Non-viral delivery of the CRISPR/Cas system: DNA RNA RNP.

Since its discovery, the CRISPR/Cas technology has rapidly become an essential tool in modern biomedical research. The opportunities to specifically modify and correct genomic DNA have also raised big hope for therapeutic applications by direct genome editing. In order to achieve the intended genome modifications, the functional unit of the CRISPR/Cas system finally has to be present in the nucleus of target cells. This can be achieved by delivery of different biomolecular Cas9 and gRNA formats: plasmid DNA (pDNA), RNA or Cas9 ribonucleoproteins (RNPs). While the initial research focussed on pDNA transfections, the currently most promising strategy for systemic non-viral delivery is based on RNA which has achieved remarkable results in the first clinical trials. RNP delivery receives much attention for applications, but the translation to systemic genome editing in patients has not been reached so far. The article summarises the characteristics and differences of each format, provides an overview of the published delivery strategies and highlights recent examples of delivery systems including the status of clinical applications.