Next Article in Journal
Design of Catalase Monolithic Tablets for Intestinal Targeted Delivery
Next Article in Special Issue
Bacterial-Derived Outer Membrane Vesicles are Potent Adjuvants that Drive Humoral and Cellular Immune Responses
Previous Article in Journal
In-Line and Off-Line Monitoring of Skin Penetration Profiles Using Confocal Raman Spectroscopy
Previous Article in Special Issue
Nanoparticles as Adjuvants and Nanodelivery Systems for mRNA-Based Vaccines
 
 
Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
Journals
Pharmaceutics
Volume 13
Issue 1
10.3390/pharmaceutics13010068
pharmaceutics-logo
Submit to this Journal Review for this Journal Propose a Special Issue
► Article Menu

Article Menu

share Share announcement Help format_quote Cite question_answer Discuss in SciProfiles thumb_up
...
Endorse textsms
...
Comment
first_page
settings
Order Article Reprints
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Review

Promising Adjuvants and Platforms for Influenza Vaccine Development

by
Wandi Zhu
,
Chunhong Dong
,
Lai Wei
and
Bao-Zhong Wang
*
Center for Inflammation, Immunity & Infection, Institute for Biomedical Sciences, Georgia State University, Atlanta, GA 30303, USA
*
Author to whom correspondence should be addressed.
Pharmaceutics 2021, 13(1), 68; https://doi.org/10.3390/pharmaceutics13010068
Submission received: 16 December 2020 / Revised: 30 December 2020 / Accepted: 4 January 2021 / Published: 7 January 2021
(This article belongs to the Special Issue Discovery and Evaluation of Novel Adjuvants for Vaccine Formulations)
Browse Figure
Review Reports Versions Notes

Abstract

:
Influenza is one of the major threats to public health. Current influenza vaccines cannot provide effective protection against drifted or shifted influenza strains. Researchers have considered two important strategies to develop novel influenza vaccines with improved immunogenicity and broader protective efficacy. One is applying fewer variable viral antigens, such as the haemagglutinin stalk domain. The other is including adjuvants in vaccine formulations. Adjuvants are promising and helpful boosters to promote more rapid and stronger immune responses with a dose-sparing effect. However, few adjuvants are currently licensed for human influenza vaccines, although many potential candidates are in different trials. While many advantages have been observed using adjuvants in influenza vaccine formulations, an improved understanding of the mechanisms underlying viral infection and vaccination-induced immune responses will help to develop new adjuvant candidates. In this review, we summarize the works related to adjuvants in influenza vaccine research that have been used in our studies and other laboratories. The review will provide perspectives for the utilization of adjuvants in developing next-generation and universal influenza vaccines.

1. Introduction

Influenza epidemics are a severe public health issue each year. During the 2019–2020 influenza season in the United States, about 38 million illnesses, 400,000 hospitalizations, and 22,000 deaths were associated with influenza [1]. Compared with previous flu seasons, higher hospitalization rates were observed among children under four and adults between 18 and 49 [1]. Besides, domestic or wild zoonotic influenza viruses may break the host barriers, jump to humans, and cause influenza pandemics. Frequent human infection with H5N1 and H7N9 in recent years foreshadows emerging pandemics. As it takes time to develop immunity for an emerging virus, an influenza pandemic can be a catastrophe for humans [2,3].
Vaccination is an effective method to protect humans from influenza viral infection or alleviate symptoms induced by influenza-associated diseases. Licensed influenza vaccines include inactivated influenza vaccines (IIV), recombinant influenza vaccines (RIV), and live attenuated influenza vaccines (LAIV) [4]. However, the formulations selected in each flu season are primarily dependent on influenza surveillance data because of the continuous mutation of influenza viruses [5]. A mismatch between the influenza vaccine strains and the circulating influenza strains could significantly reduce vaccine effectiveness. A panel of methods was developed for viral isolation, identification, and sequencing, allowing scientists to rapidly identify mutant strains when a mismatch occurs at the early stage of an influenza outbreak. In this circumstance, novel manufacturing methods would be required to produce large-scale of vaccine supply quickly.
With the above challenges to the seasonal influenza vaccine strategy, universal influenza vaccines that elicit comprehensive, long-term, and broad protection are urgently needed. Various approaches are undertaken to realize such influenza vaccines. The two primary distinctive methods are: (1) Applying conserved epitopes and domains in place of different influenza strains as vaccine immunogens. The well-known conserved antigens include the head-removed hemagglutinin stalk domain (hrHA), neuraminidase (NA), matrix protein 2 (M2), and T cell epitopes resident in influenza internal proteins (such as nucleoprotein (NP) and matrix protein 1 (M1). Some combinations of these antigens have proven to provide cross-protection against different virus challenges in laboratory animals. (2) Improving immune responses by various complementary adjuvants. Adjuvants are molecules or ingredients that are administered with vaccines to improve immune responses. The early innate immune responses in an infection or vaccination program the dimension and magnitude of antigen-specific immune responses [6]. As triggers of innate immune responses, appropriate adjuvants tailor antigen-specific immune responses for optimal protection and immune memory. Through a deep understanding of the immunological mechanisms underlying natural influenza infection for immunity generation and memory, safe and effective adjuvants will be discovered and applied to develop universal influenza vaccines. This article will review the adjuvants that are under preclinical study and early phases of clinical trials. We will focus on the novel adjuvants that might have potent effects in bridging innate and adaptive immune responses and discuss the delivery strategies and routes used to improve influenza vaccine outcomes.

2. Licensed Influenza Adjuvants

Aluminium salts (Alum) are the most widely used adjuvants in human influenza vaccines. Other adjuvants licensed for human influenza vaccines in different areas include oil-in-water emulsions (MF59, AS03, and AF03), virosomes, and heat-labile enterotoxin (LT) [7]. Studies have suggested that Alum functions in several ways, such as helping with antigen uptake [8], the induction of interleukin-1ß release by inflammasomes [9], enhancing antigen presentation, and strengthening the interaction between dendritic cells (DCs) and CD4+ T cells [10]. The immunological mechanism underlying the function of Alum is still not entirely understood.
During the 2020–2021 influenza season, both trivalent and quadrivalent FLUAD inactivated influenza vaccines containing the adjuvant MF59 were approved for people 65 and older. MF59 is an oil-in-water emulsion, which works very distinctly from Alum. MF59 injection leads to the release of some specific chemokines and cytokines, like CCL2, CCL3 IL-8, and IL-5 [11,12]. MF59 preferentially induces Th2-biased immune responses [13]. Like MF59, AS03 and AF03 are oil-in-water adjuvants that take effect in the fashion of MF59.
Virosomes are lipid vesicles that incorporate the influenza antigens on the surface and encapsulate an aqueous solution. Influenza virosomes incorporate influenza antigens onto the vesicle surfaces to mimic the physical features of viruses, such as shapes and sizes, which enhances antigen uptake and presentation and the subsequent immune cell activation [14,15]. Inflexal® V is a commercially available virosome-based influenza vaccine [16]. LT was previously licensed as a mucosal adjuvant for the influenza vaccine; however, it was later found that LT induced Bell’s palsy in the recipients [17].
The advantages and disadvantages of Alum [7,18], oil-in-water emulsions [18,19], virosomes [20,21], and LT [22] were listed in Table 1. More adjuvants are being developed and studied to improve influenza vaccine outcomes in preclinical and clinical trials.

3. Adjuvants in Immune Responses

The progress in understanding innate immunity and its role in directing adaptive immune responses have provided new thoughts for the next generation of adjuvants [23]. As the early responders in an infection, various cell types—including macrophages, DCs, γδ T cells, and NKT cells—can sense and respond to adjuvants. Pattern recognition receptors (PRRs) are expressed inside or on the surfaces of these innate cells. Transmembrane receptors, like Toll-like receptors (TLRs), and cytoplasmic receptors, like the nucleotide-binding and oligomerization domain (NOD)-like receptors (NLRs), are two kinds of PRRs that have been well studied. PRRs recognize pathogen-associated molecular patterns (PAMPs) and danger-associated molecular patterns (DAMPs) and activate the downstream signaling pathways, resulting in pro-inflammatory cytokine generation modulating the humoral and cellular immune responses. PAMPs, DAMPs, or other innate signaling molecules could be potential adjuvants to guide immune outcomes during immunization [24,25]. Some adjuvants (systems) are summarized in Table 2.

