Physiochemical and functional characterization of antigen proteins eluted from aluminum hydroxide adjuvant

Development of a multiplex-based immunoassay for the characterization of diphtheria, tetanus and acellular pertussis antigens in human combined DTaP vaccines

Routine batch quality testing before vaccine release, notably for potency evaluation, still relies on animal use for several animal and human vaccines. In this context, the VAC2VAC project is a public-private consortium of 22 partners funded by EU whose the main objective is to reduce the number of animal used for batch testing by developing immunoassays that could be implemented for routine potency assessment of vaccines. This paper focused on the development of a Luminex-based multiplex assay to monitor the consistency of antigen quantity and quality throughout the production process of DTaP vaccines from two human vaccine manufacturers. Indepth characterized monoclonal antibody pairs were used for development and optimization of the Luminex assay with non-adsorbed and adsorbed antigens and with complete vaccine formulations from both manufacturers. The multiplex assay demonstrated good specificity, reproducibility and absence of cross-reactivity. Analysis of over and underdosed formulations, heat and H2O2-degraded products as well as batch to batch consistency of vaccines from both manufacturers brought the proof of concept for a future application of the multiplex immunoassay as a useful tool in the frame of DTaP vaccine quality control.

Rapid, high throughput protein estimation method for saponin and alhydrogel adjuvanted R21 VLP Malaria vaccine based on intrinsic fluorescence

Protein content estimation of recombinant vaccines at drug product (DP) stage is a crucial lot release and stability indicating assay in biopharmaceutical industries. Regulatory bodies such as US-FDA and WHO necessitates the quantitation of protein content to assess process parameters as well as formulation losses. Estimation of protein content at DP stage in presence of adjuvants (e.g AlOOH, AlPO₄, saponin and squalene) is quite challenging, and the challenge intensifies when the target protein is in Virus like particles (VLP) form, owing to its size and structural complexity. Methods available for protein estimation of adjuvanted vaccines mostly suffer from inaccuracy at lower protein concentrations and in most cases require antigen desorption before analysis. Present research work is based on the development of a rapid plate-based method for protein estimation through intrinsic fluorescence by using Malaria vaccine R21 VLP as a model protein. Present method exhibited linearity for protein estimation of R21, in the range of 5-30 µg/mL in Alhydrogel and 4-20 µg/mL for Matrix M adjuvant. The method was validated as per ICH guidelines. The limit of quantification was found to be 0.94 µg/mL for both Alhydrogel and Matrix M adjuvanted R21. The method was found specific, precise and repeatable. This method is superior in terms of less sample quantity requirement, multiple sample analysis, short turnaround time and is non-invasive. This method was found to be stability indicating, works for other proteins containing tryptophan residues and operates well even in presence of host cell proteins. Based on the study, present method can be used in vaccine industries for routine in-process sample analysis (both inline and offline), lot release of VLP based drug products in presence of Alhydrogel and saponin based adjuvant systems.

The immunostimulatory effects of hydroxypropyltrimethyl ammonium chloride chitosan-carboxymethyl chitosan nanoparticles

In this study, we generated chitosan nanoparticles by exploiting the electrostatic interactions between positively charged hydroxypropyltrimethyl ammonium chloride chitosan (HACC) and negatively charged carboxymethyl chitosan (CMC), and examined the effects of altering the molecular weight and carboxymethyl substitution sites of the chitosan molecules. Particle size, potential, and encapsulation efficiency of the various chitosan nanoparticles were examined; the particle size range was 162.40-332.80 nm, the charge range was 19.50-40.60 mV, and the encapsulation efficiency range was 48.4-70.7%. We then examined the immunostimulatory effects of the nanoparticle variants on dendritic cells (DCs); we found that the site of carboxymethyl substitution significantly affected the immunostimulatory effects of the nanoparticles. Two nanoparticle types, 200 kDa N,O-carboxymethyl chitosan-HACC (NO-CMC-HACC) and N-carboxymethyl chitosan-HACC (N-CMC-HACC), greatly promoted the expression of interleukin-6, tumor necrosis factor, and interleukin-1β in DCs. Moreover, NO-CMC-HACC nanoparticles caused an increase in major histocompatibility complex-II (MHC-II), CD11c, CD80, and CD86 secretion in DCs, indicating that these nanoparticles promoted antigen presentation. We then examined chitosan nanoparticle uptake by DCs using laser confocal microscopy; we found that the NO-CMC-HACC nanoparticles were more readily absorbed by DCs compared to the N-CMC-HACC nanoparticles. Therefore, we concluded that 200 kDa NO-CMC-HACC nanoparticles exhibited strong potential as immunological adjuvants.

Recombinant protein vaccines, a proven approach against coronavirus pandemics

With the COVID-19 pandemic now ongoing for close to a year, people all over the world are still waiting for a vaccine to become available. The initial focus of accelerated global research and development efforts to bring a vaccine to market as soon as possible was on novel platform technologies that promised speed but had limited history in the clinic. In contrast, recombinant protein vaccines, with numerous examples in the clinic for many years, missed out on the early wave of investments from government and industry. Emerging data are now surfacing suggesting that recombinant protein vaccines indeed might offer an advantage or complement to the nucleic acid or viral vector vaccines that will likely reach the clinic faster. Here, we summarize the current public information on the nature and on the development status of recombinant subunit antigens and adjuvants targeting SARS-CoV-2 infections.

