New Lipid Nanoparticles Supercharge CRISPR Delivery of Bulky Gene-Editing RNA

Lipid nanoparticles have become one of the most celebrated delivery vehicles in modern medicine, ferrying the mRNA instructions behind the leading COVID-19 vaccines and, more recently, carrying gene-editing machinery into living animals. Yet a stubborn weakness has shadowed the technology: the larger the RNA cargo, the worse the nanoparticles perform. Now a team at the University of Toronto reports a way to design ionizable lipids specifically for oversized transcripts, and the resulting particle, dubbed LC-1, delivers striking improvements in genome editing across the liver, brain and lung of living mice. The work, published in Nature Biotechnology, establishes the size of the RNA payload itself as a critical design parameter in the search for next-generation delivery vehicles.

The problem the researchers set out to solve is rooted in the physics of how lipid nanoparticles form. These particles assemble spontaneously when ionizable lipids, helper lipids, cholesterol, polyethylene glycol lipids and RNA are mixed in carefully controlled conditions. The ionizable lipid is the star of the show: it is positively charged at acidic pH, which allows it to bind and encapsulate negatively charged RNA, but neutral in the bloodstream, which limits toxicity. Decades of optimization have produced lipids such as ALC-0315, used in the Pfizer-BioNTech vaccine, and LP-01, a benchmark for in vivo editing studies. But those lipids were largely selected using short reporter RNAs, and their efficiency drops measurably when the transcript grows to the size of a full-length Cas9 mRNA, which can exceed four kilobases.

That size penalty matters enormously for genome editing. Unlike small interfering RNAs or compact vaccine transcripts, the mRNAs that encode CRISPR nucleases and base editors are among the largest RNAs anyone would want to deliver. Adenine base editor mRNA, for example, stretches to roughly 5.7 kilobases, and it must be co-delivered with a guide RNA and then translated into a functional protein inside the target cell. Viral vectors such as adeno-associated virus struggle to fit such cargo into a single genome, and preexisting immunity to Cas9 proteins and to viral capsids raises additional safety concerns. Nonviral delivery by lipid nanoparticles avoids those constraints, but only if the particle can actually get its bulky payload into the cytoplasm.

To find lipids suited to large transcripts, the Toronto group, led by Bowen Li with co-first authors Songtao Dong, Fanglin Gong and Tyler Thomson, built a combinatorial library of 384 ionizable lipids and screened them against a 5.7-kilobase reporter mRNA encoding an adenine base editor fused to NanoLuc, a luminescent protein. Crucially, the screen was conducted with the large cargo in hand, so the selection pressure reflected the real-world payload rather than a convenient stand-in. The top performer from that screen, LC-1, outshone both LP-01 and ALC-0315 when the same formulations were challenged with large mRNAs, and the advantage held across multiple cell types in culture.

The in vivo results are the heart of the study. When LC-1 nanoparticles carrying Cas9 mRNA and guide RNAs were injected intravenously into Ai9 reporter mice, which light up fluorescently when Cre-mediated recombination occurs, the team measured knockout of the reporter gene in up to 79 percent of liver cells. More remarkable still, LC-1 achieved 48 percent editing in the brain and 27 percent in the lung, depending on the route of administration, which included intrathecal injection into the spinal fluid and intratracheal delivery to the airways. Those figures represent up to fourfold improvements over the benchmark lipids LP-01 and ALC-0315 under the same conditions. For a field in which extrahepatic delivery has long been the bottleneck, editing nearly half of the relevant cells in brain tissue is a striking result.

The researchers then pushed the platform toward therapeutic targets. LC-1 supported base editing of PCSK9 in the liver, a gene whose disruption durably lowers LDL cholesterol and has already been validated in nonhuman primates as a potential one-time treatment for cardiovascular disease. In the lung, the team edited CFTR carrying the R55X mutation, a nonsense variant relevant to cystic fibrosis, where even partial restoration of functional protein is expected to ameliorate disease severity. And in the brain, delivered via intrathecal injection, LC-1 enabled editing at the Ube3a-ATS locus, the long noncoding RNA that silences the paternal copy of Ube3a in neurons. Reactivating that paternal allele is a leading strategy for treating Angelman syndrome, a severe neurodevelopmental disorder. Across all three routes of administration, LC-1 also produced higher correction rates in the LumA reporter mouse model of adenine base editing than the comparison lipids.

Why does LC-1 succeed where established lipids falter? The mechanistic studies in the paper offer an answer grounded in lipid physical chemistry. Using structural analyses, the team found that LC-1 forms stronger interactions with RNA and, critically, retains an ordered, fusogenic inverted-hexagonal phase as mRNA size increases. The inverted hexagonal phase is a nonbilayer lipid arrangement long associated with membrane fusion: lipids in this geometry promote contact between the nanoparticle and the endosomal membrane, allowing the RNA to escape into the cytoplasm rather than being routed to the lysosome for degradation. LC-1 also preserves pH-responsive membrane disruption as the cargo grows. The benchmark lipids, by contrast, become structurally disordered when loaded with large transcripts, losing the very geometry that enables endosomal escape. In other words, big RNA destabilizes ordinary particles but leaves LC-1’s fusogenic architecture intact.

The authors traced these properties to specific subchemical features of the lipid structure, showing how variations in the lipid’s building blocks influence both endosomal escape and the internal organization of the particle. That structure-function insight is arguably the study’s most consequential contribution, because it converts cargo size from an afterthought into a rational design variable. Screening libraries against a representative large transcript, the work suggests, should become standard practice for anyone developing ionizable lipids intended for genome editing, self-amplifying RNA, or other oversized payloads. It also complements a growing toolkit of approaches for tissue targeting, from selective organ targeting formulations to ligand-decorated particles, by ensuring that once a particle reaches its destination cell, it can actually deliver the goods.

Caveats remain before such particles reach the clinic. The results are in mice, and serum factors are known to create species-specific barriers to lipid nanoparticle delivery, meaning performance in larger animals and humans must be demonstrated. Dosing, biodistribution, immune responses to repeated administration, and long-term safety all require further study. The inventors have filed an invention disclosure through the University of Toronto, and the corresponding author serves as an advisor to biotechnology companies, so commercial development is likely to follow. Still, the demonstration that a single optimized lipid can mediate efficient editing in liver, brain and lung through intravenous, intrathecal and intratracheal routes marks a meaningful advance. If the large-cargo-informed design principle generalizes, it could widen the path toward nonviral, potentially redosable gene-editing medicines for diseases of the heart, the airway and the nervous system.

Subject of Research: Design of large-cargo-optimized ionizable lipids for lipid nanoparticle delivery of genome-editing RNA in vivo

Article Title: Lipid nanoparticles optimized for large RNA cargo and tissue targeting enhance in vivo genome editing

Article References: Dong, S., Gong, F., Thomson, T., Cai, Y., Healy, L., Lu, R. X. Z., Zhou, Z., Xu, Y., Chen, J., Savguira, M., Fu, X., Luozhong, S., Zhou, M., Kirtley, P., Wilder, B. K., & Li, B. (2026). Lipid nanoparticles optimized for large RNA cargo and tissue targeting enhance in vivo genome editing. Nature Biotechnology. https://doi.org/10.1038/s41587-026-03298-8

Image Credits: AI Generated

DOI: 10.1038/s41587-026-03298-8

Keywords: lipid nanoparticles, ionizable lipids, genome editing, CRISPR, Cas9, base editing, mRNA delivery, endosomal escape, PCSK9, CFTR, Angelman syndrome, drug delivery