PLATELETS GENERATED IN-VITRO FROM PROPLATELET-DISPLAYING HUMAN MEGAKARYOCYTES ARE FUNCTIONAL

An in vitro culture system demonstrating the transitions from megakary ocyte progenitors to functional platelets is described. CD34-selected cells from normal human peripheral blood are cultured under conditions that promote megakaryocyte formation. After 8 to 11 days, enriched po pulations of mature megakaryocytes are replated under conditions that favor the development of proplatelets. Proplatelets express the platel et-specific proteins, glycoproteins Ib and IIb (GPIb and GPIIb), and f ibrinogen and also contain microtubule coils equal in size to those fo und in plasma-derived platelets. In addition, proplatelets have ultras tructural features in common with plasma-derived platelets. Platelet-s ized particles from the proplatelet culture supernatants are examined. Ultrastructurally, these particles are identical to plasma-derived pl atelets. Functionally, these culture-derived platelets aggregate in re sponse to both thrombin and adenosine diphosphate (ADP) plus fibrinoge n. This aggregation is specifically inhibited by the addition of a fun ction-blocking anti GPIIbIIIa antibody. Culture-derived platelets stim ulated with agonists also express the activation-dependent antigens P- selectin and functional fibrinogen receptor. This is the first descrip tion of an in vitro culture system that sequentially demonstrates mega karyocyte growth, development, and platelet production. (C) 1995 by Th e American Society of Hematology.