M. M. Shapiro1,2, B. Nandi1,2, G. Gonzalez1, R. Prabhala1,2,3, Q. Huang1,4, N. C. Munshi1,2,3, N. Y. Frank1,2,4, J. S. Gold1,2,3 4Brigham And Women’s Hospital,Boston, MA, USA 1VA Boston Healthcare System,West Roxbury, MA, USA 2Harvard School Of Medicine,Brookline, MA, USA 3Dana Farber Cancer Insititute,Boston, MA, USA
Introduction: Interest in the use of the cytokine IL-21 as an immunotherapeutic agent grew out of the initial success with interferon gamma and IL-2 in the treatment of melanoma. IL-21 functions by increasing proliferation and survival of B and T cells. It also increases granzyme B-mediated cytotoxicity of NK and T cells. Due to these properties, IL-21 has been investigated in the treatment of both renal cell carcinoma and melanoma. The role of IL-21 in spontaneous intestinal carcinogenesis has not been fully explored.
Methods: Mice with a targeted knockout of IL-21 (KO) were bred with APCMIN/+ (MIN) mice. MIN mice spontaneously develop numerous intestinal adenomas. Wild-type C57/Bl6 mice (WT) were used as a control. Mouse small intestines were harvested at 15 weeks. Polyps were measured and counted under a dissecting microscope. Mouse ileum was also either preserved for paraffin embedding and immunohistochemical staining or snap frozen for cDNA preparation and q-RT-PCR.
Results: Polyp-bearing ileum from MIN mice had a five-fold increase in IL-21 expression by q-RT-PCR as compared to the non-polyp bearing ileum of WT mice (p=0.03). MIN mice lacking IL-21 had increased intestinal polyp number and tumor load as compared to MIN mice with functional IL-21 (55 vs. 40 polyps, p=0.007; Figure panel A; tumor load 88 vs. 68, p=0.02). The differences in polyp number and tumor load were significant in the jejunum and ileum but not in the duodenum (duodenum 5.4 vs. 4.1 polyps, p=0.3 and tumor load 14 vs. 7.8, p=0.5; jejunum 21 vs. 14, p=0.02 and 31 vs. 22, p=0.04; ileum 29 vs. 22, p=0.01 and 44 vs. 36, p=0.03). KO-MIN mice had fewer CD3+ cells (T cells) and B220+ cells (B cells) in the polyp-bearing ileum than MIN mice (50 vs. 78 cells/0.07mm2, p<0.001 for T cells; 13 vs. 18, p<0.001 for B cells). Similarly, the number of granzyme B+ cells was much lower in polyp-bearing ileum of KO-MIN mice when compared to that of MIN mice (20 vs. 41 cells/0.07 mm2, p<0.001; Figure panel B).
Conclusion: Adenoma development is associated with upregulation of IL-21 in the intestine in a mouse model of spontaneous intestinal neoplasia. Deficiency of IL-21 leads to accelerated tumor development in this model. Loss of IL-21 is also associated with a decrease in B and T cell populations in the polyp-prone intestine as well as a concomitant decrease in granzyme B-releasing cells. These data support the hypothesis that IL-21 is involved in mediating spontaneous anti-tumor immunity controlling adenoma development. The use of IL-21 for the treatment of colorectal cancer warrants further investigation.
