Distinct Immunologic Properties of Soluble Versus Particulate Antigens

Reducing the solubility of the major birch pollen allergen Bet v 1 by particle-loading mitigates Th2 responses

BACKGROUND

Solubility is a common feature of allergens. However, the causative relationship between this protein-intrinsic feature and sensitization capacity of allergens is not fully understood. This study aimed to proof the concept of solubility as a protein intrinsic feature of allergens.

METHODS

The soluble birch pollen allergen Bet v 1 was covalently coupled to 1 μm silica particles. IgE-binding and -cross-linking capacity was assessed by inhibition ELISA and mediator release assay, respectively. Alterations in adjuvanticity by particle-loading were investigated by activation of dendritic cells, mast cells and the Toll-like receptor 4 pathway as well as by Th2 polarization in an IL-4 reporter mouse model. In BALB/c mice, particle-loaded and soluble Bet v 1 were compared in a model of allergic sensitization. Antigen uptake and presentation was analysed by restimulating human Bet v 1-specific T cell lines.

RESULTS

Covalent coupling of Bet v 1 to silica particles resulted in an insoluble antigen with retained IgE-binding and -cross-linking capacity and no increase in adjuvanticity. In vivo, particle-loaded Bet v 1 induced significantly lower Bet v 1-specific (s)IgE, whereas sIgG1 and sIgG2a levels remained unaffected. The ratio of Th2 to Th1 cells was significantly lower in mice sensitized with particle-loaded Bet v 1. Particle-loading of Bet v 1 resulted in a 24-fold higher T cell activation capacity in Bet v 1-specific T cell lines, indicating more efficient uptake and presentation than of soluble Bet v 1.

CONCLUSIONS

Our results show that solubility is a decisive factor contributing to the sensitization capacity of allergens. The reduction in sensitization capacity of insoluble, particle-loaded antigens results from enhanced antigen uptake and presentation compared to soluble allergens.

Boosting antigen-specific T cell activation with lipid-stabilized protein nanoaggregates

Vaccines based on protein antigens have numerous advantages over inactivated pathogens, including easier manufacturing and improved safety. However, purified antigens are weakly immunogenic, as they lack the spatial organization and the associated 'danger signals' of the pathogen. Formulating vaccines as nanoparticles enhances the recognition by antigen presenting cells, boosting the cell-mediated immune response. This study describes a nano-precipitation method to obtain stable protein nanoaggregates with uniform size distribution without using covalent cross-linkers. Nanoaggregates were formed via microfluidic mixing of ovalbumin (OVA) and lipids in the presence of high methanol concentrations. A purification protocol was set up to separate the nanoaggregates from OVA and liposomes, obtained as byproducts of the mixing. The nanoaggregates were characterized in terms of morphology, ζ-potential and protein content, and their interaction with immune cells was assessed in vitro. Antigen-specific T cell activation was over 6-fold higher for nanoaggregates compared to OVA, due in part to the enhanced uptake by immune cells. Lastly, a two-dose immunization with nanoaggregates in mice induced a significant increase in OVA-specific CD8+ T splenocytes compared to soluble OVA. Overall, this work presents for the first time the microfluidic production of lipid-stabilized protein nanoaggregates and provides a proof-of-concept of their potential for vaccination.

Preclinical proof of principle for orally delivered Th17 antagonist miniproteins

Interleukin (IL)-23 and IL-17 are well-validated therapeutic targets in autoinflammatory diseases. Antibodies targeting IL-23 and IL-17 have shown clinical efficacy but are limited by high costs, safety risks, lack of sustained efficacy, and poor patient convenience as they require parenteral administration. Here, we present designed miniproteins inhibiting IL-23R and IL-17 with antibody-like, low picomolar affinities at a fraction of the molecular size. The minibinders potently block cell signaling in vitro and are extremely stable, enabling oral administration and low-cost manufacturing. The orally administered IL-23R minibinder shows efficacy better than a clinical anti-IL-23 antibody in mouse colitis and has a favorable pharmacokinetics (PK) and biodistribution profile in rats. This work demonstrates that orally administered de novo-designed minibinders can reach a therapeutic target past the gut epithelial barrier. With high potency, gut stability, and straightforward manufacturability, de novo-designed minibinders are a promising modality for oral biologics.

Immune memory shapes human polyclonal antibody responses to H2N2 vaccination

Influenza A virus subtype H2N2, which caused the 1957 influenza pandemic, remains a global threat. A recent phase 1 clinical trial investigating a ferritin nanoparticle vaccine displaying H2 hemagglutinin (HA) in H2-naive and H2-exposed adults enabled us to perform comprehensive structural and biochemical characterization of immune memory on the breadth and diversity of the polyclonal serum antibody response elicited. We temporally map the epitopes targeted by serum antibodies after vaccine prime and boost, revealing that previous H2 exposure results in higher responses to the variable HA head domain. In contrast, initial responses in H2-naive participants are dominated by antibodies targeting conserved epitopes. We use cryoelectron microscopy and monoclonal B cell isolation to describe the molecular details of cross-reactive antibodies targeting conserved epitopes on the HA head, including the receptor-binding site and a new site of vulnerability deemed the medial junction. Our findings accentuate the impact of pre-existing influenza exposure on serum antibody responses post-vaccination.

Translational and structural vaccinomics approach to design a multi-epitope vaccine against NOL4 autologous antigen of small cell lung cancer

Small cell lung cancer (SCLC) is one of the most common cancers and it is the sixth common cause for cancer-related deaths. The high plasticity and metastasis have been a major challenge for humanity to treat the disease. Hence, a vaccine for SCLC has become an urgent need of the hour due to public health concern. Implementation of immunoinformatics technique is one of the best way to find a suitable vaccine candidate. Immunoinformatics tools can be used to overcome the limitations and difficulties of traditional vaccinological techniques. Multi-epitope cancer vaccines have become a next-generation technique in vaccinology which can be used to stimulate more potent immune response against a particular antigen by eliminating undesirable molecules. In this study, we used multiple computational and immunoinformatics approach to design a novel multi-epitope vaccine for small cell lung cancer. Nucleolar protein 4 (NOL4) is an autologous cancer-testis antigen overexpressed in SCLC cells. Seventy-five percent humoral immunity have been identified for this particular antigen. In this study, we mapped immunogenic cytotoxic T lymphocyte, helper T lymphocyte, and interferon-gamma epitopes present in NOL4 antigen and designed a multi-epitope-based vaccine using the predicted epitopes. The designed vaccine was antigenic, non-allergenic, and non-toxic with 100% applicability on human population. The chimeric vaccine construct showed stable and significant interaction with endosomal and plasmalemmal toll-like receptors in molecular docking and protein-peptide interaction analysis, thus assuring a strong potent immune response against the vaccine upon administration. Therefore, these preliminary results can be used to carry out further experimental investigations.

Engineered Curli Nanofilaments as a Self-Adjuvanted Antigen Delivery Platform

Proteinaceous nanoparticles constitute efficient antigen delivery systems in vaccine formulations due to their size and repetitive nature that mimic most invading pathogens and promote immune activation. Nonetheless, the coadministration of an adjuvant with subunit nanovaccines is usually required to induce a robust, long-lasting, and protective immune response. Herein, the protein Curli-specific gene A (CsgA), which is known to self-assemble into nanofilaments contributing to bacterial biofilm, is exploited to engineer an intrinsically immunostimulatory antigen delivery platform. Three repeats of the M2e antigenic sequence from the influenza A virus matrix 2 protein are merged to the N-terminal domain of engineered CsgA proteins. These chimeric 3M2e-CsgA spontaneously self-assemble into antigen-displaying cross-β-sheet nanofilaments that activate the heterodimeric toll-like receptors 2 and 1. The resulting nanofilaments are avidly internalized by antigen-presenting cells and stimulate the maturation of dendritic cells. Without the need of any additional adjuvants, both assemblies show robust humoral and cellular immune responses, which translate into complete protection against a lethal experimental infection with the H1N1 influenza virus. Notably, these CsgA-based nanovaccines induce neither overt systemic inflammation, nor reactogenicity, upon mice inoculation. These results highlight the potential of engineered CsgA nanostructures as self-adjuvanted, safe, and versatile antigen delivery systems to fight infectious diseases.

