Adjuvants in the Driver's Seat: How Magnitude, Type, Fine Specificity and Longevity of Immune Responses Are Driven by Distinct Classes of Immune Potentiators

Differentially Charged Liposomes Stimulate Dendritic Cells with Varying Effects on Uptake and Processing When Used Alone or in Combination with an Adjuvant

Liposomes carrying differential charges have been extensively studied for their role in stimulating dendritic cells (DCs), major antigen-presenting cells, known to serve as a pivotal bridge between innate and adaptive immunity. However, the impact of the differentially charged liposomes on activating DCs remains to be understood. In this study, we have investigated the impact of 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC)-based neutral, anionic, and cationic liposomes on the uptake, immunostimulation, and intracellular fate in mouse bone-marrow-derived DCs. We observed that liposomes could induce phenotypic maturation of DCs by inducing the expression of costimulatory molecules (CD40 and CD86) and production of cytokines tumor necrosis factor-α, interleukin-12,and nitric oxide. Interestingly, admixing monophosphoryl lipid A with charged liposomes further enhances the expression of the costimulatory molecules and production of cytokines, with preferential activation by positively charged liposomes. Fluorometric analysis using a pH-sensitive dye and flow-cytometry-based pathway inhibition assays revealed that cationic liposomes were taken up more efficiently by DCs through endocytosis and transported to neutral compartments for further processing, whereas anionic and neutral liposomes were inclined to accumulate in acidic compartments. These findings therefore endorse the use of cationic DSPC liposomes as a preferred option for vaccine delivery vehicles over neutral and negatively charged liposomes, particularly for the preferential activation of DCs.

Analysis of the Immunostimulatory Effects of Cytokine-Expressing Internal Ribosome Entry Site-Based RNA Adjuvants and Their Applications

Developing new adjuvants that can effectively induce humoral and cellular immune responses while broadening the immune response is of great value. In this study, we aimed to develop single-stranded RNA adjuvants expressing (1) granulocyte monocyte colony-stimulating factor or (2) interleukin 18 based on the encephalomyocarditis virus internal ribosome entry site; we also tested their efficacy in combination with ovalbumin or inactivated influenza vaccines. Notably, cytokine-expressing RNA adjuvants increased the expression of antigen-presenting cell activation markers in mice. Specifically, when combined with ovalbumin, RNA adjuvants expressing granulocyte monocyte colony-stimulating factor increased CD4+ T-cell responses, while those expressing interleukin 18 increased CD8+ T-cell responses. Cytokine-expressing RNA adjuvants further increased the frequency of polyclonal T cells with the influenza vaccine and reduced the clinical illness scores and weight loss of mice after viral challenge. Collectively, our results suggest that cytokine-expressing RNA adjuvants can be applied to protein-based or inactivated vaccines to increase their efficacy.

Boosting Mouse Defense against Lethal Toxoplasma gondii Infection with Full-Length and Soluble SAG1 Recombinant Protein

Toxoplasmosis is a major worldwide protozoan zoonosis. The surface antigen 1 (SAG1) of Toxoplasma gondii (T. gondii) has always been recognized as an ideal vaccine candidate antigen. However, the intact and soluble SAG1 protein is usually difficult to acquire in vitro, which is unfavorable for employing the recombinant protein as a vaccine candidate antigen. In the present study, we obtained the full-length SAG1 recombinant protein in soluble form by Escherichia coli Transetta (DE3) cells under optimized expression conditions. The immunogenicity and protective ability of this recombinant protein against T. gondii acute infection were evaluated in a mouse model. Monitoring changes in serum antibody levels and types, the presence of cytokines, and the rate of lymphocyte proliferation in vaccinated mice were used to assess humoral and cellular immune responses. Additional assessments were performed to determine the protective potency of the recombinant protein in combating T. gondii RH tachyzoites. It was found that the titers of both IgG2a and IgG2b were considerably greater in the immunized mice compared to the titers of IgG1 and IgG3. The levels of Th1-type cytokines (IFN-γ, IL-12p70, IL-2, and TNF-α) and Th2-type cytokines (IL-10) significantly increased when splenocytes from immunological group mice were treated with T. gondii lysate antigen. Compared to the control group, a recombinant protein substantially increased the longevity of infected mice, with an average death time prolonged by 14.50 ± 0.34 days (p < 0.0001). These findings suggest that the full-length and soluble SAG1 recombinant protein produced potent immune responses in mice and could be a preferred subunit vaccine candidate for T. gondii, offering a feasible option for vaccination against acute toxoplasmosis.

Cell-targeted vaccines: implications for adaptive immunity

Recent advancements in immunology and chemistry have facilitated advancements in targeted vaccine technology. Targeting specific cell types, tissue locations, or receptors can allow for modulation of the adaptive immune response to vaccines. This review provides an overview of cellular targets of vaccines, suggests methods of targeting and downstream effects on immune responses, and summarizes general trends in the literature. Understanding the relationships between vaccine targets and subsequent adaptive immune responses is critical for effective vaccine design. This knowledge could facilitate design of more effective, disease-specialized vaccines.

Self-Adjuvanting Calcium-Phosphate-Coated Microcrystal-Based Vaccines Induce Pyroptosis in Human and Livestock Immune Cells

Successful vaccines require adjuvants able to activate the innate immune system, eliciting antigen-specific immune responses and B-cell-mediated antibody production. However, unwanted secondary effects and the lack of effectiveness of traditional adjuvants has prompted investigation into novel adjuvants in recent years. Protein-coated microcrystals modified with calcium phosphate (CaP-PCMCs) in which vaccine antigens are co-immobilised within amino acid crystals represent one of these promising self-adjuvanting vaccine delivery systems. CaP-PCMCs has been shown to enhance antigen-specific IgG responses in mouse models; however, the exact mechanism of action of these microcrystals is currently unclear. Here, we set out to investigate this mechanism by studying the interaction between CaP-PCMCs and mammalian immune cells in an in vitro system. Incubation of cells with CaP-PCMCs induced rapid pyroptosis of peripheral blood mononuclear cells and monocyte-derived dendritic cells from cattle, sheep and humans, which was accompanied by the release of interleukin-1β and the activation of Caspase-1. We show that this pyroptotic event was cell-CaP-PCMCs contact dependent, and neither soluble calcium nor microcrystals without CaP (soluble PCMCs) induced pyroptosis. Our results corroborate CaP-PCMCs as a promising delivery system for vaccine antigens, showing great potential for subunit vaccines where the enhancement or find tuning of adaptive immunity is required.

Next-Generation Adjuvants: Applying Engineering Methods to Create and Evaluate Novel Immunological Responses

Adjuvants are a critical component of vaccines. Adjuvants typically target receptors that activate innate immune signaling pathways. Historically, adjuvant development has been laborious and slow, but has begun to accelerate over the past decade. Current adjuvant development consists of screening for an activating molecule, formulating lead molecules with an antigen, and testing this combination in an animal model. There are very few adjuvants approved for use in vaccines, however, as new candidates often fail due to poor clinical efficacy, intolerable side effects, or formulation limitations. Here, we consider new approaches using tools from engineering to improve next-generation adjuvant discovery and development. These approaches will create new immunological outcomes that will be evaluated with novel diagnostic tools. Potential improved immunological outcomes include reduced vaccine reactogenicity, tunable adaptive responses, and enhanced adjuvant delivery. Evaluations of these outcomes can leverage computational approaches to interpret "big data" obtained from experimentation. Applying engineering concepts and solutions will provide alternative perspectives, further accelerating the field of adjuvant discovery.

