Directed evolution of CRISPR-Cas9 to increase its specificity

Area of Science:

• Molecular Biology
• Gene Editing Technologies
• Biotechnology

Background:

• CRISPR-Cas9 gene editing is powerful but limited by off-target effects.
• Existing high-specificity Cas9 variants often have reduced efficiency in human cells.
• Developing safer and more effective CRISPR tools is crucial for therapeutic applications.

Purpose of the Study:

• To engineer a CRISPR-Cas9 variant with high specificity and retained on-target efficiency.
• To overcome the limitations of current Cas9 variants in human cell applications.
• To enable precise and efficient DNA-free genome editing.

Main Methods:

• Employed a directed evolution approach in E. coli to generate novel Cas9 variants.
• Screened and selected variants for high specificity and on-target activity in human cells.
• Evaluated the performance of the engineered Sniper-Cas9 variant using various sgRNAs and in a ribonucleoprotein (RNP) format.

Main Results:

• Identified Sniper-Cas9, a variant demonstrating high specificity and wild-type (WT)-level on-target activities.
• Sniper-Cas9 exhibits reduced off-target effects even with extended or truncated sgRNAs.
• The engineered variant functions effectively in a preassembled ribonucleoprotein (RNP) format, facilitating DNA-free genome editing.

Conclusions:

• Sniper-Cas9 represents a significant advancement in CRISPR-Cas9 technology, offering enhanced safety and efficiency.
• This variant overcomes the trade-off between specificity and activity seen in other engineered Cas9 proteins.
• Sniper-Cas9 holds promise for precise and reliable genome editing applications, particularly in therapeutic contexts.