Surface expression of CD44 on CD34⁺ cells treated with PMA, H90 MoAb, or cytokines. Cells were treated with either 10⁻⁷ mol/L PMA for 16 hours, H90 MoAb (5 μg/mL), or cytokines SCF (10 ng/mL), GM-CSF (0.1 ng/mL), or IL-3 (10 ng/mL) for 15 minutes at 37°C as described in the Materials and Methods. Control cells were either untreated cells or cells treated with IgG1. Thereafter, cells were washed and labeled with FITC-conjugated J173 MoAb. Negative controls (dotted lines) were treated cells labeled with FITC-conjugated IgG1. Flow cytometry analysis was performed as described in the Materials and Methods.