Chirality of TLR-2 ligand Pam3CysSK4 in fully synthetic peptide conjugates critically influences the induction of specific CD8+ T-cells

The lipopeptide Pam3CSK4 inhibits Rift Valley fever virus infection and protects from encephalitis

Rift Valley fever virus (RVFV) is an encephalitic bunyavirus that can infect neurons in the brain. There are no approved therapeutics that can protect from RVFV encephalitis. Innate immunity, the first line of defense against infection, canonically antagonizes viruses through interferon signaling. We found that interferons did not efficiently protect primary cortical neurons from RVFV, unlike other cell types. To identify alternative neuronal antiviral pathways, we screened innate immune ligands and discovered that the TLR2 ligand Pam3CSK4 inhibited RVFV infection, and other bunyaviruses. Mechanistically, we found that Pam3CSK4 blocks viral fusion, independent of TLR2. In a mouse model of RVFV encephalitis, Pam3CSK4 treatment protected animals from infection and mortality. Overall, Pam3CSK4 is a bunyavirus fusion inhibitor active in primary neurons and the brain, representing a new approach toward the development of treatments for encephalitic bunyavirus infections.

Innovative Vaccine Strategy: Self-Adjuvanting Conjugate Vaccines

Self-adjuvanting vaccines, covalent conjugates between antigens and adjuvants, are chemically well-defined compared with conventional vaccines formulated through mixing antigens with adjuvants. Innate immune receptor ligands effectively induce acquired immunity through the activation of innate immunity, thereby enhancing host immune responses. Thus, innate immune receptor ligands are often used as adjuvants in self-adjuvanting vaccines. In a self-adjuvanting vaccine, the covalent linkage of antigen and adjuvant enables their simultaneous uptake into immune cells where the adjuvant consequently induces antigen-specific immune responses. Importantly, self-adjuvanting vaccines do not require immobilization to carrier proteins or co-administration of additional adjuvants and thus avoid inducing undesired immune responses. Because of these excellent properties, self-adjuvanting vaccines are expected to be candidates for next-generation vaccines. Here, we take an overview of vaccine adjuvants, mainly focusing on those utilized in self-adjuvanting vaccines and then we review recent reports on self-adjuvanting conjugate vaccines.

Signal sequence contributes to the immunogenicity of Pasteurella multocida lipoprotein E

Recombinant Pasterurella multocida lipoprotein E (PlpE) has been shown to protect against fowl cholera. This study aimed to determine if the signal sequence may contribute to the antigenicity and protective efficacy of recombinant PlpE. A small antigenic domain of PlpE (termed truncated PlpE, tPlpE) was constructed with (SP-tPlpE) or without (tPlpE) the signal sequence and evaluated in vitro and in vivo. In vitro, the HEK-Bule hTLR2 Cells were used to evaluate the activation of NF-kB in the test associated with the stimulation of the SP-tPlpE and tPlpE proteins. When chickens were immunized, compared to the tPlpE vaccine group, the SP-tPlpE group showed higher antibody levels and enhanced CD4⁺ T cell response. In a challenge test, the SP-tPlpE group showed a survival rate of 87.5% (n = 8), compared to 25% for the tPlpE group. It is confirmed that the inclusion of the native signal sequence enhanced protective efficacy against fowl cholera and may act as a vaccine adjuvant. The short SP-tPlpE construct is amenable to further vaccine engineering and has potential to be developed as a fowl cholera vaccine.

The influence of component structural arrangement on peptide vaccine immunogenicity

Peptide-based subunit vaccines utilise minimal immunogenic components (i.e. peptides) to generate highly specific immune responses, without triggering adverse reactions. However, strong adjuvants and/or effective delivery systems must be incorporated into such vaccines, as peptide antigens cannot induce substantial immune responses on their own. Unfortunately, many adjuvants are too weak or too toxic to be used in combination with peptide antigens. These shortcomings have been addressed by the conjugation of peptide antigens with lipidic/ hydrophobic adjuvanting moieties. The conjugates have shown promising safety profiles and improved immunogenicity without the help of traditional adjuvants and have been efficient in inducing desired immune responses following various routes of administration, including subcutaneous, oral and intranasal. However, not only conjugation per se, but also component arrangement influences vaccine efficacy. This review highlights the importance of influence of the vaccine chemical structure modification on the immune responses generated. It discusses a variety of factors that affect the immunogenicity of peptide conjugates, including: i) self-adjuvanting moiety length and number; ii) the orientation of epitopes and self-adjuvanting moieties in the conjugate; iii) the presence of spacers between conjugated components; iv) multiepitopic arrangement; and v) the effect of chirality on vaccine efficacy.

Current Prospects in Peptide-Based Subunit Nanovaccines

Vaccination renders protection against pathogens via stimulation of the body's natural immune responses. Classical vaccines that utilize whole organisms or proteins have several disadvantages, such as induction of undesired immune responses, poor stability, and manufacturing difficulties. The use of minimal immunogenic pathogen components as vaccine antigens, i.e., peptides, can greatly reduce these shortcomings. However, subunit antigens require a specific delivery system and immune adjuvant to increase their efficacy. Recently, nanotechnology has been extensively utilized to address this issue. Nanotechnology-based formulation of peptide vaccines can boost immunogenicity and efficiently induce cellular and humoral immune responses. This chapter outlines the recent developments and advances of nano-sized delivery platforms for peptide antigens, including nanoparticles composed of polymers, peptides, lipids, and inorganic materials.

Chirality Bias Tissue Homeostasis by Manipulating Immunological Response

The physiological chirality of extracellular environments is substantially affected by pathological diseases. However, how this stereochemical variation drives host immunity remains poorly understood. Here, it is reported that pathology-mimetic M-nanofibrils-but not physiology-mimetic P-nanofibrils-act as a defense mechanism that helps to restore tissue homeostasis by manipulating immunological response. Quantitative multi-omics in vivo and in vitro shows that M-nanofibrils significantly inhibit inflammation and promote tissue regeneration by upregulating M2 macrophage polarization and downstream immune signaling compared with P-nanofibrils. Molecular analysis and theoretical simulation demonstrate that M-chirality displays higher stereo-affinity to cellular binding, which induces higher cellular contractile stress and activates mechanosensitive ion channel PIEZOl to conduct Ca²⁺ influx. In turn, the nuclear transfer of STAT is biased by Ca²⁺ influx to promote M2 polarization. These findings underscore the structural mechanisms of disease, providing design basis for immunotherapy with bionic functional materials.

