p21 message and protein in CD34⁺ blast cells and in differentiated cells. (Top) In situ analysis of p21 message in CD34⁺ blast cells (above) and in neutrophils (below). (A) and (D), Wright Giemsa; (B) and (E), digoxigenin-labeled control; (C) through (F), digoxigenin-labeled p21 probe. (Bottom) Immunohistochemical demonstration of p21 protein in differentiating cells. Day 0 CD34⁺ blasts stained with isotype control (G) or anti-p21 antibodies. Some nonspecific staining of antibody-coated magnetic beads is present. Differentiated progeny arising after 11 days of culture stained with isotype control (I) or anti-p21 antibody (J) stain strongly for p21.