CD133 expression in circulating hematopoietic progenitor cells

Background: Circulating hematopoietic progenitors (HPCs) are involved in inflammatory diseases such as atherosclerosis, the immune response to cancer, and disorders of the hematopoietic system. HPC characterization by flow cytometry typically utilizes CD34 in combination with other cell surface markers to identify cell populations that give rise to specific hematopoietic lineages. CD133, also known as prominin-1, is a cell surface protein found in HPCs that has a similar but not interchangeable expression pattern with CD34 for characterization of HPC populations. Our goal was to determine the distribution of CD133 expression within HPC sub-types amongst circulating CD34+ cells. Methods: The quantity of different HPC populations within the CD34+ CD133+ and CD34+ CD133− fractions of venous blood obtained from healthy human subjects was measured using multicolor flow cytometry. Results: The majority of circulating CD34+ cells is CD133−. CD133+ CD34+ cells express low levels of CD38, contain cell populations bearing cell surface markers of hematopoietic stem cells, multipotent progenitors, and multilymphoid progenitors, and are largely devoid of CD38 expressing lineage specified progenitors. These findings clarify the composition of circulating CD133+ CD34+ cell types in adult human subjects.