Both in humans and in mouse models, a clonal expansion, mostly of CD8+ T cells, during M. tuberculosis infection arises and, in the specific case of C57BL/6 mice, 30 to 50% of the CD8+ T cells recognise a single epitope upon infection [34–36]; prominent TCR clonal expansions have been associated with more severe tuberculosis cases [37,38]. The gene discussed is CD8A; the disease is infection.