Development of synthetic, self-adjuvanting, and self-assembling anticancer vaccines based on a minimal saponin adjuvant and the tumor-associated MUC1 antigen

The overexpression of aberrantly glycosylated tumor-associated mucin-1 (TA-MUC1) in human cancers makes it a major target for the development of anticancer vaccines derived from synthetic MUC1-(glyco)peptide antigens. However, glycopeptide-based subunit vaccines are weakly immunogenic, requiring adjuvants and/or additional immunopotentiating approaches to generate optimal immune responses. Among these strategies, unimolecular self-adjuvanting vaccine constructs that do not need coadministration of adjuvants or conjugation to carrier proteins emerge as a promising but still underexploited approach. Herein, we report the design, synthesis, immune-evaluation in mice, and NMR studies of new, self-adjuvanting and self-assembling vaccines based on our QS-21-derived minimal adjuvant platform covalently linked to TA-MUC1-(glyco)peptide antigens and a peptide helper T-cell epitope. We have developed a modular, chemoselective strategy that harnesses two distal attachment points on the saponin adjuvant to conjugate the respective components in unprotected form and high yields via orthogonal ligations. In mice, only tri-component candidates but not unconjugated or di-component combinations induced significant TA-MUC1-specific IgG antibodies able to recognize the TA-MUC1 on cancer cells. NMR studies revealed the formation of self-assembled aggregates, in which the more hydrophilic TA-MUC1 moiety gets exposed to the solvent, favoring B-cell recognition. While dilution of the di-component saponin-(Tn)MUC1 constructs resulted in partial aggregate disruption, this was not observed for the more stably-organized tri-component candidates. This higher structural stability in solution correlates with their increased immunogenicity and suggests a longer half-life of the construct in physiological media, which together with the enhanced antigen multivalent presentation enabled by the particulate self-assembly, points to this self-adjuvanting tri-component vaccine as a promising synthetic candidate for further development.

Oral vaccination for sustainable disease prevention in aquaculture-an encapsulation approach

The prevalence of infectious diseases in the aquaculture industry and a limited number of safe and effective oral vaccines has imposed a challenge not only for fish immunity but also a threat to human health. The availability of fish oral vaccines has expanded recently, but little is known about how well they work and how they affect the immune system. The unsatisfactory efficacy of existing oral vaccinations is partly attributable to the antigen degradation in the adverse gastrointestinal environment of fishes, the highly tolerogenic gut environment, and inferior vaccine formulation. To overcome such challenges in designing: an easier, cost-efficient, and effective vaccination method, several encapsulation methods are being adopted to safeguard antigens from the intestinal atmosphere for their immunogenic functions. Oral vaccination is easily degraded by gastric acids and enzymes before reaching the immunological site; however, this issue can be solved by encapsulating antigens in poly-biodegradable nanoparticles, transgenic designed bacteria, plant systems, and live feeds. To enhance the immunological impact, each antigen delivery method operates at a different level. Utilizing nanotechnology, it has been possible to regulate vaccination parameters, target particular cells, and lower the antigen dosage with potent nanomaterials such as chitosan, poly D,L-lactic-co-glycolic acid (PLGA) as vaccine carriers. Live feeds such as Artemia salina can be utilized as bio-carrier, owing to their appropriate size and non-filter feed system, through a process called bio-encapsulation. It ensures the protection of antigens over the fish intestine and ensures complete uptake by immune cells in the hindgut for increased immune response. This review comprises recent advances in oral vaccination in aquaculture in terms of an encapsulation approach that can aid in future research.

Polyethyleneimine-based immunoadjuvants for designing cancer vaccines

Despite extensive efforts to improve the effectiveness of cancer vaccines, the lack of immunogenicity remains an issue. Adjuvants are required to enhance the immunogenicity of antigens and activate the immune response. However, only a few adjuvants with acceptable toxicity have sufficient potency for use in cancer vaccines, necessitating the discovery of potent adjuvants. The most well-known cationic polymer polyethyleneimine (PEI) acts as a carrier for delivering antigens, and as an immunoadjuvant for enhancing the innate and adaptive immunity. In this review, we have summarized PEI-based adjuvants and discussed how to improve and boost the immune response to vaccines. We further focused on PEI-based adjuvants in cancer vaccines. Finally, we have proposed the potential challenges and future issues of PEI-based adjuvants to elicit the effectiveness of cancer vaccines.

Multicomponent encapsulation into fully degradable protein nanocarriers via interfacial azide-alkyne click reaction in miniemulsion allows the co-delivery of immunotherapeutics

Encapsulation of multiple adjuvants along with antigens into nanocarriers allows a co-delivery to antigen-presenting cells for the synergistic induction of robust immune responses. However, loading cargoes of different molar masses, polarities, and solubilities in high efficiencies remains a challenge. Therefore, we developed a strategy to encapsulate a triple combination of the so-called adjuvants, i.e. with Resiquimod (R848), muramyl dipeptide (MDP) and polyinosinic-polycytidylic acid (Poly(I : C)) into human serum albumin (HSA) nanocarriers. The loading is conducted in situ while the nanocarrier is formed by an orthogonal and metal-free click reaction at the interface of an inverse miniemulsion. By this unique approach, high encapsulation efficiency without harming the cargo during the nanocarrier formation process and regardless of their physical properties is achieved, thus keeping their bioactivity. Furthermore, we demonstrated high control over the encapsulation efficiency and varying the amount of each cargo did not influence the efficiency of multicomponent encapsulation. Azide-modified HSA was crosslinked with hexanediol dipropiolate (HDDP) at the interface of a water-in-oil miniemulsion. Varying the crosslinker amount allowed us to tailor the density and degradation rates of the protein shell. Additional installation of disulfide bonds into the crosslinker created redox-responsive nanocarriers, which degraded both by protease and under reducing conditions with dithiothreitol. The prepared HSA nanocarriers were efficiently taken up by dendritic cells and exhibited an additive cell activation and maturation, exceeding the nanocarriers loaded with only a single drug. This general protocol allows the orthogonal and metal-free encapsulation of various drugs or adjuvants at defined concentrations into the protein nanocarriers.

Photosynthetic microorganisms coupled photodynamic therapy for enhanced antitumor immune effect

The ideal photodynamic therapy (PDT) should effectively remove the primary tumor, and produce a stronger immune memory effect to inhibit the tumor recurrence and tumor metastasis. However, limited by the hypoxic and immunosuppressive microenvironment, the PDT efficiency is apparently low. Here, Chlorella (Chl.) is exploited to enhance local effect by producing oxygen to reverse hypoxia, and release adjuvants to reverse immunosuppressive microenvironment to enhance abscopal effect afterwards. Results from different animal models indicated that Chl. could enhance local effect and PDT related immune response. Ultimately, Chl. coupled PDT elicited anti-tumor effects toward established primary tumors (inhibition rate: 90%) and abscopal tumors (75%), controlled the challenged tumors (100%) and alleviated metastatic tumors (90%). This Chl. coupled PDT strategy can also produce a stronger anti-tumor immune memory effect. Overall, this Chl. coupled PDT strategy generates enhanced local tumor killing, boosts PDT-induced immune responses and promotes anti-tumor immune memory effect, which may be a great progress for realizing systemic effect of PDT.

