Toll-like Receptor-4 (TLR4) Agonist-Based Intranasal Nanovaccine Delivery System for Inducing Systemic and Mucosal Immunity

The Yin and Yang of TLR4 in COVID-19

Various pattern recognition receptors (PRRs), including toll-like receptors (TLRs), play a crucial role in recognizing invading pathogens as well as damage-associated molecular patterns (DAMPs) released in response to infection. The resulting signaling cascades initiate appropriate immune responses to eliminate these pathogens. Current evidence suggests that SARS-CoV-2-driven activation of TLR4, whether through direct recognition of the spike glycoprotein (alone or in combination with endotoxin) or by sensing various TLR4-activating DAMPs or alarmins released during viral infection, acts as a critical mediator of antiviral immunity. However, TLR4 exerts a dual role in COVID-19, demonstrating both beneficial and deleterious effects. Dysregulated TLR4 signaling is implicated in the proinflammatory consequences linked to the immunopathogenesis of COVID-19. Additionally, TLR4 polymorphisms contribute to severity of the disease. Given its significant immunoregulatory impact on COVID-19 immunopathology and host immunity, TLR4 has emerged as a key target for developing inhibitors and immunotherapeutic strategies to mitigate the adverse effects associated with SARS-CoV-2 and related infections. Furthermore, TLR4 agonists are also being explored as adjuvants to enhance immune responses to SARS-CoV-2 vaccines.

Role of toll-like receptors in post-COVID-19 associated neurodegenerative disorders?

In the intricate realm of interactions between hosts and pathogens, Toll-like receptors (TLRs), which play a crucial role in the innate immune response, possess the ability to identify specific molecular signatures. This includes components originating from pathogens such as SARS-CoV-2, as well as the resulting damage-associated molecular patterns (DAMPs), the endogenous molecules released after cellular damage. A developing perspective suggests that TLRs play a central role in neuroinflammation, a fundamental factor in neurodegenerative conditions like Alzheimer's and Parkinson's disease (PD). This comprehensive review consolidates current research investigating the potential interplay between TLRs, their signaling mechanisms, and the processes of neurodegeneration following SARS-CoV-2 infection with an aim to elucidate the involvement of TLRs in the long-term neurological complications of COVID-19 and explore the potential of targeting TLRs as a means of implementing intervention strategies for the prevention or treatment of COVID-19-associated long-term brain outcomes.

Next-Generation SARS-CoV-2 Vaccine Formulations and Alternative Routes of Administration

The development of SARS-CoV-2 next-generation vaccines with the potential for increased effectiveness, durability, breadth, and ability to decrease transmission are of public health importance. We highlight alternative routes of administration of next-generation SARS-CoV-2 vaccines such as mucosal and intradermal administration.

In Silico-Guided Discovery of Polysaccharide Derivatives as Adjuvants in Nanoparticle Vaccines for Cancer Immunotherapy

Cancer vaccines utilizing nanoparticle (NP) structures that integrate antigens and adjuvants to enhance delivery and stimulate immune responses are emerging as a promising avenue in cancer immunotherapy. However, the development of cancer vaccines has been significantly hindered by the low immunogenicity of tumor antigens. To address this challenge, substantial efforts have been made in developing innovative adjuvants to elicit effective immune responses. In this study, we develop a NP cancer vaccine assisted by a polysaccharide derivative adjuvant, designed through a computational strategy, to evoke effective antigen-specific antitumor immunity. Using TLR4 as the putative receptor, we conducted a comprehensive evaluation of a prescreening library consisting of 34 inulin derivatives through docking and molecular dynamics simulation. Consequently, a new derivative, benzoylated inulin (InBz), is selected as the most promising TLR4 agonist. The adjuvant effect of InBz is evaluated by fabricating InBz NPs encapsulating the model antigen ovalbumin (OVA). In vitro, InBz-OVA NPs effectively activate the TLR4 signaling pathways and facilitate dendritic cell maturation, thereby enhancing the antigen delivery and presentation. In vivo, InBz-OVA NPs outperform a commercial aluminum-based adjuvant, elicit robust antibody titers, induce antigen-specific cytotoxic T lymphocytes, and achieve significant tumor suppression in murine models. Besides, the adjuvant effects of other representative derivatives, namely, acetylated and chloroacetylated inulin, with moderate and low potential from the library, are also chemically synthesized and experimentally evaluated and found to be in agreement with computational predictions, confirming the credibility of the strategy. This study provides an effective platform for the pursuit of efficient polysaccharide-based vaccine adjuvants.

