Jerry S. Powell

Recombinant human erythropoietin: Purification and analysis of carbohydrate linkage

Erythropoietin was purified to homogeneity from the culture medium of a baby hamster kidney cell line stably transfected with a human erythropoietin gene. A three-step procedure was used, which included affinity chromatography, ion-exchange chromatography, and reverse-phase chromatography. Purity of the protein was confirmed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and amino-terminal sequence analysis. Overall recovery was 35%. The biological activity of purified recombinant erythropoietin was similar to that of the native hormone in vitro. The purified recombinant hormone contained N-linked carbohydrate at residues 24, 38, and 83, and and O-linked carbohydrate at residue 126.

Platelet-derived growth factor enhances in vitro erythropoiesis via stimulation of mesenchymal cells.

The growth of erythroid colonies (from erythroid colony-forming cells) and erythroid bursts (from burst-forming cells [BFU-E]) is enhanced in the presence of serum as compared with plasma. A significant proportion of the enhanced growth is due to the platelet release product, platelet-derived growth factor (PDGF). Colony growth in cultures of whole marrow cells in platelet-poor plasma-derived serum (PDS) and erythropoietin was enhanced in a dose-dependent fashion by increasing concentrations of purified human PDGF with optimal enhancement at 12.5 ng/ml. However, no effect of platelet-release products or PDGF was observed on nonadherent human marrow cells or peripheral blood BFU-E, suggesting that an accessory cell population was required for the effect of PDGF on hematopoietic progenitors. In a two-layer culture system, pure populations of fibroblasts or smooth muscle cells, known to be present in the marrow microenvironment, restored the response of nonadherent marrow cells in the overlayer to PDGF and also conferred responsiveness to peripheral blood BFU-E. Endothelial cells in the two-layer culture system and macrophages, in contrast, lacked the ability to restore the enhancing effect of PDGF. Because other platelet-release mitogenic products are also found in serum, a monospecific anti-PDGF IgG preparation was added to cultures grown in platelet rich plasma-derived serum. Only partial reduction in colony and burst growth was seen, suggesting that other platelet-release products were acting in this system. These results demonstrate that PDGF enhancement of human hematopoietic progenitor cell growth requires mesenchymal cells, and provide an example and mechanism by which growth factors may influence hematopoietic progenitors via cells of the marrow microenvironment.

Pure red cell aplasia: lymphocyte inhibition of erythropoiesis

The pathogenesis of pure red cell aplasia (PRCA) was studied in a patient who had no evidence of malignancy. In marrow culture, no erythroid colonies (from late erythroid progenitors [CFU‐E]) but normal numbers of well‐haemoglobinized erythroid bursts (from early erythroid progenitors [BFU‐E]) were found, indicating that BFU‐E existed in the patient but that their subsequent in vivo differentiation was inhibited. Autologous coculture studies suggested that inhibition was mediated by the patients ER+ lymphocytes. After remission was induced with cyclophosphamide, autologous ER + cells no longer suppressed in vitro erythropoiesis. However, cryopreserved ER + cells, obtained with anaemia, suppressed BFU‐E growth from remission marrow. An expanded population of large granular lymphocytes (LGL) with ER +, Fcγ+. T3 +, T8 +, HNK‐1 +, Ia —, M1 — phenotype and no functional natural killer (NK) cell activity was noted during PRCA that reverted to normal with remission. For this patient, both in vivo and in vitro evidence demonstrates a cellular inhibition of erythropoiesis at the level of differentiation between BFU‐E and CFU‐E.