like receptor 4 (TLR4) is one such non-GPCR receptor, which involves MyD88-dependent and TRIF-dependent signaling pathways. Moreover, the dysregulation of TLR4 contributes to numerous diseases, which highlights the importance of biased modulator development targeting TLR4. In this review, we aim to provide an overview of the recent progress in the discovery of biased modulators of TLR4. The challenges and methods for the discovery of TLR4 biased modulators are also outlined. Small molecules biasedly modulating the TLR4 signaling axis not only provide probes to fine-tune receptor conformation and signaling but also provide an opportunity to identify promising drug candidates. The discovery of biased modulators of TLR4 would provide insight for the future development of biased modulators for other non-GPCR receptors.

Toll-Like Receptors: General Molecular and Structural Biology

BACKGROUND/AIM

Toll-like receptors (TLRs) are pivotal biomolecules in the immune system. Today, we are all aware of the importance of TLRs in bridging innate and adaptive immune system to each other. The TLRs are activated through binding to damage/danger-associated molecular patterns (DAMPs), microbial/microbe-associated molecular patterns (MAMPs), pathogen-associated molecular patterns (PAMPs), and xenobiotic-associated molecular patterns (XAMPs). The immunogenetic molecules of TLRs have their own functions, structures, coreceptors, and ligands which make them unique. These properties of TLRs give us an opportunity to find out how we can employ this knowledge for ligand-drug discovery strategies to control TLRs functions and contribution, signaling pathways, and indirect activities. Hence, the authors of this paper have a deep observation on the molecular and structural biology of human TLRs (hTLRs).

METHODS AND MATERIALS

To prepare this paper and fulfill our goals, different search engines (e.g., GOOGLE SCHOLAR), Databases (e.g., MEDLINE), and websites (e.g., SCOPUS) were recruited to search and find effective papers and investigations. To reach this purpose, we tried with papers published in the English language with no limitation in time. The iCite bibliometrics was exploited to check the quality of the collected publications.

RESULTS

Each TLR molecule has its own molecular and structural biology, coreceptor(s), and abilities which make them unique or a complementary portion of the others. These immunogenetic molecules have remarkable roles and are much more important in different sections of immune and nonimmune systems rather than that we understand to date.

CONCLUSION

TLRs are suitable targets for ligand-drug discovery strategies to establish new therapeutics in the fields of infectious and autoimmune diseases, cancers, and other inflammatory diseases and disorders.

TLR Agonists as Mediators of Trained Immunity: Mechanistic Insight and Immunotherapeutic Potential to Combat Infection

Despite advances in critical care medicine, infection remains a significant problem that continues to be complicated with the challenge of antibiotic resistance. Immunocompromised patients are highly susceptible to development of severe infection which often progresses to the life-threatening condition of sepsis. Thus, immunotherapies aimed at boosting host immune defenses are highly attractive strategies to ward off infection and protect patients. Recently there has been mounting evidence that activation of the innate immune system can confer long-term functional reprogramming whereby innate leukocytes mount more robust responses upon secondary exposure to a pathogen for more efficient clearance and host protection, termed trained immunity. Toll-like receptor (TLR) agonists are a class of agents which have been shown to trigger the phenomenon of trained immunity through metabolic reprogramming and epigenetic modifications which drive profound augmentation of antimicrobial functions. Immunomodulatory TLR agonists are also highly beneficial as vaccine adjuvants. This review provides an overview on TLR signaling and our current understanding of TLR agonists which show promise as immunotherapeutic agents for combating infection. A brief discussion on our current understanding of underlying mechanisms is also provided. Although an evolving field, TLR agonists hold strong therapeutic potential as immunomodulators and merit further investigation for clinical translation.

Streptococcus pneumoniae PepO promotes host anti-infection defense via autophagy in a Toll-like receptor 2/4 dependent manner

Macrophage is essential for host anti-bacterial defense by directly eliminating invading microbes and inducing a series of immune reactions. Here we identified a Streptococcus pneumoniae protein, PepO, as a TLR2/TLR4 bi-ligand. We found that PepO enhances macrophage unspecific phagocytosis and bactericidal activity, which is related to the induction of autophagy in macrophage, for the inhibition of autophagy significantly decreased the phagocytosis and bactericidal activity of PepO-treated macrophage. We confirmed that these effects of PepO are dependent on interacting with both TLR2 and TLR4. The tlr2 or tlr4 deficiency partially abolished the effect of PepO while tlr2/tlr4 deficiency abolished it completely. In vivo study demonstrated that PepO reduced the bacteria load in WT mice significantly, while the depletion of macrophage or tlr2/tlr4 deficiency abrogated the effect of PepO. Our findings suggested the therapeutic potential of PepO and provided experimental evidence for immunotherapy against infectious disease.

Self-Adjuvanting Cancer Vaccines from Conjugation-Ready Lipid A Analogues and Synthetic Long Peptides

Self-adjuvanting vaccines, wherein an antigenic peptide is covalently bound to an immunostimulating agent, have been shown to be promising tools for immunotherapy. Synthetic Toll-like receptor (TLR) ligands are ideal adjuvants for covalent linking to peptides or proteins. We here introduce a conjugation-ready TLR4 ligand, CRX-527, a potent powerful lipid A analogue, in the generation of novel conjugate-vaccine modalities. Effective chemistry has been developed for the synthesis of the conjugation-ready ligand as well as the connection of it to the peptide antigen. Different linker systems and connection modes to a model peptide were explored, and in vitro evaluation of the conjugates showed them to be powerful immune-activating agents, significantly more effective than the separate components. Mounting the CRX-527 ligand at the N-terminus of the model peptide antigen delivered a vaccine modality that proved to be potent in activation of dendritic cells, in facilitating antigen presentation, and in initiating specific CD8⁺ T-cell-mediated killing of antigen-loaded target cells in vivo. Synthetic TLR4 ligands thus show great promise in potentiating the conjugate vaccine platform for application in cancer vaccination.