Lipid A-Mediated Bacterial-Host Chemical Ecology: Synthetic Research of Bacterial Lipid As and Their Development as Adjuvants

Gram-negative bacterial cell surface component lipopolysaccharide (LPS) and its active principle, lipid A, exhibit immunostimulatory effects and have the potential to act as adjuvants. However, canonical LPS acts as an endotoxin by hyperstimulating the immune response. Therefore, LPS and lipid A must be structurally modified to minimize their toxic effects while maintaining their adjuvant effect for application as vaccine adjuvants. In the field of chemical ecology research, various biological phenomena occurring among organisms are considered molecular interactions. Recently, the hypothesis has been proposed that LPS and lipid A mediate bacterial-host chemical ecology to regulate various host biological phenomena, mainly immunity. Parasitic and symbiotic bacteria inhabiting the host are predicted to possess low-toxicity immunomodulators due to the chemical structural changes of their LPS caused by co-evolution with the host. Studies on the chemical synthesis and functional evaluation of their lipid As have been developed to test this hypothesis and to apply them to low-toxicity and safe adjuvants.

Lipopeptides for Vaccine Development

The development of lipopeptides (lipidated peptides) for vaccines is discussed, including their role as antigens and/or adjuvants. Distinct classes of lipopeptide architectures are covered including simple linear and ligated constructs and lipid core peptides. The design, synthesis, and immunological responses of the important class of glycerol-based Toll-like receptor agonist lipopeptides such as Pam₃CSK₄, which contains three palmitoyl chains and a CSK₄ hexapeptide sequence, and many derivatives of this model immunogenic compound are also reviewed. Self-assembled lipopeptide structures including spherical and worm-like micelles that have been shown to act as vaccine agents are also described. The work discussed includes examples of lipopeptides developed with model antigens, as well as for immunotherapies to treat many infectious diseases including malaria, influenza, hepatitis, COVID-19, and many others, as well as cancer immunotherapies. Some of these have proceeded to clinical development. The research discussed highlights the huge potential of, and diversity of roles for, lipopeptides in contemporary and future vaccine development.

Extracellular HMGB1 augments macrophage inflammation by facilitating the endosomal accumulation of ALD-DNA via TLR2/4-mediated endocytosis

Systemic lupus erythematosus (SLE) is a chronic autoimmune disease with unclear pathogenesis. We previously reported that syngenetic, activated lymphocyte-derived DNA (ALD-DNA) could robustly elicit macrophage activation, which plays an important role in the pathogenesis of murine lupus nephritis. In addition, extracellular HMGB1 obviously facilitated the accumulation of ALD-DNA in endosomes and promoted macrophage inflammation. While the detailed mechanism was still unknown. In this study, we found that HMGB1 could obviously change the DNA uptake pathways in macrophages. ALD-DNA alone was mainly uptake by the low efficient and unselective macropinocytosis, while extracellular HMGB1 potently promoted the more efficient and specific clathrin-/caveolin-1-dependent receptor-mediated endocytosis pathways, and led to the rapid and abundant aggregation of ALD-DNA in endosomes. This effect relied on the DNA binding ability and TLR2/TLR4 of HMGB1. Our study not only helped us to understand the promotion mechanisms of extracellular HMGB1 on ALD-DNA-induced macrophage inflammation, but also provided some clues to the pathogenesis of SLE.

Palmitoylated antigens for the induction of anti-tumor CD8+ T cells and enhanced tumor recognition

Induction of tumor-specific cytotoxic CD8⁺ T cells (CTLs) via immunization relies on the presentation of tumor-associated peptides in major histocompatibility complex (MHC) class I molecules by dendritic cells (DCs). To achieve presentation of exogenous peptides into MHC class I, cytosolic processing and cross-presentation are required. Vaccination strategies aiming to induce tumor-specific CD8⁺ T cells via this exogenous route therefore pose a challenge. In this study, we describe improved CD8⁺ T cell induction and in vivo tumor suppression of mono-palmitic acid-modified (C16:0) antigenic peptides, which can be attributed to their unique processing route, efficient receptor-independent integration within lipid bilayers, and continuous intracellular accumulation and presentation through MHC class I. We propose that this membrane-integrating feature of palmitoylated peptides can be exploited as a tool for quick and efficient antigen enrichment and MHC class I loading. Importantly, both DCs and non-professional antigen-presenting cells (APCs), similar to tumor cells, facilitate anti-tumor immunity by efficient CTL priming via DCs and effective recognition of tumors through enhanced presentation of antigens.

The Role of Macrophages in Cancer Development and Therapy

Macrophages are critical mediators of tissue homeostasis and influence various aspects of immunity. Tumor-associated macrophages are one of the main cellular components of the tumor microenvironment. Depending on their activation status, macrophages can exert a dual influence on tumorigenesis by either antagonizing the cytotoxic activity of immune cells or, less frequently, by enhancing antitumor responses. In most situations, TAMs suppress T cell recruitment and function or regulate other aspects of tumor immunity. The importance of TAMs targeting in cancer therapy is derived from the strong association between the high infiltration of TAMs in the tumor tissue with poor patient prognosis. Several macrophage-targeting approaches in anticancer therapy are developed, including TAM depletion, inhibition of new TAM differentiation, or re-education of TAM activation for cancer cell phagocytosis. In this review, we will describe the role of TAMs in tumor development, including such aspects as protumorigenic inflammation, immune suppression, neoangiogenesis, and enhancement of tissue invasion and distant metastasis. Furthermore, we will discuss therapeutic approaches that aim to deplete TAMs or, on the contrary, re-educate TAMs for cancer cell phagocytosis and antitumor immunity.

Simplified Monopalmitoyl Toll-like Receptor 2 Ligand Mini-UPam for Self-Adjuvanting Neoantigen-Based Synthetic Cancer Vaccines

Synthetic vaccines, based on antigenic peptides that comprise MHC-I and MHC-II T-cell epitopes expressed by tumors, show great promise for the immunotherapy of cancer. For optimal immunogenicity, the synthetic peptides (SPs) should be adjuvanted with suitable immunostimulatory additives. Previously, we have shown that improved immunogenicity in vivo is obtained with vaccine modalities in which an SP is covalently connected to an adjuvanting moiety, typically a ligand to Toll-like receptor 2 (TLR2). SPs were covalently attached to UPam, which is a derivative of the classic TLR2 ligand Pam₃ CysSK₄ . A disadvantage of the triply palmitoylated UPam is its high lipophilicity, which precludes universal adoption of this adjuvant for covalent modification of various antigenic peptides as it renders the synthetic vaccine insoluble in several cases. Here, we report a novel conjugatable TLR2 ligand, mini-UPam, which contains only one palmitoyl chain, rather than three, and therefore has less impact on the solubility and other physicochemical properties of a synthetic peptide. In this study, we used SPs that contain the clinically relevant neoepitopes identified in a melanoma patient who completely recovered after T-cell therapy. Homogeneous mini-UPam-SP conjugates have been prepared in good yields by stepwise solid-phase synthesis that employed a mini-UPam building block pre-prepared in solution and the standard set of Fmoc-amino acids. The immunogenicity of the novel mini-UPam-SP conjugates was demonstrated by using the cancer patient's T-cells.

