Cell surface expression of CD38 and HLA-DR II on input and HA-adherent CD34⁺ HPC. CD34⁺ HPC were stained with MoAbs to CD38 (PE-conjugated) and to HLA-DR (FITC-conjugated). Negative controls (grey lines) are cells labeled with PE-conjugated IgG1 or FITC-conjugated IgG2a. Flow cytometric analysis was performed as described in the Materials and Methods. Data are from a representative experiment. Four independent experiments gave similar results.