CD34⁺CD41^low population from MSC coculture has enhanced proplatelet and platelet-producing capacity. (A) Flow sorting and culture protocol of CD34⁺CD41^low cells. CD34⁺ cells cultured for 10 days in the presence of MSCs were sorted according to their CD34⁺CD41^low phenotype (G1) using a FACS Aria II flow cytometer and then cultured for 7 days in a medium containing TPO with or without MSCs. Representative DIC microscopy photographs of culture wells at day 7 showed extensive proplatelet development in the presence of MSCs. Scale bar, 50 μm. (B) Proportion of MK-extending proplatelets at day 7 (6.6 ± 0.8% for TPO vs 46.4 ± 5.2% for TPO + MSCs; mean ± SEM in 3 experiments; Student t test, **P < .01). (C) Amount of culture-derived platelets at day 7 (0.5 ± 0.04 × 10⁵ in the control vs 9.1 ± 0.7 × 10⁵ with MSCs; mean ± SEM in 3-4 experiments; Student t test, ***P < .001).