Scientists use CRISPR to edit immune cell DNA

Researchers have successfully used the technique CRISPR/Cas 9 to cut and paste DNA into T-cells of the immune system.

The method could lead to new ways to treat cancer, type 1 diabetes and viral infections as well as facilitating research into T-cell function.

‘Genome editing in human T-cells has been a notable challenge for the field,’ said lead author Dr Alexander Marson from the University of California, San Francisco.

‘We have now been able to cut as well as paste pieces of the genome into human T-cells – for the first time to our knowledge,’ he added.

In the experiment, the team were able to disable a protein found on T-cells, called CXCR4, resulting in those cells no longer being prone to invasion by the HIV virus.

They also used CRISPR/Cas9 to shut down a protein found on T-cells, known as PD-1, which has been shown to up-regulate the body’s attack on invasive cancer cells when blocked. The researchers hope that, in this way, T-cells could be manipulated to control cancer or possibly eliminate a tumour entirely.

CRISPR/Cas9 involves the identification of specific areas on the DNA. With the use of an enzyme, Cas9, the strands are cut and replaced with alternative copies of the DNA sequence, usually using a modified virus as a vector. However, to date, scientists have not been able to use the technique to modify specific sequences of DNA in T-cells with sufficient success.

In this study, which is published in PNAS, the researchers modified the technique by attaching guide RNA to the Cas9 enzyme in the lab. Then, instead of using a viral vector, they used a technique called electroporation, which involves subjecting the cells to an electric field that temporarily makes their membranes permeable, allowing the CRISPR/Cas9 molecule to enter.

Using cell-surface markers, the researchers were then able to sift out the 20 percent of cells that had successfully undergone gene editing.

‘It has been really challenging to get CRISPR to work in T-cells. This, in our hands, allows us to achieve a new level of efficiency for cutting and repair,’ said Dr Marson, who worked alongside CRISPR pioneer Jennifer Doudna on the study.

Dr Marson said that there was still work to be done to make sure that the technique correctly targets DNA before being used in humans.

‘I think CRISPR-edited T-cells will eventually go into patients, and it would be wrong not to think about the steps we need to take to get there safely and effectively,’ he commented.