Innate immune response and programmed cell death following carrier-mediated delivery of unmodified mRNA to respiratory cells.

In this report we show that carrier-mediated delivery of mRNA may activate TLR3 signaling in respiratory cells. This activation of the innate immune system was accompanied with a massive production of type 1 interferons and other immunostimulating cytokines. The recognition of mRNA by the innate immune system was also associated with cell death, which proceeded in human respiratory cells via pyroptosis, a form of programmed cell death mediated by substantial overexpression of caspase-1. This indicated that the delivered mRNA is most likely also recognized by NOD-like receptors which regulate caspase-1 production. The viability of murine respiratory cells was less affected by mRNA transfection, which is in line with the lower transfection efficiency, lower innate immune response and the absence of a massive caspase-1 upregulation in these cells. Finally, we also demonstrated that the recognition of the delivered mRNA by the innate immune system had a negative effect on mRNA translation.