CD133 is a positive marker for a distinct class of primitive human cord blood-derived CD34-negative hematopoietic stem cells

Abstract

The identification of human CD34-negative (CD34 -) hematopoietic stem cells (HSCs) provides a new concept for the hierarchy in the human HSC compartment. Previous studies demonstrated that CD34 - severe combined immunodeficiency (SCID)-repopulating cells (SRCs) are a distinct class of primitive HSCs in comparison to the well-characterized CD34 + CD38 - SRCs. However, the purification level of rare CD34 - SRCs in 18 lineage marker-negative (Lin -) CD34 - cells (1/1000) is still very low compared with that of CD34 + CD38 - SRCs (1/40). As in the mouse, it will be necessary to identify useful positive markers for a high degree of purification of rare human CD34 - SRCs. Using 18Lin - CD34 - cells, we analyzed the expression of candidate positive markers by flow cytometric analysis. We finally identified CD133 as a reliable positive marker of human CB-derived CD34 - SRCs and succeeded in highly purifying primitive human CD34 - HSCs. The limiting dilution analysis demonstrated that the incidence of CD34 - SRCs in 18Lin - CD34 - CD133 + cells was 1/142, which is the highest level of purification of these unique CD34 - HSCs to date. Furthermore, CD133 expression clearly segregated the SRC activities of 18Lin - CD34 - cells, as well as 18Lin - CD34 + cells, in their positive fractions, indicating its functional significance as a common cell surface maker to isolate effectively both CD34 + and CD34 - SRCs. © 2014 Macmillan Publishers Limited.