HCA expression by human hematopoietic cells in different tissues. Cells from 18-week FBM (A and D), ABM (B and E), and MPB from a multiple myeloma patient (C and F ) were stained as described in the Materials and Methods with Rh123 dye and MoAbs against CD34 and HCA. Isotype control staining was on all samples. The MPB sample was taken from day-2 leukapheresis, whereas the patient was treated with a high dose of cyclophosphamide and with GM-CSF. This particular MPB sample contained the highest percentage of CD34⁺ cells as compared with other leukapheresis harvests made at different days from the same patient. The percentage of cells in each quadrant is indicated. The bottom row (D, E, and F ) shows the Rh123 staining versus huHCA expression by CD34⁺ cells from each tissue analyzed above (A, B, and C).