Metformin (Met) increases the number of HbF-expressing cells in HSPCs and prevents sickling under hypoxic conditions. (A) CD34⁺ cells from normal individuals were cultured under conditions to promote erythroid maturation. The indicated drugs were added at day 7 and samples were collected on day 14. HbF-immunostained cells (F cells) were measured by flow cytometry at day 14. (B) Aggregate of 3 independent assays. (C) CD34⁺ cells from a patient with SCD, treated with the indicated drugs from days 7 to 28. On day 28, cells were placed in 2% O₂ for 4 hours, fixed, and stained with Wright/Giemsa; scale bars, 10 µm. Error bar represents SD from 3 experiments using CD34⁺ cells from 3 patients with SCD. ***P < .0001, **P < .005, *P < .01.