The first trials of CRISPR-edited cells injected into a human has now taken place in China. The individual in question was a patient with a particular type of lung cancer. Lu You, an oncologist at Sichuan University in Chengdu, took white blood cells from the patient and used the editing technique to knock out the gene PD-1. The altered cells were cultured and then injected back in.
PD-1: What does it do?
The immune system has to be carefully regulated at all times. Too little activity and it doesn't function properly, but too much and it might start attacking the body it's trying to protect.
PD-1 (Programmed cell death protein 1) is a protein that is found on the surface of T cells, a type of immune lymphocyte cell. It forms part of the negative-regulatory system for the cells; if a particular molecule called PD-1L binds to it, it inhibits the cell, stopping it from working.
Tumour cells take advantage of this system for their own ends by expressing the PD-1L molecule in large amounts and suppressing the immune response, allowing them to grow and proliferate in the body. By knocking out the PD-1 gene, Lu You's team hope to stop this inhibition and allow the modified T-cells to attack and kill the cancer cells.
Image from http://blogs.nature.com/spoonful/2013/04/melanoma-drug-joins-breakthrough-club.html
There are several unknowns for this approach. Checks and balances are there for a reason, and turning off the gene may have an adverse effect on the cells or the body. The process of editing the gene may also create undesired 'off-target effects', where the Cas9 enzyme cuts in unintended places.
Trials are also due to start in the USA early next year, which will also target cancer. Therapies for inhibiting PD-1 to fight cancer using antibodies are also being developed.