Promises and challenges of mucosal COVID-19 vaccines

Coronavirus disease-2019 (COVID-19) is an ongoing pandemic caused by the newly emerged virus severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Currently, COVID-19 vaccines are given intramuscularly and they have been shown to evoke systemic immune responses that are highly efficacious towards preventing severe disease and death. However, vaccine-induced immunity wanes within a short time, and booster doses are currently recommended. Furthermore, current vaccine formulations do not adequately restrict virus infection at the mucosal sites, such as in the nasopharyngeal tract and, therefore, have limited capacity to block virus transmission. With these challenges in mind, several mucosal vaccines are currently being developed with the aim of inducing long-lasting protective immune responses at the mucosal sites where SARS-COV-2 infection begins. Past successes in mucosal vaccinations underscore the potential of these developmental stage SARS-CoV-2 vaccines to reduce disease burden, if not eliminate it altogether. Here, we discuss immune responses that are triggered at the mucosal sites and recent advances in our understanding of mucosal responses induced by SARS-CoV-2 infection and current COVID-19 vaccines. We also highlight several mucosal SARS-COV-2 vaccine formulations that are currently being developed or tested for human use and discuss potential challenges to mucosal vaccination.

Mucoadhesive Vaccine Delivery Systems for the Oral Mucosa

Vaccine technology has evolved continuously since its beginning, and mucosal vaccination, including intranasal, sublingual, and oral administrations, has recently gained great scientific interest. The oral mucosa represents a promising minimally invasive route for antigen delivery, mainly at sublingual and buccal mucosal sites, and it is easily accessible, immunologically rich, and able to promote an effective systemic and local immune response. The aim of this review is to provide an updated overview on the technologies for oral mucosal vaccination, with emphasis on mucoadhesive biomaterial-based delivery systems. Polymeric-based nanoparticles, multilayer films and wafers, liposomes, microneedles, and thermoresponsive gels are the most investigated strategies to deliver antigens locally, showing mucoadhesive properties, controlled release of the antigen, and the ability to enhance immunological responses. These formulations have achieved adequate properties in terms of vaccine stability, are minimally invasive, and are easy to produce and manage. To date, oral mucosa vaccine delivery systems represent a promising and open field of research. Future directions should focus on the role of these systems to induce sustained innate and adaptive immune responses, by integrating the recent advances achieved in mucoadhesion with those related to vaccine technology. Being painless, easy to administer, highly stable, safe, and effective, the antigen delivery systems via the oral mucosa may represent a useful and promising strategy for fast mass vaccination, especially during pandemic outbreaks.

Self-Boosting Vaccination Based on Pulsatile Antigen Release from Core-Shell Microparticles

Vaccination is among the most effective ways to prevent infectious diseases. Subunit vaccines are safe but usually require multiple booster shots, which may lead to immunity loss and economic consume. In this study, a self-boosting vaccine is developed based on the pulsatile release of antigen from the core-shell microparticle after single-injection immunization. Self-healing technology applied to form an "antigen core" can avoid organic solvents from destroying the spatial structure of the antigen. The "antigen shell" is built-up by self-assemble of the antigen with the opposite charged polypeptide. Primary immunization occurs with the self-assembled film disintegration, and the booster comes with the microparticle degradation. The changing of antigen-specific antibodies after immunization with the core-shell microparticle vaccine is consistent with that caused by the two shots of immunization. The immune effect and safety evaluation results support the translational potential of this self-boosting core-shell microparticle vaccine.

Active immunization with a structurally aggregated PD-L1 antigen breaks T and B immune tolerance in non-human primates and exhibits in vivo anti-tumoral effects in immunocompetent mouse tumor models

Despite the clinical success of the programmed death ligand 1 (PD-L1) blocking therapy in cancer treatment, only a subset of patients exhibits durable responses, therefore further exploration of other immunotherapeutic alternatives are needed. This paper reported the development of the PKPD-L1^Vac vaccine, a new protein vaccine candidate that uses aluminum phosphate as an adjuvant and as an antigen the extracellular domain of human PD-L1 fused to a 47 amino-terminal portion of the LpdA protein from N. meningitides (PKPD-L1). The PKPD-L1 antigen has different physical and biological characteristics than those found in the natural molecule and in others PD-L1 vaccine candidates. The quimeric protein has a reduced binding capacity to the PD-1 and CD80 receptors to decrease their pro-tumoral activity. Besides, the distinctive feature of the PKPD-L1 polypeptide to be structurally aggregated could be desirable for its immunogenic properties. PKPD-L1^Vac elicited anti-PD-L1-specific IgG antibodies and T lymphocyte-mediated immunity in mice and non-human primates. The vaccine administration demonstrated antitumor activity on CT-26 and B16-F10 primary tumor models in mice. Moreover, the immunization with PKPD-L1^Vac increased the tumor-infiltrating lymphocytes and decreased the proportion of CD3⁺CD8⁺PD1^+high anergic T cells in CT-26 tumor tissues, suggesting that the vaccine may remodel the tumor microenvironment. In summary, the PKPD-L1^Vac vaccine exhibits very promising preclinical results and deserves to move forward to a phase I clinical trial.

An Adjuvanted Inactivated SARS-CoV-2 Microparticulate Vaccine Delivered Using Microneedles Induces a Robust Immune Response in Vaccinated Mice

SARS-CoV-2, the causal agent of COVID-19, is a contagious respiratory virus that frequently mutates, giving rise to variant strains and leading to reduced vaccine efficacy against the variants. Frequent vaccination against the emerging variants may be necessary; thus, an efficient vaccination system is needed. A microneedle (MN) vaccine delivery system is non-invasive, patient-friendly, and can be self-administered. Here, we tested the immune response produced by an adjuvanted inactivated SARS-CoV-2 microparticulate vaccine administered via the transdermal route using a dissolving MN. The inactivated SARS-CoV-2 vaccine antigen and adjuvants (Alhydrogel® and AddaVax™) were encapsulated in poly(lactic-co-glycolic acid) (PLGA) polymer matrices. The resulting MP were approximately 910 nm in size, with a high percentage yield and percent encapsulation efficiency of 90.4%. In vitro, the vaccine MP was non-cytotoxic and increased the immunostimulatory activity measured as nitric oxide release from dendritic cells. The adjuvant MP potentiated the immune response of the vaccine MP in vitro. In vivo, the adjuvanted SARS-CoV-2 MP vaccine induced high levels of IgM, IgG, IgA, IgG1, and IgG2a antibodies and CD4+ and CD8+ T-cell responses in immunized mice. In conclusion, the adjuvanted inactivated SARS-CoV-2 MP vaccine delivered using MN induced a robust immune response in vaccinated mice.

Precision-engineering of subunit vaccine particles for prevention of infectious diseases

Vaccines remain the best approach for the prevention of infectious diseases. Protein subunit vaccines are safe compared to live-attenuated whole cell vaccines but often show reduced immunogenicity. Subunit vaccines in particulate format show improved vaccine efficacy by inducing strong immune responses leading to protective immunity against the respective pathogens. Antigens with proper conformation and function are often required to induce functional immune responses. Production of such antigens requiring post-translational modifications and/or composed of multiple complex domains in bacterial hosts remains challenging. Here, we discuss strategies to overcome these limitations toward the development of particulate vaccines eliciting desired humoral and cellular immune responses. We also describe innovative concepts of assembling particulate vaccine candidates with complex antigens bearing multiple post-translational modifications. The approaches include non-covalent attachments (e.g. biotin-avidin affinity) and covalent attachments (e.g. SpyCatcher-SpyTag) to attach post-translationally modified antigens to particles.

