S100A4 exerts robust mucosal adjuvant activity for co-administered antigens in mice

The lack of clinically applicable mucosal adjuvants is a major hurdle in designing effective mucosal vaccines. We hereby report that the calcium-binding protein S100A4, which regulates a wide range of biological functions, is a potent mucosal adjuvant in mice for co-administered antigens, including the SARS-CoV-2 spike protein, with comparable or even superior efficacy as cholera toxin but without causing any adverse reactions. Intranasal immunization with recombinant S100A4 elicited antigen-specific antibody and pulmonary cytotoxic T cell responses, and these responses were remarkably sustained for longer than six months. As a self-protein, S100A4 did not stimulate antibody responses against itself, a quality desired of adjuvants. S100A4 prolonged nasal residence of intranasally delivered antigens and promoted migration of antigen-presenting cells. S100A4-pulsed dendritic cells potently activated cognate T cells. Furthermore, S100A4 induced strong germinal center responses revealed by both microscopy and mass spectrometry, a novel technique for measuring germinal center activity. In conclusion, S100A4 may be a promising adjuvant in formulating mucosal vaccines, including vaccines against pathogens that infect via the respiratory tract, such as SARS-CoV-2.

Activation of mucosal immunity and novel prophylactic and therapeutic strategy in combating COVID-19

Coronavirus disease 2019 (COVID-19) emerges as an expeditiously growing pandemic, in the human population caused by the highly transmissible RNA virus severe acute respiratory syndrome of coronavirus 2 (SARS-CoV-2). Prognosis of SARS-CoV-2 infection predominantly occurs at the angiotensin-converting enzyme 2 receptor and transmembrane protease serine type 2 positive (ACE2 + TMPRSS2)+ epithelial cells of the mucosal surface like nasal, oral mucosae, and/or the conjunctival surface of the eye where it has interacted along with the immune system. The primary host response towards the pathogen starts from an immune microenvironment of nasopharynx-associated lymphoid tissue (NALT) and mucosa-associated lymphoid tissue (MALT). The presence of exhausted lymphocytes, lymphopenia, pneumonia and cytokine storm is the hallmark of COVID-19. The multifaceted nature of co-morbidity factors like obesity and type 2 diabetes and its effects on immunity can alter the pathogenesis of SARS-CoV-2 infection. Adipose tissue is a crucial endocrine organ that secretes a plethora of factors like adipokines, cytokines, and chemokines that have a profound impact on metabolism and augments the expression of mucosal pro-inflammatory cytokines, like tumor necrosis factor-alpha (TNF-α), interferon-gamma (IFN-γ), and the interleukin-12 (IL-12)/IL-23. Mucosal immunization could be a superior approach to activate mucosal and systemic immune responses against pathogenic invasion at mucosal surface entry ports. Mucosal vaccines are also able to generate strong systemic humoral immunity—required to neutralize any virus particle that dodges the primary immune response. To develop an efficient vaccine against mucosal pathogens, considering the designing of the delivery route, immunomodulatory features, and adjuvants are very important. In this article, we further provide evidence to understand the significant role of mucosal immunity, along with secretory and circulating immunoglobulin A (IgA) antibodies in generating a novel mucosal vaccine against COVID-19. Moreover, along with mucosal vaccines, we should look for combination treatment strategies with plant bioactive molecules. Glycan-binding lectins against viral proteins for targeted activation of mucosal immune response are one of such examples. This might play a promising role to halt this emerging virus.

Harnessing the Potential of MAIT Cells as Cellular Adjuvants in Mucosal Vaccines

<p>The development of vaccines is considered one of the most successful medical interventions to date, preventing millions of deaths every year. However, the majority of vaccines are administered peritoneally, despite the vast majority of pathogens invade the human host at mucosal sites. By vaccinating at distal sites, little to no protection is developed at the mucosa where the initial invasion occurs. There are however, a handful of licenced mucosally administered vaccines against infections such as poliovirus, influenza and Salmonella Typhi that are able to induce both a systemic and mucosal protective immune response. All but one of the current licenced mucosal vaccines are live attenuated due in part to the difficulty of developing new mucosal adjuvants. Recombinant cholera toxin subunit B is the only adjuvant used in the current licenced mucosal vaccines. While inactivated and subunit vaccines are considered safer as they are unable to revert back to virulent pathogens, adjuvants are required to boost their immunogenicity. This thesis therefore explores whether mucosal-associated invariant T (MAIT) cells which are found in mucosal tissues, are invariant in nature and have rapid activation, could be exploited as cellular adjuvants in mucosal vaccines. This thesis was able to show that intranasally administered MAIT cell agonist components, 5-A-RU and methylglyoxal (MG), are able to induce both MAIT cell and conventional dendritic cell (cDC) activation in the lung tissue and mediastinal lymph node (mLN). In this model CD40L and RANKL co-stimulatory interactions are involved in ICOSL expression on cDCs in the lung and associated with cDC activation. The MAIT cells within this model also maintained a RORyT and GATA3 phenotype after both one and three doses of the 5-A-RU + MG vaccine. Furthermore, a prime-boost intranasal vaccine scheme of 5-A-RU + MG and the model antigen OVA, was able to induce MR1-dependent accumulation of TFH cells and antigen-specific germinal center B cells in the mLN along with systemic antigen-specific IgG antibody production. This humoral response was also dependent on the presence of both cDC1 and cDC2 populations. Together, this thesis suggests MAIT cells have the potential to be utilised as cellular adjuvants in mucosal vaccines.</p>

