Isolation and Culture of Megakaryocyte Precursors

Megakaryocyte (MK) precursor cells correspond to a spectrum of cells extending from an early progenitor to the promegakaryoblast, a 2N cell that switches from a mitotic to an endomitotic process ( 1 ). The MK progenitors express the CD34 ⁺ antigen and are either CD38 ^– or CD38 ⁺ , depending upon their maturation stage. The most primitive progenitors (BFU-MK and the mixed erythro-MK progenitors) are negative for CD38, while the others are CD38 positive ( 2 ). Other differentiation markers, such as HLA-DR or AC133 ( 3 , 4 ), have also been used to study MK differentiation. In the adult, CD41 (platelet GPIIb) appears during differentiation and can be used to select a subset of MK progenitors that essentially correspond to the more mature MK progenitors and promegakaryoblasts. In contrast, CD41 is more widely expresssed on neonatal hematopoietic progenitors. CD42 has a slightly later expression than CD41 (5), although after the beginning of CD42 synthesis, expression levels of CD41 and CD42 are well correlated. Thus, MK differentiation may proceed by different stages: CD34 ⁺ CD38 ^– CD41 ^– , CD34 ⁺ CD38 ⁺ CD41 ^– , CD34 ⁺ CD38 ⁺ CD41 ⁺ CD42 ^– , CD34 ⁺ CD41 ⁺ CD4 ²⁺ , CD34 ^– CD41 ⁺ CD4 ²⁺ , CD34 ^– CD41 ⁺⁺⁺ CD4 ²⁺⁺⁺ (Fig. 1 ).

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