Programming the magnitude and persistence of antibody responses with innate immunity

Enhancing Immune Responses to a DNA Vaccine Encoding Toxoplasma gondii GRA7 Using Calcium Phosphate Nanoparticles as an Adjuvant

Toxoplasma gondii infects almost all warm-blooded animals, including humans. DNA vaccines are an effective strategy against T. gondii infection, but these vaccines have often been poorly immunogenic due to the poor distribution of plasmids or degradation by lysosomes. It is necessary to evaluate the antigen delivery system for optimal vaccination strategy. Nanoparticles (NPs) have been shown to modulate and enhance the cellular humoral immune response. Here, we studied the immunological properties of calcium phosphate nanoparticles (CaPNs) as nanoadjuvants to enhance the protective effect of T. gondii dense granule protein (GRA7). BALB/c mice were injected three times and then challenged with T. gondii RH strain tachyzoites. Mice vaccinated with GRA7-pEGFP-C2+nano-adjuvant (CaPNs) showed a strong cellular immune response, as monitored by elevated levels of anti-T. gondii-specific immunoglobulin G (IgG), a higher IgG2a-to-IgG1 ratio, elevated interleukin (IL)-12 and interferon (IFN)-γ production, and low IL-4 levels. We found that a significantly higher level of splenocyte proliferation was induced by GRA7-pEGFP-C2+nano-adjuvant (CaPNs) immunization, and a significantly prolonged survival time and decreased parasite burden were observed in vaccine-immunized mice. These data indicated that CaPN-based immunization with T. gondii GRA7 is a promising approach to improve vaccination.

Designing spatial and temporal control of vaccine responses

Vaccines are the key technology to combat existing and emerging infectious diseases. However, increasing the potency, quality and durability of the vaccine response remains a challenge. As our knowledge of the immune system deepens, it becomes clear that vaccine components must be in the right place at the right time to orchestrate a potent and durable response. Material platforms, such as nanoparticles, hydrogels and microneedles, can be engineered to spatially and temporally control the interactions of vaccine components with immune cells. Materials-based vaccination strategies can augment the immune response by improving innate immune cell activation, creating local inflammatory niches, targeting lymph node delivery and controlling the time frame of vaccine delivery, with the goal of inducing enhanced memory immunity to protect against future infections. In this Review, we highlight the biological mechanisms underlying strong humoral and cell-mediated immune responses and explore materials design strategies to manipulate and control these mechanisms.

Tetravalent formulation of Polymeric nanoparticle-based vaccine induces a potent immune response against Dengue virus

Dengue is a mosquito-borne disease caused by the four serotypes of dengue virus (DENV 1-4). It is growing at an alarming rate globally, which could be partly attributed to the...

Modulation of immune responses to vaccination by the microbiota: implications and potential mechanisms

The need for highly effective vaccines that induce robust and long-lasting immunity has never been more apparent. However, for reasons that are still poorly understood, immune responses to vaccination are highly variable between different individuals and different populations. Furthermore, vaccine immunogenicity is frequently suboptimal in the very populations who are at most risk from infectious disease, including infants, the elderly, and those living in low-income and middle-income countries. Although many factors have the potential to influence vaccine immunogenicity and therefore vaccine effectiveness, increasing evidence from clinical studies and animal models now suggests that the composition and function of the gut microbiota are crucial factors modulating immune responses to vaccination. In this Review, we synthesize this evidence, discuss the immunological mechanisms that potentially mediate these effects and consider the potential of microbiota-targeted interventions to optimize vaccine effectiveness.

A two-adjuvant multiantigen candidate vaccine induces superior protective immune responses against SARS-CoV-2 challenge

An ideal vaccine against SARS-CoV-2 is expected to elicit broad immunity to prevent viral infection and disease, with efficient viral clearance in the upper respiratory tract (URT). Here, the N protein and prefusion-full S protein (SFLmut) are combined with flagellin (KF) and cyclic GMP-AMP (cGAMP) to generate a candidate vaccine, and this vaccine elicits stronger systemic and mucosal humoral immunity than vaccines containing other forms of the S protein. Furthermore, the candidate vaccine administered via intranasal route can enhance local immune responses in the respiratory tract. Importantly, human ACE2 transgenic mice given the candidate vaccine are protected against lethal SARS-CoV-2 challenge, with superior protection in the URT compared with that in mice immunized with an inactivated vaccine. In summary, the developed vaccine can elicit a multifaceted immune response and induce robust viral clearance in the URT, which makes it a potential vaccine for preventing disease and infection of SARS-CoV-2.

Injectable and Biodegradable Chitosan Hydrogel-Based Drug Depot Contributes to Synergistic Treatment of Tumors

Combined therapy provides a more effective method in the treatment of tumors and becomes a research hotspot. To improve treatment outcomes and reduce serious side effects, hydrogel-based local delivery was developed herein to form a drug depot in suit to eliminate tumors. Indocyanine green and imiquimod were coencapsulated in the novel temperature-sensitive chitosan hydrogel. After intratumoral injection of the hydrogel, indocyanine green that accumulated in the tumor area could induce thermal ablation of primary tumors under laser irradiation. In the presence of imiquimod, the immune effects increased the probability of complete ablation of primary tumors and inhibition of metastases. Combined with cyclophosphamide, the enhanced immunological responses would further inhibit tumors and prolong the survival time. In a word, this work offered an excellent local delivery platform that enabled a remarkable combined antitumor strategy and achieved synergistic therapeutic effects.

Engineering mannosylated pickering emulsions for the targeted delivery of multicomponent vaccines

While research on cancer vaccines has made great strides in the field of immunotherapy, the targeted delivery of multiple effective components (rational-tailored antigens and adjuvants) remains a challenge. Here, we utilized the unique hierarchical structures of Pickering emulsions (particles, oil core, and water-oil interface) to develop mannosylated (M) Pickering emulsions (PE) that target antigen presenting cells and synergistically deliver antigenic peptides and the TLR9 agonist CpG (C) as an enhanced cancer vaccine (MPE-C). We chemically linked mannose residues to PLGA/PLAG-PEG nanoparticles and produced a dense array of mannose on the nanopatterned surface of Pickering emulsions, allowing for increased cellular targeting. Together with the inherent deformability of the oily core, MPE-C increased the droplet-cellular contact area and provoked the cellular recognition of mannose and CpG for enhanced immune activation. We found that MPE-C attracted a large number of APCs to the local site of administration, evidently increasing cellular uptake and activation. Additionally, we observed increased antigen-specific cellular immune responses, with potent anti-tumor effects against both E.G7-OVA and B16-MUCI tumors. Furthermore, MPE-C combined with PD-1 antibodies produced a significant tumor regression, resulting in synergistic increases in anti-tumor effects. Thus, through the strategic loading of mannose, antigens, and CpG, Pickering emulsions could serve as a targeted delivery platform for enhanced multicomponent cancer vaccines.