3.1. TLR Agonists

The activation of TLR signaling pathways is essential for protection against influenza virus infection [26]. Administration of TLR3, TLR9, TLR7, or TLR7/8 agonists resulted in viral inhibition and improved mouse survival [27]. Recent publications have further demonstrated that the combinations of synthesized TLR4, TLR7, and TLR7/8 ligands were potent adjuvants for recombinant influenza HA vaccines in different animal models [28,29,30,31]. Significantly, the TLR4 and TLR7 ligands—such as MPL/R837, TRAC-478, and 1Z105/1V270—synergistically increased antigen-specific, long-lasting humoral immune responses, Th1 cell-mediated or Th1/Th2-balanced immunity, and protection against homologous, heterologous, and heterosubtypic viral challenges [6,28,30]. Intranasal co-administration of a synthetic TLR3 ligand, poly I:C, with inactivated human, avian, or swine influenza vaccines activated mucosal and systemic humoral responses in mice, ducks, or pigs [32,33,34,35]. Thus, the inclusion of appropriate TLR agonists can alter the directions of the immune response.
Flagellin (FliC) is a natural ligand of TLR5 and has proven to be a potent adjuvant when administered with influenza antigens [36]. Our laboratory has studied FliC as a potent adjuvant by constructing various antigen-FliC formulations [37,38,39,40,41,42,43,44]. Skin immunization with recombinant fusion protein 4M2e-FliC induced strong M2e-specific humoral and mucosal immune responses [37]. We also redesigned the 4M2e-FliC construct to include M2e sequences from different influenza subtypes. We demonstrated that microneedle patch (MNP)-based boosting immunizations with the 4M2e-FliC could rapidly broaden influenza-vaccine-induced immunity [43]. An MNP encapsulating 4M2e-FliC and inactivated influenza vaccines (H1N1 and H3N2) was developed and demonstrated to have antiviral efficacy against reassortant A/Vietnam/1203/2004 H5N1 and A/Shanghai/2013 H7N9 virus challenge. However, a recent clinical trial showed an overproduction of inflammatory molecules from the vaccination of a flagellin-M2e fusion protein vaccine (STF2.4 × M2e) [45]. In the trial, the ratio of flagellin to the antigen was fixed due to the fusion protein state of STF2.4 × M2e. One of our previous studies in guinea pigs demonstrated that 0.5 µg of flagellin-adjuvanted HIV virus-like particles (VLPs) induced significantly higher levels of neutralizing antibody responses than non-adjuvanted VLPs without over-production of inflammatory cytokines [46]. An optimal dose of flagellin is to be studied as a safe adjuvant in influenza vaccine development.
TLR9 agonists—unmethylated CpG oligodeoxynucleotides (CpG ODN or CpG)—are among the most promising adjuvants that could be used in humans. The administration of CpG has induced Th1-biased responses. The inclusion of CpG in the inactivated influenza vaccines enhanced T cell responses and provided protection against a heterosubtypic influenza infection [47]. Two research groups simultaneously reported that combinations of MPL and CpG (MPL + CpG) induced various inflammatory cytokines and chemokines within one day. MPL + CpG double-adjuvanted influenza vaccines improved protective efficacy with elevated IgG2a antibodies and Th1-biased immune response [48,49].

3.2. Cytosolic Nucleic Acids

In addition to TLR signaling pathways, detecting and responding to pathogens through nucleic acid sensors is another approach to activating innate immune responses. Various RNA and DNA-sensing receptors, such as RIG-I-like receptors (RLRs) and cyclic GMP-AMP synthase (cGAS), regulate downstream signaling pathways and subsequent cytokine secretion. The activation of RIG-I induced the production of type I interferons (IFNs) and pro-inflammatory cytokines. 5′ triphosphorylated and diphosphorylated short dsRNAs (5′pppRNA), synthesized small molecule compounds, and poly I: C are well-studied RIG-I-associated adjuvants for enhancing the efficacy of influenza vaccines [50,51,52].
The cGAS-STING pathway was activated during an influenza virus infection and played essential roles in the battle against the infection [53]. 2′3′-cyclic GMP-AMP (cGAMP) is a natural agonist of stimulator of interferon genes (STING), which strongly augmented protective cellular and humoral immune responses induced by influenza vaccines. Meanwhile, compared with intramuscular injection, cGAMP showed a superior adjuvant effect on cutaneous vaccination. cGAMP-adjuvanted H5N1 induced long-lasting protective immunity [54]. An important discovery is that lung delivery of pulmonary surfactant (PS)-biomimetic liposomes encapsulating cGAMP-augmented influenza vaccines induced humoral and CD8+ T cell immune responses in mice. The immunity conferred strong cross-protection against distant H1N1 and heterosubtypic H3N2, H5N1, and H7N9 viruses for at least 6 months [55,56]. cGAMP was also reported as a mucosal adjuvant by intranasal immunization. Co-delivery of H7N9 vaccines with cGAMP enhanced humoral, cellular, and mucosal immune responses in mice [57]. These studies suggest that cGAMP is a promising adjuvant for developing a universal influenza vaccine.

3.3. Agonists for Inflammasomes Activation

Inflammasomes are another essential component of the innate immune system. The three major types are NOD-like receptor protein 3 (NLRP3) inflammasomes, NLR-family CARD domain-containing protein 4 (NLRC4) inflammasomes, and absent in melanoma 2 (AIM2) inflammasomes [58].
Inflammasomes regulate inflammation by activating caspase-1 and releasing pro-inflammatory cytokines such as IL-1β and IL-18 [59]. Aluminium salts [60], MF-59, AS03, QS-21 [61], and chitosan [62] have been shown to activate inflammasome as part of their mechanisms of immunological activities [63]. Flagellin can also activate inflammasomes through its cytosolic receptor NLRC4 [64]. Nucleic acids (DNA and RNA) could be used for both vaccines and potential adjuvants, as both DNA and RNA can activate inflammasomes [65]. Single- and double-stranded RNAs (ssRNAs and dsRNAs) are recognized by RIG-I, which can subsequently activate NLRP3 inflammasome [66]. In contrast, double-stranded DNA (dsDNA) can be sensed by the AIM2 inflammasome signaling pathway [67].
The activation of inflammasomes vitally inhibits influenza virus infection by limiting the lung damage or enhancing adaptive immune responses through the activation of downstream IL-1R signaling events [68,69,70]. While most works have been focused on the role of NLRP3 in adjuvanticity, the characteristics of other NLR-associated inflammasomes are also being investigated, such as the NRLC5 inflammasome [71]. Inflammasome activators could be used as adjuvants to strengthen immune responses.

3.4. Activators of Immune Cells

Besides the primary professional antigen-presenting cells (APCs), i.e., DCs and macrophages, γδ T cells, NK cells, NKT cells, neutrophils, eosinophils, and mast cells are essential components of the innate immune system. Synergistically activating the function of different innate immune cells could facilitate comprehensive immune responses and provide broad protection. Molecules participating in the activation of these cells are promising adjuvants.
Invariant (i) NKT cells, a significant subset of NKT cells, serve as a bridge between the innate and adaptive immune responses. Activated iNKT cells rapidly secrete both Th1 and Th2 cytokines to facilitate DCs maturation and germinal center (GC) B cell responses [72]. Glycolipid ligand α-galactosylceramide (α-GalCer) is a stimulator of iNKT cells. The adjuvanticity of α-GalCer has been studied for influenza vaccines in different animal models. α-GalCer is a promising adjuvant for influenza vaccines, which enhances antigen-specific antibody production and increases protective efficacy.
Mast cells are important innate immune cells and play a crucial role in fighting against bacterial and viral infection. Activated mast cells regulate the migration of immune cells and the induction of adaptive immune responses. Mast cells can be stimulated by various activators, including compound 48/80 (C48/80), IL-33, IL-18, alum, and IgG immune complexes [73,74]. Intranasal immunization with C48/80 adjuvanted recombinant influenza HA elicited protective immunity against 2009 pandemic H1N1 influenza in mice [75]. Intranasal vaccination with the IL-18 and IL-33 adjuvanted recombinant influenza vaccine significantly enhanced antigen-specific antibody responses in systemic compartments and mucosal sites and increased mouse survival during lethal influenza challenges [76].

