Detection of p21 and p27 by flow cytometry. Cord blood–derived CD34 cells differentiated for 5 days were permeabilized for staining of nuclear cdki’s p21 and p27. Cells were stained with (Neomarkers) monoclonal p21 Ab-2 (left) or Ab-3 (center), or with p27 Ab-1 (Neomarkers) as indicated by blackened histogram; isotype control is shown as open histogram. Similar staining of p21⁻ K562 cells with anti-p21 antibodies showed no shift from isotype control (not shown).