Delivery of STING agonists for adjuvanting subunit vaccines

Adjuvant is an essential component in subunit vaccines. Many agonists of pathogen recognition receptors have been developed as potent adjuvants to optimize the immunogenicity and efficacy of vaccines. Recently discovered cyclic GMP-AMP synthase-stimulator of interferon genes (cGAS-STING) pathway has attracted much attention as it is a key mediator for modulating immune responses. Vaccines adjuvanted with STING agonists are found to mediate a robust immune defense against infections and cancer. In this review, we first discuss the mechanisms of STING agonists in the context of vaccination. Next, we present recent progress in novel STING agonist discovery and the delivery strategies. We next highlight recent work in optimizing the efficacy while minimizing toxicity of STING agonist-assisted subunit vaccines for protection against infectious diseases or treatment of cancer. Finally, we share our perspectives of current issues and future directions in further developing STING agonists for adjuvanting subunit vaccines.

Thermal-sensitive lipid nanoparticles potentiate anti-PD therapy through enhancing drug penetration and T lymphocytes infiltration in metastatic tumor

The response rate of anti-PD therapy in most cancer patients remains low. Therapeutic drug and tumor-infiltrating lymphocytes (TILs) are usually obstructed by the stromal region within tumor microenvironment (TME) rather than distributed around tumor cells, thus unable to induce the immune response of cytotoxic T cells. Here, we constructed the cationic thermosensitive lipid nanoparticles IR780/DPPC/BMS by introducing cationic NIR photosensitizer IR-780 iodide (IR780) modified lipid components, thermosensitive lipid DPPC and PD-1/PD-L1 inhibitor BMS202 (BMS). Upon laser irradiation, IR780/DPPC/BMS penetrated into deep tumor, and reduced cancer-associated fibroblasts (CAFs) around tumor cells to remodel the spatial distribution of TILs in TME. Interestingly, the cationic IR780/DPPC/BMS could capture released tumor-associated antigens (TAAs), thereby enhancing the antigen-presenting ability of DCs to activate cytotoxic T lymphocytes. Moreover, IR780/DPPC/BMS initiated gel-liquid crystal phase transition under laser irradiation, accelerating the disintegration of lipid bilayer structure and leading to the responsive release of BMS, which would reverse the tumor immunosuppression state by blocking PD-1/PD-L1 pathway for a long term. This combination treatment can synergistically exert the antitumor immune response and inhibit the tumor growth and metastasis.

Methylated (-)-epigallocatechin 3-O-gallate potentiates the effect of split vaccine accompanied with upregulation of Toll-like receptor 5

Split-virus vaccine serves as a major countermeasure against influenza virus, but its effectiveness and protective action are not complete. We previously demonstrated the effect of Benifuuki, a green tea cultivar in Japan, on enhancing the split-virus vaccine-elicited immune response. However, little is known about the detail mechanisms. Here, we show that EGCG3"Me intake significantly potentiated the vaccine-elicited hemagglutination inhibition titer increase. Flow cytometry analysis revealed the increased Toll-like receptor 5 (TLR5) expression after EGCG3"Me treatment in lamina propria dendritic cells (LPDCs) and macrophages, which play crucial roles in the humoral immune system. TLR5 expression correlated with the level of interleukin-6 (IL-6)/C-C chemokine type receptor 5, which are important mediators of the humoral immunity. Taken together, In vivo and ex vivo studies showed that EGCG3"Me potentiated the split-virus vaccine-elicited immune response accompanied with the upregulation of TLR5 in intestine and splenocyte macrophages.

Imaging the different timescales of germinal center selection

Germinal centers (GCs) are the site of antibody affinity maturation, a fundamental immunological process that increases the potency of antibodies and thereby their ability to protect against infection. GC biology is highly dynamic in both time and space, making it ideally suited for intravital imaging. Using multiphoton laser scanning microscopy (MPLSM), the field has gained insight into the molecular, cellular, and structural changes and movements that coordinate affinity maturation in real time in their native environment. On the other hand, several limitations of MPLSM have had to be overcome to allow full appreciation of GC events taking place across different timescales. Here, we review the technical advances afforded by intravital imaging and their contributions to our understanding of GC biology.

Co-delivery of PLGA nanoparticles loaded with rSAG1 antigen and TLR ligands: An efficient vaccine against chronic toxoplasmosis

Although vaccination is a promising approach for the control of toxoplasmosis, there is currently no commercially available human vaccine. Adjuvants such as delivery vehicles and immunomodulators are critical components of vaccine formulations. In this study, Poly (D, l-lactide-co-glycolide) (PLGA) nanoparticles were applied to serve as delivery system for both surface antigen-1 (SAG1), a candidate vaccine against toxoplasmosis and two TLR ligands, monophosphoryl lipid A (MPL) and imiquimod (IMQ), respectively. Compared to rSAG1 alone, CBA/J mice immunized with rSAG1-PLGA produced higher anti-SAG1 IgG antibodies titers. This response was increased by the co-administration of IMQ-PLGA (p < 0.01). Compared to IMQ-PLGA co-administration, MPL-PLGA co-administration further increased the humoral response (p < 0.01) and potentiated the Th1 humoral response. Compared to rSAG1 alone, rSAG1-PLGA, or rSAG1-PLGA mixed with IMQ-PLGA or MPL-PLGA similarly enhanced the cellular response characterized by the production of IFN-γ, IL-2, TNF-α and low levels of IL-5, indicating a Th1-biased immunity. The induced immune responses, led to significant brain cyst reductions (p < 0.01) after oral challenge with T. gondii cysts in mice immunized with either rSAG1-PLGA, rSAG1-PLGA + IMQ-PLGA, rSAG1-PLGA + MPL-PLGA formulations. Taken together the results indicated that PLGA nanoparticles could serve as a platform for dual-delivery of antigens and immunomodulators to provide efficacious vaccines against toxoplasmosis.

PLAN B for immunotherapy: Promoting and leveraging anti-tumor B cell immunity

Current immuno-oncology primarily focuses on adaptive cellular immunity mediated by T lymphocytes. The other important lymphocytes, B cells, are largely ignored in cancer immunotherapy. B cells are generally considered to be responsible for humoral immune response to viral and bacterial infections. The role of B cells in cancer immunity has long been under debate. Recently, increasing evidence from both preclinical and clinical research has shown that B cells can also induce potent anti-cancer immunity, via humoral and cellular immune responses. Yet it is unclear how to efficiently integrate B cell immunity in cancer immunotherapy. In the current perspective, anti-tumor immunity of B cells is discussed regarding antibody production, antigen presentation, cytokine release and contribution to intratumoral tertiary lymphoid structures. Afterwards, immunosuppressive regulatory phenotypes of B cells are summarized. Furthermore, strategies to activate and modulate B cells using nanomedicines and biomaterials are discussed. This article provides a unique perspective on "PLAN B" (promoting and leveraging anti-tumor B cell immunity) using nanomedicines and biomaterials for cancer immunotherapy. This is envisaged to form a new research direction with the potential to reach the next breakthrough in immunotherapy.

Nanotechnology-based products for cancer immunotherapy

Abstract

Currently, nanoscale materials and scaffolds carrying antitumor agents to the tumor target site are practical approaches for cancer treatment. Immunotherapy is a modern approach to cancer treatment in which the body’s immune system adjusts to deal with cancer cells. Immuno-engineering is a new branch of regenerative medicine-based therapies that uses engineering principles by using biological tools to stimulate the immune system. Therefore, this branch’s final aim is to regulate distribution, release, and simultaneous placement of several immune factors at the tumor site, so then upgrade the current treatment methods and subsequently improve the immune system’s handling. In this paper, recent research and prospects of nanotechnology-based cancer immunotherapy have been presented and discussed. Furthermore, different encouraging nanotechnology-based plans for targeting various innate and adaptive immune systems will also be discussed. Due to novel views in nanotechnology strategies, this field can address some biological obstacles, although studies are ongoing.

