Conjugation of protein to immunostimulatory DNA results in a rapid, long-lasting and potent induction of cell-mediated and humoral immunity

A Click-Type Enzymatic Method for Antigen-Adjuvant Conjugation

The Toll-like receptor 9 (TLR9) stimulator, CpG oligodeoxynucleotide, has emerged as a potent enhancer of protein subunit vaccines. Incorporating the protein antigen directly with the CpG adjuvant presents a novel strategy to significantly reduce the required dosage of CpG compared to traditional methods that use separate components. In contrast to existing chemical conjugation methods, this study introduces an enzymatic approach for antigen-adjuvant coupling using a recombinant endonuclease DCV fused with SpyTag. This fusion protein catalyzes the covalent linkage between itself and the CpG adjuvant under mild conditions. These conjugates can be further linked with target protein antigens containing the SpyCatcher sequence, yielding stable, covalently-linked antigen-adjuvant complexes. The corresponding complex utilizing the receptor-binding domain (RBD) of SARS-CoV-2 spike protein as the model antigen, elicits high-titer, specific antibody production in mice via both subcutaneous administration and intratracheal inoculation. Notably, the tumor vaccine candidate fabricated by this method has also shown significant inhibition of cancer progression after intratracheal administration. The technique ensures precise, site-specific coupling and preserves the antigen's structural integrity due to the post-purification coupling strategy that simplifies manufacturing and aids in developing inhalable vaccines.

Advances in vaccine development for Chlamydia trachomatis

Chlamydia trachomatis is the most prevalent bacterial sexually transmitted infection globally. Antibiotic treatment is highly effective, but infection is often asymptomatic resulting in most individuals going undetected and untreated. This untreated infection can ascend to the upper female genital tract to cause pelvic inflammatory disease, tubal factor infertility, and ectopic pregnancy. Chlamydia screening and treatment programs have failed to control this epidemic and demonstrate the need for an efficacious vaccine to prevent transmission and disease. Animal models and human epidemiological data reveal that natural immunity can provide partial or short-lived sterilizing immunity. These data further demonstrate the importance of eliciting interferon gamma (IFNγ)-producing cluster of differentiation 4 (CD4) T cells (Th1 and Th1/17 cells) that can likely synergize with antibody-mediated opsonophagocytosis to provide optimal protection. These studies have guided preclinical rational vaccine design for decades and the first Phase 1 clinical trials have recently been completed. Recent advances have led to improvements in vaccine platforms and clinically safe adjuvants that help provide a path forward. This review describes vaccine models, correlates of immunity, antigen and adjuvant selection, and future clinical testing for Chlamydia vaccine development.

Lipid A analog CRX-527 conjugated to synthetic peptides enhances vaccination efficacy and tumor control

Adjuvants play a determinant role in cancer vaccination by optimally activating APCs and shaping the T cell response. Bacterial-derived lipid A is one of the most potent immune-stimulators known, and is recognized via Toll-like receptor 4 (TLR4). In this study, we explore the use of the synthetic, non-toxic, lipid A analog CRX-527 as an adjuvant for peptide cancer vaccines. This well-defined adjuvant was covalently conjugated to antigenic peptides as a strategy to improve vaccine efficacy. We show that coupling of this TLR4 agonist to peptide antigens improves vaccine uptake by dendritic cells (DCs), maturation of DCs and T cell activation in vitro, and stimulates DC migration and functional T cell priming in vivo. This translates into enhanced tumor protection upon prophylactic and therapeutic vaccination via intradermal injection against B16-OVA melanoma and HPV-related TC1 tumors. These results highlight the potential of CRX-527 as an adjuvant for molecularly defined cancer vaccines, and support the design of adjuvant-peptide conjugates as a strategy to optimize vaccine formulation.

Immunotherapies in the treatment of immunoglobulin E‑mediated allergy: Challenges and scope for innovation (Review)

Immunoglobulin E (IgE)‑mediated allergy or hypersensitivity reactions are generally defined as an unwanted severe symptomatic immunological reaction that occurs due to shattered or untrained peripheral tolerance of the immune system. Allergen‑specific immunotherapy (AIT) is the only therapeutic strategy that can provide a longer‑lasting symptomatic and clinical break from medications in IgE‑mediated allergy. Immunotherapies against allergic diseases comprise a successive increasing dose of allergen, which helps in developing the immune tolerance against the allergen. AITs exerttheirspecial effectiveness directly or indirectly by modulating the regulator and effector components of the immune system. The number of success stories of AIT is still limited and it canoccasionallyhave a severe treatment‑associated adverse effect on patients. Therefore, the formulation used for AIT should be appropriate and effective. The present review describes the chronological evolution of AIT, and provides a comparative account of the merits and demerits of different AITs by keeping in focus the critical guiding factors, such as sustained allergen tolerance, duration of AIT, probability of mild to severe allergic reactions and dose of allergen required to effectuate an effective AIT. The mechanisms by which regulatory T cells suppress allergen‑specific effector T cells and how loss of natural tolerance against innocuous proteins induces allergy are reviewed. The present review highlights the major AIT bottlenecks and the importantregulatory requirements for standardized AIT formulations. Furthermore, the present reviewcalls attention to the problem of 'polyallergy', which is still a major challenge for AIT and the emerging concept of 'component‑resolved diagnosis' (CRD) to address the issue. Finally, a prospective strategy for upgrading CRD to the next dimension is provided, and a potential technology for delivering thoroughly standardized AIT with minimal risk is discussed.

One Hundred Ten Years of Allergen Immunotherapy: A Broad Look Into the Future

Allergen immunotherapy (AIT) is the only disease-modifying treatment option for patients with type 1-mediated allergic diseases such as allergic rhinitis/rhinoconjunctivitis with/without allergic asthma. Although many innovations have been developed since the first clinical report of Noon et al in 1911, the improvement of clinical efficacy and tolerability of this treatment is still an important unmet need. Hence, much progress has been made in the characterization of the cell types, cytokines, and intracellular signaling events involved in the development, maintenance, and regulation of allergic reactions, and also in the understanding of the mechanisms of tolerance induction in AIT. This comprehensive review aims to summarize the current innovative approaches in AIT, but also gives an outlook on promising candidates of the future. On the basis of an extensive literature review, integrating a clinical point of view, this article focuses on recent and future innovations regarding biologicals, allergen-derived peptides, recombinant allergens, "Toll"-like receptor agonists and other adjuvants, and novel application routes being developed for future AIT.

