As well as being highly statistically significant, the size of the effect was striking: in an individual with 2 iKIR-ligand pairs in their genome, after correcting for viral infection and cell phenotype (i.e., for the baseline of Tcm cells in an uninfected individual), their memory CD8+ T cells lived, on average, for 125 days; in contrast, in an individual with 4 iKIR-ligand pairs in their genome, their memory CD8+ T cells lived for 250 days — a doubling in survival. The gene discussed is CD8A; the disease is viral infectious disease.