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Chlorella can act as oxygen supplier and release adjuvants under light irradiation to enhance photodynamic therapy (PDT).

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The dual characteristics of Chlorella strengthen the occurrence of effective anti-tumor immune responses.

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Enhanced local and abscopal anti-tumor effect can be achieved by Chlorella with good biocompatibility.

Rational Development of a Polysaccharide-Protein-Conjugated Nanoparticle Vaccine Against SARS-CoV-2 Variants and Streptococcus pneumoniae

The ongoing COVID-19 pandemic caused by SARS-CoV-2 has led to millions of deaths worldwide. Streptococcus pneumoniae (S. pneumoniae) remains a major cause of mortality in underdeveloped countries. A vaccine that prevents both SARS-CoV-2 and S. pneumoniae infection represents a long-sought "magic bullet". Herein, a nanoparticle vaccine, termed SCTV01B, is rationally developed by using the capsular polysaccharide of S. pneumoniae serotype 14 (PPS14) as the backbone to conjugate with the recombinant receptor-binding domain (RBD) of the SARS-CoV-2 spike protein. The final formulation of conjugated nanoparticles in the network structure exhibits high thermal stability. Immunization with SCTV01B induces potent humoral and Type 1/Type 2 T helper cell (Th1/Th2) cellular immune responses in mice, rats, and rhesus macaques. In particular, SCTV01B-immunized serum not only broadly cross-neutralizes all SARS-CoV-2 variants of concern (VOCs), including the most recent Omicron variant, but also shows high opsonophagocytic activity (OPA) against S. pneumoniae serotype 14. Finally, SCTV01B vaccination confers protection against challenges with the SARS-CoV-2 mouse-adapted strain and the original strain in established murine models. Collectively, these promising preclinical results support further clinical evaluation of SCTV01B, highlighting the potency of polysaccharide-RBD-conjugated nanoparticle vaccine platforms for the development of vaccines for COVID-19 and other infectious diseases.

Chrysin Enhances Anti-tumor Immunity Response through IL-12-STAT4 Signal Pathway in B16F10 Melanoma Mouse Model

Chrysin (CHR) is a flavonoid with extensive pharmacological activity. The molecular formula of CHR is C₁₅ H₁₀ O₄ . CHR is reported to have antioxidative, anti-tumor and anti-viral functions. To evaluate its potential function as a vaccine adjuvant, we prepared a melanoma vaccine using a soluble protein extract of B16F10 melanoma cells as antigen and CHR as an adjuvant. The melanoma model was developed after two immunisations, and it was discovered that combining B16F10 soluble protein antigen-mixed CHR vaccine could inhibit tumor growth in the mouse model, and the overall survival rate was higher than that of the B16F10 antigen vaccine alone. In vivo and in vitro experiments were conducted to determine whether CHR functioned as an adjuvant by activating antigen-presenting cells (APCs). We discovered that CHR activated APCs both in vivo and in vitro and may enhance Th1 cell function by activating the IL12-STAT4 signal pathway, thereby enhancing the anti-tumor response of cytotoxic T lymphocytes (CTL) in vivo. Next, to verify the critical role of CD8⁺ T cells in suppressing melanoma development, we transplanted CD8⁺ T cells from immunised mice to B16F10 tumor-bearing mice and discovered that the survival rate of tumor-bearing mice was significantly prolonged. In summary, our experimental results indicate that CHR can be used as a potential adjuvant to enhance antigen immunogenicity, inhibit B16F10 tumor growth in mice and improve tumor immune response.

Advance research in biomedical applications on marine sulfated polysaccharide

Marine ecosystem associated organisms are an affluent source of bioactive compounds. Polysaccharides with unique structural and practical entities have gained special studies interest inside the current biomedical zone. Polysaccharides are the main components of marine algae, plants, animals, insects, and microorganisms. In recent times research on seaweed is more persistent for extraction of natural bioactive "Sulfated polysaccharides" (SPs). The considerable amount of SP exists in the algae in the form of fucans, fucoidans, carrageenans, ulvan, etc. Major function of SPs is to act as a defensive lattice towards the infective organism. All SPs possess the high potential and possess a broad range of therapeutic applications as antitumor, immunomodulatory, vaccine adjuvant, anti-inflammatory, anticoagulant, antiviral, antiprotozoal, antimicrobial, antilipemic, therapy of regenerative medicine, also in drug delivery and tissue engineering application. This review aims to discuss the biomedicine applications of sulfated polysaccharides from marine seaweeds.

SARS-CoV-2 ferritin nanoparticle vaccine induces robust innate immune activity driving polyfunctional spike-specific T cell responses

The emergence of variants of concern, some with reduced susceptibility to COVID-19 vaccines underscores consideration for the understanding of vaccine design that optimizes induction of effective cellular and humoral immune responses. We assessed a SARS-CoV-2 spike-ferritin nanoparticle (SpFN) immunogen paired with two distinct adjuvants, Alhydrogel® or Army Liposome Formulation containing QS-21 (ALFQ) for unique vaccine evoked immune signatures. Recruitment of highly activated multifaceted antigen-presenting cells to the lymph nodes of SpFN+ALFQ vaccinated mice was associated with an increased frequency of polyfunctional spike-specific memory CD4+ T cells and Kb spike-(539-546)-specific long-lived memory CD8+ T cells with effective cytolytic function and distribution to the lungs. The presence of this epitope in SARS-CoV, suggests that generation of cross-reactive T cells may be induced against other coronavirus strains. Our study reveals that a nanoparticle vaccine, combined with a potent adjuvant that effectively engages innate immune cells, enhances SARS-CoV-2-specific durable adaptive immune T cell responses.

Peptide vaccines designed with the aid of immunoinformatic against Caseous Lymphadenitis promotes humoral and cellular response induction in mice

Caseous Lymphadenitis (CLA) is a chronic disease that affects also small ruminants. CLA is caused by Corynebacterium pseudotuberculosis and is responsible for high economic losses due to the formation of superficial and visceral granulomas, the latter is considered as asymptomatic CLA causing high levels of dissemination. Several vaccination strategies, in which the use of synthetic peptides stands out. Thus, this work aimed to evaluate the protective potential of peptide vaccines designed to determine the immunodominant epitopes of CP40 against CLA in mice. The animals were divided into eight groups separated in controls (G1-PBS, G2-Saponin and G9-rCP40) and experimental (G3-pep1, G4- pep2, G5-pep3, G6-pep4, G7-pep5 and G8-pep6), these were vaccinated on days 0 and 15 by a subcutaneous route. 60 days after the first immunization, all animals were challenged with C. pseudotuberculosis. On days 0, 15, 60, and 120 after the first immunization, blood samples were taken to measure immunoglobulins. On the same day of the challenge, the splenocytes were isolated and assayed for the production of IL-2, IL-4, IL-6, IFN-γ, TNF-α, IL-17, and IL-10. After vaccinations, the animals were challenged and all of them were affected by the disease which led to their death. The G6 and G8 groups provided 10% protection and the G7 provided 20%. The G3 and G4 groups provided 30% and 40% protection respectively. The peptides showed the production of Total IgG antibodies and cytokines (IL-2, IL-4, IL-6, IFN-γ, and TNF-α), indicating a possible activation of the Th1 type response. However, groups G3, G5, G6, and G8 showed production of IL-17. None of the study groups showed IL-10 production. The immunogenicity of the peptides was not enough to protect these animals and it is believed that the use of adjuvants based on PAMPs may improve the immune response offered by these peptides.

