Acquired aplastic anemia is a bone marrow failure syndrome characterized by hypocellular bone marrow and peripheral blood pancytopenia. Frequent clinical responses to calcineurin inhibition and anti-thymocyte globulin strongly suggest critical roles for hematopoietic stem/progenitor cell-reactive T cell clones in disease pathophysiology; however, their exact contribution and antigen specificities remain unclear. We determined differentiation states and targets of dominant T cell clones …