Michael J. A. Wilkinson

The authors would like to make the following corrections to the published paper

Background/Objectives: Murine models play a key role in guiding formulation and immunogenicity studies across various vaccine platforms, including mRNA-based vaccines. Typically, a narrow age range (6 to 8 weeks) is used in these studies. Here, we investigated whether widening this age range could provide greater flexibility in experimental design without impacting pre-clinical outcomes. Methods: To achieve this, we evaluated two commonly used lipid nanoparticle (LNP) formulations (based on SM102 and ALC-0315 ionizable lipids) containing either firefly luciferase or ovalbumin mRNA in female BALB/c mice aged 4, 8, and 16 weeks. LNPs were prepared and purified via microfluidics, and their size, polydispersity, zeta potential, and encapsulation efficiency were measured. Mice were injected intramuscularly, and the in vivo bioluminescence and antibody titers were measured to evaluate mRNA expression profiles and immunogenicity across the three age groups. Results: Our findings show that the 4-week-old mice exhibited higher protein expression following mRNA administration compared to the older groups; however, no significant differences were observed between the 8- and 16-week-old mice. Despite the initial higher protein expression, the antibody responses after the prime dose were lower in the 4-week-old mice compared to the other two groups. However, following the booster dose, antibody levels were comparable across all three age groups. Conclusions: By identifying a broader age range window, we provide greater flexibility in study design, enhance data comparability across studies, and promote more efficient use of animal resources, all while maintaining reliable and representative results in these murine models.

Driven by the longer lifespans of humans, particularly in Westernised societies, and the need to know more about ‘healthy ageing’, ageing mice are being used increasingly in scientific research. Many departments and institutes involved with ageing research have developed their own systems to determine intervention points for potential refinements and to identify humane end points. Several good systems are in use, but variations between them could contribute to poor reproducibility of the science achieved. Working with scientific and regulatory communities in the UK, we have reviewed the clinical signs observed in ageing mice and developed recommendations for enhanced monitoring, behaviour assessment, husbandry and veterinary interventions. We advocate that the default time point for enhanced monitoring should be 15 months of age, unless prior information is available. Importantly, the enhanced monitoring should cause no additional harms to the animals. Where a mouse strain is well characterised, the onset of age-related enhanced monitoring may be modified based on knowledge of the onset of an expected age-related clinical sign. In progeroid models where ageing is accelerated, enhanced monitoring may need to be brought forward. Information on the background strain must be considered, as it influences the onset of age-related clinical signs. The range of ageing models currently used means that there will be no ‘one-size fits all’ solution. Increased awareness of the issues will lead to more refined and consistent husbandry of ageing mice, and application of humane end points will help to reduce the numbers of animals maintained for longer than is scientifically justified.