Epithelial cell MUC1 is aberrantly expressed on human epithelial adenocarcinomas where it functions as a regulator of immune responses and an oncogene. Normally expressed at low levels in healthy colonic epithelium, MUC1 was reported to be overexpressed in human inflammatory bowel disease (IBD) and thus may be expected to play an important role in regulating chronic inflammation and its progression to colitis-associated colon cancer. Studies in the immunobiology and pathology of IBD and colitis-associated colon cancer have been done in various mouse models but none could properly address the role of MUC1 due to low homology between the mouse and the human molecule. We report that IL-10−/− mice, a widely accepted mouse model of IBD, crossed to human MUC1-transgenic mice, develop MUC1+ IBD characterized by an earlier age of onset, higher inflammation scores, and a much higher incidence and number of colon cancers compared with IL-10−/− mice.

Myeloid derived suppressor cells (MDSC) are a heterogeneous population of immature myeloid cells that accumulate in circulation of cancer patients and at tumor sites where they suppress anti-tumor immunity. We previously reported that in a colon cancer prevention trial of a MUC1 vaccine tested in individuals at increased risk for colon cancer, those who did not mount immune response to the vaccine had higher pre-vaccination levels of circulating MDSC compared to those who did. We also reported that individuals with pancreatic premalignancy, Intraductal Papillary Mucinous Neoplasm (IPMN), had increased circulating levels of MDSC that inversely correlated with spontaneous antibody responses against the pancreatic tumor associated antigen MUC1, abnormally expressed on IPMN. Accumulation of MDSC in cancer and their immunosuppressive role had been well established but their presence in premalignancy was unexpected. In this study we compared MDSC in premalignancy with those in cancer with the hypothesis that there might be differences in the composition of various MDSC subpopulations and their immunosuppressive functions due to different lengths of exposure to disease and/or different tissue microenvironments. In cohorts of patients with premalignant polyps, colon cancer, premalignant IPMN, and pancreatic cancer, we confirmed higher levels of MDSC in premalignancy compared to healthy controls, higher levels of MDSC in cancer compared to premalignancy, but no difference in their subpopulation composition or immunosuppressive capacity. We show that levels of MDSC in premalignancy correlate negatively in vivo with spontaneous MUC1-specific antibody responses and in vitro with polyclonal T cell proliferation and IFN-γ secretion.

Association of chronic inflammation with an increased risk of cancer is well established, but the contributions of innate versus adaptive immunity are not fully delineated. There has furthermore been little consideration of the role played by chronic inflammation-associated antigens, including cancer antigens, and the possibility of using them as vaccines to lower the cancer risk. We studied the human tumor antigen MUC1 which is abnormally expressed in colon cancers and also in inflammatory bowel disease (IBD) that gives rise to colitis-associated colon cancer (CACC). Using our new mouse model of MUC1 + IBD that progresses to CACC, interleukin-10 knockout mice crossed with MUC1 transgenic mice, we show that vaccination against MUC1 delays IBD and prevents progression to CACC. One mechanism is the induction of MUC1-specific adaptive immunity (anti-MUC1 IgG and anti-MUC1 CTL), which seems to eliminate abnormal MUC1 + cells in IBD colons. The other mechanism is the change in the local and the systemic microenvironments. Compared with IBD in vaccinated mice, IBD in control mice is dominated by larger numbers of neutrophils in the colon and myeloid-derived suppressor cells in the spleen, which can compromise adaptive immunity and facilitate tumor growth. This suggests that the tumor-promoting microenvironment of chronic inflammation can be converted to a tumor-inhibiting environment by increasing adaptive immunity against a disease-associated antigen.

Objectives-Pancreatitis occurs as extraintestinal complication of IBD but the cause is poorly understood. MUC1 is overexpressed in an abnormal, hypoglycosylated form on the colonic epithelium in human IBD where it contributes to inflammation. MUC1 is also expressed on pancreatic ductal epithelia. We tested the possibility that in IBD, MUC1 expression on pancreatic ducts is also abnormal leading to inflammation and pancreatitis.Methods-We used MUC1+/IL-10-/-mice that develop IBD. We imaged abnormal MUC1 expression in these mice by adoptively transferring T cells from T cell receptor transgenic mice specific for abnormal MUC1. Cells were labeled with a novel perfluorocarbon tracer reagent and quantified and visualized in vivo using high-throughput 19 F NMR spectroscopy and MRI.Results-MUC1-specific T cells migrated to the colon in mice with IBD, and also to the pancreas. Immunohistochemistry confirmed increased expression on the pancreatic ducts of the abnormal MUC1 seen in the colon and the presence of cellular infiltrate.Conclusions-Migration of MUC1-specific T cells to the colon and the pancreas in diseased mice suggests that pancreatitis is an extraintestinal site of IBD, characterized by pro-inflammatory abnormal expression of MUC1. Therapies directed against abnormal MUC1 have the potential of targeting the disease in both sites.