Toll-like receptor 4 - a multifunctional virus recognition receptor

Since the initial description of Toll receptors in Drosophila and their mammalian counterparts Toll-like receptors (TLRs), numerous fundamental and applied studies have explored their crucial role as sensors of pathogen-associated molecular patterns (PAMPs). Among the ten human TLRs, TLR4 is particularly well known for its ability to detect lipopolysaccharides (LPS), a component of the Gram-negative bacterial cell wall. In addition to its archetypal functions, TLR4 is also a versatile virus sensor. This review provides a background on the discovery of TLR4 and how this knowledge laid a foundation for characterization of its diverse roles in antiviral responses, examined through genetic, biochemical, structural, and immunological approaches. These advances have led to a deeper understanding of the molecular functions that enable TLR4 to orchestrate multi-nodal control by professional antigen-presenting cells (APCs) to initiate appropriate and regulated antiviral immune responses.

The dual role of toll-like receptors in COVID-19: Balancing protective immunity and immunopathogenesis

Toll-like receptors (TLRs) of human are considered as the most critical immunological mediators of inflammatory pathogenesis of COVID-19. These immunoregulatory glycoproteins are located on the surface and/or intracellular compartment act as innate immune sensors. Upon binding with distinct SARS-CoV-2 ligand(s), TLRs signal activation of different transcription factors that induce expression of the proinflammatory mediators that collectively induce 'cytokine storm'. Similarly, TLR activation is also pivotal in conferring protection to infection and invasion as well as upregulating the tissue repair pathways. This dual role of the human TLRs in deciding the fate of SARS-CoV-2 has made these receptor proteins as the critical mediators of immunoprotective and immunopathogenic consequences associated with COVID-19. Herein, pathbreaking discoveries exploring the immunobiological importance of the TLRs in COVID-19 and developing TLR-directed therapeutic intervention have been reviewed by accessing the up-to-date literatures available in the public domain/databases. In accordance with our knowledge in association with the importance of TLRs' role against viruses and identification of viral particles, they have been recognized as suitable candidates with high potential as vaccine adjuvants. In this regard, the agonists of TLR4 and TLR9 have effective potential in vaccine technology while the others need further investigations. This comprehensive review suggests that basal level expression of TLRs can act as friends to keep our body safe from strangers but act as a foe via overexpression. Therefore, selective inhibition of the overexpressed TLRs appears to be a solution to counteract the cytokine storm while TLR-agonists as vaccine adjuvants could lessen the risk of infection in the naïve population.

Bacterial extracellular vesicles as intranasal postbiotics: Detailed characterization and interaction with airway cells

Escherichia coli A0 34/86 (EcO83) is a probiotic strain used in newborns to prevent nosocomial infections and diarrhoea. This bacterium stimulates both pro- and anti-inflammatory cytokine production and its intranasal administration reduces allergic airway inflammation in mice. Despite its benefits, there are concerns about the use of live probiotic bacteria due to potential systemic infections and gene transfer. Extracellular vesicles (EVs) derived from EcO83 (EcO83-EVs) might offer a safer alternative to live bacteria. This study characterizes EcO83-EVs and investigates their interaction with host cells, highlighting their potential as postbiotic therapeutics. EcO83-EVs were isolated, purified, and characterised following the Minimal Information of Studies of Extracellular Vesicles (MISEV) guidelines. Ex vivo studies conducted in human nasal epithelial cells showed that EcO83-EVs increased the expression of proteins linked to oxidative stress and inflammation, indicating an effective interaction between EVs and the host cells. Further in vivo studies in mice demonstrated that EcO83-EVs interact with nasal-associated lymphoid tissue, are internalised by airway macrophages, and stimulate neutrophil recruitment in the lung. Mechanistically, EcO83-EVs activate the NF-κΒ signalling pathway, resulting in the nitric oxide production. EcO83-EVs demonstrate significant potential as a postbiotic alternative to live bacteria, offering a safer option for therapeutic applications. Further research is required to explore their clinical use, particularly in mucosal vaccination and targeted immunotherapy strategies.

