Improved storage of influenza HA-VLPs using a trehalose-glycerol natural deep eutectic solvent system

Vaccines are typically stored under refrigerated conditions (2-8 degrees C) to limit potency and efficacy loss. Maintaining the cold chain is costly and prone to vaccine wastage due to unexpected changes in the stor-age conditions. The development of formulations conferring enhanced stability can extend vaccine shelf-life and facilitate storage under non-refrigerated conditions, thus simplifying the distribution process and reducing vaccine wastage. In this study, the suitability of a natural deep eutectic system (NADES) consist-ing of trehalose and glycerol (TGly) for storage of influenza hemagglutinin (HA)-displaying virus-like par-ticles (VLPs) was successfully demonstrated. TGly was efficient in maintaining the activity and physical integrity of HA-VLPs for up to 4 h at 50 degrees C (accelerated stability study), with half-life values = 20-34 h for the best TGly formulations. Importantly, improved storage is achieved at increasingly higher TGly con-centrations, hence confirming the importance of TGly content in its protective capacity. In addition, HA-VLPs were stable in TGly for over one month at room temperature (short-term stability study), with no impact on HA titer or particle size distribution. This work highlights the potential of NADES to improve stability of VLP-based vaccines, showing promising protective capacity under non-refrigerated conditions and short-term thermal stress, and thus having a notable impact on vaccine's cold chain. (c) 2021 Elsevier Ltd. All rights reserved.