Vitamins as influenza vaccine adjuvant components

Differences in the microbiome of the small intestine of Leghorn lines divergently selected for antibody titer to sheep erythrocytes suggest roles for commensals in host humoral response

For forty generations, two lines of White Leghorn chickens have been selected for high (HAS) or low (LAS) antibody response to a low dose injection of sheep red blood cells (SRBCs). Their gut is home to billons of microorganisms and the largest number of immune cells in the body; therefore, the objective of this experiment was to gain understanding of the ways the microbiome may influence the differential antibody response observed in these lines. We achieved this by characterizing the small intestinal microbiome of HAS and LAS chickens, determining their functional microbiome profiles, and by using machine learning to identify microbes which best differentiate HAS from LAS and associating the abundance of those microbes with host gene expression. Microbiome sequencing revealed greater diversity in LAS but statistically higher abundance of several strains, particularly those of Lactobacillus, in HAS. Enrichment of microbial metabolites implicated in immune response such as lactic acid, short chain fatty acids, amino acids, and vitamins were different between HAS and LAS. The abundance of several microbial strains corresponds to enriched host gene expression pathways related to immune response. These data provide a compelling argument that the microbiome is both likely affected by host divergent genetic selection and that it exerts influence on host antibody response by various mechanisms.

In silico and in vitro arboviral MHC class I-restricted-epitope signatures reveal immunodominance and poor overlapping patterns

INTRODUCTION

The present work sought to identify MHC-I-restricted peptide signatures for arbovirus using in silico and in vitro peptide microarray tools.

METHODS

First, an in-silico analysis of immunogenic epitopes restricted to four of the most prevalent human MHC class-I was performed by identification of MHC affinity score. For that, more than 10,000 peptide sequences from 5 Arbovirus and 8 different viral serotypes, namely Zika (ZIKV), Dengue (DENV serotypes 1-4), Chikungunya (CHIKV), Mayaro (MAYV) and Oropouche (OROV) viruses, in addition to YFV were analyzed. Haplotype HLA-A*02.01 was the dominant human MHC for all arboviruses. Over one thousand HLA-A2 immunogenic peptides were employed to build a comprehensive identity matrix. Intending to assess HLAA*02:01 reactivity of peptides in vitro, a peptide microarray was designed and generated using a dimeric protein containing HLA-A*02:01.

RESULTS

The comprehensive identity matrix allowed the identification of only three overlapping peptides between two or more flavivirus sequences, suggesting poor overlapping of virus-specific immunogenic peptides amongst arborviruses. Global analysis of the fluorescence intensity for peptide-HLA-A*02:01 binding indicated a dose-dependent effect in the array. Considering all assessed arboviruses, the number of DENV-derived peptides with HLA-A*02:01 reactivity was the highest. Furthermore, a lower number of YFV-17DD overlapping peptides presented reactivity when compared to non-overlapping peptides. In addition, the assessment of HLA-A*02:01-reactive peptides across virus polyproteins highlighted non-structural proteins as "hot-spots". Data analysis supported these findings showing the presence of major hydrophobic sites in the final segment of non-structural protein 1 throughout 2a (Ns2a) and in nonstructural proteins 2b (Ns2b), 4a (Ns4a) and 4b (Ns4b).

DISCUSSION

To our knowledge, these results provide the most comprehensive and detailed snapshot of the immunodominant peptide signature for arbovirus with MHC-class I restriction, which may bring insight into the design of future virus-specific vaccines to arboviruses and for vaccination protocols in highly endemic areas.

SARS-CoV-2 vaccines: What we know, what we can do to improve them and what we could learn from other well-known viruses

In recent weeks, the rate of SARS-CoV-2 infections has been progressively increasing all over the globe, even in countries where vaccination programs have been strongly implemented. In these regions in 2021, a reduction in the number of hospitalizations and deaths compared to 2020 was observed. This decrease is certainly associated with the introduction of vaccination measures. The process of the development of effective vaccines represents an important challenge. Overall, the breakthrough infections occurring in vaccinated subjects are in most cases less severe than those observed in unvaccinated individuals. This review examines the factors affecting the immunogenicity of vaccines against SARS-CoV-2 and the possible role of nutrients in modulating the response of distinct immune cells to the vaccination.

