Characterization of TLR4 agonist effects on alhydrogel® sedimentation: a novel application of laser scattering optical profiling

Silicon or Calcium Doping Coordinates the Immunostimulatory Effects of Aluminum Oxyhydroxide Nanoadjuvants in Prophylactic Vaccines

Aluminum salts still remain as the most popular adjuvants in marketed human prophylactic vaccines due to their capability to trigger humoral immune responses with a good safety record. However, insufficient induction of cellular immune responses limits their further applications. In this study, we prepare a library of silicon (Si)- or calcium (Ca)-doped aluminum oxyhydroxide (AlOOH) nanoadjuvants. They exhibit well-controlled physicochemical properties, and the dopants are homogeneously distributed in nanoadjuvants. By using Hepatitis B surface antigen (HBsAg) as the model antigen, doped AlOOH nanoadjuvants mediate higher antigen uptake and promote lysosome escape of HBsAg through lysosomal rupture induced by the dissolution of the dopant in the lysosomes in bone marrow-derived dendritic cells (BMDCs). Additionally, doped nanoadjuvants trigger higher antigen accumulation and immune cell activation in draining lymph nodes. In HBsAg and varicella-zoster virus glycoprotein E (gE) vaccination models, doped nanoadjuvants induce high IgG titer, activations of CD4+ and CD8+ T cells, cytotoxic T lymphocytes, and generations of effector memory T cells. Doping of aluminum salt-based adjuvants with biological safety profiles and immunostimulating capability is a potential strategy to mediate robust humoral and cellular immunity. It potentiates the applications of engineered adjuvants in the development of vaccines with coordinated immune responses.

Co-Delivery of Novel Synthetic TLR4 and TLR7/8 Ligands Adsorbed to Aluminum Salts Promotes Th1-Mediated Immunity against Poorly Immunogenic SARS-CoV-2 RBD

Despite the availability of effective vaccines against COVID-19, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) continues to spread worldwide, pressing the need for new vaccines with improved breadth and durability. We developed an adjuvanted subunit vaccine against SARS-CoV-2 using the recombinant receptor-binding domain (RBD) of spikes with synthetic adjuvants targeting TLR7/8 (INI-4001) and TLR4 (INI-2002), co-delivered with aluminum hydroxide (AH) or aluminum phosphate (AP). The formulations were characterized for the quantities of RBD, INI-4001, and INI-2002 adsorbed onto the respective aluminum salts. Results indicated that at pH 6, the uncharged RBD (5.73 ± 4.2 mV) did not efficiently adsorb to the positively charged AH (22.68 ± 7.01 mV), whereas it adsorbed efficiently to the negatively charged AP (-31.87 ± 0.33 mV). Alternatively, pre-adsorption of the TLR ligands to AH converted it to a negatively charged particle, allowing for the efficient adsorption of RBD. RBD could also be directly adsorbed to AH at a pH of 8.1, which changed the charge of the RBD to negative. INI-4001 and INI-2002 efficiently to AH. Following vaccination in C57BL/6 mice, both aluminum salts promoted Th2-mediated immunity when used as the sole adjuvant. Co-delivery with TLR4 and/or TLR7/8 ligands efficiently promoted a switch to Th1-mediated immunity instead. Measurements of viral neutralization by serum antibodies demonstrated that the addition of TLR ligands to alum also greatly improved the neutralizing antibody response. These results indicate that the addition of a TLR7/8 and/or TLR4 agonist to a subunit vaccine containing RBD antigen and alum is a promising strategy for driving a Th1 response and neutralizing antibody titers targeting SARS-CoV-2.

Analysis of the Adsorbed Vaccine Formulations Using Water Proton Nuclear Magnetic Resonance-Comparison with Optical Analytics

PURPOSE

To evaluate wNMR, an emerging noninvasive analytical technology, for characterizing aluminum-adjuvanted vaccine formulations.

METHODS

wNMR stands for water proton nuclear magnetic resonance. In this work, wNMR and optical techniques (laser diffraction and laser scattering) were used to characterize vaccine formulations containing different antigen loads adsorbed onto AlPO4 adjuvant microparticles, including the fully dispersed state and the sedimentation process. All wNMR measurements were done noninvasively on sealed vials containing the adsorbed vaccine suspensions, while the optical techniques require transferring the adsorbed vaccine suspensions out of the original vial into specialized cuvette/tube for analysis. For analyzing fully dispersed suspensions, optical techniques also require sample dilution.