The Content of CpG-DNA in Antigen-CpG Conjugate Vaccines Determines Their Cross-Presentation Activity

Cross-presentation, the process that facilitates display of exogenous antigens on MHC-I molecules, is a crucial step in the cascade of CD8 T cell activation. Potentiation of cross-presentation therefore represents an essential design criterion for development of subunit vaccines that target the induction of CD8 T cell immunity. Covalent conjugation of CpG-DNA to antigenic proteins has shown the potential to promote cross-presentation and has attracted great interest as a promising approach for vaccine development. However, heterogeneous product mixtures that result from typical conjugation schemes precluded identification of active conjugate species and impeded optimization of cross-presentation activity. In this report, we explore the effect of molecular composition of antigen-CpG conjugates on their cross-presentation activity using model Ovalbumin (OVA)-CpG conjugates. We developed a method to generate antigen-CpG conjugates with defined molecular compositions and leveraged this method to produce a series of OVA-CpG conjugates with one, two, and three CpG molecules linked to OVA. We observed that conjugates containing one CpG per OVA enhanced cross-presentation by 4-fold compared to native OVA, while conjugates with higher contents of CpG provided no cross-presentation enhancement. These differences are likely due to enhanced aggregation propensity observed for conjugates that carry more than one CpG per OVA. Our findings suggest that tuning molecular composition of antigen-CpG conjugates to maintain physical stability may be essential for achieving potent cross-presentation activity. Our method to generate defined conjugates could facilitate such molecular tuning and may be useful for continued development of antigen-CpG vaccines.

Investigations into the efficacy of multi-component cocaine vaccines

Although cocaine addiction remains a serious health and societal problem in the United States, no FDA-approved treatment has been developed. Vaccines offer an exciting strategy for the treatment of cocaine addiction; however, vaccine formulations need to be optimized to improve efficacy. Herein, we examine the effectiveness of a tricomponent cocaine vaccine, defined as having its hapten (GNE) and adjuvant (cytosine-guanine oligodeoxynucleotide 1826, CpG ODN 1826) covalently linked via the immunogenic protein ovalbumin (OVA). The tricomponent vaccine (GNE-OVA-CpG 1826) and a vaccine of analogous, individual components (GNE-OVA+CpG ODN 1826) were found to similarly induce highly specific anticocaine antibody production in mice and block cocaine's stimulant effects in hyperlocomotor testing.

Suppression of Allergic Response by CpG Motif Oligodeoxynucleotide–House-Dust Mite Conjugate in Animal Model of Allergic Rhinitis

Background

Although there have been many therapeutic options for allergic disease, the true allergen desensitization remains a challenging goal. The classic immunotherapy has a limited efficacy, is inconvenient, and has a risk of anaphylaxis. Recent reports revealed that immunostimulatory DNA sequences (ISS-oligdeoxynucleotide [ODN], CpG motif) act as a strong Th1 response–inducing adjuvants and that DNA-based vaccination might be an effective therapeutic option. In this study, we investigate whether ISS-ODN/Dermatophagoides farinae (Der f) conjugate has antiallergic effects in the allergic rhinitis mouse model, sensitive to house-dust mites. Der f is the most common allergen-inducing allergic rhinitis in Korea.

Methods

C57BL/6 mice were sensitized with crude extract of Der f. After injection of ISS-ODN or ISS-ODN/Der f conjugate, several parameters of allergic response were evaluated.

Results

Scratching and sneezing symptoms and eosinophilic infiltration into nasal mucosa were suppressed by injection with ISS-ODN only and ISS-ODN/Der f conjugate. Interleukin-5 level was decreased and interferon γ level was increased in nasal lavage fluid by injection of ISS-ODN/Der f conjugate. Der f–specific immunoglobulin E was decreased by injection of ISS-ODN or Der f /ISS-ODN conjugate; however, these were not statistically significant. Transforming growth factor β1 secreted by cultured splenocyte was increased significantly in ISS-ODN/Der f conjugate group.

Conclusion

These results suggest ISS-ODN/Der f conjugate induces an antiallergic effect and induces an increase in transforming growth factor β1 level in the allergic rhinitis model using Der f allergen. Allergic response developed by Der f allergen could be more effectively reduced by injection with ISS-ODN/Der f conjugate than by injection with ISS-ODN only.

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.

Adjuvants

Developing new vaccines against emerging pathogens or pathogens where variability of antigenic sites presents a challenge, the inclusion of stimulators of the innate immune system is critical to mature the immune response in a way that allows high avidity recognition while preserving the ability to react to drifted serovars. The innate immune system is an ancient mechanism for recognition of nonself and the first line of defense against pathogen insult. By triggering innate receptors, adjuvants can boost responses to vaccines and enhance the quality and magnitude of the resulting immune response. This chapter: (1) describes the innate immune system, (2) provides examples of how adjuvants are formulated to optimize their effectiveness, and (3) presents examples of how adjuvants can improve outcomes of immunization.

Dendritic cell targeted vaccines: Recent progresses and challenges

Dendritic cells (DCs) are known to be a set of morphology, structure and function of heterogeneous professional antigen presenting cells (APCs), as well as the strongest functional antigen presenting cells, which can absorb, process and present antigens. As the key regulators of innate and adaptive immune responses, DCs are at the center of the immune system and capable of interacting with both B cells and T cells, thereby manipulating the humoral and cellular immune responses. DCs provide an essential link between the innate and adaptive immunity, and the strong immune activation function of DCs and their properties of natural adjuvants, make them a valuable target for antigen delivery. Targeting antigens to DC-specific endocytic receptors in combination with the relevant antibodies or ligands along with immunostimulatory adjuvants has been recently recognized as a promising strategy for designing an effective vaccine that elicits a strong and durable T cell response against intracellular pathogens and cancer. This opinion article provides a brief summary of the rationales, superiorities and challenges of existing DC-targeting approaches.

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.

Immunogenicity of a Bivalent Adjuvanted Glycoconjugate Vaccine against Salmonella Typhimurium and Salmonella Enteritidis

Salmonella enterica serovars Typhimurium and Enteritidis are the predominant causes of invasive non-typhoidal Salmonella (iNTS) disease. Considering the co-endemicity of S. Typhimurium and S. Enteritidis, a bivalent vaccine formulation against both pathogens is necessary for protection against iNTS disease, thus investigation of glycoconjugate combination is required. In the present work, we investigated the immune responses induced by S. Typhimurium and S. Enteritidis monovalent and bivalent glycoconjugate vaccines adjuvanted with aluminum hydroxide (alum) only or in combination with cytosine-phosphorothioate-guanine oligodeoxynucleotide (CpG). Humoral and cellular, systemic and local, immune responses were characterized in two different mouse strains. All conjugate vaccines elicited high levels of serum IgG against the respective O-antigens (OAg) with bactericidal activity. The bivalent conjugate vaccine induced systemic production of antibodies against both S. Typhimurium and S. Enteritidis OAg. The presence of alum or alum + CpG adjuvants in vaccine formulations significantly increased the serum antigen-specific antibody production. The alum + CpG bivalent vaccine formulation triggered the highest systemic anti-OAg antibodies and also a significant increase of anti-OAg IgG in intestinal washes and fecal samples, with a positive correlation with serum levels. These data demonstrate the ability of monovalent and bivalent conjugate vaccines against S. Typhimurium and S. Enteritidis to induce systemic and local immune responses in different mouse strains, and highlight the suitability of a bivalent glycoconjugate formulation, especially when adjuvanted with alum + CpG, as a promising candidate vaccine against iNTS disease.