TLR4 agonist protects against Trypanosoma cruzi acute lethal infection by decreasing cardiac parasite burdens

E6020 is a synthetic agonist of Toll-like receptor-4 (TLR4). The purpose of this study was to evaluate the effect of different doses of E6020-SE on Trypanosoma cruzi-specific immune responses and its ability to confer protection against acute lethal infection in mice. Forty female BALB/c were infected with 500 trypomastigotes of T cruzi H1 strain, divided into four groups (n = 10) and treated at 7- and 14-day post-infection (dpi) with different doses of E6020-SE or PBS (control). Survival was followed for 51 days, mice were euthanized and hearts were collected to evaluate parasite burden, inflammation and fibrosis. We found significantly higher survival and lower parasite burdens in mice injected with E6020-SE at all doses compared to the control group. However, E6020-SE treatment did not significantly reduce cardiac inflammation or fibrosis. On the other hand, E6020-SE modulated Th1 and Th2 cytokines, decreasing IFN-γ and IL-4 in a dose-dependent manner after stimulation with parasite antigens. We conclude that E6020-SE alone increased survival by decreasing cardiac parasite burdens in BALB/c mice acutely infected with T cruzi but failed to prevent cardiac damage. Our results suggest that for optimal protection, a vaccine antigen is necessary to balance and orient a protective immune response.

Dissociation of TRIF bias and adjuvanticity

Toll-like receptors (TLRs), a family of "pattern recognition receptors," bind microbial and host-derived molecules, leading to intracellular signaling and proinflammatory gene expression. TLR4 is unique in that ligand-mediated activation requires the co-receptor myeloid differentiation 2 (MD2) to initiate two signaling cascades: the MyD88-dependent pathway is initiated at the cell membrane, and elicits rapid MAP kinase and NF-κB activation, while the TIR-domain containing adaptor inducing interferon-β (TRIF)-dependent pathway is initiated from TLR4-containing endosomes and results in IRF3 activation. Previous studies associated inflammation with the MyD88 pathway and adjuvanticity with the TRIF pathway. Gram-negative lipopolysaccharide (LPS) is a potent TLR4 agonist, and structurally related molecules signal through TLR4 to differing extents. Herein, we compared monophosphoryl lipid A (sMPL) and E6020, two synthetic, non-toxic LPS lipid A analogs used as vaccine adjuvants, for their capacities to activate TLR4-mediated innate immune responses and to enhance antibody production. In mouse macrophages, high dose sMPL activates MyD88-dependent signaling equivalently to E6020, while E6020 exhibits significantly more activation of the TRIF pathway (a "TRIF bias") than sMPL. Eritoran, a TLR4/MD2 antagonist, competitively inhibited sMPL more strongly than E6020. Despite these differences, sMPL and E6020 adjuvants enhanced antibody responses to comparable extents, with balanced immunoglobulin (Ig) isotypes in two immunization models. These data indicate that a TRIF bias is not necessarily predictive of superior adjuvanticity.

Pattern Recognition Receptor Signaling and Innate Responses to Influenza A Viruses in the Mallard Duck, Compared to Humans and Chickens

Mallard ducks are a natural host and reservoir of avian Influenza A viruses. While most influenza strains can replicate in mallards, the virus typically does not cause substantial disease in this host. Mallards are often resistant to disease caused by highly pathogenic avian influenza viruses, while the same strains can cause severe infection in humans, chickens, and even other species of ducks, resulting in systemic spread of the virus and even death. The differences in influenza detection and antiviral effectors responsible for limiting damage in the mallards are largely unknown. Domestic mallards have an early and robust innate response to infection that seems to limit replication and clear highly pathogenic strains. The regulation and timing of the response to influenza also seems to circumvent damage done by a prolonged or dysregulated immune response. Rapid initiation of innate immune responses depends on viral recognition by pattern recognition receptors (PRRs) expressed in tissues where the virus replicates. RIG-like receptors (RLRs), Toll-like receptors (TLRs), and Nod-like receptors (NLRs) are all important influenza sensors in mammals during infection. Ducks utilize many of the same PRRs to detect influenza, namely RIG-I, TLR7, and TLR3 and their downstream adaptors. Ducks also express many of the same signal transduction proteins including TBK1, TRIF, and TRAF3. Some antiviral effectors expressed downstream of these signaling pathways inhibit influenza replication in ducks. In this review, we summarize the recent advances in our understanding of influenza recognition and response through duck PRRs and their adaptors. We compare basal tissue expression and regulation of these signaling components in birds, to better understand what contributes to influenza resistance in the duck.

Targeting toll-like receptor 4 to modulate neuroinflammation in central nervous system disorders

Introduction: Adverse immune activation contributes to many central nervous system (CNS) disorders. All main CNS cell types express toll-like receptor 4 (TLR 4). This receptor is critical for a myriad of immune functions such as cytokine secretion and phagocytic activity of microglia; however, imbalances in TLR 4 activation can contribute to the progression of neurodegenerative diseases. Areas covered: We considered available evidence implicating TLR 4 activation in the following CNS pathologies: Alzheimer's disease, Parkinson's disease, ischemic stroke, traumatic brain injury, multiple sclerosis, multiple systems atrophy, and Huntington's disease. We reviewed studies reporting effects of TLR 4-specific antagonists and agonists in models of peripheral and CNS diseases from the perspective of possible future use of TLR 4 ligands in CNS disorders. Expert opinion: TLR 4-specific antagonists could suppress neuroinflammation by reducing overproduction of inflammatory mediators; however, they may interfere with protein clearance mechanisms and myelination. Agonists that specifically activate myeloid differentiation primary-response protein 88 (MyD88)-independent pathway of TLR 4 signaling could facilitate beneficial glial phagocytic activity with limited activity as inducers of proinflammatory mediators. Deciphering the disease stage-specific involvement of TLR 4 in CNS pathologies is crucial for the future clinical development of TLR 4 agonists and antagonists.

