Correlation of the composition of biominerals with their ability of stimulating intracellular DNA sensors and inflammatory cytokines

The orientation of CpG conjugation on aluminum oxyhydroxide nanoparticles determines the immunostimulatory effects of combination adjuvants

In subunit vaccines, aluminum salts (Alum) are commonly used as adjuvants, but with limited cellular immune responses. To overcome this limitation, CpG oligodeoxynucleotides (ODNs) have been used in combination with Alum. However, current combined usage of Alum and CpG is limited to linear mixtures, and the underlying interaction mechanism between CpG and Alum is not well understood. Thus, we propose to chemically conjugate Alum nanoparticles and CpG (with 5' or 3' end exposed) to design combination adjuvants. Our study demonstrates that compared to the 3'-end exposure, the 5'-end exposure of CpG in combination adjuvants (Al-CpG-5') enhances the activation of bone-marrow derived dendritic cells (BMDCs) and promotes Th1 and Th2 cytokine secretion. We used the SARS-CoV-2 receptor binding domain (RBD) and hepatitis B surface antigen (HBsAg) as model antigens to demonstrate that Al-CpG-5' enhanced antigen-specific antibody production and upregulated cytotoxic T lymphocyte markers. Additionally, Al-CpG-5' allows for coordinated adaptive immune responses even at lower doses of both CpG ODNs and HBsAg antigens, and enhances lymph node transport of antigens and activation of dendritic cells, promoting Tfh cell differentiation and B cell activation. Our novel Alum-CPG strategy points the way towards broadening the use of nanoadjuvants for both prophylactic and therapeutic vaccines.

Aluminum oxyhydroxide-Poly(I:C) combination adjuvant with balanced immunostimulatory potentials for prophylactic vaccines

The development of high-purity antigens promotes the urgent need of novel adjuvant with the capability to trigger high levels of immune response. Polyinosinic-polycytidylic (Poly(I:C)) is a synthetic double-stranded RNA (dsRNA) that can engage Toll-like receptor 3 (TLR3) to initiate immune responses. However, the Poly(I:C)-induced toxicity and inefficient delivery prevent its applications. In our study, combination adjuvants are formulated by aluminum oxyhydroxide nanorods (AlOOH NRs) and Poly(I:C), named Al-Poly(I:C), and the covalent interaction between the two components is further demonstrated. Al-Poly(I:C) mediates enhanced humoral and cellular immune responses in three antigen models, i.e., HBsAg virus-like particles (VLPs), human papilloma virus (HPV) VLPs and varicella-zoster virus (VZV) glycoprotein E (gE). Further mechanistic studies demonstrate that the dose and molecular weight (MW) of Poly(I:C) determine the physicochemical properties and adjuvanticity of the Al-Poly(I:C) combination adjuvants. Al-Poly(I:C) with higher Poly(I:C) dose promotes antigen-bearing dendritic cells (DCs) recruitment and B cells proliferation in lymph nodes. Al-Poly(I:C) formulated with higher MW Poly(I:C) induces higher activation of helper T cells, B cells, and CTLs. This study demonstrates that Al-Poly(I:C) potentiates the humoral and cellular responses in vaccine formulations. It offers insights for adjuvant design to meet the formulation requirements in both prophylactic and therapeutic vaccines.