RESULTS

wNMR outperformed laser diffraction in differentiating high- and low-dose formulations of the same vaccine, while wNMR and laser scattering achieved comparable results on vaccine sedimentation kinetics and the compactness of fully settled vaccines.

CONCLUSION

wNMR could be used to analyze aluminum-adjuvanted formulations and to differentiate between formulations containing different antigen loads adsorbed onto aluminum adjuvant microparticles. The results demonstrate the capability of wNMR to characterize antigen-adjuvant complexes and to noninvasively inspect finished vaccine products.

Monitoring of the sedimentation kinetics of vaccine adjuvants using water proton NMR relaxation

Suspensions of solid particles find applications in many areas-mining, waste treatment, and in pharmaceutical formulations. Pharmaceutical suspensions include aluminum-adjuvanted vaccines are widely administered to millions of people worldwide annually. Hence, the stability parameters of such suspensions, for example, sedimentation rate and the compactness of the formed sediments, are of great interest to achieve the most optimal and stable formulations. Unlike currently used analytical techniques involving visual observations and/or monitoring of several optical properties using specialized glassware, water proton nuclear magnetic resonance (wNMR) used in this work allows one to analyze samples in their original sealed container regardless of its opacity and/or labeling. It was demonstrated that the water proton transverse relaxation rate could be used to monitor in real time the sedimentation process of two widely used aluminum adjuvants-Alhydrogel® and Adju-Phos®. Using wNMR, we obtained valuable information on the sedimentation rate, dynamics of the supernatant and sediment formation, and the sedimentation volume ratio (SVR) reflecting the compactness of the formed sediment. Results on SVR from wNMR were verified by caliper measurements. Verification of the sedimentation rate results from wNMR by other analytical techniques is challenging due to differences in the measured attributes and even units of the reported rate. Nonetheless, our results demonstrate the practical applicability of wNMR as an analytical tool to study pharmaceutical suspensions, for example, aluminum-adjuvanted vaccines, to provide higher quality and more efficient vaccines. Such analyses could be carried out in the original container of a suspension drug product to study its colloidal stability and to monitor its quality over time without compromising product integrity.

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.

Analytical Characterization of an Oil-in-Water Adjuvant Emulsion

Adjuvants are typically used in subunit vaccine formulations to enhance immune responses elicited by individual antigens. Physical chemical characterization of novel adjuvants is an important step in ensuring their effective use in vaccine formulations. This paper reports application of a panel of quantitative assays developed to analyze and characterize an oil-in-water adjuvant emulsion, which contains glucopyranosyl lipid A (GLA) and is a squalene-based emulsion. GLA is a fully synthetic analogue of monophosphoryl lipid A, which is a Toll-like receptor type 4 agonist and an FDA-approved adjuvant. The GLA-stable emulsion (GLA-SE) is currently being used for a respiratory syncytial virus vaccine in a phase 2 clinical trial. GLA was quantitated using reverse-phased high-performance liquid chromatography (RP-HPLC) coupled to a mass spectrometric detector, achieving higher assay sensitivity than the charged aerosol detection routinely used. Quantitation of the excipients of GLA-SE, including squalene, egg phosphatidyl choline, and Poloxamer 188, was achieved using a simple and rapid RP-HPLC method with evaporative light scattering detection, eliminating chemical derivatization typically required for these chromophore-lacking compounds. DL-α-tocopherol, the antioxidant of the GLA-SE, was quantitated using a RP-HPLC method with conventional UV detection. The experimental results compared well with values expected for these compounds based on targeted composition of the adjuvant. The assays were applied to identify degradation of individual components in a GLA-SE sample that degraded into distinct aqueous and oil phases. The methods developed and reported here are effective tools in monitoring physicochemical integrity of the adjuvant, as well as in formulation studies.

A simple fluorescence-based assay for quantification of the Toll-Like Receptor agonist E6020 in vaccine formulations

Despite the generally accepted immunostimulatory effect of Toll-Like Receptor 4 (TLR4) agonists and their value as vaccine adjuvants, there remains a demand for fast and easy quantification assays for these TLR4 agonists in order to accelerate and improve vaccine formulation studies. A new medium-throughput method was developed for the quantification of the TLR4 agonist, E6020, independent of the formulation composition. The assay uses a fluorescent hydrazide (DCCH) to label the synthetic lipopolysaccharide (LPS) analog E6020 through its diketone groups. This novel, low-cost, and fluorescence based assay may obviate the need for traditional approaches that primarily rely on Fourier transform infrared spectroscopy (FTIR) or mass spectrometry. The experiments were performed in a wide diversity of vaccine formulations containing E6020 to assess method robustness and accuracy. The assay was also expanded to evaluate the loading efficiency of E6020 in poly(lactic-co-glycolic acid) (PLGA) micro-particles.