3.5. Cytokines and Chemokines

Other cytokines that modulate immune cells are potential adjuvants for influenza vaccines. IL-1β is an inflammatory cytokine released from its proprotein by inflammasome-mediated caspase-1 activation [77]. Mucosal delivery of recombinant adenoviral vectors (rAd) encoding IL-1β enhanced influenza HA-specific antibody responses. rAd-IL-1β-adjuvanted immunization increased mucosal and systemic T cell immune responses, local tissue-resident memory T cell population, and improved protection against heterologous influenza strains H1N1, pH1N1, H3N2, and H7N7 [78].
Tumor necrosis factor (TNF) is one product of C48/80 stimulation, which directs DC migration [74]. A combination of influenza antigens with particulate TNF increased GC activities and mouse survival rates after a lethal influenza challenge [79].
Granulocyte-macrophage colony-stimulating factor (GM-CSF) is an immunomodulatory cytokine that promotes the maturation of granulocytes and macrophages and regulates DC homeostasis [80]. Skin vaccination with GM-CSF-adjuvanted influenza vaccines induced robust long-term antibody responses and improved mouse protection against lethal influenza challenges [81]. GIFT4 is a novel cytokine that was constructed in our lab by fusing GM-CSF and interleukin-4. We found that a glycolipid (GPI)-anchoring GIFT4 enhanced the immunogenicity of HIV VLPs [82].
Chemokines are a group of small chemoattractant proteins that play a critical role in the tissue-directed migration of immune cells. The use of chemokines as adjuvants is a potential option for developing novel influenza vaccines to direct immune effectors to vulnerable sites for intensive protection [83]. Mucosa-associated epithelial chemokine (CCL28) and cutaneous T-cell-attracting chemokine (CCL27) represent attractive homing chemokines. CCL27, CCL28, and their receptor, CCR10, are essential regulators of mucosal immune responses and important for lymphocyte recruitment to specific mucosal sites. Our lab has previously demonstrated that GPI-anchored CCL28 (GPI-CCL28) acted as an effective adjuvant in an influenza VLP vaccine, which induced robust immune responses at systemic and mucosal compartments and provided significant cross-protection against heterologous viral infection [84] (Figure 1B).

4. Particulate Adjuvants and Self-Adjuvanted Particulate Vaccine Platforms

Particles of various types have been investigated as vaccine adjuvants for both injection and mucosal routes. Encapsulating antigens into nanoparticles or onto their surfaces has been shown to enhance antigen-specific antibody responses and cell-mediated immunity. Nanoparticles are an important class of nanoscale materials that have been engineered with controllable and tunable physicochemical properties, including size, shape, structure, and surface chemistry.
The development of self-adjuvanted nanoparticle platforms carrying molecular adjuvants and antigens is highly desirable because such particles can efficiently transport antigens to target cells and activate innate signaling. Different self-adjuvanted nanoparticle platforms are displayed in Figure 1.

4.1. Gold (Au) Nanoparticles

Gold (Au) nanoparticles are one of the most common inorganic nanoparticles used for vaccine formulations. Due to the strong affinity of thiol moieties with Au nanoparticle surfaces, thiol-modified polymers or biomolecules (proteins, peptides, oligonucleotides, targeting ligands) can be readily conjugated onto the nanoparticles. With good biosafety and biocompatibility, Au nanoparticles have been used for developing influenza and HIV vaccines [42,85,86,87]. We previously developed multifunctionalized dual-linker gold nanoparticles (AuNPs) to co-deliver influenza antigens and FliC [86] (Figure 1A). Compared with soluble proteins, self-adjuvanted AuNPs-HA/FliC enhanced antigen uptake and induced significantly improved antibody responses. We reported later that the AuNP-HA and AuNP-FliC particle mixtures generated strong mucosal and systemic immune responses and protected immunized mice against lethal influenza virus challenges [42]. The self-adjuvanted Au nanoparticle influenza vaccines demonstrated a high potential for an intranasal influenza vaccine with enhanced vaccine efficacy.

4.2. Lipid Nanoparticles

Lipid nanoparticles (LNPs), typically composed of an ionizable lipid, cholesterol, lipid conjugated with polyethylene glycol (PEGylated lipid) and a helper lipid, have recently been recognized as a novel delivery system. LNPs have been used for antigen and adjuvant codelivery. CpG-incorporated LNPs improved the adjuvant effects of CpG ODN and broadened the protection against influenza virus infection [88]. Combinations of TLR ligands with lipid formulations are of particular interest. A split influenza vaccine with co-encapsulated TRAC-478 (a synthetic dual TLR adjuvant) liposome delivery system stimulated strong humoral immune responses and induced Th1-cell-mediated immunity; The immunity protected immunized mice against a heterologous influenza challenge [28] (Figure 1E).
mRNA vaccines are a promising alternative to other vaccine approaches. One mRNA vaccine formulation could easily include multiple mRNAs encoding different viral antigens and innate signaling triggers. mRNA LNPs are one of the novel mRNA vaccine technologies. Nucleoside-modified mRNA LNPs have induced increased GC responses. Full-length influenza HA mRNA-encapsulated LNPs induced HA-stalk-specific antibodies that provided cross-protection in mice [89]. Meanwhile, intradermal (ID) delivery of combined influenza HA stalk, neuraminidase (NA), matrix-2 ion channel (M2), and NP mRNA LNPs have induced robust immune responses and provided broad protection [89,90,91,92]. Thus, codelivery of appropriate adjuvants with the mRNA LNPs is an effective method to enhance the immune response.

4.3. Protein Nanoparticles

Compared with other particulate platforms, protein nanoparticles are exclusively antigenic and adjuvant proteins. With self-assembling motifs or under some physical condition (like desolvation), proteins can automatically assemble into nanoparticles. With virtually no polymer or nanocarrier, protein nanoparticles have an extremely high antigen-loading capacity. The methods for the preparation and characterization of double-layered protein nanoparticles have been well established in our laboratory. We have found that layered protein nanoparticles composed of an HA stalk from both H1N1 and H3N2 influenza strains and M2e induced immune protection against homo- and heterosubtypic influenza A viruses [93]. This double-layered protein nanoparticle platform can be adapted to accommodate different influenza conserved antigens. We have developed nanoparticles by desolvating M2e or NP into cores and crosslinking HA stalks, HA, NA, or NP on the core surfaces as coating antigens [94,95] (Figure 1C). The immunogenicity and protective efficiency of these nanoparticles have been determined. Based on this nanoplatform, we are interested in incorporating different adjuvants or targeting molecules together with influenza antigenic proteins into nanoparticles to improve the vaccine outcomes. These self-adjuvanted nanoparticles will be fabricated into MNP for skin delivery in our laboratory.

4.4. Other Nano-Platforms

Other types of nanoparticles have also been studied to construct self-adjuvanted vaccine formulations, such as silver (Ag) nanoparticles and calcium phosphate (CaP) nanoparticles. In a recent report, Ag nanoparticles demonstrated promising results in boosting the mucosal immunity of inactivated flu vaccines in a pulmonary immunization and protected against lethal influenza infection [96]. The inclusion of silver nanoparticles induced much stronger antigen-specific IgA in bronchus-associated lymphoid tissue (BALT), reducing the lung viral titers and concomitant lung inflammation. Compared with other adjuvants, such as poly I:C and AddaVax, Ag nanoparticles displayed superior potential in providing potent mucosal immunity potency and protecting mice against influenza infection. For example, a single oral immunization of the AgNP/H5 DNA vaccine in chickens successfully induced antigen-specific antibody responses and cell-mediated immune responses, and enhanced cytokine production [97].
Calcium phosphate nanoparticles (CaP) are a kind of biodegradable nanoparticle with excellent biocompatibility. Knuschke et al. reported the high potential of CaP nanoparticles in inducing cellular immunity when formulated with a conserved influenza A/PR/8/34 (H1N1) HA peptide and a TLR9 agonist, CpG [98]. These nanoparticles were efficiently internalized by DCs in vivo and elicited potent T-cell-mediated immunity; Greatly increased numbers of antigen-specific, IFN-γ-producing CD4+ and CD8+ effector T cells were detected. Moreover, CaP nanoparticles were useful adjuvants in multiple administration routes and powerfully induce the balanced T helper type-1 (Th1) and Th2 immune responses [99,100].
Biodegradable synthetic polymeric (PLGA) nanoparticles containing influenza antigens, TLR4, and TLR7 ligands (MPL + R387) have been reported to induce synergistic increases in antigen-specific antibodies and complete protection against lethal influenza virus strains challenge in mice and rhesus macaques [6] (Figure 1D). The immune-stimulating complex (ISCOM) is another type of particulate adjuvant. It is composed of antigens, cholesterol, phospholipid, and the immunostimulatory saponin. Matrix M was the third generation of ISCOM and used as an adjuvant in clinical trials for influenza vaccines [101,102].
In addition to three-dimensional nanomaterials, two-dimensional sheet-like nanomaterials, such as graphene oxide (GO) nanoparticles, also attract interest in constructing novel self-adjuvanted vaccine platforms. As the typical example, GO nanoparticles demonstrated great potential as vaccine delivery systems, because of their extraordinary advantages, including the high loading capacity resulting from the intrinsically high aspect ratio and ultra-large surface area, the easy and flexible surface modification with the presence of a wealth of chemical groups (carboxylic acid, epoxy and hydroxyl groups, etc.), and the biocompatible and nonimmunogenic features. GO-nanoparticle-based vaccines can be prepared in many ways, including direct absorption via hydrogen bonding, hydrophobic or π–π stacking interactions, and chemical conjugation with the rich chemical groups. Flexible surface modification with polymers makes the design and fabrication of GO vaccine formulations amiable.
Inorganic materials possess many advantages for drug delivery, like increased loading efficacy, controlled release, stability, and low-toxicity. These properties make them ideal vectors for vaccine delivery. Although various inorganic nanoparticles, such as Au nanoparticles, are extensively studied in vaccine research, the safety issues, such as toxicity, metabolism and side effects, still need to be further evaluated [103,104]. Lipid and protein nanoparticles belong to the organic nanoparticles, which are relatively safe. PLGA is one kind of biocompatible and biodegradable polymer that has been approved by the US Food and Drug Administration (FDA) for human use [105], thus PLGA-based nanoparticles will be a promising platform for vaccine delivery. Besides the platforms, the fabrication process, particle size, dose, characteristics of carried antigens and adjuvants are also important factors that could influence the application of vaccines.

