The CRISPR-Cas9 “tool” is a DNA construct that can be injected into any organism—in this case, human immune system T cells—to modify the genome of that organism. It works in three steps: an RNA sequence guides the CRISPR construct to the correct part of the organisms DNA, the Cas9 enzyme “cuts out” that segment of DNA, and then, as an optional third step, a new DNA sequence can be inserted to replace the deleted segment of the genome. 
In the case of the Chinese trial, conducted October 28 at the West China Hospital in Chengdu, only the first two steps of the CRISPR-Cas9 process were carried out. Immune system cells were extracted from a patient with metastatic lung cancer, and then the gene code that produces a protein called PD-1 was deleted by the Cas9 enzyme. PD-1 instructs T cells to stop or slow an immune system response, and cancer cells can take advantage of this protein to trick the body into not responding to the ailment with full force. 
Once the PD-1 protein was removed with CRISPR, the edited cells were cultivated to increase their numbers and then injected back into the patient. This is the first of two injections for the first patient, and an additional nine patients in the trial will receive between two and four injections of edited cells, depending on their individual conditions.
Both the Chinese trial and the upcoming U.S. trial—which will edit immune system cells from 18 patients to add a protein that helps target cancer cells in addition to removing the PD-1 protein—are primarily designed to test the safety of CRISPR treatments rather than cure the patients of cancer. If no complications arise, the technique could be scaled up and possibly become a true replacement for current treatments that use antibodies to neutralize PD-1. 
It is worth noting that a last-ditch treatment of an infant girl in the U.K. using TALEN, a similar gene-editing tool, successfully neutralized the girl’s cancer and saved her life. Who knows how far we will take this newfound ability modify human genomes—it has already been used to do some strange things in the livestock industry—but for now, CRISPR is emerging as a successful and cost-effective way to battle some of the most deadly forms of cancer.
By: popularmechanics.com
