Reduced MyD88 dependency of ISCOMATRIX™ adjuvant in a DNA prime-protein boost HIV vaccine

Nanoparticle-Based Delivery Systems for Vaccines

Vaccination is still the most cost-effective way to combat infectious illnesses. Conventional vaccinations may have low immunogenicity and, in most situations, only provide partial protection. A new class of nanoparticle-based vaccinations has shown considerable promise in addressing the majority of the shortcomings of traditional and subunit vaccines. This is due to recent breakthroughs in chemical and biological engineering, which allow for the exact regulation of nanoparticle size, shape, functionality, and surface characteristics, resulting in improved antigen presentation and robust immunogenicity. A blend of physicochemical, immunological, and toxicological experiments can be used to accurately characterize nanovaccines. This narrative review will provide an overview of the current scenario of the nanovaccine.

Methodical Design of Viral Vaccines Based on Avant-Garde Nanocarriers: A Multi-Domain Narrative Review

The current health crisis caused by coronavirus 2019 (COVID-19) and associated pathogens emphasize the urgent need for vaccine systems that can generate protective and long-lasting immune responses. Vaccination, employing peptides, nucleic acids, and other molecules, or using pathogen-based strategies, in fact, is one of the most potent approaches in the management of viral diseases. However, the vaccine candidate requires protection from degradation and precise delivery to the target cells. This can be achieved by employing different types of drug and vaccine delivery strategies, among which, nanotechnology-based systems seem to be more promising. This entry aims to provide insight into major aspects of vaccine design and formulation to address different diseases, including the recent outbreak of SARS-CoV-2. Special emphasis of this review is on the technical and practical aspects of vaccine construction and theranostic approaches to precisely target and localize the active compounds.

Nanoparticles and Vaccine Development

In spite of the progress of conventional vaccines, improvements are required due to concerns about the low immunogenicity of the toxicity, instability, and the need for multiple administrations of the vaccines. To overcome the mentioned problems, nanotechnology has recently been incorporated into vaccine development. Nanotechnology increasingly plays an important role in vaccine development nanocarrier-based delivery systems that offer an opportunity to increase the cellular and humoral immune responses. The use of nanoparticles in vaccine formulations allows not only enhanced immunogenicity and stability of antigen, but also targeted delivery and slow release. Over the past decade, nanoscale size materials such as virus-like particles, liposomes, ISCOMs, polymeric, inorganic nanoparticles and emulsions have gained attention as potential delivery vehicles for vaccine antigens, which can both stabilize vaccine antigens and act as adjuvants. This advantage is attributable to the nanoscale particle size, which facilitates uptake by Antigen- Presenting Cells (APCs), then leading to efficient antigen recognition and presentation. Modifying the surfaces of nanoparticles with different targeting moieties permits the delivery of antigens to specific receptors on the cell surface, thereby stimulating selective and specific immune responses. This review provides an overview of recent advances in nanovaccinology.

Quillaja brasiliensis saponin-based nanoparticulate adjuvants are capable of triggering early immune responses

Commercially available saponins are extracted from Quillaja saponaria barks, being Quil A® the most widely used. Nanoparticulate immunostimulating complexes (ISCOMs or ISCOMATRIX) formulated with these, are able to stimulate strong humoral and cellular immune responses. Recently, we formulated novel ISCOMs replacing QuilA® by QB-90 (IQB-90), a Quillaja brasiliensis leaf-extracted saponin fraction, and reported that IQB-90 improved antigen uptake, and induced systemic and mucosal antibody production, and T-cell responses. However, its mechanism of action remains unclear. In this study we provide a deeper insight into the immune stimulatory properties of QB-90 and ISCOMATRIX-like based on this fraction (IMXQB-90). We show herein that, when used as a viral vaccine adjuvant, QB-90 promotes an "immunocompetent environment". In addition, QB-90 and IMXQB-90 induce immune-cells recruitment at draining-lymph nodes and spleen. Subsequently, we prove that QB-90 or IMXQB-90 stimulated dendritic cells secret IL-1β by mechanisms involving Caspase-1/11 and MyD88 pathways, implying canonical inflammasome activation. Finally, both formulations induce a change in the expression of cytokines and chemokines coding genes, many of which are up-regulated. Findings reported here provide important insights into the molecular and cellular mechanisms underlying the adjuvant activity of Q. brasiliensis leaf-saponins and its respective nanoparticles.

