Maturation of Aluminium Adsorbed Antigens Contributes to the Creation of Homogeneous Vaccine Formulations

Although aluminium-based vaccines have been used for almost over a century, their mechanism of action remains unclear. It is established that antigen adsorption to the adjuvant facilitates delivery of the antigen to immune cells at the injection site. To further increase our understanding of aluminium-based vaccines, it is important to gain additional insights on the interactions between the aluminium and antigens, including antigen distribution over the adjuvant particles. Immuno-assays can further help in this regard. In this paper, we evaluated how established formulation strategies (i.e., sequential, competitive, and separate antigen addition) applied to four different antigens and aluminium oxyhydroxide, lead to formulation changes over time. Results showed that all formulation samples were stable, and that no significant changes were observed in terms of physical-chemical properties. Antigen distribution across the bulk aluminium population, however, did show a maturation effect, with some initial dependence on the formulation approach and the antigen adsorption strength. Sequential and competitive approaches displayed similar results in terms of the homogeneity of antigen distribution across aluminium particles, while separately adsorbed antigens were initially more highly poly-dispersed. Nevertheless, the formulation sample prepared via separate adsorption also reached homogeneity according to each antigen adsorption strength. This study indicated that antigen distribution across aluminium particles is a dynamic feature that evolves over time, which is initially influenced by the formulation approach and the specific adsorption strength, but ultimately leads to homogeneous formulations.

Immunostimulant plant proteins: Potential candidates as vaccine adjuvants

The COVID-19 pandemic is shaking up global scientific structures toward addressing antibiotic resistance threats and indicates an urgent need to develop more cost-effective vaccines. Vaccine adjuvants play a crucial role in boosting immunogenicity and improving vaccine efficacy. The toxicity and adversity of most adjuvant formulations are the major human immunization problems, especially in routine pediatric and immunocompromised patients. The present review focused on preclinical studies of immunoadjuvant plant proteins in use with antiparasitic, antifungal, and antiviral vaccines. Moreover, this report outlines the current perspective of immunostimulant plant protein candidates that can be used by researchers in developing new generations of vaccine-adjuvants. Future clinical studies are required to substantiate the plant proteins' safety and applicability as a vaccine adjuvant in pharmaceutical manufacturing.

Developments in Vaccine Adjuvants

Vaccines, including subunit, recombinant, and conjugate vaccines, require the use of an immunostimulator/adjuvant for maximum efficacy. Adjuvants not only enhance the strength and longevity of immune responses but may also influence the type of response. In this chapter, we review the adjuvants that are available for use in human vaccines, such as alum, MF59, AS03, and AS01. We extensively discuss their composition, characteristics, mechanism of action, and effects on the immune system. Additionally, we summarize recent trends in adjuvant discovery, providing a brief overview of saponins, TLRs agonists, polysaccharides, nanoparticles, cytokines, and mucosal adjuvants.

Seasonal influenza vaccination and technologies

Seasonal influenza is a serious respiratory illness that causes annual worldwide epidemics resulting in significant morbidity and mortality. Influenza pandemics occur about every 40 yrs, and may carry a greater burden of illness and death than seasonal influenza. Both seasonal influenza and pandemic influenza have profound economic consequences. The combination of current vaccine efficacy and viral antigenic drifts and shifts necessitates annual vaccination. New manufacturing technologies in influenza vaccine development employ cell culture and recombinant techniques. Both allow more rapid vaccine creation and production. In the past 5 years, brisk, highly creative activity in influenza vaccine research and development has begun. New vaccine technologies and vaccination strategies are addressing the need for viable alternatives to egg production methods and improved efficacy. At present, stubborn problems of sub-optimal efficacy and the need for annual immunization persist. There is an obvious need for more efficacious vaccines and improved vaccination strategies to make immunization easier for providers and patients. Mitigating this serious annual health threat remains an important public health priority.

Highly effective generic adjuvant systems for orphan or poverty-related vaccines

Safe and effective adjuvants are needed for many vaccines with limited commercial appeal, such as vaccines to infrequent (orphan) diseases or to neglected and poverty-related diseases. Here we found that three nonproprietary liposome formulations containing monophosphoryl lipid A each induced 3-fold to 5-fold increased titers of binding and neutralizing antibodies to anthrax protective antigen compared to aluminum hydroxide-adsorbed antigen in monkeys. All vaccinated monkeys were protected against lethal challenge with aerosolized Ames strain spores.

