Research and develop a new tool for base editing delivery - virus-like particles can be multi-organ targeted editing

Article source: Medicine Cube Pro

Author: Li Yuan

AAV virus is a commonly used delivery tool for base editors.
It works by delivering the DNA encoding the base editor to the target tissue, but this delivery method may prolong the expression time of the base editor in vivo, correspondingly , the risk of off-target editing will also increase
.

An ideal editor delivery method is to directly deliver the editor protein or ribonucleoprotein (RNP), which has a shorter duration of action in vivo and reduces the risk of off-target editing

One possible approach may be the use of virus-like particles (VLPs), which behave like viruses and can enter cells and deliver cargoes such as therapeutic proteins, which may be safer than viral vectors because they do not contain viral genetic material
.

Although the use of VLPs to deliver RNPs can combine the delivery efficiency and tissue targeting advantages of viruses, past studies have shown that VLP-delivered gene editors have limited editing efficacy in vivo

In new research published Jan.
11 in the journal Cell, a research team in David Liu's lab at the Broad Institute of MIT and Harvard has developed an engineered DNA-free virus-like particle (eVLP) that can efficiently package and delivery of base editors or Cas9 ribonucleoproteins
.

A single injection of eVLPs in mice reduced serum PCSK9 protein levels by 78% and partially restored visual function in a mouse model of genetic blindness.

The researchers optimized eVLPs by using different molecules on the particle surface.
They systematically designed different parts of the eVLP structure to optimize the key steps of eVLP production, cargo encapsulation, and intracellular release and distribution of the cargo.
The fourth-generation eVLP (v4 BE-eVLP) can package 16-fold more base editor RNP proteins than the initially reported VLPs
.

Designing multiple versions of eVLP to solve the VLP bottleneck problem (Source: Cell)

v4 BE-eVLPs performed efficient base editing in several major mouse and human cell types, and few off-target edits were detected upon delivery of the editor RNP protein
.

Furthermore, the DNA-free nature of eVLPs avoids the possibility of DNA integration into the cell genome

High security of v4 BE-eVLP (Source: Cell)

The researchers edited primary human or mouse cells in vitro, and in primary fibroblasts with a homozygous COL7A1 mutation, the v4 BE-eVLP was more than 95% efficient at the target adenine base
.

v4 BE-eVLP can achieve near 100% base editing levels in human and mouse primary fibroblasts (Source: Cell)

In in vivo editing experiments, v4 BE-eVLP still exhibited high editing efficiency
.

After the researchers delivered the base editor to the livers of mice using v4 BE-eVLPs, PSCK9 protein levels dropped by 78 percent

A single systemic injection of v4 BE-eVLP knockdown Pcsk9 in vivo (Source: Cell)

The researchers also corrected the mutation in the Rpe65 gene using v4 BE-eVLP in genetically blind mice, restoring some of the mice's visual function
.

v4BE-eVLP performs base editing in a mouse model of genetic blindness (Source: Cell)

The team also injected v4 BE-eVLPs directly into the brains of mice and observed an editing efficiency of about 50% in cells exposed to eVLPs.
In the future, they will focus on improving the distribution of eVLPs throughout the brain
.

v4 BE-eVLP performs base editing in the central nervous system (Source: Cell)

Overall, eVLPs combine the advantages of viral and non-viral delivery systems and can be used not only for base editing but also for delivery of other therapeutic proteins
.

The research team is broadening the range of organs and cell types that eVLPs target, and in the future they will continue to characterize eVLPs to better predict and mitigate any unwanted immune responses that the particles may generate

References:

[1] Banskota S.

[2] Engineered particles efficiently deliver gene editing proteins to cells in mice (Source: Broad Institute)