An intrinsic progenitor defect in Diamond-Blackfan anaemia

To determine whether the erythropoietin (epo) insensitivity of erythroid progenitor differentiation in congenital pure red cell aplasia or Diamond-Blackfan anaemia is intrinsic to the progenitor itself or is due to defective accessory cell function or active suppression, progenitors from normals and two patients (one steroid resistant and one spontaneously remitting), separated from all known accessory cells using sequential negative selection techniques (adherence, E-rosetting, and direct and indirect immune-panning), were studied. Initially, we evaluated three patients with DBA using unfractionated bone marrow mononuclear cells. Progenitors from two steroid non-responsive patients showed insensitivity to crude epo (c-epo) while one steroid responsive patient demonstrated normal in vitro sensitivity to c-epo. When recombinant epo (r-epo) was used in place of c-epo, the two steroid non-responders continued to demonstrate in vitro progenitor epo insensitivity. However, sensitivity of progenitors from the steroid responder, which was normal in the presence of c-epo, became abnormal when recombinant epo (r-epo) was substituted. Thus, using unfractionated bone marrow, the abnormal response to epo of progenitors from some patients with DBA appears to be obscured by stimulating factors termed erythroid burst-promoting activity (BPA) which are present in c-epo. Using fractionated highly enriched progenitors, from normals and a steroid responsive patient a final 3-10-fold enrichment of progenitors was achieved, but no such enrichment was seen when marrow from a steroid resistant patient was cultured. The epo sensitivities of normal and of patient erythroid progenitors were similar. However, at sub-optimal epo concentrations in both patients CFU-E responsiveness to crude BPA was abnormal compared to the three controls. We conclude from these studies that in DBA: (a) the failure of erythropoiesis is due to an intrinsic progenitor defect; (b) this defect involves progenitor insensitivity to factors in addition to erythropoietin: and (c) there exists a spectrum of disease reflected in the degree of the in vitro abnormality observed.