The spontaneous uptake of naked nucleic acids by cells is a very inefficient process. Therefore, systems are needed which will facilitate their entry into the cell. Two major classes of delivery vehicles can be distinguished. Viral systems are known to be very efficient, yet their use raises some safety concerns. Non-viral delivery systems might be less efficient, yet they are cheaper to produce and they are more susceptible to chemical modifications serving their improvement. Non-viral vectors could be classified in two categories. Electroporation, gene gun and sonoporation are physical methods that compromise the barrier function of the plasma membrane. The cargo introduced by means of these methods is delivered directly to the cytosol. Complexes formed upon mixing nucleic acids with cationic carriers (lipids and polymers) will be internalized by endocytosis.
Over the last ten years of my scientific career I have used all non-viral delivery methods to deliver nucleic acids (mRNA and pDNA). In this process I learned that the IDEAL delivery system does not exist. The onset and duration of nucleic acid-induced protein production strongly depends on the nature of the nucleic acid and the carrier used as well as on the way the complexes are prepared. The desired time frame of protein production depends on the cell type to be transfected and the specific application.
My current research mainly focuses on exploiting possibilities to transfect cells with mRNA which has some clear advantages over the use of pDNA. The higher safety, due to the avoidance of genomic insertion, and the absence of the need to provide for a promoter and a terminator are clearly in favor of mRNA. mRNA-based gene therapy is likely to be quite effective when transient production of a protein is required. This includes transient modification of stem cells and dendritic cells which can be further used in the clinical set-up.