Advances in genome editing - CRISPR library screens
To make use of CRISPR technology in CRISPR screenings some prerequisites need to be fulfilled:
- Availability of CRISPR libraries for the respective gene family or disease pathway
- Relevant cell types to investigate consequences of gene alterations
- Reliable method to introduce CRISPR RNPs (ribonucleoproteins) into the cells and produce gene knockouts with high efficiency
- Options to automate screening applications dealing with knockouts of several hundreds or even thousands of genes
The commercial availability of CRISPR screening libraries from many sources enables scientists to make use of this technology in the field of functional genomics. A certain gene family or pathway can be analyzed by creating specific gene knockouts and investigating the phenotypic alterations as a result of the knockout. CRISPR screens were initially performed mostly by transduction of cell lines with pooled or arrayed lentiviral of retroviral libraries. Viral transduction however, has its limitations when it comes to fast generation of libraries, using a different cell type for studying loss or gain of function mutations in functional genomics and costs for maintaining and monitoring a BSL-2 (or greater) laboratory, if live viruses are being used.
Taking advantage of the biological relevance of primary cells in contrast to cell lines is a hurdle for host specific viral transduction often leading to inefficient transduction of the primary cells. Primary cells however are superior to cell lines when it comes to investigation of cell signaling pathways, representing a biologically more relevant model.
In this light, introducing RNPs into primary cells was cumbersome and time-consuming, when using viral libraries. Transfection methods as lipofection and other chemical transfection methods have their challenges when it comes to transfecting primary cells or regarding reproducibility. Electroporation is another option regarding transfection efficiencies and reproducibility of transfection results in primary cells. However, the option for multi-well transfection and automation integration is lacking for most electroporation systems, making this option labor-intensive and time consuming.