CD133 (prominin 1) is a 5-transmembrane glycoprotein with extracellular N- and intracellular C-terminus. CD133 function remains to be elucidated, but it can be used as a cancer stem cell marker. Its expression pattern in progenitor cells is similar to CD34, i.e. on hematopoietic stem cells in bone marrow, cord blood, neural stem cells, retinoblastoma, or endothelial precursor cells (not mature endothelial cells). It is being used for identification and isolation of hematopoietic stem cells, including isolation for stem cell transplantation. Expression of CD133 correlates with differentiation of human colon cancer cells.