To address the contribution of effector memory CD8+ T cells in mediating long-lasting immunity after re-infection with the wild type Lm, the expression level of the cell surface adhesion molecule CD62L was quantified. Expression of CD62L is down regulated on the surface of cytotoxic CD8 + T-cells when developed to protective memory T cells [21] . Two months after the primary infection, the number of CD8 + CD62L lo lymphocytes was approximately identical in all groups of primarily infected mice. This number increased dramatically upon re-infection with the wild type Lm (2610 3 ) in mice pre-immunized with Lm as well as with L.inn::vgc while pre-immunization with L.inn was not able to induce CD62L down-regulation seen in the other groups (Fig. 5 ). In addition we have monitored the expression of CD44 on CD8 + T-cells. CD44 is expressed at high levels on memory but not in naïve T-cells [26] . In mice that were primarily infected with Lm and L.inn::vgc, the expression of CD44 was upregulated on CD8 + T-cells 5 days post-challenge infection with the wild type Lm (2610 3 ) while primary infection with L.inn did not lead to a significant change in CD44 expression pattern (Fig. S3 ).