Induction of a balanced Th1/Th2 immune responses by co-delivery of PLGA/ovalbumin nanospheres and CpG ODNs/PEI-SWCNT nanoparticles as TLR9 agonist in BALB/c mice

To develop effective and safe vaccines with reduced dose of antigen and adjuvant, intelligent delivery systems are required. Many delivery systems have been developed to enhance the biological activity of cytosine-phosphorothioate-guanine oligodeoxynucleotides (CpG ODN) as both immunotherapeutic agents and vaccine adjuvants. In this study we designed a novel CpG ODN delivery system based on single-walled carbon nanotube (SWCNT) functionalized with polyethylenimine (PEI) and alkylcarboxylated PEI (AL-PEI). The physicochemical characteristics, cytotoxicity and cellular uptake studies of these carriers were performed. All carriers were conjugated with CpG ODN followed by co-delivery with ovalbumin (OVA) encapsulated into poly (lactic-co-glycolic acid) nanospheres (PLGA NSs) to enhance the induction of immune responses. The effect of these formulations on antibody (IgG1, IgG2a) and cytokine (IL-1β, IFN-γ, IL-4) production was evaluated in an in vivo experiment. The results showed that all nano-adjuvant formulations had a strong influence in up-regulation of IFN-γ and IL-4 in parallel with high IgG1-IgG2a isotype antibody titers in mice. In particular, SWCNT-AL-PEI nano-adjuvant formulation generated a balanced Th1 and Th2 immune response with more biased toward Th1 response without exhibiting any inflammatory and toxic effects. Therefore this nano-adjuvant formulation could be used as an efficient prophylactic immune responses agent.

Adjuvant-Loaded Subcellular Vesicles Derived From Disrupted Cancer Cells for Cancer Vaccination

Targeted subunit vaccines for cancer immunotherapy do not capture tumor antigenic complexity, and approaches employing tumor lysate are often limited by inefficient antigen uptake and presentation, and low immunogenicity. Here, whole cancer cells are processed to generate antigen-rich, membrane-enclosed subcellular particles, termed "reduced cancer cells", that reflect the diversity and breadth of the parent cancer cell antigen repertoire, and can be loaded with disparate adjuvant payloads. These vesicular particles enhance the uptake of the adjuvant payload, and potentiate the activation of primary dendritic cells in vitro. Similarly, reduced cancer cell-associated antigens are more efficiently presented by primary dendritic cells in vitro than their soluble counterparts or lysate control. In mice, vaccination using adjuvant-loaded reduced cancer cells facilitates the induction of antigen-specific cellular and humoral immune responses. Taken together, these observations demonstrate that adjuvant-loaded reduced cancer cells could be utilized in cancer vaccines as an alternative to lysate.

Liposome-Based Adjuvants for Subunit Vaccines: Formulation Strategies for Subunit Antigens and Immunostimulators

The development of subunit vaccines has become very attractive in recent years due to their superior safety profiles as compared to traditional vaccines based on live attenuated or whole inactivated pathogens, and there is an unmet medical need for improved vaccines and vaccines against pathogens for which no effective vaccines exist. The subunit vaccine technology exploits pathogen subunits as antigens, e.g., recombinant proteins or synthetic peptides, allowing for highly specific immune responses against the pathogens. However, such antigens are usually not sufficiently immunogenic to induce protective immunity, and they are often combined with adjuvants to ensure robust immune responses. Adjuvants are capable of enhancing and/or modulating immune responses by exposing antigens to antigen-presenting cells (APCs) concomitantly with conferring immune activation signals. Few adjuvant systems have been licensed for use in human vaccines, and they mainly stimulate humoral immunity. Thus, there is an unmet demand for the development of safe and efficient adjuvant systems that can also stimulate cell-mediated immunity (CMI). Adjuvants constitute a heterogeneous group of compounds, which can broadly be classified into delivery systems or immunostimulators. Liposomes are versatile delivery systems for antigens, and they can carefully be customized towards desired immune profiles by combining them with immunostimulators and optimizing their composition, physicochemical properties and antigen-loading mode. Immunostimulators represent highly diverse classes of molecules, e.g., lipids, nucleic acids, proteins and peptides, and they are ligands for pattern-recognition receptors (PRRs), which are differentially expressed on APC subsets. Different formulation strategies might thus be required for incorporation of immunostimulators and antigens, respectively, into liposomes, and the choice of immunostimulator should ideally be based on knowledge regarding the specific PRR expression profile of the target APCs. Here, we review state-of-the-art formulation approaches employed for the inclusion of immunostimulators and subunit antigens into liposome dispersion and their optimization towards robust vaccine formulations.

Experimental Immunization Based on Plasmodium Antigens Isolated by Antibody Affinity

Vaccines blocking malaria parasites in the blood-stage diminish mortality and morbidity caused by the disease. Here, we isolated antigens from total parasite proteins by antibody affinity chromatography to test an immunization against lethal malaria infection in a murine model. We used the sera of malaria self-resistant ICR mice to lethal Plasmodium yoelii yoelii 17XL for purification of their IgGs which were subsequently employed to isolate blood-stage parasite antigens that were inoculated to immunize BALB/c mice. The presence of specific antibodies in vaccinated mice serum was studied by immunoblot analysis at different days after vaccination and showed an intensive immune response to a wide range of antigens with molecular weight ranging between 22 and 250 kDa. The humoral response allowed delay of the infection after the inoculation to high lethal doses of P. yoelii yoelii 17XL resulting in a partial protection against malaria disease, although final survival was managed in a low proportion of challenged mice. This approach shows the potential to prevent malaria disease with a set of antigens isolated from blood-stage parasites.

TLR-9 agonist immunostimulatory sequence adjuvants linked to cancer antigens

The primary goal of cancer vaccines is to elicit tumor-specific cytotoxic T lymphocytes (CTL) capable of eradicating established tumors and preventing/eradicating their metastatic spread. CpG oligonucleotides (CpG ODN) activate and support the maturation of immune cells, including plasmacytoid dendritic cells and B lymphocytes, that express Toll-like receptor 9 (TLR9) and are capable of presenting tumor antigens to T cells. Thus, CpG ODN are effective vaccine adjuvants. The adjuvant activity of CpG ODN is improved by maintaining them in close physical and temporal proximity to the co-administered vaccine antigen. This work describes a method of chemically conjugating CpG ODN to antigens and/or cancer cells that improve the resulting CTL response.

Dendritic cell-targeted vaccines--hope or hype?

The development of an effective vaccine that elicits a strong and durable T cell response against intracellular pathogens and cancer is a challenge. One strategy to enhance the effectiveness of vaccination is by targeting dendritic cells (DCs). In this Opinion article, we discuss existing DC-targeting approaches that induce adaptive immunity. We highlight the crucial issues that need to be addressed to move the field forward and discuss whether targeting DCs could be better than current vaccine approaches.

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.