TLRs in pulmonary diseases

Toll-like receptors (TLRs) comprise a clan of proteins involved in identification and triggering a suitable response against pathogenic attacks. As lung is steadily exposed to multiple infectious agents, antigens and host-derived danger signals, the inhabiting stromal and myeloid cells of the lung express an aggregate of TLRs which perceive the endogenously derived damage-associated molecular patterns (DAMPs) along with pathogen associated molecular patterns (PAMPs) and trigger the TLR-associated signalling events involved in host defence. Thus, they form an imperative component of host defence activation in case of microbial infections as well as non-infectious pulmonary disorders such as interstitial lung disease, acute lung injury and airways disease, such as COPD and asthma. They also play an equally important role in lung cancer. Targeting the TLR signalling network would pave ways to the design of more reliable and effective vaccines against infectious agents and control deadly infections, desensitize allergens and reduce inflammation. Moreover, TLR agonists may act as adjuvants by increasing the efficiency of cancer vaccines, thereby contributing their role in treatment of lung cancer too. Overall, TLRs present a compelling and expeditiously bolstered area of research and addressing their signalling events would be of significant use in pulmonary diseases.

Inhibition of Cyclin-dependent Kinase 2 Signaling Prevents Liver Ischemia and Reperfusion Injury

BACKGROUND

Liver ischemia and reperfusion injury (IRI) is a major complication of liver transplant, hepatectomy, and hemorrhagic shock. The cyclin-dependent kinase 2 (CDK2) acts as a pivotal regulator of cell cycle and proliferation.

METHODS

This study evaluated the modulation and therapeutic potential of CDK2 inhibition in a mouse model of partial liver warm IRI.

RESULTS

Liver IR-triggered intrinsic CDK2 expression, peaking by 0.5 hour of reperfusion and maintaining a high-level throughout 1 to 24 hours. Roscovitine, a specific CDK2 inhibitor, prevented liver IR-mediated damage with abolished serum alanine aminotransferase levels and reserved liver pathology. CDK2 inhibition-mediated liver protection was accompanied by decreased macrophage/neutrophil infiltration, diminished hepatocyte apoptosis, abolished toll like receptor 4 signaling and downstream gene inductions (C-X-C motif ligand-10, Tumor necrosis factor-α, interleukin-1β, and interleukin-6), yet augmented interleukin-10 expression. In vitro, CDK2 inhibition by Roscovitine suppressed macrophage TLR4 activation and further depressed downstream inflammatory signaling (myeloid differentiation factor 88, interferon regulatory transcription factor 3, p38, c-Jun N-terminal kinase, and extracellular-regulated kinase).

CONCLUSIONS

Our novel findings revealed the critical role of CDK2 in hepatic cytoprotection and homeostasis against liver IRI. As CDK2 inhibition regulated local immune response and prevented hepatocyte death, this study provided the evidence for new treatment approaches to combat IRI in liver transplant.

A Systems and Treatment Perspective of Models of Influenza Virus-Induced Host Responses

Severe influenza infections are often characterized as having unique host responses (e.g., early, severe hypercytokinemia). Neuraminidase inhibitors can be effective in controlling the severe symptoms of influenza but are often not administered until late in the infection. Several studies suggest that immune modulation may offer protection to high risk groups. Here, we review the current state of mathematical models of influenza-induced host responses. Selecting three models with conserved immune response components, we determine if the immune system components which most affect virus replication when perturbed are conserved across the models. We also test each model’s response to a pre-induction of interferon before the virus is administered. We find that each model emphasizes the importance of controlling the infected cell population to control viral replication. Moreover, our work shows that the structure of current models does not allow for significant responses to increased interferon concentrations. These results suggest that the current library of available published models of influenza infection does not adequately represent the complex interactions of the virus, interferon, and other aspects of the immune response. Specifically, the method used to model virus-resistant cells may need to be adapted in future work to more realistically represent the immune response to viral infection.

CD14 is critical for TLR2-mediated M1 macrophage activation triggered by N-glycan recognition

Agonist interaction with Toll-like receptors (TLRs) induces T cell-mediated immunity, which is effective against intracellular pathogens. Consequently, TLR agonists are being tried as immunomodulatory agents. The lectin ArtinM targets TLR2 N-glycans on macrophages, induces cytokines production, and promotes T helper-1 immunity, a process that culminates in resistance to several parasitic and fungal infections in vivo. Because co-receptors influence agonist binding to TLRs, we investigated whether CD14 is required for macrophage activation induced by ArtinM. Macrophages from wild-type mice stimulated by ArtinM not only produced cytokines but also had the following activation profile: (i) expression of M1 polarization markers; (ii) nitrite oxide production; (iii) cellular migration; (iv) enhanced phagocytic and fungicide activity; (v) modulation of TLR2 expression; and (vi) activation of NF-κB pathway. This activation profile induced by ArtinM was evaluated in macrophages lacking CD14 that showed none of the ArtinM effects. We demonstrated by immunoprecipitation and sugar inhibition assays the physical interaction of ArtinM, TLR2, and CD14, which depends on recognition of the trimannoside that constitutes the core of N-glycans. Thus, our study showed that CD14 is critical for ArtinM-induced macrophage activation, providing fundamental insight into the design of anti-infective therapies based on carbohydrate recognition.

Role of Toll-like receptor 4 in drug-drug interaction between paclitaxel and irinotecan in vitro

The bacterial receptor, Toll-like receptor (TLR) 4 mediates inflammatory responses and has been linked to a broad array of diseases. TLR4 agonists are being explored as potential treatments for cancer and other diseases. We have previously shown that activation of TLR4 by lipopolysaccharide (LPS) leads to down-regulation of drug metabolizing enzymes/transporters (DMETs), and altered pharmacokinetics/pharmacodynamics (PK/PD) of drugs. These changes can increase the risk of drug-drug interactions (DDIs) in patients on multiple medications. Clinically, DDI was observed for combination chemotherapy of paclitaxel (TLR4 ligand) and irinotecan. To determine the role of TLR4 in DDI between paclitaxel and irinotecan in vitro, primary hepatocytes from TLR4-wild-type (WT) and mutant mice were pre-treated with paclitaxel, followed by irinotecan. Gene expression of DMETs was determined. Paclitaxel treatment increased the levels of irinotecan metabolites, SN-38 and SN-38 glucuronide (SN-38G) in TLR4-dependent manner. Paclitaxel-mediated induction of genes involved in irinotecan metabolism such as Cyp3a11 and Ugt1a1 was TLR4-dependent, while induction of the transporter Mrp2 was TLR4-independent. These novel findings demonstrate that paclitaxel can affect irinotecan metabolism by a TLR4-dependent mechanism. This provides a new perspective towards evaluation of marketed drugs according to their potential to exert DDIs in TLR4-dependent manner.

