Hepatotoxicity and Toxicology of In Vivo Lentiviral Vector Administration in Healthy and Liver-Injury Mouse Models

General safety and toxicology assessments supporting in vivo lentiviral vector-based therapeutic development are sparse. We have previously demonstrated the efficacy of a lentiviral vector expressing fumarylacetoacetate hydrolase (LV-FAH) to cure animal models of hereditary tyrosinemia type 1. Therefore, we performed a complete preclinical toxicological evaluation of LV-FAH, in a large cohort (n = 20/group) of wildtype mice and included matched groups of N-nitrosodiethylamine/carbon tetrachloride (DEN/CCl₄)–induced liver injury mice to assess specific toxicity in fibrotic liver tissue. Mice receiving LV-FAH alone (10⁹ TU/mouse) or in combination with DEN/CCl₄ presented clinically similar to control animals, with only slight reductions in total body weight gains over the study period (3.2- to 3.7-fold vs. 4.2-fold). There were no indications of toxicity attributed to administration of LV-FAH alone over the duration of this study. The known hepatotoxic combination of DEN/CCl₄ induced fibrotic liver injury, and co-administration with LV-FAH was associated with exaggeration of some findings such as an increased liver:body weight ratio and progression to focal hepatocyte necrosis in some animals. Hepatocellular degeneration/regeneration was present in DEN/CCl₄-dosed animals regardless of LV-FAH as evaluated by Ki-67 immunohistochemistry and circulating alpha fetoprotein levels, but there were no tumors identified in any tissue in any dose group. These data demonstrate the inherent safety of LV-FAH and support broader clinical development of lentiviral vectors for in vivo administration.