Vaccine adjuvants: mechanisms and platforms

Gaston Ramon's Big Four

When immunology was still in its infancy, Gaston Ramon made several major contributions to humoral immunology [...].

The role of TNC in atherosclerosis and drug development opportunities

Tenascin C (TNC), a rich glycoprotein of the extracellular matrix, exhibits a pro-atherosclerosis or anti-atherosclerosis effect depending on its location. TNC, especially its C domain/isoform (TNC-C), is strongly overexpressed in atherosclerotic plaque active areas but virtually undetectable in most normal adult tissues, suggesting that TNC is a promising delivery vector target for atherosclerosis-targeted drugs. Many delivery vectors were investigated by recognizing TNC-C, including G11, G11-iRGD, TN11, PL1, and PL3. F16 and FNLM were also investigated by recognizing TNC-A1 and TNC, respectively. Notably, iRGD was undergoing clinical trials. PL1 not only recognizes TNC-C but also the extra domain-B (EDB) of fibronectin (FN), which is also a promising delivery vector for atherosclerosis-targeted drugs, and several conjugate agents are undergoing clinical trials. The F16-conjugate agent F16IL2 is undergoing clinical trials. Therefore, G11-iRGD, PL1, and F16 have great development value. Furthermore, ATN-RNA and IMA950 were investigated in clinical trials as therapeutic drugs and vaccines by targeting TNC, respectively. Therefore, targeting TNC could greatly improve the success rate of atherosclerosis-targeted drugs and/or specific drug development. This review discussed the role of TNC in atherosclerosis, atherosclerosis-targeted drug delivery vectors, and agent development to provide knowledge for drug development targeting TNC.

Nanoparticles and Antiviral Vaccines

Viruses have threatened human lives for decades, causing both chronic and acute infections accompanied by mild to severe symptoms. During the long journey of confrontation, humans have developed intricate immune systems to combat viral infections. In parallel, vaccines are invented and administrated to induce strong protective immunity while generating few adverse effects. With advancements in biochemistry and biophysics, different kinds of vaccines in versatile forms have been utilized to prevent virus infections, although the safety and effectiveness of these vaccines are diverse from each other. In this review, we first listed and described major pathogenic viruses and their pandemics that emerged in the past two centuries. Furthermore, we summarized the distinctive characteristics of different antiviral vaccines and adjuvants. Subsequently, in the main body, we reviewed recent advances of nanoparticles in the development of next-generation vaccines against influenza viruses, coronaviruses, HIV, hepatitis viruses, and many others. Specifically, we described applications of self-assembling protein polymers, virus-like particles, nano-carriers, and nano-adjuvants in antiviral vaccines. We also discussed the therapeutic potential of nanoparticles in developing safe and effective mucosal vaccines. Nanoparticle techniques could be promising platforms for developing broad-spectrum, preventive, or therapeutic antiviral vaccines.

Uptake Quantification of Antigen Carried by Nanoparticles and Its Impact on Carrier Adjuvanticity Evaluation

Nanoparticles have been identified in numerous studies as effective antigen delivery systems that enhance immune responses. However, it remains unclear whether this enhancement is a result of increased antigen uptake when carried by nanoparticles or the adjuvanticity of the nanoparticle carriers. Consequently, it is important to quantify antigen uptake by dendritic cells in a manner that is free from artifacts in order to analyze the immune response when antigens are carried by nanoparticles. In this study, we demonstrated several scenarios (antigens on nanoparticles or inside cells) that are likely to contribute to the generation of artifacts in conventional fluorescence-based quantification. Furthermore, we developed the necessary assay for accurate uptake quantification. PLGA NPs were selected as the model carrier system to deliver EsxB protein (a Staphylococcus aureus antigen) in order to testify to the feasibility of the established method. The results showed that for the same antigen uptake amount, the antigen delivered by PLGA nanoparticles could elicit 3.6 times IL-2 secretion (representative of cellular immune response activation) and 1.5 times IL-12 secretion (representative of DC maturation level) compared with pure antigen feeding. The findings above give direct evidence of the extra adjuvanticity of PLGA nanoparticles, except for their delivery functions. The developed methodology allows for the evaluation of immune cell responses on an antigen uptake basis, thus providing a better understanding of the origin of the adjuvanticity of nanoparticle carriers. Ultimately, this research provides general guidelines for the formulation of nano-vaccines.

