Combination of a poxvirus-based vaccine with a cyclooxygenase-2 inhibitor (celecoxib) elicits antitumor immunity and long-term survival in CEA.Tg/MIN mice

The present study was designed to determine whether: (a) chronic administration of dietary celecoxib (Celebrex), a potent nonsteroidal antiinflammatory drug, which targets the cyclooxygenase-2 (COX-2) enzyme, negatively impacts host immunity; and (b) celecoxib can be coupled with a poxvirus-based vaccine to impact tumor burden in a murine tumor model of spontaneous adenomatous polyposis coli. Naive mice fed the celecoxib-supplemented diets developed eosinophilia with lowered plasma prostaglandin E₂ levels and reduced COX-2 mRNA expression levels in their splenic T cells. Responses of splenic T, B, and natural killer cells to broad-based and antigen-specific stimuli were, for the most part, unchanged in those mice as well as COX-2 knockout mice; exceptions included: (a) reduced IFN-γ production by concanavalin A- or antigen-stimulated T cells; and (b) heightened lipopolysaccharide response of naive B cells from mice fed a diet supplemented with 1000 ppm of celecoxib. When transgenic mice that express the human carcinoembryonic antigen (CEA) gene (CEA transgenic) were bred with mice bearing a mutation in the Apc^Δ850 gene (multiple intestinal neoplasia mice), the progeny (CEA transgenic/multiple intestinal neoplasia) spontaneously develop multiple intestinal neoplasms that overexpress CEA and COX-2. Beginning at 30 days of age, the administration of a diversified prime/boost recombinant CEA-poxvirus-based vaccine regimen or celecoxib (1000 ppm)-supplemented diet reduced the number of intestinal neoplasms by 54% and 65%, respectively. Combining the CEA-based vaccine with the celecoxib-supplemented diet reduced tumor burden by 95% and significantly improved overall long-term survival. Both tumor reduction and improved overall survival were achieved without any evidence of autoimmunity directed at CEA-expressing or other normal tissues. Celecoxib is prescribed for the treatment of familial adenomatous polyposis in humans, and the CEA-based vaccines have been well tolerated and capable of eliciting anti-CEA host immune responses in early clinical studies. The results suggest that the administration of a recombinant poxvirus-based vaccine is compatible with celecoxib, and this combined chemoimmuno-based approach might lead to an additive therapeutic antitumor benefit not only in patients diagnosed with familial adenomatous polyposis but, perhaps, in other preventive settings in which COX-2 overexpression is associated with progression from premalignancy to neoplasia.