In Vitro Production of Erythrocytes

Abstract SCI-39

The generation of red blood cells (RBCs) in vitro using biotechnologies could represent an interesting alternative to classical transfusion products, in that it would combine adequate supplies with the specific production of blood products of a particular phenotype and the reduction of infection risks. This presentation will review how it is now possible to obtain in vitro complete maturation of the erythroid line to the stage of enucleation, starting from hematopoietic stem cells (HSCs) from peripheral blood, bone marrow or umbilical cord blood, or embryonic stem cells or adult pluripotent stem cells (induced pluripotent stem cells, iPSCs). This presentation will discuss how the functionality of cultured human RBCs (cRBCs) is settled in terms of deformability, hemoglobin maturation, oxygen carrying capacity, enzyme content, and terminal maturation from the reticulocyte stage to mature RBC after infusion into the NOD/SCID mouse model. The clinical feasibility of this concept has recently been demonstrated by reporting that cRBCs generated in vitro from peripheral HSCs under GMP conditions encounter in vivo the conditions required for their maturation and that they persist in the circulation for several weeks in humans. These data have established the proof of principle for transfusion of in vitro-generated RBCs and the pathway toward new developments in transfusion medicine. The most proliferative source of stem cells for generating cRBCs is cord blood, but it is limited in terms of HSCs and is dependent on donations. Pluripotent stem cell technology represents a potentially unlimited source of RBCs and opens the door to the development of a new generation of allogeneic transfusion products. Because iPSCs can be selected for a phenotype of interest, they are obviously the best candidate for organizing complementary sources of RBCs for transfusion. It is established that only three human iPSC clones would have been sufficient to match more than 99 percent of the patients in need of RBC transfusions. As a whole, a very limited number of RBC clones would provide for the needs of most alloimmunized patients and those with a rare blood group. Generating cRBCs from iPSCs has been done but needs to be optimized to lead to a clinical application in blood transfusion. Several crucial points remain to be resolved, notably, the choice of the initial cell type, the method of reprogramming (i.e., to ensure the safety of the iPSCs and to ensure their clinical grade), the optimization of the erythrocyte differentiation, and the definition of GMP conditions for industrial production. Assuming that in vitro large-scale cultured RBC production efficiently operates in the near future, this presentation will highlight the potential applications for alloimmunized patients and those with a rare blood group.