GENE EDITING WITH ENGINEERED VIRUS-LIKE PARTICLES

Engineered virus-like particles (eVLPs) that they had previously designed to carry base editors, (another type of precision gene editor that makes single-letter changes in DNA.) are now adapted to deliver prime editors to cells in mice at a high enough efficiency to rescue a genetic disorder. eVLPs and parts of the prime editing protein and RNA machinery are re-engineered to boost editing efficiency up to 170 times in human cells compared to the previous eVLPs that deliver base editors. This new system was proved to correct disease-causing mutations in the eyes of two mouse models presenting genetic blindness and partially restoring their vision.  Prime editors delivered to the mouse brain, and did not detect any off-target editing.

The three elements of the prime editing system are the Cas9 protein, which can nick DNA, the engineered prime editing guide RNA (pegRNA), which both indicates the edit location and contains the new edited sequence to be installed there, and the reverse transcriptase, which uses the pegRNA as a template to specifically alter the DNA.These molecular components have been injected into cells by researchers using a range of techniques, such as viruses and lipid nanoparticles. Virus-like particles (VLPs), which are made up of a shell of viral proteins that carry cargo but do not contain any viral genetic material, have also piqued curiosity. However, VLPs have historically only shown mediocre delivery results in animals, and in order to effectively distribute to cells, each unique type of cargo requires a customized engineering approach.

The process was initially tested on mice to treat two distinct genetic abnormalities in the eyes. A mutation in the Mfrp gene results in retinitis pigmentosa, a condition that worsens retinal degeneration over time. The other, found in the gene Rpe65, is linked to blindness in those suffering from Leber congenital amaurosis (LCA). Additionally, the eVLPs equipped with primary editing machinery could successfully modify genes in the living mice's brains. When the editing apparatus was applied to cerebral cortex cells, over half of all the cells had a gene edit.

As a potential option for in vivo PE delivery, designed VLPs provide a number of benefits over alternative delivery systems. Firstly, there is no need to split PEs into numerous independent vectors because eVLPs are exempt from strict cargo size constraints. Furthermore, eVLPs can package RNPs, the most transient form of gene editing agents, limiting the probability of off-target editing by minimizing the genome's exposure time to editing agents. eVLPs prevent undesirable integration of viral genetic material into the transduced cells' genomes since they do not contain DNA. Lastly, envelope protein engineering efforts can specifically target target cell types of interest by pseudotyping eVLPs with distinct glycoproteins.

To fully utilize the therapeutic potential of eVLPs, more optimization in large-scale eVLP production will be required. However, compared to DNA or mRNA delivery techniques, the PE-eVLP system described here presents the distinct benefits of nonviral, single-particle administration of PEs in their most transitory form as RNPs, offering advantages in terms of target selectivity and safety.

REFERENCE:

An, M., et al. (2024). Engineered virus-like particles for transient delivery of prime editor ribonucleoprotein complexes in vivo. Nature Biotechnology. doi.org/10.1038/s41587-023-02078-y.

https://www.news-medical.net/news/20240108/Engineered-virus-like-particles-power-up-gene-editing-correcting-blindness-in-mice.aspx

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