Regression of established tumors in mice mediated by the oral administration of a recombinant Listeria monocytogenes vaccine.

We have shown previously that Listeria monocytogenes, a gram-positive, facultative intracellular bacterium, is a potent vector for targeting tumor-specific antigens to the immune system. After parenteral administration, we observed protection against both renal and colorectal mouse tumors and regression of established renal tumors. In the present study, we have exploited the fact that the normal route of infection of this organism is through the gut. We show that an L. monocytogenes recombinant that expresses a model tumor antigen is an effective cancer immunotherapeutic agent when delivered orally in that it causes regression of established, macroscopic mouse renal and colorectal tumors expressing the same antigen.