Ex vivo EXEL-0862 treatment inhibits the viability of primary bone marrow mast cells. (A) Bone marrow mononuclear cells from 3 patients with ISM who carried D816V KIT were incubated for 7 days with EXEL-0862 at 0.1 μM and 1 μM. Then, the mast-cell content in cultures was determined by flow cytometry. (B) Mast cells without D816V KIT mutation in samples from 3 donors were derived from bone marrow CD34⁺ cells by culture in Stem-Pro and SCF (100 ng/mL) and IL-3 (30 ng/mL, only for the first week) and weekly hemirepletion of the culture medium for approximately 9 to 14 weeks. Mast cells were then incubated with or without EXEL-0862 for 48 hours at the indicated concentrations. Viable cells, defined as Annexin-V-FITC–negative cells, were measured by flow cytometry. Data are expressed as percentage of mast-cell survival normalized to results obtained in cells incubated in the absence of drug (control). Each point represents the mean ± SEM values from 3 patients with ISM. *P < .05; **P < .005; Student t test.