Liver-Targeted Lentiviral Gene Therapy Shows Safety and Efficacy in Preclinical ARC Syndrome Model
Key Insights
Researchers at UCL and Great Ormond Street Hospital (search) demonstrated that a liver-specific lentiviral gene therapy (LP1-VPS (search)) safely rescued liver disease in a mouse model of ARC syndrome (search), a fatal childhood genetic disorder.
LP1-VPS (search)-treated mice achieved 80% survival compared to 33.3% in mock-treated animals (p=0.0255), with significant reductions in serum alkaline phosphatase and cholesterol levels.
A ubiquitous promoter version (EF1-VPS) caused liver tumors in 50% of treated mice, highlighting that vector design—specifically liver-specific targeting—is critical for safety.
A team of researchers at UCL and Great Ormond Street Hospital (search) (GOSH) has demonstrated that a liver-targeted lentiviral gene therapy can safely and effectively treat the liver manifestations of Arthrogryposis, Renal dysfunction and Cholestasis (ARC) syndrome in a preclinical mouse model. The findings, published in Nature Communications, offer the first proof-of-concept that gene therapy could become a realistic treatment for this devastating childhood disease, which is typically fatal within the first year of life.
ARC syndrome (search) is a lethal autosomal recessive multisystem disorder caused by mutations in the VPS33B (search) gene, which encodes a key component of the CHEVI complex responsible for intracellular protein trafficking in hepatocytes. The resulting cholestasis leads to progressive liver damage, sepsis, and death. In the UK, as many as six pregnancies per year may be affected.
Liver-specific vector design proves critical for safety
The researchers developed and compared two lentiviral vectors carrying a codon-optimized VPS33B (search) gene: LP1-VPS (search), driven by a liver-specific promoter (LP1), and EF1-VPS, driven by the ubiquitous EF1α promoter previously used in clinical studies. Both vectors successfully rescued VPS33B expression in vitro, restoring bile canaliculi formation in HepG2 VPS33B knockout cells.
However, long-term safety testing in heterozygous Vps33b (search) knockout mice (Vps33bLiver+/-) revealed a stark divergence. While no liver abnormalities were observed in mice treated with LP1-VPS (search) or LP1-GFP vectors over nine months, liver tumors developed in 3 of 5 mice injected with EF1-GFP and 2 of 5 with EF1-VPS—including two hepatic adenomas and three hepatocellular carcinomas.
Integration site analysis of the tumors revealed clonal expansion events, with dominant integration sites including Hs2st1 (over 25% frequency), Cep78, Arfgap2, and Cdh18. RNA sequencing identified 3,541 significantly downregulated and 4,830 significantly upregulated genes in tumors compared to healthy tissue, with top upregulated pathways involved in cell cycle processes. The Shannon Equitability Index in tumor samples dropped to 0.46, indicating substantial clonal proliferation, while healthy samples maintained an index close to 1.
"The final version of the treatment is shown to be safe so far. The earlier version gave us a new window into the understanding of how to make gene therapies safer for the patients," said co-author Professor Paul Gissen, Clinical Professor of Paediatric Metabolic Medicine at UCL Great Ormond Street Institute of Child Health. "One of these insights is to keep the levels of genes as close to those found in healthy cells as possible."
Efficacy: survival benefit and biomarker improvement
In the Vps33bLiver-/- disease model, neonatal mice pretreated with clodronate liposomes to transiently deplete liver macrophages and enhance hepatocyte transduction received LP1-VPS (search) at 5 × 10¹⁰ TU/kg. After eight weeks on a 0.25% cholic acid diet, LP1-VPS-treated animals demonstrated an 80% survival rate compared to 33.3% for mock-treated mice (p=0.0255).
Treated animals gained four times more weight than mock-treated animals in the first week of cholic acid supplementation (0.30 g, IQR: −0.010–1.27 g, p=0.0003). At sacrifice, serum alkaline phosphatase (ALP) levels in the treatment group reached a median of 778 U/L—nearly 10 times lower than the mock group's 7,201 U/L (p=0.0015). Total serum cholesterol decreased to wild-type levels (92.0 mg/dl, p=0.0016), and total serum phospholipids were significantly reduced (1.88 mM, p=0.0101).
Histological analysis confirmed that LP1-VPS (search) therapy restored CEA polarization at bile canaliculi across large areas of the liver and reduced fibrosis compared to mock-treated animals. The average liver vector copy number reached 5, with a 110-fold increase in codon-optimized VPS33B (search) RNA expression relative to wild-type levels.
Mechanism insights and clinical implications
The study's findings support a two-hit model of cancer development, where reduced VPS33B (search) expression—which has been associated with hepatocellular carcinoma (search)—acts as a predisposing event, with additional alterations from vector integration and strong promoter-driven gene expression changes leading to tumor formation. The researchers noted that EF1α-containing vectors did not cause tumors in wild-type animals, suggesting the Vps33bLiver+/- genetic background may serve as a sensitive model for future liver-directed gene therapy safety studies.
Dr. Claudiu Cozmescu, lead author from UCL Great Ormond Street Institute of Child Health, stated: "Our findings are important because it provides proof-of-concept that gene therapy could become a realistic treatment for ARC syndrome (search) and potentially other inherited liver diseases that currently have few or no effective options. It also highlights that how a gene therapy is designed is critical: targeting treatment specifically to the liver improved safety while maintaining benefit."
George Orphanides, Chief Scientific Officer at LifeArc (search), which co-funded the study alongside GOSH Charity, added: "ARC syndrome (search) is a serious, ultra-rare condition with very limited treatment options. These early findings are an important step towards understanding whether gene therapy could one day offer a new approach for affected children and their families."
Before human trials can commence, further long-term toxicology and safety studies with larger sample sizes, along with comparative integration site analysis between murine and human hepatocytes, will be required. The researchers also noted that while clodronate liposome-mediated macrophage depletion is not currently an established clinical intervention, clinically relevant bisphosphonate formulations have demonstrated tolerability in human trials, suggesting the hepatic macrophage barrier may be clinically surmountable.