TLR2 Agonistic Small Molecules: Detailed Structure-Activity Relationship, Applications, and Future Prospects

Toll-like receptors (TLRs) are the pattern recognition receptors (PRRs) that recognize pathogen-associated molecular patterns (PAMPs) in microbial species. Among the various TLRs, TLR2 has a special place due to its ability to sense the widest repertoire of PAMPs owing to its heterodimerization with either TLR1 or TLR6, broadening its ligand diversity against pathogens. Various scaffolds are reported to activate TLR2, which include naturally occurring lipoproteins, synthetic lipopeptides, and small heterocyclic molecules. We described a detailed SAR in TLR2 agonistic scaffolds and also covered the design and chemistry for the conjugation of TLR2 agonists to antigens, carbohydrates, polymers, and fluorophores. The approaches involved in delivery of TLR2 agonists such as lipidation of antigen, conjugation to polymers, phosphonic acids, and other linkers to achieve surface adsorption, liposomal formulation, and encapsulating nanoparticles are elaborated. The crystal structure analysis and computational modeling are also included with the structural features that facilitate TLR2 activation.

Carvone Enantiomers Differentially Modulate IgE-Mediated Airway Inflammation in Mice

Carvone is a monoterpene found in nature in the form of enantiomers (S- and R-). While previous research has demonstrated the anti-inflammatory and anti-allergic effects of carvone, the influence of carvone enantiomeric composition on its anti-allergic activity remains to be investigated. This study aimed to evaluate the anti-allergic activity of carvone enantiomers in a murine model of airway allergic inflammation induced by sensitization and challenge with ovalbumin (OVA). The oral treatment with R-carvone or S-carvone 1 h before each challenge inhibited the number of leukocytes and eosinophils in the bronchoalveolar lavage (BAL). R-carvone inhibited leukocyte infiltration and mucus production in the lung, which was correlated with decreased production of OVA-specific IgE in the serum and increased concentrations of IL-10 in the BAL. On the other hand, the administration of S-carvone had little inhibitory effect on inflammatory infiltration and mucus production in the lung, which might be associated with increased production of IFN-γ in the BAL. When administered 1 h before each sensitization, both enantiomers inhibited eosinophil recruitment to the BAL but failed in decreasing the titers of IgE in the serum of allergic mice. Our data indicate that carvone enantiomers differentially modulated IgE-mediated airway inflammation in mice. In conclusion, unlike S-carvone, R-carvone has the potential to be used in anti-allergic drug development.

Recent advances in self-adjuvanting glycoconjugate vaccines

Compared to traditional vaccines that are formulated into mixtures of an adjuvant and an antigen, a self-adjuvanting vaccine consists of an antigen that is covalently conjugated to a well-defined adjuvant. In self-adjuvanting vaccines, innate immune receptor ligands are usually used as adjuvants. Innate immune receptor ligands effectively trigger acquired immunity through the activation of innate immunity to enhance host immune responses to antigens. When a self-adjuvanting vaccine is used, immune cells simultaneously uptake the antigen and the adjuvant because they are covalently linked. Consequently, the adjuvant can specifically induce immune responses against the conjugated antigen. Importantly, self-adjuvanting vaccines do not require co-administration of additional adjuvants or immobilization to carrier proteins, which enables avoidance of the use of highly toxic adjuvants or the induction of undesired immune responses. Given these excellent properties, self-adjuvanting vaccines are expected to serve as candidates for the next generation of vaccines. Herein, we review vaccine adjuvants, with a focus on the adjuvants used in self-adjuvanting vaccines, and then overview recent advances made with self-adjuvanting conjugate vaccines.

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.

Nanomedicine-mediated alteration of the pharmacokinetic profile of small molecule cancer immunotherapeutics

The advent of immunotherapy is a game changer in cancer therapy with monoclonal antibody- and T cell-based therapeutics being the current flagships. Small molecule immunotherapeutics might offer advantages over the biological drugs in terms of complexity, tissue penetration, manufacturing cost, stability, and shelf life. However, small molecule drugs are prone to rapid systemic distribution, which might induce severe off-target side effects. Nanotechnology could aid in the formulation of the drug molecules to improve their delivery to specific immune cell subsets. In this review we summarize the current efforts in changing the pharmacokinetic profile of small molecule immunotherapeutics with a strong focus on Toll-like receptor agonists. In addition, we give our vision on limitations and future pathways in the route of nanomedicine to the clinical practice.

Design of TLR2-ligand-synthetic long peptide conjugates for therapeutic vaccination of chronic HBV patients

Synthetic long peptide (SLP) vaccination is a promising new treatment strategy for patients with a chronic hepatitis B virus (HBV) infection. We have previously shown that a prototype HBV-core protein derived SLP was capable of boosting CD4⁺ and CD8⁺ T cell responses in the presence of a TLR2-ligand in chronic HBV patients ex vivo. For optimal efficacy of a therapeutic vaccine in vivo, adjuvants can be conjugated to the SLP to ensure delivery of both the antigen and the co-stimulatory signal to the same antigen-presenting cell (APC). Dendritic cells (DCs) express the receptor for the adjuvant and are optimally equipped to efficiently process and present the SLP-contained epitopes to T cells. Here, we investigated TLR2-ligand conjugation of the prototype HBV-core SLP. Results indicated that TLR2-ligand conjugation reduced cross-presentation efficiency of the SLP-contained epitope by both monocyte-derived and naturally occurring DC subsets. Importantly, cross-presentation was improved after optimization of the conjugate by either shortening the SLP or by placing a valine-citrulline linker between the TLR2-ligand and the long SLP, to facilitate endosomal dissociation of SLP and TLR2-ligand after uptake. HBV-core SLP conjugates also triggered functional patient T cell responses ex vivo. These results provide an import step forward in the design of a therapeutic SLP-based vaccine to cure chronic HBV.

