Defective Host Immunity in a Mouse Hindlimb Ischemia Model Attenuates the Blood Flow Recovery Promoted by an mRNA/LNP Formulation.

mRNA therapeutics represent a relatively new therapeutic modality with the potential for a diverse range of clinical applications, from vaccines to regenerative therapy. Recent clinical advances in mRNA-based vaccines have revealed that the inflammatory nature of lipid nanoparticle (LNP) formulations leads to acute side effects and plays an important adjuvant role in enhancing efficacy (i.e., immunogenicity). Therefore, understanding the biological responses associated with LNP formulations is broadly interesting for further advancing the therapeutic application of the mRNA platform while ensuring safety and efficacy. Here, we report that an intramuscularly administered firefly luciferase (Fluc) mRNA/LNP formulation enhanced proinflammatory responses, characterized by upregulation of proinflammatory chemokine expression and local leukocyte infiltration. Furthermore, in a mouse hindlimb ischemia (HLI) model, this mRNA/LNP formulation induced blood flow recovery without mRNA encoding any pro-angiogenic gene. In an attempt to mitigate the immune response, we employed severely immunocompromised NSG mice, which exhibit multiple defects in host immunity, as an HLI model and demonstrated that the mRNA/LNP formulation was unable to induce blood flow recovery in this condition. These findings suggest that the mRNA/LNP formulation can be the primary substance in enhancing the blood flow recovery after ischemia through immune activation.