5. Conclusions

Taken together, adjuvants participating in innate immunity could initiate innate immune responses and orchestrate the direction and scale of adaptive immune responses. Appropriate administration routes for different adjuvants could differentiate the effects of vaccines because of the uneven distribution of innate sentinel cells. The optimization of combinations of adjuvants is important to regulate the magnitude and breadth of influenza vaccines.
The immune system recognizes many molecules as ligands of innate sensors. The use of the functionally characterized molecules as adjuvants will significantly promote the rational design of influenza vaccines. Simultaneous applications of different adjuvants via particulate carriers are a potential approach to achieve universal influenza vaccines.

Author Contributions

Conceptualization, B.-Z.W. and W.Z.; writing—original draft preparation, W.Z., C.D. and L.W.; writing—review and editing, B.-Z.W. and W.Z. All authors have read and agreed to the published version of the manuscript.

Funding

This work was funded by the US National Institutes of Health (NIH) under grants R01AI101047, R01AI116835, and R01AI143844 to B.-Z.W.

Acknowledgments

The authors are thankful to Gilbert Gonzalez for his help in the preparation of the manuscript.

Conflicts of Interest

The authors declare no conflict of interest.

References

  1. Centers for Disease Control and Prevention. Estimated Influenza Illnesses, Medical visits, Hospitalizations, and Deaths in the United States—2019–2020 Influenza Season. Available online: https://www.cdc.gov/flu/about/burden/2019-2020.html#anchor_1601407136591 (accessed on 6 October 2020).
  2. Valkenburg, S.A.; Rutigliano, J.A.; Ellebedy, A.H.; Doherty, P.C.; Thomas, P.G.; Kedzierska, K. Immunity to seasonal and pandemic influenza A viruses. Microbes Infect. 2011, 13, 489–501. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  3. Koutsakos, M.; Kedzierska, K.; Subbarao, K. Immune Responses to Avian Influenza Viruses. J. Immunol. 2019, 202, 382–391. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  4. Centers for Disease Control and Prevention. Seasonal Influenza Vaccine Safety: A Summary for Clinicians. Available online: https://www.cdc.gov/flu/professionals/vaccination/vaccine_safety.htm (accessed on 4 September 2020).
  5. Centers for Disease Control and Prevention. U.S. Influenza Surveillance System: Purpose and Methods. Available online: https://www.cdc.gov/flu/weekly/overview.htm (accessed on 6 October 2020).
  6. Kasturi, S.P.; Skountzou, I.; Albrecht, R.A.; Koutsonanos, D.G.; Hua, T.; Nakaya, H.I.; Ravindran, R.; Stewart, S.; Alam, M.; Kwissa, M.; et al. Programming the magnitude and persistence of antibody responses with innate immunity. Nat. Cell Biol. 2011, 470, 543–547. [Google Scholar] [CrossRef] [PubMed]
  7. Tregoning, J.S.; Russell, R.F.; Kinnear, E. Adjuvanted influenza vaccines. Hum. Vaccines Immunother. 2018, 14, 550–564. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  8. Ghimire, T.R.; Benson, R.; Garside, P.; Brewer, J.M. Alum increases antigen uptake, reduces antigen degradation and sustains antigen presentation by DCs in vitro. Immunol. Lett. 2012, 147, 55–62. [Google Scholar] [CrossRef] [Green Version]
  9. Eisenbarth, S.C.; Colegio, O.R.; O’Connor, W.; Sutterwala, F.S.; Flavell, R.A. Crucial role for the Nalp3 inflammasome in the immunostimulatory properties of aluminium adjuvants. Nat. Cell Biol. 2008, 453, 1122–1126. [Google Scholar] [CrossRef]
  10. McKee, A.S.; Burchill, M.A.; Munks, M.W.; Jin, L.; Kappler, J.W.; Friedman, R.S.; Jacobelli, J.; Marrack, P. Host DNA released in response to aluminum adjuvant enhances MHC class II-mediated antigen presentation and prolongs CD4 T-cell interactions with dendritic cells. Proc. Natl. Acad. Sci. USA 2013, 110, E1122–E1131. [Google Scholar] [CrossRef] [Green Version]
  11. Seubert, A.; Monaci, E.; Pizza, M.; O’Hagan, D.T.; Wack, A. The Adjuvants Aluminum Hydroxide and MF59 Induce Monocyte and Granulocyte Chemoattractants and Enhance Monocyte Differentiation toward Dendritic Cells. J. Immunol. 2008, 180, 5402–5412. [Google Scholar] [CrossRef]
  12. McDonald, J.U.; Zhong, Z.; Groves, H.T.; Tregoning, J.S. Inflammatory responses to influenza vaccination at the extremes of age. Immunology 2017, 151, 451–463. [Google Scholar] [CrossRef] [Green Version]
  13. Ko, E.-J.; Kang, S.-M. Immunology and efficacy of MF59-adjuvanted vaccines. Hum. Vaccines Immunother. 2018, 14, 3041–3045. [Google Scholar] [CrossRef]
  14. Bachmann, M.F.; Jennings, G.T. Vaccine delivery: A matter of size, geometry, kinetics and molecular patterns. Nat. Rev. Immunol. 2010, 10, 787–796. [Google Scholar] [CrossRef]
  15. Huckriede, A.; Bungener, L.; Daemen, T.; Wilschut, J. Influenza virosomes in vaccine development. Methods Enzymol. 2003, 373, 74–91. [Google Scholar] [CrossRef]
  16. Mischler, R.; Metcalfe, I.C. Inflexal®V a trivalent virosome subunit influenza vaccine: Production. Vaccine 2002, 20, B17–B23. [Google Scholar] [CrossRef]
  17. Mutsch, M.; Zhou, W.; Rhodes, P.; Bopp, M.; Chen, R.T.; Linder, T.; Spyr, C.; Steffen, R. Use of the Inactivated Intranasal Influenza Vaccine and the Risk of Bell’s Palsy in Switzerland. N. Engl. J. Med. 2004, 350, 896–903. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  18. Moni, S.S.; Safhi, M.M.; Kannadasan, M.; Sukumaran, N. Vaccine adjuvants—Current status and prospects on controlled release adjuvancity. Saudi Pharm. J. 2011, 19, 197–206. [Google Scholar] [CrossRef] [Green Version]
  19. Sanina, N.M. Vaccine Adjuvants Derived from Marine Organisms. Biomology 2019, 9, 340. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  20. Moser, C.; Amacker, M.; Kammer, A.R.; Rasi, S.; Westerfeld, N.; Zurbriggen, R. Influenza virosomes as a combined vaccine carrier and adjuvant system for prophylactic and therapeutic immunizations. Expert Rev. Vaccines 2007, 6, 711–721. [Google Scholar] [CrossRef]
  21. Liu, H.; Tu, Z.; Feng, F.; Shi, H.; Chen, K.; Xu, X. Virosome, a hybrid vehicle for efficient and safe drug delivery and its emerging application in cancer treatment. Acta Pharm. 2015, 65, 105–116. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  22. Lewis, D.J.; Huo, Z.; Barnett, S.; Kromann, I.; Giemza, R.; Galiza, E.; Woodrow, M.; Thierry-Carstensen, B.; Andersen, P.; Novicki, D.; et al. Transient Facial Nerve Paralysis (Bell’s Palsy) following Intranasal Delivery of a Genetically Detoxified Mutant of Escherichia coli Heat Labile Toxin. PLoS ONE 2009, 4, e6999. [Google Scholar] [CrossRef]