TLR2 agonists and their structure–activity relationships

We review the structure–activity relationships and synthetic studies of TLR2 agonists – important chemical targets in immunotherapy.

Semisynthetic, self-adjuvanting vaccine development: Efficient, site-specific sortase A-mediated conjugation of Toll-like receptor 2 ligand FSL-1 to recombinant protein antigens under native conditions and application to a model group A streptococcal vaccine

Protein antigens are, in general, weakly immunogenic, and therefore require co-delivery with adjuvants to stimulate potent immune responses. The fusion of (poly)peptide antigens to immunostimulatory adjuvants (e.g. Toll-like receptor (TLR) agonists) has been demonstrated to greatly improve vaccine potency compared to mixtures of antigen and adjuvant. Chemical approaches, to enable the rapid, site-specific and high-yielding linkage of TLR2 ligands to recombinant protein antigens, have been previously optimized. These approaches require the use of denaturing conditions to ensure high reaction yields, which limits their application, as maintenance of native protein folding is necessary to elicit antibodies against conformational epitopes. Here, this work aimed to optimize an alternative method, to ensure the efficient bioconjugation of TLR2 ligands onto folded protein antigens. An enzyme-mediated approach, using Staphylococcus aureus sortase A (or a penta mutant with enhanced efficiency), was optimized for reaction yield and time, as well as enzyme type and amount. This approach enabled the site-specific conjugation of the TLR2-agonist fibroblast-stimulating lipopeptide-1 (FSL-1) onto a model group A Streptococcus (GAS) recombinant polytope antigen under conditions that maintain protein folding, yielding a homogeneous, molecularly-defined product, with ligation yields as high as 90%. Following intramuscular (IM) administration of the ligation product to humanized plasminogen AlbPLG1 mice, high-titer, antigen-specific IgG antibodies were observed, which conferred protection against subcutaneous challenge with GAS strain 5448. In comparison, mixtures of the GAS antigen with aluminum hydroxide or FSL-1 failed to provide protection, with the FSL-1 mixture yielding ~1000-fold lower antigen-specific IgG antibody titers, and the mixture with alum yielding a Th2-biased response compared to the more balanced Th1/Th2 responses observed with the FSL-1 conjugate. Overall, a FSL-1 bioconjugation method for the efficient production of antigen-TLR2 agonist conjugates, which maintain protein folding, was produced, with broad utility for the development of self-adjuvanting vaccines against subunit protein antigens.

A new synthetic toll-like receptor 1/2 ligand is an efficient adjuvant for peptide vaccination in a human volunteer

BACKGROUND

We previously showed that the bacterial lipopeptide Pam₃Cys-Ser-Ser, meanwhile established as a toll-like receptor (TLR) 1/2 ligand, acts as a strong adjuvant for the induction of virus specific CD8⁺ T cells in mice, when covalently coupled to a synthetic peptide.

CASE PRESENTATION

We now designed a new water-soluble synthetic Pam₃Cys-derivative, named XS15 and characterized it in vitro by a TLR2 NF-κB luciferase reporter assay. Further, the capacity of XS15 to activate immune cells and stimulate peptide-specific CD8⁺ T and NK cells by 6-sulfo LacNAc⁺ monocytes was assessed by flow cytometry as well as cytokine induction using immunoassays. The induction of a functional immune response after vaccination of a volunteer with viral peptides was assessed by ELISpot assay and flow cytometry in peripheral blood cells and infiltrating cells at the vaccination site, as well as by immunohistochemistry and imaging. XS15 induced strong ex vivo CD8⁺ and T_H1 CD4⁺ responses in a human volunteer upon a single injection of XS15 mixed to uncoupled peptides in a water-in-oil emulsion (Montanide™ ISA51 VG). A granuloma formed locally at the injection site containing highly activated functional CD4⁺ and CD8⁺ effector memory T cells. The total number of vaccine peptide-specific functional T cells was experimentally assessed and estimated to be 3.0 × 10⁵ in the granuloma and 20.5 × 10⁶ in peripheral blood.

CONCLUSION

Thus, in one volunteer we show a granuloma forming by peptides combined with an efficient adjuvant in a water-in-oil-emulsion, inducing antigen specific T cells detectable in circulation and at the vaccination site, after one single vaccination only. The ex vivo T cell responses in peripheral blood were detectable for more than one year and could be strongly boosted by a second vaccination. Hence, XS15 is a promising adjuvant candidate for peptide vaccination, in particular for tumor peptide vaccines in a personalized setting.

Identification of a neo-epitope dominating endogenous CD8 T cell responses to MC-38 colorectal cancer

The murine MC-38 colorectal cancer model is a commonly used model for cancer with high mutational burden, which is sensitive for immune checkpoint immunotherapy. We set out to analyze endogenous CD8+ T cell responses to MC-38 neo-antigens in tumor-bearing mice and after anti-PD-L1 checkpoint therapy. Through combination of whole-exome sequencing analysis with mass spectrometry of MHC class I eluted peptides we could identify eight candidate epitopes. Of these, a neo-epitope encoded by a point-mutation in the sequence of the ribosomal protein L18 (Rpl18) strongly dominated the CD8+ T cell response to our MC-38 cell-line in comparison to a previously described neo-epitope in the Adpgk protein. Therapeutic vaccination with synthetic peptides induced CD8+ T cell responses against the mutated Rpl18 epitope, which controlled tumor growth in vivo. This immunologically dominant response to mutated Rpl18 is of great importance in the development and optimization of immunotherapeutic strategies with the MC-38 tumor model.

Molecular modelling of TLR agonist Pam3CSK4 entrapment in PLA nanoparticles as a tool to explain loading efficiency and functionality

Designing potent and safe-of-use therapies against cancers and infections remains challenging despite the emergence of novel molecule classes like checkpoint inhibitors or Toll-Like-Receptor ligands. The latest therapeutic perspectives under development for immune modulator administration exploits vectorization, and biodegradable delivery systems are one of the most promising vehicles. Nanoparticles based on Poly (D,L) Lactic Acid (PLA) as polymer for formulation are widely investigated due to its bioresorbable, biocompatible and low immunogen properties. We propose a PLA-based nanoparticle delivery system to vectorize Pam₃CSK₄, a lipopeptide TLR1/2 ligand and a potent activator of the proinflammatory transcription factor NF-κB that shows a self-assembling behavior from 30 µg/mL onwards. We demonstrate successful encapsulation of Pam₃CSK₄ in PLA nanoparticles by nanoprecipitation in a 40-180 µg/mL concentration range, with 99% of entrapment efficiency. By molecular modelling, we characterize drug/carrier interactions and conclude that Pam₃CSK₄ forms clusters onto the nanoparticle and is not encapsulated into the hydrophobic core. In silico predictions provide nanoprecipitation optimization and the mechanistic understanding of the particle dynamics. The loaded-Pam₃CSK₄ maintains bioactivity on TLR2, confirmed by in vitro experiments using reporter cell line HEK-Blue hTLR2. Our presented data and results are convincing evidence that Pam₃CSK₄-loaded in PLA nanoparticles represent a promising immune modulating system.

