New gene-editing tools move beyond CRISPR to rewrite large DNA segments

Scientists are developing advanced genome-editing tools to replace entire faulty genes and build complex cellular circuits, moving past the limits of traditional CRISPR-Cas9. While CRISPR-Cas9 and base editing are useful for making small changes or turning off genes, they struggle to insert large DNA segments and can be difficult to use in non-dividing cells like neurons. Furthermore, base editing must be tailored to an individual's specific DNA, making it impractical for diseases like Stargardt's disease, which can be caused by any of more than 1,200 variants of the ABCA4 gene.

New Techniques

To solve this bottleneck, researchers are combining CRISPR elements with other enzymes to stitch large DNA segments into genomes. Omar Abudayyeh and Jonathan Gootenberg at Harvard Medical School developed a technique called PASTE, which uses a large serine integrase called Bxb1 along with a Cas9 protein to insert DNA without breaking both strands. Researchers at Tome Biosciences used a variation of PASTE in cynomolgus monkeys to replace a gene linked to haemophilia B, successfully correcting about half of the liver cells after a single treatment. Another system called evoCAST, optimized by Sam Sternberg and David Liu, can insert up to 15,000 DNA bases into human cells using CRISPR-associated transposases.

Context

These emerging techniques represent the next wave of genetic medicine, aiming to move from simply breaking or modifying single letters of DNA to writing entire functional genes. However, delivering multiple complex components into human cells remains a major hurdle for researchers working on clinical applications.