NIP-004 displays species-specific activity. (A) NIP-004 failed to stimulate proliferation of UT-7/EPO-MuMpl– and Ba/F3-MuMpl–expressing murine Mpl. In contrast, EPO and TPO stimulated induced proliferation of UT-7/EPO-MuMpl as a positive control. IL-3 and TPO enhanced proliferation of Ba/F3-MuMpl as a positive control. Data are expressed as the mean ± SEM from 3 independent experiments. (B) Recombinant human TPO stimulated CFU-MK colony formation from murine and cynomolgus monkey–derived bone marrow cells in a dose-dependent manner. In contrast, NIP-004 failed to induce CFU-MK colonies under the same conditions. Data are expressed as the mean ± SD of duplicate assays. NC indicates negative control; E, 0.1 U/mL rhEPO; IL-3, 0.1 ng/mL rmIL-3; T, 10 ng/mL rhTPO; NIP₁, 1μg/mL NIP-004.