TLR4 agonists as immunomodulatory agents

Monophosphoryl lipid A (MPL®) is a potent vaccine adjuvant derived from Salmonella minnesota that was recently licensed in Europe as a component of an improved vaccine for hepatitis B (Fendrix®). MPL, like lipopolysaccharide from which it is derived, signals via the TLR4/MD-2 complex. We have produced a series of synthetic Toll-like receptor 4 (TLR4) agonists that are based upon the structure of the major hexa-acylated congener contained within MPL. These TLR4 agonists, termed the aminoalkyl glucosaminide phosphates (AGPs), stimulate the production of various cytokines by human peripheral blood mononuclear cells in vitro and up-regulate cell surface markers on monocytes, NK cells and B cells. In addition, AGPs provide non-specific resistance to challenge with viral and bacterial pathogens when administered to the upper airways of mice. Structure—activity relationship studies have shown that the activation of innate immune effectors by AGPs depends primarily on the length of the secondary acyl chains and the nature of the functional group attached to the aglycon component. Moreover, AGPs can act as potent adjuvants for mucosal administration of vaccine antigens, enhancing both antigen-specific antibody and cell-mediated immune responses. Thus, by combining the adjuvant and non-specific resistance induction properties of AGPs it may be possible to generate mucosal vaccines that provide innate protection immediately following administration together with long-term acquired immunity.

Innate Immunity and Immune Evasion by Enterovirus 71

Enterovirus 71 (EV71) is a major infectious disease affecting millions of people worldwide and it is the main etiological agent for outbreaks of hand foot and mouth disease (HFMD). Infection is often associated with severe gastroenterological, pulmonary, and neurological diseases that are most prevalent in children. Currently, no effective vaccine or antiviral drugs exist against EV71 infection. A lack of knowledge on the molecular mechanisms of EV71 infection in the host and the virus-host interactions is a major constraint to developing specific antiviral strategies against this infection. Previous studies have identified and characterized the function of several viral proteins produced by EV71 that interact with the host innate immune proteins, including type I interferon signaling and microRNAs. These interactions eventually promote efficient viral replication and increased susceptibility to the disease. In this review we discuss the functions of EV71 viral proteins in the modulation of host innate immune responses to facilitate viral replication.

Gene expression profiles identify both MyD88-independent and MyD88-dependent pathways involved in the maturation of dendritic cells mediated by heparan sulfate: a novel adjuvant

The traditional vaccine adjuvant research is mainly based on the trial and error method, and the mechanisms underlying the immune system stimulation remaining largely unknown. We previously demonstrated that heparan sulfate (HS), a TLR-4 ligand and endogenous danger signal, effectively enhanced humoral and cellular immune responses in mice immunized by HBsAg. This study aimed to evaluate whether HS induces better humoral immune responses against inactivated Hepatitis A or Rabies Vaccines, respectively, compared with traditional adjuvants (e.g. Alum and complete Freund's adjuvant). In order to investigate the molecular mechanisms of its adjuvanticity, the gene expression pattern of peripheral blood monocytes derived DCs (dendritic cells) stimulated with HS was analyzed at different times points. Total RNA was hybridized to Agilent SurePrint G3 Human Gene Expression 8×60 K one-color oligo-microarray. Through intersection analysis of the microarray results, we found that the Toll-like receptor signaling pathway was significantly activated, and NF-kB, TRAF3 and IRF7 were activated as early as 12 h, and MyD88 was activated at 48 h post-stimulation. Furthermore, the expression of the surface marker CD83 and the co-stimulatory molecules CD80 and CD86 was up-regulated as early as 24 h. Therefore, we speculated that HS-induced human monocyte-derived DC maturation may occur through both MyD88-independent and dependent pathways, but primarily through the former (TRIF pathway). These data provide an important basis for understanding the mechanisms underlying HS enhancement of the immune response.

Modulating LPS signal transduction at the LPS receptor complex with synthetic Lipid A analogues

Sepsis, defined as a clinical syndrome brought about by an amplified and dysregulated inflammatory response to infections, is one of the leading causes of death worldwide. Despite persistent attempts to develop treatment strategies to manage sepsis in the clinical setting, the basic elements of treatment have not changed since the 1960s. As such, the development of effective therapies for reducing inflammatory reactions and end-organ dysfunction in critically ill patients with sepsis remains a global priority. Advances in understanding of the immune response to sepsis provide the opportunity to develop more effective pharmaceuticals. This article details current information on the modulation of the lipopolysaccharide (LPS) receptor complex with synthetic Lipid A mimetics. As the initial and most critical event in sepsis pathophysiology, the LPS receptor provides an attractive target for antisepsis agents. One of the well-studied approaches to sepsis therapy involves the use of derivatives of Lipid A, the membrane-anchor portion of an LPS, which is largely responsible for its endotoxic activity. This article describes the structural and conformational requirements influencing the ability of Lipid A analogues to compete with LPS for binding to the LPS receptor complex and to inhibit the induction of the signal transduction pathway by impairing LPS-initiated receptor dimerization.

The stimulatory effect of the TLR4-mediated adjuvant glucopyranosyl lipid A is well preserved in old age

Many subunit vaccines require adjuvants to improve their limited immunogenicity. Various adjuvant candidates targeting toll-like receptors (TLRs) are currently under development including the synthetic TLR4 agonist glucopyranosyl lipid A (GLA). GLA has been investigated in the context of influenza vaccine, which is of particular importance for the elderly population. This study investigates the effect of GLA on antigen-presenting cells from young (median age 29 years, range 26-33 years) and older (median age 72 years, range 61-78 years) adults. Treatment with GLA efficiently increases the expression of co-stimulatory molecules on human monocyte-derived dendritic cells (DC) as well as on ex vivo myeloid DC. Expression of co-stimulatory molecules is less pronounced on ex vivo monocytes. Production of pro-inflammatory cytokines (IL-6, TNF-α, IL-12) as well as of the anti-inflammatory cytokine IL-10 is induced in monocyte-derived DC. In PBMC cultures myeloid DC and to an even greater extent monocytes produce TNF-α and IL-6 after stimulation with GLA. Production of IL-12 can also be observed in these cultures. There are no age-related differences in the capacity of GLA to induce expression of co-stimulatory molecules or production of cytokines by human antigen-presenting cells. Therefore, TLR4 agonists like GLA are particularly promising candidates as adjuvants of vaccines designed for elderly individuals.

