Figure 1.

Three translational challenges for in vivo somatic cell genome editing with CRISPR-Cas9

(1) Off-target DNA double-strand break formation. The gene of interest is targeted by the single guide RNA (sgRNA) and cut by Cas9, and it results in double-stranded breaks that can subsequently be repaired to generate on-target edits. However, with prolonged exposure of Cas9 to the genome, there can be an increase in unwanted modifications at off-target sites. (2) Antibody neutralization to delivery vectors. Antigen-presenting cells may bind capsid proteins or other components from the delivery vector (e.g., polyethylene glycol [PEG]) to trigger an antibody-mediated immune response. (3) Immune response to Cas and vector proteins. MHC class I molecules may bind peptides from degradation of Cas9 and/or the viral vector and present them on the cell surface. These peptides could be presented to T cells and trigger an adaptive immune response.