The role of macrophages in human erythropoiesis

Despite the many donors who donate blood, for some patients it is difficult to find compatible blood. In addition, a low but prevalent risk of bloodborne pathogens is associated with donor blood. Especially patients in need of chronic transfusions are at risk of developing alloantigens to unmatched blood groups and exposure to bloodborne pathogens. Therefore, research to in vitro cultured, specific blood group-expressing erythrocytes is essential to forfeit these donor blood-associated risks. Erythropoiesis to erythrocytes can, to some extent, be recapitulated without any feeder cells, however, bone marrow erythropoiesis is occurring on specific macrophages. The research in this thesis aimed to optimize erythroid cell cultures by focusing on the supporting macrophages. We showed that CD14+ cells isolated from PBMC increase HSC survival early during erythroid culture by the secretion of specific factors. This eventually resulted in increased erythroid yield. With this knowledge, a new three-stage culture method was designed to produce large amounts of cultured red blood cells (cRBC) from PBMC under GMP-conditions. This allows clinical trials to test the functionality of transfused cRBC and investigate the usability of cRBC as a transfusion product. To study the interaction between macrophages and erythroid cells, we described a culture method using glucocorticoids to differentiate CD14+ monocytes towards erythroid-supporting macrophages. These in vitro glucocorticoid-macrophages shared phenotypical and morphological features with their in vivo counterparts. In addition, their proteomic landscape was comparable to human fetal liver and adult bone marrow macrophages, thus providing a convenient human model system