Unmet needs in modern vaccinology: adjuvants to improve the immune response

The key objective of vaccination is the induction of an effective pathogen-specific immune response that leads to protection against infection and/or disease caused by that pathogen, and that may ultimately result in its eradication from humanity. The concept that the immune response to pathogen antigens can be improved by the addition of certain compounds into the vaccine formulation was demonstrated about one hundred years ago when aluminium salts were introduced. New vaccine technology has led to vaccines containing highly purified antigens with improved tolerability and safety profiles, but the immune response they induce is suboptimal without the help of adjuvants. In parallel, the development of effective vaccines has been facing more and more important challenges linked to complicated pathogens (e.g. malaria, TB, HIV, etc.) and/or to subjects with conditions that jeopardize the induction or persistence of a protective immune response. A greater understanding of innate and adaptive immunity and their close interaction at the molecular level is yielding insights into the possibility of selectively stimulating immunological pathways to obtain the desired immune response. The better understanding of the mechanism of 'immunogenicity' and 'adjuvanticity' has prompted the research of new vaccine design based on new technologies, such as naked DNA or live vector vaccines and the new adjuvant approaches. Adjuvants can be used to enhance the magnitude and affect the type of the antigen-specific immune response, and the combination of antigens with more than one adjuvant, the so called adjuvant system approach, has been shown to allow the development of vaccines with the ability to generate effective immune responses adapted to both the pathogen and the target population. This review focuses on the adjuvants and adjuvant systems currently in use in vaccines, future applications, and the remaining challenges the field is facing.

Needle-free influenza vaccination

Vaccination is the cornerstone of influenza control in epidemic and pandemic situations. Influenza vaccines are typically given by intramuscular injection. However, needle-free vaccinations could offer several distinct advantages over intramuscular injections: they are pain-free, easier to distribute, and easier to give to patients, and their use could reduce vaccination costs. Moreover, vaccine delivery via the respiratory tract, alimentary tract, or skin might elicit mucosal immune responses at the site of virus entry and better cellular immunity, thus improving effectiveness. Although various needle-free vaccination methods for influenza have shown preclinical promise, few have progressed to clinical trials-only live attenuated intranasal vaccines have received approval, and only in some countries. Further clinical investigation is needed to help realise the potential of needle-free vaccination for influenza.

Safety Evaluation of Calcium Administered Intranasally to Mice

Calcium, a component of approved human vaccines administered via systemic routes, has a good safety profile. Recently, intranasally administered vaccines containing calcium have shown promise in generating mucosal immune responses in animal models. However, the safety of intranasally administered calcium is unknown. This study evaluates the safety of intranasally administered calcium at 2- to 13-fold higher doses than used in experimental vaccines. At a calcium dose of 22 mg/kg, 80% of the Balb/c and 20% of the C57BL/6 mice die within the first 24 hours. At 11.0 mg/kg, there is no overt toxicity in either strain, based on body weight, clinical scores, blood chemistry, and histopathology of major organs at 7 days post administration. In C57BL/6 mice, apart from acute and subacute inflammation in the lungs at up to 3 days post administration, especially at the 22-mg/kg dose, there is no overt toxicity. Doses of calcium up to 11 mg/kg appear to be safe in a mouse model.

Transcutaneous immunization with cross-reacting material CRM(197) of diphtheria toxin boosts functional antibody levels in mice primed parenterally with adsorbed diphtheria toxoid vaccine

Transcutaneous immunization (TCI) capitalizes on the accessibility and immunocompetence of the skin, elicits protective immunity, simplifies vaccine delivery, and may be particularly advantageous when frequent boosting is required. In this study we examined the potential of TCI to boost preexisting immune responses to diphtheria in mice. The cross-reacting material (CRM(197)) of diphtheria toxin was used as the boosting antigen and was administered alone or together with either one of two commonly used mucosal adjuvants, cholera toxin (CT) and a partially detoxified mutant of heat-labile enterotoxin of Escherichia coli (LTR72). We report that TCI with CRM(197) significantly boosted preexisting immune responses elicited after parenteral priming with aluminum hydroxide-adsorbed diphtheria toxoid (DTxd) vaccine. In the presence of LTR72 as an adjuvant, toxin-neutralizing antibody titers were significantly higher than those elicited by CRM(197) alone and were comparable to the functional antibody levels induced after parenteral booster immunization with the adsorbed DTxd vaccine. Time course study showed that high levels of toxin-neutralizing antibodies persisted for at least 14 weeks after the transcutaneous boost. In addition, TCI resulted in a vigorous antigen-specific proliferative response in all groups of mice boosted with the CRM(197) protein. These findings highlight the promising prospect of using booster administrations of CRM(197) via the transcutaneous route to establish good herd immunity against diphtheria.