Transabdominal ultrasound guided AAV9-GFP delivery in fetal pigs: a translational and minimally invasive model for in utero fetal gene therapy

In utero fetal gene therapy (IUFGT) has the potential to correct severe monogenic disorders before irreversible damage occurs. Despite promising results in small and large animal models, its translation to clinical practice remains limited by technical challenges, safety concerns, and the lack of standardized protocols in relevant disease models species. We established and validated a minimally invasive, ultrasound-guided approach for systemic gene delivery in fetal pigs using a self-complementary AAV9 vector encoding GFP under a CAG promoter. Injections were performed at different gestational ages (GA 80 and GA 108) via intracardiac or umbilical venous routes. Postnatal outcomes were monitored, and transgene biodistribution and expression were assessed by qPCR, ddPCR, immunofluorescence, and Western blotting. Inflammatory response, toxicity, and maternal safety were evaluated through cytokine profiling and histological analyses. The procedure was well tolerated, with no significant maternal morbidity or adverse obstetric outcomes beyond one preterm delivery. Biodistribution analysis revealed widespread vector presence in peripheral tissues, with robust GFP expression in liver and heart. Importantly, there was no evidence of significant tissue toxicity, necrosis, or fibrosis in any of the organs analyzed. Mild increases in pro-inflammatory cytokines (GM-CSF, GRO-α, IFN-γ) were observed but were not associated with histopathological changes. No anti-AAV9 capsid antibodies were detected in sera from piglets or sows, suggesting a minimal immune response to the vector. These findings demonstrate the safety, feasibility, and efficacy of ultrasound-guided IUFGT in pigs, supporting its potential as a translational platform for therapeutic gene delivery in fetuses affected by severe congenital diseases. This model offers a valuable framework for further preclinical development of prenatal interventions, particularly for disorders with early onset, such as mitochondrial diseases.