Impairment of hematopoietic stem cell niches in patients with aplastic anemia.

Aplastic anemia (AA) is a serious hematological disorder characterized by pancytopenia and defective bone marrow (BM) microenvironment. Previous investigations have demonstrated that there is a defect of angiogenesis in the BM of patients with AA. However, whether abnormalities of the BM microenvironment, particularly the overall specialization of niches, which have been classified into osteoblastic, vascular, and perivascular niches, are involved in the pathogenesis of AA is unknown. In the present study, 46 patients with AA and 15 controls were selected. The cellular elements of the BM microenvironment, including endosteal, vascular, and perivascular cells, were analyzed by immunohistochemical staining in situ. Patients with AA showed markedly fewer endosteal cells [0.33 vs 3.67 per high-power field (hpf); P < 0.05], vascular cells (8.00 vs 12.67 per hpf; P < 0.05), and perivascular cells (7.17 vs 10.67 per hpf; P < 0.05) compared with controls. These data indicate that AA is associated with impaired hematopoietic stem cell niches.