Self-assembled flagella protein nanofibers induce enhanced mucosal immunity

Nanofibers are potential vaccines or adjuvants for vaccination at the mucosal interface. However, how their lengths affect the mucosal immunity is not well understood. Using length-tunable flagella (self-assembled from a protein termed flagellin) as model protein nanofibers, we studied the mechanisms of their interaction with mucosal interface to induce immune responses length-dependently. Briefly, through tuning flagellin assembly, length-controlled protein nanofibers were prepared. The shorter nanofibers exhibited more pronounced toll-like receptor 5 (TLR5) and inflammasomes activation accompanied by pyroptosis, as a result of cellular uptake, lysosomal damage, and mitochondrial reactive oxygen species generation. Accordingly, the shorter nanofibers elevated the IgA level in mucosal secretions and enhanced the serum IgG level in ovalbumin-based intranasal vaccinations. These mucosal and systematic antibody responses were correlated with the mucus penetration capacity of the nanofibers. Intranasal administration of vaccines (human papillomavirus type 16 peptides) adjuvanted with shorter nanofibers significantly elicited cytotoxic T lymphocyte responses, strongly inhibiting tumor growth and improving survival rates in a TC-1 cervical cancer model. This work suggests that length-dependent immune responses of nanofibers can be elucidated for designing nanofibrous vaccines and adjuvants for both infectious diseases and cancer.

Mineralized vectors for gene therapy

There is an intense interest in developing materials for safe and effective delivery of polynucleotides using non-viral vectors. Mineralization of organic templates has long been used to produce complex materials with outstanding biocompatibility. However, a lack of control over mineral growth has limited the applicability of mineralized materials to a few in vitro applications. With better control over mineral growth and surface functionalization, mineralized vectors have advanced significantly in recent years. Here, we review the recent progress in chemical synthesis, physicochemical properties, and applications of mineralized materials in gene therapy, focusing on structure-function relationships. We contrast the classical understanding of the mineralization mechanism with recent ideas of mineralization. A brief introduction to gene delivery is summarized, followed by a detailed survey of current mineralized vectors. The vectors derived from calcium phosphate are articulated and compared to other minerals with unique features. Advanced mineral vectors derived from templated mineralization and specialty coatings are critically analyzed. Mineral systems beyond the co-precipitation are explored as more complex multicomponent systems. Finally, we conclude with a perspective on the future of mineralized vectors by carefully demarcating the boundaries of our knowledge and highlighting ambiguous areas in mineralized vectors. STATEMENT OF SIGNIFICANCE: Therapy by gene-based medicines is increasingly utilized to cure diseases that are not alleviated by conventional drug therapy. Gene medicines, however, rely on macromolecular nucleic acids that are too large and too hydrophilic for cellular uptake. Without tailored materials, they are not functional for therapy. One emerging class of nucleic acid delivery system is mineral-based materials. The fact that they can undergo controlled dissolution with minimal footprint in biological systems are making them attractive for clinical use, where safety is utmost importance. In this submission, we will review the emerging synthesis technology and the range of new generation minerals for use in gene medicines.

Engineered Hydroxyapatite Nanoadjuvants with Controlled Shape and Aspect Ratios Reveal Their Immunomodulatory Potentials

Hydroxyapatite (HAP) has been formulated as adjuvants in vaccines for human use. However, the optimal properties required for HAP nanoparticles to elicit adjuvanticity and the underlying immunopotentiation mechanisms have not been fully elucidated. Herein, a library of HAP nanorods and nanospheres was synthesized to explore the effect of the particle shape and aspect ratio on the immune responses in vitro and adjuvanticity in vivo. It was demonstrated that long aspect ratio HAP nanorods induced a higher degree of cell membrane depolarization and subsequent uptake, and the internalized particles elicited cathepsin B release and mitochondrial reactive oxygen species generation, which further led to pro-inflammatory responses. Furthermore, the physicochemical property-dependent immunostimulation capacities were correlated with their humoral responses in a murine hepatitis B surface antigen immunization model, with long aspect ratio HAP nanorods inducing higher antigen-specific antibody productions. Importantly, HAP nanorods significantly up-regulated the IFN-γ secretion and CD107α expression on CD8⁺ T cells in immunized mice. Further mechanistic studies demonstrated that HAP nanorods with defined properties exerted immunomodulatory effects by enhanced antigen persistence and immune cell recruitments. Our study provides a rational design strategy for engineered nanomaterial-based vaccine adjuvants.

