These observations were confirmed by antigen-elicited skin responses showing corresponding results (Fig. 3C ). Mice were injected into the left hind footpads with 50 ml of somatic soluble Lm EGD-e antigen (60 ng/ml) at day 9 post-infection. Twentyfour hours later, thickness of the left and right footpads of individual mice were measured. Footpads of mice pre-immunized with L.inn::vgc showed reduced thickness than those of mice preimmunized with the wild type Lm. The wild type L.inn strain did not induce a DTH response in the footpads of these mice. Moreover, antigen-induced CD4+ T cell-derived IFN-gamma production of spleen cells was measured as an indication for a proinflammatory T cell response. Spleen cells were isolated at day 9 post-infection and stimulated in vitro with the released soluble antigen of L. monocytogenes EGD-e (100 ng). Spleen cells from mice immunized with L.inn::vgc produced significantly lower levels of IFN-gamma when compared to spleen cells from mice immunized with wild type Lm. The wild type L.inn strain failed to prime T cells for the production of IFN-gamma (Fig. S1 , supplementary information).