The developmental requirements for immunological memory, a central feature of adaptive immune responses, is largely obscure. We show that as naive CD8 T cells undergo homeostasis-driven proliferation in lymphopenic mice in the absence of overt antigenic stimulation, they progressively acquire phenotypic and functional characteristics of antigen-induced memory CD8 T cells. Thus, the homeostasis-induced memory CD8 T cells express typical memory cell markers, lyse target cells directly in vitro and in vivo, respond to lower doses of antigen than naive cells, and secrete interferon γ faster upon restimulation. Like antigen-induced memory T cell differentiation, the homeostasis-driven process requires T cell proliferation and, initially, the presence of appropriate restricting major histocompatibility complexes, but it differs by occurring without effector cell formation and without requiring interleukin 2 or costimulation via CD28. These findings define repetitive cell division plus T cell receptor ligation as the basic requirements for naive to memory T cell differentiation.

It is generally agreed that most colon cancers develop from adenomatous polyps, and it is this fact on which screening strategies are based. Although there is overwhelming evidence to link intrinsic genetic lesions with the formation of these preneoplastic lesions, recent data suggest that the tumor stromal environment also plays an essential role in this disease. In particular, it has been suggested that CD34 ؉ immature myeloid precursor cells are required for tumor development and invasion. Here we have used mice conditional for the stabilization of ␤-catenin or defective for the adenomatous polyposis coli (APC) gene to reinvestigated the identity and importance of tumor-infiltrating hematopoietic cells in polyposis. We show that, from the onset, polyps are infiltrated with proinflammatory mast cells (MC) and their precursors. Depletion of MC either pharmacologically or through the generation of chimeric mice with genetic lesions in MC development leads to a profound remission of existing polyps. Our data suggest that MC are an essential hematopoietic component for preneoplastic polyp development and are a novel target for therapeutic intervention.cancer ͉ inflammation ͉ polyposis ͉ TNF␣

Inflammation associated with bacterial infections is a risk factor for cancers in humans, yet its role in breast cancer remains poorly understood. We have previously shown that innate immune inflammatory response against intestinal bacteria is sufficient to induce colon cancer. Here we report that infecting Rag2-deficient C57BL/6 Apc Min/+ mice with an intestinal bacterial pathogen, Helicobacter hepaticus, significantly promotes mammary carcinoma in females and enhances intestinal adenoma multiplicity by a tumor necrosis factor A (TNFA)-dependent mechanism. The mammary and intestinal tumor development as well as the increase in proinflammatory mediators is suppressed by adoptive transfer of interleukin 10-competent CD4 + CD45RB lo CD25 + regulatory (T R ) cells. Furthermore, prior exposure of donor mice to H. hepaticus significantly enhances antitumor potency of their T R cells. Interestingly, these microbially experienced T R cells suppress tumorigenesis more effectively in recipient mice irrespective of their tumor etiology. These data suggest that infections with enteric pathogens enhance T R -cell potency and protect against epithelial cancers later in life, potentially explaining paradoxical increases in cancer risk in developed countries having more stringent hygiene practices. The possibility that dysregulated gut microbial infections in humans may lead to cancer in anatomically distant organs, such as breast, highlights the need for novel immune-based strategies in cancer prevention and treatment. (Cancer Res 2006; 66(15): 7395-400)

