Cells expressing JAK2V617F undergo apoptosis when treated with a selective JAK inhibitor. Ba/F3-EpoR-JAK2V617F cells were treated with various concentrations of INCB018424 for approximately 24 hours and analyzed for hallmarks of apoptosis by annexin V/propidium iodide staining (A) or mitochondrial membrane depolarization (B). Cells treated with INCB018424 were stained with a combination of fluorescein isothiocyanate-annexin V and propidium iodide and analyzed using flow cytometry to determine the percentages of viable (bottom left), early apoptotic (bottom right), and late apoptotic or dead (top right) cells. The effects of JAK inhibition on mitochondrial membrane potential were determined by flow cytometry using JC-1 as a molecular probe (B). Total and relative percentages of cells with depolarized mitochondria are shown.