Non-glycosylated G protein with CpG ODN provides robust protection against respiratory syncytial virus without inducing eosinophilia

Introduction

Respiratory syncytial virus (RSV) vaccines targeting the fusion glycoprotein (F protein) are highly effective clinically in preventing RSV challenges. The attachment glycoprotein (G protein) is a potentially effective vaccine antigen candidate, as it is important for cell adhesion during infection. However, vaccine-associated enhanced diseases in mice, such as eosinophilic lung inflammation following RSV challenge, are a concern with G protein vaccines. This study aimed to design an effective G protein vaccine with enhanced safety and efficacy by evaluating the efficacy and adverse reactions of vaccines composed of different recombinant G proteins and adjuvants in mice.

Methods

Mice were subcutaneously immunized with glycosylated G protein expressed in mammalian cells (mG), non-glycosylated G protein expressed in Escherichia coli (eG), or F protein with or without aluminum salts (alum), CpG oligodeoxynucleotide (CpG ODN), or AddaVax. After vaccination, the levels of G-specific antibody and T-cell responses were measured. The immunized mice were challenged with RSV and examined for the viral load in the lungs and nasal turbinates, lung-infiltrating cells, and lung pathology.

Results

mG with any adjuvant was ineffective at inducing G-specific antibodies and had difficulty achieving both protection against RSV challenge and eosinophilia suppression. In particular, mG+CpG ODN induced G-specific T helper 1 (Th1) cells but only a few G-specific antibodies and did not protect against RSV challenge. However, eG+CpG ODN induced high levels of G-specific antibodies and Th1 cells and protected against RSV challenge without inducing pulmonary inflammation. Moreover, the combination vaccine of eG+F+CpG ODN showed greater protection against upper respiratory tract RSV challenge than using each single antigen vaccine alone.

Discussion

These results indicate that the efficacy of recombinant G protein vaccines can be enhanced without inducing adverse reactions by using appropriate antigens and adjuvants, and their efficacy is further enhanced in the combination vaccine with F protein. These data provide valuable information for the clinical application of G protein vaccines.

Ginseng Polysaccharide Enhances the Humoral and Cellular Immune Responses to SARS-CoV-2 RBD Protein Subunit Vaccines

The COVID-19 pandemic remarkably accelerated vaccine research progress. The role of adjuvants in enhancing vaccine immune intensity and influencing immune types has been considered. Ginseng polysaccharide (GPS) has been demonstrated to have strong immunoregulatory properties. It is important to explore the feasibility of adding GPS to vaccine adjuvant components to improve the immune response effect of RBD vaccines. Here, we prepared a SARS-CoV-2 RBD antigen using the Escherichia coli expression system and determined that subcutaneous administration of GPS at a dose of 40 mg/kg could effectively activate dendritic cells (DCs) and macrophages (MΦ) in mice. Compared with the RBD group, the RBD+GPS triggered stronger and persistent antibody responses. It is also notable that higher levels of RBD-specific IgG and IgA were distributed in the lungs of RBD+GPS-immunized BALB/c mice. In addition, the RBD+GPS also resulted in lower percentages of IFN-γ+ CD4+ T cells and higher percentages of IFN-γ+ CD8+ T cells and CD8+ Tcm cells. These results suggest that GPS could be a promising vaccine immuno-enhancer for SARS-CoV-2 RBD subunit vaccines to establish stronger systemic and pulmonary mucosal protective immunity.

Improving DNA vaccination performance through a new microbubble design and an optimized sonoporation protocol

As a non-viral transfection method, ultrasound and microbubble-induced sonoporation can achieve spatially targeted gene delivery with synergistic immunostimulatory effects. Here, we report for the first time the application of sonoporation for improving DNA vaccination performance. This study developed a new microbubble design with nanoscale DNA/PEI complexes loaded onto cationic microbubbles to attain significant increases in DNA-loading capacity (0.25 pg per microbubble) and in vitro transfection efficiency. Using live-cell imaging, we revealed the membrane perforation and cellular delivery characteristics of sonoporation. Using luciferase reporter gene for in vivo transfection, we showed that sonoporation increased the transfection efficiency by 40.9-fold when compared with intramuscular injection. Moreover, we comprehensively optimized the sonoporation protocol and further increased the transfection efficiency by 43.6-fold. Immunofluorescent staining results showed that sonoporation effectively activated the MHC-II+ immune cells. Using a hepatitis B DNA vaccine, sonoporation induced significantly higher serum antibody levels when compared with intramuscular injection, and the antibodies sustained for 56 weeks. In addition, we recorded the longest reported expression period (400 days) of the sonoporation-delivered gene. Whole genome resequencing confirmed that the gene with stable expression existed in an extrachromosomal state without integration. Our results demonstrated the potential of sonoporation for efficient and safe DNA vaccination.

