The availability of persistently infected RAG1-/-mice allowed us to determine the role of CD4 and CD8 T cells in clearance of MNV infection using adoptive transfer of splenocytes from MNV immune WT mice into persistently infected RAG1-/-mice. Transfer of immune, but not non-immune, splenocytes signifi- To define which cells were required for MNV clearance, CD4 or CD8 T cells were depleted from splenocytes transferred into RAG1-/-recipients. Anti-T cell antibodies effectively depleted the appropriate T cell populations, as measured six days post-transfer by flow cytometry (Figure 7A ). Depletion of either CD4 or CD8 T cells individually led to a significant increase in MNV titers in duodenum/jejunum compared to control depletion ( Figure 7B , CD4 depletion p = 0.0042; CD8 depletion p = 0.0002). Depletion of both CD4 and CD8 T cells from transferred immune splenocytes caused a significant additional increase in MNV titers when compared to either CD4 depletion alone (p = 0.02) or CD8 depletion alone (p = 0.03). In the distal ileum, depletion of either CD4 T cells (p = 0.0003) or CD8 T cells (p,0.0001) led to a significant increase in MNV titers ( Figure 7C ). These data demonstrated that both immune CD4 and CD8 T cells were necessary for clearance of persistent MNV infection from the intestine.