Comparison of immunogenicity, efficacy and transcriptome changes of inactivated rabies virus vaccine with different adjuvants

Role of NLRP3 inflammasome in nanoparticle adjuvant-mediated immune response

The nucleotide-binding oligomerization domain (NOD)-like receptor (NLR) family pyrin domain-containing 3 (NLRP3) inflammasome is pivotal in orchestrating the immune response induced by nanoparticle adjuvants. Understanding the intricate mechanisms underlying the activation of NLRP3 inflammasome by these adjuvants is crucial for deciphering their immunomodulatory properties. This review explores the involvement of the NLRP3 inflammasome in mediating immune responses triggered by nanoparticle adjuvants. It delves into the signaling pathways and cellular mechanisms involved in NLRP3 activation, highlighting its significance in modulating the efficacy and safety of nanoparticle-based adjuvants. A comprehensive grasp of the interplay between NLRP3 inflammasome and nanoparticle adjuvants holds promise for optimizing vaccine design and advancing immunotherapeutic strategies.

Immune Response of Inactivated Rabies Vaccine Inoculated via Intraperitoneal, Intramuscular, Subcutaneous and Needle-Free Injection Technology-Based Intradermal Routes in Mice

Inoculation routes may significantly affect vaccine performance due to the local microenvironment, antigen localization and presentation, and, therefore, final immune responses. In this study, we conducted a head-to-head comparison of immune response and safety of inactivated rabies vaccine inoculated via intraperitoneal (IP), intramuscular (IM), subcutaneous (SC) and needle-free injection technology-based intradermal (ID) routes in ICR mice. Immune response was assessed in terms of antigen-specific antibodies, antibody subtypes and neutralizing antibodies for up to 28 weeks. A live rabies virus challenge was also carried out to evaluate vaccine potency. The dynamics of inflammatory cell infiltration at the skin and muscle levels were determined via histopathological examination. The kinetics and distribution of a model antigen were also determined by using in vivo fluorescence imaging. Evidence is presented that the vaccine inoculated via the ID route resulted in the highest antigen-specific antibody and neutralizing antibody titers among all administration routes, while IP and IM routes were comparable, followed by the SC route. Antibody subtype analysis shows that the IP route elicited a Th1-biased immune response, while SC and IM administration elicited a prominent Th2-type immune response. Unexpectedly, the ID route leads to a balanced Th1 and Th2 immune response. In addition, the ID route conferred effective protection against lethal challenge with 40 LD50 of the rabies CVS strain, which was followed by IP and IM routes. Moreover, a one-third dose of the vaccine inoculated via the ID route provided comparable or higher efficacy to a full dose of the vaccine via the other three routes. The superior performance of ID inoculation over other routes is related to longer local retention at injection sites and higher lymphatic drainage. Histopathology examination reveals a transient inflammatory cell infiltration at ID and IM injection sites which peaked at 48 h and 24 h, respectively, after immunization, with all side effects disappearing within one week. These results suggest that needle-free injection technology-based ID inoculation is a promising strategy for rabies vaccination in regard to safety and efficacy.

Nanoalum Formulations Containing Aluminum Hydroxide and CpG 1018TM Adjuvants: The Effect on Stability and Immunogenicity of a Recombinant SARS-CoV-2 RBD Antigen

Aluminum-salt vaccine adjuvants (alum) are commercially available as micron-sized particles with varying chemical composition and crystallinity. There are reports of enhanced adjuvanticity when the alum's particle size is reduced to the nanometer range. Previously, we demonstrated that a recombinant receptor-binding domain (RBD)-based COVID-19 vaccine candidate (RBD-J; RBD-L452K-F490W) formulated with aluminum hydroxide (Alhydrogel^®; AH) and CpG 1018™ (CpG) adjuvants induced potent neutralizing antibody responses in mice yet displayed instability during storage. In this work, we evaluated whether sonication of AH to the nanometer size range (nanoAH) could further enhance immunogenicity or improve storage stability of the above formulation. The addition of CpG to nanoAH (at mouse doses), however, caused re-agglomeration of nanoAH. AH-CpG interactions were evaluated by Langmuir binding isotherms and zeta potential measurements, and stabilized nanoAH + CpG formulations of RBD-J were then designed by (1) optimizing CpG:Aluminum dose ratios or (2) adding a small-molecule polyanion (phytic acid, PA). Compared with the micron-sized AH + CpG formulation, the two stabilized nanoAH + CpG formulations of RBD-J demonstrated no enhancement in SARS-CoV-2 pseudovirus neutralizing titers in mice, but the PA-containing nanoAH + CpG formulation showed improved RBD-J storage stability trends (at 4, 25, and 37 °C). The formulation protocols presented herein can be employed to evaluate the potential benefits of the nanoAH + CpG adjuvant combination with other vaccine antigens in different animal models.

