CD135 is a 130-160 kD type III tyrosine kinase receptor expressed on CD34+ hematopoietic stem cells, myelomonocytic progenitors, primitive B cell progenitors, and thymocytes. CD135 is also expressed on malignant hematopoietic cells including AML, ALL and CML-BC. CD135, also known as FMS-like tyrosine kinase-3, FLT3, STK-1, and Flk-2, is a growth factor receptor that binds the FLT3 ligand to promote the growth and differentiation of primitive hematopoietic cells. The intracytoplasmic domain of CD135 is modified by phosphorylation and has been shown to interact with Grb2, SOCS1, VAV1, and Shc.