Nanoformulation of synergistic TLR ligands to enhance vaccination against Entamoeba histolytica

Diarrheal infectious diseases represent a major cause of global morbidity and mortality. There is an urgent need for vaccines against diarrheal pathogens, especially parasites. Modern subunit vaccines rely on combining a highly purified antigen with an adjuvant to increase their efficacy. In the present study, we evaluated the ability of a nanoliposome adjuvant system to trigger a strong mucosal immune response to the Entamoeba histolytica Gal/GalNAc lectin LecA antigen. CBA/J mice were immunized with alum, emulsion or liposome based formulations containing synthetic TLR agonists. A liposome formulation containing TLR4 and TLR7/8 agonists was selected based on its ability to generate intestinal IgA, plasma IgG2a/IgG1, IFN-γ and IL-17A. Immunization with a mucosal prime followed by a parenteral boost generated a high mucosal IgA response that inhibited adherence of parasites to mammalian cells. Inclusion of the immune potentiator all-trans retinoic acid in the regimen further improved the mucosal IgA response. Immunization protected from infection with up to 55% efficacy. Our results show that a nanoliposome delivery system containing TLR agonists is a promising prospect for the development of vaccines against enteric pathogens, especially when a multifaceted immune response is desired.

Adsorption of a synthetic TLR7/8 ligand to aluminum oxyhydroxide for enhanced vaccine adjuvant activity: A formulation approach

For nearly a century, aluminum salts have been the most widely used vaccine adjuvant formulation, and have thus established a history of safety and efficacy. Nevertheless, for extremely challenging disease targets such as tuberculosis or HIV, the adjuvant activity of aluminum salts may not be potent enough to achieve protective efficacy. Adsorption of TLR ligands to aluminum salts facilitates enhanced adjuvant activity, such as in the human papilloma virus vaccine Cervarix®. However, some TLR ligands such as TLR7/8 agonist imidazoquinolines do not efficiently adsorb to aluminum salts. The present report describes a formulation approach to solving this challenge by developing a lipid-based nanosuspension of a synthetic TLR7/8 ligand (3M-052) that facilitates adsorption to aluminum oxyhydroxide via the structural properties of the helper lipid employed. In immunized mice, the aluminum oxyhydroxide-adsorbed formulation of 3M-052 enhanced antibody and TH1-type cellular immune responses to vaccine antigens for tuberculosis and HIV.

Quantitative measurement of Toll-like receptor 4 agonists adsorbed to Alhydrogel(®) by Fourier transform infrared-attenuated total reflectance spectroscopy

Aluminum salts have a long history as safe and effective vaccine adjuvants. In addition, aluminum salts have high adsorptive capacities for vaccine antigens and adjuvant molecules, for example, Toll-like receptor 4 (TLR4) agonists. However, the physicochemical properties of aluminum salts make direct quantitation of adsorbed molecules challenging. Typical methods for quantifying adsorbed molecules require advanced instrumentation, extreme sample processing, often destroy the sample, or rely on an indirect measurement. A simple, direct, and quantitative method for analysis of adsorbed adjuvant molecules is needed. This report presents a method utilizing Fourier transform infrared spectroscopy with a ZnSe-attenuated total reflectance attachment to directly measure low levels (<30 μg/mL) of TLR4 agonists adsorbed on aluminum salts with minimal sample preparation.

A nanoliposome delivery system to synergistically trigger TLR4 AND TLR7

Background

Recent reports that TLR4 and TLR7 ligands can synergistically trigger Th1 biased immune responses suggest that an adjuvant that contains both ligands would be an excellent candidate for co-administration with vaccine antigens for which heavily Th1 biased responses are desired. Ligands of each of these TLRs generally have disparate biochemical properties, however, and straightforward co-formulation may represent an obstacle.

Results

We show here that the TLR7 ligand, imiquimod, and the TLR4 ligand, GLA, synergistically trigger responses in human whole blood. We combined these ligands in an anionic liposomal formulation where the TLR7 ligand is in the interior of the liposome and the TLR4 ligand intercalates into the lipid bilayer. The new liposomal formulations are stable for at least a year and have an attractive average particle size of around 140 nm allowing sterile filtration. The synergistic adjuvant biases away from Th2 responses, as seen by significantly reduced IL-5 and enhanced interferon gamma production upon antigen-specific stimulation of cells from immunized mice, than any of the liposomal formulations with only one TLR agonist. Qualitative alterations in antibody responses in mice demonstrate that the adjuvant enhances Th1 adaptive immune responses above any adjuvant containing only a single TLR ligand as well.

