US scientists have succeeded in genetically editing the immune systems of three cancer patients using Crispr, without creating any side effects, a first for the tool which is revolutionizing biomedical research. The highly anticipated results from the first phase of a clinical trial were published in the journal Science on Thursday. They represent a stepping stone that doesn’t yet prove Crispr can be used to fight cancer. Indeed, one of the patients has since died and the disease has worsened in the other two — but the trial does show that the technique is non-toxic. Researchers at the University of Pennsylvania (UPenn) removed T-cells from the patients’ blood and used CRISPR to delete genes from the cells that might interfere with the immune system’s ability to fight cancer. They then used a virus to arm the T-cells to attack a protein typically found on cancer cells called NY-ESO-1, and infused the cells back into the patients.