CD44 is a receptor for hyaluronic acid and can also interact with other ligands, such as osteopontin, collagens and matrix metalloproteinases (MMPs). CD44 function is controlled by its posttranslational modifications. One critical modification involves discrete sialofucosylations rendering the selectin-binding glycoform of CD44 called HCELL (for Hematopoietic Cell E-selectin/L-selectin Ligand). The HCELL glycoform was originally discovered on human hematopoietic stem cells and leukemic blasts, and was subsequently identified on cancer cells.