AbstractBackground & Aims Isolated methylmalonic acidemia (MMA) is a severe inherited metabolic disorder caused by a deficiency of the mitochondrial enzyme methylmalonyl-CoA mutase, encoded by the MMUT gene. Lentiviral vector (LV)–based liver gene therapy may offer sustained therapeutic benefits even in pediatric patients, whose livers are still growing, due to the stable genomic integration of the therapeutic transgene. Methods We evaluated the efficacy of liver-directed LV gene therapy in a mouse model of MMA and in patient-derived human fibroblasts. Results Systemic administration of an MMUT-expressing LV to 2-week-old MMA mice yielded a rapid, strong, and long-lasting (>1 year) therapeutic effect, with normalization of liver histology and mitochondrial ultrastructure. LV-mediated supraphysiological hepatic expression of MMUT promoted detoxification of the kidney and brain from methylmalonic acid and achieved broad correction of metabolomic, lipidomic, and proteomic profiles. Subsequently, we developed a codon-optimized MMUT transgene to increase expression and lower the minimal therapeutic dose. In 2-week-old MMA mice, this LV variant showed a dose-dependent improvement in metabolic biomarkers, clinical phenotype, and hepatocyte transduction efficiency (exceeding 80%). At the lower LV doses, corrected hepatocytes gained a selective proliferative advantage. Throughout all treated animals, LV integration site analysis revealed a high number of integrations without dominant clones, supporting a polyclonal profile. LV gene therapy provided metabolic improvement even in adult MMA mice, which had a more advanced disease stage than 2-week-old MMA mice. In vitro, LV delivery restored MMUT expression in patient-derived fibroblasts and partially corrected their metabolic abnormalities. Conclusion These data provide preclinical proof-of-concept for the efficacy, safety, and extrahepatic therapeutic benefit of liver-directed LV gene therapy for MMA. Impact and implications Methylmalonic acidemia (MMA) is a severe metabolic disorder with few treatment options. A liver-targeted gene therapy using integrating lentiviral vectors (LV) could allow treatment of pediatric patients with a single dose, due to the stable integration of the therapeutic transgene into the DNA of target cells. In this study, we showed that in a relevant MMA mouse model, systemic LV administration led to long-lasting expression of the therapeutic enzyme in hepatocytes, which corrected metabolic abnormalities and significantly improved the disease phenotype. Supranormal enzyme levels in the liver enabled systemic detoxification and widespread metabolic normalization without detectable LV-related toxicity. We provide a detailed LV dose-response study evaluating the efficiency of gene transfer to hepatocytes and its therapeutic outcomes. Overall, these findings offer strong preclinical evidence to support progressing to clinical trials for MMA patients and help guide the potential use of liver-directed LV gene therapy for other inherited metabolic diseases.
Barbon et al. (Fri,) studied this question.