Mind the Age Gap: Expanding the Age Window for mRNA Vaccine Testing in Mice

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.

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.

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.

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.