Congenically distinct control (CD45.1+) or Ifnar1-/- (CD45.1.2+, IFNAR1-deficient) CD8+ P14 T cells were labeled with CFSE, mixed at a 1:1 ratio, and adoptively transferred into CD45.2+ recipients prior to infection with LCMV-Cl13 and cells that had undergone their first division (second CFSE peak) were analyzed. The gene discussed is CD8A; the disease is infection.