The effect of TLR9 agonist CpG oligodeoxynucleotides on the intestinal immune response of cobia (Rachycentron canadum)

Cytosine-guanine oligodeoxynucleotide (CpG ODN) motifs of bacterial DNA are recognized through toll-like receptor 9 (TLR9) and are potent activators of innate immunity. However, the interaction between TLR9 and CpG ODN in aquatic species has not been well characterized. Hence, cobia TLR9 isoform B (RCTLR9B) was cloned and its expression and induction in intestine were investigated. RCTLR9B cDNA consists of 3113bp encoding 1009 amino acids containing three regions, leucine rich repeats, transmembrane domain, and toll/interleukin-1 receptor (TIR) domain. Intraperitoneal injection of CpG ODN 2395 upregulated RCTLR9 A and B and MyD88 and also induced the expressions of Mx, chemokine CC, and interleukin IL-1β. Cobia intraperitoneally injected with CpG ODN 1668 and 2395 had increased survival rates after challenge with Photobacterium damselae subsp. piscicida. In addition, formulation of CpG ODN with formalin-killed bacteria (FKB) and aluminum hydroxide gel significantly increased expressions of RCTLR9 A (50 folds) and B (30 folds) isoforms at 10 dpi (CpG ODN 1668) and MyD88 (21 folds) at 6 dpv (CpG ODN 2395). Subsequently, IL-1β increased at 6 dpv in 1668 group. No histopathological damage and inflammatory responses were observed in the injected cobia. Altogether, these results facilitate CpG ODNs as an adjuvant to increase bacterial disease resistance and efficacy of vaccines in cobia.

A fusion protein between streptavidin and the endogenous TLR4 ligand EDA targets biotinylated antigens to dendritic cells and induces T cell responses in vivo

The development of tools for efficient targeting of antigens to antigen presenting cells is of great importance for vaccine development. We have previously shown that fusion proteins containing antigens fused to the extra domain A from fibronectin (EDA), an endogenous TLR4 ligand, which targets antigens to TLR4-expressing dendritic cells (DC), are highly immunogenic. To facilitate the procedure of joining EDA to any antigen of choice, we have prepared the fusion protein EDAvidin by linking EDA to the N terminus of streptavidin, allowing its conjugation with biotinylated antigens. We found that EDAvidin, as streptavidin, forms tetramers and binds biotin or biotinylated proteins with a Kd ~ 2.6 × 10(-14) mol/L. EDAvidin favours the uptake of biotinylated green fluorescent protein by DC. Moreover, EDAvidin retains the proinflammatory properties of EDA, inducing NF- κβ by TLR4-expressing cells, as well as the production of TNF- α by the human monocyte cell line THP1 and IL-12 by DC. More importantly, immunization of mice with EDAvidin conjugated with the biotinylated nonstructural NS3 protein from hepatitis C virus induces a strong anti-NS3 T cell immune response. These results open a new way to use the EDA-based delivery tool to target any antigen of choice to DC for vaccination against infectious diseases and cancer.

Chemical cross-linking of HIV-1 Env for direct TLR7/8 ligand conjugation compromises recognition of conserved antigenic determinants

Covalent conjugation of immune-stimulatory compounds to protein antigens is a potential means to self-adjuvant non-replicating subunit vaccines. Previously, it was demonstrated that covalent coupling of a Toll-like receptor (TLR) ligand to the exterior HIV-1 envelope glycoprotein, gp120, enhanced its immunogenicity. However, the consequences of chemical conjugation to gp120 on broadly neutralizing antibody (bNAb) epitopes were so far not examined. Here, we conjugated a TLR7/8 ligand to lysine residues on gp120 using NHS-PEO8-maleimide linkers and investigated if this affected Ab recognition of the CD4 binding site (CD4bs), a highly conserved target for bNAbs. We demonstrate that the recognition of the CD4bs was reduced following coupling, especially at a higher coupling ratio. These results have implications for the coupling of ligands to vaccine antigens where elicitation of humoral immune responses to specific neutralizing determinants is desired.

Modern subunit vaccines: development, components, and research opportunities

Traditional vaccines, based on the administration of killed or attenuated microorganisms, have proven to be among the most effective methods for disease prevention. Safety issues related to administering these complex mixtures, however, prevent their universal application. Through identification of the microbial components responsible for protective immunity, vaccine formulations can be simplified, enabling molecular-level vaccine characterization, improved safety profiles, prospects to develop new high-priority vaccines (e.g. for HIV, tuberculosis, and malaria), and the opportunity for extensive vaccine component optimization. This subunit approach, however, comes at the expense of decreased immunity, requiring the addition of immunostimulatory agents (adjuvants). As few adjuvants are currently used in licensed vaccines, adjuvant development represents an exciting area for medicinal chemists to play a role in the future of vaccine development. In addition, immune responses can be further customized though optimization of delivery systems, tuning the size of particulate vaccines, targeting specific cells of the immune system (e.g. dendritic cells), and adding components to aid vaccine efficacy in whole immunized populations (e.g. promiscuous T-helper epitopes). Herein we review the current state of the art and future direction in subunit vaccine development, with a focus on the described components and their potential to steer the immune response toward a desired response.

Encapsulating immunostimulatory CpG oligonucleotides in listeriolysin O-liposomes promotes a Th1-type response and CTL activity

Immunostimulatory sequences (ISS) are short DNA sequences containing unmethylated CpG dimers that have multiple effects on the host immune system, including the ability to stimulate antigen-specific cytotoxic T lymphocytes (CTLs) and drive Th1-type immune responses. Listeriolysin O (LLO)-containing pH-sensitive liposomes have been shown to efficiently deliver macromolecules to the cytosol of APCs and efficiently stimulate CTLs. We hypothesized that encapsulating ISS-oligodeoxyribonucleotides (ODNs) in this delivery system would enhance the cell-mediated immune response and skew Th1-type responses in protein antigen-based vaccination utilizing LLO-liposomes. In vitro studies indicated that coencapsulation of ISS in LLO-liposomes engendered activation of the NF-κB pathway while maintaining the efficient cytosolic delivery of antigen mediated by the coencapsulated LLO. Antigen-specific CTL responses monitored by using the model antigen ovalbumin (OVA) in mice were enhanced when mice were immunized with OVA and ISS-ODN-containing LLO-liposomes compared with those immunized with OVA-containing LLO-liposomes. The enhanced immune responses were of the Th1-type as monitored by the robust OVA-specific IgG2a induction and the OVA CD8 peptide-stimulated IFN-γ secretion. Our study suggests that including ISS-ODN in LLO-containing pH-sensitive liposomes yields a vaccine delivery system that enhances the cell-mediated immune response and skews this response toward the Th1-type.