Mycobacterium avium subsp. paratuberculosis antigens induce cellular immune responses in cattle without causing reactivity to tuberculin in the tuberculosis skin test

Mycobacterium avium subspecies paratuberculosis (MAP) causes chronic progressive granulomatous enteritis leading to diarrhea, weight-loss, and eventual death in ruminants. Commercially available vaccine provides only partial protection against MAP infection and can interfere with the use of current diagnostic tests for bovine tuberculosis in cattle. Here, we characterized immune responses in calves to vaccines containing four truncated MAP antigens as a fusion (Ag85A^202-347-SOD^1-72-Ag85B^173-330-74F^{1-148+669-786}), either displayed on protein particles, or expressed as a soluble recombinant MAP (rMAP) fusion protein as well as to commercially available Silirum^® vaccine. The rMAP fusion protein elicited the strongest antigen-specific antibody responses to both PPDA and recombinant antigen and strong and long-lasting T-cell immune responses to these antigens, as indicated by increased production of IFN-γ and IL-17A in antigen-stimulated whole blood cultures. The MAP fusion protein particle vaccine induced minimal antibody responses and weak IFN-γ responses but stimulated IL-17A responses to recombinant antigen. The immune response profile of Silirum^® vaccine was characterized by weak antibodies and strong IFN-γ and IL-17A responses to PPDA. Transcription analysis on antigen-stimulated leukocytes from cattle vaccinated with rMAP fusion protein showed differential expression of several immune response genes and genes involved in costimulatory signaling, TLR4, TLR2, PTX3, PTGS2, PD-L1, IL1B, IL2, IL6, IL12B, IL17A, IL22, IFNG, CD40, and CD86. Moreover, the expression of several genes of immune pathways correlated with cellular immune responses in the rMAP fusion protein vaccinated group. These genes have key roles in pathways of mycobacterial immunity, including autophagy, manipulation of macrophage-mediated killing, Th17- and regulatory T cells- (Treg) mediated responses. Calves vaccinated with either the rMAP fusion protein or MAP fusion protein particle vaccine did not induce reactivity to PPDA and PPDB in a comparative cervical skin test, whereas Silirum^® induced reactivity to these tuberculins in most of the vaccinated animals. Overall, our results suggest that a combination of recombinant MAP antigens in the form of a soluble fusion protein vaccine are capable of inducing strong antigen-specific humoral and a balanced Th1/Th17-cell immune response. These findings, together with the absence of reactivity to tuberculin, suggest this subunit vaccine could provide protective immunity against intracellular MAP infection in cattle without compromising the use of current bovine tuberculosis surveillance test.

Generation of multi-layered protein bodies in N. benthamiana for the encapsulation of vaccine antigens

The ability of plants to assemble particulate structures such as virus-like particles and protein storage organelles allows the direct bioencapsulation of recombinant proteins during the manufacturing process, which holds promise for the development of new drug delivery vehicles. Storage organelles found in plants such as protein bodies (PBs) have been successfully used as tools for accumulation and encapsulation of recombinant proteins. The fusion of sequences derived from 27-kDa-γ-zein, a major storage protein of maize, with a protein of interest leads to the incorporation of the chimeric protein into the stable and protected environment inside newly induced PBs. While this procedure has proven successful for several, but not all recombinant proteins, the aim of this study was to refine the technology by using a combination of PB-forming proteins, thereby generating multi-layered protein assemblies in N. benthamiana. We used fluorescent proteins to demonstrate that up to three proteinaceous components can be incorporated into different layers. In addition to 27-kDa-γ-zein, which is essential for PB initiation, 16-kDa-γ-zein was identified as a key element to promote the incorporation of a third zein-component into the core of the PBs. We show that a vaccine antigen could be incorporated into the matrix of multi-layered PBs, and the protein microparticles were characterized by confocal and electron microscopy as well as flow cytometry. In future, this approach will enable the generation of designer PBs that serve as drug carriers and integrate multiple components that can be functionalized in different ways.

Molecular Bases of Protein Antigenicity and Determinants of Immunogenicity, Anergy, and Mitogenicity

BACKGROUND

The immune system is able to recognize substances that originate from inside or outside the body and are potentially harmful. Foreign substances that bind to immune system components exhibit antigenicity and are defined as antigens. The antigens exhibiting immunogenicity can induce innate or adaptive immune responses and give rise to humoral or cell-mediated immunity. The antigens exhibiting mitogenicity can cross-link cell membrane receptors on B and T lymphocytes leading to cell proliferation. All antigens vary greatly in physicochemical features such as biochemical nature, structural complexity, molecular size, foreignness, solubility, and so on.

OBJECTIVE

Thus, this review aims to describe the molecular bases of protein-antigenicity and those molecular bases that lead to an immune response, lymphocyte proliferation, or unresponsiveness.

CONCLUSION

The epitopes of an antigen are located in surface areas; they are about 880-3,300 Da in size. They are protein, carbohydrate, or lipid in nature. Soluble antigens are smaller than 1 nm and are endocytosed less efficiently than particulate antigens. The more the structural complexity of an antigen increases, the more the antigenicity increases due to the number and variety of epitopes. The smallest immunogens are about 4,000-10,000 Da in size. The more phylogenetically distant immunogens are from the immunogen-recipient, the more immunogenicity increases. Antigens that are immunogens can trigger an innate or adaptive immune response. The innate response is induced by antigens that are pathogen-associated molecular patterns. Exogenous antigens, T Dependent or T Independent, induce humoral immunogenicity. TD protein-antigens require two epitopes, one sequential and one conformational to induce antibodies, whereas, TI non-protein-antigens require only one conformational epitope to induce low-affinity antibodies. Endogenous protein antigens require only one sequential epitope to induce cell-mediated immunogenicity.

Pan-neutralizing, germline-encoded antibodies against SARS-CoV-2: Addressing the long-term problem of escape variants

Despite the initially reported high efficacy of vaccines directed against ancestral SARS-CoV-2, repeated infections in both unvaccinated and vaccinated populations remain a major global health challenge. Because of mutation-mediated immune escape by variants-of-concern (VOC), approved neutralizing antibodies (neutAbs) effective against the original strains have been rendered non-protective. Identification and characterization of mutation-independent pan-neutralizing antibody responses are therefore essential for controlling the pandemic. Here, we characterize and discuss the origins of SARS-CoV-2 neutAbs, arising from either natural infection or following vaccination. In our study, neutAbs in COVID-19 patients were detected using the combination of two lateral flow immunoassay (LFIA) tests, corroborated by plaque reduction neutralization testing (PRNT). A point-of-care neutAb LFIA, NeutraXpress™, was validated using serum samples from historical pre-COVID-19 negative controls, patients infected with other respiratory pathogens, and PCR-confirmed COVID-19 patients. Surprisingly, potent neutAb activity was mainly noted in patients generating both IgM and IgG against the Spike receptor-binding domain (RBD), in contrast to samples possessing anti-RBD IgG alone. We propose that low-affinity, high-avidity, germline-encoded natural IgM and subsequent generation of class-switched IgG may have an underappreciated role in cross-protection, potentially offsetting immune escape by SARS-CoV-2 variants. We suggest Reverse Vaccinology 3.0 to further exploit this innate-like defense mechanism. Our proposition has potential implications for immunogen design, and provides strategies to elicit pan-neutAbs from natural B1-like cells. Refinements in future immunization protocols might further boost long-term cross-protection, even at the mucosal level, against clinical manifestations of COVID-19.

Recent advances in coiled-coil peptide materials and their biomedical applications

Extensive research has gone into deciphering the sequence requirements for peptides to fold into coiled-coils of varying oligomeric states. More recently, additional signals have been introduced within coiled-coils to promote higher order assembly into biomaterials with a rich distribution of morphologies. Herein we describe these strategies for association of coiled-coil building blocks and biomedical applications. With many of the systems described herein having proven use in protein storage, cargo binding and delivery, three dimensional cell culturing and vaccine development, the future potential of coiled-coil materials to have significant biomedical impact is highly promising.

Design and development of a self-assembling protein nanoparticle displaying PfHAP2 antigenic determinants recognized by natural acquired antibodies

Backgrounds

In order to move towards the elimination and eradication of malaria in the world, the development of vaccines is inevitable. Many modern vaccines are based on recombinant technology; however, they may not provide a fully protective, long-lasting immune response. One of the strategies to improve recombinant vaccines is designing the nanovaccines such as self-assembling protein nanoparticles (SAPNs). Hence, the presentation of epitopes in a repeat array and correct conformation should be considered. P. falciparum generative cell-specific 1 (PfGCS1) is a main transmission-blocking vaccine candidate with two highly conserved fragments, HAP2-GCS1 and cd loop, inducing partial malaria transmission inhibitory antibodies. Therefore, to design an effective malaria vaccine, we used cd loop and HAP2-GCS1 fragments at the amino and carboxy terminuses of the SAPN-forming amino acid sequence, respectively.

Methodology/Principal findings

The SAPN monomer (PfGCS1-SAPN) sequence was designed, and the three-dimensional (3D) structure was predicted. The result of this prediction ensured the presence of antigens on the SAPN surface. Then the accuracy of the predicted 3D structure and its stability were confirmed by 100 ns molecular dynamics (MD) simulation. The designed SAPN substructure sequence was synthesized, cloned, and expressed in Escherichia coli. With a gradual decrease in urea concentration in dialysis solutions, the purified proteins progressed to the final desired structure of the SAPN, which then was confirmed by Dynamic Light Scattering (DLS) and Field Emission Scanning Electron Microscopy (FESEM) tests. According to the Enzyme-Linked Immunosorbent Assay (ELISA), antigenic determinants were presented on the SAPN surface and interacted with antibodies in the serum of malaria patients.

