In humans, repertoire constriction in the CD8+ memory T cell compartment is characterised by the presence of large numbers of clonally expanded T cells (Blackman and Woodland, 2011), which is thought to be driven by chronic antigenic stimulation, typically due to persistent viral infection, such as with cytomegalovirus (Hadrup et al., 2006, Khan et al., 2002). Here, CD8A is linked to viral infectious disease.