Toll-like receptor 4 is essential to preserving cardiac function and survival in low-grade polymicrobial sepsis

BACKGROUND

Toll-like receptor 4 (TLR4), the receptor for endotoxin, mediates hyperinflammatory response and contributes to high mortality during both endotoxin shock and severe sepsis. However, little is known about the role of TLR4 in the pathogenesis of low-grade polymicrobial sepsis, which is often associated with immunosuppression.

METHODS

Low-grade polymicrobial sepsis was generated by cecum ligation and puncture. Mortality was monitored in wild- type (C57BL/10ScSn) and TLR4def (C57BL/10ScCr) mice. Ex vivo heart and individual cardiomyocyte function were assessed in Langendorff (Hugo Sachs Elektronik; Harvard Apparatus, Holliston, MA) and IonOptix systems (IonOptix, Milton, MA), respectively. Serum chemistry was tested for liver and kidney injury. Cytokines were examined using a multiplex immunoassay. Neutrophil migratory and phagocytic functions were assessed using flow cytometry. Reactive oxygen species were measured using redox-sensitive dichlorodihydrofluorescein dye.

RESULTS

Following cecum ligation and puncture, wild-type mice developed bacterial peritonitis with mild cardiac dysfunction (n=3 in sham and n=8 in cecum ligation and puncture) and a mortality of 23% within 14 days (n=22). In comparison, septic TLR4def mice had deleterious cardiac dysfunction (n=6 in sham and n=10 in cecum ligation and puncture), kidney and liver injury (n=7), and much higher mortality at 81% (n=21). The deleterious effects observed in septic TLR4def mice were associated with increased local and systemic cytokine response, reduced neutrophil migratory and phagocytic function, increased reactive oxygen species generation in leukocytes, and impaired bacterial clearance.

CONCLUSION

TLR4 plays an essential role in host defense against low-grade polymicrobial sepsis by mediating neutrophil migratory/phagocytic functions, attenuating inflammation, reducing reactive oxygen species generation, and enhanced bacterial clearance.

Toll-like receptor 7 promotes the apoptosis of THP-1-derived macrophages through the CHOP-dependent pathway

Macrophage apoptosis is a prominent characteristic of advanced atherosclerotic plaques and leads to plaque destabilization. Certain studies have confirmed that influenza virus A (IVA) infection is related to acute myocardial infarction (AMI). However, it remains unknown as to whether this phenomenon is associated with Toll-like receptor (TLR)7, since single-stranded RNA (ssRNA) of IVA is a natural ligand of TLR7. Thus, in the present study, THP-1‑derived macrophages were infected with IVA or treated with imiquimod (IMQ) in the presence or absence of pre-treatment with oxidized low-density lipoprotein (oxLDL). The macrophages were pre-treated with oxLDL (5 µg/ml) for 24 h to mimic high lipid conditions. Cell viability and apoptosis were detected by 3-(4,5-dimethylthiazol-2-y-1)‑2,5-diphenyl-2H-tetrazolium bromide (MTT) assay and flow cytometry, respectively. Our results revealed that TLR7 played an important role in macrophage apoptosis and cytokine secretion. Both IVA infection and IMQ treatment increased TLR7 expression, as well as the secretion of pro-inflammatory cytokines [interleukin (IL)-6, monocyte chemotactic protein (MCP)-1] and apoptosis. However, this increase in cytokine secretion occurred independently of cell apoptosis. oxLDL had potential synergistic pro-apoptotic effects combined with TLR7 activation. To determine whether endoplasmic reticulum (ER) stress plays a role in cell apoptosis, the mRNA and protein expression of known markers of ER stress [glucose-regulated protein (GRP)78 and C/EBP homologous protein (CHOP)] was detected by reverse transcription PCR (RT-PCR), quantitative reverse transcription PCR (qRT-PCR) and western blot analysis. Our results revealed that apoptosis aggravated ER stress, as shown by the overexpression of the pro-apoptotic sensor, CHOP. In conclusion, our study demonstrates the converging role of oxLDL pre-treatment, IVA infection and IMQ in ER stress-induced cell apoptosis.

TLR Agonists as Modulators of the Innate Immune Response and Their Potential as Agents Against Infectious Disease

Immunotherapies that can either activate or suppress innate immune responses are being investigated as treatments against infectious diseases and the pathology they can cause. The objective of these therapies is to elicit protective immune responses thereby limiting the harm inflicted by the pathogen. The Toll-like receptor (TLR) signaling pathway plays critical roles in numerous host immune defenses and has been identified as an immunotherapeutic target against the consequences of infectious challenge. This review focuses on some of the recent advances being made in the development of TLR-ligands as potential prophylactic and/or therapeutic agents.

