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.