Background: Despite the recent understanding that colon cancer is immunogenic and the level of tumor infiltrating T-cells identified is associated with disease outcome; few studies evaluate the immunomodulation of the disease. Cancer vaccines targeting colon cancer are limited and focus on only a few antigens such as CEA and MUC-1. Overexpression of self-proteins that are involved in cancer proliferation has been shown to be a mechanism by which self-proteins become immunogenic. We questioned whether overexpressed proteins that are found in high incidence in colon cancer and associated with poor prognosis could be colon cancer antigens. We further questioned whether vaccines targeting these antigens could prevent the development of colon cancer in biologically relevant mouse models.
Methods: Four proteins overexpressed in colon cancer and associated with prognosis were identified. Indirect ELISA was used to evaluate antibody immunity against these proteins in 50 colon cancer patients and 50 age-matched controls. Selected MHC-II binding peptides reactivity was assessed using IFN-gamma ELISPOT. Peptides that were highly homologous between mouse and man and tested for immunogenicity in mice. Mice treated with AOM were vaccinated starting at 8 weeks, 4 times with CFA/IFA as an adjuvant and monitored for the development of intestinal polys or cancers. Tumor sections were stained for CD8 positive cells by immunohistochemistry. CD8 T-cell quantitation was based on the mean of three 40X fields per section.
Results: CDC25B, COX2, RCAS1, and FASCIN are immunogenic in colon cancer patients. Serum IgG responses for all four antigens were significantly elevated in colorectal cancer patient sera when compared to donor controls (CDC25B p=0.0016, COX-2 p=0.001, FASCIN1 and RCAS1 p<0.0001). Adenomas in APC Min− mice were significantly inhibited after vaccination with CDC25B (39%, p=0.01), COX-2 (43%, p=0.02), and FASCIN (38%, p=0.03) but not after immunization with RCAS1 (28%, p=0.096). Tumor growth could be inhibited in mice treated with AOM after vaccination with CDC25B (78%, p=0.0002) and COX-2 (83%, p<0.0001). Vaccination with CDC25B and COX-2 significantly increased tumor infiltrating CD8 T-cells.
Discussion: Colon cancer is immunogenic and overexpressed proteins involved in important biologic pathways can serve as vaccine immunogens in colorectal cancer. Active immunization against colon cancer antigens can prevent the formation of disease and inhibit tumor growth in both transgenic mouse models as well as models where cancer is chemically induced. Vaccination was associated with no adverse events in the mice and could significantly increase tumor infiltrating Type I T-cells. These data lay the foundation for the development of multi-antigen vaccines for the prevention of colon cancer as well as disease relapse.