Immunochemistry-Based Diagnosis of Extrapulmonary Tuberculosis: A Strategy for Large-Scale Production of MPT64-Antibodies for Use in the MPT64 Antigen Detection Test

Tuberculosis (TB) is a global health problem. The immunohistochemistry (IHC)-based MPT64 antigen detection test has shown promising results for diagnosing extrapulmonary TB in previous studies. However, the anti-MPT64 antibody currently used in the test is in limited supply, and reproduction of a functional antibody is a prerequisite for further large-scale use. Various antigen-adjuvant combinations and immunisation protocols were tested in mice and rabbits to generate monoclonal and polyclonal antibodies. Antibodies were screened in IHC, and the final new antibody was validated on clinical human specimens. We were not able to generate monoclonal antibodies that were functional in IHC, but we obtained multiple functional polyclonal antibodies through careful selection of antigen-adjuvant and comprehensive screening in IHC of both pre-immune sera and antisera. To overcome the limitation of batch-to-batch variability with polyclonal antibodies, the best performing individual polyclonal antibodies were pooled to one final large-volume new anti-MPT64 antibody. The sensitivity of the new antibody was in the same range as the reference antibody, while the specificity was somewhat reduced. Our results suggest that it possible to reproduce a large-volume functional polyclonal antibody with stable performance, thereby securing stable supplies and reproducibility of the MPT64 test, albeit further validation remains to be done.

Carbohydrate-containing nanoparticles as vaccine adjuvants

Introduction: Adjuvants are essential to vaccines for immunopotentiation in the elicitation of protective immunity. However, classical and widely used aluminum-based adjuvants have limited capacity to induce cellular response. There are increasing needs for appropriate adjuvants with improved profiles for vaccine development toward emerging pathogens. Carbohydrate-containing nanoparticles (NPs) with immunomodulatory activity and particulate nanocarriers for effective antigen presentation are capable of eliciting a more balanced humoral and cellular immune response.Areas covered: We reviewed several carbohydrates with immunomodulatory properties. They include chitosan, β-glucan, mannan, and saponins, which have been used in vaccine formulations. The mode of action, the preparation methods, characterization of these carbohydrate-containing NPs and the corresponding vaccines are presented.Expert opinion: Several carbohydrate-containing NPs have entered the clinical stage or have been used in licensed vaccines for human use. Saponin-containing NPs are being evaluated in a vaccine against SARS-CoV-2, the pathogen causing the on-going worldwide pandemic. Vaccines with carbohydrate-containing NPs are in different stages of development, from preclinical studies to late-stage clinical trials. A better understanding of the mode of action for carbohydrate-containing NPs as vaccine carriers and as immunostimulators will likely contribute to the design and development of new generation vaccines against cancer and infectious diseases.

Orally administered β-glucan improves the hemolytic activity of the complement system in horses

Background and Aim:

Immune-modulating molecules mainly act on innate immune cells, which are central to early defense against invading pathogens and contribute to developing adaptive immunity. Yeast-extracted β-glucan, a model immune-modulating molecule, is widely used in several animal species; however, its effect on horse immune parameters has not been thoroughly investigated yet. This study aimed to evaluate the effects of orally administered β-glucan on selected innate immune parameters in horses.

Materials and Methods:

Eighteen thoroughbred horses were assigned equally into three groups as follows: One control group (no β-glucan) and two β-glucan experimental groups (one received 125 mg and the other 2 g of β-glucan per day for 28 days). Blood samples were collected before and at the end of the experiment for hematological analysis, whole blood phagocytosis, respiratory burst assays, and to assess the serum lysozyme and complement hemolytic activities.

Results:

At the end of the experiment, significant decreases (p<0.05) in monocyte numbers were observed in the control horses (258.8±45.9 vs. 115.3±41.5) and in those fed 125 mg/day of β-glucan (208.8±72.3 vs. 99.2±60.7), whereas a significant increase in numbers was noted in the horses that were fed 2 g/day of β-glucan (303.5±45.8 vs. 429.8±86.0; p<0.05). The natural hemolytic activity of the complement was higher only in horses fed 2 g/day of β-glucan (p=0.018) compared to the other groups. The hemolytic activity in the classical pathway was higher in those fed 125 mg/day (p=0.0035) and 2 g/day of β-glucan (p=0.0001).

Conclusion:

β-glucan improves important innate immune parameters and might be fed to horses before stressful events.

Trehalose diamide glycolipids augment antigen-specific antibody responses in a Mincle-dependent manner

Many studies have investigated how trehalose glycolipid structures can be modified to improve their Macrophage inducible C-type lectin (Mincle)-mediated adjuvanticity. However, in all instances, the ester-linkage of α,ά-trehalose to the lipid of choice remained. We investigated how changing this ester-linkage to an amide influences Mincle signalling and agonist activity and demonstrated that Mincle tolerates this functional group change. In in vivo vaccination studies in murine and ovine model systems, using OVA or Mannheimia haemolytica and Mycoplasma ovipneumoniae as vaccine antigens, respectively, it was demonstrated that a representative trehalose diamide glycolipid was able to enhance antibody-specific immune responses. Notably, IgG titres against M. ovipneumoniae were significantly greater when using trehalose dibehenamide (A-TDB) compared to trehalose dibehenate (TDB). This is particularly important as infection with M. ovipneumoniae predisposes sheep to pneumonia.

Zika Virus Envelope Domain III Recombinant Protein Delivered With Saponin-Based Nanoadjuvant From Quillaja brasiliensis Enhances Anti-Zika Immune Responses, Including Neutralizing Antibodies and Splenocyte Proliferation

Nanoadjuvants that combine immunostimulatory properties and delivery systems reportedly bestow major improvements on the efficacy of recombinant, protein-based vaccines. Among these, self-assembled micellar formulations named ISCOMs (immune stimulating complexes) show a great ability to trigger powerful immunological responses against infectious pathogens. Here, a nanoadjuvant preparation, based on saponins from Quillaja brasiliensis, was evaluated together with an experimental Zika virus (ZIKV) vaccine (IQB80-zEDIII) and compared to an equivalent vaccine with alum as the standard adjuvant. The preparations were administered to mice in two doses (on days zero and 14) and immune responses were evaluated on day 28 post-priming. Serum levels of anti-Zika virus IgG, IgG1, IgG2b, IgG2c, IgG3 were significantly increased by the nanoadjuvant vaccine, compared to the mice that received the alum-adjuvanted vaccine or the unadjuvanted vaccine. In addition, a robust production of neutralizing antibodies and in vitro splenocyte proliferative responses were observed in mice immunized with IQB80-zEDIII nanoformulated vaccine. Therefore, the IQB80-zEDIII recombinant preparation seems to be a suitable candidate vaccine for ZIKV. Overall, this study identified saponin-based delivery systems as an adequate adjuvant for recombinant ZIKV vaccines and has important implications for recombinant protein-based vaccine formulations against other flaviviruses and possibly enveloped viruses.

