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Recombinant adeno-associated virus (AAV) vectors have been broadly adopted as a gene delivery tool in clinical trials, owing to their high efficiency of transduction of several host tissues and their low immunogenicity. However, a considerable proportion of the population is naturally exposed to the WT virus from which AAV vectors are derived, which leads to the acquisition of immunological memory that can directly determine the outcome of gene transfer. Here, we show that prior exposure to AAV drives distinct capsid immunity profiles in healthy subjects. In peripheral blood mononuclear cells (PBMCs) isolated from AAV-seropositive donors, recombinant AAV triggered TNF-α secretion in memory CD8+ T cells, B cell differentiation into antibody-secreting cells, and anti-capsid antibody production. Conversely, PBMCs isolated from AAV-seronegative individuals appeared to carry a population of NK cells reactive to AAV. Further, we demonstrated that the AAV capsid activates IL-1β and IL-6 cytokine secretion in monocyte-related dendritic cells (moDCs). IL-1β and IL-6 blockade inhibited the anti-capsid humoral response in vitro and in vivo. These results provide insights into immune responses to AAV in humans, define a possible role for moDCs and NK cells in capsid immunity, and open new avenues for the modulation of vector immunogenicity.
Introduction
With several successful adeno-associated virus (AAV) vectorbased gene therapy clinical trials (1-4) and the recent approval by the FDA of a gene therapy for congenital blindness (5), the promise of a definitive cure for numerous genetic diseases is becoming a reality. Despite the dazzling progress thus far in the field, untoward immune responses to the AAV vector capsid remain the primary obstacle to the widespread adoption of this technology and, in some cases, to the achievement of long-lasting efficacy (6). Experience in the clinic with AAV vectors highlighted 3 main issues related to vector immunogenicity: (a) cellular immune responses against vector-transduced cells; (b) humoral immune responses occurring upon initial vector infusion; and (c) preexisting anticapsid antibodies able to neutralize the vector in individuals who were already exposed to WT AAV (7, 8).
The innate immune response to the AAV capsid in humans, compared with responses to adenoviral or lentiviral vectors, appears to be low and self-limited (9-12), although its impact on adaptive immune responses is poorly understood. In nonparenchymal liver cells, capsid particles are first sensed...