The T cell surface glycoprotein CD6 was first identified in 1981 by Kamoun et al. who for that purpose used a monoclonal antibody 12.1, raised against a human secondary mixed leukocyte reaction, that labeled all normal T cells and many T- and B-cell leukemias and lymphomas (Kamoun et al. 1981). The CD6 gene was later cloned from HPB-ALL cells by the group of Brian Seed using his pioneering cloning strategy, and revealed sequences with high homology with the cysteine-rich domain of the type I scavenger receptor of macrophages (Aruffo et al. 1991). Nevertheless, the obtained cDNA was incomplete such that the sequence corresponding to the cytoplasmic tail only coded for 44 amino acids. Based on comparisons with the mouse CD6 gene, Jane Parnes and colleagues finally published the currently known sequence, which includes a cytoplasmic tail of 244 amino acids (Robinson et al. 1995).
CD6 is highly...