A Polysaccharide-Based Oral-Vaccine Delivery System and Adjuvant for the Influenza Virus Vaccine

Influenza virus enters the host body through the mucosal surface of the respiratory tract. An efficient immune response at the mucosal site can interfere with virus entry and prevent infection. However, formulating oral vaccines and eliciting an effective mucosal immune response including at respiratory mucosa presents numerous challenges including the potential degradation of antigens by acidic gastric fluids and the risk of antigen dilution and dispersion over a large surface area of the gut, resulting in minimal antigen uptake by the immune cells. Additionally, oral mucosal vaccines have to overcome immune tolerance in the gut. To address the above challenges, in the current study, we evaluated inulin acetate (InAc) nanoparticles (NPs) as a vaccine adjuvant and antigen delivery system for oral influenza vaccines. InAc was developed as the first polysaccharide polymer-based TLR4 agonist; when tailored as a nanoparticulate vaccine delivery system, it enhanced antigen delivery to dendritic cells and induced a strong cellular and humoral immune response. This study compared the efficacy of InAc-NPs as a delivery system for oral vaccines with Poly (lactic-co-glycolic acid) (PLGA) NPs, utilizing influenza A nucleoprotein (Inf-A) as an antigen. InAc-NPs effectively protected the encapsulated antigen in both simulated gastric (pH 1.1) and intestinal fluids (pH 6.8). Moreover, InAc-NPs facilitated enhanced antigen delivery to macrophages, compared to PLGA-NPs. Oral vaccination studies in Balb/c mice revealed that InAc-Inf-A NPs significantly boosted the levels of Influenza virus-specific IgG and IgA in serum, as well as total and virus-specific IgA in the intestines and lungs. Furthermore, mice vaccinated with InAc-Inf-A-NPs exhibited notably higher hemagglutination inhibition (HI) titers at mucosal sites compared to those receiving the antigen alone. Overall, our study underscores the efficacy of InAc-NPs in safeguarding vaccine antigens post-oral administration, enhancing antigen delivery to antigen-presenting cells, and eliciting higher virus-neutralizing antibodies at mucosal sites following vaccination.

Promising brain biodistribution of insulin via intranasal dry powder for nose-to-brain delivery

Nose-to-brain delivery (NTBD) offering potential benefits for treating Alzheimer's disease. In previous research, insulin dry powder (IDP) formulation for NTBD was developed, exhibiting favorable stability. This study aims to conduct in vitro and ex vivo assessment of release, permeation, mucoadhesion and histopathology, as well as an in vivo biodistribution study to produce IDP for NTBD and evaluate brain biodistribution. Spray-freeze-dried IDP formulations with varying weight ratios of trehalose-to-inulin were produced and analyzed. The release study was carried out in PBS with a pH of 5.8 stirred at 50 rpm and maintained at 37 °C ± 0.5 °C. Goat nasal mucosa was used for ex vivo permeation and mucoadhesion testing under similar conditions. An ex vivo histopathological examination and an in vivo study using enzyme-linked immunosorbent assay, were also performed. The IDP dissolution study demonstrated complete release of all IDPs within 120 min. The permeation study indicated that steady-state conditions were observed between 30 and 240 min. The mucoadhesion study unveiled that IDP F5 exhibited the fastest mucoadhesion time and the least force required within the fastest time of 43.60 ± 2.57 s. The histopathological study confirmed that none of the tested IDPs induced irritation in the nasal mucosa. Furthermore, the biodistribution study demonstrated the absence of detectable insulin in the plasma, while IDP F3 exhibited the highest deposited concentration of insulin within both the olfactory bulb and the whole brain. The extensive evaluation of the IDP formulations through in vitro, ex vivo, and in vivo studies implies their strength non-invasive NTBD. IDP F3, with a 1:1 wt ratio of trehalose to inulin, exhibited favorable brain biodistribution outcomes and was recommended for further investigation and development in the context of NTBD.