Developments in Rabies Vaccines: The Path Traversed from Pasteur to the Modern Era of Immunization

Rabies is a disease of antiquity and has a history spanning millennia ever since the first interactions between humans and dogs. The alarming fatalities caused by this disease have triggered rabies prevention strategies since the first century BC. There have been numerous attempts over the past 100 years to develop rabies vaccineswith the goal of preventing rabies in both humans and animals. Thepre-Pasteurian vaccinologists, paved the way for the actual history of rabies vaccines with the development of first generation vaccines. Further improvements for less reactive and more immunogenic vaccines have led to the expansion of embryo vaccines, tissue culture vaccines, cell culture vaccines, modified live vaccines, inactivated vaccines, and adjuvanted vaccines. The adventof recombinant technology and reverse genetics have given insight into the rabies viral genome and facilitated genome manipulations, which in turn led to the emergence of next-generation rabies vaccines, such as recombinant vaccines, viral vector vaccines, genetically modified vaccines, and nucleic acid vaccines. These vaccines were very helpful in overcoming the drawbacks of conventional rabies vaccines with increased immunogenicity and clinical efficacies. The path traversed in the development of rabies vaccines from Pasteur to the modern era vaccines, though, faced numerous challenges;these pioneering works have formed the cornerstone for the generation of thecurrent successful vaccines to prevent rabies. In the future, advancements in the scientific technologies and research focus will definitely lay the path for much more sophisticated vaccine candidates for rabies elimination.

Nano alum: A new solution to the new challenge

Alum adjuvant has always been the first choice when designing a vaccine. Conventional aluminum adjuvant includes aluminum hydroxide, aluminum phosphate, and amorphous aluminum hydroxyphosphate (AAHS), which could effectively induce the humoral, and to a lesser extent, cellular immune responses. Their safety is widely accepted for a variety of vaccines. However, conventional alum adjuvant is not an ideal choice for a vaccine antigen with poor immunogenicity, especially the subunit vaccine in which cellular response is highly demanded. The outbreak of COVID-19 requires a delicately designed vaccine without the antibody-dependent enhancement (ADE) effect to ensure the safety. A sufficiently powerful adjuvant that can induce both Th₁ and Th₂ immune responses is necessary to reduce the risk of ADE. These circumstances all bring new challenges to the conventional alum adjuvant. However, turning conventional microscale alum adjuvant into nanoscale is a new solution to these problems. Nanoscale alum owns a higher surface volume ratio, can absorb much more antigens, and promote the ability to stimulate the antigen-presenting cells (APCs) via different mechanisms. In this review, the exceptional performance of nano alum adjuvant and their preparation methods will be discussed. The potential safety concern of nano alum is also addressed. Based on the different mechanisms, the potential application of nano alum will also be introduced.

Intramuscular Inoculation of AS02-Adjuvanted Respiratory Syncytial Virus (RSV) F Subunit Vaccine Shows Better Efficiency and Safety Than Subcutaneous Inoculation in BALB/c Mice

We previously explored a panel of adjuvants formulated with pre-fusion RSV-F protein and found that AS02 may be a promising candidate adjuvant for developing RSV-F subunit vaccines with improved immunogenicity and desired immune response type. In this study, we performed a head-to-head comparison of the effect of intramuscular injection to that of subcutaneous injection on the immune response and protective efficacy of recombinant RSV-F subunit vaccine with or without adjuvants (Alhydrogel, squalene-based emulsion adjuvants MF59, AS03, and AS02) in BALB/c mice. After inoculations, antigen-specific antibodies, neutralizing antibodies, antibody subtypes, cytokines, and the persistence of immune response were evaluated. Moreover, challenge tests were also performed to illustrate the possible effect of inoculation routes and adjuvant on virus clearance and histochemistry changes in the lungs of mice. The results indicated that intramuscular inoculation is a more effective and antigen dose-sparing route to enhance the immune response, although subcutaneous inoculation induced faster and stronger IgG antibodies after the initial immunization. Furthermore, adjuvant, but not immunization route, is a more critical factor to affect the humoral/cellular immune response and the immune bias. In addition, adjuvant inoculated via the intramuscular route is safer than that via the subcutaneous route, especially for AS02. This study highlights the importance of the adjuvant and immunization routes in the design and clinical transformation of adjuvanted vaccines. Further investigation is needed to illustrate the mechanism underlying the above difference in both efficiency and safety.