Structure-dependent immunostimulatory effect of CpG oligodeoxynucleotides and their delivery system

Unmethylated cytosine-phosphate-guanosine (CpG) oligodeoxynucleotides (ODNs) are recognized by Toll-like receptor 9 (TLR9) found in antigen-presenting cells and B cells and can activate the immune system. Using CpG ODNs as an adjuvant has been found to be effective for treating infectious diseases, cancers, and allergies. Because natural ODNs with only a phosphodiester backbone are easily degraded by nuclease (deoxyribonuclease [DNase]) in serum, CpG ODNs with a phosphorothioate backbone have been studied for clinical application. CpG ODNs with a phosphorothioate backbone have raised concern regarding undesirable side effects; however, several CpG ODNs with only a phosphodiester backbone have been reported to be stable in serum and to show an immunostimulatory effect. In recent years, research has been conducted on delivery systems for CpG ODNs using nanoparticles (NPs). The advantages of NP-based delivery of CpG ODN include (1) it can protect CpG ODN from DNase, (2) it can retain CpG ODN inside the body for a long period of time, (3) it can improve the cellular uptake efficiency of CpG ODN, and (4) it can deliver CpG ODN to the target tissues. Because the target cells of CpG ODN are cells of the immune system and TLR9, the receptor of CpG ODN is localized in endolysosomes, CpG ODN delivery systems are required to have qualities different from other nucleic acid drugs such as antisense DNA and small interfering RNA. Studies until now have reported various NPs as carriers for CpG ODN delivery. This review presents DNase-resistant CpG ODNs with various structures and their immunostimulatory effects and also focuses on delivery systems of CpG ODNs that utilize NPs. Because CpG ODNs interact with TLR9 and activate both the innate and the adaptive immune system, the application of CpG ODNs for the treatment of cancers, infectious diseases, and allergies holds great promise.

Combination of a TLR4 ligand and anaphylatoxin C5a for the induction of antigen-specific cytotoxic T cell responses

The complement system and Toll-like receptors (TLR) are key innate defense systems which might interact synergistically on dendritic cells (DC) to reinforce adaptive immunity. In a previous work, we found that the extra domain A from fibronectin EDA (an endogenous ligand for TLR4) can favour antigen delivery to DC and induce their maturation. Given the potential of anaphylatoxins to cause inflammation and activation of myeloid cells, we hypothesized that a fusion protein between EDA, and anaphylatoxins C3a, C4a or C5a together with an antigen might improve the immunogenicity of the antigen. Naked DNA immunization with a construct expressing the fusion protein between C5a, EDA and the cytotoxic T cell epitope SIINFEKL from ovalbumin, induced strong antigen specific T cell responses. The purified recombinant fusion protein EDA-SIINFEKL-C5a induced activation of dendritic cells, the production of proinflammatory cytokines/chemokines and stimulated antigen presenting cell migration and NK cell activation. As compared to EDA-SIINFEKL, the fusion protein EDA-SIINFEKL-C5a did not induce the production of the immunosuppressive molecules IL-10, CCL17, CCL1, CXCL12 or XCL1 by DC. Moreover, EDA-SIINFEKL-C5a induced strong specific T cell responses in vivo and protected mice against E.G7-OVA tumor growth more efficiently than EDA-SIINFEKL or SIINFEKL-C5a recombinant proteins. Our results suggest that fusion proteins containing EDA, the anaphylatoxin C5a and the antigen may serve as a suitable strategy for the development of anti-tumor or anti-viral vaccines.

CpG still rocks! Update on an accidental drug

The discovery of the CpG motif in 1995 led to a change in the perception of the immune stimulatory effects of oligodeoxynucleotides (ODN) from an unwanted nonspecific effect to a highly evolved immune defense that can be selectively triggered for a wide range of therapeutic applications. Over the last decade dozens of human clinical trials have been conducted with different CpG ODN in thousands of humans for applications ranging from vaccine adjuvant to immunotherapies for allergy, cancer, and infectious diseases. Along with many positive results have come some failures showing the limitations of several therapeutic approaches. This review summarizes these results to provide an overview of the clinical development of CpG ODN.

MF59 and Pam3CSK4 boost adaptive responses to influenza subunit vaccine through an IFN type I-independent mechanism of action

The innate immune pathways induced by adjuvants required to increase adaptive responses to influenza subunit vaccines are not well characterized. We profiled different TLR-independent (MF59 and alum) and TLR-dependent (CpG, resiquimod, and Pam3CSK4) adjuvants for the ability to increase the immunogenicity to a trivalent influenza seasonal subunit vaccine and to tetanus toxoid (TT) in mouse. Although all adjuvants boosted the Ab responses to TT, only MF59 and Pam3CSK4 were able to enhance hemagglutinin Ab responses. To identify innate immune correlates of adjuvanticity to influenza subunit vaccine, we investigated the gene signatures induced by each adjuvant in vitro in splenocytes and in vivo in muscle and lymph nodes using DNA microarrays. We found that flu adjuvanticity correlates with the upregulation of proinflammatory genes and other genes involved in leukocyte transendothelial migration at the vaccine injection site. Confocal and FACS analysis confirmed that MF59 and Pam3CSK4 were the strongest inducers of blood cell recruitment in the muscle compared with the other adjuvants tested. Even though it has been proposed that IFN type I is required for adjuvanticity to influenza vaccines, we found that MF59 and Pam3CSK4 were not good inducers of IFN-related innate immunity pathways. By contrast, resiquimod failed to enhance the adaptive response to flu despite a strong activation of the IFN pathway in muscle and lymph nodes. By blocking IFN type I receptor through a mAb, we confirmed that the adjuvanticity of MF59 and Pam3CSK4 to a trivalent influenza vaccine and to TT is IFN independent.

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.

Targeting HIV-1 envelope glycoprotein trimers to B cells by using APRIL improves antibody responses

An HIV-1 vaccine remains elusive, in part because various factors limit the quantity and quality of the antibodies raised against the viral envelope glycoprotein complex (Env). We hypothesized that targeting Env vaccines directly to B cells, by fusing them to molecules that bind and activate these cells, would improve Env-specific antibody responses. Therefore, we fused trimeric Env gp140 to A PRoliferation-Inducing Ligand (APRIL), B-cell Activating Factor (BAFF), and CD40 Ligand (CD40L). The Env-APRIL, Env-BAFF, and Env-CD40L gp140 trimers all enhanced the expression of activation-induced cytidine deaminase (AID), the enzyme responsible for inducing somatic hypermutation, antibody affinity maturation, and antibody class switching. They also triggered IgM, IgG, and IgA secretion from human B cells in vitro. The Env-APRIL trimers induced higher anti-Env antibody responses in rabbits, including neutralizing antibodies against tier 1 viruses. The enhanced Env-specific responses were not associated with a general increase in total plasma antibody concentrations, indicating that the effect of APRIL was specific for Env. All the rabbit sera raised against gp140 trimers, irrespective of the presence of CD40L, BAFF, or APRIL, recognized trimeric Env efficiently, whereas sera raised against gp120 monomers did not. The levels of trimer-binding and virus-neutralizing antibodies were strongly correlated, suggesting that gp140 trimers are superior to gp120 monomers as immunogens. Targeting and activating B cells with a trimeric HIV-1 Env-APRIL fusion protein may therefore improve the induction of humoral immunity against HIV-1.