Graphic abstract

Exploiting viral sensing mediated by Toll-like receptors to design innovative vaccines

Toll-like receptors (TLRs) are transmembrane proteins belonging to the family of pattern-recognition receptors. They function as sensors of invading pathogens through recognition of pathogen-associated molecular patterns. After their engagement by microbial ligands, TLRs trigger downstream signaling pathways that culminate into transcriptional upregulation of genes involved in immune defense. Here we provide an updated overview on members of the TLR family and we focus on their role in antiviral response. Understanding of innate sensing and signaling of viruses triggered by these receptors would provide useful knowledge to prompt the development of vaccines able to elicit effective and long-lasting immune responses. We describe the mechanisms developed by viral pathogens to escape from immune surveillance mediated by TLRs and finally discuss how TLR/virus interplay might be exploited to guide the design of innovative vaccine platforms.

Applications of Magnetite Nanoparticles in Cancer Immunotherapies: Present Hallmarks and Future Perspectives

Current immuno-oncotherapeutic protocols that inhibit tumor immune evasion have demonstrated great clinical success. However, the therapeutic response is limited only to a percentage of patients, and the immune-related adverse events can compromise the therapeutic benefits. Therefore, improving cancer immunotherapeutic approaches that pursue high tumor suppression efficiency and low side effects turn out to be a clinical priority. Novel magnetite nanoparticles (MNPs) exhibit great potential for therapeutic and imaging applications by utilizing their properties of superparamagnetism, good biocompatibility, as well as the easy synthesis and modulation/functionalization. In particular, the MNPs can exert magnetic hyperthermia to induce immunogenic cell death of tumor cells for effective antigen release and presentation, and meanwhile polarize tumor-associated macrophages (TAMs) to M1 phenotype for improved tumor killing capability, thus enhancing the anti-tumor immune effects. Furthermore, immune checkpoint antibodies, immune-stimulating agents, or tumor-targeting agents can be decorated on MNPs, thereby improving their selectivity for the tumor or immune cells by the unique magnetic navigation capability of MNPs to promote the tumor killing immune therapeutics with fewer side effects. This mini-review summarizes the recent progress in MNP-based immuno-oncotherapies, including activation of macrophage, promotion of cytotoxic T lymphocyte (CTL) infiltration within tumors and modulation of immune checkpoint blockade, thus further supporting the applications of MNPs in clinical therapeutic protocols.

Synergistic effect of non-neutralizing antibodies and interferon-γ for cross-protection against influenza

Current influenza vaccines do not typically confer cross-protection against antigenically mismatched strains. To develop vaccines conferring broader cross-protection, recent evidence indicates the crucial role of both cross-reactive antibodies and viral-specific CD4+ T cells; however, the precise mechanism of cross-protection is unclear. Furthermore, adjuvants that can efficiently induce cross-protective CD4+ T cells have not been identified. Here we show that CpG oligodeoxynucleotides combined with aluminum salts work as adjuvants for influenza vaccine and confer strong cross-protection in mice. Both cross-reactive antibodies and viral-specific CD4+ T cells contributed to cross-protection synergistically, with each individually ineffective. Furthermore, we found that downregulated expression of Fcγ receptor IIb on alveolar macrophages due to IFN-γ secreted by viral-specific CD4+ T cells improves the activity of cross-reactive antibodies. Our findings inform the development of optimal adjuvants for vaccines and how influenza vaccines confer broader cross-protection.

Mechanism of a COVID-19 nanoparticle vaccine candidate that elicits a broadly neutralizing antibody response to SARS-CoV-2 variants

Vaccines that induce potent neutralizing antibody (NAb) responses against emerging variants of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) are essential for combating the coronavirus disease 2019 (COVID-19) pandemic. We demonstrated that mouse plasma induced by self-assembling protein nanoparticles (SApNPs) that present 20 rationally designed S2GΔHR2 spikes of the ancestral Wuhan-Hu-1 strain can neutralize the B.1.1.7, B.1.351, P.1, and B.1.617 variants with comparable potency. The adjuvant effect on vaccine-induced immunity was investigated by testing 16 formulations for the multilayered I3-01v9 SApNP. Using single-cell sorting, monoclonal antibodies (mAbs) with diverse neutralization breadth and potency were isolated from mice immunized with the receptor binding domain (RBD), S2GΔHR2 spike, and SApNP vaccines. The mechanism of vaccine-induced immunity was examined in the mouse model. Compared with the soluble spike, the I3-01v9 SApNP showed sixfold longer retention, fourfold greater presentation on follicular dendritic cell dendrites, and fivefold stronger germinal center reactions in lymph node follicles.

Developing Acid-Responsive Glyco-Nanoplatform Based Vaccines for Enhanced Cytotoxic T-lymphocyte Responses Against Cancer and SARS-CoV-2

Cytotoxic T-lymphocytes (CTLs) are central for eliciting protective immunity against malignancies and infectious diseases. Here, for the first time, partially oxidized acetalated dextran nanoparticles (Ox-AcDEX NPs) with an average diameter of 100 nm are fabricated as a general platform for vaccine delivery. To develop effective anticancer vaccines, Ox-AcDEX NPs are conjugated with a representative CTL peptide epitope (CTLp) from human mucin-1 (MUC1) with the sequence of TSAPDTRPAP (referred to as Mp1) and an immune-enhancing adjuvant R837 (referred to as R) via imine bond formation affording AcDEX-(imine)-Mp1-R NPs. Administration of AcDEX-(imine)-Mp1-R NPs results in robust and long-lasting anti-MUC1 CTL immune responses, which provides mice with superior protection from the tumor. To verify its universality, this nanoplatform is also exploited to deliver epitopes from severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) to prevent coronavirus disease 2019 (COVID-19). By conjugating Ox-AcDEX NPs with the potential CTL epitope of SARS-CoV-2 (referred to as Sp) and R837, AcDEX-(imine)-Sp-R NPs are fabricated for anti-SARS-CoV-2 vaccine candidates. Several epitopes potentially contributing to the induction of potent and protective anti-SARS-CoV-2 CTL responses are examined and discussed. Collectively, these findings shed light on the universal use of Ox-AcDEX NPs to deliver both tumor-associated and virus-associated epitopes.

Safety Evaluation of Nanotechnology Products

Nanomaterials are now being used in a wide variety of biomedical applications. Medical and health-related issues, however, have raised major concerns, in view of the potential risks of these materials against tissue, cells, and/or organs and these are still poorly understood. These particles are able to interact with the body in countless ways, and they can cause unexpected and hazardous toxicities, especially at cellular levels. Therefore, undertaking in vitro and in vivo experiments is vital to establish their toxicity with natural tissues. In this review, we discuss the underlying mechanisms of nanotoxicity and provide an overview on in vitro characterizations and cytotoxicity assays, as well as in vivo studies that emphasize blood circulation and the in vivo fate of nanomaterials. Our focus is on understanding the role that the physicochemical properties of nanomaterials play in determining their toxicity.

