Adeno-associated virus capsid antigen presentation is dependent on endosomal escape
Chengwen Li, Yi He, Sarah Nicolson, Matt Hirsch, Marc S. Weinberg, Ping Zhang, Tal Kafri, R. Jude Samulski
Chengwen Li, Yi He, Sarah Nicolson, Matt Hirsch, Marc S. Weinberg, Ping Zhang, Tal Kafri, R. Jude Samulski
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Research Article Genetics

Adeno-associated virus capsid antigen presentation is dependent on endosomal escape

Abstract

Adeno-associated virus (AAV) vectors are attractive for gene delivery-based therapeutics, but data from recent clinical trials have indicated that AAV capsids induce a cytotoxic T lymphocyte (CTL) response that eliminates transduced cells. In this study, we used traditional pharmacological agents and AAV mutants to elucidate the pathway of capsid cross-presentation in AAV-permissive cells. Endosomal acidification inhibitors blocked AAV2 antigen presentation by over 90%, while proteasome inhibitors completely abrogated antigen presentation. Using mutant viruses that are defective for nuclear entry, we observed a 90% decrease in capsid antigen presentation. Different antigen presentation efficiencies were achieved by selectively mutating virion nuclear localization signals. Low antigen presentation was demonstrated with basic region 1 (BR1) mutants, despite relatively high transduction efficiency, whereas there was no difference in antigen presentation between BR2 and BR3 mutants defective for transduction, as compared with wild-type AAV2. These results suggest that effective AAV2 capsid antigen presentation is dependent on AAV virion escape from the endosome/lysosome for antigen degradation by proteasomes, but is independent of nuclear uncoating. These results should facilitate the design of effective strategies to evade capsid-specific CTL-mediated elimination of AAV-transduced target cells in future clinical trials.

Authors

Chengwen Li, Yi He, Sarah Nicolson, Matt Hirsch, Marc S. Weinberg, Ping Zhang, Tal Kafri, R. Jude Samulski

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Figure 8

Putative model of AAV2 capsid antigen cross-presentation in AAV-transduced cells.

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Putative model of AAV2 capsid antigen cross-presentation in AAV-transduc...
Following binding on the cell surface in permissive cells via receptors and coreceptors, an AAV2 virion is uptaken by endocytosis into endosomes and lysosomes. PLA2 and NLSs are exposed on the virion surface to help the AAV virion escape into the cytosol. This is followed by AAV2 capsid ubiquitination and degradation by the proteasome. Resulting peptides are transported to the ER by TAP to bind MHC class I molecules. This complex is then trafficked to the cell surface via the Golgi network for recognition by capsid-specific CTLs. AAV2 virions also may travel to the Golgi complex and MTOC after endosomal/lysosomal escape. These organelles are then sequestered by the autophagosome and delivered to proteasomes for capsid antigen processing, or AAV2 virions are released from the Golgi complex and the MTOC into the cytoplasm for proteasomal degradation. Additionally, uncoated AAV2 capsid may enter the proteasome after the AAV2 virion enters the nucleus. Solid line indicates the pathways from the prior studies and this study. Dotted line suggests possible routes for AAV2 capsid antigen processing and presentation.