Towards animal free and science based measures of critical quality attributes for vaccine quality control and release

Aluminum Adjuvants-'Back to the Future'

Aluminum-based adjuvants will continue to be a key component of currently approved and next generation vaccines, including important combination vaccines. The widespread use of aluminum adjuvants is due to their excellent safety profile, which has been established through the use of hundreds of millions of doses in humans over many years. In addition, they are inexpensive, readily available, and are well known and generally accepted by regulatory agencies. Moreover, they offer a very flexible platform, to which many vaccine components can be adsorbed, enabling the preparation of liquid formulations, which typically have a long shelf life under refrigerated conditions. Nevertheless, despite their extensive use, they are perceived as relatively 'weak' vaccine adjuvants. Hence, there have been many attempts to improve their performance, which typically involves co-delivery of immune potentiators, including Toll-like receptor (TLR) agonists. This approach has allowed for the development of improved aluminum adjuvants for inclusion in licensed vaccines against HPV, HBV, and COVID-19, with others likely to follow. This review summarizes the various aluminum salts that are used in vaccines and highlights how they are prepared. We focus on the analytical challenges that remain to allowing the creation of well-characterized formulations, particularly those involving multiple antigens. In addition, we highlight how aluminum is being used to create the next generation of improved adjuvants through the adsorption and delivery of various TLR agonists.

Maturation of Aluminium Adsorbed Antigens Contributes to the Creation of Homogeneous Vaccine Formulations

Although aluminium-based vaccines have been used for almost over a century, their mechanism of action remains unclear. It is established that antigen adsorption to the adjuvant facilitates delivery of the antigen to immune cells at the injection site. To further increase our understanding of aluminium-based vaccines, it is important to gain additional insights on the interactions between the aluminium and antigens, including antigen distribution over the adjuvant particles. Immuno-assays can further help in this regard. In this paper, we evaluated how established formulation strategies (i.e., sequential, competitive, and separate antigen addition) applied to four different antigens and aluminium oxyhydroxide, lead to formulation changes over time. Results showed that all formulation samples were stable, and that no significant changes were observed in terms of physical-chemical properties. Antigen distribution across the bulk aluminium population, however, did show a maturation effect, with some initial dependence on the formulation approach and the antigen adsorption strength. Sequential and competitive approaches displayed similar results in terms of the homogeneity of antigen distribution across aluminium particles, while separately adsorbed antigens were initially more highly poly-dispersed. Nevertheless, the formulation sample prepared via separate adsorption also reached homogeneity according to each antigen adsorption strength. This study indicated that antigen distribution across aluminium particles is a dynamic feature that evolves over time, which is initially influenced by the formulation approach and the specific adsorption strength, but ultimately leads to homogeneous formulations.

Development of a cell line-based in vitro assay for assessment of Diphtheria, Tetanus and acellular Pertussis (DTaP)-induced inflammasome activation

Safety and potency assessment for batch release testing of established vaccines still relies partly on animal tests. An important avenue to move to batch release without animal testing is the consistency approach. This approach is based on thorough characterization of the vaccine to identify critical quality attributes that inform the use of a comprehensive set of non-animal tests to release the vaccine, together with the principle that the quality of subsequent batches follows from their consistent production. Many vaccine antigens are by themselves not able to induce a protective immune response. The antigens are therefore administered together with adjuvant, most often by adsorption to aluminium salts. Adjuvant function is an important component of vaccine potency, and an important quality attribute of the final product. Aluminium adjuvants are capable of inducing NLRP3 inflammasome activation. The aim of this study was to develop and evaluate an in vitro assay for NLRP3 inflammasome activation by aluminium-adjuvanted vaccines. We evaluated the effects of Diphtheria-Tetanus-acellular Pertussis combination vaccines from two manufacturers and their respective adjuvants, aluminium phosphate (AP) and aluminium hydroxide (AH), in an in vitro assay for NLRP3 inflammasome activation. All vaccines and adjuvants tested showed a dose-dependent increase in IL-1β production and a concomitant decrease in cell viability, suggesting NLRP3 inflammasome activation. The results were analysed by benchmark dose modelling, showing a similar 50% effective dose (ED50) for the two vaccine batches and corresponding adjuvant of manufacturer A (AP), and a similar ED50 for the two vaccine batches and corresponding adjuvant of manufacturer B (AH). This suggests that NLRP3 inflammasome activation is determined by the adjuvant only. Repeated freeze-thaw cycles reduced the adjuvant biological activity of AH, but not AP. Inflammasome activation may be used to measure adjuvant biological activity as an important quality attribute for control or characterization of the adjuvant.

National control laboratory independent lot testing of COVID-19 vaccines: the UK experience

The past 18 months have seen an unprecedented approach to vaccine development in the global effort against the COVID-19 pandemic. The process from discovery research, through clinical trials and regulatory approval often takes more than 10 years. However, the critical need to expedite vaccine availability in the pandemic has meant that new approaches to development, manufacturing, and regulation have been required: this has necessitated many stages of product development, clinical trials, and manufacturing to be undertaken in parallel at a global level. Through the development of these innovative products, the world has the best chance of finding individual, or combinations of, vaccines that will provide adequate protection for the world’s population. Despite the huge scientific and regulatory achievements and significant investment to accelerate vaccine availability, it is essential that safety measures are not compromised. Here we focus on the post regulatory approval testing by independent laboratories that provides an additional assurance of the safety and quality of a product, with an emphasis on the UK experience through the National Institute for Biological Standards and Control (NIBSC), an expert centre of the UK’s Medicines and Healthcare products Regulatory Agency (MHRA).