CRISPR gene editing was borrowed from bacteria

CRISPR-Cas9 lets scientists cut and edit DNA at a chosen spot with unprecedented ease, but the system wasn’t invented from scratch. It was adapted from a natural defense that bacteria use to fight viruses, stashing snippets of a virus’s DNA so they can recognize and shred the invader if it returns.

Researchers turned this into a programmable tool. A short guide RNA steers the Cas9 enzyme to a matching DNA sequence, but Cas9 will only cut if a short adjacent signature called the PAM (protospacer adjacent motif) sits right next to the target, a safeguard that stops the bacterium from chopping up its own genome. Where the conditions match, Cas9 snips both strands, leaving a double-strand break. The cell then scrambles to repair it, and scientists exploit that repair to disable a gene or paste in new sequence.

Because you can rewrite the guide to target almost any sequence, CRISPR is faster, cheaper, and more precise than earlier methods. In 2020, Emmanuelle Charpentier and Jennifer Doudna won the Nobel Prize in Chemistry for developing it. In December 2023, the first CRISPR therapy, Casgevy (exagamglogene autotemcel), won FDA approval to treat sickle-cell disease by editing a patient’s own blood stem cells.

The power cuts both ways. In 2018, Chinese scientist He Jiankui announced he had edited the embryos of twin girls, altering the CCR5 gene to confer HIV resistance, producing the first gene-edited babies. The work drew near-universal condemnation: it crossed the bright line into heritable germline editing, the edits were mosaic and imprecise, and the risk of unintended off-target cuts made it reckless. He was later imprisoned, and the episode hardened the consensus against editing embryos destined for birth.