Inhibition of MK spontaneous growth by the sMpl-Fc. Number of MKs obtained after 10 days of serum-free liquid culture without growth factor (0) (▪), with the sMpl-Fc at 5 μg/mL (▩), with a combination of rhuIL-3, rhuIL-6, and rhuSCF (IL-3+IL-6+SCF) (▨), or with the three cytokine combination and the sMpl-Fc (IL-3+IL-6+SCF+sMpl-Fc) (▥). CD34⁺cells were seeded at 2 × 10⁴ cells/mL in 100 μL in triplicate, and MKs were quantitated by morphological analysis.