ALCAM/CD166 is a member of the immunoglobulin gene superfamily belonging to a subgroup with five extracellular immunoglobulin-like domains(VVC2C2C2), which includes MCAM/CD146/MUC18 and B-CAM/Lutheran.

These molecules are involved in the development and maintenance of tissue architecture, neurogenesis, hematopoiesis, immune responses and tumor progression. ALCAM/CD166 mediates cell-cell clustering through homophilic (ALCAM-ALCAM) and heterophilic (ALCAM-CD6) interactions. Its pattern of expression in human tissues and cells is broad and includes epithelia, neurons, lymphoid and myeloid cells, hematopoietic and mesenchymal stem cells. The relevance of the engagement of the heterophilic pair CD166-CD6 for optimal activation of T cells has been recently demonstrated.