Biodistribution of mRNA vaccines in rats: Enrichment in injection site and lymph tissues and rapid clearance without tissue persistence.
Level 5 - mechanism / opinion, no new human data
Preclinical animal biodistribution and pharmacokinetic study
PubMed 42233109 · doi:10.1016/j.omtn.2026.102948
What was done
Researchers evaluated the tissue distribution, clearance kinetics, and metabolism of three intramuscular mRNA lipid nanoparticle (LNP) products sharing an identical LNP matrix in rats: mRNA-1273 (Spikevax), mRNA-1647 (an investigational cytomegalovirus vaccine), and a reporter luciferase mRNA product. They assessed organ exposure, unbound spike protein clearance, repeat-dose accumulation, and the excretion pathways of the ionizable lipid component (lipid H).
What was found
The highest exposures occurred at the injection site, draining lymph nodes, and spleen, with minimal distribution to other organs across all three formulations. Vaccine component concentrations declined rapidly, with model projections reaching low or unquantifiable levels by approximately 2 weeks. Free spike protein after mRNA-1273 administration was transient, with a modeled decline in under 5 days and no accumulation following repeated dosing. The ionizable lipid (lipid H) underwent biotransformation and excretion via renal and hepatic pathways without human-specific metabolites.
Why it matters
These findings demonstrate that diverse mRNA payloads sharing a common LNP platform exhibit consistent, predictable biodistribution and rapid clearance in an animal model, supporting safety platform-extrapolation across different mRNA-LNP therapeutics.
Limits
The study was conducted exclusively in rats, so human pharmacokinetic and biodistribution parameters may differ. The abstract does not disclose exact sample sizes, specific quantitative exposure metrics, or assay detection limits.
Cited by
- context Following mRNA vaccine injection into muscle cells, translated spike protein levels peak after 24 hours, vaccine mRNA has a half-life of 48 to 72 hours, and the lipid nanoparticle vehicle degrades within hours.