What is CRISPR?

What is CRISPR-Cas9?

CRISPR-Cas9 (Clustered Regularly Interspaced Short Palindromic Repeats) is a revolutionary gene editing technology derived from the natural immune system that bacteria developed against viruses. It was developed by Jennifer Doudna and Emmanuelle Charpentier in 2012 and won the 2020 Nobel Prize in Chemistry.

How Does It Work?

1. Targeting

A short RNA fragment called guide RNA (gRNA) is designed. This gRNA recognizes and binds to the target sequence on the DNA — like a GPS.

2. Cutting

The Cas9 protein cuts both strands of DNA at the point indicated by the gRNA. This "molecular scissors" function creates a precise double-strand break in the DNA.

3. Repair

The cut region is repaired by the cell's natural repair mechanisms. During this process:

• Gene knockout: The disease-causing gene is silenced
• Gene correction: A healthy copy is inserted into the mutated region
• Gene insertion: A new gene sequence is inserted

First FDA-Approved CRISPR Treatment

Casgevy (exagamglogene autotemcel) — The first CRISPR-based gene therapy approved by the FDA in December 2023. Used for the treatment of sickle cell disease and transfusion-dependent beta-thalassemia.

Clinical results: 29 out of 30 patients were free from severe vaso-occlusive crises for 12 months or more.

Active Clinical Targets

• Sickle cell disease — FDA Approved
• Beta-thalassemia — FDA Approved
• Duchenne muscular dystrophy — Phase 1/2 (gene therapy active)
• Huntington's disease — Phase 1/2 (gene silencing)
• Familial hypercholesterolemia — Phase 1 (CRISPR base editing). Note: Leqvio (inclisiran) is approved but uses siRNA technology, not CRISPR
• Leukemia types (CAR-T) — Approved (most CAR-T uses lentiviral vectors; CRISPR-based CAR-T in Phase 1/2)
• Hereditary hearing loss — Phase 1/2
• Hereditary blindness — Preclinical

Next-Generation Technologies

Base Editing

Technology capable of making single letter (nucleotide) changes without double-strand cutting of DNA. More precise, less risk of side effects. First human clinical trials began in 2025.

Prime Editing

The most advanced CRISPR derivative working on a "search-and-replace" principle. Can make single nucleotide changes, small insertions, and deletions.

Limitations and Risks

• Off-target effects: Cas9 cutting unintended DNA regions
• Delivery challenge: Delivering CRISPR components to the right cells (requires AAV vector or LNP)
• Ex vivo limitation: Some treatments require cells to be processed outside the body
• Immune response: The body may recognize the Cas9 protein as foreign
• Ethical debates: Germline editing (heritable changes) is controversial