Illustration depicting how CRISPR/Cas9 can be packaged for gene-modifying therapy. Cas9 and gRNA are delivered via a vector without donor template (left) or with donor template (right). When given without donor template, gene ablation can be achieved at a target sequence specified by gRNA. Cas9 variants can be used to create a shorter sequenced, single construct. Precise homology-directed repair is achieved when the vector includes a donor template. ITR sequences allow identification and encapsulation of the construct by the viral vector. ITR, inverted terminal repeat; gRNA, guide RNA; Cas9, CRISPR-associated protein 9.