A Small CEACAM5 Peptide Restores the Protective Function of CD8+ Regulatory T Cells in Crohn’s Disease

Intestinal epithelial cells (IECs) play a pivotal role in controlling immune responses by activation of suppressive CD8+ T regulatory (Treg) cells.1,2 Indeed, we have shown that at homeostasis, IECs interact with CD8+ T cells through a complex formed by CEACAM5 and CD1d on IECs and CD8α and T-cell receptor (TCR) on CD8+ T cells.2 CEACAM5 interacts with CD8α through its N-domain, and it is the only CEACAM family member that interacts with CD1d through its B3-domain.1 This unique set of interactions facilitates antigen presentation by CD1d to T cells, allowing the subsequent activation of CD8+ Treg cells, which possess a potent function in suppressing effector T cell responses and hence are essential to prevent autoimmune disorders.