Adjuvanted, antigen loaded N-trimethyl chitosan nanoparticles for nasal and intradermal vaccination: adjuvant- and site-dependent immunogenicity in mice

N-trimethyl chitosan (TMC) nanoparticles have been shown to increase the immunogenicity of subunit antigens after nasal and intradermal administration. This work describes a second generation of TMC nanoparticles containing ovalbumin as a model antigen (TMC/OVA nanoparticles) and an immunopotentiator (TMC/OVA/immunopotentiator nanoparticles). The selection of immunopotentiators included Toll-like receptor (TLR) ligands lipopolysaccharide (LPS), PAM(3)CSK(4) (PAM), CpG DNA, the NOD-like receptor 2 ligand muramyl dipeptide (MDP) and the GM1 ganglioside receptor ligand, cholera toxin B subunit (CTB). The TMC/OVA/immunopotentiator nanoparticles were characterised physico-chemically and their immunogenicity was assessed by determining the serum IgG, IgG1, IgG2a titres and secretory IgA levels in nasal washes after intradermal and nasal vaccination in mice. After nasal vaccination, TMC/OVA nanoparticles containing LPS or MDP elicited higher IgG, IgG1 and sIgA levels than non-adjuvanted TMC/OVA particles, whereas nanoparticles containing CTB, PAM or CpG did not. After intradermal vaccination, the TMC/OVA/CpG and TMC/OVA/LPS nanoparticles provoked higher IgG titres than plain TMC/OVA particles. Altogether, our results show that co-encapsulation of an additional immunopotentiator with the antigen into TMC nanoparticles can further improve the immunogenicity of the vaccine. However, the strength and quality of the response depends on the immunopotentiator as well as the route of administration.

TLR7 enables cross-presentation by multiple dendritic cell subsets through a type I IFN-dependent pathway

Conjugation of TLR agonists to protein or peptide antigens has been demonstrated in many studies to be an effective vaccine formula in inducing cellular immunity. However, the molecular and cellular mediators involved in TLR-induced immune responses have not been carefully examined. In this study, we identify Type I IFN and IL-12 as critical mediators of cross-priming induced by a TLR7 agonist-antigen conjugate. We demonstrate that TLR7-driven cross-priming requires both Type I IFN and IL-12. Signaling through the IFN-αβR was required for the timely recruitment and accumulation of activated dendritic cells in the draining lymph nodes. Although IL-12 was indispensable during cross-priming, it did not regulate DC function. Therefore, the codependency for these 2 cytokines during TLR7-induced cross-priming is the result of their divergent effects on different cell-types. Furthermore, although dermal and CD8α(+) DCs were able to cross-prime CD8(+) T cells, Langerhans cells were unexpectedly found to potently cross-present antigen and support CD8(+) T-cell expansion, both in vitro and in vivo. Collectively, the data show that a TLR7 agonist-antigen conjugate elicits CD8(+) T-cell responses by the coordinated recruitment and activation of both tissue-derived and lymphoid organ-resident DC subsets through a Type I IFN and IL-12 codependent mechanism.

Conjugation of lipid and CpG-containing oligonucleotide yields an efficient method for liposome incorporation

For optimal stimulation of T cells, protein-based vaccines must deliver protein antigens to antigen-presenting cells while simultaneously providing immunostimulatory signals. Listeriolysin O (LLO)-containing liposomes have been utilized to efficiently deliver protein antigens to the cytosolic pathway for antigen processing and major histocompatibility complex class I-dependent presentation while codelivering immunostimulatory CpG-oligodeoxyribonuceotides (ODNs). In this report, we describe the synthesis of lipid-CpG-ODN conjugates utilizing maleimide-phosphatidylethanolamine (PE) lipids and 5'-sulfhdryl-containing CpG-ODNs as a method for facile incorporation of CpG-ODNs in liposomal vaccine carriers, an alternative to co-encapsulation inside liposomes and as a means to enhance delivery of CpG-ODNs to their major receptor, Toll-like receptor 9 (TLR9), in the endosome. The characterization and biological evaluation of the vaccine delivery system made of liposomes, which contain the lipid-CpG-ODN conjugates inserted in the liposomal membrane, is described. We demonstrate in vitro in bone marrow derived macrophages that the lipid-CpG-ODN conjugates incorporated onto the liposome bilayers interact with their receptor TLR9 as readily as liposome-encapsulated ODNs and exert their immunostimulatory capabilities. The liposomal vaccine delivery systems were evaluated in mice using ovalbumin (OVA) as a model antigen, and the results indicate equally robust OVA-specific cytotoxic T lymphocyte responses and similar Th1 immune skewing capabilities between liposomes containing lipid-conjugated or encapsulated CpG-ODNs. Overall, this work indicates that conjugating PE lipids and CpG-ODNs results in an efficient method that allows facile incorporation of CpG-ODNs into a liposome-based delivery platform while retaining the immune-stimulating capabilities of CpG-ODNs.

Use of defined TLR ligands as adjuvants within human vaccines

Our improved understanding of how innate immune responses can be initiated and how they can shape adaptive B- and T-cell responses is having a significant impact on vaccine development by directing the development of defined adjuvants. Experience with first generation vaccines, as well as rapid advances in developing defined vaccines containing Toll-like receptor ligands (TLRLs), indicate that an expanded number of safe and effective vaccines containing such molecules will be available in the future. In this review, we outline current knowledge regarding TLRs, detailing the different cell types that express TLRs, the various signaling pathways TLRs utilize, and the currently known TLRLs. We then discuss the current status of TLRLs within vaccine development programs, including the importance of appropriate formulation, and how recent developments can be used to better define the mechanisms of action of vaccines. Finally, we introduce the possibility of using TLRLs, either in combination or with non-TLRLs, to synergistically potentiate vaccine-induced responses to provide not only prophylactic, but therapeutic protection against infectious diseases and cancer.

Soluble proteins induce strong CD8+ T cell and antibody responses through electrostatic association with simple cationic or anionic lipopeptides that target TLR2

The low immunogenicity exhibited by most soluble proteins is generally due to the absence of molecular signatures that are recognized by the immune system as dangerous. In this study, we show that electrostatic binding of synthetic branched cationic or anionic lipopeptides that contain the TLR-2 agonist Pam(2)Cys markedly enhance a protein's immunogenicity. Binding of a charged lipopeptide to oppositely charged protein Ags resulted in the formation of stable complexes and occurs at physiologic pH and salt concentrations. The induction of cell-mediated responses is dependent on the electrostatic binding of lipopeptide to the protein, with no CD8(+) T cells being elicited when protein and lipopeptide possessed the same electrical charge. The CD8(+) T cells elicited after vaccination with lipopeptide-protein Ag complexes produced proinflammatory cytokines, exhibited in vivo lytic activity, and protected mice from challenge with an infectious chimeric influenza virus containing a single OVA epitope as part of the influenza neuraminidase protein. Induction of a CD8(+) T cell response correlated with the ability of lipopeptide to facilitate Ag uptake by DCs followed by trafficking of Ag-bearing cells into draining lymph nodes. Oppositely charged but not similarly charged lipopeptides were more effective in DC uptake and trafficking. Very high protein-specific Ab titers were also achieved by vaccination with complexes composed of oppositely charged lipopeptide and protein, whereas vaccination with similarly charged constituents resulted in significant but lower Ab titers. Regardless of whether similarly or oppositely charged lipopeptides were used in the induction of Ab, vaccination generated dominant IgG1 isotype Abs rather than IgG2a.