Harnessing the Potential of MAIT Cells as Cellular Adjuvants in Mucosal Vaccines

<p>The development of vaccines is considered one of the most successful medical interventions to date, preventing millions of deaths every year. However, the majority of vaccines are administered peritoneally, despite the vast majority of pathogens invade the human host at mucosal sites. By vaccinating at distal sites, little to no protection is developed at the mucosa where the initial invasion occurs. There are however, a handful of licenced mucosally administered vaccines against infections such as poliovirus, influenza and Salmonella Typhi that are able to induce both a systemic and mucosal protective immune response. All but one of the current licenced mucosal vaccines are live attenuated due in part to the difficulty of developing new mucosal adjuvants. Recombinant cholera toxin subunit B is the only adjuvant used in the current licenced mucosal vaccines. While inactivated and subunit vaccines are considered safer as they are unable to revert back to virulent pathogens, adjuvants are required to boost their immunogenicity. This thesis therefore explores whether mucosal-associated invariant T (MAIT) cells which are found in mucosal tissues, are invariant in nature and have rapid activation, could be exploited as cellular adjuvants in mucosal vaccines. This thesis was able to show that intranasally administered MAIT cell agonist components, 5-A-RU and methylglyoxal (MG), are able to induce both MAIT cell and conventional dendritic cell (cDC) activation in the lung tissue and mediastinal lymph node (mLN). In this model CD40L and RANKL co-stimulatory interactions are involved in ICOSL expression on cDCs in the lung and associated with cDC activation. The MAIT cells within this model also maintained a RORyT and GATA3 phenotype after both one and three doses of the 5-A-RU + MG vaccine. Furthermore, a prime-boost intranasal vaccine scheme of 5-A-RU + MG and the model antigen OVA, was able to induce MR1-dependent accumulation of TFH cells and antigen-specific germinal center B cells in the mLN along with systemic antigen-specific IgG antibody production. This humoral response was also dependent on the presence of both cDC1 and cDC2 populations. Together, this thesis suggests MAIT cells have the potential to be utilised as cellular adjuvants in mucosal vaccines.</p>

Vaccine Types

Vaccines are biological preparations, often made from attenuated or killed forms of microorganisms or fractions thereof. They work by stimulating the immune system to produce antibodies and cells directed against a particular organism, mimicking "natural infection". Based on their biological and chemical characteristics, vaccines can be categorized into two basic types, "Live-attenuated" (bacterial or viral) vaccines and "inactivated" or "non-live" vaccines. Examples of live-attenuated vaccines include: measles-, mumps-, and rubella-, varicella-, yellow fever-, oral polio- (OPV), rotavirus-, ("nasal-spray") live-attenuated influenza- (LAIV), and BCG-vaccine. Attenuation results in micro-organisms that may still infect and multiply in humans, but they do not cause disease. Some of these vaccines are associated with life-long immunity. Inactivated or non-live vaccines include those against hepatitis A, influenza, pertussis, rabies or the polysaccharide vaccines directed against encapsulated bacteria (Haemophilus influenzae type b, Streptococcus pneumoniae, Neisseria meningitidis). Most non-live vaccines generally require additional doses ("boosters") to maintain long-term protective immunity. There are many other subcategories of these basic groups, like subunit vaccines, whole cell vaccines, toxoid vaccines, polysaccharide vaccines, recombinant protein vaccines, mucosal vaccines, or DNA-, mRNA- and vector-vaccines.

Sublingual Immunization with Chimeric C1q/CD40 Ligand/HIV Virus-like Particles Induces Strong Mucosal Immune Responses against HIV

