Figure 2. Pathophysiology and treatment of aplastic anemia. The left panel illustrates induction of disease by an inciting event (for example, viral infection or chemical exposure) followed by an aberrant immune response that leads to destruction of hematopoietic stem cells and progenitor cells. When destruction is sufficiently advanced, pancytopenia and clinical disease result. Hematopoietic stem-cell transplantation both replaces the missing hematopoietic cells and is potently immunosuppressive. Immunosuppression reduces or eliminates the aberrant immune process. Late complications of transplantation include graft failure or relapse (presumably caused by resurgent autoimmune attack) and, more frequently, graft-versus-host disease (GVHD) and infection. Immunosuppressive therapies based on antithymocyte globulin can often partially or fully improve blood cell counts and stem-cell recovery, but patients are susceptible to recurrence of pancytopenia or the development of other hematologic diseases (such as myelodysplasia).

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