CD133 is a novel 5-transmembrane cell surface antigen with a molecular weight of 117 kDa. CD133/2 (AC141) antibodies recognize epitope 2 of the human CD133 antigen (CD133/2). In the hematopoietic system, CD133 expression is restricted to a subset of CD34bright
stem and progenitor cells in human fetal liver, bone marrow, cord blood and peripheral blood. Additionally, CD133 is expressed by a small portion of CD34–
cells in these tissues. The CD34+
cell population, which includes CD34+
cells, was shown to be capable of repopulating NOD/SCID mice. Recently, CD133 has also been found to be expressed on endothelial precursor cells and fetal neural stem cells as well as on developing epithelium. The putative murine homologue, prominin, which is expressed on neuroepithelial and epithelial mouse cells, was identified. In contrast to the other CD133 clones, the clone AC141 shows cross-reactivity with the intracellular protein cytokeratin 18.