New definition and methods for isolation of the earliest peripheral blood-derived hematopoietic stem cells.

Abstract

Peripheral blood contains transplantable pluripotent hematopoietic progenitor cells, which are defined by the expression of certain surface antigens, such as CD34, and the absence of lineage-specific markers (lin-). Here we describe CD34- DR- adherent growing hematopoietic progenitor precursors which were separated and isolated from peripheral blood by interleukin 6(IL-6)-mediated plastic adherence. These peripheral blood mononuclear cells attach to the plastic surface of tissue culture flasks in the presence of human recombinant IL-6 and assume fibroblast-like morphology. These adherent cells are CD34- and HLA-DR-, and respond to various growth factors with the expression of surface antigens, changes in morphology and the expression of cell cycle-controlling kinases. Stem cell factor induces differentiation of the CD34- DR- adherent cells to become nonadherent and to differentiate into CD34+, and eventually HLA-DR+ cells, and produce colony-forming units (CFU) in semi-solid agar. While IL-6 conveys adherence of these cells, the addition of stem cell factor induces differentiation into nonadherent cells. Our observations suggest the possibility of isolating a true hematopoietic stem cell before the level of CD34 and HLA-DR expression.