Concise review: stem cell-based approaches to red blood cell production for transfusion

Abstract

Blood transfusion is a common procedure in modern medicine, and it is practiced throughout the world; however, many countries report a less than sufficient blood supply. Even in developed countries where the supply is currently adequate, projected demographics predict an insufficient supply as early as 2050. The blood supply is also strained during occasional widespread disasters and crises. Transfusion of blood components such as red blood cells (RBCs), platelets, or neutrophils is increasingly used from the same blood unit for multiple purposes and to reduce alloimmune responses. Even for RBCs and platelets lacking nuclei and many antigenic cell-surface molecules, alloimmunity could occur, especially in patients with chronic transfusion requirements. Once alloimmunization occurs, such patients require RBCs from donors with a different blood group antigen combination, making it a challenge to find donors after every successive episode of alloimmunization. Alternative blood substitutes such as synthetic oxygen carriers have so far proven unsuccessful. In this review, we focus on current research and technologies that permit RBC production ex vivo from hematopoietic stem cells, pluripotent stem cells, and immortalized erythroid precursors.

Keywords: Erythropoiesis; Hematopoietic stem cells; Pluripotent stem cells; Red blood cell transfusion; Reticulocytes.

Figure 1.

A current model of erythropoiesis. Adult bone marrow HSPCs undergo proliferation and differentiation cycles and, through the proerythroblast and subsequent intermediates, give rise to the enucleate reticulocytes. These reticulocytes enter the peripheral bloodstream, lose additional plasma membrane and cellular organelles, and achieve the distinctive biconcave disc shape of erythrocytes, or RBCs. Abbreviations: BFU-E, burst-forming unit-erythroid; CFU-E, colony-forming unit-erythroid; HSC, hematopoietic stem cell; HSPC, hematopoietic stem and progenitor cell; RBC, red blood cell.

Figure 2.

Summary of current protocols for in vitro RBC generation. The figure provides a brief summary of all factors used for RBC generation by various published protocols. Hematopoietic stem and progenitor cells are expanded and driven to the erythroid lineage in the first step. The second stage involves further expansion of the erythroblast precursor stages and may involve further differentiation down the erythroid lineage. The final step is the maturation phase, in which all cells are driven toward the reticulocyte/erythrocyte (RBC) stage. The various supplementary and growth factors and coculture requirements are shown for each of the three steps. Factors common for all three steps are shown in the lower bottom corner. In the only instance in which IGF-I was used, cells did not mature (enucleate) in vitro. Hydrocortisone/dexamethasone are glucocorticoid receptor agonists. Mifepristone is a glucocorticoid receptor antagonist. Abbreviations: EPO, erythropoietin; hMSC, human mesenchymal stromal cell; IGF-I, insulin-like growth factor I; IGF-II, insulin-like growth factor II; IL, interleukin; MAP: d-mannitol, adenine, and disodium hydrogen phosphate dodecahydrate; mMS-5, murine marrow stromal cell line MS-5; mOP9, murine marrow stromal cell line OP9; RBC, red blood cell; SCF, stem cell factor.

Figure 3.

Approaches to ex vivo red blood cell generation. Approach 1 involves isolation of HSPCs from umbilical cord blood, whereas approach 2 involves density separation of adult peripheral blood cells to obtain the mononuclear cell fraction. The HSPCs can be isolated from this fraction, or the fraction can be reprogrammed to form induced pluripotent stem cells (iPSCs), forming approach 3. Approach 3, reprogramming to iPSCs, can also use fibroblast skin cells obtained from a donor. These iPSCs can then be differentiated to HSPCs. Approach 4 is differentiating hESCs to HSPCs. HSPCs so obtained can be differentiated further to an immature erythroblast stage and then matured further to reticulocytes. Approach 5 uses transdifferentiation of fibroblasts to immature erythroblasts. Immature erythroblasts can also be immortalized, which forms approach 6. Abbreviations: hiPSC, human induced pluripotent stem cell; HSC, hematopoietic stem cell; HSPC, hematopoietic stem and progenitor cell; hESC, human embryonic stem cell.