HITI Genome Editing Repairs Native OTC Gene in Liver Cells, Offering Mutation-Agnostic Strategy for Pediatric Gene Therapy
核心洞察
Researchers at Australia's Children's Medical Research Institute used homology-independent targeted integration (HITI) to repair the faulty OTC gene directly at its natural liver location rather than adding an extra gene copy.
In laboratory models of OTC deficiency, urinary orotic acid levels normalized within three weeks and blood ammonia showed no significant difference from healthy controls after a protein challenge.
OTC activity was detected in up to 40% of liver cells in animal models and restored OTC expression in up to 48% of patient-derived human liver cells.
Researchers at the Children's Medical Research Institute (CMRI) in Australia have developed a genome-editing approach that repairs a faulty gene directly at its natural location in the liver, an advance they say could provide a more durable treatment for children with a rare metabolic liver disorder whose growing organs gradually dilute conventional gene therapies.
The work, published in the journal Molecular Therapy and led by Associate Professor Samantha Ginn, focused on ornithine transcarbamylase (OTC) deficiency — a severe genetic liver disorder that prevents the body from properly breaking down waste products from protein digestion. More than 500 different gene mutations can cause OTC deficiency, making treatments tailored to each individual mutation enormously impractical.
Targeting the Native Locus
Conventional gene therapy for OTC deficiency delivers a working copy of the gene into liver cells, allowing the liver to function normally. But because this extra gene copy exists separately from a person's own DNA, it can be diluted or lost over time as a child's liver grows and cells divide, since treated cells are eventually outnumbered by new, untreated ones.
The CMRI team's method, known as homology-independent targeted integration (HITI), instead repairs the faulty gene at its natural location. The approach uses two viral delivery vehicles working together: one carries the gene-editing tools and the other carries the corrective DNA, which has no built-in "on switch" of its own because it captures the gene's natural one. The strategy is designed to work regardless of which specific mutation is causing a patient's OTC deficiency.
"This is an important advance because we achieved high levels of functional, targeted repair at the native OTC locus in human liver cells, using a mutation-agnostic strategy," Ginn said. "Unlike conventional gene therapy, which introduces an extra copy of the gene, this approach places the therapeutic sequence under the control of the gene's own regulatory machinery and restored its normal metabolic zonation across the liver."
Preclinical Results
In laboratory models of OTC deficiency, urinary orotic acid concentrations — a key marker of urea cycle function — normalized within three weeks of treatment. By the study's endpoint, blood ammonia concentrations showed no significant difference from healthy control levels, even after a protein challenge designed to stress the system.
OTC activity was detected in up to 40% of liver cells, and whole-liver OTC activity more than doubled compared with untreated models. The team then tested the approach in patient-derived human liver cells transplanted into specially engineered models, where it restored OTC expression in up to 48% of human cells.
An Unexpected Finding
The research also produced an unexpected result regarding how the therapeutic DNA integrated into the genome.
"The most surprising finding was that, although the therapeutic DNA reached the intended location and restored gene function at high efficiency, it was incorporated in more complex arrangements than we had predicted," Ginn said. "Understanding these previously underappreciated outcomes gives us important insights for improving the precision of genome-editing therapies moving forward."
Toward Scalable Rare Disease Therapies
According to Ginn, the research speaks directly to the challenge of making gene therapy durable in young children who still have years of growth ahead of them. She added that it contributes to a broader discussion about moving genome editing beyond treatments tailored to individual mutations toward scalable approaches that could benefit larger groups of patients with rare genetic diseases.
The mutation-agnostic strategy addresses what the researchers describe as a central obstacle in pediatric gene therapy: the liver's growth can gradually dilute treatment as new, untreated cells emerge, eroding the benefit of therapies that rely on an episomal gene copy.