Carcinoembryonic antigen cell adhesion molecule 1 (CEACAM1) has traditionally been viewed as an adhesion molecule associated with signal transduction pathways in epithelial surfaces that is involved in regulating epithelial cell growth and development. Recent work from this laboratory has revealed a role for CEACAM1 in regulating of T cell responses. The laboratory has found that CEACAM1 is expressed on activated T cells and regulates the activity of T cells in vitro and in vivo. This regulation of T cells by CEACAM1 is consistent with the signalling properties of this molecule and the possession of two immune receptor tyrosine-based inhibitory motifs in the cytoplasmic tail of this molecule. The laboratory is interested in defining the molecular mechanisms underlying co-inhibition of T cells by CEACAM1. This is of central importance to tumor immunity and its therapeutic implications.