Low oxygen enhances sickle and normal erythropoiesis and fetal hemoglobin synthesis in vitro.

Erythropoiesis is increased in cultures of human blood progenitors when oxygen tension is reduced from 20% (room air) to 5% (low oxygen, closer to physiological bone marrow levels). The effects of low oxygen on gamma-globin synthesis and colony growth in methyl cellulose cultures of blood mononuclear cells from normal individuals and patients with sickle cell diseases were examined. Low oxygen increased colony numbers by 1.5- to 2-fold and erythropoietin sensitivity by almost 2-fold. The interval required for maximal colony growth in cultures from patients with sickle cell disease (sickle colonies) was reduced from 17 days in 20% oxygen to 13 days in 5% oxygen. Relative synthesis of gamma-globin was examined by labeling with 3H-leucine and electrophoresis on Triton acid urea polyacrylamide gels. The % gamma was 1.7-fold higher in normal and 1.4-fold higher in sickle cultures on day 13 in low oxygen. On day 16 the expected temporal decline was not seen in low oxygen, and the % gamma was 2-fold higher in normal and 1.8-fold higher in the sickle studies. Hemin increased colony growth and gamma-globin synthesis in normal cultures in air, and the effects of hemin and low oxygen were additive. In sickle cultures, hemin and low oxygen had additive effects on colony growth, but only low oxygen increased gamma-globin synthesis. Interleukin-3 increased colony numbers on day 13, primarily by acceleration of peak growth. Interleukin-3 also increased gamma-globin synthesis in low oxygen in normal but not sickle cultures. Thus, low oxygen increases in vitro sensitivity to erythropoietin, colony numbers, and relative gamma-globin synthesis in normal and sickle cultures.

Effect of stem cell factor on in vitro erythropoiesis in patients with bone marrow failure syndromes.

Stem cell factor (SCF) enhances normal hematopoiesis. We examined its effect in vitro on bone marrow and blood progenitors from patients with inherited bone marrow failure syndromes, including 17 patients each with Diamond-Blackfan anemia (DBA) and Fanconi's anemia (FA), 3 with dyskeratosis congenita (DC), and 1 each with amegakaryocytic thrombocytopenia (amega) and transient erythroblastopenia of childhood (TEC). Mononuclear cells were cultured with erythropoietin (Ep) alone or combined with SCF or other factors. SCF increased the growth of erythroid progenitors in cultures from 50% of normal controls, 90% of DBA, 70% of FA, 30% of DC, and the amega and TEC patients; normal numbers were reached in 25% of DBA studies. Improved in vitro erythropoiesis with SCF in all types of inherited marrow failure syndromes does not suggest a common defect involving kit or SCF, but implies that SCF may be helpful in the treatment of hematopoietic defects of varied etiologies.

Sickle and thalassemic erythroid progenitor cells are different from normal.

Blood erythroid progenitors (BFU-E) from patients with sickle and thalassemic syndromes were compared with those from normal individuals. The day of maximal colony formation in methyl cellulose was slightly later in the cultures from the patients with hemoglobinopathies than in the normal cultures. The number of colonies/100,000 mononuclear cells was similar in all cultures on day 13, but was higher in the hemoglobinopathy cultures on the day of maximal growth. The number of BFU-E/mL of blood was significantly higher than normal at all times in both sickle cell anemia and thalassemia. The proportional synthesis of gamma globin was twice normal in all sickle cultures, and 4 times normal in those from beta+-thalassemia. Hemin and interleukin-3 increased the numbers of erythroid colonies in all cultures, but did not consistently alter the globin synthesis patterns. Each progenitor population has a unique pattern in terms of time course, number of BFU-E, and level of gamma globin synthesis. These features indicate distinct types of BFU-E, or differences in accessory cells, or both, which distinguish blood-borne erythropoiesis in normals and those with hemoglobinopathies.

Erythropoiesis in Fanconi's anemia.

Fanconi's anemia (FA) is an autosomal recessive condition in which greater than 90% of the homozygotes develop aplastic anemia. To determine the relation between erythroid progenitors and clinical status, blood and marrow mononuclear cells were cultured in methyl cellulose with erythropoietin, plus other hematopoietic growth factors, and growth in normal oxygen (20%) was compared with growth in low, physiologic oxygen (5%). Peripheral blood cultures were performed from 24 patients, and marrows from six. Patients were classified into six clinical groups. Group 1: Severe aplasia, transfused; one patient; no erythroid progenitors. Group 2: Severe, transfused, androgen unresponsive; one patient; no blood burst-forming units-erythroid (BFU-E). Group 3: Androgen responsive; eight patients, with decreased blood BFU-E. Group 4: Aplastic, about to start treatment; two patients; below normal numbers of colony-forming units-erythroid (CFU-E) and BFU-E. Group 5: Stable, with mild anemia, and/or thrombocytopenia, and/or macrocytosis; seven patients; with below normal numbers of blood BFU-E. Group 6: Hematologically normal; five patients; blood BFU-E low normal to normal. One marrow had normal numbers of CFU-E and BFU-E. Incubation in 5% oxygen doubled CFU-E and BFU-E only in the patients with close to normal or normal growth in 20% oxygen. Hemin and interleukin-3 increased growth slightly in those cultures where there was some growth with erythropoietin alone. Our data show that there is a correlation between current clinical status and in vitro erythropoiesis. Cultures of erythroid progenitors may also be useful predictors of hematologic prognosis in FA, although our follow-up period is too short to prove this hypothesis.