Cryo-EM: A key tool for comparative characterization of liposome-based adjuvant system AS01 manufacturing processes.

Session

LSA.12 - Application of EM in health industry

Authors

Frederic Fontaine (1), Astrid Coppens (1), Agnes Miseur (1), Michel Deschuyteneer (1), Ghislain Delpierre (1)

Affiliations

1. GSK

Keywords

adjuvant, cryo-EM, liposome

Abstract text

Adjuvants used in combination with specific vaccine antigens enhance antigen-specific immune responses, thus providing increased immunity to the targeted disease. The adjuvant system AS01 is a liposome-based adjuvant containing two immunostimulants: 3-O-desacyl-4ʹ-monophosphoryl lipid A (MPL) and the saponin QS-21. It is included in commercial vaccines such as the recombinant zoster vaccine.

The current manufacturing of AS01 is based on batch process. A new production strategy based on microfluidics is under development. This technology allows the continuous production of liposomes inside micro-channels by mixing the organic phase with a precise control of stoichiometry, temperature and reaction time. It both optimizes the use of the raw materials while increasing the productivity required to supply reliably the market with the vaccines. 

Among the various quality attributes considered to ensure an equivalent quality standard compared to the current commercial process, cryo-EM provides key information about liposome structure.

For current process, multi- or mono-layered spherical to sub-spherical liposomes with heterogeneous sizes and shapes were observed. Cryo-EM, in addition with negative staining displayed the characteristic membrane perforations of the AS01 adjuvants. Some complex liposomes or elongated structures were observed as well.

We will present here some comparative results between the current process and the new microfluidic process. 

In conclusion, cryo-EM is a critical tool for characterization of liposome-based compounds such as the AS01 adjuvant system.