Transcriptional Targeting of Dendritic Cells Using an Optimized Human Fascin1 Gene Promoter

Deeper knowledge about the role of the tumor microenvironment (TME) in cancer development and progression has resulted in new strategies such as gene-based cancer immunotherapy. Whereas some approaches focus on the expression of tumoricidal genes within the TME, DNA-based vaccines are intended to be expressed in antigen-presenting cells (e.g., dendritic cells, DCs) in secondary lymphoid organs, which in turn induce anti-tumor T cell responses. Besides effective delivery systems and the requirement of appropriate adjuvants, DNA vaccines themselves need to be optimized regarding efficacy and selectivity. In this work, the concept of DC-focused transcriptional targeting was tested by applying a plasmid encoding for the luciferase reporter gene under the control of a derivative of the human fascin1 gene promoter (pFscnLuc), comprising the proximal core promoter fused to the normally more distantly located DC enhancer region. DC-focused activity of this reporter construct was confirmed in cell culture in comparison to a standard reporter vector encoding for luciferase under the control of the strong ubiquitously active cytomegalovirus promoter and enhancer (pCMVLuc). Both plasmids were also compared upon intravenous administration in mice. The organ- and cell type-specific expression profile of pFscnLuc versus pCMVLuc demonstrated favorable activity especially in the spleen as a central immune organ and within the spleen in DCs.

Advancements in Vaccine Adjuvants: The Journey from Alum to Nano Formulations

Vaccination is a groundbreaking approach in preventing and controlling infectious diseases. However, the effectiveness of vaccines can be greatly enhanced by the inclusion of adjuvants, which are substances that potentiate and modulate the immune response. This review is based on extensive searches in reputable databases such as Web of Science, PubMed, EMBASE, Scopus, and Google Scholar. The goal of this review is to provide a thorough analysis of the advances in the field of adjuvant research, to trace the evolution, and to understand the effects of the various adjuvants. Historically, alum was the pioneer in the field of adjuvants because it was the first to be approved for use in humans. It served as the foundation for subsequent research and innovation in the field. As science progressed, research shifted to identifying and exploiting the potential of newer adjuvants. One important area of interest is nano formulations. These advanced adjuvants have special properties that can be tailored to enhance the immune response to vaccines. The transition from traditional alum-based adjuvants to nano formulations is indicative of the dynamism and potential of vaccine research. Innovations in adjuvant research, particularly the development of nano formulations, are a promising step toward improving vaccine efficacy and safety. These advances have the potential to redefine the boundaries of vaccination and potentially expand the range of diseases that can be addressed with this approach. There is an optimistic view of the future in which improved vaccine formulations will contribute significantly to improving global health outcomes.

Nanovaccines: A game changing approach in the fight against infectious diseases

The field of nanotechnology has revolutionised global attempts to prevent, treat, and eradicate infectious diseases in the foreseen future. Nanovaccines have proven to be a valuable pawn in this novel technology. Nanovaccines are made up of nanoparticles that are associated with or prepared with components that can stimulate the host's immune system. In addition to their delivery capabilities, the nanocarriers have been demonstrated to possess intrinsic adjuvant properties, working as immune cell stimulators. Thus, nanovaccines have the potential to promote rapid as well as long-lasting humoral and cellular immunity. The nanovaccines have several possible benefits, including site-specific antigen delivery, increased antigen bioavailability, and a diminished adverse effect profile. To avail these benefits, several nanoparticle-based vaccines are being developed, including virus-like particles, liposomes, polymeric nanoparticles, nanogels, lipid nanoparticles, emulsion vaccines, exomes, and inorganic nanoparticles. Inspired by their distinctive properties, researchers are working on the development of nanovaccines for a variety of applications, such as cancer immunotherapy and infectious diseases. Although a few challenges still need to be overcome, such as modulation of the nanoparticle pharmacokinetics to avoid rapid elimination from the bloodstream by the reticuloendothelial system, The future prospects of this technology are also assuring, with multiple options such as personalised vaccines, needle-free formulations, and combination nanovaccines with several promising candidates.