Nanovaccine: an emerging strategy

INTRODUCTION

Vaccination is so far the most effective way of eradicating infections. Rapidly emerging drug resistance against infectious diseases and chemotherapy-related toxicities in cancer warrant immediate vaccine development to save mankind. Subunit vaccines alone, however, fail to elicit sufficiently strong and long-lasting protective immunity against deadly pathogens. Nanoparticle (NP)-based delivery vehicles like microemulsions, liposomes, virosomes, nanogels, micelles and dendrimers offer promising strategies to overcome limitations of traditional vaccine adjuvants. Nanovaccines can improve targeted delivery, antigen presentation, stimulation of body's innate immunity, strong T cell response combined with safety to combat infectious diseases and cancers. Further, nanovaccines can be highly beneficial to generate effective immutherapeutic formulations against cancer.

AREAS COVERED

This review summarizes the emerging nanoparticle strategies highlighting their success and challenges in preclinical and clinical trials in infectious diseases and cancer. It provides a concise overview of current nanoparticle-based vaccines, their adjuvant potential and their cellular delivery mechanisms.

EXPERT OPINION

The nanovaccines (50-250 nm in size) are most efficient in terms of tissue targeting, prolonged circulation and preferential uptake by the professional APCs chiefly due to their small size. More rational designing, improved antigen loading, extensive functionalization and targeted delivery are some of the future goals of ideal nanovaccines.

Toll-Like Receptors in Adaptive Immunity

The immune (innate and adaptive) system has evolved to protect the host from any danger present in the surrounding outer environment (microbes and associated MAMPs or PAMPs, xenobiotics, and allergens) and dangers originated within the host called danger or damage-associated molecular patterns (DAMPs) and recognizing and clearing the cells dying due to apoptosis. It also helps to lower the tissue damage during trauma and initiates the healing process. The pattern recognition receptors (PRRs) play a crucial role in recognizing different PAMPs or MAMPs and DAMPs to initiate the pro-inflammatory immune response to clear them. Toll-like receptors (TLRs) are first recognized PRRs and their discovery proved milestone in the field of immunology as it filled the gap between the first recognition of the pathogen by the immune system and the initiation of the appropriate immune response required to clear the infection by innate immune cells (macrophages, neutrophils, dendritic cells or DCs, and mast cells). However, in addition to their expression by innate immune cells and controlling their function, TLRs are also expressed by adaptive immune cells. We have identified 10 TLRs (TLR1-TLR10) in humans and 12 TLRs (TLR1-TLR13) in laboratory mice till date as TLR10 in mice is present only as a defective pseudogene. The present chapter starts with the introduction of innate immunity, timing of TLR evolution, and the evolution of adaptive immune system and its receptors (T cell receptors or TCRs and B cell receptors or BCRs). The next section describes the role of TLRs in the innate immune function and signaling involved in the generation of inflammation. The subsequent sections describe the expression and function of different TLRs in murine and human adaptive immune cells (B cells and different types of T cells, including CD4⁺T cells, CD8⁺T cells, CD4⁺CD25⁺T_regs, and CD8⁺CD25⁺T_regs, etc.). The modulation of TLRs expressed on T and B cells has a great potential to develop different vaccine candidates, adjuvants, immunotherapies to target various microbial infections, including current COVID-19 pandemic, cancers, and autoimmune and autoinflammatory diseases.

Mechanism of a COVID-19 nanoparticle vaccine candidate that elicits a broadly neutralizing antibody response to SARS-CoV-2 variants

Vaccines that induce potent neutralizing antibody (NAb) responses against emerging variants of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) are essential for combating the coronavirus disease 2019 (COVID-19) pandemic. We demonstrated that mouse plasma induced by self-assembling protein nanoparticles (SApNPs) that present 20 rationally designed S2GΔHR2 spikes of the ancestral Wuhan-Hu-1 strain can neutralize the B.1.1.7, B.1.351, P.1, and B.1.617 variants with the same potency. The adjuvant effect on vaccine-induced immunity was investigated by testing 16 formulations for the multilayered I3-01v9 SApNP. Using single-cell sorting, monoclonal antibodies (mAbs) with diverse neutralization breadth and potency were isolated from mice immunized with the receptor binding domain (RBD), S2GΔHR2 spike, and SApNP vaccines. The mechanism of vaccine-induced immunity was examined in mice. Compared with the soluble spike, the I3-01v9 SApNP showed 6-fold longer retention, 4-fold greater presentation on follicular dendritic cell dendrites, and 5-fold stronger germinal center reactions in lymph node follicles.

COVID-19 vaccine platforms: Delivering on a promise?

The emergence of the novel SARS-CoV-2 and COVID-19 has brought into sharp focus the need for a vaccine to prevent this disease. Vaccines have saved millions of lives since their introduction to the public over 200 years ago. The potential for vaccination reached new heights in the mid-20th century with the development of technologies that expanded the ability to create novel vaccines. Since then, there has been continued technological advancement in vaccine development. The resulting platforms provide the promise for solutions for many infectious diseases, including those that have been with us for decades as well as those just now emerging. Each vaccine platform represents a different technology with a unique set of advantages and challenges, especially when considering manufacturing. Therefore, it is essential to understand each platform as a separate product and process with its specific quality considerations. This review outlines the relevant platforms for developing a vaccine for SARS-CoV-2 and discusses the advantages and disadvantages of each.

Bio-mimic particles for the enhanced vaccinations: Lessons learnt from the natural traits and pathogenic invasion

In the combat against pathogens, the immune systems were evolved with the immune recognitions against the various danger signals, which responded vigorously upon the pathogen invasions and elicited potent antibodies or T cell engagement against the re-infections. Envisage with the prevailing pandemics and increasing demands for cancer vaccines, bio-mimic particles were developed to imitate the natural traits of the pathogens, which conferred the optimal strategies to stimulate the immune engagement and let to the increased vaccine efficacy. Here, the recent development in bio-mimic particles, as well as the natural cues from the pathogens were discussed. As such, the designing principles that adapted from the physiochemical properties of the pathogens were unfolded as the surface characteristics (hydrophobic, nano-pattern, antigen display, charge), properties (size, shape, softness) and the delivered components (peptide, protein, nuclear acids, toll-like receptor (TLR) agonist, antibody). Additionally, the strategies for the efficient delivery, regarding the biodistribution, internalization and presentation of the antigens were also illustrated. Through reviewing the state-of-art in biomimetic particles, the lesson learnt from the natural traits and pathogenic invasion may shed light on the rational design for the enhanced vaccinations.

A Double-blind, Randomized Phase 2 Controlled Trial of Intradermal Hepatitis B Vaccination With a Topical Toll-like Receptor 7 Agonist Imiquimod, in Patients on Dialysis

BACKGROUND

Patients on dialysis are hyporesponsive to the hepatitis B virus vaccines (HBVv). We examined intradermal (ID) HBVv Sci-B-Vac, with topical Toll-like receptor 7 (TLR7) agonist imiquimod pretreatment in dialysis patients.

METHODS

We enrolled and prospectively followed adult patients on dialysis between January 2016 and September 2018. Eligible patients were randomly allocated (1:1:1) into 1 treatment group, topical imiquimod cream followed by ID HBVv (IMQ + ID); and 2 control groups: topical aqueous cream (placebo) followed by ID HBVv (AQ + ID) or topical aqueous cream followed by intramuscular HBVv (AQ + IM). The primary endpoint was the seroprotection rate (hepatitis B surface antibody ≥10 mIU/mL) at 52 weeks.

