Culture system for extensive production of CD19+IgM+ cells by human cord blood CD34+ progenitors

We established a co-culture system with a monolayer of the murine bone marrow (BM) stroma cell line, MS-5, in which human cord blood CD34(+) cells differentiated to CD19(+) cells. The addition of stem cell factor (SCF) and granulocyte colony-stimulating factor (G-CSF) highly enhanced the production of CD19(+) cells. The expansion of the cell numbers was over 10(3)-fold. Furthermore, a significant proportion (<45%) of the cells expressed surface IgM (slgM) after 5 weeks of co-culture. CD34(+)CD19(-) cells also showed a similar development of CD19(+) cells and CD19(+)slgM(+) cells. Filter separation of MS-5 cells and CD34(+) cells did not inhibit the growth of CD19(+) cells. However, when further purified CD34(+)CD19(-)CD13(-) CD33(-) cells were cultured in the presence of MS-5 cells with or without a separation filter, CD19(+) cells did not appear in the non-contact setting. This result suggested that the highly purified CD34(+)CD19(-)CD13(-)CD33(-) progenitors require the cell-cell contact for the development of CD19(+) cells, whereas other CD34(+) fractions contain progenitors that do not require the contact. This co-culture system should be useful for the study of early human B-lymphopoiesis.