ERVW-1 and infection: To analyse the localization of Env-specific CD4+ T cells, we collected lymph nodes, spleens and peripheral blood mononuclear cells (PBMC) from MCMV.env immunized or unvaccinated mice 14 days after MCMV.env immunization or 21 days after FV challenge infection and subjected the cells to MHC II tetramer staining to detect Env123-141-specific CD4+ T cells.