We next determined whether CD4 and CD8 T cells from vaccinated mice can, alone or in combination, clear MNV infection from mucosal sites. We have previously shown that MNV infected RAG1-/-mice have high levels of viral RNA present in multiple tissues up to 90 days post-infection [27] . We therefore determined MNV viral titers in RAG1-/-mice. By 42 days postinfection, all RAG1-/-mice had consistent, high levels of MNV in both duodenum/jejunum and distal ileum ( Figure 6A and 6B) , as well as several other tissues (data not shown). These data confirmed that mice lacking adaptive immunity fail to clear MNV infection [27] .