Oil-in-ionic liquid nanoemulsion-based adjuvant simultaneously enhances the stability and immune responses of inactivated foot-and-mouth disease virus

Maintaining structural integrity and enhancing stability of inactivated foot-and-mouth disease virus (iFMDV) antigen in adjuvants is crucial to ensure the vaccine potency. Unfortunately, formulation with most reported adjuvants leads to the accelerated dissociation of iFMDV into inactive pentamers. Here, an ionic liquid, i.e., choline and niacin ([Cho][Nic]), which was found to stabilize iFMDV against the acid- and thermo- induced dissociation in buffer solution, was applied to construct a novel oil-in-ionic liquid (o/IL) nanoemulsion adjuvant composed of [Cho][Nic], squalene, and Tween 80. The o/IL nanoemulsion formulated with iFMDV has a monodisperse diameter of 135.8 ± 40.4 nm. The thermostability and long-term stability of iFMDV were remarkably enhanced in o/IL nanoemulsion compared with that in the o/w emulsion without [Cho][Nic] and in the commercial Montanide ISA 206 adjuvant. The o/IL nanoemulsion exerted its adjuvant effects by improving the humoral immune responses. Immunization of o/IL nanoemulsion adjuvanted iFMDV induced specific IgG titers similar to that adjuvanted by Montanide ISA 206 and about 4-fold higher than the un-adjuvanted iFMDV, also promoted the activation of B lymphocytes and the secretion of interleukin-4 in the mice model. This [Cho][Nic]-based o/IL nanoemulsion can serve as a promising adjuvant platform for the foot-and-mouth disease vaccine.

Immunomodulatory Effects of α-Tocopherol on the H1N1 Influenza Vaccine: Improving the Potency and Efficacy of the Influenza Vaccine in Aged Mice

Declined immune response is the main cause of decreased potency of the influenza vaccine in the elderly, regardless of virus mutations. Herein, we hypothesized that the addition of α-tocopherol to the influenza vaccine formulation might increase vaccine potency and efficacy. Hemagglutinin of the H1N1 virus was formulated in Alum and α-tocopherol, and then aged (16-20-month-old) and young (6-8-week-old) mice were immunized subcutaneously two times with 2-week intervals with 5 μg of different vaccine formulations. Two weeks after the final boosting, IFN-γ and IL-4 cytokines were assessed by using ELISA. Humoral immune responses were assessed by hemagglutination inhibition (HI). In addition, vaccine efficacy was determined by intranasal viral challenge of mice using mouse-adapted H1N1 virus. Our results showed that the new vaccine formulation improved IFN-γ and IL-4 responses in the experimental mice. However, the increase was evident mainly in the aged group and, to some extent, in the young group. Results from the HI assay showed that α-tocopherol in the vaccine formulation could increase HI activity in both young and aged mice. Furthermore, α-tocopherol, as an adjuvant, increased the protectivity of the influenza vaccine in both aged and young groups through the decreased lung viral load and increased survival rate of the experimental mice. In conclusion, it seems that α-tocopherol can not only be used as an appropriate adjuvant for aged people, but also empower old and worn out cells to increase the effectiveness of the vaccine in the elderly.

"World in motion" - emulsion adjuvants rising to meet the pandemic challenges

Emulsion adjuvants such as MF59 and AS03 have been used for more than two decades as key components of licensed vaccines, with over 100 million doses administered to diverse populations in more than 30 countries. Substantial clinical experience of effectiveness and a well-established safety profile, along with the ease of manufacturing have established emulsion adjuvants as one of the leading platforms for the development of pandemic vaccines. Emulsion adjuvants allow for antigen dose sparing, more rapid immune responses, and enhanced quality and quantity of adaptive immune responses. The mechanisms of enhancement of immune responses are well defined and typically characterized by the creation of an "immunocompetent environment" at the site of injection, followed by the induction of strong and long-lasting germinal center responses in the draining lymph nodes. As a result, emulsion adjuvants induce distinct immunological responses, with a mixed Th1/Th2 T cell response, long-lived plasma cells, an expanded repertoire of memory B cells, and high titers of cross-neutralizing polyfunctional antibodies against viral variants. Because of these various properties, emulsion adjuvants were included in pandemic influenza vaccines deployed during the 2009 H1N1 influenza pandemic, are still included in seasonal influenza vaccines, and are currently at the forefront of the development of vaccines against emerging SARS-CoV-2 pandemic variants. Here, we comprehensively review emulsion adjuvants, discuss their mechanism of action, and highlight their profile as a benchmark for the development of additional vaccine adjuvants and as a valuable tool to allow further investigations of the general principles of human immunity.

The cationic liposome CCS/C adjuvant induces immunity to influenza independently of the adaptor protein MyD88

Traditional non-living vaccines are often least effective in the populations that need them most, such as neonates and elderly adults. Vaccine adjuvants are one approach to boost the immunogenicity of antigens in populations with reduced immunity. Ideally, vaccine adjuvants will increase the seroconversion rates across the population, lead to stronger immune responses, and enable the administration of fewer vaccine doses. We previously demonstrated that a cationic liposomal formulation of the commercial influenza split virus vaccine (CCS/C-HA) enhanced cellular and humoral immunity to the virus, increased seroconversion rates, and improved survival after live virus challenge in a preclinical model, as compared to the commercial vaccine as is (F-HA). We now evaluated vaccine efficacy in different strains and sexes of mice and determined the role of innate immunity in the mechanism of action of the CCS/C adjuvant by testing the response of mice deficient in Toll-like receptors or the TLR/IL-1 adaptor protein MyD88 following immunization with CCS/C-HA vs. F-HA. Although TLR2- and TLR4-deficient mice responded to F-HA immunization, F-HA immunization failed to engender a significant immune response in the absence of MyD88. In contrast, immunization with the CCS/C-HA vaccine overcame the requirement for MyD88 in the response to the commercial vaccine and improved the immune responses and seroconversion rates in all strains of mice tested, including those deficient in TLR2 and TLR4.

