People with cancer show no serious side effects after treatment with gene-edited immune cells.

The first human trial of cells modified with CRISPR gene-editing technology shows that the treatment is safe and lasting.

A team led by You Lu at the West China Hospital in Chengdu took immune cells from people with aggressive lung cancer and applied CRISPR to them to disable a gene called PD-1. Usually, the PD-1 protein sends signals that keep immune cells from mounting an attack against the body’s own tissues, but active PD-1 can open the door to the spread of cancer.

The team injected each study participant with edited versions of their own immune cells. Participants experienced only mild side effects, and potentially dangerous mutations caused by gene editing — the researcher’s main fear — were limited.

The modified cells remained in the blood for at least four weeks, showing that the strategy could have a lasting effect. This experiment, however, involved only 12 people with cancer, and did not lengthen participants’ lives. The authors call for a larger study with newer gene-editing systems.

The experiment ushered in a slew of CRISPR-based trials, some of which have already been reported.