In this study, we found that reinfection with MuPyV was more efficiently controlled in CD4 T cell-sufficient than -deficient mice when CD4 T cells were systemically depleted at the time of naïve virus-specific CD8 T cell priming; however, in MuPyVinfected mice where CD4 T cell depletion was delayed, no difference in viral control was seen on i.c. reinfection (Fig 8) .