In 2019, the Food and Drug Administration approved Trikafta for patients with cystic fibrosis (CF) who have the most common disease-causing mutation. Trikafta targets the defective protein—a misfolded form of cystic fibrosis transmembrane conductance regulator (CFTR)—produced as a result of this mutation.1
However, people with other mutations in the CFTR gene, including those with variants that result in no proteins being made at all, cannot benefit from the drug. “Therefore, interest is being placed on genetic therapies,” said Daniel Siegwart, a chemist at the University of Texas Southwestern Medical Center.
Current gene therapy methods involve delivering mutation-correcting gene-editing tools directly to lung cells. However, such tools are often administered through inhalation and struggle to cross the thick, sticky mucus on their way to the cells.2
Now, in a paper published in Science, Siegwart and his team showed that lipid nanoparticles (LNPs) delivered intravenously successfully delivered gene-editing tools to all lung cell types, including stem cells.3 This approach enabled long-lasting gene correction in a mouse model of CF and in patient cells. The LNP-based system offers new therapeutic avenues for delivering gene-editing tools to specific tissues.
Siegwart and his team wanted to assess a delivery system that would specifically reach lung cells and avoid off-target effects. For this, they used a strategy they previously described called selective organ targeting (SORT), which uses engineered LNPs (SORT LNPs) carrying clustered regularly interspaced short palindromic repeats (CRISPR)-based editing machinery.4 By tweaking the concentration of a supplemental molecule, Siegwart and his team could shuttle the LNPs and their genetic cargo to the spleen, liver, or lung. In the present study, the researchers set out to discover what cell types in the lung received the LNP’s precious genetic cargo.
The researchers injected lung-targeted SORT LNPs intravenously to healthy mice engineered to express a red fluorescent protein in any cell that underwent gene editing. When Siegwart’s team isolated lung tissue from treated mice and observed it under the microscope, they saw cells uniformly glowing red, indicating widespread gene editing. After 22 months, they observed that cells still appeared red, highlighting the durability of the delivery system.
To understand which cell types had undergone long-lasting editing, they isolated lung cells and ran flow cytometry. They identified a variety of cell types, including epithelial cells, immune cells, and stem cells. These experiments revealed that gene editing persisted in 45 to 80 percent of the stem cells.
While the ability of LNPs to access stem cells did not surprise Siegwart, he did not expect to see the gene editing to last so long. “I almost fell out of my chair,” he said. Sustained editing opens the door to a single treatment, he explained.
Although they knew that their system targeted the lung, they didn’t know exactly how it achieved this. Siegwart and his team have previously shown that SORT LNPs bind to plasma proteins after injection into the body, which helps them reach the target cells.5 To study how these LNPs homed in on the lungs, the researchers studied the proteins that coat the LNP surface after its injection. They found that the particle was enriched in a protein called vitronectin, whose receptor is present in several lung cell types.
Equipped with an effective delivery system, Siegwart and his team set out to test the system’s therapeutic potential in genetic disease. For this, they used a mouse line that carries a mutation in the CFTR gene. Intravenous injections of SORT LNPs carrying a gene editor targeted to this mutation resulted in its correction in almost half the lung cells.
To test the system in a human-relevant context, the researchers used lung cells isolated from a patient with CF who carried a CFTR gene mutation that is resistant to existing small molecule therapies and cultured these cells in conditions that mimic the human airway biology.6
Treatment of these cells with LNPs carrying a CRISPR editor targeted to the CFTR mutation resulted in its correction with very few off-target edits, as assessed by DNA sequencing. To see whether this correction translated to the protein level, the researchers carried out immunoblotting and chemical assays, which revealed restoration of CFTR levels and function.
“The goal of delivery using a nanoparticle to only one cell type in the body is an impossible dream,” said Siegwart. He thinks that researchers should instead focus on maximizing enrichment in the target cells, while studying delivery to other cell types. Siegwart and his team engineered their system such that LNP accumulation in off-target tissues would be minimal, he added.
“This is very exciting,” said Gaurav Sahay, a drug delivery scientist at Oregon State University. According to him, the LNPs’ ability to deliver gene-editing machinery to lung stem cells is a significant breakthrough in the field. “The next step for this study is to show that you could do [it] in a higher animal, like a non-human primate, and safely deliver intravenous gene editors,” he said.
“We're eager to collaborate with other investigators who have developed CF models in different species,” said Siegwart. Although he hopes that LNPs will eventually reach clinical trials, he said that may take time.
“We're far from this being a clinical reality,” he said. But if this can be translated to humans, it could enable a lifelong cure, he added.
- Jia S, Taylor-Cousar JL. Cystic fibrosis modulator therapies. Annu Rev Med. 2022;74(1):413-426.
- Patel AK, et al. Inhaled nanoformulated mRNA polyplexes for protein production in lung epithelium. Adv Mater. 2019;31(8):1805116.
- Sun Y, et al. In vivo editing of lung stem cells for durable gene correction in mice. Science. 2024;384(6701):1196-1202.
- Cheng Q, et al. Selective organ targeting (SORT) nanoparticles for tissue-specific mRNA delivery and CRISPR-Cas gene editing. Nat Nanotechnol. 2020;15(4):313-320.
- Dilliard SA, et al. On the mechanism of tissue-specific mRNA delivery by selective organ targeting nanoparticles. Proc Natl Acad Sci USA. 2021;118(52):e2109256118.
- Van Goor F, et al. Correction of the F508del-CFTR protein processing defect in vitro by the investigational drug VX-809. Proc Natl Acad Sci USA. 2011;108(46):18843-18848.