Intranasal delivery of a self-adjuvanted nanovaccine composed of the curli filaments and the highly conserved M2e epitope confers protection against influenza a virus in mice

Intranasal administration of vaccines is an attractive delivery route to fight viral respiratory infections. However, there are only a few intranasal vaccines used in human, emphasizing the critical need to identify novel safe mucosal adjuvants and antigen delivery systems to expand their usage. We recently revealed an immunostimulating nanoparticle based on a fragment (R4R5) of the Curli-specific gene A (CsgA) protein that confers protection against influenza A virus (IAV) when conjugated to three repeats of the highly conserved M2e epitope and administrated intramuscularly. Herein, the efficacy of this 3M2e-R4R5 nanovaccine was investigated upon administration by intranasal instillation. By triggering robust M2e-specific humoral and cellular responses, both systemic and locally in the respiratory tract, and by priming alveolar macrophages, the intranasal vaccine protected mice against a lethal IAV challenge without the use of additional adjuvant. Thus, CsgA-based nanostructures could serve as a safe and self-adjuvanted antigen delivery system for mucosal immunization.

Immune cell receptor-specific nanoparticles as a potent adjuvant for nasal split influenza vaccine delivery

Mucosal delivery systems have gained much attention as effective way for antigen delivery that induces both systemic and mucosal immunity. However, mucosal vaccination faces the challenges of mucus barrier and effective antigen uptake and presentation. In particular, split, subunit and recombinant protein vaccines that do not have an intact pathogen structure lack the efficiency to stimulate mucosal immunity. In this study, poly (lactic acid-co-glycolic acid-polyethylene glycol) (PLGA-PEG) block copolymers were modified by mannose to form a PLGA-PEG-Man conjugate (mannose modified PLGA-PEG), which were characterized. The novel nanoparticles (NPs) prepared with this material had a particle size of about 150 nm and a zeta potential of -15 mV, and possessed ideal mucus permeability, immune cell targeting, stability and low toxicity. Finally, PLGA-PEG-Man nanoparticles (PLGA-PEG-Man NPs) were successfully applied for intranasal delivery of split influenza vaccine in rat for the first time, which triggered strong systemic and mucosal immune responses. These studies suggest that PLGA-PEG-Man NPs could function as competitive potential nano-adjuvants to address the challenge of inefficient mucosal delivery of non-allopathogenic antigens.

Next Generation Mucosal Vaccine Strategy for Respiratory Pathogens

Inducing humoral and cytotoxic mucosal immunity at the sites of pathogen entry has the potential to prevent the infection from getting established. This is different from systemic vaccination, which protects against the development of systemic symptoms. The field of mucosal vaccination has seen fewer technological advances compared to nucleic acid and subunit vaccine advances for injectable vaccine platforms. The advent of the next-generation adenoviral vectors has given a boost to mucosal vaccine research. Basic research into the mechanisms regulating innate and adaptive mucosal immunity and the discovery of effective and safe mucosal vaccine adjuvants will continue to improve mucosal vaccine design. The results from clinical trials of inhaled COVID-19 vaccines demonstrate their ability to induce the proliferation of cytotoxic T cells and the production of secreted IgA and IgG antibodies locally, unlike intramuscular vaccinations. However, these mucosal vaccines induce systemic immune responses at par with systemic vaccinations. This review summarizes the function of the respiratory mucosa-associated lymphoid tissue and the advantages that the adenoviral vectors provide as inhaled vaccine platforms.