Nucleic acids presenting polymer nanomaterials as vaccine adjuvants

Most vaccines developed today include only the antigens that best stimulate the immune system rather than the entire virus or microbe, which makes vaccine production and use safer and easier, though they lack potency to induce acceptable immunity and long-term protection. The incorporation of additional immune stimulating components, named adjuvants, is required to generate a strong protective immune response. Nucleic acids (DNA and RNA) and their synthetic analogs are promising candidates as vaccine adjuvants activating Toll-like receptors (TLRs). Additionally, in the last few years several nanocarriers have emerged as platforms for targeted co-delivery of antigens and adjuvants. In this review, we focus on the recent developments in polymer nanomaterials presenting nucleic acids as vaccine adjuvants. We aim to compare the effectiveness of the various classes of polymers in immune modulating materials (nanoparticles, dendrimers, single-chain particles, nanogels, polymersomes and DNA-based architectures). In particular, we address the critical role of parameters such as size, shape, complexation and release of TLR ligands, cellular uptake, stability, toxicity and potential importance of spatial control in ligand presentation.

An intrinsic fluorescence method for the determination of protein concentration in vaccines containing aluminum salt adjuvants

Determination of protein concentration in vaccines containing aluminum salt adjuvant typically necessitates desorption of the protein prior to analysis. Here we describe a method based on the intrinsic fluorescence of tyrosine and tryptophan that requires no desorption of proteins. Adjuvanted formulations of three model Bordetella pertussis antigens were excited at 280 nm and their emission spectra collected from 290 to 400 nm. Emission spectra of protein antigens in the presence of aluminum salt adjuvants were able to be detected, the effects of adjuvants on the spectra were analyzed, and linear regressions were calculated. The fluorescence method proved to be very sensitive with a limit of quantification between 0.4 and 4.4 µg/mL and limit of linearity between 100 and 200 µg/mL, across the formulations tested. The fluorescence method was found to be influenced by adjuvant presence, type of adjuvant, adjuvant concentration, buffer and pH conditions. The method also demonstrated ability to monitor the percent adsorption of antigens to the adjuvants. Furthermore, intrinsic fluorescence showed good correlation with micro-Kjeldahl elemental assay in quantifying protein concentration. Being a non-invasive, quick and sensitive method, intrinsic fluorescence has the potential to be utilized as a high throughput tool for vaccine development and conceivably implemented in-line, using in-line fluorimeters, to monitor antigen concentration during formulation processing.

Multiplex immunoassay for in vitro characterization of acellular pertussis antigens in combination vaccines

Vaccines characterization is required to ensure physical, chemical, and biological integrity of antigens and adjuvants. Current analytical methods mostly require complete antigen desorption from aluminum-based adjuvants and are not always suitable to distinguish individual antigens in multivalent formulations. Here, Luminex technology is proposed to improve the analytics of vaccine characterization. As proof of concept, TdaP (tetanus, diphtheria and acellular pertussis) combination, adjuvanted with aluminum hydroxide, was chosen as model formulation to quantify and determine the level of adsorption of acellular pertussis (aP) antigens onto adjuvant surface at the same time. The assay used specific antibodies bound to magnetic microspheres presenting unique digital signatures for each pertussis antigen, allowing the simultaneous recognition of respective antigens in the whole vaccine, avoiding laborious procedures for adjuvant separation. Accurate and reproducible quantification of aP antigens in TdaP vaccine has been achieved in the range 0.78-50 ng/mL, providing simultaneously information on antigen identity, quantity, and degree of adsorption to aluminum hydroxide. The current study could further be considered as a model to set up in vitro potency assays thus supporting the replacement of animal tests accordingly to the 3Rs concept.

Comparable quality attributes of hepatitis E vaccine antigen with and without adjuvant adsorption-dissolution treatment

Most vaccines require adjuvants for antigen stabilization and immune potentiation. Aluminum-based adjuvants are the most widely used adjuvants for human vaccines. Previous reports demonstrated the preservation of antigen conformation and other antigen characteristics after recovery from adjuvanted Hepatitis B and human papillomavirus vaccines. In this study, we used a combination of various physiochemical and immunochemical methods to analyze hepatitis E vaccine antigen quality attributes after recovery from adjuvants. All biochemical and biophysical methods showed similar characteristics of the p239 protein after recovery from adjuvanted vaccine formulation compared to the antigen in solution which never experienced adsorption/desorption process. Most importantly, we demonstrated full preservation of key antigen epitopes post-recovery from adjuvanted vaccine using a panel of murine monoclonal antibodies as exquisite probes. Antigenicity of p239 was probed with a panel of 9 mAbs using competition/blocking ELISA, surface plasmon resonance and sandwich ELISA methods. These multifaceted analyses demonstrated the preservation of antigen key epitopes and comparable protein thermal stability when adsorbed on adjuvants or of the recovered antigen post-dissolution treatment. A better understanding of the antigen conformation in adjuvanted vaccine will enhanced our knowledge of antigen-adjuvant interactions and facilitate an improved process control and development of stable vaccine formulation.