Enhanced Immune Adjuvant Activity of Aluminum Oxyhydroxide Nanorods through Cationic Surface Functionalization

Aluminum-salt-based vaccine adjuvants are prevailingly used in FDA-approved vaccines for the prevention of infectious diseases for over eighty years. Despite their safe applications, the mechanisms regarding how the material characteristics affect the interactions at nano-bio interface and immunogenicity remain unclear. Recently, studies have indicated that the activation of NLRP3 inflammasome plays a critical role in inducing adjuvant effects that are controlled by the inherent shape and hydroxyl contents of aluminum oxyhydroxide (AlOOH) nanoparticles; however, the detailed relationship between surface properties and adjuvant effects for these materials remains unknown. Thus, we engineered AlOOH nanorods (ALNRs) with controlled surface functionalization and charge to assess their effects on the activation of NLRP3 inflammasome in vitro and the potentiation of immunogenicity in vivo. It is demonstrated that NH₂-functionalized ALNRs exhibited higher levels of cellular uptake, lysosomal damage, oxidative stress, and NLRP3 inflammasome activation than pristine and SO₃H-functionalized ALNRs in cells. This structure-activity relationship also correlates with the adjuvant activity of the material using ovalbumin (OVA) in a mouse vaccination model. This study demonstrates that surface functionalization of ALNRs is critical for rational design of aluminum-based adjuvants to boost antigen-specific immune responses for more effective and long-lasting vaccination.

Structure Activity Relationships of Engineered Nanomaterials in inducing NLRP3 Inflammasome Activation and Chronic Lung Fibrosis

It has been demonstrated that certain engineered nanomaterials (ENMs) could induce chronic lung inflammation and fibrosis, however, the key structure activity relationships (SARs) that the link the physicochemical properties and the fibrogenic effects have not been thoroughly reviewed. Recently, significant progress has been made in our understanding of the SAR, and it has been demonstrated that ENMs including rare earth oxides (REOs), graphene and graphene oxides (GO), fumed silica, as well as high aspect ratio materials (such as CNTs and CeO₂ nanowires etc.) could trigger the NLRP3 inflammasome activation and IL-1β production in macrophages and subsequent series of profibrogenic cytokines, i.e. TGF-β1 and PDGF-AA in vitro and in vivo, resulting in synergistically cell-cell communication among macrophages, epithelial cells, and fibroblasts in a process named epithelial-mesenchymal transition (EMT) and collagen deposition in the lung as the adverse outcomes. Interestingly, different ENMs engage a range of distinct pathways leading to the NLRP3 inflammasome activation and IL-1β production in macrophages, which include frustrated phagocytosis, physical piercing, plasma membrane perturbation or damage to lysosomes due to high aspect ratio, particle structure, surface reactivity, transformation, etc. Furthermore, ENM's properties determine the biopersistence in vivo, which also play a major role in chronic lung fibrosis. Based on these progresses, we reviewed recent findings in the literature on the major SARs leading to chronic lung effects.

Nanomaterial-Based Vaccine Adjuvants

Vaccination is a biological process that administrates antigenic materials to stimulate an individual's immune system to develop immunity to a specific pathogen. It is the most effective tool to prevent illness and death from infectious diseases or diseases leading to cancers. Because many recombinant and synthetic antigens are poorly immunogenic, adjuvant is essentially added to vaccine formula that can potentiate the immune responses, offer better protection against pathogens and reduce the amount of antigens needed for protective immunity. To date, there are nearly 100 different types of adjuvants associated with about 400 vaccines that are either commercially available or under development. Among these adjuvants, many of them are particulates and nano-scale in nature. Nanoparticles represent a wide range of materials with novel physicochemical properties that exhibit immunostimulatory effects. However, the mechanistic understandings on how their physicochemical properties affect immunopotentiation remain elusive. In this article, we aim to review current development status of nanomaterial-based vaccine adjuvants, and further discuss their acting mechanisms, understanding of which will benefit the rational design of effective vaccine adjuvants with improved immunogenicity for prevention of infectious disease as well as therapeutic cancer treatment.