RESULTS

Ninety-four patients were enrolled, among which 57.4% were previous nonresponders. Seroprotection rate was significantly better at week 52 for the IMQ + ID group with 96.9% compared to 74.2% and 48.4% for AQ + ID and AQ + IM groups, respectively (P < .0001). The geometric mean concentration was significantly higher at week 52 for the IMQ + ID group: 1135 (95% confidence interval [CI], 579.4-2218.2) mIU/mL, compared to 86.9 (95% CI, 18.5-409.3) mIU/mL and 7.2 (2.0-26.5) mIU/mL for the AQ + ID and AQ + IM groups, respectively (P < .0001). IMQ + ID vaccination (odds ratio, 3.70 [95% CI, 1.16-11.81]; P = .027) was the only factor independently associated with higher 52-week seroprotection rate. Adverse reaction was infrequent.

CONCLUSIONS

Pretreatment with topical imiquimod before ID HBVv Sci-B-Vac was safe with favorable seroprotection in dialysis patients.

CLINICAL TRIALS REGISTRATION

NCT02621112.

Evolution of Toll-like receptor 7/8 agonist therapeutics and their delivery approaches: From antiviral formulations to vaccine adjuvants

Imidazoquinoline derivatives (IMDs) and related compounds function as synthetic agonists of Toll-like receptors 7 and 8 (TLR7/8) and one is FDA approved for topical antiviral and skin cancer treatments. Nevertheless, these innate immune system-activating drugs have potentially much broader therapeutic utility; they have been pursued as antitumor immunomodulatory agents and more recently as candidate vaccine adjuvants for cancer and infectious disease. The broad expression profiles of TLR7/8, poor pharmacokinetic properties of IMDs, and toxicities associated with systemic administration, however, are formidable barriers to successful clinical translation. Herein, we review IMD formulations that have advanced to the clinic and discuss issues related to biodistribution and toxicity that have hampered the further development of these compounds. Recent strategies aimed at enhancing safety and efficacy, particularly through the use of bioconjugates and nanoparticle formulations that alter pharmacokinetics, biodistribution, and cellular targeting, are described. Finally, key aspects of the biology of TLR7 signaling, such as TLR7 tolerance, that may need to be considered in the development of new IMD therapeutics are discussed.

A yeast expressed RBD-based SARS-CoV-2 vaccine formulated with 3M-052-alum adjuvant promotes protective efficacy in non-human primates

Ongoing severe acute respiratory syndrome coronavirus–2 (SARS-CoV-2) vaccine development is focused on identifying stable, cost-effective, and accessible candidates for global use, specifically in low- and middle-income countries. Here, we report the efficacy of a rapidly scalable, novel yeast-expressed SARS-CoV-2–specific receptor binding domain (RBD)–based vaccine in rhesus macaques. We formulated the RBD immunogen in alum, a licensed and an emerging alum-adsorbed TLR-7/8-targeted, 3M-052-alum adjuvant. The RBD + 3M-052-alum-adjuvanted vaccine promoted better RBD binding and effector antibodies, higher CoV-2 neutralizing antibodies, improved T_H1-biased CD4⁺ T cell reactions, and increased CD8⁺ T cell responses when compared with the alum-alone adjuvanted vaccine. RBD + 3M-052-alum induced a significant reduction of SARS-CoV-2 virus in the respiratory tract upon challenge, accompanied by reduced lung inflammation when compared with unvaccinated controls. Anti-RBD antibody responses in vaccinated animals inversely correlated with viral load in nasal secretions and bronchoalveolar lavage (BAL). RBD + 3M-052-alum blocked a post-SARS-CoV-2 challenge increase in CD14⁺CD16⁺⁺ intermediate blood monocytes, and fractalkine, MCP-1 (monocyte chemotactic protein–1), and TRAIL (tumor necrosis factor–related apoptosis-inducing ligand) in the plasma. Decreased plasma analytes and intermediate monocyte frequencies correlated with reduced nasal and BAL viral loads. Last, RBD-specific plasma cells accumulated in the draining lymph nodes and not in the bone marrow, contrary to previous findings. Together, these data show that a yeast-expressed, RBD-based vaccine + 3M-052-alum provides robust immune responses and protection against SARS-CoV-2, making it a strong and scalable vaccine candidate.

Expression of Foxp3 by T follicular helper cells in end-stage germinal centers

Germinal centers (GCs) are the site of immunoglobulin somatic hypermutation and affinity maturation, processes essential to an effective antibody response. The formation of GCs has been studied in detail, but less is known about what leads to their regression and eventual termination, factors that ultimately limit the extent to which antibodies mature within a single reaction. We show that contraction of immunization-induced GCs is immediately preceded by an acute surge in GC-resident Foxp3⁺ T cells, attributed at least partly to up-regulation of the transcription factor Foxp3 by T follicular helper (T_FH) cells. Ectopic expression of Foxp3 in T_FH cells is sufficient to decrease GC size, implicating the natural up-regulation of Foxp3 by T_FH cells as a potential regulator of GC lifetimes.

Germinal Centre Shutdown

Germinal Centres (GCs) are transient structures in secondary lymphoid organs, where affinity maturation of B cells takes place following an infection. While GCs are responsible for protective antibody responses, dysregulated GC reactions are associated with autoimmune disease and B cell lymphoma. Typically, ‘normal’ GCs persist for a limited period of time and eventually undergo shutdown. In this review, we focus on an important but unanswered question – what causes the natural termination of the GC reaction? In murine experiments, lack of antigen, absence or constitutive T cell help leads to premature termination of the GC reaction. Consequently, our present understanding is limited to the idea that GCs are terminated due to a decrease in antigen access or changes in the nature of T cell help. However, there is no direct evidence on which biological signals are primarily responsible for natural termination of GCs and a mechanistic understanding is clearly lacking. We discuss the present understanding of the GC shutdown, from factors impacting GC dynamics to changes in cellular interactions/dynamics during the GC lifetime. We also address potential missing links and remaining questions in GC biology, to facilitate further studies to promote a better understanding of GC shutdown in infection and immune dysregulation.

Emerging nanomaterials for cancer immunotherapy

Immunotherapy is a unique approach to treat cancer that targets tumours besides triggering the immune cells. It attempts to harness the supremacy and specificity of immune cells for the regression of malignancy. The key strategy of immunotherapy is that it boosts the natural defence and manipulates the immune system at both cellular and molecular levels. Long-lasting anti-tumour response, reduced metastasis, and recurrence can be achieved with immunotherapy than conventional treatments. For example, targeting cytotoxic T-lymphocyte antigen-4 (CTLA4) by monoclonal antibody is reported as an effective strategy against cancer progression in vivo and chimeric antigen receptor (CAR) modified T-cells are known to express a stronger anti-tumour activity. CTLA4 and CAR are, therefore, beneficial in cancer immunotherapy; however, in clinical settings, both are expensive and cause adverse side effects. Nanomaterials have augmented advantages in cancer immunotherapy, besides their utility in effective delivery and diagnostics. In particular, materials based on lipids, polymers, and metals have been sought-after for delivery technologies. Moreover, the surface of nanomaterials can be engineered using ligands, antigens, and antibodies to target immune cells. In this sense, checkpoint inhibitors, cytokines, agonistic antibodies, surface receptors, and engineered T-cells are promising to regulate the immune system against tumours. Therefore, emerging nanomaterials that can be used for the treatment of cancer is the prime focus of this review. The correlation of mode of administration and biodistribution of various nanomaterials is reviewed here. Besides, the acute and chronic side effects and outcome of clinical trials in the context of cancer immunotherapy are discussed.

