CD135 is a cytokine receptor expressed on the surface of hematopoietic progenitor cells.Cluster of differentiation (CD) molecules are markers on the cell surface, as recognized by specific sets of antibodies, used to identify the cell type, stage of differentiation and activity of a cell.

CD135 is an important cell surface marker used to identify certain types of hematopoietic (blood) progenitors in the bone marrow. Specifically, multipotent progenitors (MPP) and common lymphoid progenitors (CLP) expresse high surface levels of CD135. This marker is therefore used to differentiate hematopoietic stem cells (HSC), which are CD135 negative, from MPPs, which are CD135 positive.