Effect of elastase on normal and CML CD34⁺ growth. 2 × 10⁴ CML or normal CD34⁺ cells/mL were cultured in 200 μL serum-free medium with or without cytokine. Daily measurement of tritiated thymidine uptake by 10 ng/mL G-CSF-stimulated CML (A) or normal (B) CD34⁺ cells (•, control; ○, 1 μg/mL elastase; ▪, no cytokine). Data represent mean ± SEM of triplicates and are representative of 2 different experiments. (C) Daily measurement of tritiated thymidine uptake by 10 ng/mL GM-CSF-stimulated CML CD34⁺ cells (•, control; ○, 1 μg/mL elastase; ▪,no cytokine; □, 5 μg/mL elastase). Data represent mean ± SEM of triplicates and are representative of 2 different experiments. (D) 10⁶ CML or normal CD34⁺ cells were plated in 12-well plates in 2 mL serum-free medium with 25 ng/mL G-CSF, GM-CSF, and SCF. Plates were then incubated at 37°C in 5% CO₂. Apoptosis was measured daily. Increased apoptosis in the presence of elastase was calculated as [% apoptosis in presence of elastase -% apoptosis without elastase] (•,normal CD34⁺ cells; ○, CML CD34⁺ cells).