Natural and synthetic carbohydrate-based vaccine adjuvants and their mechanisms of action

Modern subunit vaccines based on homogeneous antigens offer more precise targeting and improved safety compared with traditional whole-pathogen vaccines. However, they are also less immunogenic and require an adjuvant to increase the immunogenicity of the antigen and potentiate the immune response. Unfortunately, few adjuvants have sufficient potency and low enough toxicity for clinical use, highlighting the urgent need for new, potent and safe adjuvants. Notably, a number of natural and synthetic carbohydrate structures have been used as adjuvants in clinical trials, and two have recently been approved in human vaccines. However, naturally derived carbohydrate adjuvants are heterogeneous, difficult to obtain and, in some cases, unstable. In addition, their molecular mechanisms of action are generally not fully understood, partly owing to the lack of tools to elucidate their immune-potentiating effects, thus hampering the rational development of optimized adjuvants. To address these challenges, modification of the natural product structure using synthetic chemistry emerges as an attractive approach to develop well-defined, improved carbohydrate-containing adjuvants and chemical probes for mechanistic investigation. This Review describes selected examples of natural and synthetic carbohydrate-based adjuvants and their application in synthetic self-adjuvanting vaccines, while also discussing current understanding of their molecular mechanisms of action.

Effective and Safe Stimulation of Humoral and Cell-Mediated Immunity by Intradermal Immunization with a Cyclic Dinucleotide/Nanoparticle Combination Adjuvant

Intradermal (ID) immunization is an attractive route of vaccination because it targets tissue rich in dendritic cells, has dose-sparing potential, and allows needle-free delivery. However, few adjuvants are effective, nonreactogenic, and compatible with needle-free delivery devices. In this study, we demonstrate that a combination adjuvant composed of cyclic-di-AMP (cdAMP) and the plant-derived nanoparticle adjuvant Nano-11 significantly enhanced the immune response to ID-injected vaccines in mice and pigs with minimal local reaction at the injection site. The cdAMP/Nano-11 combination adjuvant increased Ag uptake by lymph node-resident and migratory skin dendritic cell subpopulations, including Langerhans cells. ID immunization with cdAMP/Nano-11 expanded the population of germinal center B cells and follicular helper T cells in the draining lymph node and Ag-specific Th1 and Th17 cells in the spleen. It elicited an enhanced immune response with a significant increase of IgG1 and IgG2a responses in mice at a reduced dose compared with i.m. immunization. An increased IgG response was observed following needle-free ID immunization of pigs. Nano-11 and cdAMP demonstrated a strong synergistic interaction, as shown in the activation of mouse, human, and porcine APC, with increased expression of costimulatory molecules and secretion of TNF and IL-1β. The combination adjuvant induced robust activation of both NF-κB and IFN regulatory factor signaling pathways and the NLRP3 inflammasome. We conclude that the combination of Nano-11 and cdAMP is a promising adjuvant for ID delivery of vaccines that supports a balanced immune response.

High- and low-molecular-weight chitosan act as adjuvants during single-dose influenza A virus protein vaccination through distinct mechanisms

The investigation of new adjuvants is essential for the development of efficacious vaccines. Chitosan (CS), a derivative of chitin, has been shown to act as an adjuvant, improving vaccine-induced immune responses. However, the effect of CS molecular weight (MW) on this adjuvanticity has not been investigated, despite MW having been shown to impact CS biological properties. Here, two MW variants of CS were investigated for their ability to enhance vaccine-elicited immune responses in vitro and in vivo, using a single-dose influenza A virus (IAV) protein vaccine model. Both low-molecular-weight (LMW) and high-molecular-weight (HMW) CS-induced interferon regulatory factor pathway signaling, antigen-presenting cell activation, and cytokine messenger RNA (mRNA) production, with LMW inducing higher mRNA levels at 24 h and HMW elevating mRNA responses at 48 h. LMW and HMW CS also induced adaptive immune responses after vaccination, indicated by enhanced immunoglobulin G production in mice receiving LMW CS and increased CD4 interleukin 4 (IL-4) and IL-2 production in mice receiving HMW CS. Importantly, both LMW and HMW CS adjuvantation reduced morbidity following homologous IAV challenge. Taken together, these results support that LMW and HMW CS can act as adjuvants, although this protection may be mediated through distinct mechanisms based on CS MW.

Carbohydrate Immune Adjuvants in Subunit Vaccines

Modern subunit vaccines are composed of antigens and a delivery system and/or adjuvant (immune stimulator) that triggers the desired immune responses. Adjuvants mimic pathogen-associated molecular patterns (PAMPs) that are typically associated with infections. Carbohydrates displayed on the surface of pathogens are often recognized as PAMPs by receptors on antigen-presenting cells (APCs). Consequently, carbohydrates and their analogues have been used as adjuvants and delivery systems to promote antigen transport to APCs. Carbohydrates are biocompatible, usually nontoxic, biodegradable, and some are mucoadhesive. As such, carbohydrates and their derivatives have been intensively explored for the development of new adjuvants. This review assesses the immunological functions of carbohydrate ligands and their ability to enhance systemic and mucosal immune responses against co-administered antigens. The role of carbohydrate-based adjuvants/delivery systems in the development of subunit vaccines is discussed in detail.

Cationic Nanostructures for Vaccines Design

Subunit vaccines rely on adjuvants carrying one or a few molecular antigens from the pathogen in order to guarantee an improved immune response. However, to be effective, the vaccine formulation usually consists of several components: an antigen carrier, the antigen, a stimulator of cellular immunity such as a Toll-like Receptors (TLRs) ligand, and a stimulator of humoral response such as an inflammasome activator. Most antigens are negatively charged and combine well with oppositely charged adjuvants. This explains the paramount importance of studying a variety of cationic supramolecular assemblies aiming at the optimal activity in vivo associated with adjuvant simplicity, positive charge, nanometric size, and colloidal stability. In this review, we discuss the use of several antigen/adjuvant cationic combinations. The discussion involves antigen assembled to 1) cationic lipids, 2) cationic polymers, 3) cationic lipid/polymer nanostructures, and 4) cationic polymer/biocompatible polymer nanostructures. Some of these cationic assemblies revealed good yet poorly explored perspectives as general adjuvants for vaccine design.

Potential of Bacteriocins from Lactobacillus taiwanensis for Producing Bacterial Ghosts as a Next Generation Vaccine

Bacteriocins are functionally diverse toxins produced by most microbes and are potent antimicrobial peptides (AMPs) for bacterial ghosts as next generation vaccines. Here, we first report that the AMPs secreted from Lactobacillus taiwanensis effectively form ghosts of pathogenic bacteria and are identified as diverse bacteriocins, including novel ones. In detail, a cell-free supernatant from L. taiwanensis exhibited antimicrobial activities against pathogenic bacteria and was observed to effectively cause cellular lysis through pore formation in the bacterial membrane using scanning electron microscopy (SEM). The treatment of the cell-free supernatant with proteinase K or EDTA proved that the antimicrobial activity is mediated by AMPs, and the purification of AMPs using Sep-Pak columns indicated that the cell-free supernatant includes various amphipathic peptides responsible for the antimicrobial activity. Furthermore, the whole-genome sequencing of L. taiwanensis revealed that the strain has diverse bacteriocins, confirmed experimentally to function as AMPs, and among them are three novel bacteriocins, designated as Tan 1, Tan 2, and Tan 3. We also confirmed, using SEM, that Tan 2 effectively produces bacterial ghosts. Therefore, our data suggest that the bacteriocins from L. taiwanensis are potentially useful as a critical component for the preparation of bacterial ghosts.