Lipoproteins: Structure, Function, Biosynthesis

The Lpp lipoprotein of Escherichia coli is the first identified protein with a covalently linked lipid. It is chemically bound by its C-terminus to murein (peptidoglycan) and inserts by the lipid at the N-terminus into the outer membrane. As the most abundant protein in E. coli (10⁶ molecules per cell) it plays an important role for the integrity of the cell envelope. Lpp represents the type protein of a large variety of lipoproteins found in Gram-negative and Gram-positive bacteria and in archaea that have in common the lipid structure for anchoring the proteins to membranes but otherwise strongly vary in sequence, structure, and function. Predicted lipoproteins in known prokaryotic genomes comprise 2.7% of all proteins. Lipoproteins are modified by a unique phospholipid pathway and transferred from the cytoplasmic membrane into the outer membrane by a special system. They are involved in protein incorporation into the outer membrane, protein secretion across the cytoplasmic membrane, periplasm and outer membrane, signal transduction, conjugation, cell wall metabolism, antibiotic resistance, biofilm formation, and adhesion to host tissues. They are only found in bacteria and function as signal molecules for the innate immune system of vertebrates, where they cause inflammation and elicit innate and adaptive immune response through Toll-like receptors. This review discusses various aspects of Lpp and other lipoproteins of Gram-negative and Gram-positive bacteria and archaea.

Novel TLR2-binding adjuvant induces enhanced T cell responses and tumor eradication

Background

Ligands for the Toll-like receptor (TLR) family can induce activation of cells of the innate immune system and are widely studied for their potential to enhance adaptive immunity. Conjugation of TLR2-ligand Pam3CSK4 to synthetic long peptides (SLPs) was shown to strongly enhance the induction of antitumor immunity. To further improve cancer vaccination, we have previously shown that the novel TLR2-L Amplivant (AV), a modified Pam3CSK4, potentiates the maturation effects on murine DCs. In the current study, we further assessed the immunological properties of AV.

Methods

Naïve mice were vaccinated with a conjugate of either Pam3CSK4 or AV and an SLP to assess specific T cell priming efficiency in vivo. The potency of AV and Pam3CSK4, either as free compounds or conjugated to different SLPs, to mature murine DCs was compared by stimulating murine dendritic cells overnight followed by ELISA and flow cytometry analysis. Murine tumor experiments were carried out by vaccinating mice carrying established HPV16 E6 and E7-expressing tumors and subsequently analyzing myeloid and lymphoid cells infiltrating the tumor microenvironment. Furthermore, tumor outgrowth after vaccination was monitored to enable comparison of the efficiency to induce antitumor immunity by Pam3CSK-SLP and AV-SLP conjugates. To enhance therapeutic efficacy, AV-SLP conjugate vaccination was combined with ablative therapies to assess whether synergism between such therapies would occur.

Results

SLPs conjugated to AV induce stronger DC maturation, in vivo T cell priming and antitumor immunity compared to conjugates with Pam3CSK4. Interestingly, AV-SLP conjugates modulate the macrophage populations in the tumor microenvironment, correlating with a therapeutic effect in an aggressive murine tumor model. The potency of AV-SLP conjugates in cancer vaccination operates optimally in combination with chemotherapy or photodynamic therapy.

Conclusion

These data allow further optimization of vaccination-based immunotherapy of cancer by use of the improved TLR2-ligand Amplivant.

Electronic supplementary material

The online version of this article (10.1186/s40425-018-0455-2) contains supplementary material, which is available to authorized users.

Toll-like Receptor Agonist Conjugation: A Chemical Perspective

Toll-like receptors (TLRs) are vital elements of the mammalian immune system that function by recognizing pathogen-associated molecular patterns (PAMPs), bridging innate and adaptive immunity. They have become a prominent therapeutic target for the treatment of infectious diseases, cancer, and allergies, with many TLR agonists currently in clinical trials or approved as immunostimulants. Numerous studies have shown that conjugation of TLR agonists to other molecules can beneficially influence their potency, toxicity, pharmacokinetics, or function. The functional properties of TLR agonist conjugates, however, are highly dependent on the ligation strategy employed. Here, we review the chemical structural requirements for effective functional TLR agonist conjugation. In addition, we provide similar analysis for those that have yet to be conjugated. Moreover, we discuss applications of covalent TLR agonist conjugation and their implications for clinical use.

TLR2 ligand-synthetic long peptide conjugates effectively stimulate tumor-draining lymph node T cells of cervical cancer patients

The potency of human papillomavirus type 16 (HPV16)-encoded synthetic long peptides (SLP), conjugated to an optimized Toll-like receptor 2 ligand (TLR2-L), was assessed in ex vivo activation of HPV16⁺ cancer patient-derived T cells. Two highly immunogenic SLP sequences derived from the oncogenic E6 protein of HPV16 were selected and conjugated to a Pam3CSK4-based TLR2-L under GMP conditions. Both conjugates were able to mature human DCs in vitro and to activate human skin-derived antigen-presenting cells (APCs) upon intradermal injection in an ex vivo skin model, associated with induction of a favorable chemokine profile to attract and activate T cells. The conjugated SLPs were efficiently processed by APCs, since HPV16-specific CD4⁺ and CD8⁺ T-cell clones isolated from HPV16+ cervical tumors proliferated in response to both conjugates. The TLR2-L SLP conjugates significantly enhanced ex vivo T helper type 1 T-cell activation in cell suspensions obtained from tumor-draining lymph nodes (LN) resected during hysterectomy of HPV16⁺ cervical cancer patients. These results show that TLR2-L SLP conjugates can activate circulating or LN-derived tumor-specific T cells, a promising outcome for studying these two conjugates in a phase I/II clinical safety and immunogenicity trial.