Identification of QS-21 as an Inflammasome-activating Molecular Component of Saponin Adjuvants

Many immunostimulants act as vaccine adjuvants via activation of the innate immune system, although in many cases it is unclear which specific molecules contribute to the stimulatory activity. QS-21 is a defined, highly purified, and soluble saponin adjuvant currently used in licensed and exploratory vaccines, including vaccines against malaria, cancer, and HIV-1. However, little is known about the mechanisms of cellular activation induced by QS-21. We observed QS-21 to elicit caspase-1-dependent IL-1β and IL-18 release in antigen-presenting cells such as macrophages and dendritic cells when co-stimulated with the TLR4-agonist adjuvant monophosphoryl lipid A. Furthermore, our data suggest that the ASC-NLRP3 inflammasome is responsible for QS-21-induced IL-1β/IL-18 release. At higher concentrations, QS-21 induced macrophage and dendritic cell death in a caspase-1-, ASC-, and NLRP3-independent manner, whereas the presence of cholesterol rescued cell viability. A nanoparticulate adjuvant that contains QS-21 as part of a heterogeneous mixture of saponins also induced IL-1β in an NLRP3-dependent manner. Interestingly, despite the role NLRP3 plays for cellular activation in vitro, NLRP3-deficient mice immunized with HIV-1 gp120 and QS-21 showed significantly higher levels of Th1 and Th2 antigen-specific T cell responses and increased IgG1 and IgG2c compared with wild type controls. Thus, we have identified QS-21 as a nonparticulate single molecular saponin that activates the NLRP3 inflammasome, but this signaling pathway may contribute to decreased antigen-specific responses in vivo.

A Novel Prime and Boost Regimen of HIV Virus-Like Particles with TLR4 Adjuvant MPLA Induces Th1 Oriented Immune Responses against HIV

HIV virus-like particles (VLPs) present the HIV envelope protein in its native conformation, providing an ideal vaccine antigen. To enhance the immunogenicity of the VLP vaccine, we sought to improve upon two components; the route of administration and the additional adjuvant. Using HIV VLPs, we evaluated sub-cheek as a novel route of vaccine administration when combined with other conventional routes of immunization. Of five combinations of distinct prime and boost sequences, which included sub-cheek, intranasal, and intradermal routes of administration, intranasal prime and sub-cheek boost (IN+SC) resulted in the highest HIV-specific IgG titers among the groups tested. Using the IN+SC regimen we tested the adjuvant VesiVax Conjugatable Adjuvant Lipid Vesicles (CALV) + monophosphoryl lipid A (MPLA) at MPLA concentrations of 0, 7.5, 12.5, and 25 μg/dose in combination with our VLPs. Mice that received 12.5 or 25 μg/dose MPLA had the highest concentrations of Env-specific IgG2c (20.7 and 18.4 μg/ml respectively), which represents a Th1 type of immune response in C57BL/6 mice. This was in sharp contrast to mice which received 0 or 7.5 μg MPLA adjuvant (6.05 and 5.68 μg/ml of IgG2c respectively). In contrast to IgG2c, MPLA had minor effects on Env-specific IgG1; therefore, 12.5 and 25 μg/dose of MPLA induced the optimal IgG1/IgG2c ratio of 1.3. Additionally, the percentage of germinal center B cells increased significantly from 15.4% in the control group to 31.9% in the CALV + 25 μg MPLA group. These mice also had significantly more IL-2 and less IL-4 Env-specific CD8⁺ T cells than controls, correlating with an increased percentage of Env-specific central memory CD4⁺ and CD8⁺ T cells. Our study shows the strong potential of IN+SC as an efficacious route of administration and the effectiveness of VLPs combined with MPLA adjuvant to induce Env specific Th1-oriented HIV-specific immune responses.