  23. Bonam, S.R.; Partidos, C.D.; Halmuthur, S.K.M.; Muller, S. An Overview of Novel Adjuvants Designed for Improving Vaccine Efficacy. Trends Pharmacol. Sci. 2017, 38, 771–793. [Google Scholar] [CrossRef]
  24. Duthie, M.S.; Windish, H.P.; Fox, C.B.; Reed, S.G. Use of defined TLR ligands as adjuvants within human vaccines. Immunol. Rev. 2010, 239, 178–196. [Google Scholar] [CrossRef] [PubMed]
  25. Maisonneuve, C.; Bertholet, S.; Philpott, D.J.; De Gregorio, E. Unleashing the potential of NOD- and Toll-like agonists as vaccine adjuvants. Proc. Natl. Acad. Sci. USA 2014, 111, 12294–12299. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  26. Wong, J.P.; Christopher, M.; Viswanathan, S.; Karpoff, N.; Dai, X.; Das, D.; Sun, L.; Wang, M.; Salazar, A. Activation of toll-like receptor signaling pathway for protection against influenza virus infection. Vaccine 2009, 27, 3481–3483. [Google Scholar] [CrossRef] [PubMed]
  27. Lee, N.L.S.; Wong, C.K.; Hui, D.S.C.; Chan, P.K.S. Role of toll-like receptors in naturally occurring influenza virus infection. Hong Kong Med. J. 2014, 20, 11–15. [Google Scholar] [PubMed]
  28. Cole, S.L.; Cybulski, V.A.; Whitacre, M.; Lathrop, S.K.; Bazin-Lee, H.; Burkhart, D.; Evans, J.T. Influenza vaccines using liposomal formulations of toll-like receptor (TLR) 7/8 and 4 agonists as adjuvants. J. Immunol. 2020, 204, 212–245. [Google Scholar]
  29. Van Hoeven, N.; Fox, C.B.; Granger, B.; Evers, T.; Joshi, S.W.; Nana, G.I.; Evans, S.C.; Lin, S.; Liang, H.; Liang, L.; et al. A Formulated TLR7/8 Agonist is a Flexible, Highly Potent and Effective Adjuvant for Pandemic Influenza Vaccines. Sci. Rep. 2017, 7, 46426. [Google Scholar] [CrossRef]
  30. Goff, P.H.; Hayashi, T.; Martínez-Gil, L.; Corr, M.; Crain, B.; Yao, S.; Cottam, H.B.; Chan, M.; Ramos, I.; Eggink, D.; et al. Synthetic Toll-Like Receptor 4 (TLR4) and TLR7 Ligands as Influenza Virus Vaccine Adjuvants Induce Rapid, Sustained, and Broadly Protective Responses. J. Virol. 2015, 89, 3221–3235. [Google Scholar] [CrossRef] [Green Version]
  31. Kaushik, D.; Dhingra, S.; Patil, M.T.; Piplani, S.; Khanna, V.; Honda-Okubo, Y.; Li, L.; Fung, J.; Sakala, I.G.; Salunke, D.B.; et al. BBIQ, a pure TLR7 agonist, is an effective influenza vaccine adjuvant. Hum. Vaccines Immunother. 2020, 16, 1989–1996. [Google Scholar] [CrossRef] [Green Version]
  32. Ichinohe, T.; Tamura, S.-I.; Kawaguchi, A.; Ninomiya, A.; Imai, M.; Itamura, S.; Odagiri, T.; Tashiro, M.; Takahashi, H.; Sawa, H.; et al. Cross-Protection against H5N1 Influenza Virus Infection Is Afforded by Intranasal Inoculation with Seasonal Trivalent Inactivated Influenza Vaccine. J. Infect. Dis. 2007, 196, 1313–1320. [Google Scholar] [CrossRef]
  33. Renu, S.; Feliciano-Ruiz, N.; Ghimire, S.; Han, Y.; Schrock, J.; Dhakal, S.; Patil, V.; Krakowka, S.; Renukaradhya, G.J. Poly(I:C) augments inactivated influenza virus-chitosan nanovaccine induced cell mediated immune response in pigs vaccinated intranasally. Veter Microbiol. 2020, 242, 108611. [Google Scholar] [CrossRef]
  34. Kim, E.-D.; Han, S.J.; Byun, Y.-H.; Yoon, S.; Choi, K.S.; Seong, B.L.; Seo, K.Y. Inactivated Eyedrop Influenza Vaccine Adjuvanted with Poly(I:C) Is Safe and Effective for Inducing Protective Systemic and Mucosal Immunity. PLoS ONE 2015, 10, e0137608. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  35. Zhang, A.; Lai, H.; Xu, J.; Huang, W.; Liu, Y.; Zhao, D.; Chen, R. Evaluation of the Protective Efficacy of Poly I:C as an Adjuvant for H9N2 Subtype Avian Influenza Inactivated Vaccine and Its Mechanism of Action in Ducks. PLoS ONE 2017, 12, e0170681. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  36. Huleatt, J.W.; Nakaar, V.; Desai, P.; Huang, Y.; Hewitt, D.; Jacobs, A.; Tang, J.; McDonald, W.; Song, L.; Evans, R.K.; et al. Potent immunogenicity and efficacy of a universal influenza vaccine candidate comprising a recombinant fusion protein linking influenza M2e to the TLR5 ligand flagellin. Vaccine 2008, 26, 201–214. [Google Scholar] [CrossRef] [PubMed]
  37. Wang, B.; Gill, H.S.; He, C.; Ou, C.; Wang, L.; Wang, Y.-C.; Feng, H.; Zhang, H.; Prausnitz, M.R.; Compans, R.W. Microneedle delivery of an M2e-TLR5 ligand fusion protein to skin confers broadly cross-protective influenza immunity. J. Control. Release 2014, 178, 1–7. [Google Scholar] [CrossRef] [Green Version]
  38. Wang, B.; Xu, R.; Quan, F.-S.; Kang, S.-M.; Wang, L.; Compans, R.W. Intranasal Immunization with Influenza VLPs Incorporating Membrane-Anchored Flagellin Induces Strong Heterosubtypic Protection. PLoS ONE 2010, 5, e13972. [Google Scholar] [CrossRef] [Green Version]
  39. Wang, B.; Quan, F.-S.; Kang, S.-M.; Bozja, J.; Skountzou, I.; Compans, R.W. Incorporation of Membrane-Anchored Flagellin into Influenza Virus-Like Particles Enhances the Breadth of Immune Responses. J. Virol. 2008, 82, 11813–11823. [Google Scholar] [CrossRef] [Green Version]
  40. Wang, B.-Z.; Gill, H.S.; Kang, S.-M.; Wang, L.; Wang, Y.-C.; Vassilieva, E.V.; Compans, R.W. Enhanced Influenza Virus-Like Particle Vaccines Containing the Extracellular Domain of Matrix Protein 2 and a Toll-Like Receptor Ligand. Clin. Vaccine Immunol. 2012, 19, 1119–1125. [Google Scholar] [CrossRef] [Green Version]
  41. Deng, L.; Kim, J.R.; Chang, T.Z.; Zhang, H.; Mohan, T.; Champion, J.A.; Wang, B. Protein nanoparticle vaccine based on flagellin carrier fused to influenza conserved epitopes confers full protection against influenza A virus challenge. Virology 2017, 509, 82–89. [Google Scholar] [CrossRef]
  42. Wang, C.; Zhu, W.; Luo, Y.; Wang, B. Gold nanoparticles conjugating recombinant influenza hemagglutinin trimers and flagellin enhanced mucosal cellular immunity. Nanomed. Nanotechnol. Biol. Med. 2018, 14, 1349–1360. [Google Scholar] [CrossRef]
  43. Zhu, W.; Pewin, W.; Wang, C.; Luo, Y.; Gonzalez, G.X.; Mohan, T.; Prausnitz, M.R.; Wang, B. A boosting skin vaccination with dissolving microneedle patch encapsulating M2e vaccine broadens the protective efficacy of conventional influenza vaccines. J. Control. Release 2017, 261, 1–9. [Google Scholar] [CrossRef]
  44. Zhu, W.; Li, S.; Wang, C.; Yu, G.; Prausnitz, M.R.; Wang, B. Enhanced Immune Responses Conferring Cross-Protection by Skin Vaccination With a Tri-Component Influenza Vaccine Using a Microneedle Patch. Front. Immunol. 2018, 9, 1705. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  45. Turley, C.B.; Rupp, R.; Johnson, C.; Taylor, D.N.; Wolfson, J.; Tussey, L.; Kavita, U.; Stanberry, L.; Shaw, A. Safety and immunogenicity of a recombinant M2e–flagellin influenza vaccine (STF2.4xM2e) in healthy adults. Vaccine 2011, 29, 5145–5152. [Google Scholar] [CrossRef] [PubMed]
