Fig. 2: In vitro virosome toxicity and uptake by antigen-presenting cells.

a Human CD34⁺-derived cells in culture were exposed to the various virosome formulations for 1 hour and cells were then stained with LIVE/DEAD dye to determine the percentage of dead cells and cells alive. b Virosomes were labeled with a stable tracer fluorescent lipid labeled with Atto 647 and their uptake after 1 hour by various APC subpopulations defined by markers HLA-DR, CD11c, CD1c, and CD1a were monitored by cytometry, gating on dull and bright virosome signals in pink gates (gating strategy described in Supplementary Methods Fig. 3). Cells that are HLA-DR⁺CD11c⁻ are not differentiated into dendritic cells and they represent the majority of the population. Cells that are HLA-DR⁺CD11c⁺CD1c⁺CD1a⁺ have a phenotype similar to Langerhans cells, and cells that are HLA-DR⁺CD11c⁺CD1c⁺CD1a⁻ are more similar to dermal DC. The stronger is the fluorescent Atto 647 signal, the more virosome uptake took place. The percentage of Atto 647 positive cells is comparable between cells exposed to the starting liquid formulation and the various solid vaccine dosage forms, suggesting that excipients did not interfere with early virosome uptake by APC. Data are from a representative experiment.