Conclusions/Significance

Our results show that the SAPN formed by PfGCS1-SAPN has produced the correct shape and size, and the antigenic determinants are presented on the surface of the SAPN, which indicates that the designed SAPN has great potential to be used in the future as a malaria vaccine.

Microneedle Delivery of an Adjuvanted Microparticulate Vaccine Induces High Antibody Levels in Mice Vaccinated against Coronavirus

This ‘proof-of-concept’ study aimed to test the microparticulate vaccine delivery system and a transdermal vaccine administration strategy using dissolving microneedles (MN). For this purpose, we formulated poly(lactic-co-glycolic) acid (PLGA) microparticles (MP) encapsulating the inactivated canine coronavirus (iCCoV), as a model antigen, along with adjuvant MP encapsulating Alhydrogel^® and AddaVax. We characterized the vaccine MP for size, surface charge, morphology, and encapsulation efficiency. Further, we evaluated the in vitro immunogenicity, cytotoxicity, and antigen-presentation of vaccine/adjuvant MP in murine dendritic cells (DCs). Additionally, we tested the in vivo immunogenicity of the MP vaccine in mice through MN administration. We evaluated the serum IgG, IgA, IgG1, and IgG2a responses using an enzyme-linked immunosorbent assay. The results indicate that the particulate form of the vaccine is more immunogenic than the antigen suspension in vitro. We found the vaccine/adjuvant MP to be non-cytotoxic to DCs. The expression of antigen-presenting molecules, MHC I/II, and their costimulatory molecules, CD80/40, increased with the addition of the adjuvants. Moreover, the results suggest that the MP vaccine is cross presented by the DCs. In vivo, the adjuvanted MP vaccine induced increased antibody levels in mice following vaccination and will further be assessed for its cell-mediated responses.

Think like a Virus: Toward Improving Nanovaccine Development against SARS-CoV-2

There is no doubt that infectious diseases present global impact on the economy, society, health, mental state, and even political aspects, causing a long-lasting dent, and the situation will surely worsen if and when the viral spread becomes out of control, as seen during the still ongoing coronavirus disease 2019 (COVID-19) pandemic. Despite the considerable achievements made in viral prevention and treatment, there are still significant challenges that can be overcome through careful understanding of the viral mechanism of action to establish common ground for innovating new preventative and treatment strategies. Viruses can be regarded as devil nanomachines, and one innovative approach to face and stop the spread of viral infections is the development of nanoparticles that can act similar to them as drug/vaccine carriers. Moreover, we can use the properties that different viruses have in designing nanoparticles that reassemble the virus conformational structures but that do not present the detrimental threats to human health that native viruses possess. This review discusses the current preventative strategies (i.e., vaccination) used in facing viral infections and the associated limitations, highlighting the importance of innovating new approaches to face viral infectious diseases and discussing the current nanoapplications in vaccine development and the challenges that still face the nanovaccine field.

Evaluation of the efficacy of polymeric antigen BLSOmp31 formulated in a new cage-like particle adjuvant (ISPA) administered by parenteral or mucosal routes against Brucella ovis in BALB/c mice

Brucella ovis is an economically important cause of epididymitis in rams worldwide. Polymeric BLSOmp31 was previously identified as a protective immunogen against this pathogen. In this study, BLSOmp31 was formulated with a modified version of ISCOMATRIX adjuvant called ISPA (BLSOmp31/ISPA) and was administered in BALB/C by the subcutaneous and ocular route. The systemic and mucosal immune responses, the opsonic activity of antibodies and the protection conferred against B. ovis were evaluated. BLSOmp31+ISPA injected subcutaneously or by ocular route induced significantly higher IgG antibody levels with a mixed Th1/Th2 profile compared to non-immunized mice. IgA and IgG were detected in sera and nasal, tracheobronchial, vaginal secretions, tears and faeces, from SC immunized mice while in the group immunized by the ocular route a slight increase in both isotypes was mainly observed in all secretions, except in vaginal fluid. Opsonic antibodies stimulated binding and increased uptake of PHrodo™ Green-labelled B. ovis by neutrophils and monocytes. BLSOmp31 administered subcutaneously induced the highest levels of IFN-ɣ. The ocular immunization not only produced significant levels of this cytokine but also IL-4 compared to non-immunized mice. Both, subcutaneous and ocular routes of immunization, significantly protected against B. ovis infection. These results indicate that BLSOmp31/ISPA administered parenterally or by ocular route is a safe and effective vaccine against B. ovis in the murine model.

A Multivalent Vaccine Based on Ferritin Nanocage Elicits Potent Protective Immune Responses against SARS-CoV-2 Mutations

The SARS-CoV-2 pandemic has created a global public crisis and heavily affected personal lives, healthcare systems, and global economies. Virus variants are continuously emerging, and, thus, the pandemic has been ongoing for over two years. Vaccines were rapidly developed based on the original SARS-CoV-2 (Wuhan-Hu-1) to build immunity against the coronavirus disease. However, they had a very low effect on the virus’ variants due to their low cross-reactivity. In this study, a multivalent SARS-CoV-2 vaccine was developed using ferritin nanocages, which display the spike protein from the Wuhan-Hu-1, B.1.351, or B.1.429 SARS-CoV-2 on their surfaces. We show that the mixture of three SARS-CoV-2 spike-protein-displaying nanocages elicits CD4⁺ and CD8⁺ T cells and B-cell immunity successfully in vivo. Furthermore, they generate a more consistent antibody response against the B.1.351 and B.1.429 variants than a monovalent vaccine. This leads us to believe that the proposed ferritin-nanocage-based multivalent vaccine platform will provide strong protection against emerging SARS-CoV-2 variants of concern (VOCs).

Multimericity Amplifies the Synergy of BCR and TLR4 for B Cell Activation and Antibody Class Switching

Sustained signaling through the B cell antigen receptor (BCR) is thought to occur only when antigen(s) crosslink or disperse multiple BCR units, such as by multimeric antigens found on the surfaces of viruses or bacteria. B cell-intrinsic Toll-like receptor (TLR) signaling synergizes with the BCR to induce and shape antibody production, hallmarked by immunoglobulin (Ig) class switch recombination (CSR) of constant heavy chains from IgM/IgD to IgG, IgA or IgE isotypes, and somatic hypermutation (SHM) of variable heavy and light chains. Full B cell differentiation is essential for protective immunity, where class switched high affinity antibodies neutralize present pathogens, memory B cells are held in reserve for future encounters, and activated B cells also serve as semi-professional APCs for T cells. But the rules that fine-tune B cell differentiation remain partially understood, despite their being essential for naturally acquired immunity and for guiding vaccine development. To address this in part, we have developed a cell culture system using splenic B cells from naive mice stimulated with several biotinylated ligands and antibodies crosslinked by streptavidin reagents. In particular, biotinylated lipopolysaccharide (LPS), a Toll-like receptor 4 (TLR4) agonist, and biotinylated anti-IgM were pre-assembled (multimerized) using streptavidin, or immobilized on nanoparticles coated with streptavidin, and used to active B cells in this precisely controlled, high throughput assay. Using B cell proliferation and Ig class switching as metrics for successful B cell activation, we show that the stimuli are both synergistic and dose-dependent. Crucially, the multimerized immunoconjugates are most active over a narrow concentration range. These data suggest that multimericity is an essential requirement for B cell BCR/TLRs ligands, and clarify basic rules for B cell activation. Such studies highlight the importance in determining the choice of single vs multimeric formats of antigen and PAMP agonists during vaccine design and development.

B-cell receptor dependent phagocytosis and presentation of particulate antigen by chronic lymphocytic leukemia cells

Aim

T-helper cells could play an important role in the pathogenesis of chronic lymphocytic leukemia (CLL), a common B-cell neoplasm. Although CLL cells can present soluble antigens targeted from the B-cell receptor to T-helper cells via major histocompatibility complex (MHC) class II, antigens recognized by some CLL cells may be encountered in a particulate form. Here the ability of CLL cells to internalize and present anti-immunoglobulin M (IgM) beads as a model for the interaction of CLL cells with particulate antigens was investigated.