Virus-like particles nanoreactors: from catalysis towards bio-applications

Virus-like particles (VLPs) are self-assembled supramolecular structures found in nature, often used for compartmentalization. Exploiting their inherent properties, including precise nanoscale structures, monodispersity, and high stability, these architectures have been widely used as nanocarriers to protect or enrich catalysts, facilitating catalytic reactions and avoiding interference from the bulk solutions. In this review, we summarize the current progress of virus-like particles (VLPs)-based nanoreactors. First, we briefly introduce the physicochemical properties of the most commonly used virus particles to understand their roles in catalytic reactions beyond the confined space. Next, we summarize the self-assembly of nanoreactors forming higher-order hierarchical structures, highlighting the emerging field of nanoreactors as artificial organelles and their potential biomedical applications. Finally, we discuss the current findings and future perspectives of VLPs-based nanoreactors.

Carbohydrates as putative pattern recognition receptor agonists in vaccine development

Adjuvants are essential components of modern vaccines. One general mechanism underlying their immunostimulatory functions is the activation of pattern recognition receptors (PRRs) of innate immune cells. Carbohydrates - as essential signaling molecules on microbial surfaces - are potent PRR agonists and candidate materials for adjuvant design. Here, we summarize the latest trends in developing carbohydrate-containing adjuvants, with fresh opinions on how the physicochemical characteristics of the glycans (e.g., molecular size, assembly status, monosaccharide components, and functional group patterns) affect their adjuvant activities in aiding antigen transport, regulating antigen processing, and enhancing adaptive immune responses. From a translational perspective, we also discuss potential technologies for solving long-lasting challenges in carbohydrate adjuvant design.

Construction of Candida albicans Adhesin-Exposed Synthetic Cells for Preventing Systemic Fungal Infection

The development of efficient fungal vaccines is urgent for preventing life-threatening systemic fungal infections. In this study, we prepared a synthetic, cell-based fungal vaccine for preventing systemic fungal infections using synthetic biology techniques. The synthetic cell EmEAP1 was constructed by transforming the Escherichia coli chassis using a de novo synthetic fragment encoding the protein mChEap1 that was composed of the E. coli OmpA peptide, the fluorescence protein mCherry, the Candida albicans adhesin Eap1, and the C-terminally transmembrane region. The EmEAP1 cells highly exposed the mChEap1 on the cell surface under IPTG induction. The fungal vaccine was then prepared by mixing the EmEAP1 cells with aluminum hydroxide gel and CpG. Fluorescence quantification revealed that the fungal vaccine was stable even after 112 days of storage. After immunization in mice, the vaccine resided in the lymph nodes, inducing the recruitment of CD11c+ dendritic cells. Moreover, the vaccine strongly activated the CD4+ T splenocytes and elicited high levels of anti-Eap1 IgG. By the prime-boost immunization, the vaccine prolonged the survival time of the mice infected by the C. albicans cells and attenuated fungal colonization together with inflammation in the kidneys. This study sheds light on the development of synthetic biology-based fungal vaccines for the prevention of life-threatening fungal infections.

Novel insights into molecular and cellular aspects of delayed drug hypersensitivity reactions

INTRODUCTION

Delayed drug hypersensitivity reactions (DDHRs) represent a major health problem. They are unpredictable and can cause life-long disability or even death. The pathophysiology of DDHRs is complicated, multifactorial, and not well understood mainly due to the lack of validated animal models or in vitro systems. The role of the immune system is well demonstrated but its exact pathophysiology still a matter of debate.

AREA COVERED

This review summarizes the current understanding of DDHRs pathophysiology and abridges the available new evidence supporting each hypothesis. A comprehensive literature search for relevant publications was performed using PubMed, Google Scholar, and Medline databases with no date restrictions and focusing on the most recent 10 years.

EXPERT OPINION

Although multiple milestones have been achieved in our understanding of DDHRs pathophysiology as a result of the development of useful experimental models, many questions are yet to be fully answered. A deeper understanding of the mechanistic basis of DDHRs would not only facilitate the development of robust and reliable diagnostic assays for diagnosis, but would also inform therapy by providing specific target(s) for immunomodulation and potentially permit pre-therapeutic risk assessment to pursue the common goal of safe and effective drug therapy.