Revolutionizing polymer-based nanoparticle-linked vaccines for targeting respiratory viruses: A perspective

Viral respiratory tract infections have significantly impacted global health as well as socio-economic growth. Respiratory viruses such as the influenza virus, respiratory syncytial virus (RSV), and the recent SARS-CoV-2 infection (COVID-19) typically infect the upper respiratory tract by entry through the respiratory mucosa before reaching the lower respiratory tract, resulting in respiratory disease. Generally, vaccination is the primary method in preventing virus pathogenicity and it has been shown to remarkably reduce the burden of various infectious diseases. Nevertheless, the efficacy of conventional vaccines may be hindered by certain limitations, prompting the need to develop novel vaccine delivery vehicles to immunize against various strains of respiratory viruses and to mitigate the risk of a pandemic. In this review, we provide an insight into how polymer-based nanoparticles can be integrated with the development of vaccines to effectively enhance immune responses for combating viral respiratory tract infections.

A single dose of self-transcribing and replicating RNA-based SARS-CoV-2 vaccine produces protective adaptive immunity in mice

A self-transcribing and replicating RNA (STARR)-based vaccine (LUNAR-COV19) has been developed to prevent SARS-CoV-2 infection. The vaccine encodes an alphavirus-based replicon and the SARS-CoV-2 full-length spike glycoprotein. Translation of the replicon produces a replicase complex that amplifies and prolongs SARS-CoV-2 spike glycoprotein expression. A single prime vaccination in mice led to robust antibody responses, with neutralizing antibody titers increasing up to day 60. Activation of cell-mediated immunity produced a strong viral antigen-specific CD8+ T lymphocyte response. Assaying for intracellular cytokine staining for interferon (IFN)γ and interleukin-4 (IL-4)-positive CD4+ T helper (Th) lymphocytes as well as anti-spike glycoprotein immunoglobulin G (IgG)2a/IgG1 ratios supported a strong Th1-dominant immune response. Finally, single LUNAR-COV19 vaccination at both 2 μg and 10 μg doses completely protected human ACE2 transgenic mice from both mortality and even measurable infection following wild-type SARS-CoV-2 challenge. Our findings collectively suggest the potential of LUNAR-COV19 as a single-dose vaccine.

Development of Toll-like Receptor Agonist-Loaded Nanoparticles as Precision Immunotherapy for Reprogramming Tumor-Associated Macrophages

Most cancers contain abundant tumor-associated macrophages (TAMs). TAMs usually display a tumor-supportive M2-like phenotype; they promote tumor growth and influence lymphocyte infiltration, leading to immunosuppression. These properties have made TAMs an attractive cancer immunotherapy target. One promising immunotherapeutic strategy involves switching the tumor-promoting immune suppressive microenvironment by reprogramming TAMs. However, clinical trials of M2-like macrophage reprogramming have yielded unsatisfactory results due to their low efficacy and nonselective effects. In this article, we describe the development of M2-like macrophage-targeting nanoparticles (PNP@R@M-T) that efficiently and selectively deliver drugs to 58% of M2-like macrophages, over 39% of M1-like macrophages, and 32% of dendritic cells within 24 h in vivo. Compared with the control groups, administration of PNP@R@M-T dramatically reprogrammed the M2-like macrophages (51%), reduced tumor size (82%), and prolonged survival. Our findings indicate that PNP@R@M-T nanoparticles provide an effective and selective reprogramming strategy for macrophage-mediated cancer immunotherapy.

Nano and Microparticles as Potential Oral Vaccine Carriers and Adjuvants Against Infectious Diseases

Mucosal surfaces are the first site of infection for most infectious diseases and oral vaccination can provide protection as the first line of defense. Unlike systemic administration, oral immunization can stimulate cellular and humoral immune responses at both systemic and mucosal levels to induce broad-spectrum and long-lasting immunity. Therefore, to design a successful vaccine, it is essential to stimulate the mucosal as well as systemic immune responses. Successful oral vaccines need to overcome the harsh gastrointestinal environment such as the extremely low pH, proteolytic enzymes, bile salts as well as low permeability and the low immunogenicity of vaccines. In recent years, several delivery systems and adjuvants have been developed for improving oral vaccine delivery and immunogenicity. Formulation of vaccines with nanoparticles and microparticles have been shown to improve antigen stability, availability and adjuvanticity as well as immunostimulatory capacity, target delivery and specific release. This review discusses how nanoparticles (NPs) and microparticles (MPs) as oral carriers with adjuvant characteristics can be beneficial in oral vaccine development.

Combined PET and whole-tissue imaging of lymphatic-targeting vaccines in non-human primates

Antigen accumulation in lymph nodes (LNs) is critical for vaccine efficacy, but understanding of vaccine biodistribution in humans or large animals remains limited. Using the rhesus macaque model, we employed a combination of positron emission tomography (PET) and fluorescence imaging to characterize the whole-animal to tissue-level biodistribution of a subunit vaccine comprised of an HIV envelope trimer protein nanoparticle (trimer-NP) and lipid-conjugated CpG adjuvant (amph-CpG). Following immunization in the thigh, PET imaging revealed vaccine uptake primarily in inguinal and iliac LNs, reaching distances up to 17 cm away from the injection site. Within LNs, trimer-NPs exhibited striking accumulation on the periphery of follicular dendritic cell (FDC) networks in B cell follicles. Comparative imaging of soluble Env trimers (not presented on nanoparticles) in naïve or previously-immunized animals revealed diffuse deposition of trimer antigens in LNs following primary immunization, but concentration on FDCs in pre-immunized animals with high levels of trimer-specific IgG. These data demonstrate the capacity of nanoparticle or "albumin hitchhiking" technologies to concentrate vaccines in genitourinary tract-draining LNs, which may be valuable for promoting mucosal immunity.

Prolonged Codelivery of Hemagglutinin and a TLR7/8 Agonist in a Supramolecular Polymer-Nanoparticle Hydrogel Enhances Potency and Breadth of Influenza Vaccination

The sustained release of vaccine cargo has been shown to improve humoral immune responses to challenging pathogens such as influenza. Extended codelivery of antigen and adjuvant prolongs germinal center reactions, thus improving antibody affinity maturation and the ability to neutralize the target pathogen. Here, we develop an injectable, physically cross-linked polymer-nanoparticle (PNP) hydrogel system to prolong the local codelivery of hemagglutinin and a toll-like receptor 7/8 agonist (TLR7/8a) adjuvant. By tethering the TLR7/8a to a NP motif within the hydrogels (TLR7/8a-NP), the dynamic mesh of the PNP hydrogels enables codiffusion of the adjuvant and protein antigen (hemagglutinin), therefore enabling sustained codelivery of these two physicochemically distinct molecules. We show that subcutaneous delivery of PNP hydrogels carrying hemagglutinin and TLR7/8a-NP in mice improves the magnitude and duration of antibody titers in response to a single injection vaccination compared to clinically used adjuvants. Furthermore, the PNP gel-based slow delivery of influenza vaccines led to increased breadth of antibody responses against future influenza variants, including a future pandemic variant, compared to clinical adjuvants. In summary, this work introduces a simple and effective vaccine delivery platform that increases the potency and durability of influenza subunit vaccines.

