Mechanisms of Antigen Adsorption Onto an Aluminum-Hydroxide Adjuvant Evaluated by High-Throughput Screening

Key Process Parameters Study for the Fill Finish of Vaccines Containing Aluminum Hydroxide Adjuvant

Vaccine manufacturing is one of the most challenging and complex processes in pharmaceutical industry, and the process control strategy is critical for the safety, effectiveness, and consistency of a vaccine. The efficacy of aluminum salt adjuvant on vaccines strongly depends on its physicochemical properties, such as size, structure, surface charge, etc. However, stresses during the vaccine manufacturing may affect the stability of adjuvant. In this study, the impacts of cold/thermal stress, autoclaving, pumping, mixing, and filling shear stress on the physicochemical properties of aluminum hydroxide (AH) adjuvant were evaluated as part of the manufacturing process development. The results showed that the autoclaving process would slightly influence the structure and properties of the investigated AH adjuvant, but thermal incubation at 2-8 °C, 25 °C and 40 °C for 4 weeks did not. However, -20 °C freezing AH adjuvant led to the adjuvant agglomeration and rapid sedimentation. For the high shear stress study with mixing at 500 rpm in a 1-L mixing bag and pumping at 220 rpm for up to 24 h, the average particle dimension of the bulk AH adjuvant decreased, along with decreasing protein adsorption ratio. The studies indicate that various stresses during manufacturing process could affect the structure and physicochemical properties of AH adjuvant, which calls for more attention on the control of adjuvant process parameters during manufacturing.

Formulation development and comparability studies with an aluminum-salt adjuvanted SARS-CoV-2 spike ferritin nanoparticle vaccine antigen produced from two different cell lines

The development of safe and effective second-generation COVID-19 vaccines to improve affordability and storage stability requirements remains a high priority to expand global coverage. In this report, we describe formulation development and comparability studies with a self-assembled SARS-CoV-2 spike ferritin nanoparticle vaccine antigen (called DCFHP), when produced in two different cell lines and formulated with an aluminum-salt adjuvant (Alhydrogel, AH). Varying levels of phosphate buffer altered the extent and strength of antigen-adjuvant interactions, and these formulations were evaluated for their (1) in vivo performance in mice and (2) in vitro stability profiles. Unadjuvanted DCFHP produced minimal immune responses while AH-adjuvanted formulations elicited greatly enhanced pseudovirus neutralization titers independent of ∼100%, ∼40% or ∼10% of the DCFHP antigen adsorbed to AH. These formulations differed, however, in their in vitro stability properties as determined by biophysical studies and a competitive ELISA for measuring ACE2 receptor binding of AH-bound antigen. Interestingly, after one month of 4°C storage, small increases in antigenicity with concomitant decreases in the ability to desorb the antigen from the AH were observed. Finally, we performed a comparability assessment of DCFHP antigen produced in Expi293 and CHO cells, which displayed expected differences in their N-linked oligosaccharide profiles. Despite consisting of different DCFHP glycoforms, these two preparations were highly similar in their key quality attributes including molecular size, structural integrity, conformational stability, binding to ACE2 receptor and mouse immunogenicity profiles. Taken together, these studies support future preclinical and clinical development of an AH-adjuvanted DCFHP vaccine candidate produced in CHO cells.

The combination of vaccines and adjuvants to prevent the occurrence of high incidence of infectious diseases in bovine

As the global population grows, the demand for beef and dairy products is also increasing. The cattle industry is facing tremendous pressures and challenges. The expanding cattle industry has led to an increased risk of disease in cattle. These diseases not only cause economic losses but also pose threats to public health and safety. Hence, ensuring the health of cattle is crucial. Vaccination is one of the most economical and effective methods of preventing bovine infectious diseases. However, there are fewer comprehensive reviews of bovine vaccines available. In addition, the variable nature of bovine infectious diseases will result in weakened or even ineffective immune protection from existing vaccines. This shows that it is crucial to improve overall awareness of bovine vaccines. Adjuvants, which are crucial constituents of vaccines, have a significant role in enhancing vaccine response. This review aims to present the latest advances in bovine vaccines mainly including types of bovine vaccines, current status of development of commonly used vaccines, and vaccine adjuvants. In addition, this review highlights the main challenges and outstanding problems of bovine vaccines and adjuvants in the field of research and applications. This review provides a theoretical and practical basis for the eradication of global bovine infectious diseases.