Safety and Efficacy of the Bordetella bronchiseptica Vaccine Combined with a Vegetable Oil Adjuvant and Multi-Omics Analysis of Its Potential Role in the Protective Response of Rabbits

Infectious respiratory diseases caused by Bordetella bronchiseptica (Bb) are seriously endangering the development of the rabbit industry in China. Unfortunately, no licensed vaccines are available for this pathogen. The present study was designed to determine whether the inactivated Bb antigen formulated with vegetable oil adjuvant (named E515) which contains soybean oil, vitamin E, and ginseng saponins, functions as a safe and effective vaccine (E515-Bb) against Bb infection in rabbits. Based on local and systemic reactions, both the E515 adjuvant alone and the E515-Bb vaccine exhibited good safety in rabbits. Immune response analysis implies that rabbits immunized with the E515-Bb vaccine produced significantly higher, earlier, and longer-lasting specific antibody responses and activated Th1/Th2/Th17 cell responses than those immunized with the aluminum hydroxide (Alum)-adjuvanted Bb vaccine (Alum-Bb) or Bb antigen alone. Moreover, the E515-Bb vaccine effectively protected rabbits from Bb infection. Additionally, integrated multi-omics analysis revealed that the immunoprotective effect of the E515-Bb vaccine was achieved through upregulation of the complement and coagulation cascades and cell adhesion molecule (CAM) pathways, and the downregulation of the P53 pathway. Overall, these results indicate that the E515-Bb vaccine is safe, elicits an efficient immune response and provides good protection against Bb infection in rabbits. Thus, the E515-adjuvanted Bb vaccine can be considered a promising candidate vaccine for preventing Bb infection.

Nano dimensions/adjuvants in COVID-19 vaccines

A favorable outcome of the COVID-19 crisis might be achieved with massive vaccination. The proposed vaccines contain several different vaccine active principles (VAP), such as inactivated virus, antigen, mRNA, and DNA, which are associated with either standard adjuvants or nanomaterials (NM) such as liposomes in Moderna's and BioNTech/Pfizer's vaccines. COVID-19 vaccine adjuvants may be chosen among liposomes or other types of NM composed for example of graphene oxide, carbon nanotubes, micelles, exosomes, membrane vesicles, polymers, or metallic NM, taking inspiration from cancer nano-vaccines, whose adjuvants may share some of their properties with those of viral vaccines. The mechanisms of action of nano-adjuvants are based on the facilitation by NM of targeting certain regions of immune interest such as the mucus, lymph nodes, and zones of infection or blood irrigation, the possible modulation of the type of attachment of the VAP to NM, in particular VAP positioning on the NM external surface to favor VAP presentation to antigen presenting cells (APC) or VAP encapsulation within NM to prevent VAP degradation, and the possibility to adjust the nature of the immune response by tuning the physico-chemical properties of NM such as their size, surface charge, or composition. The use of NM as adjuvants or the presence of nano-dimensions in COVID-19 vaccines does not only have the potential to improve the vaccine benefit/risk ratio, but also to reduce the dose of vaccine necessary to reach full efficacy. It could therefore ease the overall spread of COVID-19 vaccines within a sufficiently large portion of the world population to exit the current crisis.

Glycyrrhiza polysaccharides can improve and prolong the response of chickens to the Newcastle disease vaccine

Licorice is a medicinal and food plant widely used to treat diseases and produce food additives, because of its unique chemical constituents like polysaccharides, flavones, and saponins. Glycyrrhiza Polysaccharides (GPS-1) are water-soluble neutral polysaccharides extracted from licorice. Currently, GPS-1 is administrated to chickens by gavage every d for 14 d to observe the impact of GPS-1 on the Newcastle disease vaccine. To determine the immunity of these chickens to NDV, blood serum levels of hemagglutinin-inhibition (HI) antibody, and immunoglobulins IgA and IgG were measured. Meanwhile, the expression levels of cytokines IL-2, IL-4, IL-17, and IFN-γ were measured to evaluate the degree of immune booster activity. The chickens' spleen and peripheral blood lymphocytes displayed a significant increase in the proportion of CD4+ and CD8+ T cells after booster treatments with GPS-1. The results indicated that GPS-1 had a significant, dose-dependent, immune-boosting effect which could enhance NDV vaccine immunity in chickens.

