TPO and myelofibrosis: We combined our murine model of TPO overexpression‐induced MPN/myelofibrosis with a knockout of S100a9 in HSPCs, and transplanted lethally irradiated WT recipients with either WT (here referred to as S100a9+/+) or S100a9−/− ckit+ HSPCs overexpressing TPO or its EV control (Figure S4A).