Rapamycin nanoparticles mitigate anti-AAV antibody formation in a mouse model of ornithine transcarbamylase deficiency

Adeno-associated virus (AAV) vector-based liver gene therapy for inherited diseases has demonstrated efficacy in clinical trials in adults. However, its application to pediatric patients is limited by loss of AAV genomes during hepatocyte proliferation, compromising long-term benefits. Additionally, the anti-AAV immune responses induced after the initial AAV-administration preclude vector re-dosing. One key driver of this immune response is mTOR-dependent activation of dendritic cells. Inhibition of this pathway with rapamycin can promote immune tolerance. We assessed the safety and efficacy of rapamycin-loaded synthetic nanoparticles (ImmTOR) in juvenile OTCSpf−Ash mice, a model of ornithine transcarbamylase (OTC) deficiency (OTCD). Treatment of postnatal day 30 mice with ImmTOR alone transiently activated autophagy and reduced urinary orotic acid levels. Treatment with a liver-specific AAV8 vector encoding codon-optimized human OTC cDNA normalized urinary orotic acid levels and significantly increased ureagenesis, OTC protein expression, and enzyme activity compared with untreated controls. AAV-vector co-administration with ImmTOR prevented IgM and IgG formation and induced a dose-dependent reduction of anti-AAV neutralizing antibodies, consistent with modulation of the humoral immune response. These findings suggest that ImmTOR can mitigate humoral immune responses to AAV vectors in OTCSpf−Ash mice and may enable AAV vector re-administration, although further optimization is required for clinical translation.