CD4 and infection: Of note, protection was critically dependent on the M2e-peptide as no protection was observed in mice immunized with the CTA1-DD adjuvant vector alone (Fig. 2d).5 The distribution of M2e-specific T cells among all CD4 T cells in the lung post-infection was two-fold higher in FTY720-treated (22%) as compared to untreated i.n immunized mice (11%) (Fig. 1e).