Protective T cell immunity in mice following protein-TLR7/8 agonist-conjugate immunization requires aggregation, type I IFN, and multiple DC subsets

The success of a non-live vaccine requires improved formulation and adjuvant selection to generate robust T cell immunity following immunization. Here, using protein linked to a TLR7/8 agonist (conjugate vaccine), we investigated the functional properties of vaccine formulation, the cytokines, and the DC subsets required to induce protective multifunctional T cell immunity in vivo. The conjugate vaccine required aggregation of the protein to elicit potent Th1 CD4+ and CD8+ T cell responses. Remarkably, the conjugate vaccine, through aggregation of the protein and activation of TLR7 in vivo, led to an influx of migratory DCs to the LN and increased antigen uptake by several resident and migratory DC subsets, with the latter effect strongly influenced by vaccine-induced type I IFN. Ex vivo migratory CD8-DEC205+CD103-CD326- langerin-negative dermal DCs were as potent in cross-presenting antigen to naive CD8+ T cells as CD11c+CD8+ DCs. Moreover, these cells also influenced Th1 CD4+ T cell priming. In summary, we propose a model in which broad-based T cell-mediated responses upon vaccination can be maximized by codelivery of aggregated protein and TLR7/8 agonist, which together promote optimal antigen acquisition and presentation by multiple DC subsets in the context of critical proinflammatory cytokines.

CpG-conjugated apoptotic tumor cells elicit potent tumor-specific immunity

The primary goal of cancer immunotherapy is to elicit an immune response capable of eradicating established tumors and preventing tumor metastasis. One strategy to achieve this goal utilizes whole killed tumor cells as the primary immunogen. Killed tumor cells provide a comprehensive source of tumor-associated antigens (TAAs), thereby eliminating the need to identify individual antigens. Unfortunately, killed tumor cells tend to be poorly immunogenic. To overcome this limitation, we covalently conjugated immunostimulatory CpG oligodeoxynucleotides (ODN) to apoptotic tumor cells and examined their ability to induce TAA-specific immune responses. Results indicate that CpG conjugation enhances the uptake of cell-based vaccines by dendritic cells (DCs), up-regulates co-stimulatory molecule expression, and promotes the production of immunostimulatory cytokines. Vaccination with CpG-conjugated tumor cells triggers the expansion of tumor-specific cytotoxic T lymphocytes (CTL) that reduce the growth of established tumors and prevents their metastatic spread. Thus, conjugating CpG ODN to cell-based tumor vaccines is an important step toward improving cancer immunotherapy.

Tumor therapy in mice by using a tumor antigen linked to modulin peptides from Staphylococcus epidermidis

Staphylococcus epidermidis releases a complex of at least four peptides, termed phenol-soluble modulins (PSM), which stimulate macrophages to produce proinflammatory cytokines via activation of TLR2 signalling pathway. We demonstrated that covalent linkage of PSM peptides to an antigen facilitate its capture by dendritic cells and, in combination with different TLR ligands, can favour the in vivo induction of strong and persistent antigen-specific immune responses. Treatment of mice grafted with HPV16-E7-expressing tumor cells (TC-1) with poly(I:C) and a peptide containing αMod linked to the H-2D(b)-restricted cytotoxic T-cell epitope E7(49-57) from HPV16-E7 protein allowed complete tumor regression in 100% of the animals. Surprisingly, this immunomodulatory property of modulin-derived peptides was TLR2 independent and partially dependent upon the EGF-receptor signalling pathway. Our results suggest that alpha or gamma modulin peptides may serve as a suitable antigen carrier for the development of anti-tumoral or anti-viral vaccines.

The capacity to induce cross-presentation dictates the success of a TLR7 agonist-conjugate vaccine for eliciting cellular immunity

Covalent conjugation of TLR agonists to protein Ags often facilitates the generation of a CD8(+) T cell response. However, mechanisms underlying the efficacy of the conjugate over its unconjugated counterpart have been largely uninvestigated. In this study, we show that conjugation of a TLR7 agonist enhances CD8(+) T cell responses without affecting Ag persistence and with minimal impact on cellular uptake of the Ag in vivo. Instead, the conjugated form induced a robust accumulation of dendritic cells (DCs) in regional lymph nodes. Perhaps more importantly, cross-presentation in DCs was detected only when the Ag was delivered in the conjugated form with the TLR7 agonist. Collectively, these data represent the first demonstration that a TLR agonist-Ag conjugate elicits CD8(+) T cell responses based not on its capacity to induce DC maturation or Ag persistence and uptake, but on the engagement of DC cross-presentation pathways.

TLR9-targeted biodegradable nanoparticles as immunization vectors protect against West Nile encephalitis

Vaccines that activate humoral and cell-mediated immune responses are urgently needed for many infectious agents, including the flaviviruses dengue and West Nile (WN) virus. Vaccine development would be greatly facilitated by a new approach, in which nanoscale modules (Ag, adjuvant, and carrier) are assembled into units that are optimized for stimulating immune responses to a specific pathogen. Toward that goal, we formulated biodegradable nanoparticles loaded with Ag and surface modified with the pathogen-associated molecular pattern CpG oligodeoxynucleotides. We chose to evaluate our construct using a recombinant envelope protein Ag from the WN virus and tested the efficiency of this system in eliciting humoral and cellular responses and providing protection against the live virus. Animals immunized with this system showed robust humoral responses polarized toward Th1 immune responses compared with predominately Th2-biased responses with the adjuvant aluminum hydroxide. Immunization with CpG oligodeoxynucleotide-modified nanoparticles resulted in a greater number of circulating effector T cells and greater activity of Ag-specific lymphocytes than unmodified nanoparticles or aluminum hydroxide. Ultimately, compared with alum, this system offered superior protection in a mouse model of WN virus encephalitis.

Induction of Th1 immune responses to Japanese cedar pollen allergen (Cry j 1) in mice immunized with Cry j 1 conjugated with CpG oligodeoxynucleotide

We determined whether a major Japanese cedar pollen allergen (Cry j 1) conjugated with CpG oligodeoxynucleotide would enhance allergen-specific Th1 responses in mice. Cry j 1 conjugated with CpG (Cry j 1-CpG) induced IL-12 in the spleen cells of naïve mice. Cry j 1-CpG immunization of BALB/c mice suppressed anti-Cry j 1 IgE response and enhanced anti-Cry j 1 IgG(2a) to subsequent Cry j 1 and alum adjuvant injection. CD4(+)T cells isolated from the spleens in mice immunized with Cry j 1-CpG produced higher IFN-γ levels than did CD4(+)T cells obtained from mice as negative controls. Our results suggested that Cry j 1-CpG immunization can induce Cry j 1-specific Th1 immune responses, thereby inhibiting IgE response to the pollen allergen.

