Broad Institute Team Overcomes eVLP Efficacy Issues

Researchers at Harvard University and the Broad Institute have successfully demonstrated the use of engineered DNA-free virus-like particles (eVLPs) to edit genes in mice associated with high cholesterol and blindness. 

Virus-like particles (VLPs)—proteins that can infect cells but lack viral genetic material—have long been studied as drug delivery vehicles because they can carry molecular cargo but are unable to affect a cell’s genome. Existing VLP delivery strategies, however,  have had limited therapeutic efficacy in vivo.

To overcome this, the team systematically engineered VLPs to overcome cargo packaging, release, and localization bottlenecks. In doing so, they developed fourth-generation eVLPs that packaged 16 times more cargo proteins than previous designs and enabled an eight- to 26-fold increase in editing efficiency in cells and animals.

“The delivery of therapeutic macromolecules into mammalian cells in animals and eventually in patients is one of the most important challenges in life sciences,” says David Liu, the paper’s senior author, Thomas Dudley Cabot Professor of the Natural Sciences, and a core faculty member of the Broad Institute. “There is often a very steep drop-off between in vitro and in vivo delivery, so we made the decision early on that our new delivery technology would need to show good efficacy in animal models.”

In both mice applications, eVLPs demonstrated the ability to deliver therapeutic levels of gene-editing proteins. In the cholesterol study, the optimized eVLP was able to deliver base editors to the liver, where they efficiently edited a gene to lower so-called “bad” cholesterol levels. One injection of eVLPs was enough to achieve 63% editing of the target gene and a 78% drop in its protein levels.

“The cholesterol target is particularly interesting because it is not only relevant to patients with a rare genetic disease,” says Aditya Raguram, a graduate student in Liu’s lab. “We are hopeful this is one example of genome editing being able to benefit a large population because cholesterol levels impact the health of billions of people.”

The team also used a single eVLP injection to correct disease-causing point mutation in mice with a genetic retinal disorder. They corrected the point mutation with less-off target editing than other base-editing delivery techniques and achieved partial restoration of vision.

Applications for the new eVLPs could be broad. “Because our system is relatively simple and easily engineered, it allows other scientists to adopt and build upon this technology quickly,” says Samagya Banskota, a graduate student in Liu’s lab.  “Beyond carrying gene-editors, eVLPs have the ability to transport other macromolecules with lots of therapeutic potential.”

The paper  was published in Cell.