Controlling timing and location in vaccines

Vaccines are one of the most powerful technologies supporting public health. The adaptive immune response induced by immunization arises following appropriate activation and differentiation of T and B cells in lymph nodes. Among many parameters impacting the resulting immune response, the presence of antigen and inflammatory cues for an appropriate temporal duration within the lymph nodes, and further within appropriate subcompartments of the lymph nodes- the right timing and location- play a critical role in shaping cellular and humoral immunity. Here we review recent advances in our understanding of how vaccine kinetics and biodistribution impact adaptive immunity, and the underlying immunological mechanisms that govern these responses. We discuss emerging approaches to engineer these properties for future vaccines, with a focus on subunit vaccines.

Role of Opsonophagocytosis in Immune Protection against Malaria

The quest for immune correlates of protection continues to slow vaccine development. To date, only vaccine-induced antibodies have been confirmed as direct immune correlates of protection against a plethora of pathogens. Vaccine immunologists, however, have learned through extensive characterizations of humoral responses that the quantitative assessment of antibody responses alone often fails to correlate with protective immunity or vaccine efficacy. Despite these limitations, the simple measurement of post-vaccination antibody titers remains the most widely used approaches for vaccine evaluation. Developing and performing functional assays to assess the biological activity of pathogen-specific responses continues to gain momentum; integrating serological assessments with functional data will ultimately result in the identification of mechanisms that contribute to protective immunity and will guide vaccine development. One of these functional readouts is phagocytosis of antigenic material tagged by immune molecules such as antibodies and/or complement components. This review summarizes our current understanding of how phagocytosis contributes to immune defense against pathogens, the pathways involved, and defense mechanisms that pathogens have evolved to deal with the threat of phagocytic removal and destruction of pathogens.

Particulate carrier systems as adjuvants for cancer vaccines

To overcome the immunosuppressive milieu of malignancy and lack of well-defined antigens, potent adjuvants are needed for cancer immunotherapy. Numerous small molecular immunomodulators have the potential to fulfill this role. To enhance the immune response and decrease the toxicity, particulate systems including nanoparticles and macroparticles have been increasingly proposed as carriers for cancer antigen and adjuvant delivery. These systems have the potential to co-deliver the antigens and adjuvants simultaneously in the same particle. In addition, the particles can be engineered for localized and targeted delivery, whether it be to the cellular or sub-cellular level. These properties limit systemic side effects and improve delivery efficiency, and thus enhance the vaccine's immune response. In particular, the particles can be constructed to mimic the size and surface patterns of microbes, organisms to which we have evolved a strong immune response. The release characteristics of the particles can likewise be controlled to simulate the body's response to infections. Boosting the immune response of vaccines by virtue of their intrinsic immunostimulatory properties, these particles can be dosing-sparing and have the potential to reduce production cost of vaccines. As the interest in personalized cancer vaccines increases with their encouraging outcomes in clinical trials, particulate carrier systems have the potential to play an important role in optimizing cancer vaccines.

Simple Nanoparticles from the Assembly of Cationic Polymer and Antigen as Immunoadjuvants

Since antigens are negatively charged, they combine well with positively charged adjuvants. Here, ovalbumin (OVA) (0.1 mg·mL^-1) and poly (diallyldimethylammonium chloride) (PDDA) (0.01 mg·mL^-1) yielded PDDA/OVA assemblies characterized by dynamic light scattering (DLS) and scanning electron microscopy (SEM) as spherical nanoparticles (NPs) of 170 ± 4 nm hydrodynamic diameter, 30 ± 2 mV of zeta-potential and 0.11 ± 0.01 of polydispersity. Mice immunization with the NPs elicited high OVA-specific IgG1 and low OVA-specific IgG2a production, indicating a Th-2 response. Delayed-type hypersensitivity reaction (DTH) was low and comparable to the one elicited by Al(OH)₃/OVA, suggesting again a Th-2 response. PDDA advantages as an adjuvant were simplicity (a single-component adjuvant), low concentration needed (0.01 mg·mL^-1 PDDA) combined with antigen yielding neglectable cytotoxicity, and high stability of PDDA/OVA dispersions. The NPs elicited much higher OVA-specific antibodies production than Al(OH)₃/OVA. In vivo, the nano-metric size possibly assured antigen presentation by antigen-presenting cells (APC) at the lymph nodes, in contrast to the location of Al(OH)₃/OVA microparticles at the site of injection for longer periods with stimulation of local dendritic cells. In the future, it will be interesting to evaluate combinations of the antigen with NPs carrying both PDDA and elicitors of the Th-1 response.

Laser adjuvant for vaccination

The use of an immunologic adjuvant to augment the immune response is essential for modern vaccines which are relatively ineffective on their own. In the past decade, researchers have been consistently reporting that skin treatment with a physical parameter, namely laser light, augments the immune response to vaccine and functions as an immunologic adjuvant. This "laser adjuvant" has numerous advantages over the conventional chemical or biological agents; it is free from cold chain storage, hypodermic needles, biohazardous sharp waste, irreversible formulation with vaccine antigen, undesirable biodistribution in vital organs, or unknown long-term toxicity. Since vaccine formulations are given to healthy populations, these characteristics render the "laser adjuvant" significant advantages for clinical use and open a new developmental path for a safe and effective vaccine. In addition, laser technology has been used in the clinic for more than three decades and is therefore technically matured and has been proved to be safe. Currently, four classes of laser adjuvant have been reported; ultrashort pulsed, non-pulsed, non-ablative fractional, and ablative fractional lasers. Since each class of the laser adjuvant shows a distinct mechanism of action, a proper choice is necessary to craft an effective vaccine formulation toward a desired clinical benefit for a clinical vaccine to maximize protection. In addition, data also suggest that further improvement in the efficacy is possible when a laser adjuvant is combined with chemical or biological adjuvant(s). To realize these goals, further efforts to uncover the molecular mechanisms of action of the laser adjuvants is warranted. This review provides a summary and comments of the recent updates in the laser adjuvant technology.

Intratumoral delivery of an HPV vaccine elicits a broad anti-tumor immune response that translates into a potent anti-tumor effect in a preclinical murine HPV model

Therapeutic cancer vaccines have met limited clinical success. In the setting of cancer, the immune system is either tolerized and/or has a limited tumor-specific T cell repertoire. In this study, we explore whether intratumoral (IT) vaccination with an HPV vaccine can elicit quantitative and qualitative differences in immune response as compared to intramuscular (IM) vaccination to overcome immune resistance in established tumors. We report that IT administration of an HPV-16 E7 peptide vaccine formulated with polyinosinic-polycytidylic acid [poly(I:C)] generated an enhanced antitumor effect relative to IM delivery. The elicited anti-tumor effect with IT vaccination was consistent among the vaccinated groups and across various C57BL/6 substrains. IT vaccination resulted in an increased frequency of PD-1^hi TILs, which represented both vaccine-targeted and non-vaccine-targeted tumor-specific CD8⁺ T cells. Overall, the CD8⁺/Treg ratio was increased within the tumor microenvironment using IT vaccination. We also assessed transcriptional changes in several immune-related genes in the tumor microenvironment of the various treated groups, and our data suggest that IT vaccination leads to upregulation of a broad complement of immunomodulatory genes, including upregulation of interferon gamma (IFNγ) and antigen presentation and processing machine (APM) components. IT vaccine delivery is superior to traditional IM vaccination routes with the potential to improve tumor immunogenicity, which has potential clinical application in the setting of accessible lesions such as head and neck squamous cell carcinomas (HNSCCs).