Intranasal vaccination promotes detrimental Th17-mediated immunity against influenza infection

Influenza disease is a global health issue that causes significant morbidity and mortality through seasonal epidemics. Currently, inactivated influenza virus vaccines given intramuscularly or live attenuated influenza virus vaccines administered intranasally are the only approved options for vaccination against influenza virus in humans. We evaluated the efficacy of a synthetic toll-like receptor 4 agonist CRX-601 as an adjuvant for enhancing vaccine-induced protection against influenza infection. Intranasal administration of CRX-601 adjuvant combined with detergent split-influenza antigen (A/Uruguay/716/2007 (H3N2)) generated strong local and systemic immunity against co-administered influenza antigens while exhibiting high efficacy against two heterotypic influenza challenges. Intranasal vaccination with CRX-601 adjuvanted vaccines promoted antigen-specific IgG and IgA antibody responses and the generation of polyfunctional antigen-specific Th17 cells (CD4⁺IL-17A⁺TNFα⁺). Following challenge with influenza virus, vaccinated mice transiently exhibited increased weight loss and morbidity during early stages of disease but eventually controlled infection. This disease exacerbation following influenza infection in vaccinated mice was dependent on both the route of vaccination and the addition of the adjuvant. Neutralization of IL-17A confirmed a detrimental role for this cytokine during influenza infection. The expansion of vaccine-primed Th17 cells during influenza infection was also accompanied by an augmented lung neutrophilic response, which was partially responsible for mediating the increased morbidity. This discovery is of significance in the field of vaccinology, as it highlights the importance of both route of vaccination and adjuvant selection in vaccine development

Influenza virus remains a global health risk causing significant morbidity and mortality each year, with the elderly (>65 years) and the very young particularly prone to severe respiratory disease. Scientists are working to develop highly efficacious vaccines capable of eliciting broad cross-clade protection from influenza infection. Adjuvants as well as the route of immunization are known to modulate the type, quality and breadth of immune responses to vaccines. In this study, we demonstrated intranasal vaccination with influenza antigens, and a novel synthetic TLR4-based adjuvant system provided protection against a lethal heterologous viral challenge. Immunization stimulated mucosal influenza-specific IgA antibody responses together with systemic IgG antibodies. While intranasal immunization stimulated the production of protective antibodies, vaccination via this route also promoted the generation of influenza-specific Th17 CD4⁺ T cells. These vaccine-induced Th17 cells increased inflammation and morbidity without contributing to viral clearance following challenge. Antibody neutralization of IL-17A during influenza infection significantly reduced the enhanced lung neutrophilic response, which was partially responsible for mediating the increased morbidity. This discovery is of significance in the field of vaccinology, as it demonstrates the importance of both route of immunization and adjuvant selection in vaccine development.

Adjuvant immunotherapies as a novel approach to bacterial infections

The rapid emergence of multidrug-resistant pathogens, especially Gram-negative bacteria and mycobacteria, represents one of the major medical challenges of the 21st century. The gradual loss of effective classical antibiotics for many bacterial pathogens, combined with an increasing population density and mobility, urgently calls for the development of novel treatments. Here, we discuss the potential of adjuvant immunotherapies to selectively stimulate protective immune responses as a treatment option for bacterial infections. In order to elicit appropriate immune responses and to avoid unwanted inflammatory tissue damage, it is essential to identify ligands and receptor pathways that specifically control protective responses at the site of infection. We summarize existing data and discuss suitable candidate targets for future immunotherapies of infectious diseases.

Transient lipopolysaccharide-induced resistance to aerosolized Bacillus anthracis in New Zealand white rabbits

Previous studies have demonstrated that prior infection by various bacterial pathogens induces nonspecific resistance to subsequent infection by other gram-negative and gram-positive bacterial pathogens. In the present study, we evaluated whether underlying inflammation enhanced host resistance to inhalational Bacillus anthracis infection in New Zealand White rabbits (SPF; Bordetella- and Pasteurella-free). Accordingly, rabbits were pretreated with either the inflammagen bacterial LPS (60,000 EU/kg), a component of the outer membrane of gram-negative bacteria, or saline (vehicle). Administration of LPS resulted in brief pyrexia and a significant increase in the proinflammatory cytokine TNFα, thus confirming LPS-induced inflammation. At 24 h after LPS treatment, rabbits were exposed to aerosolized B. anthracis spores (Ames strain; approximately 300 LD50). Blood samples collected at various times after challenge were cultured. Compared with their saline-pretreated counterparts, LPS-pretreated, B. anthracis challenged rabbits exhibited delays in 2 biomarkers of B. anthracis infection-anthrax-induced pyrexia (25 h versus 66 h after challenge, respectively) and bacteremia (26 h versus 63 h, respectively)-and survived longer (41 h versus 90 h, respectively). Similar to control animals, all LPS-pretreated, B. anthracis-challenged rabbits exhibited pathology consistent with inhalational anthrax. Taken together, these results suggest that prior or underlying stimulation of the innate immune system induces transient host resistance to subsequent B. anthracis infection in SPF New Zealand white rabbits. In particular, our results emphasize the importance of using animals that are free of underlying infections to prevent confounding data in studies for inhalational anthrax characterization and medical countermeasure evaluation.

Moraxella catarrhalis: from interactions with the host immune system to vaccine development

Moraxella catarrhalis is a human-restricted commensal that over the last two decades has developed into an emerging respiratory tract pathogen. The bacterial species is equipped with various adhesins to facilitate its colonization. Successful evasion of the human immune system is a prerequisite for Moraxella infection. This strategy involves induction of an excessive proinflammatory response, intervention of granulocyte recruitment to the infection site, activation of selected pattern recognition receptors and cellular adhesion molecules to counteract the host bacteriolytic attack, as well as, finally, reprogramming of antigen presenting cells. Host immunomodulator molecules are also exploited by Moraxella to aid in resistance against complement killing and host bactericidal molecules. Thus, breaking the basis of Moraxella immune evasion mechanisms is fundamental for future invention of effective therapy in controlling Moraxella infection.

Prophylactic treatment with Toll-like receptor ligands enhances host immunity to avian influenza virus in chickens

Avian influenza viruses (AIV) pose a threat towards the health of both poultry and humans. To interrupt the transmission of the virus, novel prophylactic strategies must be considered which may reduce the shedding of AIV. One potential is the prophylactic use of Toll-like receptor (TLR) ligands. Many cells of the immune system express TLRs, and cellular responses to TLR stimulation include activation and the production of cytokines. TLR ligands have been employed as prophylactic treatments to enhance host resistance to pathogens both in mammals and chickens. Therefore, the present study was conducted to determine whether TLR ligands may be used prophylactically in chickens to enhance host immunity to AIV. Chickens received intramuscular injections of either low or high doses of the TLR ligands poly I:C, lipopolysaccharide (LPS) and CpG ODN. Twenty-four hours post-treatment, chickens were infected with the low pathogenic avian influenza virus H4N6, and both oropharyngeal and cloacal virus shedding were assessed on days 4 and 7 post-infection. To identify potential correlates of immunity, spleen and lungs were collected on days 2, 4 and 7 post-infection for RNA extraction. The results suggested that all of the TLR ligand treatments induced a significant reduction in virus shedding, with the TLR3 ligand poly I:C conferring the greatest AIV immunity compared to control birds, followed by CpG ODN and LPS. Furthermore, transcriptional analysis of gene expression in the spleen and lungs suggest IFN-α and IL-8 as correlates of immunity conferred by poly I:C, and IFN-γ for CpG ODN and LPS. In conclusion, TLR ligands, have the ability to enhance host immunity against AIV, and future studies should consider exploring the combinatory effects of poly I:C and CpG ODN prophylaxis in conjunction with AIV vaccination.

