745. Innate Immune Responses to Adeno-Associated Virus Vectors

Abstract

Top of pageAbstract The innate immune response against invading pathogens is an acute inflammatory response that limits the initial infection and initiates host adaptive immunity. Adenovirus vectors (Ad-vectors) cause acute inflammation in vivo, whereas adeno-associated virus (AAV) vectors are not associated with significant inflammation. We previously found that in contrast to Ad-vectors, AAV vectors do not induce the expression of chemokines/cytokines in epithelium-derived cells in vitro. However, in vivo studies showed that AAV vectors induce transient expression of chemokines/cytokines and leukocyte recruitment to mouse liver. This transient activation of innate immune responses by AAV vectors in vivo might contribute to the generation of an adaptive response; the formation of neutralizing antibodies to AAV capsid proteins. Innate immune responses to AAV vectors in the liver were completely abolished in the absence of Kupffer cells (liver macrophages) suggesting that AAV vectors may interact significantly with macrophages. To test whether AAV can directly infect and activate macrophages, THP-1 cells (human monocytes) were transduced with AAV vectors and chemokine expression was analyzed 6 hours post transduction. In contrast to the response in epithelium-derived cells, AAV vectors carrying different transgenes were able to induce various chemokine and pro-inflammatory cytokine mRNAs, including RANTES, IP-10, MIP-1β, MIP-1α, MCP-1 and IL-8 in THP-1 cells in a dose dependent manner. Transductions in the presence of polymyxin B and the use of appropriate vehicles confirmed that the responses were not induced through endotoxin (LPS) or transgene protein contamination. Southern blots indicated internalized vector genomes, suggesting a direct infection and activation of these cells. Furthermore, AAV induced the expression of chemokines in THP-1 cells in the presence or absence of serum suggesting the activation occurs independent of opsonizing proteins or co-factors. Understanding the mechanism of innate immune activation by AAV vectors may allow strategies to minimize humoral adaptive responses permitting the re-administration of these vectors in vivo.