Long-term bone marrow cultures in Diamond-Blackfan anemia reveal a defect of both granulomacrophage and erythroid progenitors

The hematopoietic defect of Diamond-Blackfan anemia (DBA) results in selective failure of erythropoiesis. Thus far, it is not known whether this defect originates from an intrinsic impediment of hematopoietic progenitors to move forward along the erythroid pathway or to the impaired capacity of the bone marrow (BM) microenvironment to support proliferation and differentiation of hematopoietic cells. Reduced longevity of long-term bone marrow cultures, the most physiologic in vitro system to study the interactions of hematopoietic progenitors and hematopoietic microenvironment, is consistent with a defect of an early hematopoietic progenitor in DBA. However, stromal adherent layers from DBA patients generated in a long-term culture system, the in vitro counterpart of BM microenvironment, did not show evidence of any morphologic, phenotypic, or functional abnormality. Our major finding was an impaired capacity of enriched CD34+ BM cell fraction from DBA patients, cultured in the presence of normal BM stromal cells, to proliferate and differentiate along the erythroid pathway. A similar impairment was observed in some DBA patients along the granulomacrophage pathway. Our result points to an intrinsic defect of a hematopoietic progenitor with bilineage potential that is earlier than previously suspected as a relevant pathogenetic mechanism of the disease. The finding of impaired granulopoiesis in some DBA patients underlines the heterogeneity of this rare disorder.