Activated Leukocyte Cell Adhesion Molecule （ALCAM）, also known as Cluster of Differentiation 166 （CD166）, is a type I transmembrane cell adhesion molecule that belongs to the immunoglobulin （Ig） superfamily. It serves as a ligand for CD6 and is expressed on T lymphocytes. The interaction between ALCAM and CD6 is crucial for T cell development, regulation, and for the binding of T- and B-cells to activated leukocytes.
ALCAM is expressed in a variety of tissues but is typically restricted to cell subsets involved in dynamic growth and/or migration. This includes processes such as neural development, branching organ development, hematopoiesis, immune response, and tumor progression. High expression levels of ALCAM on melanoma cell lines seem to promote metastasis, whereas in breast cancer, it has been associated with anti-metastatic activity.
ALCAM may also influence the expression or adhesion of the neuronal adhesion molecule NCAM-L1, as observed in both the developing retina and invasive melanoma.