Formulation development and comparability studies with an aluminum-salt adjuvanted SARS-CoV-2 Spike ferritin nanoparticle vaccine antigen produced from two different cell lines

The development of safe and effective second-generation COVID-19 vaccines to improve affordability and storage stability requirements remains a high priority to expand global coverage. In this report, we describe formulation development and comparability studies with a self-assembled SARS-CoV-2 spike ferritin nanoparticle vaccine antigen (called DCFHP), when produced in two different cell lines and formulated with an aluminum-salt adjuvant (Alhydrogel, AH). Varying levels of phosphate buffer altered the extent and strength of antigen-adjuvant interactions, and these formulations were evaluated for their (1) in vivo performance in mice and (2) in vitro stability profiles. Unadjuvanted DCFHP produced minimal immune responses while AH-adjuvanted formulations elicited greatly enhanced pseudovirus neutralization titers independent of ∼100%, ∼40% or ∼10% of the DCFHP antigen adsorbed to AH. These formulations differed, however, in their in vitro stability properties as determined by biophysical studies and a competitive ELISA for measuring ACE2 receptor binding of AH-bound antigen. Interestingly, after one month of 4°C storage, small increases in antigenicity with concomitant decreases in the ability to desorb the antigen from the AH were observed. Finally, we performed a comparability assessment of DCFHP antigen produced in Expi293 and CHO cells, which displayed expected differences in their N-linked oligosaccharide profiles. Despite consisting of different DCFHP glycoforms, these two preparations were highly similar in their key quality attributes including molecular size, structural integrity, conformational stability, binding to ACE2 receptor and mouse immunogenicity profiles. Taken together, these studies support future preclinical and clinical development of an AH-adjuvanted DCFHP vaccine candidate produced in CHO cells.

Oral vaccination using microdevices to deliver α-GalCer adjuvanted vaccine afford a mucosal immune response

Oral vaccination has in the recent years gained a lot of attraction, mainly due to optimized patient compliance and logistics. However, the development of oral vaccines, especially oral subunit vaccines is challenging. Micro technology can be utilized to overcome some of these challenges, by facilitating protection and effective delivery of the vaccine components in the gastrointestinal tract (GI tract). One such technology is Microcontainers (MCs), which can be realized to be mucoadhesive and to target specific regions of the GI tract via oral delivery. Here, we test MCs, for oral delivery of the C. trachomatis vaccine candidate CTH522, in combination with effective mucosal adjuvants. The adjuvants alpha- galactosylceramide (α-GalCer), C-di-GMP and cholera toxin B were compared in vivo, to identify the most prominent adjuvant for formulation with CTH522. Formulations were administered both purely oral and as boosters following a subcutaneous (s.c.) prime with CTH522 in combination with the CAF®01 adjuvant. CTH522 formulated with α-GalCer showed to be the most efficient combination for the oral vaccine, based on the immunological analysis. Lyophilized formulation of CTH522 and α-GalCer was loaded into MCs and these were subsequently coated with Eudragit L100-55 and evaluated in vivo in mice for the ability of MCs to mediate intestinal vaccine delivery and increase immunogenicity of the vaccine. Mice receiving oral prime and boosters did show a significantly enhanced mucosal immune responses compared to naive mice. This indicates the MCs are indeed capable of delivering the vaccine formulation intact and able to stimulate the immune cells. Mice orally boosted with MCs following a s.c. prime with CAF01, demonstrated improved systemic and local Th17 responses, along with increased local IFN-γ and IgA levels compared to both the s.c. prime alone and the homologous oral prime-boost immunization. However, due to the relatively weak observed effect of the MC delivery on the immune responses, it was hypothesized that the MCs are proportionally too large for the GI tract of mice, and thus cleared before an effective immune response can be induced. To investigate this, MCs were loaded with BaSO4, and orally administered to mice. Analysis with X-ray and CT showed a transit time of approximately 1-1.5 h from the stomach to the cecum, corresponding to the standard transit time in mice, and an extremely narrow absorption window. This indicates that mice is not a suitable animal model for evaluation of MCs. These data should be taken into consideration in future in vivo trials with this and similar technologies, where larger animals might be a necessity for proof-of-concept studies.

Solid-state NMR methods for the characterization of bioconjugations and protein-material interactions

Protein solid-state NMR has evolved dramatically over the last two decades, with the development of new hardware and sample preparation methodologies. This technique is now ripe for complex applications, among which one can count bioconjugation, protein chemistry and functional biomaterials. In this review, we provide our account on this aspect of protein solid-state NMR.

