Supercharged GFP is a nice tool from the Liu lab but is quite variable in terms of nucleic acid delivery across cell types. For gRNA delivery, while transfection is feasible, the best results in primary cells have been with viral-based expression systems that give stable and nuclear-based expression. Lenti-CRISPR v2 from the Zhang lab works quite well in most primary cells, and would probably have superior editing efficiency to any transfection-based method.

Regardless of the method of Cas9 and gRNA delivery, genome editing takes several days and typically requires selection to enrich for Cas9 transfected or transduced cells. If your monocytes only live a few days in culture, you will not be able to perform gene editing fast enough to perform any functional assays. Instead, you might need to target a progenitor cell type and then differentiate monocytes from a genome-edited precursor.

David Liu's group at Harvard published what looks like a brilliant method in Nature Biotechnology last week.  His method employs using cationic lipids and proteins fused to supercharged GFP.  Transfecting protein allows the CRISPR process to take place very rapidly which seems to be a big advantage for primary cells.  They even show that the technique works in vivo in mice!

See

Cationic lipid-mediated delivery of proteins enables efficient protein-based genome editing in vitro and in vivo.

Zuris JA, Thompson DB, Shu Y, Guilinger JP, Bessen JL, Hu JH, Maeder ML, Joung JK, Chen ZY, Liu DR.

Nat Biotechnol. 2015 Jan;33(1):73-80. doi: 10.1038/nbt.3081. Epub 2014 Oct 30.

Supercharged GFP is a nice tool from the Liu lab but is quite variable in terms of nucleic acid delivery across cell types. For gRNA delivery, while transfection is feasible, the best results in primary cells have been with viral-based expression systems that give stable and nuclear-based expression. Lenti-CRISPR v2 from the Zhang lab works quite well in most primary cells, and would probably have superior editing efficiency to any transfection-based method.

Regardless of the method of Cas9 and gRNA delivery, genome editing takes several days and typically requires selection to enrich for Cas9 transfected or transduced cells. If your monocytes only live a few days in culture, you will not be able to perform gene editing fast enough to perform any functional assays. Instead, you might need to target a progenitor cell type and then differentiate monocytes from a genome-edited precursor.

Thanks a lot for your detailled comments. It's very helpful.

Eric - could you let us know what you decided to do? I am speculating on the utility of using Cas9 to immortalise human microglia, as the currently available lines are dissimilar from the primary cells (or not provided by the researcher to share). Microglia will live longer so maybe not such a problem. :-) Thanks!

We are using a different approach for primary human cells: adénovirus and siRNAs

Thanks Eric.