  46. Vassilieva, E.V.; Wang, B.; Vzorov, A.N.; Wang, L.; Wang, Y.-C.; Bozja, J.; Xu, R.; Compans, R.W. Enhanced Mucosal Immune Responses to HIV Virus-Like Particles Containing a Membrane-Anchored Adjuvant. mBio 2011, 2, e00328-10. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  47. Vogel, A.J.; Brown, D.M. Single-Dose CpG Immunization Protects Against a Heterosubtypic Challenge and Generates Antigen-Specific Memory T Cells. Front. Immunol. 2015, 6, 327. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  48. Kang, S.-M.; Ko, E.-J.; Lee, Y.; Kim, K.-H. Immunology of vaccine adjuvants enhancing respiratory viral vaccine efficacy. J. Immunol. 2020, 204, 224–245. [Google Scholar]
  49. Lampe, A.T.; Clark, M.; Brown, D.M. Combined CpG and MPL as vaccine adjuvants improve duration of protection induced by single dose influenza A virus protein vaccination. J. Immunol. 2020, 204, 245–246. [Google Scholar]
  50. Beljanski, V.; Chiang, C.; Kirchenbaum, G.A.; Olagnier, D.; Bloom, C.E.; Wong, T.; Haddad, E.K.; Trautmann, L.; Ross, T.M.; Hiscott, J. Enhanced Influenza Virus-Like Particle Vaccination with a Structurally Optimized RIG-I Agonist as Adjuvant. J. Virol. 2015, 89, 10612–10624. [Google Scholar] [CrossRef] [Green Version]
  51. Toy, R.; Keenum, M.C.; Pradhan, P.; Phang, K.; Chen, P.; Chukwu, C.; Nguyen, L.A.H.; Liu, J.; Jain, S.; Kozlowski, G.; et al. TLR7 and RIG-I dual-adjuvant loaded nanoparticles drive broadened and synergistic responses in dendritic cells in vitro and generate unique cellular immune responses in influenza vaccination. J. Control. Release 2020. [Google Scholar] [CrossRef]
  52. Yong, H.Y.; Luo, D. RIG-I-Like Receptors as Novel Targets for Pan-Antivirals and Vaccine Adjuvants Against Emerging and Re-Emerging Viral Infections. Front. Immunol. 2018, 9, 1379. [Google Scholar] [CrossRef] [Green Version]
  53. Moriyama, M.; Koshiba, T.; Ichinohe, T. Influenza A virus M2 protein triggers mitochondrial DNA-mediated antiviral immune responses. Nat. Commun. 2019, 10, 1–14. [Google Scholar] [CrossRef] [Green Version]
  54. Wang, J.; Li, P.; Wu, M.X. Natural STING Agonist as an “Ideal” Adjuvant for Cutaneous Vaccination. J. Investig. Dermatol. 2016, 136, 2183–2191. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  55. Wang, J.; Li, P.; Yu, Y.; Fu, Y.; Jiang, H.; Lu, M.; Sun, Z.; Jiang, S.; Lu, L.; Wu, M.X. Pulmonary surfactant–biomimetic nanoparticles potentiate heterosubtypic influenza immunity. Science 2020, 367, eaau0810. [Google Scholar] [CrossRef] [PubMed]
  56. Yi, C.; Yi, Y.; Li, J.; Sacitharan, P.K. Protecting against different subtypes of influenza viruses: A nanoparticle approach. Signal Transduct. Target. Ther. 2020, 5, 1–2. [Google Scholar] [CrossRef] [PubMed]
  57. Luo, J.; Liu, X.-P.; Xiong, F.-F.; Gao, F.-X.; Yi, Y.-L.; Zhang, M.; Chen, Z.; Tan, W.-S. Enhancing Immune Response and Heterosubtypic Protection Ability of Inactivated H7N9 Vaccine by Using STING Agonist as a Mucosal Adjuvant. Front. Immunol. 2019, 10, 2274. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  58. Strowig, T.; Henao-Mejia, J.; Elinav, E.; Flavell, R. Inflammasomes in health and disease. Nat. Cell Biol. 2012, 481, 278–286. [Google Scholar] [CrossRef]
  59. Schroder, K.; Tschopp, J. The Inflammasomes. Cell 2010, 140, 821–832. [Google Scholar] [CrossRef] [Green Version]
  60. Li, H.; Nookala, S.; Re, F. Aluminum Hydroxide Adjuvants Activate Caspase-1 and Induce IL-1β and IL-18 Release. J. Immunol. 2007, 178, 5271–5276. [Google Scholar] [CrossRef]
  61. Marty-Roix, R.; Vladimer, G.I.; Pouliot, K.; Weng, D.; Buglione-Corbett, R.; West, K.; MacMicking, J.D.; Chee, J.D.; Wang, S.; Lu, S.; et al. Identification of QS-21 as an Inflammasome-activating Molecular Component of Saponin Adjuvants. J. Biol. Chem. 2015, 291, 1123–1136. [Google Scholar] [CrossRef] [Green Version]
  62. Bueter, C.L.; Lee, C.K.; Rathinam, V.A.K.; Healy, G.J.; Taron, C.H.; Specht, C.A.; Levitz, S.M. Chitosan but Not Chitin Activates the Inflammasome by a Mechanism Dependent upon Phagocytosis. J. Biol. Chem. 2011, 286, 35447–35455. [Google Scholar] [CrossRef] [Green Version]
  63. Ivanov, K.; Garanina, E.E.; Rizvanov, A.; Khaiboullina, S.F. Inflammasomes as Targets for Adjuvants. Pathogens 2020, 9, 252. [Google Scholar] [CrossRef] [Green Version]
  64. Vijay-Kumar, M.; Carvalho, F.A.; Aitken, J.D.; Fifadara, N.H.; Gewirtz, A.T. TLR5 or NLRC4 is necessary and sufficient for promotion of humoral immunity by flagellin. Eur. J. Immunol. 2010, 40, 3528–3534. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  65. Yamazaki, T.; Ichinohe, T. Inflammasomes in antiviral immunity: Clues for influenza vaccine development. Clin. Exp. Vaccine Res. 2014, 3, 5–11. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  66. Poeck, H.; Bscheider, M.; Gross, O.; Finger, K.; Roth, S.; Rebsamen, M.; Hannesschläger, N.; Schlee, M.; Rothenfusser, S.; Barchet, W.; et al. Recognition of RNA virus by RIG-I results in activation of CARD9 and inflammasome signaling for interleukin 1β production. Nat. Immunol. 2010, 11, 63–69. [Google Scholar] [CrossRef]
  67. Hornung, V.; Ablasser, A.; Charrel-Dennis, M.; Bauernfeind, F.G.; Horvath, G.; Caffrey, D.R.; Latz, E.; Fitzgerald, K.A. AIM2 recognizes cytosolic dsDNA and forms a caspase-1-activating inflammasome with ASC. Nat. Cell Biol. 2009, 458, 514–518. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  68. Allen, I.C.; Scull, M.A.; Moore, C.B.; Holl, E.K.; McElvania-TeKippe, E.; Taxman, D.J.; Guthrie, E.H.; Pickles, R.J.; Ting, J. The NLRP3 Inflammasome Mediates In Vivo Innate Immunity to Influenza A Virus through Recognition of Viral RNA. Immunity 2009, 30, 556–565. [Google Scholar] [CrossRef] [Green Version]
  69. Thomas, P.G.; Dash, P.; Aldridge, J.R.; Ellebedy, A.H.; Reynolds, C.; Funk, A.J.; Martin, W.J.; Lamkanfi, M.; Webby, R.J.; Boyd, K.L.; et al. The Intracellular Sensor NLRP3 Mediates Key Innate and Healing Responses to Influenza A Virus via the Regulation of Caspase. Immunity 2009, 30, 566–575. [Google Scholar] [CrossRef] [Green Version]
  70. Ichinohe, T.; Lee, H.K.; Ogura, Y.; Flavell, R.; Iwasaki, A. Inflammasome recognition of influenza virus is essential for adaptive immune responses. J. Exp. Med. 2009, 206, 79–87. [Google Scholar] [CrossRef] [Green Version]
  71. Chothe, S.K.; Nissly, R.H.; Lim, L.; Bhushan, G.; Bird, I.; Radzio-Basu, J.; Jayarao, B.M.; Kuchipudi, S.V. NLRC5 Serves as a Pro-viral Factor During Influenza Virus Infection in Chicken Macrophages. Front. Cell. Infect. Microbiol. 2020, 10, 230. [Google Scholar] [CrossRef]
