The latter include human autoimmune diseases, such as celiac disease21 and multiple sclerosis72, infections, such as human immunodeficiency virus8, and tumors, such as colorectal cancer73, glioblastoma74, melanoma75 and head and neck tumors76–79 often in association with markers indicative of dysfunctional T cells such as TIM-3; this is consistent with mouse studies showing CEACAM1 is involved in and necessary for the development of T cell tolerance8. Here, CEACAM1 is linked to infection.