HCl pH 7.4 and layered onto Percoll Plus gradients (GE Healthcare). Gradients were spun at 4°C, 20 minutes at 2000 RPM in a GS-6R tabletop centrifuge (Beckman). A brown, flocculent layer of cell debris was removed from the top of the gradients with a pipette, and the remainder of the gradient was pooled with 40 ml PBS +2 mM EDTA. Cells were harvested by centrifugation, resuspended in 45 mL PBS +2 mM EDTA and purified on an Automacs Pro separator system (Miltenyi Biotek).