Colloidal Manganese Salt Improves the Efficacy of Rabies Vaccines in Mice, Cats, and Dogs

Rabies, caused by rabies virus (RABV), remains a serious threat to public health in most countries worldwide. At present, the administration of rabies vaccines has been the most effective strategy to control rabies. Herein, we evaluate the effect of colloidal manganese salt (Mn jelly [MnJ]) as an adjuvant of rabies vaccine in mice, cats, and dogs. The results showed that MnJ promoted type I interferon (IFN-I) and cytokine production in vitro and the maturation of dendritic cells (DCs) in vitro and in vivo. Besides, MnJ serving as an adjuvant for rabies vaccines could significantly facilitate the generation of T follicular helper (Tfh) cells, germinal center (GC) B cells, plasma cells (PCs), and RABV-specific antibody-secreting cells (ASCs), consequently improve the immunogenicity of rabies vaccines, and provide better protection against virulent RABV challenge. Similarly, MnJ enhanced the humoral immune response in cats and dogs as well. Collectively, our results suggest that MnJ can facilitate the maturation of DCs during rabies vaccination, which can be a promising adjuvant candidate for rabies vaccines. IMPORTANCE Extending the humoral immune response by using adjuvants is an important strategy for vaccine development. In this study, a novel adjuvant, MnJ, supplemented in rabies vaccines was evaluated in mice, cats, and dogs. Our results in the mouse model revealed that MnJ increased the numbers of mature DCs, Tfh cells, GC B cells, PCs, and RABV-specific ASCs, resulting in enhanced immunogenicity and protection rate of rabies vaccines. We further found that MnJ had the same stimulative effect in cats and dogs. Our study provides the first evidence that MnJ serving as a novel adjuvant of rabies vaccines can boost the immune response in both a mouse and pet model.

Immune response of C57BL/6J mice to herpes zoster subunit vaccines formulated with nanoemulsion-based and liposome-based adjuvants

Herpes zoster (HZ) is a recurrent nerve tissue infection caused by the reactivation of varicella-zoster virus (VZV). At present, two vaccines, the live attenuated vaccine Zostavax™ and AS01B-adjuvanted recombinant subunit vaccine Shingrix™, are commercially available for HZ. The latter is superior to the former in terms of efficacy and duration of immunity in the elderly. In this study, we used glycoprotein E (gE) as an antigen, and investigated the effects of various adjuvants (MF59, MF59/CpG 2006, and MF59/QS-21) on the immune response of C57BL/6J mice to find an alternative adjuvant to AS01B-like adjuvant of liposome/QS-21/MPL. In addition to safety, the gE-specific antibody, IgG antibody subtype, and cytokine secretion by splenocytes, and cell-mediated immune responses were determined using ELISA and ELISPOT assays, respectively. Our results showed no significant effects on the body weight, temperature, or behavior of mice vaccinated with PBS or all adjuvanted vaccines. All adjuvanted vaccine groups showed significantly higher gE-specific IgG antibody levels than the gE-alone group on day 28 after the first vaccine dose. In addition, all adjuvants induced a remarkable increase in both IgG1 and IgG2b levels. However, MF59/QS-21 and MF59/CpG 2006 showed comparable capacities to those of liposome/QS-21/MPL in increasing the IgG2c levels, being superior to MF59. Further investigation revealed that MF59 only induced a limited increase in the levels of Th1 and Th2 cytokines, while MF59/QS-21, MF59/CpG 2006, and liposome/QS-21/MPL led to a significant increase in the secretion of interferon gamma (IFN-γ), IL-2, IL-4, and IL-10 and showed a Th1-biased immune response. Moreover, MF59/QS-21, MF59/CpG 2006, and liposome/QS-21/MPL adjuvanted vaccines resulted in comparable gE-specific IFN-γ + immune cell responses. These results suggest that the combination of MF59 with QS-21 or CpG 2006 may be a promising adjuvant candidate for subunit HZ vaccines. Further investigations are needed to illustrate their durability and efficacy in aged mice.