Role of toll-like receptors in the pathogenesis of COVID-19: Current and future perspectives

The coronavirus disease 2019 (COVID-19) pandemic underlines a persistent threat of respiratory tract infectious diseases and warrants preparedness for a rapid response. At present, COVID-19 has had a serious social impact and imposed a heavy global burden on public health. The exact pathogenesis of COVID-19 has not been fully elucidated. Since the outbreak of COVID-19, a renewed attention has been brought to Toll-like receptors (TLRs). Available data and new findings have demonstrated that the interaction of human TLRs and SARS-CoV-2 is a vital mediator of COVID-19 immunopathogenesis. TLRs such as TLR2, 4, 7 and 8 are potentially important in viral combat and activation of immunity in patients with COVID-19. Therapeutics targeting TLRs are currently considered promising options against the pandemic. A number of TLR-targeting immunotherapeutics are now being investigated in preclinical studies and different phases of clinical trials. In addition, innovative vaccines based on TLRs under development could be a promising approach for building a new generation of vaccines to solve the current challenges. In this review, we summarize recent progress in the role of TLRs in COVID-19, focusing the new candidate drugs targeting TLRs, the current technology and potential paths forward for employing TLR agonists as vaccine adjuvants.

From Co-Infections to Autoimmune Disease via Hyperactivated Innate Immunity: COVID-19 Autoimmune Coagulopathies, Autoimmune Myocarditis and Multisystem Inflammatory Syndrome in Children

Neutrophilia and the production of neutrophil extracellular traps (NETs) are two of many measures of increased inflammation in severe COVID-19 that also accompany its autoimmune complications, including coagulopathies, myocarditis and multisystem inflammatory syndrome in children (MIS-C). This paper integrates currently disparate measures of innate hyperactivation in severe COVID-19 and its autoimmune complications, and relates these to SARS-CoV-2 activation of innate immunity. Aggregated data include activation of Toll-like receptors (TLRs), nucleotide-binding oligomerization domain (NOD) receptors, NOD leucine-rich repeat and pyrin-domain-containing receptors (NLRPs), retinoic acid-inducible gene I (RIG-I) and melanoma-differentiation-associated gene 5 (MDA-5). SARS-CoV-2 mainly activates the virus-associated innate receptors TLR3, TLR7, TLR8, NLRP3, RIG-1 and MDA-5. Severe COVID-19, however, is characterized by additional activation of TLR1, TLR2, TLR4, TLR5, TLR6, NOD1 and NOD2, which are primarily responsive to bacterial antigens. The innate activation patterns in autoimmune coagulopathies, myocarditis and Kawasaki disease, or MIS-C, mimic those of severe COVID-19 rather than SARS-CoV-2 alone suggesting that autoimmunity follows combined SARS-CoV-2-bacterial infections. Viral and bacterial receptors are known to synergize to produce the increased inflammation required to support autoimmune disease pathology. Additional studies demonstrate that anti-bacterial antibodies are also required to account for known autoantigen targets in COVID-19 autoimmune complications.

COVID-19 intranasal vaccines: current progress, advantages, prospects, and challenges

Multiple vaccines have recently been developed, and almost all the countries are presently vaccinating their population to tackle the COVID-19 pandemic. Most of the COVID-19 vaccines in use are administered via intramuscular (IM) injection, eliciting protective humor and cellular immunity. COVID-19 intranasal (IN) vaccines are also being developed that have shown promising ability to induce a significant amount of antibody-mediated immune response and a robust cell-mediated immunity as well as hold the added ability to stimulate protective mucosal immunity along with the additional advantage of the ease of administration as compared to IM injected vaccines. By inducing secretory IgA antibody responses specifically in the nasal compartment, the intranasal SARS-CoV-2 vaccine can prevent virus infection, replication, shedding, and disease development, as well as possibly limits virus transmission. This article highlights the current progress, advantages, prospects, and challenges in developing intranasal COVID-19 vaccines for countering the ongoing pandemic.

