Monitoring mRNA vaccine antigen expression in vivo using PET/CT

The aim of this study was to evaluate the ability of PET/CT imaging to track mRNA vaccine antigen expression in mammalian systems. The researchers used E. coli dihydrofolate reductase (eDHFR) as a PET reporter gene, fused to the SARS-CoV-2 spike protein, to enable precise imaging of mRNA vaccine expression.

To assess the effectiveness of this approach, experiments were done in both mice and non-human primates. Mice were intramuscularly administered mRNA-lipid nanoparticles (mRNA-LNPs) encoding the eDHFR-SARS-CoV-2 spike fusion protein and imaged using [18F]fluoropropyl-trimethoprim ([18F]FP-TMP) PET/CT. Non-human primates were similarly vaccinated and imaged to evaluate the translational potential of the technique.

PET/CT imaging provided clear visualization of mRNA vaccine expression in both mice and non-human primates, showing transient expression in injection sites and draining lymph nodes. The [18F]FP-TMP radiotracer showed strong binding to the eDHFR reporter, allowing for specific tracking of mRNA translation and protein expression. Importantly, the eDHFR reporter gene did not elicit an immune response, ensuring that it does not interfere with the vaccine’s efficacy.

The data suggest that PET/CT imaging can be used to monitor mRNA vaccines, providing valuable insights into the spatiotemporal dynamics of mRNA vaccine expression. This technique offers a powerful tool for optimizing dosing and delivery routes, as well as evaluating the efficacy and safety of mRNA-based therapeutics in both preclinical and clinical settings.

Left: Representative PET/CT images of mice on day 1 and 3. Red arrow indicates [18F]FP-TMP signal in the ipsilateral popliteal LN of the S2PΔf-eDHFR vaccinated mouse on day 1. Right: [18F]FP-TMP SUVmax quantification in the ipsilateral LN and injected muscle on day 1 (n = 6 mice per group) and day 3 (n = 4 mice per group).