Respiratory Syncytial Virus F Subunit Vaccine With AS02 Adjuvant Elicits Balanced, Robust Humoral and Cellular Immunity in BALB/c Mice

Respiratory syncytial virus (RSV) is a leading cause of lower respiratory illness, particularly in infants, the elderly, and immunocompromised adults. There is no licensed commercial vaccine against RSV. Importantly, formalin-inactivated RSV vaccines mediate enhanced respiratory disease. RSV fusion (F) protein with pre-fusion conformation is a promising candidate subunit vaccine. However, some problems remain to be solved, such as low immunogenicity and humoral immunity bias. Adjuvants can effectively enhance and adjust vaccine immune responses. In this study, we formulated pre-fusion RSV-F protein with the adjuvants, Alhydrogel, MF59, AS03, AS02, and glycol chitosan (GCS). We then conducted head-to-head comparisons of vaccine-induced immune responses in BALB/c mice. All adjuvanted vaccines enhanced antigen-specific and neutralizing antibody titers and viral clearance and gave an order of adjuvant activity: AS02 > AS03, MF59 > GCS, and Alhydrogel. Among them, AS02 elicited the highest antibody expression, which persisted until week 18. Moreover, AS02 significantly enhanced Th1 type immune response in immunized mice. Mice in the AS02 group also showed faster recovery from viral attacks in challenge tests. Further transcriptome analysis revealed that AS02 regulates immune balance by activating TLR-4 and promotes Th1-type immune responses. These results suggest that AS02 may be an excellent candidate adjuvant for RSV-F subunit vaccines. This study also provides valuable information regarding the effect of other adjuvants on immune responses of RSV-F subunit vaccines.

Better Adjuvants for Better Vaccines: Progress in Adjuvant Delivery Systems, Modifications, and Adjuvant-Antigen Codelivery

Traditional aluminum adjuvants can trigger strong humoral immunity but weak cellular immunity, limiting their application in some vaccines. Currently, various immunomodulators and delivery carriers are used as adjuvants, and the mechanisms of action of some of these adjuvants are clear. However, customizing targets of adjuvant action (cellular or humoral immunity) and action intensity (enhancement or inhibition) according to different antigens selected is time-consuming. Here, we review the adjuvant effects of some delivery systems and immune stimulants. In addition, to improve the safety, effectiveness, and accessibility of adjuvants, new trends in adjuvant development and their modification strategies are discussed.

A comparative study on the mechanisms of innate immune responses in mice induced by Alum and Actinidia eriantha polysaccharide

The innate immune mechanisms by which adjuvants enhance the potency and protection of vaccine remain at cellular level, but the molecular mechanisms, especially in vivo, are ill-identified. Actinidia eriantha polysaccharide (AEPS) is a potent adjuvant with dual Th1 and Th2 potentiating activity, while Alum elicits a strict Th2 response. The current experiments were designed to compare the innate immune responses in the peritoneal cavity of mice induced by two adjuvants and explore their molecular mechanisms using gene expression microarray including long noncoding RNAs (lncRNAs). AEPS induced the recruitment of monocytes, neutrophils and dendritic cells. However, Alum recruited neutrophils and eosinophils. AEPS and Alum specifically induced the differential expression of 546 and 922 genes in peritoneal cells, respectively. AEPS induced higher mRNA expression of CCL2, CCL3, CCL4, CCL7, CXCL2, CXCL3, CXCL5, CXCL10, IL-12β, and IL-23α in immune effector process, while Alum tended to Th17 response mRNAs such as IL-7A, IL-17F and IL-17RA. Furthermore, a robust adjuvant-specific expression pattern of lncRNAs was found in above mentioned biological processes, suggesting the involvement of lncRNAs in immune responses induced by AEPS and Alum. This study led to a better understanding of different molecular mechanisms of adjuvants and benefited the rational design of effective vaccines.

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.

New Rabies Vaccines for Use in Humans

Although vaccines are available, rabies still claims more than 55,000 human lives each year. In most cases, rabies vaccines are given to humans after their exposure to a rabid animal; pre-exposure vaccination is largely reserved for humans at high risk for contacts with the virus. Most cases of human rabies are transmitted by dogs. Dog rabies control by mass canine vaccination campaigns combined with intensive surveillance programs has led to a decline of human rabies in many countries but has been unsuccessful in others. Animal vaccination programs are also not suited to control human rabies caused by bat transmission, which is common in some Central American countries. Alternatively, or in addition, more widespread pre-exposure vaccination, especially in highly endemic remote areas, could be implemented. With the multiple dose regimens of current vaccines, pre-exposure vaccination is not cost effective for most countries and this warrants the development of new rabies vaccines, which are as safe as current vaccines, but achieve protective immunity after a single dose, and most importantly, are less costly. This chapter discusses novel rabies vaccines that are in late stage pre-clinical testing or have undergone clinical testing and their potential for replacing current vaccines.