Development of a vaccine that can elicit robust HIV specific antibody responses in the mucosal compartments is desired for effective prevention of HIV via sexual transmission. However, the current mucosal vaccines have either poor immunogenicity when administered orally or invite safety concerns when administered intranasally. Sublingual immunization has received more attention in recent years based on its efficiency in inducing systemic and mucosal immune responses in both mucosal and extra-mucosal tissues. To facilitate the transport of the immunogen across the sub-mucosal epithelial barrier, we found that CD91, the receptor of C1q, is prevalently expressed in the sublingual mucosal lining, and thus, a modified chimeric C1q surface conjugated CD40L/HIV VLP was generated. The ability of this chimeric C1q/CD40L/HIV VLP to bind, cross the epithelial layer, access and activate the sub-mucosal layer dendritic cells (DCs), and ultimately induce enhanced mucosal and systemic immune responses against HIV is evaluated in this study. We found that C1q/CD40L/HIV VLPs have enhanced binding, increased transport across the epithelial layer, and upregulate DC activation markers as compared to CD40L/HIV VLPs alone. Mice immunized with C1q/ CD40L/HIV VLPs by sublingual administration showed higher levels of IgA salivary antibodies against both HIV Gag and Env than mice immunized with CD40L/HIV VLPs. Moreover, sublingual immunization with C1q/CD40L/HIV VLPs induced more Env- and Gag-specific IFN-γ producing T cells than the CD40L/HIV VLPs group. Interestingly, C1q/CD40L/HIV VLP immunization can also induce more mucosal homing T cells than that in CD40L/HIV VLP group. Our data suggest that incorporation of C1q to CD40L/HIV VLPs is a promising novel strategy and that the sublingual immunization can be a favorite immunization route for HIV mucosal vaccines.

Co-Ordination of Mucosal B Cell and CD8 T Cell Memory by Tissue-Resident CD4 Helper T Cells

Adaptive cellular immunity plays a major role in clearing microbial invasion of mucosal tissues in mammals. Following the clearance of primary pathogens, memory lymphocytes are established both systemically and locally at pathogen entry sites. Recently, resident memory CD8 T and B cells (TRM and BRM respectively), which are parked mainly in non-lymphoid mucosal tissues, were characterized and demonstrated to be essential for protection against secondary microbial invasion. Here we reviewed the current understanding of the cellular and molecular cues regulating CD8 TRM and BRM development, maintenance and function. We focused particularly on elucidating the role of a novel tissue-resident helper T (TRH) cell population in assisting TRM and BRM responses in the respiratory mucosa following viral infection. Finally, we argue that the promotion of TRH responses by future mucosal vaccines would be key to the development of successful universal influenza or coronavirus vaccines, providing long-lasting immunity against a broad spectrum of viral strains.

Oral Delivery of Novel Recombinant Lactobacillus Elicit High Protection against Staphylococcus aureus Pulmonary and Skin Infections

Staphylococcus aureus is a leading cause of nosocomial and community-associated infection worldwide; however, there is no licensed vaccine available. S. aureus initiates infection via the mucosa; therefore, a mucosal vaccine is likely to be a promising approach against S. aureus infection. Lactobacilli, a non-pathogenic bacterium, has gained increasing interest as a mucosal delivery vehicle. Hence, we attempted to develop an oral S. aureus vaccine based on lactobacilli to cushion the stress of drug resistance and vaccine needs. In this study, we designed, constructed, and evaluated recombinant Lactobacillus strains synthesizing S. aureus nontoxic mutated α-hemolysins (HlaH35L). The results from animal clinical trials showed that recombinant Lactobacillus can persist for at least 72 h and can stably express heterologous protein in vivo. Recombinant L. plantarum WXD234 (pNZ8148-Hla) could induce robust mucosal immunity in the GALT, as evidenced by a significant increase in IgA and IL-17 production and the strong proliferation of T-lymphocytes derived from Peyer’s patches. WXD234 (pNZ8148-Hla) conferred up to 83% protection against S. aureus pulmonary infection and significantly reduced the abscess size in a S. aureus skin infection model. Of particular interest is the sharp reduction of the protective effect offered by WXD234 (pNZ8148-Hla) vaccination in γδ T cell-deficient or IL-17-deficient mice. In conclusion, for the first time, genetically engineered Lactobacillus WXD234 (pNZ8148-Hla) as an oral vaccine induced superior mucosal immunity, which was associated with high protection against pulmonary and skin infections caused by S. aureus. Taken together, our findings suggest the great potential for a delivery system based on lactobacilli and provide experimental data for the development of mucosal vaccines for S. aureus.

Mucosal vaccines: wisdom from now and then

The oral and nasal cavities are covered by the mucosal epithelium that starts at the beginning of the aero-digestive tract. These mucosal surfaces are continuously exposed to environmental antigens including pathogens and allergens and are thus equipped with a mucosal immune system that mediates initial recognition of pathogenicity and initiates pathogen-specific immune responses. At the dawn of our scientific effort to explore the mucosal immune system, dental science was one of the major driving forces as it provided insights into the importance of mucosal immunity and its application for the control of oral infectious diseases. The development of mucosal vaccines for the prevention of dental caries was thus part of a novel approach that contributed to building the scientific foundations of the mucosal immune system. Since then, mucosal immunology and vaccines have gone on a scientific journey to become one of the major entities within the discipline of immunology. Here, we introduce our past and current efforts and future directions for the development of mucosal vaccines, specifically a rice-based oral vaccine (MucoRice) and a nanogel-based nasal vaccine, with the aim of preventing and controlling gastrointestinal and respiratory infectious diseases using the interdisciplinary fusion of mucosal immunology with agricultural science and biomaterial engineering, respectively.