Looking at the bottom of the computer screen, I was delighted to see that this was exactly what had transpired: the DNA sequence from the sickle cell patient now looked indistinguishable from the sequence taken from the healthy patient. Using CRISPR, Kiran’s team had perfectly swapped out the disease-causing letter A for the normal letter T without disturbing the genome in any other way. In one simple experiment using a patient’s blood cells, they had shown that the CRISPR-Cas9 system was capable of curing a crippling disease affecting millions of people worldwide.