Linking T cell epitopes to a common linear B cell epitope: A targeting and adjuvant strategy to improve T cell responses

Immune complexes are potent mediators of cellular immunity and have been extensively studied for their disease mediating properties in humans and for their role in anti-cancer immunity. However, a viable approach to use antibody-complexed antigen as vehicle for specific immunotherapy has not yet reached clinical use. Since virtually all people have endogenous antibodies against tetanus toxoid (TTd), such commonly occurring antibodies are promising candidates to utilize for immune modulation. As an initial proof-of-concept we investigated if anti-tetanus IgG could induce potent cross-presentation of a conjugate with SIINFEKL, a MHC class I presented epitope of ovalbumin (OVA), to TTd. This protein conjugate enhanced OVA-specific CD8+ T cell responses when administrated to seropositive mice. Since TTd is poorly defined, we next investigated whether a synthetic peptide-peptide conjugate, with a chemically defined linear B cell epitope of tetanus toxin (TTx) origin, could improve cellular immune responses. Herein we identify one linear B cell epitope, here after named MTTE thru a screening of overlapping peptides from the alpha and beta region of TTx, and by assessment of the binding of pooled IgG, or individual human IgG from high-titer TTd vaccinated donors, to these peptides. Subsequently, we developed a chemical protocol to synthesize defined conjugates containing multiple copies of MTTE covalently attached to one or more T cell epitopes of choice. To demonstrate the potential of the above approach we showed that immune complexes of anti-MTTE antibodies with MTTE-containing conjugates are able to induce DC and T cell activation using model antigens.

Bioconjugation Approaches to Producing Subunit Vaccines Composed of Protein or Peptide Antigens and Covalently Attached Toll-Like Receptor Ligands

Traditional vaccines derived from attenuated or inactivated pathogens are effective at inducing antibody-based protective immune responses but tend to be highly reactogenic, causing notable adverse effects. Vaccines with superior safety profiles can be produced by subunit approaches, utilizing molecularly defined antigens (e.g., proteins and polysaccharides). These antigens, however, often elicit poor immunological responses, necessitating the use of adjuvants. Immunostimulatory adjuvants have the capacity to activate antigen presenting cells directly through specific receptors (e.g., Toll-like receptors (TLRs)), resulting in enhanced presentation of antigens as well as the secretion of proinflammatory chemokines and cytokines. Consequently, innate immune responses are amplified and adaptive immunity is generated. Recently, site-specific conjugation of such immunostimulatory adjuvants (e.g., TLR ligands) onto defined antigens has shown superior efficacy over unconjugated mixtures, suggesting that the development of chemically characterized immunostimulatory adjuvants and optimized approaches for their conjugation with antigens may provide a better opportunity for the development of potent, novel vaccines. This review briefly summarizes various TLR agonists utilized as immunostimulatory adjuvants and focuses on the development of techniques (e.g., recombinant, synthetic, and semisynthetic) for generating adjuvant-antigen fusion vaccines incorporating peptide or protein antigens.

Cross-talk between pathogen recognizing Toll-like receptors and immunoglobulin Fc receptors in immunity

The individual role of pathogen-binding Toll-like receptors (TLRs) and antibody-binding Fc receptors (FcRs) during pathogenic infections has been studied extensively. However, combined activation of these different receptor classes has received little attention, even though they are triggered simultaneously when immune cells bind antibody-opsonized pathogens. In the last few years, it has become evident that joined activation of TLRs and FcRs substantially tailors inflammatory immune responses, which is an efficient and controlled mechanism of the host to act upon invading pathogens. In this review, we discuss the mechanisms of cross-talk between different TLRs and FcRs and the resulting inflammatory immune responses. Furthermore, we propose how chronic activation via this cross-talk might be detrimental in inflammatory (auto) immune diseases. We conclude with the potential exploitation of the interplay between TLRs and FcRs for monoclonal antibody therapy to target tumors. Future interests in this field of research include establishing a more detailed and mechanistic understanding of the mode of action of TLR and FcR cross-talk and exploration of its physiological importance in health and disease. This may furthermore open up novel therapeutic options for intervention in inflammatory diseases or cancer.

PLGA particulate delivery systems for subunit vaccines: Linking particle properties to immunogenicity

Among the emerging subunit vaccines are recombinant protein- and synthetic peptide-based vaccine formulations. However, proteins and peptides have a low intrinsic immunogenicity. A common strategy to overcome this is to co-deliver (an) antigen(s) with (an) immune modulator(s) by co-encapsulating them in a particulate delivery system, such as poly(lactic-co-glycolic acid) (PLGA) particles. Particulate PLGA formulations offer many advantages for antigen delivery as they are biocompatible and biodegradable; can protect the antigens from degradation and clearance; allow for co-encapsulation of antigens and immune modulators; can be targeted to antigen presenting cells; and their particulate nature can increase uptake and cross-presentation by mimicking the size and shape of an invading pathogen. In this review we discuss the pros and cons of using PLGA particulate formulations for subunit vaccine delivery and provide an overview of formulation parameters that influence their adjuvanticity and the ensuing immune response.

Immune response profile elicited by the model antigen ovalbumin expressed in fusion with the bacterial OprI lipoprotein

The use of immunogenic formulations targeting pattern recognition receptors towards modulation of immune responses is a promising strategy to develop better vaccines against infectious and malignant diseases. Molecules targeting TLR2 offer interesting properties that are relevant for vaccine development, including the possibility to covalently attach the lipidic ligands to the antigens. However, the type of immune response elicited by these formulations is still controversial. In this work, we used the model antigen ovalbumin (OVA) expressed in fusion with the bacterial lipoprotein OprI in order to characterize the immunomodulatory properties of this TLR ligand. Murine bone marrow-derived dendritic cells stimulated with OprI-OVA fusion lipoprotein produced high levels of the pro-inflammatory cytokines TNF-α and IL-6 and also IL-10, IL-12(p70) and IL-27, while TGF-β and IL-23 were not detected. Using OT-II and OT-I mice, an enhancement of MHC class II and class I antigen presentation was observed for the OVA antigen in fusion with OprI. Mice immunized by intraperitoneal route with this fusion lipoprotein in prime-boost protocols developed strong specific antibody responses including IgG1, IgG2c, IgG2b, IgG3 and IgE. These results, together with data obtained by restimulation of splenocytes from the immunized mice, point to an immune response profile that does not correspond to a strict Th1 or Th2 polarization. Finally, in a challenge experiment using a melanoma syngeneic mouse model (B16-OVA), prophylactic inoculation with OprI fused with the unrelated antigen eGFP increased the tumor growth, while the fusion with the tumor-associated antigen OVA delayed the tumor growth and increased mice survival.

