Expansion of CD34⁺ human cord blood-derived progenitor cells in the presence of IL-6 or IL-6/soluble IL-6R. Two thousand CD34⁺ cord blood cells containing 684 progenitors were cultured in serum containing suspension culture medium supplemented with the factors indicated. The expansion of hematopoietic progenitor cells was tested after 2 weeks of liquid culture in methylcellulose assays. Adapted and reprinted with permission from Sui et al.54 Copyright 1995 National Academy of Sciences, U.S.A.