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.