Schematic representation of the protocol used to sort rare double-stained CD34⁺CD45⁺ HSCs contained in the aorta of a single 5-week human embryo. Less than 20 double-positive cells were finally recovered from 30,000 total cells obtained after collagenase dissociation. An analogous protocol was used to sort CD34⁺CD45⁺ and CD34⁺CD38⁻ HSCs from a 5- and a 6.5-week embryonic liver, respectively.