  72. Gaya, M.; Barral, P.; Burbage, M.; Aggarwal, S.; Montaner, B.; Navia, A.W.; Aid, M.; Tsui, C.; Maldonado, P.; Nair, U.; et al. Initiation of Antiviral B Cell Immunity Relies on Innate Signals from Spatially Positioned NKT Cells. Cell 2018, 172, 517–533.e20. [Google Scholar] [CrossRef] [Green Version]
  73. Fang, Y.; Xiang, Z. Roles and relevance of mast cells in infection and vaccination. J. Biomed. Res. 2016, 30, 253–263. [Google Scholar] [CrossRef] [Green Version]
  74. McLachlan, J.B.; Shelburne, C.P.; Hart, J.P.; Pizzo, S.V.; Goyal, R.; Brooking-Dixon, R.; Staats, H.F.; Abraham, S.N. Mast cell activators: A new class of highly effective vaccine adjuvants. Nat. Med. 2008, 14, 536–541. [Google Scholar] [CrossRef] [PubMed]
  75. Meng, S.; Liu, Z.; Xu, L.; Li, L.; Mei, S.; Bao, L.; Deng, W.; Li, L.; Lei, R.; Xie, L.; et al. Intranasal Immunization with Recombinant HA and Mast Cell Activator C48/80 Elicits Protective Immunity against 2009 Pandemic H1N1 Influenza in Mice. PLoS ONE 2011, 6, e19863. [Google Scholar] [CrossRef] [PubMed]
  76. Kayamuro, H.; Yoshioka, Y.; Abe, Y.; Arita, S.; Katayama, K.; Nomura, T.; Yoshikawa, T.; Kubota-Koketsu, R.; Ikuta, K.; Okamoto, S.; et al. Interleukin-1 Family Cytokines as Mucosal Vaccine Adjuvants for Induction of Protective Immunity against Influenza Virus. J. Virol. 2010, 84, 12703–12712. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  77. Tschopp, J.; Schroder, K. NLRP3 inflammasome activation: The convergence of multiple signalling pathways on ROS production? Nat. Rev. Immunol. 2010, 10, 210–215. [Google Scholar] [CrossRef] [PubMed]
  78. Lapuente, D.; Bonsmann, M.S.G.; Maaske, A.; Stab, V.; Heinecke, V.; Watzstedt, K.; Heß, R.; Westendorf, A.M.; Bayer, W.; Ehrhardt, C.; et al. IL-1β as mucosal vaccine adjuvant: The specific induction of tissue-resident memory T cells improves the heterosubtypic immunity against influenza A viruses. Mucosal Immunol. 2018, 11, 1265–1278. [Google Scholar] [CrossRef] [Green Version]
  79. John, A.L.S.; Chan, C.Y.; Staats, H.F.; Leong, K.W.; Abraham, S.N. Synthetic mast-cell granules as adjuvants to promote and polarize immunity in lymph nodes. Nat. Mater. 2012, 11, 250–257. [Google Scholar] [CrossRef] [Green Version]
  80. Van De Laar, L.; Coffer, P.; Woltman, A.M. Regulation of dendritic cell development by GM-CSF: Molecular control and implications for immune homeostasis and therapy. Blood 2012, 119, 3383–3393. [Google Scholar] [CrossRef]
  81. Littauer, E.Q.; Mills, L.K.; Brock, N.; Esser, E.S.; Romanyuk, A.; Pulit-Penaloza, J.A.; Vassilieva, E.V.; Beaver, J.T.; Antao, O.; Krammer, F.; et al. Stable incorporation of GM-CSF into dissolvable microneedle patch improves skin vaccination against influenza. J. Control. Release 2018, 276, 1–16. [Google Scholar] [CrossRef]
  82. Feng, H.; Zhang, H.; Deng, J.; Wang, L.; He, Y.; Wang, S.; Seyedtabaei, R.; Wang, Q.; Liu, L.; Galipeau, J.; et al. Incorporation of a GPI-anchored engineered cytokine as a molecular adjuvant enhances the immunogenicity of HIV VLPs. Sci. Rep. 2015, 5, 11856. [Google Scholar] [CrossRef]
  83. Mohan, T.; Zhu, W.; Wang, Y.; Wang, B. Applications of chemokines as adjuvants for vaccine immunotherapy. Immunobiology 2018, 223, 477–485. [Google Scholar] [CrossRef]
  84. Mohan, T.; Kim, C.H.; Berman, Z.; Wang, S.; Compans, R.W.; Wang, B. Co-delivery of GPI-anchored CCL28 and influenza HA in chimeric virus-like particles induces cross-protective immunity against H3N2 viruses. J. Control. Release 2016, 233, 208–219. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  85. Tao, W.; Ziemer, K.S.; Gill, H.S. Gold nanoparticle–M2e conjugate coformulated with CpG induces protective immunity against influenza A virus. Nanomedicine 2014, 9, 237–251. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  86. Wang, C.; Zhu, W.; Wang, B. Dual-linker gold nanoparticles as adjuvanting carriers for multivalent display of recombinant influenza hemagglutinin trimers and flagellin improve the immunological responses in vivo and in vitro. Int. J. Nanomed. 2017, 12, 4747–4762. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  87. Xu, L.; Liu, Y.; Chen, Z.; Li, W.; Liu, Y.; Wang, L.; Liu, Y.; Wu, X.; Ji, Y.; Zhao, Y.; et al. Surface-Engineered Gold Nanorods: Promising DNA Vaccine Adjuvant for HIV-1 Treatment. Nano Lett. 2012, 12, 2003–2012. [Google Scholar] [CrossRef] [PubMed]
  88. Shirai, S.; Shibuya, M.; Kawai, A.; Tamiya, S.; Munakata, L.; Omata, D.; Suzuki, R.; Aoshi, T.; Yoshioka, Y. Lipid Nanoparticles Potentiate CpG-Oligodeoxynucleotide-Based Vaccine for Influenza Virus. Front. Immunol. 2020, 10, 3018. [Google Scholar] [CrossRef]
  89. Pardi, N.; Parkhouse, K.; Kirkpatrick, E.; McMahon, M.; Zost, S.J.; Mui, B.L.; Tam, Y.K.; Karikó, K.; Barbosa, C.J.; Madden, T.D.; et al. Nucleoside-modified mRNA immunization elicits influenza virus hemagglutinin stalk-specific antibodies. Nat. Commun. 2018, 9, 1–12. [Google Scholar] [CrossRef] [Green Version]
  90. Freyn, A.W.; Da Silva, J.R.; Rosado, V.C.; Bliss, C.M.; Pine, M.; Mui, B.L.; Tam, Y.K.; Madden, T.D.; Ferreira, L.C.D.S.; Weissman, D.; et al. A Multi-Targeting, Nucleoside-Modified mRNA Influenza Virus Vaccine Provides Broad Protection in Mice. Mol. Ther. 2020, 28, 1569–1584. [Google Scholar] [CrossRef]
  91. Pardi, N.; Hogan, M.J.; Naradikian, M.S.; Parkhouse, K.; Cain, D.W.; Jones, L.; Moody, M.A.; Verkerke, H.P.; Myles, A.; Willis, E.; et al. Nucleoside-modified mRNA vaccines induce potent T follicular helper and germinal center B cell responses. J. Exp. Med. 2018, 215, 1571–1588. [Google Scholar] [CrossRef]
  92. Zhuang, X.; Qi, Y.; Wang, M.; Yu, N.; Nan, F.; Zhang, H.; Tian, M.; Li, C.; Lu, H.; Jin, N. mRNA Vaccines Encoding the HA Protein of Influenza A H1N1 Virus Delivered by Cationic Lipid Nanoparticles Induce Protective Immune Responses in Mice. Vaccines 2020, 8, 123. [Google Scholar] [CrossRef] [Green Version]
  93. Deng, L.; Mohan, T.; Chang, T.Z.; Gonzalez, G.X.; Wang, Y.; Kwon, Y.-M.; Kang, S.-M.; Compans, R.W.; Champion, J.A.; Wang, B. Double-layered protein nanoparticles induce broad protection against divergent influenza A viruses. Nat. Commun. 2018, 9, 1–12. [Google Scholar] [CrossRef]
