Peripheral blood hematopoietic progenitor cells in beta‐thalassemia major

Colony assays in methylcellulose (semisolid medium) of erythroid precursors and granulocyte‐macrophage precursors from the peripheral blood of 34 patients with β‐thalassemia major and 31 age‐matched normal controls were studied. In patients homozygous for β‐thalassemia, a significant increase of circulating erythroid progenitor cells to 3–5 times of normal controls was observed. Furthermore, the number of circulating colony forming units‐granulocyte‐macrophage (CFU‐GM) and colony forming units‐mixed (CFU‐Mixed) also increased significantly. In these subjects, there was a linear relationship between the number of burst forming units‐erythroid (BFU‐E) and CFU‐GM. The serum level of erythropoietin (EPO) was also significantly higher than that of normal controls (p < 0.05). The increased hematopoiesis, indicated by an increased number of circulating hematopoietic progenitor cells and an elevated serum level of EPO, suggests that the physiologic regulation of erythropoiesis still operated in patients with β‐thalassemia major.