Myeloid differentiation of human cord blood CD34+ cells during ex vivo expansion using thrombopoietin, flt3‐ligand and/or granulocyte‐colony stimulating factor

We investigated the phenotypic changes of human umbilical cord blood (CB) CD34+ cells during ex vivo expansion using thrombopoietin (TPO), flt3‐ligand (FL), and/or granulocyte‐colony stimulating factor (G‐CSF). During ex vivo expansion of CD34+ cells isolated from human CB for up to 5 weeks, surface expression of molecules on the cultured cells including CD64 (FcγRI), CD32 (FcγRII), CD16 (FcγRIII), CD11b (MAC‐1) and CD18 (β2‐integrin) was analysed by flow cytometry along with simultaneous measurement of apoptosis by 7‐aminoactinomycin D staining method. CD64, CD32 and/or CD18 expressing cells appeared in the cultures both with and without the addition of G‐CSF until the tenth day. However, without G‐CSF, CD16+ fractions did not appear and CD11b+ fractions were not maintained. With G‐CSF, the CD16+ or CD11b+ fractions appeared only from the second week. These results suggest that G‐CSF is necessary for the late stage of myeloid maturation during which CD16 and CD11b are expressed.