Prophylactic Prednisolone Promotes AAV5 Hepatocyte Transduction Through the Novel Mechanism of AAV5 Coreceptor Platelet-Derived Growth Factor Receptor Alpha Upregulation and Innate Immune Suppression.

Adeno-associated virus (AAV) vectors are used to deliver therapeutic transgenes, but host immune responses may interfere with transduction and transgene expression. We evaluated prophylactic corticosteroid treatment on AAV5-mediated expression in liver tissue. Wild-type C57BL/6 mice received 6 × 10¹³ vg/kg AAV5-HLP-hA1AT, an AAV5 vector carrying a human α1-antitrypsin (hA1AT) gene with a hepatocyte-specific promoter. Mice received 4 weeks of daily 2 mg/kg prednisolone or water starting day -1 or 0 before vector dosing. Mice that received prophylactic corticosteroids had significantly higher serum hA1AT protein than mice that did not, starting at 6 weeks and persisting to the study end at 12 weeks, potentially through a decrease in the number of low responders. RNAseq and proteomic analyses investigating mechanisms mediating the improvement of transgene expression found that prophylactic corticosteroid treatment upregulated the AAV5 coreceptor platelet-derived growth factor receptor alpha (PDGFRα) on hepatocytes and downregulated its competitive ligand PDGFα, thus increasing the uptake of AAV5 vectors. Evidently, prophylactic corticosteroid treatment also suppressed acute immune responses to AAV. Together, these mechanisms resulted in increased uptake and preservation of the transgene, allowing more vector genomes to be available to assemble into stable, full-length structures mediating long-term transgene expression. Prophylactic corticosteroids represent a potential actionable strategy to improve AAV5-mediated transgene expression and decrease intersubject variability.