Proteasome Inhibitors Decrease AAV2 Capsid-Derived Peptide Epitope Presentation On MHC Class I Following Transduction.

Abstract 695

Adeno-associated viral (AAV) vectors are one of the most extensively studied and highly used vector platforms for gene therapy applications. We have recently provided evidence for AAV capsid-derived antigen presentation through MHC class I on the surface of AAV-transduced cells, supporting the hypothesis that in the first clinical trial using AAV to treat Hemophilia B, AAV capsid proteins were presented on the surface of transduced hepatocytes, resulting in clearance by antigen-specific CD8+ T cells and consequent loss of therapeutic transgene expression. Proteasome inhibitors are small molecule compounds that are able to specifically inhibit the activity of the proteasome, resulting in a buildup of ubiquitinated proteins, increased intracellular reactive oxygen species, and a general decrease in presentation of MHCI-peptide complexes. It has previously been shown that proteasome inhibitors can have a dramatic effect on AAV transduction in vitro and in vivo. Here we describe using the FDA approved proteasome inhibitor, bortezomib, to decrease capsid antigen presentation on hepatocytes in vitro, while at the same time, enhancing gene expression in vivo. Using an AAV capsid specific T cell reporter line to analyze effects of proteasome inhibitor on antigen presentation, we demonstrated capsid antigen presentation at low MOI's, as well as inhibition of antigen presentation at clinically relevant levels of bortezomib. We also demonstrate that bortezomib can enhance FIX expression from an AAV2 vector in C57Bl/6 mice, however does not appear to enhance expression of AAV8. Based on the data presented here, it appears as if future studies using proteasome inhibitors in large animal models may be warranted. A pharmacological agent that can enhance AAV transduction, decrease T-cell activation/proliferation, and decrease antigen presentation would be a promising solution to many of the obstacles to successful translation of AAV-mediated, liver-directed gene transfer to the clinic.