The gene-editing tool CRISPR-Cas9 has been used in a human for the first time, marking a major milestone in genomic research.

Chinese scientists injected a patient with cells genetically edited using CRISPR-Cas9, a revolutionary technique that allows precise and easy modification of DNA.

According to Nature, a team led by oncologist Lu You from Sichuan University in Chengdu inserted the modified cells into a patient with aggressive lung cancer on October 28 as part of a clinical trial.

What is CRISPR-Cas9?

CRISPR (clustered regularly interspaced short palindromic repeats) are patterns of DNA sequences found in the genomes of bacteria and other microorganisms. If a virus threatens, the bacteria use the CRISPR immune system to identify and destroy the viral genome. Scientists have adapted this system to use in cells from animals and, now, humans.

Cas9 is an enzyme that works like a pair of “molecular scissors”. A guide molecule is programmed to tell the enzyme exactly where to cut in the DNA sequence.

Image: Reuters/Massachusetts Institute of Technology

CRISPR-Cas9 could have enormous benefits for human development, with the potential to treat genetic defects, eradicate diseases, and even end the organ transplant shortage.

The technology is also being used in other areas of biomedical research such as diseases that devastate crops and may become an important tool in future medicine and agriculture.

But it has also sparked a debate over the possibility that it could be used to create “designer babies”.

The technique allows scientists to tweak the DNA of almost any living being, from bacteria to people. Unlike other gene-editing methods, CRISPR is relatively cheap, quick and easy to use. As a result, it is now being used in labs around the world and has already been used to fix genetic defects in animals and non-viable human embryos.

However, until now, it has not been used on living, breathing humans.

How does it work?

CRISPR-Cas9 allows scientists to swap "problem" genes with "healthy" ones. In the case of the patient in China, the scientists used it to modify genes in immune cells. Then they cultured the edited cells, increasing their number, and injected them back into the patient. It is hoped that the genetically modified cells will attack the cancerous cells and destroy them.

What next?

The team in China plans to treat a total of 10 people. Their trial will be used primarily to determine whether the technique is safe enough to use on humans.

Though China has forged ahead in the race to test CRISPR-Cas9 on humans, there are more trials in the pipeline.

Nature reports that a planned trial in the US, awaiting approval from the Food and Drug Administration (FDA), will use the technology to target three genes, aimed at treating several forms of cancer.

There are also proposals for three CRISPR trials in Beijing for bladder, prostate and renal-cell cancers that do not yet have approval or funding. And there are plans for human trials in the US covering the genes causing blindness and sickle cell anaemia.