Methods

The effect of anti-IgM beads on antigen presentation pathways was analyzed using RNA-seq and internalization of anti-IgM beads by primary CLL cells was investigated using confocal microscopy and flow cytometry. Antigen presentation was investigated by analyzing activation of a T-cell line expressing a T-cell receptor specific for a peptide derived from mouse κ light chains after incubating CLL cells with a mouse κ light chain-containing anti-IgM monoclonal antibody. Kinase inhibitors were used to characterize the pathways mediating internalization and antigen presentation.

Results

Stimulation of surface IgM of CLL cells increased expression of the antigen presentation machinery and CLL cells were able to phagocytose anti-IgM beads. Internalization of anti-IgM beads was associated with MHC class II-restricted activation of cognate T-helper cells. Antigen presentation by CLL cells was dependent on activity of spleen tyrosine kinase (SYK) and phosphatidylinositol 3-kinase delta (PI3Kδ) but was unaffected by inhibitors of Bruton's tyrosine kinase (BTK).

Conclusions

CLL cells can internalize and present antigen from anti-IgM beads. This capacity of CLL cells may be particularly important for recruitment of T-cell help in vivo in response to particulate antigens.

Immunization with GP1 but Not Core-like Particles Displaying Isolated Receptor-Binding Epitopes Elicits Virus-Neutralizing Antibodies against Junín Virus

New World arenaviruses are rodent-transmitted viruses and include a number of pathogens that are responsible for causing severe human disease. This includes Junín virus (JUNV), which is the causative agent of Argentine hemorrhagic fever. The wild nature and mobility of the rodent reservoir host makes it difficult to control the disease, and currently passive immunization with high-titer neutralizing antibody-containing plasma from convalescent patients is the only specific therapy. However, dwindling supplies of naturally available convalescent plasma, and challenges in developing similar resources for other closely related viruses, have made the development of alternative antibody-based therapeutic approaches of critical importance. In this study, we sought to induce a neutralizing antibody response in rabbits against the receptor-binding subunit of the viral glycoprotein, GP1, and the specific peptide sequences in GP1 involved in cellular receptor contacts. While these specific receptor-interacting peptides did not efficiently induce the production of neutralizing antibodies when delivered as a particulate antigen (as part of hepatitis B virus core-like particles), we showed that recombinant JUNV GP1 purified from transfected mammalian cells induced virus-neutralizing antibodies at high titers in rabbits. Further, neutralization was observed across a range of unrelated JUNV strains, a feature that is critical for effectiveness in the field. These results underscore the potential of GP1 alone to induce a potent neutralizing antibody response and highlight the importance of epitope presentation. In addition, effective virus neutralization by rabbit antibodies supports the potential applicability of this species for the future development of immunotherapeutics (e.g., based on humanized monoclonal antibodies). Such information can be applied in the design of vaccines and immunogens for both prevention and specific therapies against this and likely also other closely related pathogenic New World arenaviruses.

Adaptive tolerance: Protection through self-recognition

The random nature of immunoglobulin gene segment rearrangement inevitably leads to the generation of self-reactive B cells. Avoidance of destructive autoimmune reactions is necessary in order to maintain physiological homeostasis. However, current central and peripheral tolerance concepts fail to explain the massive number of autoantibody-borne autoimmune diseases. Moreover, recent studies have shown that in physiological mouse models autoreactive B cells were neither clonally deleted nor kept in an anergic state, but were instead able to mount autoantibody responses. We propose that activation of autoreactive B cells is induced by polyvalent autoantigen complexes that can occur under physiological conditions. Repeated encounter of autoantigen complexes leads to the production of affinity-matured autoreactive IgM that protects its respective self-targets from degradation. We refer to this novel mechanism as adaptive tolerance. This article discusses the discovery of adaptive tolerance and the unexpected role of high affinity IgM autoantibodies.

The quest for a better fight: How can nanomaterials address the current therapeutic and diagnostic obstacles in the fight against COVID-19?

The inexorable coronavirus disease 2019 (COVID-19) pandemic with around 226 million people diagnosed and approximately 4.6 million deaths, is still moving toward more frightening statistics, calling for the urgent need to explore solutions for the current challenges in therapeutic and diagnostic approaches. The challenges associated with existing therapeutics in COVID-19 include lack of in vivo stability, efficacy, and safety. Nanoparticles (NPs) can offer a handful of tools to tackle these problems by enabling efficacious and safe delivery of both virus- and host-directed therapeutics. Furthermore, they can enable maximized clinical outcome while eliminating the chance of resistance to therapy by tissue-targeting and concomitant delivery of multiple therapeutics. The promising application of NPs as vaccine platforms is reflected by the major advances in developing novel COVID-19 vaccines. Two of the most critical COVID-19 vaccines are mRNA-based vaccines delivered via NPs, making them the first FDA-approved mRNA vaccines. Besides, NPs have been deployed as simple, rapid, and precise tools for point of care disease diagnosis. Not enough said NPs can also be exploited in novel ways to expedite the drug discovery process. In light of the above, this review discusses how NPs can overcome the hurdles associated with therapeutic and diagnostic approaches against COVID-19.

Farnesylthiosalicylic acid-derivatized PEI-based nanocomplex for improved tumor vaccination

Cancer vaccines that make use of tumor antigens represent a promising therapeutic strategy by stimulating immune responses against tumors to generate long-term anti-tumor immunity. However, vaccines have shown limited clinical efficacy due to inefficient delivery. In this study, we focus on vaccine delivery assisted by nanocomplexes for cancer immunotherapy. Nanocomplex-mediated vaccination can efficiently deliver nucleic acids encoding neoantigens to lymphoid tissues and antigen-presenting cells. Polyethylenimine (PEI) was conjugated with farnesylthiosalicylic acid (FTS) to form micelles. Subsequent interaction with nucleic acids led to formation of polymer/nucleic acid nanocomplexes of well-controlled structure. Tumor transfection via FTS-PEI was much more effective than that by PEI, other PEI derivatives, or naked DNA. Significant numbers of transfected cells were also observed in draining lymph nodes (LNs). In vivo delivery of ovalbumin (OVA; a model antigen) expression plasmid (pOVA) by FTS-PEI led to a significant growth inhibition of the OVA-expressing B16 tumor through presentation of OVA epitopes as well as other epitopes via epitope spreading. Moreover, in vivo delivery of an endogenous melanoma neoantigen tyrosinase-related protein 2 (Trp2) also led to substantial tumor growth inhibition. FTS-PEI represents a promising transfection agent for effective gene delivery to tumors and LNs to mediate effective neoantigen vaccination.

Intranasal vaccination with protein bodies elicit strong protection against Streptococcus pneumoniae colonization

Protein bodies (PBs) are particles consisting of insoluble, aggregated proteins with potential as a vaccine formulation. PBs can contain high concentrations of antigen, are stable and relatively resistant to proteases, release antigen slowly and are cost-effective to manufacture. Yet, the capacity of PBs to provoke immune responses and protection in the upper respiratory tract, a major entry route of respiratory pathogens, is largely unknown. In this study, we vaccinated mice intranasally with PBs comprising antigens from Streptococcus pneumoniae and evaluated the level of protection against nasopharyngeal colonization. PBs composed of the α-helical domain of pneumococcal surface protein A (PspAα) provided superior protection against colonization with S. pneumoniae compared to soluble PspAα. Immunization with soluble protein or PBs induced differences in antibody binding to pneumococci as well as a highly distinct antigen-specific nasal cytokine profile upon in vivo stimulation with inactivated S. pneumoniae. Moreover, immunization with PBs composed of conserved putative pneumococcal antigens reduced colonization by S. pneumoniae in mice, both as a single- and as a multi-antigen formulation. In conclusion, PBs represent a vaccine formulation that elicits strong mucosal immune responses and protection. The versatility of this platform offers opportunities for development of next-generation vaccine formulations.

