Expression of CD4 by CD34⁺ human fetal liver, fetal BM, and umbilical cord blood cells. LDFL, LDFBM, and LDCB cells were depleted of GPA⁺ cells and analyzed for the expression of CD34 in combination with CD8 or CD4. The analysis of antigen expression was limited to cells with a low side scatter, containing the bulk of the CD34⁺ cells, as defined by the gates shown in the top row. The expression of CD4 and CD34 on LDFL, LDFBM, and LDCB cells, depleted of Lin⁺ cells by magnetic bead depletion of CD3⁺, CD8⁺, CD14⁺, CD19⁺, CD20⁺, and CD56⁺ cells, is shown in the bottom row. CD4⁺ CD34⁺⁺ Lin⁻ and CD4⁻ CD34⁺⁺ Lin⁻ LDFL cells are indicated in the bottom-left panel by regions representative of those used for the isolation of these cells by FACS in subsequent experiments. The percentage of events found in each quadrant is indicated. Contour plots were made using a linear density scale at the degree of resolution indicated in the top-right corner of each plot (% Lin). Dot plots are used to show data on cord blood cells containing a low percentage of CD34⁺ cells. These data are representative of at least three analyses per tissue type.