Using the gene editing tool CRISPR-Cas9 to specifically target the lung of a developing fetus, researchers were able to correct a mutation associated with a human lung disease that is fatal after birth, a study in mice shows.
These findings highlight the potential of gene editing strategies to correct mutations associated with genetic lung diseases, including cystic fibrosis (CF).
CF, along with other lung diseases such as inherited surfactant protein (SP) syndromes and alpha-1 antitrypsin deficiency, are caused by mutations in surfactant genes that are essential for normal lung function.
While symptoms usually arise during late childhood or early adulthood, in rare cases such as with SP deficiency syndrome, infants prematurely die from respiratory failure. Treatment for these cases is limited to palliative care or pediatric lung transplant, which highlights the urgent need for therapies that may correct the genetic defect early.
Researchers at the Children’s Hospital of Philadelphia (CHOP) and University of Pennsylvania evaluated the potential of using the gene editing tool CRISPR-Cas9 — a strategy that allows the correction of genomic defects, and is currently at the forefront of many therapeutics for human diseases.
“The developing fetus has many innate properties that make it an attractive recipient for therapeutic gene editing,” William H. Peranteau, MD, an investigator at CHOP’s Center for Fetal Research, and the study’s co-author, said in a press release.
“Furthermore, the ability to cure or mitigate a disease via gene editing in mid- to late gestation before birth and the onset of irreversible pathology is very exciting. This is particularly true for diseases that affect the lungs, whose function becomes dramatically more important at the time of birth,” added Peranteau, who is also a pediatric and fetal surgeon in CHOP’s Center for Fetal Diagnosis and Treatment.
In a proof-of-concept study, the researchers used mice to assess the potential of gene editing to correct a mutation during fetal development.
They introduced the CRISPR-Cas9 gene-editing reagents into mice fetuses via intra-amniotic injections, and saw that the genetic information was successfully delivered to the fetal lungs. The procedure was done in mice four days before birth, the equivalent to the third trimester in humans.
“We wanted to know if this could work at all,” said Edward E. Morrisey, PhD, a professor of cardiovascular medicine in the Perelman School of Medicine at the University of Pennsylvania and the study’s co-author. “The trick was how to direct the gene-editing machinery to target cells that line the airways of the lungs.”
Pulmonary epithelial cells were the predominant targets of the gene editing tool, with alveolar type 1, alveolar type 2, and airway secretory cells exhibiting high and persistent gene editing. The alveolar cell lineage is the one responsible for the production of pulmonary surfactant, which prevents lungs from collapsing with every breath.
The researchers then used a mouse model of genetic surfactant deficiency, which carried a mutation in the surfactant protein C gene (SFTPC) that is also found in humans (called SFTPCI73T). All mice carrying this mutation die from respiratory failure within hours of birth.
By delivering the gene editing tools to these fetuses (to correct the defect in the SFTPC gene), the researchers were able to correct the mutation in at least 20% of the cells. This resulted in improved lung morphology, and increased the animals’ survival by 22.8%. The genetically edited lung cells transformed into functional lung cells, improving the formation of the lung alveoli — the tiny “balloon” sacs where oxygen and carbon dioxide exchanges occur.
Future studies are required to develop novel ways to increase the efficiency of gene editing tools, and their delivery into the cells lining the lung, the researchers said.
“Different gene editing techniques are also being explored that may one day be able to correct the exact mutations observed in genetic lung diseases in infants,” Morrisey said.
Overall, “our proof-of-concept studies demonstrating the feasibility of prenatal gene editing with high specificity for the lung represent a promising approach to address the unmet need for therapeutic approaches to congenital lung diseases that are fatal at birth,” the researchers concluded.