Diasteroselective Colloidal Self-Assembly Affects the Immunological Response of the Molecular Adjuvant Sulfavant

Adjuvants are components of vaccine that enhance the specific immune response against co-inoculated antigens. Recently, we reported the characterization of a synthetic sulfolipid named Sulfavant A (1) as a promising candidate of a novel class of molecular adjuvants based on the sulfoquinovosyl-diacylglycerol skeleton. Here, we report an improved synthesis of the sulfolipid scaffold, as well as the preparation of two analogs named Sulfavant-S (2) and Sulfavant-R (3) with enhanced property to modulate master immune targets such as human dendritic cells (DCs). According to the present approach, synthesis of 1 is reduced from 14 to 11 steps with nearly triplication of the overall yield (11%). The new members 2 and 3 elicit DC maturation at a concentration of 10 nM, which is 1000 times more potent than the parent molecule 1. Analysis of dynamic light scattering indicates self-assembly of Sulfavants and formation of colloidal particles with a small hydrodynamic radius (50 nm) for the epimers 2 and 3 and a larger radius (150 nm) for 1. The colloidal aggregates are responsible for the bell-shaped dose-response curve of these products. We conclude that the particle size also affects the equilibrium with free monomers, thus determining the effective concentration of the sulfolipid molecule at the cellular targets and the different immunological efficacy of 1-3. Sulfavants (1-3) do not show in vitro cytotoxicity at concentrations 10⁵ higher than the dose that triggers maximal immune response, thus predicting a low level of toxicological risk in their formulation in vaccines.

Selection of adjuvants for vaccines targeting specific pathogens

INTRODUCTION

Adjuvants form an integral component in most of the inactivated and subunit vaccine formulations. Careful and proper selection of adjuvants helps in promoting appropriate immune responses against target pathogens at both innate and adaptive levels such that protective immunity can be elicited. Areas covered: Herein, we describe the recent progress in our understanding of the mode of action of adjuvants that are licensed for use in human vaccines or in clinical or pre-clinical stages at both innate and adaptive levels. Different pathogens have distinct characteristics, which require the host to mount an appropriate immune response against them. Adjuvants can be selected to elicit a tailor-made immune response to specific pathogens based on their unique properties. Identification of biomarkers of adjuvanticity for several candidate vaccines using omics-based technologies can unravel the mechanism of action of modern and experimental adjuvants. Expert opinion: Adjuvant technology has been revolutionized over the last two decades. In-depth understanding of the role of adjuvants in activating the innate immune system, combined with systems vaccinology approaches, have led to the development of next-generation, novel adjuvants that can be used in vaccines against challenging pathogens and in specific target populations.

Aspects of intradermal immunization with different adjuvants: The role of dendritic cells and Th1/Th2 response

Intradermal (i.d.) application of vaccine is promising way how to induce specific immune response against particular pathogens. Adjuvants, substances added into vaccination dose with the aim to increase immunogenicity, play important role in activation of dendritic cells with subsequent activation of lymphocytes. They can, however, induce unwanted local reactions. The aim of the study was to determine the effect of i.d. administration of model antigen keyhole limped hemocyanine alone or with different adjuvants-aluminium hydroxide and oil-based adjuvants-on local histopathological reaction as well as dendritic cell activation at the site of administration and local cytokine and chemokine response. This was assessed at 4 and 24 hours after application. Selection of the adjuvants was based on the fact, that they differently enhance antibody or cell-mediated immunity. The results showed activation of dendritic cells and both Th1 and Th2 response stimulated by oil-based adjuvants. It was associated with higher expression of set of genes, incl. chemokine receptor CCR7 or Th1-associated chemokine CXCL10 and cytokine IFNγ. Application of the antigen with aluminium hydroxide induced higher expression of Th2-associated IL4 or IL13. On the other hand, both complete and incomplete Freund´s adjuvants provoked strong local reaction associated with influx of neutrophils. This was accompanied with high expression of proinflammatory IL1 or neutrophil chemoattractant CXCL8. Surprisingly, similarly strong local reaction was detected also after application of aluminium hydroxide-based adjuvant. The best balanced local reaction with sufficient activation of immune cells was detected after application of oil-based adjuvants Montanide and Emulsigen.

The Biologics Revolution and Endotoxin Test Concerns

The advent of “at will” production of biologics in lieu of harvesting animal proteins (i.e. insulin) or human cadaver proteins (i.e. growth hormone) has revolutionized the treatment of disease. While the fruits of the biotechnology revolution are widely acknowledged, the realization of the differences in the means of production and changes in the manner of control of potential impurities and contaminants in regard to the new versus the old are less widely appreciated. This chapter is an overview of the biologics revolution in terms of the rigors of manufacturing required to produce them, their mechanism of action, and caveats of endotoxin control. It is a continulation of the previous chapter that established a basic background knowledge of adaptive immune principles necessary to understand the mode of action of both disease causation and biologics therapeutic treatment via immune modulation.

Divergent Primary Immune Responses Induced by Human Immunodeficiency Virus-1 gp120 and Hepatitis B Surface Antigen Determine Antibody Recall Responses

The development of a vaccine based on human immunodeficiency virus type 1 (HIV-1) envelope glycoprotein (Env) that elicits potent protective antibodies against infection has been challenging. Recently, we compared the antibody production patterns of HIV-1 Env gp120 and hepatitis B virus surface antigen (HBsAg) to provide insights into how we may improve the protective efficacy of Env-based immunogens. Our previous study showed that HIV Env and HBsAg display different mechanisms of antibody elicitation and that T cells facilitate the responses to repeated immunizations. Here, to elucidate the detailed roles of primary immunization in immune memory response formation and antibody production, we immunized C57BL/6 mice with each antigen and evaluated the development of T follicular helper (Tfh) cells, germinal centers, and the memory responses involved in prime and boost immunizations. We found that after prime immunization, compared with HBsAg, gp120 induced higher frequencies of Tfh cells and programmed death (PD)-1⁺ T cells, greater major histocompatibility complex II expression on B cells, comparable activated B cells, but weaker germinal center (GC) reactions and memory B cell responses in the draining lymph nodes, accompanied by slower antibody recall responses and poor immune memory responses. The above results suggested that more PD-1⁺ T cells arising in primary immunization may serve as major contributors to the slow antibody recall response elicited by HIV-1 Env.

