CD4 and infection: For this study, we used a chronic LCMV infection model in which CD4 T cells were transiently depleted prior to clone 13 infection to induce lifelong viremia, and we followed the GP33- and GP276-specific CD8 T cell responses for one-year p.i. in the spleen, where a high frequency of Tpex cells had already been observed during chronic LCMV infection.