CRISPR-Cas method

The CRISPR-Cas method is a genome editing technology derived from a prokaryotic adaptive immune system and repurposed as a programmable laboratory and therapeutic tool. Its core components are a guide RNA and a CRISPR-associated nuclease, most commonly Cas9, though alternative effectors such as Cas12a are also used. The guide RNA base-pairs with a complementary genomic sequence located next to a protospacer adjacent motif (PAM), positioning the nuclease to introduce a site-specific double-strand break. Cells repair that break either by error-prone non-homologous end joining, which typically disrupts the targeted gene, or by homology-directed repair, which can incorporate a supplied template such as a single-stranded oligodeoxynucleotide to correct a mutation or insert new sequence. Catalytically modified derivatives extend the platform beyond cutting: base editing and prime editing install defined sequence changes without a double-strand break, and CRISPR interference (CRISPRi) uses a nuclease-dead Cas protein to repress transcription. Cas9 has also been adapted for purposes other than editing, notably targeted enrichment of specific genomic regions ahead of long-read nanopore sequencing, which enables deep analysis of variable or repetitive loci in native, unamplified DNA.

Because targeting is specified by the guide RNA sequence and the presence of a compatible PAM, CRISPR-Cas can be redirected to essentially any locus in any organism, making it a foundational tool for functional genomics, disease modeling, and gene therapy. In practice, its clinical utility is limited less by the nuclease than by delivery: the editing machinery must reach the intended cells as DNA, messenger RNA, protein, or ribonucleoprotein, and strategies under investigation include lipid nanoparticle, polymeric carriers, engineered bacteria or yeast that secrete Cas9-loaded extracellular vesicles, and ex vivo electroporation of cells that are subsequently transplanted. Ex vivo approaches are furthest advanced in hematopoietic stem and progenitor cells, evaluated in humanized mouse models, and in hepatocyte transplantation for inherited metabolic liver disease. Therapeutic interest spans monogenic disorders such as beta-thalassemia, hemophilia, and Duchenne muscular dystrophy; oncology applications including melanoma and colorectal cancer, where editing is combined with Targeted cancer therapy strategies; and complex neurodegenerative disease, where CRISPR-Cas is being explored against Alzheimer's disease risk genes and pathways involving apolipoprotein E4, TREM2, amyloid beta, and microtubule-associated protein tau, with the blood–brain barrier posing an added delivery obstacle. Persistent technical concerns across all applications include off-target editing, immune responses to bacterial Cas proteins, and the efficiency and tissue specificity of delivery.