Live replicating bacteria expressing heterologous antigens are vaccine candidates that are able to induce complex immune responses. Yersinia pseudotuberculosis employs a type III secretion system for translocation of several virulence factors directly to the cytosol of eukaryotic cells. Mice orally inoculated with an attenuated recombinant Yersinia strain translocating a chimeric Yersinia outer protein E (YopE) molecule reveal high numbers of foreign antigen-specific CD4 and CD8 T cells. Thus, cytosolic display of a single hybrid protein results in concomitant CD4 and CD8 T-cell priming. This "one-size-fits-it-all"-feature of Yersinia-translocated heterologous antigens might be advantageous to mount T-cellular immune responses against complex microbes and tumors.