Ma J, McDonald KA, Murad A, Nandi S, O’Keef B, Parthiban S, Paul MJ, Ponndorf D, Rech E, Rodrigues JC, Ruf S, Schillberg S, Schwestka J, Shah PS, Singh R, Stoger E, Twyman RM, Varghese IP, Vianna GR, Webster G, Wilbers RHP, Christou P, Oksman‐Caldentey K, Capell T. Contributions of the international plant science community to the fight against infectious diseases in humans-part 2: Affordable drugs in edible plants for endemic and re-emerging diseases

The fight against infectious diseases often focuses on epidemics and pandemics, which demand urgent resources and command attention from the health authorities and media. However, the vast majority of deaths caused by infectious diseases occur in endemic zones, particularly in developing countries, placing a disproportionate burden on underfunded health systems and often requiring international interventions. The provision of vaccines and other biologics is hampered not only by the high cost and limited scalability of traditional manufacturing platforms based on microbial and animal cells, but also by challenges caused by distribution and storage, particularly in regions without a complete cold chain. In this review article, we consider the potential of molecular farming to address the challenges of endemic and re-emerging diseases, focusing on edible plants for the development of oral drugs. Key recent developments in this field include successful clinical trials based on orally delivered dried leaves of Artemisia annua against malarial parasite strains resistant to artemisinin combination therapy, the ability to produce clinical-grade protein drugs in leaves to treat infectious diseases and the long-term storage of protein drugs in dried leaves at ambient temperatures. Recent FDA approval of the first orally delivered protein drug encapsulated in plant cells to treat peanut allergy has opened the door for the development of affordable oral drugs that can be manufactured and distributed in remote areas without cold storage infrastructure and that eliminate the need for expensive purification steps and sterile delivery by injection.

Peptide-based supramolecular vaccine systems

Currently approved replication-competent and inactivated vaccines are limited by excessive reactogenicity and poor safety profiles, while subunit vaccines are often insufficiently immunogenic without co-administering exogenous adjuvants. Self-assembling peptide-, peptidomimetic-, and protein-based biomaterials offer a means to overcome these challenges through their inherent modularity, multivalency, and biocompatibility. As these scaffolds are biologically derived and present antigenic arrays reminiscent of natural viruses, they are prone to immune recognition and are uniquely capable of functioning as self-adjuvanting vaccine delivery vehicles that improve humoral and cellular responses. Beyond this intrinsic immunological advantage, the wide range of available amino acids allows for facile de novo design or straightforward modifications to existing sequences. This has permitted the development of vaccines and immunotherapies tailored to specific disease models, as well as generalizable platforms that have been successfully applied to prevent or treat numerous infectious and non-infectious diseases. In this review, we briefly introduce the immune system, discuss the structural determinants of coiled coils, β-sheets, peptide amphiphiles, and protein subunit nanoparticles, and highlight the utility of these materials using notable examples of their innate and adaptive immunomodulatory capacity.

Glatiramer acetate enhances tumor retention and innate activation of immunostimulants

Cancer immunotherapy aims to stimulate immune cells to recognize and attack tumor tissue. The immunostimulatory polyanions polyI:C and CpG induce potent pro-inflammatory immune responses as TLR3 and TLR9 agonists, respectively. Clinical trials of TLR agonists, however, have been fraught with immune-related adverse events, even when injecting intratumorally in an effort to minimize systemic exposure. We identified Glatiramer Acetate (GA), a positively-charged polypeptide approved for multiple sclerosis, as a delivery agent capable of complexing with polyI:C or CpG and reducing the mobility of these actives. Small nanoparticles termed polyplexes form when mixing positively-charged GA and negatively-charged immunostimulant (polyI:C or CpG). The ratio of GA to immunostimulant directly affected the potency of TLR activation and the mobility of these actives in simulated tumor tissue. Polyplexes of GA and CpG were injected intratumorally in a tumor model of head and neck cancer (HNC) and significantly mitigated tumor growth as compared to the vehicle controls. Intratumoral injections of CpG showed the slowest tumor growth but exhibited dramatically higher systemic proinflammatory cytokine levels compared to polyplexes of GA with CpG. Sequencing of RNA from resected tumors revealed a similar pattern of upregulated proinflammatory cytokines for CpG and polyplexes, a finding supported by histological tumor staining showing similar infiltration of immune cells induced by these treatments. Intratumoral administration of polyplexes of GA with immunostimulant represents a translational approach to enhance local immune responses while mitigating systemic immune-related adverse events.

Solubility Controlling Peptide Tags of Opposite Charges Generate a Bivalent Immune Response Against Dengue ED3 Serotypes 3 and 4

We previously demonstrated that a protein’s immunogenicity could be substantially increased by attaching a hydrophobic solubility controlling peptide tag (SCP-tag) producing small sub-visible aggregates. Here, we report the oligomerization of Dengue envelop protein domain 3 (ED3), and consequently, its immunogenicity increase by mixing ED3s attached with SCP-tags of opposite charges at equimolar concentration. We used ED3 of serotype 3 (D3ED3) and serotype 4 (D4ED3), which are, respectively, moderately and poorly immunogenic, and their SCP tagged variants constructed by attaching either a C-termini 5-Aspartic acid (C5D) or a 5-Lysine (C5K) tag. Light scattering indicated that the isolated tagged ED3s remained monomeric, but mixing the C5D and C5K tagged ED3s at equimolar concentration generated sub-visible aggregates or oligomers of ~500 nm through electrostatic interaction. In addition, the oligomerized ED3s remained in a native-like state, as assessed by fluorescence spectroscopy and circular dichroism. The in vivo immunogenicity of the D3ED3 and D4ED3 oligomers generated by the charged tags increased by 5 and 16 fold, respectively. Furthermore, injection of heterotypic ED3 oligomers (D3C5D+D4C5K) induced an immune response against both D3ED3 and D4ED3 in 3 of 4 responsive mice, and the IgG titer of the bivalent anti-D3C5D-D4C5K sera was over 100 times higher than that generated by co-injecting the untagged D3ED3 and D4ED3 (D3+D4). Altogether, these observations suggest that SCP-tags could be used as a platform for producing a long-sought tetravalent dengue vaccine.

Microneedles: A New Generation Vaccine Delivery System

Transdermal vaccination route using biodegradable microneedles is a rapidly progressing field of research and applications. The fear of painful needles is one of the primary reasons most people avoid getting vaccinated. Therefore, developing an alternative pain-free method of vaccination using microneedles has been a significant research area. Microneedles comprise arrays of micron-sized needles that offer a pain-free method of delivering actives across the skin. Apart from being pain-free, microneedles provide various advantages over conventional vaccination routes such as intramuscular and subcutaneous. Microneedle vaccines induce a robust immune response as the needles ranging from 50 to 900 μm in length can efficiently deliver the vaccine to the epidermis and the dermis region, which contains many Langerhans and dendritic cells. The microneedle array looks like band-aid patches and offers the advantages of avoiding cold-chain storage and self-administration flexibility. The slow release of vaccine antigens is an important advantage of using microneedles. The vaccine antigens in the microneedles can be in solution or suspension form, encapsulated in nano or microparticles, and nucleic acid-based. The use of microneedles to deliver particle-based vaccines is gaining importance because of the combined advantages of particulate vaccine and pain-free immunization. The future of microneedle-based vaccines looks promising however, addressing some limitations such as dosing inadequacy, stability and sterility will lead to successful use of microneedles for vaccine delivery. This review illustrates the recent research in the field of microneedle-based vaccination.

Microparticles and Nanoparticles from Plants-The Benefits of Bioencapsulation

The efficacy of drugs and vaccines depends on their stability and ability to interact with their targets in vivo. Many drugs benefit from encapsulation, which protects them from harsh conditions and allows targeted delivery and controlled release. Although many encapsulation methods are inexpensive, such as the formulation of tablets for oral delivery, others require complex procedures that add significantly to production costs and require low-temperature transport and storage, making them inaccessible in developing countries. In this review we consider the benefits of encapsulation technologies based on plants. Plant-derived biopolymers such as starch and the maize storage protein zein are already used as protective coatings, but plant cells used as production host provide natural in vivo bioencapsulation that survives passage through the stomach and releases drugs in the intestine, due to the presence of microbes that can digest the cell wall. Proteins can also be encapsulated in subcellular compartments such as protein bodies, which ensure stability and activity while often conferring additional immunomodulatory effects. Finally, we consider the incorporation of drugs and vaccines into plant-derived nanoparticles assembled from the components of viruses. These are extremely versatile, allowing the display of epitopes and targeting peptides as well as carrying cargoes of drugs and imaging molecules.