Network analysis between neuron dysfunction and neuroimmune response based on neural single-cell transcriptome of COVID-19 patients

Despite global vaccination efforts, COVID-19 breakthrough infections caused by variant virus continue to occur frequently, long-term sequelae of COVID-19 infection like neuronal dysfunction emerge as a noteworthy issue. Neuroimmune disorder induced by Inflammatory factor storm was considered as a possible reason, however, little was known about the functional factors affecting neuroimmune response to this virus. Here, using medial prefrontal cortex single cell data of COVID-19 patients, expression pattern analysis indicated that some immune-related pathway genes expressed specifically, including genes associated with T cell receptor, TNF signaling in microglia and Cytokine-cytokine receptor interaction and HIF-1 signaling pathway genes in astrocytes. Besides the well-known immune-related cell type microglia, we also observed immune-related factors like IL17D, TNFRSF1A and TLR4 expressed in Astrocytes. Based on the ligand-receptor relationship of immune-related factors, crosstalk landscape among cell clusters were analyzed. The findings indicated that astrocytes collaborated with microglia and affect excitatory neurons, participating in the process of immune response and neuronal dysfunction. Moreover, subset of astrocytes specific immune factors (hinged neuroimmune genes) were proved to correlate with Covid-19 infection and ventilator-associated pneumonia using multi-tissue RNA-seq and scRNA-seq data. Function characterization clarified that hinged neuroimmune genes were involved in activation of inflammation and hypoxia signaling pathways, which could lead to hyper-responses related neurological sequelae. Finally, a risk model was constructed and testified in RNA-seq and scRNA data of peripheral blood.

A rational strategy for the maintenance of antiviral immunity to new SARS-CoV-2 strains

New variants of SARS-CoV-2 such as Omicron BA.2, BA.4/5, BA.2.12.1 and BA 2.75 are characterized by higher infectivity and the ability to escape virus-neutralizing antibodies against previous coronavirus variants. The S-trimer of BA.2 and its phylogenetic derivatives are characterized by a predominant Up-conformation, which facilitates the interaction with ACE2 on target cells and promotes the resistance to neutralizing antibodies. The immunity acquired from the infection with earlier strains is non-sterile for both early and later strains; the booster systemic immunization does not significantly affect the effectiveness of antiviral immunity, and its feasibility is currently being questioned. Studies of the mucosal immune response have shown that intranasal immunization with adenovirus vaccines provides more pronounced protective immunity than systemic reimmunization does. A promising approach is the creation of multivalent inhaled next generation vaccines containing immunoadjuvants that activate B- and T-cell mucosal immunity. Currently, a large number of intranasal vaccines are undergoing phase I/II trials, while the preclinical and preliminary clinical results indicate that this method of vaccination provides a better mucosal immune response at the entry site of the virus than systemic immunization does. This strategy may provide a long-term immune protection against the currently existing and yet unknown new strains of SARS-CoV-2.

Towards novel nano-based vaccine platforms for SARS-CoV-2 and its variants of concern: Advances, challenges and limitations

Vaccination is the most effective tool available for fighting the spread of COVID-19. Recently, emerging variants of SARS-CoV-2 have led to growing concerns about increased transmissibility and decreased vaccine effectiveness. Currently, many vaccines are approved for emergency use and more are under development. This review highlights the ongoing advances in the design and development of different nano-based vaccine platforms. The challenges, limitations, and ethical consideration imposed by these nanocarriers are also discussed. Further, the effectiveness of the leading vaccine candidates against all SARS-CoV-2 variants of concern are highlighted. The review also focuses on the possibility of using an alternative non-invasive routes of vaccine administration using micro and nanotechnologies to enhance vaccination compliance and coverage.