Virus-Like Particle-Templated Silica-Adjuvanted Nanovaccines with Enhanced Humoral and Cellular Immunity

Virus-like particles (VLPs) are self-assembled viral proteins that represent a superior form of antigens in vaccine formulations. To enhance immunogenicity, adjuvants, especially the aluminum salts (Alum), are essentially formulated in VLP vaccines. However, Alum only induce biased humoral immune responses that limits further applications of VLP-based vaccines. To stimulate more balanced immunity, we, herein, develop a one-step strategy of using VLPs as the biotemplates to synthesize raspberry-like silica-adjuvanted VLP@Silica nanovaccines. Hepatitis B surface antigen (HBsAg) VLPs and human papillomavirus type 18 (HPV 18) VLPs are selected as model templates. Circular dichroism (CD) and affinity analyses demonstrate that HBsAg VLPs in the nanovaccines maintain their secondary structure and immunogenicity, respectively. VLP@Silica promote silica dissolution-induced lysosomal escape and cytosolic delivery of antigens, and enhance the secretion of both Th1 and Th2 type cytokines in murine bone marrow-derived dendritic cells (BMDCs). Additionally, they could improve antigen trafficking and mediate DC activation in draining lymph nodes (DLNs). Vaccination study demonstrate that both HBsAg VLP@Silica and HPV 18 VLP@Silica nanovaccines induce enhanced antigen-specific antibody productions and T-cell mediated adaptive immune responses. This design strategy can utilize VLPs derived from a diversity of viruses or their variants as templates to construct both prophylactic and therapeutic vaccines with improved immunogenicity.

Engineering the hydroxyl content on aluminum oxyhydroxide nanorod for elucidating the antigen adsorption behavior

The interaction between the aluminum salt-based adjuvants and the antigen in the vaccine formulation is one of the determining factors affecting the immuno-potentiation effect of vaccines. However, it is not clear how the intrinsic properties of the adjuvants could affect this interaction, which limits to benefit the improvement of existing adjuvants and further formulation of new vaccines. Here, we engineered aluminum oxyhydroxide (AlOOH) nanorods and used a variety of antigens including hepatitis B surface antigen (HBsAg), SARS-CoV-2 spike protein receptor-binding domain (RBD), bovine serum albumin (BSA) and ovalbumin (OVA) to identify the key physicochemical properties of adjuvant that determine the antigen adsorption at the nano-bio interface between selected antigen and AlOOH nanorod adjuvant. By using various physicochemical and biophysical characterization methods, it was demonstrated that the surface hydroxyl contents of AlOOH nanorods affected the adsorptive strength of the antigen and their specific surface area determined the adsorptive capacity of the antigen. In addition, surface hydroxyl contents had an impact on the stability of the adsorbed antigen. By engineering the key intrinsic characteristics of aluminum-based adjuvants, the antigen adsorption behavior with the aluminum adjuvant could be regulated. This will facilitate the design of vaccine formulations to optimize the adsorption and stability of the antigen in vaccine.

Freeze-thaw stability of aluminum oxide nanoparticles

The use of inorganic nanoparticles (NPs) gains interest for pharmaceutical applications, e.g. as adjuvants or drug delivery vehicles. Colloidal stability of NPs in aqueous suspensions is a major development challenge. Both frozen and lyophilized liquids are alternative presentations to liquid dispersion. To improve the basic understanding, we investigated the freeze-thawing stability of model α-Al₂O₃ NPs. Freeze-thawing was conducted in three different buffer types at pH5 and 8 without and with additives to determine fundamental formulation principles. Before freeze-thawing, α-Al₂O₃ NPs could be stabilized in sodium citrate buffer at pH5 and 8, and in sodium or potassium phosphate at pH8. Particles revealed low zeta potential values in phosphate buffers at pH5 indicating insufficient electrostatic stabilization. After freeze-thawing, an increase in NP size was strongly reduced in potassium phosphate and sodium citrate buffers. Subsequent pH measurements upon freezing revealed a drastic acidic pH shift in sodium phosphate which was further demonstrated to destabilize NPs. The ionic stabilizers gelatin A/B, Na-CMC, and SDS, were suitable to improve colloidal stability in phosphate buffers at pH5 highlighting the importance of charge stabilization. Freeze-thawing stability was best in presence of gelatin A/B, followed by PVA, mannitol, or sucrose. Depletion and steric stabilization were insufficient using PEG and surfactants respectively. Thus, we could identify the fundamental formulation principles to preserve inorganic NPs upon freezing: i) sufficient charge stabilization, ii) a maintained pH during freezing, and iii) the addition of a suitable stabilizer, preferably gelatin, not necessarily surfactants. This forms the basis for future studies, e.g. on lyophilization.