Peptide conjugation at the 5'-end of oligodeoxynucleotides abrogates toll-like receptor 9-mediated immune stimulatory activity

Bacterial and synthetic DNA containing unmethylated CpG motifs act as ligands of Toll-like receptor 9 (TLR9). Our earlier studies showed that 5'-accessibility of synthetic oligodeoxynucleotides containing CpG motif (ODN) is required for TLR9-mediated immune stimulatory activity. Blocking the 5'-end of ODN through conjugation to a variety of moieties reduces immune stimulatory activity (Bioconjugate Chem. 2002, 13, 966-974). In the present study, we conjugated a model peptide, a 28-amino-acid-long beta-amyloid peptide, to either the 5'- or the 3'-end of an ODN via C3 and C6 alkyl linkers. We compared the immune stimulatory activity of the resulting conjugates with that of a parent ODN without conjugation in TLR9-transfected cells, mouse spleen cell cultures, and in vivo in mice. ODN with the peptide conjugated at the 3'-end via C3 and C6 linkers had immune stimulatory activity similar to that of the parent ODN in both in vitro and in vivo in mice. On the contrary, conjugation of peptide at the 5'-end of the ODN significantly abrogated immune stimulatory activity. In conclusion, the results presented here demonstrate that peptide/protein conjugation to ODN is optimal at the 3'-end with either C3 or C6 linker and conjugation at the 5'-end leads to significant loss of TLR9-mediated immune stimulation.

Immunization against hepatitis C virus with a fusion protein containing the extra domain A from fibronectin and the hepatitis C virus NS3 protein

BACKGROUND/AIMS

Vaccination strategies able to induce strong T-cell responses might contribute to eradicate hepatitis C virus (HCV) infection. We previously demonstrated that fusion of an antigen to the extra domain A from fibronectin (EDA) targets the antigen to TLR4-expressing dendritic cells (DC) and improves its immunogenicity. Here, we studied if fusion of EDA with the non-structural HCV protein NS3 might constitute an effective immunogen against HCV.

METHODS

Recombinant NS3 and the fusion protein EDA-NS3 were produced and purified from E. coli, and tested in vitro for their capacity to activate maturation of DC and to favour antigen presentation. HHD transgenic mice expressing the human HLA-A2 molecule were immunized with recombinant proteins in the absence or presence of poly(I:C) and anti-CD40 agonistic antibodies and responses elicited by vaccination were tested in vitro, and in vivo, by their capacity to downregulate intrahepatic expression of HCV-NS3 RNA.

RESULTS

EDA-NS3, but not NS3 alone, upregulated the expression of maturation markers, as well as Delta-like 1 and Delta-like 4 Notch ligands in DC and induced the production of IL-12. Mice immunized with EDA-NS3 had strong and long lasting NS3-specific CD4+ and CD8+ T-cell responses and, in combination with poly(I:C) and anti-CD40, downregulated intrahepatic expression of HCV-NS3 RNA.

CONCLUSIONS

Recombinant EDA-NS3 may be considered for the development of vaccines against HCV infection.

CpG DNA: Trigger of Sepsis, Mediator of Protection, or Both?

Unmethylated CpG motifs are prevalent in bacterial but not vertebrate genomic DNAs and activate immune cells that express the TLR9 receptor. This triggers the production of reactive oxygen species and the secretion of proinflammatory cytokines and chemokines. Under some conditions these effects can result in the systemic inflammatory response syndrome. Under other conditions, the immune stimulatory effects of CpG motifs can protect against pathogen challenge and initiate prophylactic and therapeutic innate and adaptive immune responses.

Immunostimulatory sequence oligdeoxynucleotide/cholera toxin B conjugate: a novel allergen-independent intranasal vaccine for allergic rhinitis

BACKGROUND

Recent studies have shown that by acting as strong TH1 response-inducing adjuvants, DNA immunostimulatory sequence oligdeoxynucleotides (ISS-ODNs) can be used in the treatment of allergic diseases, and efforts are being made to enhance these TH1 adjuvant actions.

OBJECTIVE

To determine whether intranasally delivered ISS-ODN/cholera toxin B (CTB) conjugate has enhanced antiallergic effects in an allergic rhinitis mouse model.

METHODS

BALB-c mice were sensitized with ovalbumin. Chemical conjugation of ISS-ODN and CTB was performed. After a single local intranasal administration of 50 microg of ISS-ODN or high- and low-dose (50- and 5-microg) ISS-ODN/CTB conjugate, we measured the allergic response in terms of sneezing events, eosinophil infiltration in the nasal mucosa, serum ovalbumin specific IgE and IgG2a levels, and TH1 and TH2 cytokine levels in nasal lavage fluid and spleen cell cultures.

RESULTS

A single local administration of 50 microg of ISS-ODN did not suppress the allergic phenotype. However, 50 and 5 microg of ISS-ODN/CTB conjugate significantly attenuated allergic symptoms, eosinophil infiltration in the nasal mucosa, and interleukin 4 production from nasal lavage fluid and cultured splenocyte supernatant compared with the allergic control. Serum specific IgG2a and interleukin 12 production in nasal lavage fluid and spleen cell cultures was significantly increased.

CONCLUSIONS

In a mouse model of allergic rhinitis, a single intranasal delivery of low-dose ISS-ODN/CTB conjugate effectively protects previously sensitized mice from allergic hypersensitivity responses. With further research, ISS-ODN/CTB conjugate may serve as a new allergen-independent intranasal vaccine for the treatment of allergic rhinitis.

Immunotherapeutic applications of CpG oligodeoxynucleotide TLR9 agonists

Toll-like receptor 9 (TLR9) agonists have demonstrated substantial potential as vaccine adjuvants, and as mono- or combination therapies for the treatment of cancer and infectious and allergic diseases. Commonly referred to as CpG oligodeoxynucleotides (ODN), TLR9 agonists directly induce the activation and maturation of plasmacytoid dendritic cells and enhance differentiation of B cells into antibody-secreting plasma cells. Preclinical and early clinical data support the use of TLR9 agonists as vaccine adjuvants, where they can enhance both the humoral and cellular responses to diverse antigens. In mouse tumor models TLR9 agonists have shown activity not only as monotherapy, but also in combination with multiple other therapies including vaccines, antibodies, cellular therapies, other immunotherapies, antiangiogenic agents, radiotherapy, cryotherapy, and some chemotherapies. Phase I and II clinical trials have indicated that these agents have antitumor activity as single agents and enhance the development of antitumor T-cell responses when used as therapeutic vaccine adjuvants. CpG ODN have shown benefit in multiple rodent and primate models of asthma and other allergic diseases, with encouraging results in some early human clinical trials. Although their potential clinical contributions are enormous, the safety and efficacy of these TLR9 agonists in humans remain to be determined.