TLR9-independent CD8<sup>+</sup> T Cell Responses in Hepatic AAV Gene Transfer Through IL-1R1-MyD88 Signaling.

Overview

Upon viral infection of the liver, CD8⁺ T cell responses may be triggered despite the immune suppressive properties that manifest in this organ. We sought to identify pathways that activate responses to a neoantigen expressed in hepatocytes, using adeno-associated viral (AAV) gene transfer. It was previously established that cooperation between plasmacytoid dendritic cells (pDCs), which sense AAV genomes by Toll-like receptor 9 (TLR9), and conventional DCs promotes cross-priming of capsid-specific CD8⁺ T cells. Surprisingly, we find local initiation of a CD8⁺ T cell response against antigen expressed in ∼20% of murine hepatocytes, independent of TLR9 or type I interferons and instead relying on IL-1 receptor 1 - MyD88 signaling. Both IL-1α and IL-1β contribute to this response, which can be blunted by IL-1 blockade. Upon AAV administration, IL-1 producing pDCs infiltrate the liver and co-cluster with XCR1⁺ DCs, CD8⁺ T and Kupffer cells. Analogous events were observed following coagulation factor VIII gene transfer in hemophilia A mice. Therefore, pDCs have alternative means of promoting anti-viral T cell responses and participate in intrahepatic immune cell networks similar to those that form in lymphoid organs. Combined TLR9 and IL-1 blockade may broadly prevent CD8⁺ T responses against AAV capsid and transgene product.