Effect of an anti–Mpl-L antibody on spontaneous MK growth. Number of MKs obtained after 10 days of serum-free liquid culture without growth factor (0) (▪), with 10 μg/mL anti–Mpl-L antibody (Ab) (▩), with PEG-rhuMGDF (10 ng/mL) (▨), with the combination of PEG-rhuMGDF (10 ng/mL) and the anti–Mpl-L antibody (PEG-rhuMGDF+Ab) (▥), with three cytokines (IL-3, IL-6, and SCF) (▤), or with three cytokines (IL-3, IL-6, and SCF) associated with the anti–Mpl-L antibody (IL-3, IL-6, and SCF+Ab ) (). CD34⁺ cells were seeded at concentration ranging from from 2 × 10⁴ cells/mL to 1 × 10⁵ cells/mL in 100 μL in triplicate. MKs were quantitated by morphological analysis and results are expressed as the number of MKs per 1 × 10³ seeded CD34⁺ cells.