GP33-tetramer staining data showed a dramatically decreased frequency of tetramer-positive viral-specific CD8 T cells in the Tcf7−/− CD8 T cell (CD45.2) population than that in the WT (CD45.1) population at both day 8 and day 25 post Cl13 infection (Figure 3B), suggesting that TCF1 is intrinsically required for CD8 T cell expansion and survival during LCMV chronic infection. The gene discussed is TCF7; the disease is infection.