Modulation of injectable hydrogel properties for slow co-delivery of influenza subunit vaccine components enhance the potency of humoral immunity

Vaccines are critical for combating infectious diseases across the globe. Influenza, for example, kills roughly 500,000 people annually worldwide, despite annual vaccination campaigns. Efficacious vaccines must elicit a robust and durable antibody response, and poor efficacy often arises from inappropriate temporal control over antigen and adjuvant presentation to the immune system. In this work, we sought to exploit the immune system's natural response to extended pathogen exposure during infection by designing an easily administered slow-delivery influenza vaccine platform. We utilized an injectable and self-healing polymer-nanoparticle (PNP) hydrogel platform to prolong the co-delivery of vaccine components to the immune system. We demonstrated that these hydrogels exhibit unique dynamic physical characteristics whereby physicochemically distinct influenza hemagglutinin antigen and a toll-like receptor 7/8 agonist adjuvant could be co-delivered over prolonged timeframes that were tunable through simple alteration of the gel formulation. We show a relationship between hydrogel physical properties and the resulting immune response to immunization. When administered in mice, hydrogel-based vaccines demonstrated enhancements in the magnitude and duration of humoral immune responses compared to alum, a widely used clinical adjuvant system. We found stiffer hydrogel formulations exhibited slower release and resulted in the greatest improvements to the antibody response while also enabling significant adjuvant dose sparing. In summary, this work introduces a simple and effective vaccine delivery platform that increases the potency and durability of influenza subunit vaccines.

Hemagglutinin Functionalized Liposomal Vaccines Enhance Germinal Center and Follicular Helper T Cell Immunity

Despite remarkable successes of immunization in protecting public health, safe and effective vaccines against a number of life-threatening pathogens such as HIV, ebola, influenza, and SARS-CoV-2 remain urgently needed. Subunit vaccines can avoid potential toxicity associated with traditional whole virion-inactivated and live-attenuated vaccines; however, the immunogenicity of subunit vaccines is often poor. A facile method is here reported to produce lipid nanoparticle subunit vaccines that exhibit high immunogenicity and elicit protection against influenza virus. Influenza hemagglutinin (HA) immunogens are functionalized on the surface of liposomes via stable metal chelation chemistry, using a scalable advanced microfluidic mixing technology (NanoAssemblr). Immunization of mice with HA-liposomes elicits increased serum antibody titers and superior protection against highly pathogenic virus challenge compared with free HA protein. HA-liposomal vaccines display enhanced antigen deposition into germinal centers within the draining lymph nodes, driving increased HA-specific B cell, and follicular helper T cell responses. This work provides mechanistic insights into highly protective HA-liposome vaccines and informs the rational design and rapid production of next generation nanoparticle subunit vaccines.

Aliphatic Polyester-Based Materials for Enhanced Cancer Immunotherapy

Poly(lactic acid) (PLA) and its copolymer, poly(lactic-co-glycolic acid) (PLGA), based aliphatic polyesters have been extensively used for biomedical applications, such as drug delivery system and tissue engineering, thanks to their biodegradability, benign toxicity, renewability, and adjustable mechanical properties. A rapidly growing field of cancer research, the development of therapeutic cancer vaccines or treatment modalities is aimed to deliver immunomodulatory signals that control the quality of immune responses against tumors. Herein, the progress and applications of PLA and PLGA are reviewed in delivering immunotherapeutics to treat cancers.

Sterilizing Immunity against SARS-CoV-2 Infection in Mice by a Single-Shot and Lipid Amphiphile Imidazoquinoline TLR7/8 Agonist-Adjuvanted Recombinant Spike Protein Vaccine*

The search for vaccines that protect from severe morbidity and mortality because of infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the virus that causes coronavirus disease 2019 (COVID-19) is a race against the clock and the virus. Here we describe an amphiphilic imidazoquinoline (IMDQ-PEG-CHOL) TLR7/8 adjuvant, consisting of an imidazoquinoline conjugated to the chain end of a cholesterol-poly(ethylene glycol) macromolecular amphiphile. It is water-soluble and exhibits massive translocation to lymph nodes upon local administration through binding to albumin, affording localized innate immune activation and reduction in systemic inflammation. The adjuvanticity of IMDQ-PEG-CHOL was validated in a licensed vaccine setting (quadrivalent influenza vaccine) and an experimental trimeric recombinant SARS-CoV-2 spike protein vaccine, showing robust IgG2a and IgG1 antibody titers in mice that could neutralize viral infection in vitro and in vivo in a mouse model.

Randomized peptide assemblies for enhancing immune responses to nanomaterials

Biomaterials capable of inducing immune responses with minimal associated inflammation are of interest in applications ranging from tissue repair to vaccines. Here we report the design of self-assembling randomized polypeptide nanomaterials inspired by glatiramoids, an immunomodulatory class of linear random copolymers. We hypothesized that peptide self-assemblies bearing similar randomized polypeptides would similarly raise responses skewed toward Type 2 immunity and T_H2 T-cell responses, additionally strengthening responses to co-assembled peptide epitopes in the absence of adjuvant. We developed a method for synthesizing self-assembling peptides terminated with libraries of randomized polypeptides (termed KEYA) with good batch-to-batch reproducibility. These peptides formed regular nanofibers and raised strong antibody responses without adjuvants. KEYA modifications dramatically improved uptake of peptide nanofibers in vitro by antigen presenting cells, and served as strong B-cell and T-cell epitopes in vivo, enhancing immune responses against epitopes relevant to influenza and chronic inflammation while inducing a KEYA-specific Type 2/T_H2/IL-4 phenotype. KEYA modifications also increased IL-4 production by T cells, extended the residence time of nanofibers, induced no measurable swelling in footpad injections, and decreased overall T cell expansion compared to unmodified nanofibers, further suggesting a T_H2 T-cell response with minimal inflammation. Collectively, this work introduces a biomaterial capable of raising strong Type 2/T_H2/IL-4 immune responses, with potential applications ranging from vaccination to tissue repair.

Strategies for Immunomonitoring after Vaccination and during Infection

Immunomonitoring is the study of an individual's immune responses over the course of vaccination or infection. In the infectious context, exploring the innate and adaptive immune responses will help to investigate their contribution to viral control or toxicity. After vaccination, immunomonitoring of the correlate(s) and surrogate(s) of protection is a major asset for measuring vaccine immune efficacy. Conventional immunomonitoring methods include antibody-based technologies that are easy to use. However, promising sensitive high-throughput technologies allowed the emergence of holistic approaches. This raises the question of data integration methods and tools. These approaches allow us to increase our knowledge on immune mechanisms as well as the identification of key effectors of the immune response. However, the depiction of relevant findings requires a well-rounded consideration beforehand about the hypotheses, conception, organization and objectives of the immunomonitoring. Therefore, well-standardized and comprehensive studies fuel insight to design more efficient, rationale-based vaccines and therapeutics to fight against infectious diseases. Hence, we will illustrate this review with examples of the immunomonitoring approaches used during vaccination and the COVID-19 pandemic.

