Sequencing of an individual’s TCRβ repertoire can be used to reveal past infections such as CMV, Epstein-Barr virus and influenza (26), while also autoimmune diseases such as type 1 diabetes (46), ankylosing spondylitis (47, 48) and psoriasis (49) have been suggested to associate with disease-specific TCR signatures. Here, TRBC1 is linked to type 1 diabetes mellitus.