CD133 (also known as Prominin-1 or AC133) has been identified as an important cell surface marker. Cells expressing the CD133 marker are commonly referred to as primitive hematopoietic stem and progenitor cells (HSCs and HPCs). While cells expressing the CD133 marker are usually undifferentiated embryonic stem cell lines, this cell type is usually harvested from bone marrow and cord blood but can be also found in multiple locations including the liver, kidney, prostate, muscle, and neural tissue.

CD133+ cells have stemness properties such as drug-resistance, self-renewal, differentiation ability, high proliferation and they are able also to form tumors in xenografts. These cells with CD133+ are more resistant to radiation and standard chemotherapy than CD133- cells.