Abstract
Because of a lack of platelet supply and a U.S. Food and Drug Administration-approved platelet growth
factor, megakaryocytes have emerged as an effective substitute for alleviating thrombocytopenia. Here, we report the development of an efficient two-stage culture system that is free of stroma, animal
components, and genetic manipulations for the production of functional megakaryocytes from
hematopoietic stem cells. Safety and functional studies were performed in murine and nonhuman
primate models. One human cryopreserved cord blood CD34+ cell could be induced ex vivo to produce up to 1.0 x 104 megakaryocytes that included CD41a+ and CD42b+ cells at 82.4% + 6.1% and 73.3% + 8.5% (mean + SD), respectively, yielding approximately 650-fold higher cell numbers than
reported previously. Induced human megakaryocytic cells were capable of engrafting and producing
functional platelets in the murine xenotransplantation model. In the nonhuman primate model, transplantation of primate megakaryocytic progenitors increased platelet count nadir and enhanced
hemostatic function with no adverse effects. In addition, primate platelets were released in vivo as
early as 3 hours after transplantation with autologous or allogeneic mature megakaryocytes and
lasted for more than 48 hours. These results strongly suggest that large-scale induction of functional
megakaryocytic cells is applicable for treating thrombocytopenic blood diseases in the clinic.
