Radiosensitive HSPC Subsets Define Early Hematopoietic Injury and Enable H-ARS Therapeutic Screening.

Early hematopoietic injury is a critical determinant of hematopoietic acute radiation syndrome (H-ARS), yet biologically relevant cellular endpoints and optimal evaluation windows for therapeutic screening remain poorly defined. Here, we combined high-dimensional mass cytometry (CyTOF) and flow cytometry to characterize early hematopoietic stem and progenitor cell (HSPC) remodeling following 6.5 Gy total-body irradiation. Radiation exposure induced rapid bone marrow injury, with substantial cellular loss and reduced viability occurring within hours after irradiation. CyTOF analysis revealed that radiation-induced injury was characterized by selective remodeling rather than uniform depletion of the HSPC compartment. While long-term hematopoietic stem cells (LT-HSCs) were relatively preserved, short-term HSCs (ST-HSCs), multipotent progenitors (MPPs), and megakaryocyte-erythroid progenitors (MEPs) exhibited marked reductions during the early phase after irradiation. Importantly, surviving cells retained partial differentiation capacity during this period, indicating that the early post-irradiation phase represents a biologically informative window for therapeutic evaluation. These radiosensitive populations were subsequently validated using a simplified flow cytometry platform and remained detectable under short-term in vitro culture conditions. Collectively, our findings identify key radiosensitive HSPC subsets and establish an early hematopoietic injury framework that integrates optimal evaluation timing with practical cellular endpoints for H-ARS therapeutic screening and radiomitigator development.