CRISPR used to activate genes in human immune cells

Scientists have used a modified version of CRISPR to activate genes in human immune cells, with potential applications in cancer treatments.

Since the CRISPR-Cas9 gene-editing tool was first shown to be able to cut and edit DNA in 2011, it has been revolutionary, allowing us to tackle a range of diseases – from cancer to HIV to chronic pain – by removing mutated parts of a gene.

Now, in a paper published in Science, US researchers reveal a new first: they have successfully used a modified version called CRISPRa at a large scale in primary human cells.

“This is an exciting breakthrough that will accelerate immunotherapy research,” says Alex Marson, director of the Gladstone-UC San Francisco Institute of Genomic Immunology and senior author of the new study.

“These CRISPRa experiments create a Rosetta Stone for understanding which genes are important for every function of immune cells. In turn, this will give us new insight into how to genetically alter immune cells so they can become treatments for cancer and autoimmune diseases.”

The CRISPR technique uses Cas9 proteins as “molecular scissors” to snip DNA. Over the last few years, Marson and team have used this tool to remove genes from various types of human immune cells. But the method was not precise enough.

“Knocking out genes is great for understanding the basics of how immune cells function, but a knock-out-only approach can miss pinpointing some really critical genes,” says co-author Zachary Steinhart, also from the Gladstone-UCSF Institute of Genomic Immunology.

So instead they used CRISPRa – a version of the tool where the Cas9 protein cannot cut DNA, but rather hosts an activator which can bind to a gene and turn it “on”. (An “off” switch also exists, called CRISPRi.)

The team were specifically interested in looking at the functions of a specific type of immune cell called T cells. This is a type of white blood cells that are a key part of our body’s defense against pathogens. They act like “leaders”, producing a variety of signalling molecules called cytokines to direct other types of immune cells against intruders or even cancer cells.

Controlling T-cell cytokines could open up new ways to shape immune responses against a variety of diseases, but first we need to understand which genes control which cytokines.

This is precisely what Marson and team were attempting. They applied CRISPRa and CRISPRi to T cells isolated directly from healthy volunteers, activating and inactivating nearly 20,000 different genes within the cells. They then watched which ones most influenced cytokine production.

This allowed them to narrow down a few hundred genes that serve as key cytokine regulators.

“Our new data give us this incredibly rich instruction manual for T cells,” says Marson. “Now we have a basic molecular language we can use to engineer a T cell to have very precise properties.”

This will be a boon for certain types of cancer treatment, including CAR-T cell therapy. This involves removing T cells from a patient’s body and re-engineering them to target cancer cells. Knowledge of which genes could boost cytokine production may make this therapy more powerful.

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