Factors affecting alum-protein interactions

Alum (or aluminum-containing) adjuvants are key components of many vaccines currently on the market. The immuno-potentiation effect of alum adjuvants is presumably due to their interaction with antigens, leading to adsorption on the alum particle surface. Understanding the mechanism of antigen adsorption/desorption and its influencing factors could provide guidance on formulation design and ensure proper in-vivo immuno-potentiation effect. In this paper, surface adsorption of several model proteins on two types of aluminum adjuvants (Alhydrogel(®) and Adjuphos(®)) are investigated to understand the underlying adsorption mechanisms, capacities, and potential influencing factors. It was found that electrostatic interactions are the major driving force for surface adsorption of all the model proteins except ovalbumin. Alhydrogel has a significantly higher adsorption capacity than Adjuphos. Several factors significantly change the adsorption capacity of both Alhydrogel and Adjuphos, including molecular weight of protein antigens, sodium chloride, phosphate buffer, denaturing agents, and size of aluminum particles. These important factors need to be carefully considered in the design of an effective protein antigen-based vaccine.

The structure of HBsAg particles is not modified upon their adsorption on aluminium hydroxide gel

Current Hepatitis B vaccines are based on recombinant Hepatitis B surface antigen (HBsAg) virus-like particles adsorbed on aluminium (Al) gel. These particles exhibit a lipoprotein-like structure with about 70 protein S molecules in association with various types of lipids. To determine whether the adsorption on Al gel affects HBsAg structure, we investigated the effect of adsorption and mild desorption processes on the protein and lipid parts of the particles, using various techniques. Electron microscopy showed that the size and morphology of native and desorbed HBsAg particles were comparable. Moreover, infrared and Raman spectroscopy revealed that the secondary structure of the S proteins was not affected by the adsorption/desorption process. Affinity measurements with Surface Plasmon Resonance showed no difference between native and desorbed HBsAg for HBsAg-specific RF-1 monoclonal antibody. Steady-state and time-resolved fluorescence data of the intrinsic fluorescence of the S proteins further indicated that the adsorption/desorption of HBsAg particles on Al gel did not modify the environment of the most emitting Trp residues, confirming that the conformation of the S proteins remains intact. Moreover, using environment-sensitive 3-hydroxyflavone probes, no significant changes of the lipid core and lipid membrane surface of the HBsAg particles were observed during the adsorption/desorption process. Finally, the ratio between lipids and proteins in the particles was found to be similar before and after the adsorption/desorption process. Taken together, our data show that adsorption on Al gel does not affect the structure of the HBsAg particles.

Flow cytometry: an alternative method for direct quantification of antigens adsorbed to aluminum hydroxide adjuvant

Flow cytometry (FC) has been widely used in biological research; however, its use for vaccine characterization has been very limited. Here we describe the development of an FC method for the direct quantification of two Neisseria meningitidis vaccine antigens, in mono- and multivalent formulations, while still adsorbed on aluminum hydroxide (AH) suspension. The antibody-based method is specific and sensitive. Because FC allows microscopic particle examination, the entire aluminum suspension carrying adsorbed antigen(s) can be analyzed directly. In addition to determining antigen concentration and identity, the assay is able to determine the distribution of the antigens on AH. High correlation coefficients (r(2)) were routinely achieved for a broad range of antigen doses from 0 to 150 μg/dose. Traditional assays for quantitative and qualitative antigen characterization on AH particles involve either complete aluminum dissolution or antigen desorption from the adjuvant. Because our direct method uses the whole AH suspension, the cumbersome steps used by traditional methods are not required. Those steps are often inefficient in desorbing the antigens and in some cases can lead to protein denaturation. We believe that this novel FC-based assay could circumvent some of the complex and tedious antigen-adjuvant desorption methods.

Nanotechnology in vaccine delivery

With very few adjuvants currently being used in marketed human vaccines, a critical need exists for novel immunopotentiators and delivery vehicles capable of eliciting humoral, cellular and mucosal immunity. Such crucial vaccine components could facilitate the development of novel vaccines for viral and parasitic infections, such as hepatitis, HIV, malaria, cancer, etc. In this review, we discuss clinical trial results for various vaccine adjuvants and delivery vehicles being developed that are approximately nanoscale (< 1000 nm) in size. Humoral immune responses have been observed for most adjuvants and delivery platforms while only viral vectors, ISCOMs and Montanide™ ISA 51 and 720 have shown cytotoxic T cell responses in the clinic. MF59 and MPL® have elicited Th1 responses, and virus-like particles, non-degradable nanoparticles and liposomes have also generated cellular immunity. Such vaccine components have also been evaluated for alternative routes of administration with clinical successes reported for intranasal delivery of viral vectors and proteosomes and oral delivery of a VLP vaccine.