N-tetradecylcarbamyl lipopeptides as novel agonists for Toll-like receptor 2

New analogues (UPam) of triacylated lipopeptide Pam3CysSK4, a popular agonist of Toll-like receptor 2 (TLR2), were designed making use of the cocrystal structure of a TLR2 heterodimer (with TLR1) with Pam3CysSK4. Twenty-two UPam derivatives that feature an N-tetradecylcarbamyl chain to mimic the native N-palmitoyl moiety and various small amino acids residues at the penultimate N-terminal position were prepared via solid-phase synthesis. In vitro evaluation of immunostimulatory properties revealed new potent TLR2 ligands.

In situ loading of skin dendritic cells with apoptotic bleb-derived antigens for the induction of tumor-directed immunity

The generation and loading of dendritic cells (DC) ex-vivo for tumor vaccination purposes is laborious and costly. Direct intradermal (i.d.) administration of tumor-associated antigens could be an attractive alternative approach, provided that efficient uptake and cross-presentation by appropriately activated skin DCs can be achieved. Here, we compare the efficiency of i.d. delivery of relatively small apoptotic blebs (diameter ∼0.1-1 μm) derived from MART-1 transduced acute myeloid leukemia (AML) HL60 cells, to that of larger apoptotic cell remnants (ACR; 2-10 μm) in a physiologically highly relevant human skin explant model. Injection of either fluorescently-labelled ACRs or blebs alone did not affect the number or distribution of migrated DC subsets from skin biopsies after 48 hours, but resulted in a general up-regulation of the co-stimulatory molecules CD83 and CD86 on skin DCs that had ingested apoptotic material. We have previously shown that i.d. administration of GM-CSF and IL-4 resulted in preferential migration of a mature and highly T cell-stimulatory CD11^hiCD1a⁺CD14^- dermal DC subset. Here, we found that co-injection of GM-CSF and IL-4 together with either ACRs or blebs resulted in uptake efficiencies within this dermal DC subset of 7.6% (±6.1%) and 19.1% (±15.9%), respectively, thus revealing a significantly higher uptake frequency of blebs (P < 0.02). Intradermal delivery of tumor-derived blebs did not affect the T-cell priming and T_H-skewing abilities of migratory skin DC. Nevertheless, in contrast to i.d. administration of ACR, the injection of blebs lead to effective cross-presentation of MART-1 to specific CD8⁺ effector T cells. We conclude that apoptotic bleb-based vaccines delivered through the skin may offer an attractive, and broadly applicable, cancer immunotherapy.

Targeting TLR2 for vaccine development

Novel and more effective immunization strategies against many animal diseases may profit from the current knowledge on the modulation of specific immunity through stimulation of innate immune receptors. Toll-like receptor (TLR)2-targeting formulations, such as synthetic lipopeptides and antigens expressed in fusion with lipoproteins, have been shown to have built-in adjuvant properties and to be effective at inducing cellular and humoral immune mechanisms in different animal species. However, contradictory data has arisen concerning the profile of the immune response elicited. The benefits of targeting TLR2 for vaccine development are thus still debatable and more studies are needed to rationally explore its characteristics. Here, we resume the main features of TLR2 and TLR2-induced immune responses, focusing on what has been reported for veterinary animals.

Design, automated synthesis and immunological evaluation of NOD2-ligand-antigen conjugates

The covalent attachment of an innate immune system stimulating agent to an antigen can provide active vaccine modalities capable of eliciting a potent immune response against the incorporated antigen. Here we describe the design, automated synthesis and immunological evaluation of a set of four muramyl dipeptide-peptide antigen conjugates. Muramyl dipeptide (MDP) represents a well-known ligand for the intracellular NOD2 receptor and our study shows that covalently linking an MDP-moiety to an antigenic peptide can lead to a construct that is capable of stimulating the NOD2 receptor if the ligand is attached at the anomeric center of the muramic acid. The constructs can be processed by dendritic cells (DCs) and the conjugation does not adversely affect the presentation of the incorporated SIINFEKL epitope on MHC-I molecules. However, stimulation of the NOD2 receptor in DCs was not sufficient to provide a strong immunostimulatory signal.

Efficient induction of antitumor immunity by synthetic toll-like receptor ligand-peptide conjugates

Chemical conjugates comprising synthetic Toll-like receptor ligands (TLR-L) covalently bound to antigenic synthetic long peptides (SLP) are attractive vaccine modalities, which can induce robust CD8(+) T-cell immune responses. Previously, we have shown that the mechanism underlying the power of TLR-L SLP conjugates is improved delivery of the antigen together with a dendritic cell activation signal. In the present study, we have expanded the approach to tumor-specific CD4(+) as well as CD8(+) T-cell responses and in vivo studies in two nonrelated aggressive tumor models. We show that TLR2-L SLP conjugates have superior mouse CD8(+) and CD4(+) T-cell priming capacity compared with free SLPs injected together with a free TLR2-L. Vaccination with TLR2-L SLP conjugates leads to efficient induction of antitumor immunity in mice challenged with aggressive transplantable melanoma or lymphoma. Our data indicate that TLR2-L SLP conjugates are suitable to promote integrated antigen-specific CD8(+) and CD4(+) T-cell responses required for the antitumor effects. Collectively, these data show that TLR2-L SLP conjugates are promising synthetic vaccine candidates for active immunotherapy against cancer.

The Interplay between Daptomycin and the Immune System

Antibiotics may have bacteriostatic or bactericidal effects but may also cause immunomodulation. Lipopeptides are known immunomodulators that interact with pattern recognition receptors such as Toll-like receptors in antigen presenting cells. Daptomycin is a novel lipopeptide antibiotic with a lipid moiety and unique structure that in the presence of divalent ions may directly interact with lipid membrane phospholipids, the major component of lipid membranes in immune cells. Daptomycin may also penetrate immune cells including neutrophils and macrophages. However, the possible immunomodulatory effects of daptomycin remain unknown. Understanding these effects is important to determine whether this agent can provide protection against infectious challenge through multiple mechanisms. Preliminary studies suggest that daptomycin may have minimal effects on cytokine production and may have synergistic immunomodulatory effects in combination with other immunomodulators. This review focuses on the hypothesis that daptomycin may also have immunomodulatory effects but further studies are needed to investigate this hypothesis.

Chemical biology of antigen presentation by MHC molecules

MHC class I and MHC class II molecules present peptides to the immune system to drive proper T cell responses. Pharmacological modulation of T-cell responses can offer treatment options for a range of immune-related diseases. Pharmacological downregulation of MHC molecules may find application in treatment of auto-immunity and transplantation rejection while pharmacological activation of antigen presentation would support immune responses to infection and cancer. Since the cell biology of MHC class I and MHC class II antigen presentation is understood in great detail, many potential targets for manipulation have been defined over the years. Here, we discuss how antigen presentation by MHC molecules can be modulated by pharmacological agents and how chemistry can further support the study of antigen presentation in general. The chemical biology of antigen presentation by MHC molecules shows surprising options for immune modulation and the development of future therapies.