A versatile photothermal vaccine based on acid-responsive glyco-nanoplatform for synergistic therapy of cancer

The race is on for therapeutic agents that stop cancer. An effective vaccine offers a safe and promising approach for cancer immunotherapy. However, substantial barriers to immunotherapy in cancer vaccines include the low immunogenicity of cancer antigens and the immunosuppression commonly present in solid tumors, resulting in significant challenges for developing a clinically effective cancer vaccine. Here, the state of the art of synergistic therapy, which includes the photothermal effect combined with immunotherapy, was investigated to target tumors. For the first time, indocyanine green (ICG, referred to as I), imiquimod (R837, referred to as R) and a foreign cytotoxic T lymphocyte antigen peptide (CTL-Ap, referred to as Ap) with the sequence of SIINFEKL from ovalbumin (OVA) were encapsulated by acetalated dextran (AcDEX) to form nanoparticles (NPs) averaging 92 nm in diameter as an immunogen. Administration of the resulting multifunctional vaccine I-R-Ap-AcDEX NPs enhanced antitumor cytotoxic T lymphocyte (CTL) immunotherapy. On the one hand, subcutaneous immunization of the NPs allows foreign Ap to enter the major histocompatibility complex class I (MHC-I) cross-presentation pathway of antigen-presenting cells, thereby presenting Ap and eliciting high levels of Ap-specific CTLs. On the other hand, intratumor/intravenous injections of the NPs allow foreign Ap to enter tumor cells and present Ap through the MHC-I cross-presentation pathway. Ap-specific CTLs can kill Ap-presented tumor cells. Furthermore, the NPs generated near-infrared laser triggered the photothermal killing of tumor cells. To our knowledge, this is the first report of AcDEX NPs in antitumor photothermal therapy. Strikingly, systemic administration of the I-R-Ap-AcDEX NPs combined with near-infrared laser irradiation allowed for complete protection to mice from the tumors when applied to two non-OVA tumor models. This quite impressive result displays the great promise of synergistic therapy by the vaccine I-R-Ap-AcDEX NPs, an approach that harnesses the photothermal effect to boost antitumor immunotherapy.

Emerging concepts in the science of vaccine adjuvants

Adjuvants are vaccine components that enhance the magnitude, breadth and durability of the immune response. Following its introduction in the 1920s, alum remained the only adjuvant licensed for human use for the next 70 years. Since the 1990s, a further five adjuvants have been included in licensed vaccines, but the molecular mechanisms by which these adjuvants work remain only partially understood. However, a revolution in our understanding of the activation of the innate immune system through pattern recognition receptors (PRRs) is improving the mechanistic understanding of adjuvants, and recent conceptual advances highlight the notion that tissue damage, different forms of cell death, and metabolic and nutrient sensors can all modulate the innate immune system to activate adaptive immunity. Furthermore, recent advances in the use of systems biology to probe the molecular networks driving immune response to vaccines ('systems vaccinology') are revealing mechanistic insights and providing a new paradigm for the vaccine discovery and development process. Here, we review the 'known knowns' and 'known unknowns' of adjuvants, discuss these emerging concepts and highlight how our expanding knowledge about innate immunity and systems vaccinology are revitalizing the science and development of novel adjuvants for use in vaccines against COVID-19 and future pandemics.

Coronavirus Disease 2019 Vaccine Development: An Overview

To this day, the coronavirus disease 2019 (COVID-19) pandemic has not shown signs of abating. Moreover, the virus responsible for the pandemic, severe acute respiratory syndrome coronavirus 2, has evolved into three different variants. This phenomenon highlights an even greater need to develop drugs and vaccines to control the rate of infection and spread of the disease. As of July 7, 2020, at least 160 vaccine candidates, 21 of which have entered the clinical trial phase, have been developed. This article describes the latest advances in development, reliable platforms, strategies used, and challenges that remain in developing COVID-19 vaccines.

Next-Generation Vaccines: Nanoparticle-Mediated DNA and mRNA Delivery

Nucleic acid vaccines are a method of immunization aiming to elicit immune responses akin to live attenuated vaccines. In this method, DNA or messenger RNA (mRNA) sequences are delivered to the body to generate proteins, which mimic disease antigens to stimulate the immune response. Advantages of nucleic acid vaccines include stimulation of both cell-mediated and humoral immunity, ease of design, rapid adaptability to changing pathogen strains, and customizable multiantigen vaccines. To combat the SARS-CoV-2 pandemic, and many other diseases, nucleic acid vaccines appear to be a promising method. However, aid is needed in delivering the fragile DNA/mRNA payload. Many delivery strategies have been developed to elicit effective immune stimulation, yet no nucleic acid vaccine has been FDA-approved for human use. Nanoparticles (NPs) are one of the top candidates to mediate successful DNA/mRNA vaccine delivery due to their unique properties, including unlimited possibilities for formulations, protective capacity, simultaneous loading, and delivery potential of multiple DNA/mRNA vaccines. This review will summarize the many varieties of novel NP formulations for DNA and mRNA vaccine delivery as well as give the reader a brief synopsis of NP vaccine clinical trials. Finally, the future perspectives and challenges for NP-mediated nucleic acid vaccines will be explored.

Advances in nanomaterial vaccine strategies to address infectious diseases impacting global health

Despite the overwhelming success of vaccines in preventing infectious diseases, there remain numerous globally devastating diseases without fully protective vaccines, particularly human immunodeficiency virus (HIV), malaria and tuberculosis. Nanotechnology approaches are being developed both to design new vaccines against these diseases as well as to facilitate their global implementation. The reasons why a given pathogen may present difficulties for vaccine design are unique and tied to the co-evolutionary history of the pathogen and humans, but there are common challenges that nanotechnology is beginning to help address. In each case, a successful vaccine will need to raise immune responses that differ from the immune responses raised by normal infection. Nanomaterials, with their defined compositions, commonly modular construction, and length scales allowing the engagement of key immune pathways, collectively facilitate the iterative design process necessary to identify such protective immune responses and achieve them reliably. Nanomaterials also provide strategies for engineering the trafficking and delivery of vaccine components to key immune cells and lymphoid tissues, and they can be highly multivalent, improving their engagement with the immune system. This Review will discuss these aspects along with recent nanomaterial advances towards vaccines against infectious disease, with a particular emphasis on HIV/AIDS, malaria and tuberculosis.

A review of combination adjuvants for malaria vaccines: a promising approach for vaccine development

It is obvious that there is a critical need for an efficient malaria vaccine to accelerate malaria eradication. Currently, recombinant subunit vaccination against malaria using proteins and peptides is gaining attention. However, one of the major drawbacks of this approach is the lack of an efficient and durable immune response. Therefore, subunit vaccines require adjuvants to make the vaccine sufficiently immunogenic. Considering the history of the RTS,S vaccine, it seems likely that no single adjuvant is capable of eliciting all the protective immune responses required in many malarial subunit vaccines and the use of combination adjuvants will be increasingly important as the science of malaria vaccines advances. In light of this, it appears that identifying the most effective mixture of adjuvants with minimal adverse effects offers tremendous opportunities in improving the efficacy of vaccines against malaria. Owing to the importance of a multi-adjuvanted approach in subunit malaria vaccine development, this review paper outlines some of the best known combination adjuvants used in malaria subunit vaccines, focusing on their proposed mechanisms of action, their immunological properties, and their notable results. The aim of the present review is to consolidate these findings to aid the application of these combination adjuvants in experimental malaria vaccines.