Preliminary results of a clinical trial that involved the use of the CRISPR-Cas9 gene-editing show that the technique was safe to use on humans. More specifically, researchers at the University of Pennsylvania in Philadelphia collected immune cells from three people with cancer, and, through genome editing, gave those cells the ability to recognise a protein produced by some cancer cells. Upon being reintroduced into the patients' bodies, the cells did not cause significant side effects.