Toll-like receptor (TLRs) agonists and antagonists for COVID-19 treatments

Severe acute respiratory syndrome coronavirus type 2 (SARS-CoV-2) rapidly infects humans and animals which make coronavirus disease 2019 (COVID-19) a grievous epidemic worldwide which broke out in 2020. According to data analysis of the other coronavirus family, for instance severe acute respiratory syndrome SARS coronavirus (SARS-CoV), can provide experience for the mutation of SARS-CoV-2 and the prevention and treatment of COVID-19. Toll-like receptors (TLRs) as a pattern recognition receptor (PRRs), have an indispensable function in identifying the invader even activate the innate immune system. It is possible for organism to activate different TLR pathways which leads to secretion of proinflammatory cytokines such as Interleukin 1 (IL-1), Interleukin 6 (IL-6), Tumor necrosis factor α (TNFα) and type Ⅰ interferon. As a component of non-specific immunity, TLRs pathway may participate in the SARS-CoV-2 pathogenic processes, due to previous works have proved that TLRs are involved in the invasion and infection of SARS-CoV and MERS to varying degrees. Different TLR, such as TLR2, TLR4, TLR7, TLR8 and TLR9 probably have a double-sided in COVID-19 infection. Therefore, it is of great significance for a correctly acknowledging how TLR take part in the SARS-CoV-2 pathogenic processes, which will be the development of treatment and prevention strategies.

Toll-Like Receptor Signaling in Severe Acute Respiratory Syndrome Coronavirus 2-Induced Innate Immune Responses and the Potential Application Value of Toll-Like Receptor Immunomodulators in Patients With Coronavirus Disease 2019

Toll-like receptors (TLRs) are key sensors that recognize the pathogen-associated molecular patterns (PAMPs) of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) to activate innate immune response to clear the invading virus. However, dysregulated immune responses may elicit the overproduction of proinflammatory cytokines and chemokines, resulting in the enhancement of immune-mediated pathology. Therefore, a proper understanding of the interaction between SARS-CoV-2 and TLR-induced immune responses is very important for the development of effective preventive and therapeutic strategies. In this review, we discuss the recognition of SARS-CoV-2 components by TLRs and the downstream signaling pathways that are activated, as well as the dual role of TLRs in regulating antiviral effects and excessive inflammatory responses in patients with coronavirus disease 2019 (COVID-19). In addition, this article describes recent progress in the development of TLR immunomodulators including the agonists and antagonists, as vaccine adjuvants or agents used to treat hyperinflammatory responses during SARS-CoV-2 infection.

Emerging vaccine nanotechnology: From defense against infection to sniping cancer

Looking retrospectively at the development of humanity, vaccination is an unprecedented medical landmark that saves lives by harnessing the human immune system. During the ongoing coronavirus disease 2019 (COVID-19) pandemic, vaccination is still the most effective defense modality. The successful clinical application of the lipid nanoparticle-based Pfizer/BioNTech and Moderna mRNA COVID-19 vaccines highlights promising future of nanotechnology in vaccine development. Compared with conventional vaccines, nanovaccines are supposed to have advantages in lymph node accumulation, antigen assembly, and antigen presentation; they also have, unique pathogen biomimicry properties because of well-organized combination of multiple immune factors. Beyond infectious diseases, vaccine nanotechnology also exhibits considerable potential for cancer treatment. The ultimate goal of cancer vaccines is to fully mobilize the potency of the immune system as a living therapeutic to recognize tumor antigens and eliminate tumor cells, and nanotechnologies have the requisite properties to realize this goal. In this review, we summarize the recent advances in vaccine nanotechnology from infectious disease prevention to cancer immunotherapy and highlight the different types of materials, mechanisms, administration methods, as well as future perspectives.

Oral and intranasal vaccines against SARS-CoV-2: Current progress, prospects, advantages, and challenges

BACKGROUND

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has caused a deadly pandemic in the 21st century, resulting in many deaths, economic loss, and international immobility. Vaccination represents the only mechanism to defeat this virus. Several intramuscular vaccines have been approved and are currently used worldwide.

MAIN BODY

However, global mass vaccination has not been achieved owing to several limitations, including the need for expertise to administer the injection-based vaccine, improper distribution of the vaccine, and lack of cold chain facilities, particularly in resource-poor, low-income countries. Mucosal vaccines are typically administered either orally or nasally, and several studies have shown promising results for developing these vaccines against SARS-CoV-2 that might serve as viable alternatives to current vaccines. SARS-CoV-2 invades the human body via oral and nasal mucosal surfaces; thus, an oral or nasal vaccine can trigger the immune system to inhibit the virus at the mucosal level, preventing further transmission via a strong mucosal and systematic immune response. Although several approaches toward developing a mucosal vaccine are currently being tested, additional attention is required.

