Proteasome Inhibition Is Partially Effective in Attenuating Pre-Existing Immunity against Recombinant Adeno-Associated Viral Vectors

Abstract

Pre-existing immunity against adeno-associated virus (AAV) remains a major challenge facing the clinical use of systemic administration of recombinant AAV vectors for the treatment of genetic and acquired diseases using gene therapy. In this study, we evaluated the potential of bortezomib (marketed under trade name Velcade) to abrogate a pre-existing immunity to AAV in mice, thereby allowing subsequent transduction by a recombinant AAV vector of the same serotype. We demonstrate that bortezomib efficiently reduces AAV-specific IgG titres and moderates the cytotoxic T cell response in mice that have a pre-existing immunity to AAV2/8. Significant depletion of AAV2/8-specific IgG-producing plasma cells in secondary lymphoid organs and bone marrow was observed. However, this inhibition of the immune response by bortezomib was insufficient to allow subsequent re-infection with a recombinant AAV vector of a similar serotype. We show that this shortcoming is probably due to the combination of residual antibody levels and the inability of bortezomib to completely deplete the memory B cells that are re-activated in response to a repeated infection with a recombinant AAV vector. Taken together, the results of this study argue for the use of immunosuppressive therapies that target both plasma and memory B cells for the efficient elimination of pre-existing immunity against AAV2/8 vectors.

Targeted Modifications in Adeno-Associated Virus Serotype 8 Capsid Improves Its Hepatic Gene Transfer Efficiency In Vivo

“…In addition, the processed vector can also be taken up the professional antigen-presenting cells, which after MHC class II restriction can activate a CD4 + T-cell response (Chen et al, 2006;High, 2012). In line with these observations, the use of proteasomal inhibitors prior to AAV8 administration has shown reduced immune response and increased transduction efficiency in vivo (Karman et al, 2012;Liu et al, 2012). More importantly, K137 is known to be within a previously described MHC class II T-cell recognition epitope (L126-P140) of AAV8 in both humans and mice (Sabatino et al, 2005;Chen et al, 2006).…”

Strategies to circumvent humoral immunity to adeno-associated viral vectors

“…For instance, bortezomib is a US FDA-approved protease inhibitor that targets plasma B cells and is used for treating multiple myeloma. Administration of bortezomib after vector injection has been shown to decrease NAb titer by 8 – 10 folds in naive mice, when compared with mock treatment [85]. This decrease in NAb titer is likely caused by inhibiting antigen processing by the proteasome, which potentially reduces subsequent presentation on B cells and contributes to increased transduction efficiency [86–88].…”

Immune System Obstacles to In vivo Gene Transfer with Adeno-Associated Virus Vectors

“…Among the drugs of interest, the clinically approved drug bortezomib seems promising, as it efficiently targets plasma cells 163 while reducing capsid antigen presentation and enhancing AAV vector transduction. 166 In this study, an 8-to 10-fold drop in anti-AAV antibody titer was observed, but the decrease was not sufficient to allow for vector re-administration, and toxicity was observed in some animals. 166 In this study, an 8-to 10-fold drop in anti-AAV antibody titer was observed, but the decrease was not sufficient to allow for vector re-administration, and toxicity was observed in some animals.…”