We also analyzed the frequency of Env-specific CD4+ T cells by MHC II tetramer staining three days after FV challenge infection, and found a significant induction of Env-specific CD4+ T cells in mice immunized with Ad.Env without pre-treatment as well as in mice that had received antibody-cleared plasma or a low dose of the neutralizing antibody 9C12 before Ad.Env immunization, and the frequency was only slightly reduced in mice that had received adenovirus-immune plasma or a high dose of the adenovirus-neutralizing antibody (Fig. 5e). This evidence concerns the gene ERVW-1 and infection.