When are lentiviral or adeno-associated viral (AAV) vectors necessary?

Vector selection for CRISPR gene editing should consider both application and cell type.

• In most easy-to-transfect cell lines non- viral vectors can work well.  
• Lentiviral transfection is typically necessary in cells with low transient transfection efficiency, such as primary cell cultures or hard-to-transfect cell lines. 
• AAV vectors have low immunogenicity and are preferred for in vivo gene delivery. Since the cargo limit of AAV vectors is generally smaller than other vectors (<5 kb), packaging the SpCas9 gene into these vectors can be challenging.  The Staphylococcus aureus Cas9 orthologue (SaCas9) is smaller than SpCas9 and is the preferred Cas9 variant for AAV vectors.