With regards to CRISPR/Cas9 cargoes, three forms have been explored: (i) plasmid DNA encoding both Cas9 protein and the sgRNA; (ii) a mixture of Cas9 mRNA and a separate sgRNA; and (iii) a mixture of Cas9 protein and the sgRNA (Cas9 ribonucleoprotein, Cas9 RNP) (Figure ). It is now widely believed that the safest delivery method for CRISPR is to deliver it as a complete RNP. By delivering the Cas enzyme and gRNA as a preformed RNP complex, the amount of time of the complex spent in the cells is reduced, minimizing the risks of triggering an immune response or off-target editing of the genome. 326 An outline of the various delivery systems for CRISPR therapeutics is summarized in Table .