Despite the many donors who donate blood every year, it is sometimes difficult for some repeatedly transfused patients to find compatible blood. This is especially true for patients (eg sickle cell disease) who have been immunized against various foreign antigens due to previous blood transfusions. The possibility of growing red blood cells to provide compatible blood for these patients has been recognized for decades. Due to technical progress, research into the efficient culture of red blood cells in order to reach quantities corresponding to a bag of blood for transfusion has accelerated in the last few years. These studies mainly focus on the intrinsic maturation program of red blood cell precursor cells (erythroblasts). For the culture of red blood cells we use two different types of sources, namely blood-forming stem cells and reprogrammed stem cells (also called induced pluripotent stem cells (iPSC)). Within humans, erythroblasts develop in an environment with specialized nurturing cells, which included macrophages. How these nurturing cells exactly affect red blood cell production is not sufficiently described. Our culture systems also contain this kind of nurturing cells.

Within this LSBR fellowship project we looked at how the production of cultured red blood cells can be increased, optimized and improved. This has been done from two viewpoints, namely by i) examining the effects of so-called transmitting cells on red blood cell development and ii) reprogramming erythroblasts to iPSC without leaving foreign genetic material in the genome and allowing it to mature to a red blood cell. We have published that special nurturing cells, the macrophages, play an important role in the total production of red blood cells. This happens because these macrophages secrete substances that act on the red blood cell precursor cells, which leads to a better survival of these cells. Furthermore, we have published that these special macrophages in our cultures are very similar to the macrophages in the body that can be found around the erythroblasts and can thus be used as a model system. We have shown that the cultured macrophages have longer interactions with erythroblasts and also take up the nucleus at the end of the differentiation process. This knowledge has led to 10-20 times more yield and dispensation of specific cell purifications, significantly reducing production costs. In the other project we reprogrammed the erythroblasts, which we culture using protocols developed in project I, into iPSC. These iPSC show great resemblance to embryonic stem cells and, depending on the differentiation program, can be induced to differentiate into every functional cell of the body. In this project the erythroblasts have been reprogrammed without leaving a genetic footprint in the genome (episomal). We have described in a few publications that with a small amount of blood from patients with various disorders (1-5ml), iPSC can be made. That this can be realized from a small amount of blood is important due to the fact that not all patients can donate large amounts of material. This research protocol is currently being converted into a good manufacturing practice (GMP) protocol. Furthermore, we have published a protocol how these iPSCs can efficiently be differentiated to red blood cells. This process also depends on nurturing cells and thus refers back to project I. However, the identity of these various nurturing cells important in iPSC differentiation is not known and is currently an active research area within our group. The outcome of the research within this LSBR fellowship has also led to a funded project (NWO-TAS) in which we will transfuse cultured red blood cells in healthy volunteers in a clinical study.