CRISPR modification overcomes major hurdle to human treatments

Scientists modify CRISPR/Cas9 to treat diabetes, kidney disease, and muscular dystrophy in mice, without cutting DNA.

In its five years of existence, CRISPR/Cas9 has revolutionized the field of gene editing, allowing researchers to edit DNA like a piece of text. While its potential is unquestionable, ethics and safety concerns have prevented CRISPR from being used to treat human diseases. Now, scientists at the Salk Institute have found a way around one of those hurdles, modifying the CRISPR system to treat several diseases in mice without cutting DNA, which means they avoid unwanted mutations. The technology works epigenetically, influencing gene activity without changing the DNA sequence.

To transport this bulkier CRISPR system into cells, the researchers delivered its components separately, attaching them to two viruses. They engineered the adapted system to activate specific genes that could reverse the symptoms of each targeted disease. In a mouse model of type 1 diabetes, for example, the team activated genes that could generate insulin-producing cells. The treatment worked, lowering blood glucose levels. The researchers saw similar success in models of acute kidney injury and a form of muscular dystrophy. We spoke with Juan Carlos Izpisua Belmonte of the Salk Gene Expression Laboratory about his work.

ResearchGate: How does CRISPR/Cas9 traditionally work?

Juan Carlos Izpisua Belmonte: The traditional CRISPR/Cas9 system works by first creating DNA double strand breaks in the targeted region of the genome. However, generating these double strand breaks has the risk of causing unwanted mutations permanently, and this increases the risk of inducing tumors or other genetic diseases in patients. This concern is a hurdle to using CRISPR/Cas9 to treat humans. The risk of causing non-specific mutations is always an issue when using gene-editing tools to treat human patients.

RG: How is your approach different?

Izpisua Belmonte: Our approach maintains the gene targeting property of CRISPR/Cas9, but without generating double strand breaks. It is therefore free of the risk of causing permanent, unwanted mutations in patients.

In this video abstract for the journal Cell, researchers Hsin-Kai Liao and Fumiyuki Hatanaka explain the modification. Credit: Salk Institute.

RG: How did you test this method?

Izpisua Belmonte: We examined this method in cells in petri dishes first, and then transferred the platform into live animals. Here we used mice as our live animal model and applied our technique to treat different mouse models of human diseases.

RG: What were the results?

Izpisua Belmonte: Our results showed that this Cas9-based epigenetic targeting approach could ameliorate disease symptoms in three different mouse models. Meanwhile, it is free from the risk of causing double strand breaks. We are very excited by the results we achieved using our system on these animal models.

RG: What are the next steps in this research?

Izpisua Belmonte: There are still multiple steps that must be taken before applying this method in human patients. For example, it must be determined whether host immune responses against the AAV-CRISPR/Cas9 TGA system arise in mice or large animals. Safety considerations will also have to be addressed before bringing this technique to human patients. These are all questions we would like to pursue.


Featured image courtesy of Mehmet Pinarci.