Toward In Vivo Gene Therapy Using CRISPR

CRISPR, a revolutionizing technology allowing researchers to navigate in and edit the genome, is moving on the fast track toward clinical use for ex vivo correction of disease-causing mutations in stem cells. As we await the first trials utilizing ex vivo CRISPR editing, implementation of CRISPR-based gene editing as an in vivo treatment directly in patients still remains an ultimate challenge. However, quickly accumulating evidence has provided proof-of-concept for efficacious editing in vivo. Attempts to edit genes directly in animals have largely relied on classical vector systems based on virus-based delivery of gene cassettes encoding the Cas9 endonuclease and single guide RNA, the key components of the CRISPR system. However, whereas persistent gene expression has been the primary goal of gene therapy for decades, things may be different in the case of CRISPR delivery. Is short-term presence of the CRISPR components perhaps sufficient for efficacy and ideal for safety?-and are strategies needed for restricting immune recognition of the bacteria-derived editing tool? Here, while answers to these questions still blow in the wind, we review prominent examples of genome editing with focus on targeting of genes with CRISPR in liver, muscles, and eyes of the mouse.