Romiplostim drives HS(P)Cs into active cell cycling and sensitizes them to CyBu chemotherapy. (A) The experimental setup to assess cell cycle activity upon RPL/PBS stimulation; BM is analyzed after 7 days of RPL/PBS application. (B) The cell cycle status of phenotypically defined HSPCs (LSK⁺) and LT-HSCs (LSK⁺FLT-3⁻CD34⁻CD150⁺CD48⁻) with or without RPL/PBS stimulation (n = 5 per group). (C) Representative flow cytometry plots from panel B. (D) The experimental setup to assess the impact of RPL on phenotypically defined HSPCs and LT-HSCs upon simultaneous treatment with CyBu30 chemotherapy; BM is analyzed 14 days after the start of RPL/PBS application equivalent to 7 days after the last dose of chemotherapy and RPL/PBS (n = 5 per group). The number of HSPCs (E) and the number of LT-HSCs (F) per 1 femur 1 week after treatment with RPL/PBS and CyBu30. (G) Representative flow cytometry plots from (E) and (F). BM, bone marrow; ctrl, control; DAPI, 4′,6-diamidino-2-phenylindole; PBS, phosphate-buffered saline.