"Cell" David Liu's team reports a new tool for in vivo gene editing - the first therapeutic-level virus-like particle!

Gene editing approaches hold promise for treating a range of diseases, but safely and effectively delivering editors to cells in animal models and humans has proven challenging

In the latest study, published in the journal Cell, the team showed how they engineered virus-like particles to deliver base editors (proteins with programmable single-letter changes in DNA) and CRISPR-Cas9 nucleases, a A protein that cuts DNA at a target location in the genome

The in vivo delivery bottleneck of gene editors

Virus-like particles (VLPs) are small structures of viral proteins that carry molecular cargo but do not contain viral genetic material and do not cause infection

Researchers have been interested in virus-like particles for decades

The new study identifies several features of VLPs that limit their delivery efficiency and designs changes in particle structure to overcome these bottlenecks

When they delivered the gene editor as a protein using eVLPs, the team did not detect any off-target edits, but did detect "off-target" when the editor was delivered as DNA

"While gene editing plays an important role in the future, in vivo delivery has proven to be a recurring challenge,

"VLPs have been one of the most attractive delivery technologies, but in vivo protein delivery is inefficient.

Liu's team systematically designed different parts of the VLPs architecture, optimizing key steps within them, including how the VLPs are produced, how the cargo is packaged into the VLPs, and how the cargo is released and distributed within the cell

The final version of the eVLPs packs 16 times more cargo proteins than previous designs, enabling 8 to 26 times higher editing efficiency in cells and animals

"Because eVLPs offer robust targeted editing and minimize untargeted editing, we hope they will become a safer method for delivering gene editing agents in vivo," said the study's first author.

multi-experimental test

Using their optimized system of eVLPs, the team corrected mutations in a range of mouse and human cells, and in some cases observed 95 percent editing efficiencies

Scientists used eVLPs to deliver a base-editing program to the livers of mice, where they effectively edited Pcsk9, a gene that, when mutated, can significantly reduce blood levels of "bad" cholesterol, reducing heart disease in some patients risk

The researchers also used a single injection of eVLPs to restore visual function in mice with the blinding mutation

The team also injected eVLPs directly into the brains of mice and observed about 50 percent editing efficiency in cells exposed to eVLPs

Liu's team now looks to the scientific community to adopt eVLPs and use them to improve therapeutic macromolecule delivery in patients
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Liu's team is now expanding the range of organs and cell types that eVLPs can target in animals
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They will also continue to study the properties of eVLPs to better predict and mitigate any unwanted immune responses these particles may generate
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"There is a great need for a better way to deliver proteins to various tissues in animals and patients," Liu said
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"We hope that these eVLPs may be useful not only for the delivery of base editing, but also for other therapeutically relevant proteins
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