Antiviral applications of Toll-like receptor agonists

In the past, antiviral research has focused mainly on viral targets. As the search for effective and differentiated antiviral therapies continues, cellular targets are becoming more common, bringing with them a variety of challenges and concerns. Toll-like receptors (TLRs) provide a unique mechanism to induce an antiviral state in the host. In this review we introduce TLRs as targets for the pharmaceutical industry, including how they signal and thereby induce an antiviral state through the production of type I interferons. We examine how TLRs are being therapeutically targeted and discuss several clinically precedented agents for which efficacy and safety data are available. We describe some of the chemistries that have been applied to both small molecule and large molecule leads to tune agonist potency, and offer a differentiated safety profile through targeting certain compartments such as the gut or the lung, thereby limiting systemic drug exposure and affecting systemic cytokine levels. The application of low-dose agonists of TLRs as vaccine adjuvants or immunoprotective agents is also presented. Some of the challenges presented by this approach are then discussed, including viral evasion strategies and mechanism-linked inflammatory cytokine induction.

Safety and immunogenicity of a novel nanoemulsion mucosal adjuvant W805EC combined with approved seasonal influenza antigens

BACKGROUND

Improving the systemic and mucosal immune response following intranasal vaccination could enhance disease protection against respiratory pathogens. We assessed the safety and immunogenicity of a novel nanoemulsion mucosal adjuvant W(80)5EC combined with approved seasonal influenza antigens.

METHODS

This was a first-in-human Phase I study in 199 healthy adult volunteers randomized to receive a single intranasal administration of 5%, 10%, 15% or 20% W(80)5EC, combined with 4 or 10 μg strain-specific Fluzone(®) HA, compared with intranasal PBS, intranasal Fluzone(®), or 15 ug strain-specific intramuscular Fluzone(®). Safety was evaluated by physical examination, laboratory parameters, symptom diaries, and adverse event reports. Serum HAI titers and nasal wash IgA were assessed at baseline as well as 28 and 60 days after vaccination.

RESULTS

W(80)5EC adjuvant combined with seasonal influenza antigens was well tolerated without safety concerns or significant adverse events. The highest dose of 20% W(80)5EC combined with 10 μg strain-specific HA elicited clinically meaningful systemic immunity based on increases in serum HAI GMT and ≥ 70% seroprotection for all 3 influenza strains, as well as a rise in antigen-specific IgA in nasal wash specimens.

CONCLUSIONS

W(80)5EC adjuvant was safe and well tolerated in healthy adult volunteers and elicited both systemic and mucosal immunity following a single intranasal vaccination.

The TLR4-TRIF pathway protects against H5N1 influenza virus infection

Prestimulation of the TLR4 pathway with lipopolysaccharide (LPS) protects mice from lethal infection with H5N1 influenza virus. Here, we reveal that the TLR4-TRIF pathway is required for this protective effect by using mice whose TLR4-related molecules were knocked out. Microarray analysis of primary mouse lung culture cells that were LPS pretreated and infected with an H5N1 virus indicated that TLR3 mRNA was upregulated. Primary lung culture cells of TLR3 knockout mice showed no response to LPS pretreatment against H5N1 virus infection, suggesting that TLR3 is also involved in the preventive effect of LPS. Our data suggest that the TLR4-TRIF axis has an important role in stimulating protective innate immunity against H5N1 influenza A virus infection and that TLR3 signaling is involved in this pathway.

Carbohydrate-based immune adjuvants

The role for adjuvants in human vaccines has been a matter of vigorous scientific debate, with the field hindered by the fact that for over 80 years, aluminum salts were the only adjuvants approved for human use. To this day, alum-based adjuvants, alone or combined with additional immune activators, remain the only adjuvants approved for use in the USA. This situation has not been helped by the fact that the mechanism of action of most adjuvants has been poorly understood. A relative lack of resources and funding for adjuvant development has only helped to maintain alum's relative monopoly. To seriously challenge alum's supremacy a new adjuvant has many major hurdles to overcome, not least being alum's simplicity, tolerability, safety record and minimal cost. Carbohydrate structures play critical roles in immune system function and carbohydrates also have the virtue of a strong safety and tolerability record. A number of carbohydrate compounds from plant, bacterial, yeast and synthetic sources have emerged as promising vaccine adjuvant candidates. Carbohydrates are readily biodegradable and therefore unlikely to cause problems of long-term tissue deposits seen with alum adjuvants. Above all, the Holy Grail of human adjuvant development is to identify a compound that combines potent vaccine enhancement with maximum tolerability and safety. This has proved to be a tough challenge for many adjuvant contenders. Nevertheless, carbohydrate-based compounds have many favorable properties that could place them in a unique position to challenge alum's monopoly over human vaccine usage.

Targeting of Toll-like receptors: a decade of progress in combating infectious diseases

Toll-like receptors (TLRs) recognise highly conserved molecular structures, collectively known as pathogen-associated molecular patterns. In the past two decades, development and clinical implementation of TLR ligands-ie, chemically modified synthetic derivatives of naturally occurring ligands and fully synthetic small molecules-have been topics of intense research. Targeted manipulation of TLR signalling has been applied clinically to boost vaccine effectiveness, promote a robust T helper 1-predominant immune response against viral infection, or dampen the exaggerated inflammatory response to bacterial infection. Use of these new therapeutic molecules as adjuncts to conventional pharmacotherapy or stand-alone treatments might offer solutions to unmet clinical needs or could replace existing partly effective therapeutic strategies.

