CRISPR gene-edited immune cells have been injected into three people with advanced cancer without any serious side effects, the first trial of its kind in the US. It is also the first CRISPR cancer trial in the world to publish its findings, and the encouraging results will pave the way for many more trials.

“It’s an important milestone,” says Waseem Qasim at the UCL Great Ormond Street Institute of Child Health in the UK, who is carrying out a similar trial there.

The US trial was intended only to assess safety. The three participants had tumours that hadn’t responded to other treatments, and were given only one dose of gene-edited cells.

“Is it safe and feasible?” says team member Edward Stadtmauer at the University of Pennsylvania. “I think that’s what we demonstrated.”

Many cancers involving blood cells are now treated by removing immune cells from individuals, adding a gene that makes them target cancer cells and putting them back in the body.

But this treatment doesn’t work for everyone, says Stadtmauer. And in some, it works at first but they later relapse.

The hope is that using gene editing to delete genes in addition to adding the targeting gene will make this approach even more effective. For instance, immune cells have a safety switch, called PD-1, that other cells can flip to say “don’t hurt me”. Many cancers exploit this to avoid immune attacks.

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