Expression of proteins through plasmid DNA transfection in monocytes, macrophages or dendritic cells is limited to certain model cell lines like RAW264.7 macrophages or THP-1 monocytes, and it is not always reliable in terms of efficiency and cell viability.
It is commonly assumed that cells of the MPS are “resistant” to plasmid transfection as part of the innate immune system. Once imported in the cytosol, double-stranded DNA is recognized by intracellular receptors activating enzymatic cascades like AIM-2/IL and cGAS-STING/IF before it can reach the nucleus, then inhibiting further processing. It does not mean that transfection reagents are not able to transport DNA into the cells, but that DNA has simply no chance to reach the nucleus.
As an alternative, transfecting cells with mRNA results in effective and reliable protein expression. Upon delivery, mRNA is directly expressed in the cytosol through a promoter-independent process and protein is detectable as early as 2 or 4h post-transfection.
As shown in the table below, mRNA provides a very productive template for translation and significantly increases the transfection efficiency of the Viromer® RED reagent. This improvement is also related to current modified mRNA chemistries that have solved much of the instability associated with its native form and its capacity to elicit innate immune responses.