Identification of AAV variants with improved transduction of human vascular endothelial cells by screening AAV capsid libraries in non-human primates.

The development of targeted vector systems for gene therapy has made impressive progress during the last decade. Promising vector candidates were identified by screening large pools of adeno-associated virus (AAV) mutants in small animal models. However, it became apparent that targeted AAV mutants isolated from rodents may not function in humans as the tropism of individual AAV mutants can differ between species. To identify novel vascular-targeted AAV capsid mutants suitable for treating human patients, we generated a set of AAV2 display peptide libraries and screened them in the common marmoset, a non-human primate. To evaluate the impact of different AAV library production methods, progress of the screening process was monitored by next generation sequencing. Particle distribution and enrichment was compared between different AAV libraries and selection rounds. We observed enrichment of AAV variants in the brain and other well-perfused organs (lung, heart, kidney) potentially mediated by high capsid affinity for the vascular endothelium in general. In vitro experiments on primary human microvascular endothelial cells isolated from a set of different organs (brain, heart, lung, liver, kidney and spleen) confirmed superior transduction of a selected AAV variant displaying the "DWP" amino acid sequence motif compared to natural AAV serotypes 1-9.