Adjuvant Activity of Synthetic Lipid A of Alcaligenes, a Gut-Associated Lymphoid Tissue-Resident Commensal Bacterium, to Augment Antigen-Specific IgG and Th17 Responses in Systemic Vaccine

Alcaligenes spp. are identified as commensal bacteria and have been found to inhabit Peyer’s patches in the gut. We previously reported that Alcaligenes-derived lipopolysaccharides (LPS) exerted adjuvant activity in systemic vaccination, without excessive inflammation. Lipid A is one of the components responsible for the biological effect of LPS and has previously been applied as an adjuvant. Here, we examined the adjuvant activity and safety of chemically synthesized Alcaligenes lipid A. We found that levels of OVA-specific serum IgG antibodies increased in mice that were subcutaneously immunized with ovalbumin (OVA) plus Alcaligenes lipid A relative to those that were immunized with OVA alone. In addition, Alcaligenes lipid A promoted antigen-specific T helper 17 (Th17) responses in the spleen; upregulated the expression of MHC class II, CD40, CD80, and CD86 on bone marrow-derived dendritic cells (BMDCs); enhanced the production of Th17-inducing cytokines IL-6 and IL-23 from BMDCs. Stimulation with Alcaligenes lipid A also induced the production of IL-6 and IL-1β in human peripheral blood mononuclear cells. Moreover, Alcaligenes lipid A caused minor side effects, such as lymphopenia and thrombocytopenia. These findings suggest that Alcaligenes lipid A is a safe and effective Th17-type adjuvant by directly stimulating dendritic cells in systemic vaccination.

Early IgG Response to Foot and Mouth Disease Vaccine Formulated with a Vegetable Oil Adjuvant

The present study evaluated soybean oil (SO) containing vitamin E (VE) and ginseng saponins (GS) (SO-VE-GS) for their adjuvant effect on foot-and-mouth disease (FMD) vaccine. Since mineral oil ISA 206 is a common adjuvant used in the FMD vaccine, it was used as a control adjuvant in this study. VE and GS were found to have a synergistic adjuvant effect. When mice were immunized with the FMD vaccine emulsified in SO with VE and GS, significantly higher serum IgG, IgG1, and IgG2a were found than VE and GS used alone. SO-VE-GS and ISA 206 behaved differently in adjuvant activities. When mice were immunized with the FMD vaccine adjuvanted with SO-VE-GS, significantly higher and earlier production of serum IgG was found than that adjuvanted with ISA 206. Although both adjuvants significantly increased the number of bone marrow plasma cells, a stimulation index of lymphocytes (SI) as well as the production of IL-4 and IL-6, SO-VE-GS promoted significantly higher SI and the ratio of CD4⁺/CD8⁺ T cells with production of increased IFN-γ and decreased TGF-β1 as compared with the ISA 206 group. The data suggested that SO-VE-GS activated Th1/Th2 immune responses. Transcriptome analysis of splenocytes showed that differentially expressed genes (DEGs), immune-related gene ontology (GO) terms, and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways were significantly enriched in the SO-VE-GS group. Therefore, the potent adjuvant effect of SO-VE-GS on the FMD vaccine may be attributed to the immune-related gene profile expressed in lymphocytes. Due to its plant origin and due to being much cheaper than imported mineral oil ISA 206, SO-VE-GS deserves further study in relation to vaccines used in food animals.

Food Additives as Novel Influenza Vaccine Adjuvants

Influenza is a major threat to public health. Vaccination is an effective strategy to control influenza; however, the current inactivated influenza vaccine has mild immunogenicity and exhibits suboptimal efficacy in clinical use. Vaccine efficacy can be improved by the addition of adjuvants, but few adjuvants have been approved for human use. To explore novel and effective adjuvants for influenza vaccines, here we screened 145 compounds from food additives approved in Japan. Of these 145 candidates, we identified 41 compounds that enhanced the efficacy of the split influenza hemagglutinin (HA) vaccine against lethal virus challenge in a mouse model. These 41 compounds included 18 novel adjuvant candidates and 15 compounds with previously reported adjuvant effects for other antigens but not for the influenza vaccine. Our results are of value to the development of novel and effective adjuvanted influenza or other vaccines for human use.