How do CRISPR-based therapies target specific genes?

Mechanism of target recognition and cutting

CRISPR-based therapies direct molecular scissors to specific DNA sequences by using complementary RNA sequences that guide a programmable nuclease. Jennifer Doudna at the University of California Berkeley and Emmanuelle Charpentier at the Max Planck Unit for Infection Biology described how a short CRISPR RNA can program a Cas nuclease to bind and cleave DNA at matching sequences. The guide RNA contains a sequence complementary to the target gene, and the Cas protein scans the genome until the guide RNA base-pairs with a matching stretch of DNA adjacent to a short motif required for binding. Once bound, the nuclease domain of Cas9 or other Cas variants cuts the DNA, producing either a double strand break or a single strand nick depending on the protein used and its engineered form.

After cutting, cellular DNA repair pathways determine the therapeutic outcome. Non-homologous end joining repairs breaks imprecisely and often introduces small insertions or deletions that can disable a faulty gene. Homology-directed repair can install precise changes when a repair template is supplied, enabling correction of single-base mutations or insertion of therapeutic sequences. To avoid double strand breaks and their risks, researchers such as David Liu at the Broad Institute developed base editors and prime editors that chemically change individual bases or write new sequences without making a full break, increasing precision and reducing some forms of collateral damage.

Delivery, specificity, and biological consequences

Targeting a gene in a patient requires delivering the guide and nuclease to the appropriate cells. Viral vectors such as adeno-associated virus are commonly used for direct in vivo delivery because of efficient cell entry, while ex vivo approaches extract patient cells, edit them in culture, and return them to the patient, a strategy used by companies developing treatments for blood disorders. Delivery method influences where edits occur in the body, the number of cells modified, and the potential for immune recognition of the bacterial-derived Cas proteins.

Off-target editing and immune responses represent leading safety concerns. Even imperfect binding can lead to cuts at unintended sites with functional consequences for genes and regulatory regions. Regulatory bodies and clinical researchers monitor these risks through deep sequencing and long-term follow-up. The U.S. Food and Drug Administration evaluates safety profiles for gene editing therapies before approval for clinical use.

Human, cultural, and environmental dimensions

Clinical successes such as ex vivo editing of hematopoietic stem cells to treat inherited blood diseases illustrate major human benefits, especially in communities where such conditions are prevalent and debilitating. At the same time, the prospect of germline editing and ecological applications such as gene drives raises ethical and territorial questions. Kevin Esvelt at the Massachusetts Institute of Technology has emphasized ecological risks when altering wild populations, and the announcement by He Jiankui at the Southern University of Science and Technology of germline edits in children provoked global debate about governance, consent, and cultural values. The technical capacity to target specific genes is now well established, but responsible deployment requires balancing molecular precision with social, ethical, and environmental safeguards.