CD20 

CD20 is a 33-37 kDa non-glycosylated protein expressed specifically on the surface of normal and malignant B lymphocytes, and belongs to the MS4A (membrane-spanning 4-domain family A) protein family. CD20 is a general B-cell marker expressed by the majority of B cells starting from late pre-B lymphocytes (it is not expressed by pro-B lymphocytes), and its expression is lost in terminally differentiated plasmablasts and plasma cells. Early experiments suggested that it was important in the regulation of human B-cell activation, proliferation, and Ca²⁺ transport. However, CD20-deficient mice appeared normal. Hence, the exact biological function of CD20 and its physiological ligand remain to be fully defined.240 Regardless of the uncertainty in the biological role of this antigen, it is a good target for cancer immunotherapy.