Introduction Adeno-associated virus (AAV)-based gene therapy can initiate host-immune responses
to the AAV vector components or the transgenic protein product which could reduce
AAV-mediated expression. Data from preclinical studies suggest that corticosteroid
treatment may limit these immune responses and improve gene therapy outcomes.
Method In an earlier study, prednisolone treatment initiated one week after valoctocogene
roxaparvovec (AAV5-hFVIII-SQ) administration had no impact on FVIII expression in
mice. In a subsequent study we investigated if corticosteroid treatment initiated
before AAV administration could improve transgene expression in mice. Mice were dosed
daily for 4 weeks with prednisolone (2 mg/kg) or water starting 1 day or 2 hours before
administration of 6x1013 vg/kg of an AAV5-HLP-hA1AT vector expressing human α1-antitrypsin
(hA1AT) as a reporter.
Results Prednisolone-treated mice had significantly higher serum hA1AT protein levels (1.5-
to 2.2-fold) starting 6 weeks after AAV dosing and through study end at 12 weeks.
Furthermore, mice treated with prednisolone had a higher percentage of hepatocytes
stained positive for vector DNA as well as higher liver full-length vector genome
DNA and transgene RNA compared to the non–prednisolone-treated groups. This demonstrates
that corticosteroid treatment before AAV administration can improve liver-directed
AAV5 expression in mice.
To better understand potential mechanisms involved in this beneficial effect of prophylactic
steroid treatment on AAV transduction we further investigated early events after AAV5
dosing in mice with or without prophylactic corticosteroid treatment. RNAseq analyses
of liver samples were performed to evaluate differential expression 2h and 24h following
AAV5-HLP-hA1AT administration in mice treated with and without prophylactic prednisolone.
These analyses showed that prophylactic steroid treatment reduces acute innate immune
responses to AAV. For example, serum IL-1b protein levels were increased 2h and 24h
after AAV administration which were suppressed with prednisolone treatment.
Moreover, RNAseq showed an upregulation of the AAV5 cell surface co-receptor, PDGFRa,
and downregulation of its competitive ligand PDGFa 2 hours after AAV administration
in prednisolone treated mice compared to mice not treated with prednisolone. This
suggests that prophylactic corticosteroid treatment may increase AAV5 capsid uptake
by upregulation of the receptor and downregulation of the ligand.
Conclusion In summary, prophylactic corticosteroid treatment before AAV5 administration improved
transgene expression potentially through multiple mechanisms, including suppression
of the innate immune response and increased AAV uptake by cells.