Conclusion

We now have a manufacturable, synergistic TLR4/TLR7 adjuvant that is made with excipients and agonists that are pharmaceutically acceptable and will have a straightforward path into human clinical trials.

Optimizing manufacturing and composition of a TLR4 nanosuspension: physicochemical stability and vaccine adjuvant activity

Background

Nanosuspensions are an important class of delivery system for vaccine adjuvants and drugs. Previously, we developed a nanosuspension consisting of the synthetic TLR4 ligand glucopyranosyl lipid adjuvant (GLA) and dipalmitoyl phosphatidylcholine (DPPC). This nanosuspension is a clinical vaccine adjuvant known as GLA-AF. We examined the effects of DPPC supplier, buffer composition, and manufacturing process on GLA-AF physicochemical and biological activity characteristics.

Results

DPPC from different suppliers had minimal influence on physicochemical and biological effects. In general, buffered compositions resulted in less particle size stability compared to unbuffered GLA-AF. Microfluidization resulted in rapid particle size reduction after only a few passes, and 20,000 or 30,000 psi processing pressures were more effective at reducing particle size and recovering the active component than 10,000 psi. Sonicated and microfluidized batches maintained good particle size and chemical stability over 6 months, without significantly altering in vitro or in vivo bioactivity of GLA-AF when combined with a recombinant malaria vaccine antigen.

Conclusions

Microfluidization, compared to water bath sonication, may be an effective manufacturing process to improve the scalability and reproducibility of GLA-AF as it advances further in the clinical development pathway. Various sources of DPPC are suitable to manufacture GLA-AF, but buffered compositions of GLA-AF do not appear to offer stability advantages over the unbuffered composition.

In vitro evaluation of TLR4 agonist activity: formulation effects

Effective in vitro evaluation of vaccine adjuvants would allow higher throughput screening compared to in vivo studies. However, vaccine adjuvants comprise a wide range of structures and formulations ranging from soluble TLR agonists to complex lipid-based formulations. The effects of formulation parameters on in vitro bioactivity assays and the correlations with in vivo adjuvant activity is not well understood. In the present work, we employ the Limulus amebocyte lysate assay and a human macrophage cellular cytokine production assay to demonstrate the differences in in vitro bioactivity of four distinct formulations of the synthetic TLR4 agonist GLA: an aqueous nanosuspension (GLA-AF), an oil-in-water emulsion (GLA-SE), a liposome (GLA-LS), and an alum-adsorbed formulation (GLA-Alum). Furthermore, we demonstrate the importance of the localization of GLA on in vitro potency. By comparing to previous published reports on the in vivo bioactivity of these GLA-containing formulations, we conclude that the most potent activators of the in vitro systems may not be the most potent in vivo adjuvant formulations. Furthermore, we discuss the formulation considerations which should be taken into account when interpreting data from in vitro adjuvant activity assays.

Adjuvant formulation structure and composition are critical for the development of an effective vaccine against tuberculosis

One third of the world is infected with Mycobacterium tuberculosis (Mtb) with eight million new cases of active tuberculosis (TB) each year. Development of a new vaccine to augment or replace the only approved TB vaccine, BCG, is needed to control this disease. Mtb infection is primarily controlled by TH1 cells through the production of IFN-γ and TNF which activate infected macrophages to kill the bacterium. Here we examine an array of adjuvant formulations containing the TLR4 agonist GLA to identify candidate adjuvants to pair with ID93, a lead TB vaccine antigen, to elicit protective TH1 responses. We evaluate a variety of adjuvant formulations including alum, liposomes, and oil-in-water emulsions to determine how changes in formulation composition alter adjuvant activity. We find that alum and an aqueous nanosuspension of GLA synergize to enhance generation of ID93-specific TH1 responses, whereas neither on their own are effective adjuvants for generation of ID93-specific TH1 responses. For GLA containing oil-in-water emulsions, the selection of the oil component is critical for adjuvant activity, whereas a variety of lipid components may be used in liposomal formulations of GLA. The composition of the liposome formulation of ID93/GLA does alter the magnitude of the TH1 response. These results demonstrate that there are multiple solutions for an effective formulation of a novel TB vaccine candidate that enhances both TH1 generation and protective efficacy.