Adjuvant Selection for Influenza and RSV Prefusion Subunit Vaccines

Subunit vaccines exhibit favorable safety and immunogenicity profiles and can be designed to mimic native antigen structures. However, pairing with an appropriate adjuvant is imperative in order to elicit effective humoral and cellular immune responses. In this study, we aimed to determine an optimal adjuvant pairing with the prefusion form of influenza haemagglutinin (HA) or respiratory syncytial virus (RSV) fusion (F) subunit vaccines in BALB/c mice in order to inform future subunit vaccine adjuvant selection. We tested a panel of adjuvants, including aluminum hydroxide (alhydrogel), QS21, Addavax, Addavax with QS21 (AdQS21), and Army Liposome Formulation 55 with monophosphoryl lipid A and QS21 (ALF55). We found that all adjuvants elicited robust humoral responses in comparison to placebo, with the induction of potent neutralizing antibodies observed in all adjuvanted groups against influenza and in AdQS21, alhydrogel, and ALF55 against RSV. Upon HA vaccination, we observed that none of the adjuvants were able to significantly increase the frequency of CD4⁺ and CD8⁺ IFN-γ⁺ cells when compared to unadjuvanted antigen. The varying responses to antigens with each adjuvant highlights that those adjuvants most suited for pairing purposes can vary depending on the antigen used and/or the desired immune response. We therefore suggest that an adjuvant trial for different subunit vaccines in development would likely be necessary in preclinical studies.

The sixth revolution in pediatric vaccinology: immunoengineering and delivery systems

Infection is the predominant cause of mortality in early life, and immunization is the most promising biomedical intervention to reduce this burden. However, very young infants fail to respond optimally to most vaccines currently in use, especially neonates. In 2005, Stanley Plotkin proposed that new delivery systems would spur a new revolution in pediatric vaccinology, just as attenuation, inactivation, cell culture of viruses, genetic engineering, and adjuvantation had done in preceding decades. Recent advances in the field of immunoengineering, which is evolving alongside vaccinology, have begun to increasingly influence vaccine formulation design. Historically, the particulate nature of materials used in many vaccine formulations was empiric, often because of the need to stabilize antigens or reduce endotoxin levels. However, present vaccine delivery systems are rationally engineered to mimic the size, shape, and surface chemistry of pathogens, and are therefore often referred to as "pathogen-like particles". More than a decade from his original assessment, we re-assess Plotkin's prediction. In addition, we highlight how immunoengineering and advanced delivery systems may be uniquely capable of enhancing vaccine responses in vulnerable populations, such as infants. IMPACT: Immunoengineering and advanced delivery systems are leading to new developments in pediatric vaccinology. Summarizes delivery systems currently in use and development, and prospects for the future. Broad overview of immunoengineering's impact on vaccinology, catering to Pediatric Clinicians and Immunologists.

Simultaneous in situ visualization and quantitation of dual antigens adsorbed on adjuvants using high content analysis

Aim: Traditional antigenicity assay requires antigen recovery from the particulate adjuvants prior to analysis. An in situ method was developed for interrogating vaccine antigens with monoclonal antibodies while being adsorbed on adjuvants. Materials & methods: The fluorescence imaging-based high content analysis was used to visualize the antigen distribution on adjuvant agglomerates and to analyze the antigenicity for adsorbed antigens. Results: Simultaneous visualization and quantitation were achieved for dual antigens in a bivalent human papillomavirus vaccine with uniquely labeled antibodies. Good agreement was observed between the in situ multiplexed assays with well-established sandwich enzyme-linked immunosorbent assays. Conclusion: The streamlined procedures and the amenability for multiplexing make the in situ antigenicity analysis a favorable choice for in vitro functional assessment of bionanoparticles as vaccine antigens.

