T cell immunity induced by a bivalent Salmonella-based CEACAM6 and 4-1BBL vaccines in a rat colorectal cancer model.

The present study investigated the anti-tumor mechanisms of recombinant non-specific cross-reacting antigen (CEACAM6) and 4-1BB ligand (4-1BBL) Salmonella-based vaccines, and the effect that these vaccinations have on memory T cells and T helper (Th) cell polarization. Colon tumors were induced in rats via 1,2-dimethylhydrazine (DMH) injections. Rats were then treated with injections of attenuated Salmonella typhimurium carrying pIRES-CEACAM6, pIRES-4-1BBL or pIRES-CEACAM6-4-1BBL. In total, 4 vaccine injections, one every other week, were administered during the 8 weeks subsequent to the DMH injection. Rats were sacrificed 18 weeks subsequent to the DMH injections, and the colons and spleens were collected for further analysis. Cluster of differentiation (CD) 45RO, interleukin (IL)-4 and IL-17 expression was analyzed in colon tumor tissues, and the expression of interferon (IFN)-γ, CD3+, CD4+, CD8+, CD56+, forkhead/winged-helix transcription factor box P3 (FOXP3+), IL-4 and IL-17 were analyzed in splenic tissues. Compared with the pIRES/SL3261 group, the pIRES-CEACAM6-4-1BBL/SL3261 treatment group had a significantly higher number of CD45RO+ expressing tumor infiltrating lymphocytes and lower expression levels of IL-4 and IL-17. Splenic tissues from the same treatment group exhibited significantly increased expression of IFN-γ, CD3+ and CD8+ and reduced expression levels of Foxp3, IL-4 and IL-7. CD56+ T cell expression was increased in all groups except for the group that received no vaccine. The present study concluded that the combined CEACAM6 and 4-1BBL-attenuated recombinant Salmonella vaccine was able to inhibit the growth of DMH-induced colorectal tumors. This was mediated by generating an anti-tumor immune response, increasing the number of of CD45RO+ memory T cells, decreasing the number of FOXP3+ cells and promoting Th1 polarization.