Exploring the cancer-testis antigen BORIS to design a novel multi-epitope vaccine against breast cancer based on immunoinformatics approaches

Recently, cancer immunotherapy has gained lots of attention to replace the current chemoradiation approaches and multi-epitope cancer vaccines are manifesting as the next generation of cancer immunotherapy. Therefore, in this study, we used multiple immunoinformatics approaches along with other computational approaches to design a novel multi-epitope vaccine against breast cancer. The most immunogenic regions of the BORIS cancer-testis antigen were selected according to the binding affinity to MHC-I and II molecules as well as containing multiple cytotoxic T lymphocyte (CTL) epitopes by multiple immunoinformatics servers. The selected regions were linked together by GPGPG linker. Also, a T helper epitope (PADRE) and the TLR-4/MD-2 agonist (L7/L12 ribosomal protein from mycobacterium) were incorporated by A(EAAAK)3A linker to form the final vaccine construct. Then, its physicochemical properties, cleavage sites, TAP transport efficiency, B cell epitopes, IFN-γ inducing epitopes and population coverage were predicted. The final vaccine construct was reverse translated, codon-optimized and inserted into pcDNA3.1 to form the DNA vaccine. The final vaccine construct was a stable, immunogenic and non-allergenic protein that contained numerous CTL epitopes, IFN-γ inducing epitopes and several linear and conformational B cell epitopes. Also, the final vaccine construct formed stable and significant interactions with TLR-4/MD-2 complex according to molecular docking and dynamics simulations. Moreover, its world population coverage for HLA-I and HLA-II were about 93% and 96%, respectively. Taking together, these preliminary results can be used as an appropriate platform for further experimental investigations.Communicated by Ramaswamy H. Sarma.

Vaccine-Induced CD8+ T Cell Responses in Children: A Review of Age-Specific Molecular Determinants Contributing to Antigen Cross-Presentation

Infections are most common and most severe at the extremes of age, the young and the elderly. Vaccination can be a key approach to enhance immunogenicity and protection against pathogens in these vulnerable populations, who have a functionally distinct immune system compared to other age groups. More than 50% of the vaccine market is for pediatric use, yet to date vaccine development is often empiric and not tailored to molecular distinctions in innate and adaptive immune activation in early life. With modern vaccine development shifting from whole-cell based vaccines to subunit vaccines also comes the need for formulations that can elicit a CD8+ T cell response when needed, for example, by promoting antigen cross-presentation. While our group and others have identified many cellular and molecular determinants of successful activation of antigen-presenting cells, B cells and CD4+ T cells in early life, much less is known about the ontogeny of CD8+ T cell induction. In this review, we summarize the literature pertaining to the frequency and phenotype of newborn and infant CD8+ T cells, and any evidence of induction of CD8+ T cells by currently licensed pediatric vaccine formulations. In addition, we review the molecular determinants of antigen cross-presentation on MHC I and successful CD8+ T cell induction and discuss potential distinctions that can be made in children. Finally, we discuss recent advances in development of novel adjuvants and provide future directions for basic and translational research in this area.

Decoding capsule synthesis in Streptococcus pneumoniae

Streptococcus pneumoniae synthesizes more than one hundred types of capsular polysaccharides (CPS). While the diversity of the enzymes and transporters involved is enormous, it is not limitless. In this review, we summarized the recent progress on elucidating the structure-function relationships of CPS, the mechanisms by which they are synthesized, how their synthesis is regulated, the host immune response against them, and the development of novel pneumococcal vaccines. Based on the genetic and structural information available, we generated provisional models of the CPS repeating units that remain unsolved. In addition, to facilitate cross-species comparisons and assignment of glycosyltransferases, we illustrated the biosynthetic pathways of the known CPS in a standardized format. Studying the intricate steps of pneumococcal CPS assembly promises to provide novel insights for drug and vaccine development as well as improve our understanding of related pathways in other species.

Protein and Peptide Nanocluster Vaccines

Recombinant protein- and peptide-based vaccines can deliver large amounts of specific antigens for tailored immune responses. One class of these are protein and peptide nanoclusters (PNCs), which are made entirely from the crosslinked antigen. PNCs leverage the inherent immunogenicity of nanoparticulate antigens while minimizing the use of excipients normally used to create them. In this chapter, we discuss PNC fabrication methods, immunostimulatory properties of nanoclusters observed in vitro and in vivo, and protective benefits of PNC vaccines against influenza and cancer mouse models. We conclude with an outlook on future studies of PNCs and PNC design strategies, as well as their use in future vaccine formulations.

Aggregation by peptide conjugation rescues poor immunogenicity of the HA stem

Influenza virus infection is a global public health threat. Current seasonal influenza vaccines are efficacious only when vaccine strains are matched with circulating strains. There is a critical need for developing "universal" vaccines that protect against all influenza viruses. HA stem is a promising target for developing broad-spectrum influenza vaccines due to its relatively conserved feature. However, HA stem is weakly immunogenic when administered alone in a soluble form. Several approaches have been employed to improve the immunogenicity of HA stem, including conjugation of HA stem with a highly immunogenic carrier protein or displaying HA stem on a nanoparticle scaffold. Converting a weakly immunologic protein into a multimer through aggregation can significantly enhance its immunogenicity, with some multimeric protein aggregates previously shown to be more immunogenic than their soluble counterparts in animal models. Here, we show that a chemically coupling a peptide derived from the head domain of PR8 HA (P35) with the poorly immunogenic HA stem protein results in aggregation of the HA stem which significantly increases stem-specific B cell responses following vaccination. Importantly, vaccination with this conjugate in the absence of adjuvant still induced robust B cell responses against stem in vivo. Improving HA stem immunogenicity by aggregation provides an alternative avenue to conjugation with exotic carrier proteins or nanoparticle formulation.

Engineering Strategies for Lymph Node Targeted Immune Activation

Development of vaccine technology that induces long lasting and potent adaptive immune responses is of vital importance to combat emerging pathogens and to design the next generation of cancer immunotherapies. Advanced biomaterials such as nanoparticle carriers are intensively explored to increase the efficacy and safety of vaccines and immunotherapies, based on their intrinsic potential to focus the therapeutic payload onto the relevant immune cells and to limit systemic distribution. With adaptive immune responses being primarily initiated in lymph nodes, the potency of nanoparticle vaccines in turn is tightly linked to their capacity to reach and accumulate in the lymph nodes draining the immunization site. Here, we discuss the main strategies applied to increase nanoparticle delivery to lymph nodes: (1) direct lymph node injection, (2) active cell-mediated transport through targeting of peripheral dendritic cells, and (3) exploiting passive transport through the afferent lymphatics.The intralymph nodal injection is obviously the most direct way for nanoparticles to reach lymph nodes, and multiple studies have demonstrated its capability in enhancing immunostimulant drugs' immune activation and increasing the therapeutic window. However, the requirement of using ultrasound guidance for mapping lymph nodes in patients renders intranodal administration unsuited for mass vaccination campaigns. As lymph nodes are fine structured organs with lymphocytes and chemokine gradients arrayed in a highly ordered fashion, the breakdown of such formats by the intralymph nodal injection is another concern. The exploitation of dendritic cells as live vectors for transporting nanoparticles to lymph nodes has intensively been studied both ex vivo and in vivo. While ex vivo engineering of dendritic cells in theory can achieve 100% dendritic cell-specific selectivity, a scenario impossible to be achieved in vivo, this procedure is usually laborious and complicated and entails the participation of professional staff and equipment. In addition, the poor efficiency of dendritic cell migration to the draining lymph node is another significant limitation following the injection of ex vivo cultured dendritic cells. Thus, in vivo targeting of surface receptors, particularly C-type lectin receptors, on dendritic cells by conjugating nanoparticles with antibodies or ligands is intensively studied by both academia and industry. Although such nanoparticles in vivo still face nonspecific engulfment by various phagocytes, multiple studies have shown its feasibility in targeting dendritic cells with high selectivity. Moreover, through optimizing the physicochemical properties of nanoparticles, nanoparticles can passively drain to lymph nodes carried by the interstitial flow. Compared to dendritic cell-mediated transport, passive draining is much faster and of higher efficiency. Of all such properties, size is the most important parameter as large particles (>500 nm) can only reach lymph nodes by an active cell-mediated transport. Other surface properties, such as the charge and the balance of hydrophobicity-vs-hydrophilicity, strongly influence the mobility of nanoparticles in the extracellular space. In addition, albumin, a natural fatty acid transporter, has recently been demonstrated capable of binding the amphiphiles through their lipid moiety and subsequent transporting them to lymph nodes.