Cancer immunotherapy is now a reality. The results are phenomenal but the cost is outrageous. Even if the cost eventually comes down and immunotherapy becomes more broadly available, using the knowledge derived from immunotherapy to apply to immunoprevention would be a good strategy. The most likely approach to cancer immunoprevention is cancer vaccines. To date, cancer vaccines have been tested mostly in the setting of advanced disease. Numerous immunosuppressive mechanisms have been identified in the tumor microenvironment as well as systemically that compromise the ability of cancer patients to respond to the vaccines. Multiple approaches are being tested to improve therapeutic cancer vaccine efficacy, including combinations with other immunotherapies. An alternative approach is to administer the vaccines to individuals without cancer but at high risk for cancer. Data in support of this approach and immunoprevention in general is accumulating and clinical testing has started.

Most tumor-associated antigens (TAA) are self-molecules that are abnormally expressed in cancer cells and become targets of antitumor immune responses. Antibodies and T cells specific for some TAA have been found in healthy individuals and are associated with lowered lifetime risk for developing cancer. Lower risk for cancer has also been associated with a history of febrile viral diseases. We hypothesized that virus infections could lead to transient expression of abnormal forms of self-molecules, some of which are TAA; facilitated by the adjuvant effects of infection and inflammation, these molecules could elicit specific antibodies, T cells and lasting immune memory simultaneously with immunity against viral antigens. Such infection-induced immune memory for TAA would be expected to provide life-long immune surveillance of cancer. Using influenza virus infection in mice as a model system, we tested this hypothesis and demonstrated that influenza-experienced mice control 3LL mouse lung tumor challenge better than infection-naive control mice. Using 2D-Difference Gel Electrophoresis (2D-DIGE) and mass spectrometry, we identified numerous molecules, some of which are known TAA, on the 3LL tumor cells recognized by antibodies elicited by two successive influenza infections. We studied in detail immune responses against GAPDH, Histone H4, HSP90, Malate Dehydrogenase 2 and Annexin A2, all of which were overexpressed in influenza-infected lungs and in tumor cells. Lastly, we show that immune responses generated through vaccination against peptides derived from these antigens correlated with improved tumor control.

Many important aspects of cancer biology, such as cancer initiation, progression, and metastasis, have been studied in animal models, mostly mice. As long as cancer was considered primarily a genetic disease, the study of transplantable mouse tumors, or even human tumor xenografts in immunocompromised mice, appeared to suffice. Many important genetic events that lead to transformation and in vivo tumor growth were elucidated. However, many even more important factors that determine whether or not the genetic potential of a tumor cell will be realized, such as the host response to the tumor and the tumor microenvironment that influences this response over a long period of time of tumor development, remained untested and unappreciated. This is slowly changing with the advent of molecular techniques that have spurred efforts to engineer better mouse models of human tumors. In this review, we show results of our efforts to combine a genetic mouse model of spontaneous human adenocarcinomas based on a Kras mutation, with an important human molecule MUC1 that is abnormally expressed on human adenocarcinomas, promoting oncogenesis, proinflammatory tumor microenvironment, and immunosurveillance.

Premalignant lesions for many cancers have been identified, and efforts are currently directed toward identification of antigens expressed on these lesions that would provide suitable targets for vaccines for cancer prevention. Intraductal papillary mucinous neoplasms (IPMNs) are premalignant pancreatic cysts of which a subset has the potential to progress to cancer. Currently, there are no validated predictive markers for progression to malignancy. We hypothesized that the presence or absence of immune surveillance of these lesions would be one such factor. Here we show that the tumor antigen MUC1, which is abnormally expressed on pancreatic cancer and is a target for cancer immunosurveillance, is also abnormally expressed on premalignant IPMN. We show that some IPMN patients make MUC1-specific IgG. Moreover, we show evidence of CD4 and CD8 T cell infiltration into IPMN areas of high dysplasia suggesting an ongoing immune response within the lesions. We also found, however, increased levels of circulating myeloid-derived suppressor cells (MDSCs) and regulatory T cells (Tregs) in some IPMN patients as well as evidence of T cell exhaustion. Further studies correlating immunosurveillance or immunosuppression with IPMN progression to malignancy will help define the immune response as a biomarker of risk, leading potentially to a vaccine to boost spontaneous immunity and prevent progression to cancer.