CONCLUSION

In this article, the current approaches used to develop effective oral and nasal mucosal vaccines against SARS-CoV-2 and their benefits, prospects, and challenges have been summarized.

Nasal Nanovaccines for SARS-CoV-2 to Address COVID-19

COVID-19 is still prevalent around the globe. Although some SARS-CoV-2 vaccines have been distributed to the population, the shortcomings of vaccines and the continuous emergence of SARS-CoV-2 mutant virus strains are a cause for concern. Thus, it is vital to continue to improve vaccines and vaccine delivery methods. One option is nasal vaccination, which is more convenient than injections and does not require a syringe. Additionally, stronger mucosal immunity is produced under nasal vaccination. The easy accessibility of the intranasal route is more advantageous than injection in the context of the COVID-19 pandemic. Nanoparticles have been proven to be suitable delivery vehicles and adjuvants, and different NPs have different advantages. The shortcomings of the SARS-CoV-2 vaccine may be compensated by selecting or modifying different nanoparticles. It travels along the digestive tract to the intestine, where it is presented by GALT, tissue-resident immune cells, and gastrointestinal lymph nodes. Nasal nanovaccines are easy to use, safe, multifunctional, and can be distributed quickly, demonstrating strong prospects as a vaccination method for SARS-CoV-2, SARS-CoV-2 variants, or SARS-CoV-n.

An Overview of Recent Insights into the Response of TLR to SARS-CoV-2 Infection and the Potential of TLR Agonists as SARS-CoV-2 Vaccine Adjuvants

The emergence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has led to coronavirus disease (COVID-19), a global health pandemic causing millions of deaths worldwide. However, the immunopathogenesis of COVID-19, particularly the interaction between SARS-CoV-2 and host innate immunity, remains unclear. The innate immune system acts as the first line of host defense, which is critical for the initial detection of invading pathogens and the activation and shaping of adaptive immunity. Toll-like receptors (TLRs) are key sensors of innate immunity that recognize pathogen-associated molecular patterns and activate downstream signaling for pro-inflammatory cytokine and chemokine production. However, TLRs may also act as a double-edged sword, and dysregulated TLR responses may enhance immune-mediated pathology, instead of providing protection. Therefore, a proper understanding of the interaction between TLRs and SARS-CoV-2 is of great importance for devising therapeutic and preventive strategies. The use of TLR agonists as vaccine adjuvants for human disease is a promising approach that could be applied in the investigation of COVID-19 vaccines. In this review, we discuss the recent progress in our understanding of host innate immune responses in SARS-CoV-2 infection, with particular focus on TLR response. In addition, we discuss the use of TLR agonists as vaccine adjuvants in enhancing the efficacy of COVID-19 vaccine.

Nanovaccines against Animal Pathogens: The Latest Findings

Nowadays, safe and efficacious vaccines represent powerful and cost-effective tools for global health and economic growth. In the veterinary field, these are undoubtedly key tools for improving productivity and fighting zoonoses. However, cases of persistent infections, rapidly evolving pathogens having high variability or emerging/re-emerging pathogens for which no effective vaccines have been developed point out the continuing need for new vaccine alternatives to control outbreaks. Most licensed vaccines have been successfully used for many years now; however, they have intrinsic limitations, such as variable efficacy, adverse effects, and some shortcomings. More effective adjuvants and novel delivery systems may foster real vaccine effectiveness and timely implementation. Emerging vaccine technologies involving nanoparticles such as self-assembling proteins, virus-like particles, liposomes, virosomes, and polymeric nanoparticles offer novel, safe, and high-potential approaches to address many vaccine development-related challenges. Nanotechnology is accelerating the evolution of vaccines because nanomaterials having encapsulation ability and very advantageous properties due to their size and surface area serve as effective vehicles for antigen delivery and immunostimulatory agents. This review discusses the requirements for an effective, broad-coverage-elicited immune response, the main nanoplatforms for producing it, and the latest nanovaccine applications for fighting animal pathogens.