Expression of CD4 on serum-free expanded hematopoietic progenitor-derived cells. CFU-GM (A and B), CFU-Meg (C and D), and BFU-E (E and F) progenitors were serum-free expanded from CD34⁺ BMMNC as described and FACS analyzed for CD4 antigen expression. Histograms (B, D, and F) represent the gated populations as indicated (A, C, and E). The isotype negative controls are overlaid (bold line), and M1 represents the positive populations. Data from at least 3 different donors were analyzed. The mean percentage of positive cells for each chemokine receptor plus or minus the standard deviation is summarized in the test. Histograms from a representative donor are presented.