Scientists at MIT have developed a new way to carry the CRISPR gene-editing tool to the target area of the genome. Normally the system uses harmless viruses, but that means patients can develop resistance to the treatment. So the new study involving mice has used nanoparticles instead, leading to what the team claims is the best success rate for the technique in adult animals.
CRISPR has the potential to change how we treat a huge range of illnesses. Genetic mutations that can cause disease can be snipped out of a patient's genome and replaced with other sequences, leading to possible treatments for muscular dystrophy, HIV and various cancers, and even help us develop hardier and more nutritional crops.
The tool contains an enzyme called Cas9, which cuts a section of DNA, and a short RNA that tells Cas9 where to make its edit. These are usually loaded into a harmless virus to deliver them to the targeted cells, but this approach has its problems: A patient's immune system can develop antibodies against the virus, either as a result of the treatment or beforehand, reducing its effectiveness.
A nonviral delivery system can bypass that hurdle, and while it's been done in part in the past, the new MIT study has removed the need for viruses completely. The team has packed both Cas9 and the guide RNA into nanoparticles and delivered them into the livers of adult mice, where they were able to cut the targeted genes from around 80 percent of the liver cells. That result, the team says, is the best success rate ever achieved with CRISPR in adult animals.
"What's really exciting here is that we've shown you can make a nanoparticle that can be used to permanently and specifically edit the DNA in the liver of an adult animal," says Daniel Anderson, senior author of the study.
First, the team chemically modified the RNA to keep it from being broken down by enzymes in the body, then loaded these enhanced sgRNA guides into lipid nanoparticles. These were injected into mice, along with other nanoparticles containing mRNA that encoded for the Cas9 enzyme.
The research mostly focused on a gene called Pcsk9, which regulates cholesterol levels and is implicated in certain disorders that can result in a build-up of bad cholesterol. The team managed to eliminate the gene in more than 80 percent of the liver cells, lowering the Pcsk9 protein to undetectable levels, and as a by-product, the total cholesterol levels in those mice dropped by 35 percent.
"I think having a fully synthetic nanoparticle that can specifically turn genes off could be a powerful tool not just for Pcsk9 but for other diseases as well," says Anderson. "The liver is a really important organ and also is a source of disease for many people. If you can reprogram the DNA of your liver while you're still using it, we think there are many diseases that could be addressed."
The scientists are currently investigating how the technique could address such other diseases.
The study was published in the journal Nature Biotechnology.