Ex vivo expansion of hematopoietic progenitor cells for clinical use.

The development of efficient stem and progenitor cell selection methods in combination with the development of hematopoietic growth factors facilitated the development of ex vivo expansion techniques. Currently, this novel domain of cellular therapy aims to generate stem and progenitor cells, as well as more differentiated post-progenitor cells and antigen-presenting dendritic cells. The feasibility of generating and transplanting hematopoietic progenitor cells ex vivo (using various cytokine combinations) has been successfully shown preclinically as well as clinically. Furthermore, cytokines (eg, Flt-3-ligand; thrombopoietin) have been identified that play important roles with regard to amplification of undifferentiated early hematopoietic cells. The use of lineage-specific cytokines such as granulocyte colony-stimulating factor and thrombopoietin facilitated the generation of large numbers of myeloid and megakaryocytic post-progenitor cells. The clinical usefulness of such ex vivo generated cells, however, has not yet been convincingly shown. Last, ex vivo expansion techniques can be used to generate large numbers of antigen-presenting dendritic cells from CD34+ peripheral blood progenitor cells that might be ideally used for immunotherapeutic approaches.