Identification of Immune Signatures of Novel Adjuvant Formulations Using Machine Learning

Adjuvants have long been critical components of vaccines, but the exact mechanisms of their action and precisely how they alter or enhance vaccine-induced immune responses are often unclear. In this study, we used broad immunoprofiling of antibody, cellular, and cytokine responses, combined with data integration and machine learning to gain insight into the impact of different adjuvant formulations on vaccine-induced immune responses. A Self-Assembling Protein Nanoparticles (SAPN) presenting the malarial circumsporozoite protein (CSP) was used as a model vaccine, adjuvanted with three different liposomal formulations: liposome plus Alum (ALFA), liposome plus QS21 (ALFQ), and both (ALFQA). Using a computational approach to integrate the immunoprofiling data, we identified distinct vaccine-induced immune responses and developed a multivariate model that could predict the adjuvant condition from immune response data alone with 92% accuracy (p = 0.003). The data integration also revealed that commonly used readouts (i.e. serology, frequency of T cells producing IFN-γ, IL2, TNFα) missed important differences between adjuvants. In summary, broad immune-profiling in combination with machine learning methods enabled the reliable and clear definition of immune signatures for different adjuvant formulations, providing a means for quantitatively characterizing the complex roles that adjuvants can play in vaccine-induced immunity. The approach described here provides a powerful tool for identifying potential immune correlates of protection, a prerequisite for the rational pairing of vaccines candidates and adjuvants.

Applications of Immunomodulatory Immune Synergies to Adjuvant Discovery and Vaccine Development

Pathogens comprise a diverse set of immunostimulatory molecules that activate the innate immune system during infection. The immune system recognizes distinct combinations of pathogenic molecules leading to multiple immune activation events that cooperate to produce enhanced immune responses, known as 'immune synergies'. Effective immune synergies are essential for the clearance of pathogens, thus inspiring novel adjuvant design to improve vaccines. We highlight current vaccine adjuvants and the importance of immune synergies to adjuvant and vaccine design. The focus is on new technologies used to study and apply immune synergies to adjuvant and vaccine development. Finally, we discuss how recent findings can be applied to the future design and characterization of synergistic adjuvants and vaccines.

Virus-derived immunostimulatory RNA induces type I IFN-dependent antibodies and T-cell responses during vaccination

Adjuvants potentiate and direct the type of immunity elicited during vaccination. However, there is a shortage of adjuvants that elicit robust type-1 immunity required for the control of intracellular pathogens, including viruses. RNA derived from Sendai virus defective viral genomes (DVGs) stimulates RIG-I-like receptor signaling leading to type-1 immunity during infection. Here, we investigated whether a 268nt DVG-derived oligonucleotide (DDO) functions as a strong type-1 immunity-inducing adjuvant during vaccination against influenza virus. We show that DDO induces robust IgG2c antibody production when used in an inactivated influenza A virus (IAV) vaccine. Additionally, DDO induces Th1 and CD8+ T-cell responses able to protect against heterosubtypic IAV challenge. Interestingly, DDO synergized with AddaVax and skewed the immune response towards type-1 immunity. The adjuvancy of DDO alone and in synergy with AddaVax was heavily dependent on type I interferon signaling. Our data support a critical role for type I interferon in the induction of type-1 immune responses during vaccination and demonstrate that DDO is a type-1 immunity orienting vaccine adjuvant that can be used alone or in synergy with other adjuvants.

Elucidating the Mechanisms of Action of Saponin-Derived Adjuvants

Numerous triterpenoid saponins are adjuvants that modify the activities of T cells and antigen-presenting cells, like dendritic cells (DCs). Saponins can induce either proinflammatory Th1/Th2 or sole anti-inflammatory Th2 immunities. Structure-activity relationships (SARs) have shown that imine-forming carbonyl groups are needed for T cell activation leading to induction of Th1/Th2 immunities. While saponins having different triterpenoid aglycons and oligosaccharide chains can activate DCs to induce Th1/Th2 immunoresponses, fucopyranosyl residues from their oligosaccharides by binding to the DC-SIGN receptor can bias DCs toward a sole Th2 immunity. Here we discuss the mechanisms of action of these saponins in view of new information, which may serve as a basis to design improved adjuvants and related drugs.

Immunization with the outer membrane proteins OmpK17 and OmpK36 elicits protection against Klebsiella pneumoniae in the murine infection model

Klebsiella pneumoniae is a Gram-negative bacterium that is increasingly reported as a serious nosocomial and community-acquired pathogen. In the current study, two K. pneumoniae antigens, OmpK17 and OmpK36, as well as their fusion protein cognate F36/17 were investigated as potential vaccine candidates in a murine infection model. Three immunoadjuvants, namely the Gram-positive Enhancer Matrix (GEM) adjuvant, synthetic hemozoin (Hz) adjuvant and incomplete Freund's adjuvant (IFA) were evaluated. Genes of OmpK17 and OmpK36 antigens as well as their fusion protein were cloned in Escherichia coli for recombinant expression. Mice were immunized thrice with the individual recombinant purified antigens adjuvanted with one of the three adjuvants. Two weeks after the last booster, animals were challenged with a lethal dose of K. pneumoniae and immune protection parameters were assessed. Animals immunized with GEM- or Hz-adjuvanted K. pneumoniae antigens did not show significant protection upon bacterial challenge. Animals immunized with subcutaneous IFA-adjuvanted antigens showed the best results with survival percentages of 50, 60 and 50% for groups immunized with OmpK17, OmpK36 and F36/17, respectively. Serum IgG1, rather than IgG2a, antibodies were the most prevalent following vaccination indicating bias towards T helper type 2 (Th2) immune response. Opsonophagocytic assays demonstrated significant percentage killing in case of animals immunized with IFA-adjuvanted antigens. Overall, OmpK17 and OmpK36 are promising vaccine antigens which are worthy of further optimization of the immunization conditions, particularly the used immunoadjuvants, in order to achieve full protection against K. pneumoniae.

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.

Identification and Characterization of Stimulator of Interferon Genes As a Robust Adjuvant Target for Early Life Immunization

Immunization is key to preventing infectious diseases, a leading cause of death early in life. However, due to age-specific immunity, vaccines often demonstrate reduced efficacy in newborns and young infants as compared to adults. Here, we combined in vitro and in vivo approaches to identify adjuvant candidates for early life immunization. We employed newborn and adult bone marrow-derived dendritic cells (BMDCs) to perform a screening of pattern recognition receptor agonists and found that the stimulator of interferon genes ligand 2′3′-cGAMP (hereafter cGAMP) induces a comparable expression of surface maturation markers in newborn and adult BMDCs. Then, we utilized the trivalent recombinant hemagglutinin (rHA) influenza vaccine, Flublok, as a model antigen to investigate the role of cGAMP in adult and early life immunization. cGAMP adjuvantation alone could increase rHA-specific antibody titers in adult but not newborn mice. Remarkably, as compared to alum or cGAMP alone, immunization with cGAMP formulated with alum (Alhydrogel) enhanced newborn rHA-specific IgG2a/c titers ~400-fold, an antibody subclass associated with the development of IFNγ-driven type 1 immunity in vivo and endowed with higher effector functions, by 42 days of life. Highlighting the amenability for successful vaccine formulation and delivery, we next confirmed that cGAMP adsorbs onto alum in vitro. Accordingly, immunization early in life with (cGAMP+alum) promoted IFNγ production by CD4⁺ T cells and increased the proportions and absolute numbers of CD4⁺ CXCR5⁺ PD-1⁺ T follicular helper and germinal center (GC) GL-7⁺ CD138⁺ B cells, suggesting an enhancement of the GC reaction. Adjuvantation effects were apparently specific for IgG2a/c isotype switching without effect on antibody affinity maturation, as there was no effect on rHA-specific IgG avidity. Overall, our studies suggest that cGAMP when formulated with alum may represent an effective adjuvantation system to foster humoral and cellular aspects of type 1 immunity for early life immunization.