Immunostimulation by synthetic lipopeptide-based vaccine candidates: structure-activity relationships

Peptide-based vaccines offer several advantages over conventional whole organism or protein approaches by offering improved purity and specificity in inducing immune response. However, peptides alone are generally non-immunogenic. Concerns remain about the toxicity of adjuvants which are critical for immunogenicity of synthetic peptides. The use of lipopeptides in peptide vaccines is currently under intensive investigation because potent immune responses can be generated without the use of adjuvant (thus are self-adjuvanting). Several lipopeptides derived from microbial origin, and their synthetic versions or simpler fatty acid moieties impart this self-adjuvanting activity by signaling via Toll-like receptor 2 (TLR2). Engagement of this innate immune receptor on antigen-presenting cell leads to the initiation and development of potent immune responses. Therefore optimization of lipopeptides to enhance TLR2-mediated activation is a promising strategy for vaccine development. Considerable structure-activity relationships that determine TLR2 binding and consequent stimulation of innate immune responses have been investigated for a range of lipopeptides. In this mini review we address the development of lipopeptide vaccines, mechanism of TLR2 recognition, and immune activation. An overview is provided of the best studied lipopeptide vaccine systems.

TLR ligand-peptide conjugate vaccines: toward clinical application

Approaches to treat cancer with therapeutic vaccination have made significant progress. In order to induce efficient antitumor immunity, a vaccine should target and activate antigen-presenting cells, such as the dendritic cell, while delivering the tumor-derived antigen of choice. Conjugates of synthetic peptides and ligands of pattern-recognition receptors (PRRs) combine these features and, given their synthetic nature, can be produced under GMP conditions. Therefore, conjugation of antigenic peptides to potent PRR ligands is a promising vaccination approach for the treatment of cancer. This review focuses on the different PRR families that can be exploited for the design of conjugates and explores the results obtained so far with PRR ligands conjugated to antigen. The uptake and processing of Toll-like receptor ligand-peptide conjugates are discussed in more detail, as well as future directions that may further enhance the immunogenicity of conjugates.

Respiratory viral infections: knowledge based therapeutics

Lung viral infections continue to kill millions of people worldwide. Virus-specific properties, replication kinetics and longevity affect the subsequent vigour of innate and adaptive immunity, which contribute to clinical manifestations. The point at which lung innate immunity activates is different between individuals and is determined by age, genetics, underlying conditions and infection history. On resolution of virus-induced lung disease an 'altered state of homeostasis' exists that in turn affects the next antigenic challenge. The last two years has produced a plethora of studies on the resolution of inflammatory lung disease; highlighting potential for immune modulation. In the future a more precise etiological diagnosis, combined with a knowledge of co-morbidities and an immune signature will lead to the development of more specifically targeted therapeutics.

Experience with synthetic vaccines for cancer and persistent virus infections in nonhuman primates and patients

Synthetic vaccines, in particular long synthetic peptides of approximately 25-50 amino acids in length, are attractive for HIV vaccine development and for induction of therapeutic immune responses in patients with (pre-)malignant disorders. In the case of preventive vaccine development against HIV, no major success has been achieved, but the possibilities are by no means exhausted. A long peptide vaccine consisting of 13 overlapping peptides, which together cover the entire length of the two oncogenic proteins E6 and E7 of high-risk human papilloma virus type 16 (HPV16), caused complete regression of all lesions and eradication of virus in 9 out of 20 women with high-grade vulvar intraepithelial neoplasia, a therapy-resistant preneoplastic disorder. The nature and strength of the vaccine-prompted T cell responses were significantly correlated with the clinical response. Synthetic peptide vaccines are attractive, because they allow rational improvement of vaccine design and detailed pharmacokinetic and pharmacodynamic studies not possible with conventional vaccines. Improvements are possible by addition or conjugation of adjuvants, notably TLR ligands, to the synthetic peptides.

The type I interferon response during viral infections: a "SWOT" analysis

The type I interferon (IFN) response is a strong and crucial moderator for the control of viral infections. The strength of this system is illustrated by the fact that, despite some temporary discomfort like a common cold or diarrhea, most viral infections will not cause major harm to the healthy immunocompetent host. To achieve this, the immune system is equipped with a wide array of pattern recognition receptors and the subsequent coordinated type I IFN response orchestrated by plasmacytoid dendritic cells (pDCs) and conventional dendritic cells (cDCs). The production of type I IFN subtypes by dendritic cells (DCs), but also other cells is crucial for the execution of many antiviral processes. Despite this coordinated response, morbidity and mortality are still common in viral disease due to the ability of viruses to exploit the weaknesses of the immune system. Viruses successfully evade immunity and infection can result in aberrant immune responses. However, these weaknesses also open opportunities for improvement via clinical interventions as can be seen in current vaccination and antiviral treatment programs. The application of IFNs, Toll-like receptor ligands, DCs, and antiviral proteins is now being investigated to further limit viral infections. Unfortunately, a common threat during stimulation of immunity is the possible initiation or aggravation of autoimmunity. Also the translation from animal models to the human situation remains difficult. With a Strengths-Weaknesses-Opportunities-Threats ("SWOT") analysis, we discuss the interaction between host and virus as well as (future) therapeutic options, related to the type I IFN system.

Surface-confined conformers and coassembly-induced conformer resolution

Stereoisomerism is a fundamental chemistry issue and has been intensively investigated because of its importance in organic chemistry, biology, and pharmacology. Molecules with freely rotatable single bonds have many interconvertable conformers. Herein, we report the surface-adsorption-induced conformer resolution by employing azobenzene-3,3-dicarboxylic acid (ADA-33) as a model compound. Two linear assembly phases composed of trans conformers on a highly oriented pyrolytic graphite (HOPG) surface are observed by scanning tunneling microscopy. With the codeposition with 1-octanoic acid (OA), only one trans conformer of ADA-33 can be recognized by OA to form a two-component assembly with alternately arranged ADA-33 and OA stripes, which can be attributed to the epitaxial assembly of ADA-33 and OA on the HOPG surface, and weak hydrogen bonding exists between conformer I and OA molecules. The results are of significance with respect to the discrimination and resolution of conformers on a solid surface and provide molecular insights into the coadsorption assembly on the surface.