Synergistic interactions of TLR2/6 and TLR9 induce a high level of resistance to lung infection in mice

Infectious pneumonias exact an unacceptable mortality burden worldwide. Efforts to protect populations from pneumonia have focused historically on antibiotic development and vaccine-enhanced adaptive immunity. However, we have reported recently that the lungs' innate defenses can be induced therapeutically by inhalation of a bacterial lysate that protects mice against otherwise lethal pneumonia. In this study, we tested in mice the hypothesis that TLRs are required for this antimicrobial phenomenon and found that resistance could not be induced in the absence of the TLR signaling adaptor protein MyD88. We then attempted to recapitulate the protection afforded by the bacterial lysate by stimulating the lung epithelium with aerosolized synthetic TLR ligands. Although most single or combination treatments yielded no protection, simultaneous treatment with ligands for TLR2/6 and TLR9 conferred robust, synergistic protection against virulent gram-positive and gram-negative pathogens. Protection was associated with rapid pathogen killing in the lungs, and pathogen killing could be induced from lung epithelial cells in isolation. Taken together, these data demonstrate the requirement for TLRs in inducible resistance against pneumonia, reveal a remarkable, unanticipated synergistic interaction of TLR2/6 and TLR9, reinforce the emerging evidence supporting the antimicrobial capacity of the lung epithelium, and may provide the basis for a novel clinical therapeutic that can protect patients against pneumonia during periods of peak vulnerability.

Toll-like receptor pre-stimulation protects mice against lethal infection with highly pathogenic influenza viruses

Since the beginning of the 20th century, humans have experienced four influenza pandemics, including the devastating 1918 'Spanish influenza'. Moreover, H5N1 highly pathogenic avian influenza (HPAI) viruses are currently spreading worldwide, although they are not yet efficiently transmitted among humans. While the threat of a global pandemic involving a highly pathogenic influenza virus strain looms large, our mechanisms to address such a catastrophe remain limited. Here, we show that pre-stimulation of Toll-like receptors (TLRs) 2 and 4 increased resistance against influenza viruses known to induce high pathogenicity in animal models. Our data emphasize the complexity of the host response against different influenza viruses, and suggest that TLR agonists might be utilized to protect against lethality associated with highly pathogenic influenza virus infection in humans.

Immunomodulators as adjuvants for vaccines and antimicrobial therapy

A highly effective strategy for combating infectious diseases is to enhance host defenses using immunomodulators, either preventatively, through vaccination, or therapeutically. The effectiveness of many vaccines currently in use is due in part to adjuvants, molecules that have little immunogenicity by themselves but which help enhance and appropriately skew the immune response to an antigen. The development of new vaccines necessitates the development of new types of adjuvants to ensure an appropriate immune response. Herein, we review commonly used vaccine adjuvants and discuss promising adjuvant candidates. We also discuss various other immunomodulators (namely cytokines, Toll-like receptor agonists, and host defense peptides) that are, or have potential to be, useful for antimicrobial therapies that exert their effects by boosting host immune responses rather than targeting pathogens directly.

Targeting Toll-like receptors: emerging therapeutics?

There is a growing interest in the targeting of Toll-like receptors (TLRs) for the prevention and treatment of cancer, rheumatoid arthritis, inflammatory bowel disease and systemic lupus erythematosus (SLE). Several new compounds are now undergoing preclinical and clinical evaluation, with a particular focus on TLR7 and TLR9 activators as adjuvants in infection and cancer, and inhibitors of TLR2, TLR4, TLR7 and TLR9 for the treatment of sepsis and inflammatory diseases. Here, we focus on TLRs that hold the most promise for drug discovery research, highlighting agents that are in the discovery phase and in clinical trials,and on the emerging new aspects of TLR-mediated signalling - such as control by ubiquitination and regulation by microRNAs - that might offer further possibilities of therapeutic manipulation.

Lipopolysaccharide, CD14 and Toll-like receptors: an emerging link between innate immunity and atherosclerotic disease

Atherosclerosis and its clinical complications are now understood to be an inflammatory syndrome in which an ongoing systemic inflammatory response is combined with the accumulation of immune cells in the atherosclerotic plaque. Both arms of the immune system, innate and adaptive, have been implicated in contributing to essentially all stages of atherosclerosis, from initiation to progression and, ultimately, atherothrombotic complications. Innate immunity is the first line of defense against invading microorganisms. The recognition units of the innate immune system are designed to respond to molecular patterns shared by a variety of infectious microorganisms, such as bacterial lipopolysaccharide. Numerous basic and clinical studies have provided evidence that responsiveness to lipopolysaccharide may be correlated to the risk of atherosclerotic disease. The molecular basis of this connection appears to lie in Toll-like receptors that are expressed on cells of the innate immune system, bind to lipopolysaccharide, and thus determine the strength of antibacterial immune responses in the host. Variations in the function of Toll-like receptors and their signaling pathways are now suspected to play a critical role in determining the risk of atherosclerosis. This review summarizes recent research advances exploring the role of innate immunity, particularly lipopolysaccharide, CD14 and Toll-like receptors, in the initiation and development of atherosclerotic disease.

Inducible innate resistance of lung epithelium to infection

Most studies of innate immunity have focused on leukocytes such as neutrophils, macrophages, and natural killer cells. However, epithelial cells play key roles in innate defenses that include providing a mechanical barrier to microbial entry, signaling to leukocytes, and directly killing pathogens. Importantly, all these defenses are highly inducible in response to the sensing of microbial and host products. In healthy lungs, the level of innate immune epithelial function is low at baseline. This is indicated by low levels of spontaneous microbial killing and cytokine release, reflecting low constitutive stimulation in the nearly sterile lower respiratory tract when mucociliary clearance mechanisms are functioning effectively. This contrasts with the colon, where bacteria are continuously present and epithelial cells are constitutively activated. Although the surface area of the lungs presents a large target for microbial invasion, activated lung epithelial cells that are closely apposed to deposited pathogens are ideally positioned for microbial killing.