  94. Wang, Y.; Deng, L.; Gonzalez, G.X.; Luthra, L.; Dong, C.; Ma, Y.; Zou, J.; Kang, S.; Wang, B. Double-Layered M2e-NA Protein Nanoparticle Immunization Induces Broad Cross-Protection against Different Influenza Viruses in Mice. Adv. Health Mater. 2020, 9, e1901176. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  95. Deng, L.; Chang, T.Z.; Wang, Y.; Li, S.; Wang, S.; Matsuyama, S.; Yu, G.; Compans, R.W.; Li, J.-D.; Prausnitz, M.R.; et al. Heterosubtypic influenza protection elicited by double-layered polypeptide nanoparticles in mice. Proc. Natl. Acad. Sci. USA 2018, 115, E7758–E7767. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  96. Sanchez-Guzman, D.; Le Guen, P.; Villeret, B.; Sola, N.; Le Borgne, R.; Guyard, A.; Kemmel, A.; Crestani, B.; Sallenave, J.-M.; Garcia-Verdugo, I. Silver nanoparticle-adjuvanted vaccine protects against lethal influenza infection through inducing BALT and IgA-mediated mucosal immunity. Biomaterials 2019, 217, 119308. [Google Scholar] [CrossRef]
  97. Jazayeri, S.D.; Ideris, A.; Zakaria, Z.; Shameli, K.; Moeini, H.; Omar, A.R. Cytotoxicity and immunological responses following oral vaccination of nanoencapsulated avian influenza virus H5 DNA vaccine with green synthesis silver nanoparticles. J. Control. Release 2012, 161, 116–123. [Google Scholar] [CrossRef]
  98. Knuschke, T.; Sokolova, V.; Rotan, O.; Wadwa, M.; Tenbusch, M.; Hansen, W.; Staeheli, P.; Epple, M.; Buer, J.; Westendorf, A.M. Immunization with Biodegradable Nanoparticles Efficiently Induces Cellular Immunity and Protects against Influenza Virus Infection. J. Immunol. 2013, 190, 6221–6229. [Google Scholar] [CrossRef] [Green Version]
  99. Mody, K.T.; Popat, A.; Mahony, D.; Cavallaro, A.S.; Yu, C.; Mitter, N. Mesoporous silica nanoparticles as antigen carriers and adjuvants for vaccine delivery. Nanoscale 2013, 5, 5167–5179. [Google Scholar] [CrossRef] [PubMed]
  100. Lin, Y.; Wang, X.; Huang, X.; Zhang, J.; Xia, N.; Zhao, Q. Calcium phosphate nanoparticles as a new generation vaccine adjuvant. Expert Rev. Vaccines 2017, 16, 895–906. [Google Scholar] [CrossRef]
  101. Bengtsson, K.L.; Morein, B.; Osterhaus, A.D.M.E. ISCOM technology-based Matrix M™ adjuvant: Success in future vaccines relies on formulation. Expert Rev. Vaccines 2011, 10, 401–403. [Google Scholar] [CrossRef]
  102. Cox, R.J.; Pedersen, G.K.; Madhun, A.S.; Svindland, S.; Sævik, M.; Breakwell, L.; Hoschler, K.; Willemsen, M.; Campitelli, L.; Nøstbakken, J.K.; et al. Evaluation of a virosomal H5N1 vaccine formulated with Matrix M™ adjuvant in a phase I clinical trial. Vaccine 2011, 29, 8049–8059. [Google Scholar] [CrossRef]
  103. De Matteis, V. Exposure to Inorganic Nanoparticles: Routes of Entry, Immune Response, Biodistribution and In Vitro/In Vivo Toxicity Evaluation. Toxics 2017, 5, 29. [Google Scholar] [CrossRef] [Green Version]
  104. Mohammadpour, R.; Dobrovolskaia, M.A.; Cheney, D.L.; Greish, K.F.; Ghandehari, H. Subchronic and chronic toxicity evaluation of inorganic nanoparticles for delivery applications. Adv. Drug Deliv. Rev. 2019, 144, 112–132. [Google Scholar] [CrossRef] [PubMed]
  105. Makadia, H.K.; Siegel, S.J. Poly Lactic-co-Glycolic Acid (PLGA) as Biodegradable Controlled Drug Delivery Carrier. Polymers 2011, 3, 1377–1397. [Google Scholar] [CrossRef] [PubMed]
Pharmaceutics 13 00068 g001 550
Figure 1. A diagram of different self-adjuvanted nanoparticle (NP) platforms. (A) Au NPs. (B) virus-like particles (VLP)s. (C) Protein NPs. (D) biodegradable synthetic polymeric (PLGA) NPs. (E) Lipid NPs.
Figure 1. A diagram of different self-adjuvanted nanoparticle (NP) platforms. (A) Au NPs. (B) virus-like particles (VLP)s. (C) Protein NPs. (D) biodegradable synthetic polymeric (PLGA) NPs. (E) Lipid NPs.
Pharmaceutics 13 00068 g001
Table
Table 1. Advantages and disadvantages of licensed influenza adjuvants.
Table 1. Advantages and disadvantages of licensed influenza adjuvants.
AdjuvantsAdvantagesDisadvantages
Aluminium Saltsa. Have minor toxicities.
b. Improve antigen uptake.
c. Increase immune responses.		a. Fail to induce cytotoxic T cell response.
b. Ineffective with weak antigens.
Oil-in-water emulsionsa. Induce stronger immune responses including both humoral and cellular immune responses.
b. Dose sparing.
c.Work efficient with less immunogenic antigens.		a. Highly local reactogenicity.
b. Cause systemic symptoms.
c. Induce autoimmune disease.
Virosomesa. Appropriate to wide age groups;
b. Facilitate antigen stability,
c. Excellent safety profile
d. Long-lasting antibody responses 		a. Unstable in blood.
b. Production and preservation problems.
Heat labile enterotoxina. Applicate as mucosal adjuvant a. Development of Bell’s palsy
Table
Table 2. Potential influenza adjuvants base on immune responses.
Table 2. Potential influenza adjuvants base on immune responses.
TLRs AgonistsTLR3 agonist-poly I:C [25,26,27,28]
TLR9 agonist-CpG [38,39,40]
TLR4 agonist-MPL, 1Z105 [20,22,24]
TLR5 agonist-FliC [29,30,31,32,33,34,35,36,37]
TLR7/8 agonist-R837, TRAC-478, 1V270 [20,21,22,23,24]
Cytosolic Nucleic AcidsRLRs receptor agonists: dsRNAs, Small nucleic acids compounds, ploy I:C [41,42,43]
STING agonist-cGAMP [45,46,47,48]
Inflammasomes AgonistsNLRC4 inflammasome-FliC [55]
NLRP3 or AIM2 inflammasomes-Nucleic acids (DNA and RNA) [56,57,58]
Immune Cells ActivatoriNKT cells activator- α-GalCer [63]
Mast cells activator-C48/80, IL-33, IL-18 [64,65,66,67]
Cytokines and ChemokinesIL-1β [68,69]
TNF [65,67]
GM-CSF, GIFT4 [71,72,73]
CCL27, CCL28 [74,75]
Abbreviations: TLRs, Toll-like receptors; RLRs, RIG-I-like receptors; STING, Stimulator of interferon genes; cGAMP, 2’3’-cyclic GMP-AMP; NLRC4, NLR-family CARD domain-containing protein 4; NLRP3, NOD-like receptor protein 3; iNKT cells, Invariant (i) natural killer T cells; α-GalCer, Glycolipid ligand α-galactosylceramide; TNF, Tumor necrosis factor; GM-CSF, Granulocyte-macrophage colony-stimulating factor.
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Share and Cite

MDPI and ACS Style

Zhu, W.; Dong, C.; Wei, L.; Wang, B.-Z. Promising Adjuvants and Platforms for Influenza Vaccine Development. Pharmaceutics 2021, 13, 68. https://doi.org/10.3390/pharmaceutics13010068

AMA Style

Zhu W, Dong C, Wei L, Wang B-Z. Promising Adjuvants and Platforms for Influenza Vaccine Development. Pharmaceutics. 2021; 13(1):68. https://doi.org/10.3390/pharmaceutics13010068

Chicago/Turabian Style

Zhu, Wandi, Chunhong Dong, Lai Wei, and Bao-Zhong Wang. 2021. "Promising Adjuvants and Platforms for Influenza Vaccine Development" Pharmaceutics 13, no. 1: 68. https://doi.org/10.3390/pharmaceutics13010068

APA Style

Zhu, W., Dong, C., Wei, L., & Wang, B. -Z. (2021). Promising Adjuvants and Platforms for Influenza Vaccine Development. Pharmaceutics, 13(1), 68. https://doi.org/10.3390/pharmaceutics13010068

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Metrics

Back to TopTop