Inactivated alpha toxin from Clostridium novyi type B in nano-emulsion protect partially protects Swiss mice from lethal alpha toxin challenge

Nano-emulsions are promising carriers for antigen delivery. Here, we evaluated the efficacy of a water-oil nano-emulsion containing concentrated, inactivated Clostridium novyi (C. novyi) type B supernatant culture (nano-iCnB) in protecting Swiss mice against a lethal dose of alpha toxin concentrated extract. Proteins were confirmed in the nano-iCnB and their stabilities were determined according physical parameters such as Zeta Potential (ZP). Biochemical, hematological parameters and morphological appearance of liver, spleen and thigh muscle alterations were examined to determine the safety of the compound. Partial protection against lethal doses was achieved in immunized mice despite low IgG titers. These data suggest that our nano-emulsion is a simple and efficient method of promoting antigen delivery for toxin-related diseases.

Physicochemical study of the influenza A virus M2 protein and aluminum salt adjuvant interaction as a vaccine candidate model

Aim: The present study evaluated the structural changes resulting from the interaction between a recombinant influenza A virus M2 protein and aluminum hydroxide adjuvant to investigate the antigen for further immunological studies. Materials & methods: Membrane protein II was produced from the H1N1 subtype of human influenza A virus. The interaction between M2 protein and alum inum hydroxide adjuvant was evaluated by physicochemical techniques including scanning electron microscope, UV-Vis spectra, Fourier-transform infrared spectroscopy and circular dichroism spectroscopy. Results: Physicochemical methods showed high-level protein adsorption and accessibility to the effective parts of the protein. Conclusion: It was concluded that M2 protein secondary structural perturbations, including the α-helix-to-β-sheet transition, enhanced its mechanical properties toward adsorption.

Structural characterization of a protein adsorbed on aluminum hydroxide adjuvant in vaccine formulation

The heterogeneous composition of vaccine formulations and the relatively low concentration make the characterization of the protein antigens extremely challenging. Aluminum-containing adjuvants have been used to enhance the immune response of several antigens over the last 90 years and still remain the most commonly used. Here, we show that solid-state NMR and isotope labeling methods can be used to characterize the structural features of the protein antigen component of vaccines and to investigate the preservation of the folding state of proteins adsorbed on Alum hydroxide matrix, providing the way to identify the regions of the protein that are mainly affected by the presence of the inorganic matrix. l-Asparaginase from E. coli has been used as a pilot model of protein antigen. This methodology can find application in several steps of the vaccine development pipeline, from the antigen optimization, through the design of vaccine formulation, up to stability studies and manufacturing process.

Unraveling the enigma: elucidating the relationship between the physicochemical properties of aluminium-based adjuvants and their immunological mechanisms of action

Aluminium salts are by far the most commonly used adjuvants in vaccines. There are only two aluminium salts which are used in clinically-approved vaccines, Alhydrogel® and AdjuPhos®, while the novel aluminium adjuvant used in Gardasil® is a sulphated version of the latter. We have investigated the physicochemical properties of these two aluminium adjuvants and specifically in milieus approximating to both vaccine vehicles and the composition of injection sites. Additionally we have used a monocytic cell line to establish the relationship between their physicochemical properties and their internalisation and cytotoxicity. We emphasise that aluminium adjuvants used in clinically approved vaccines are chemically and biologically dissimilar with concomitantly potentially distinct roles in vaccine-related adverse events.

Optimizing the utilization of aluminum adjuvants in vaccines: you might just get what you want

Aluminum-containing adjuvants have been used for over 90 years to enhance the immune response to vaccines. Recent work has significantly advanced our understanding of the physical, chemical, and biological properties of these adjuvants, offering key insights on underlying mechanisms. Given the long-term success of aluminum adjuvants, we believe that they should continue to represent the “gold standard” against which all new adjuvants should be compared. New vaccine candidates that require adjuvants to induce a protective immune responses should first be evaluated with aluminum adjuvants before other more experimental approaches are considered, since use of established adjuvants would facilitate both clinical development and the regulatory pathway. However, the continued use of aluminum adjuvants requires an appreciation of their complexities, in combination with access to the necessary expertise to optimize vaccine formulations. In this article, we will review the properties of aluminum adjuvants and highlight those elements that are critical to optimize vaccine performance. We will discuss how other components (excipients, TLR ligands, etc.) can affect the interaction between adjuvants and antigens, and impact the potency of vaccines. This review provides a resource and guide, which will ultimately contribute to the successful development of newer, more effective and safer vaccines.