Enhancing immunogenicity of a reporter protein by fusion to glycoprotein and nucleoprotein of viral hemorrhagic septicemia virus (VHSV) particles

The introduction of reverse genetic technology to generate recombinant VHSVs (rVHSVs) has contributed to the uncovering of functional roles of viral genes and to the development of attenuated prophylactic vaccines. In this study, to assess the possible use of rVHSVs as a tool of combined vaccines, we newly rescued rVHSVs that harbor viral envelop-studded eGFP (rVHSV-A-SGT) or nucleoprotein-fused eGFP (rVHSV-A-NLG), and the ability of these rVHSVs to induce adaptive humoral immunity in olive flounder (Paralichthys olivaceus) was compared with that of rVHSV-A-eGFP that expresses eGFP as a soluble form in the cytoplasm of infected cells. The results showed that antibodies against eGFP were efficiently induced by the immunization of olive flounder with rVHSV-A-SGT and rVHSV-A-NLG, while rVHSV-A-eGFP was poor in the ability to induce antibody response against eGFP. These results suggest that the display of heterologous antigens on VHSV envelop is a good way to develop efficient combined vaccines and the fusion of foreign antigen with N protein can also be a way to enhance immunogenicity of a foreign antigen. The present recombinant VHSVs - rVHSV-A-SGT and rVHSV-A-NLG - not only express foreign antigens in host cell cytoplasm but also display antigens in or on the virus particles. Further researches on the availability of recombinant VHSVs as combined vaccines against multiple fish pathogens are needed.

Comparative Study of Immunogenic Properties of Purified Capsular Polysaccharides from Streptococcus suis Serotypes 3, 7, 8, and 9: the Serotype 3 Polysaccharide Induces an Opsonizing IgG Response

Streptococcus suis is an encapsulated bacterium and one of the most important swine pathogens and a zoonotic agent for which no effective vaccine exists. Bacterial capsular polysaccharides (CPSs) are poorly immunogenic, but anti-CPS antibodies are essential to the host defense against encapsulated bacteria. In addition to the previously known serotypes 2 and 14, which are nonimmunogenic, we have recently purified and described the CPS structures for serotypes 1, 1/2, 3, 7, 8, and 9.

Streptococcus suis is an encapsulated bacterium and one of the most important swine pathogens and a zoonotic agent for which no effective vaccine exists. Bacterial capsular polysaccharides (CPSs) are poorly immunogenic, but anti-CPS antibodies are essential to the host defense against encapsulated bacteria. In addition to the previously known serotypes 2 and 14, which are nonimmunogenic, we have recently purified and described the CPS structures for serotypes 1, 1/2, 3, 7, 8, and 9. Here, we aimed to elucidate how these new structurally diverse CPSs interact with the immune system to generate anti-CPS antibody responses. CPS-stimulated dendritic cells produced significant levels of C–C motif chemokine ligand 3 (CCL3), partially via Toll-like receptor 2 (TLR2)- and myeloid differentiation factor 88-dependent pathways, and CCL2, via TLR-independent mechanisms. Mice immunized with purified serotype 3 CPS adjuvanted with TiterMax Gold produced an opsonizing IgG response, whereas other CPSs or adjuvants were negative. Mice hyperimmunized with heat-killed S. suis serotypes 3 and 9 both produced anti-CPS type 1 IgGs, whereas serotypes 7 and 8 remained negative. Also, mice infected with sublethal doses of S. suis serotype 3 produced primary anti-CPS IgM and IgG responses, of which only IgM were boosted after a secondary infection. In contrast, mice sublethally infected with S. suis serotype 9 produced weak anti-CPS IgM and IgG responses following a secondary infection. This study provides important information on the divergent evolution of CPS serotypes with highly different structural and/or biochemical properties within S. suis and their interaction with the immune system.

Engineering anti-cancer nanovaccine based on antigen cross-presentation

Dendritic cells (DCs) present exogenous antigens on major histocompatibility complex (MHC) class I molecules, thereby activating CD8⁺ T cells, contributing to tumor elimination through a mechanism known as antigen cross-presentation. A variety of factors such as maturation state of DCs, co-stimulatory signals, T-cell microenvironment, antigen internalization routes and adjuvants regulate the process of DC-mediated antigen cross-presentation. Recently, the development of successful cancer immunotherapies may be attributed to the ability of DCs to cross-present tumor antigens. In this review article, we focus on the underlying mechanism of antigen cross-presentation and ways to improve antigen cross-presentation in different DC subsets. We have critically summarized the recent developments in the generation of novel nanovaccines for robust CD8⁺ T-cell response in cancer. In this context, we have reviewed nanocarriers that have been used for cancer immunotherapeutics based on antigen cross-presentation mechanism. Additionally, we have also expressed our views on the future applications of this mechanism in curing cancer.

Adaptable antigen matrix platforms for peptide vaccination strategies and T cell-mediated anti-tumor immunity

Injection of antigenic peptides has been widely used as a vaccine strategy to boost T cell immunity. However, the poor immunogenicity of single peptides can potentially be strengthened through modification of the tertiary structure and the selection of the accompanying adjuvant. Here, we generated antigenic peptides into non-linear trimers by solid phase peptide synthesis, thereby enhancing antigen presentation by dendritic cells to CD8⁺ T cells in vitro and in vivo. CD8⁺ T cells from mice vaccinated with trimers showed an KLRG1⁺ effector phenotype and were able to recognize and kill antigen-expressing tumor cells ex vivo. Importantly, trimers outperformed synthetic long peptide in terms of T cell response even when equal number of epitopes were used for immunization. To improve the synthesis of trimers containing difficult peptide sequences, we developed a novel small molecule that functions as conjugation platform for synthetic long peptides. This platform , termed Antigen MAtriX (AMAX) improved yield, purity and solubility of trimers over conventional solid phase synthesis strategies. AMAX outperformed synthetic long peptides in terms of both CD8⁺ and CD4⁺ T cell responses and allowed functionalization with DC-SIGN-binding carbohydrates for in vivo dendritic cell targeting strategies, boosting T cell responses even further. Moreover, we show that agonistic CD40 antibody combined with MF59 (AddaVax) emulsion synergistically improves the antigen-specific T cell response of the AMAX in vivo. Also, tumor-associated antigens and neo-antigens could be incorporated in AMAX for tumor-specific CD8⁺ T cell responses. Importantly, immunization with a mix of neoantigen AMAX could reduce tumor growth in a pre-clinical syngeneic mouse model. Hence, we provide pre-clinical support for the induction of effector CD8⁺ T cells through the adaptable AMAX platform as easy implementable peptidic vaccination strategy against any antigen of choice, including neoantigens for anti-tumor immunity.

Development of an Enzyme-Mediated, Site-Specific Method to Conjugate Toll-Like Receptor 2 Agonists onto Protein Antigens: Toward a Broadly Protective, Four Component, Group A Streptococcal Self-Adjuvanting Lipoprotein-Fusion Combination Vaccine

Subunit vaccines composed of protein antigens covalently attached to Toll-like receptor (TLR) agonists elicit superior immune responses compared to mixtures of antigens and TLR agonists. Among different conjugation approaches, enzyme-mediated ligation is one of the few that provides an opportunity for the generation of homogeneous, molecularly defined products in which protein antigens are maintained with native structures, which is most critical to elicit protective immune responses upon vaccination. Four highly conserved protein antigens from Group A Streptococcus (GAS) have the potential to be safe and efficacious vaccine candidates. After a TLR2 agonist fibroblast-stimulating lipopeptide-1 (FSL-1) was successfully attached onto each antigen using sortase A and techniques for their purification were developed, a combination vaccine containing interleukin 8 (IL-8) protease (Streptococcus pyogenes cell envelope proteinase [SpyCEP]), Group A Streptococcal C5a peptidase (SCPA), anchorless virulence factor arginine deiminase (ADI), and trigger factor (TF)-TLR2 conjugates was produced. This combination was assessed for immunity in mice and compared with mixtures of the four antigens with FSL-1 or alum. High titer antigen-specific IgG antibodies were detected from all vaccine groups, with antibodies elicited from FSL-1 conjugates around 10-fold higher compared to the FSL-1 mixture group. Furthermore, the FSL-1 conjugates afforded a more balanced T_H1/T_H2 immune response than the alum-adjuvanted group, suggesting that this combination vaccine represents a promising candidate for the prevention of GAS diseases. Thus, we established a conjugation platform that allows for the production of defined, site-specific antigen-adjuvant conjugates, which maintain the native three-dimensional structure of antigens and can be potentially applied to a variety of protein antigens.