Recombinase-activating gene-2-deficient (Rag2 ؊/؊ ) mice lacking functional lymphocytes provide a useful model of chronic inflammatory bowel disease-emulating events in human colon cancer. Infection of Rag2 ؊/؊ mice with Helicobacter hepaticus led to accumulation of macrophages and neutrophils in the colon, a process temporally related to up-regulation of tissue inducible nitric oxide synthase (iNOS) expression at the site of infection and increased nitric oxide (NO) production, as evidenced by urinary excretion of nitrate. Progressive development of increasingly severe inflammation, hyperplasia, dysplasia, and cancer accompanied these changes. Concurrent administration of an iNOS inhibitor prevented NO production and abrogated epithelial pathology and inhibited the onset of cancer. The presence of Gr-1 ؉ neutrophils and elevated tumor necrosis factor-␣ (TNF-␣) expression in colon were required for increased iNOS expression and cancer, whereas interleukin-10 (IL-10) down-regulated TNF-␣ and iNOS expression and suppressed cancer. Anti-inflammatory CD4 ؉ regulatory lymphocytes also down-regulated iNOS and reduced cancer formation. Collectively, these results confirm essential roles for inflammation, increased TNF-␣ expression, and elevated NO production in colon carcinogenesis.colorectal cancer ͉ IBD ͉ innate immunity C hronic Helicobacter pylori infection in humans leads to gastritis and has been established as a causative agent for human gastric cancer (1). Inflammatory bowel diseases (IBDs), such as Crohn's disease and ulcerative colitis, also increase risk for colon cancer (2, 3). Generation of nitric oxide (NO) by inducible NO synthase (iNOS) is a central feature of chronic inflammatory diseases in the gastrointestinal tract (4-9), but precise mechanistic roles for NO in colon cancer development remain undefined.Colon cancer patients exhibit evidence of nitrosative and oxidative stresses that increase cancer risk (10), resulting from mutagenic reactive oxygen and nitrogen species derived from NO generated by immune cells (6,(11)(12)(13)(14)(15). Roles for chronic bacterial infection in IBD and colon cancer have been identified recently in recombinase-activating gene-2-deficient mice (Rag2 Ϫ/Ϫ ), which completely lack functional lymphocytes (16-18). We have exploited this mouse model of chronic IBDassociated cancer for studies of the role of NO and its products because it emulates naturally occurring inflammatory events in humans (16,19,20).Rag2 Ϫ/Ϫ mice have been used to assess functions of lymphocytes by adoptive transfer. Populations of CD4 ϩ T cells with low or high expression of CD45RB (17,21, 22) or CD25 (16,18,23,24) prevent or accelerate colitis in these animals. In wild-type (wt) mice, protection against inflammatory pathology induced by bacterial infection has been attributed to interleukin-10 (IL-10) and IL-10-dependent functions of CD4 ϩ cells (18,20,25,26). Collectively, this evidence forms the rationale for the hypothesis that NO overproduction comprises a linkage between Helicobacter hepaticus-i...

No abstract

Activities of CD4+ regulatory (TREG) cells restore immune homeostasis during chronic inflammatory disorders. Roles for TREG cells in inflammation-associated cancers, however, are paradoxical. It is widely believed that TREG function in cancer mainly to suppress protective anticancer responses. However, we demonstrate here that TREG cells also function to reduce cancer risk throughout the body by efficiently downregulating inflammation arising from the gastrointestinal (GI) tract. Building on a “hygiene hypothesis” model in which GI infections lead to changes in TREG that reduce immune-mediated diseases, here we show that gut bacteria-triggered TREG may function to inhibit cancer even in extraintestinal sites. Ability of bacteria-stimulated TREG to suppress cancer depends on interleukin (IL)-10, which serves to maintain immune homeostasis within bowel and support a protective antiinflammatory TREG phenotype. However, under proinflammatory conditions, TREG may fail to provide antiinflammatory protection and instead contribute to a T helper (Th)-17-driven procarcinogenic process; a cancer state that is reversible by downregulation of inflammation. Consequently, hygienic individuals with a weakened IL-10 and TREG-mediated inhibitory loop are highly susceptible to the carcinogenic consequences of elevated IL-6 and IL-17 and show more frequent inflammation-associated cancers. Taken together, these data unify seemingly divergent disease processes such as autoimmunity and cancer and help explain the paradox of TREG and inflammation in cancer. Enhancing protective TREG functions may promote healthful longevity and significantly reduce risk of cancer.

Chronic inflammation of mucosal surfaces renders them increasingly susceptible to epithelial cancers both in humans and mice. We have previously shown that anti-inflammatory CD4(+)CD45RB(lo)CD25(+) regulatory (Treg or T(R)) lymphocytes down-regulate inflammation and block development of bacteria-triggered colitis and colorectal cancer (CRC) in 129/SvEv Rag2-/- mice. Interestingly, T(R) cells collected from Interleukin (IL)-10-deficient cell donors not only failed to suppress carcinogenesis but instead promoted invasive mucinous colonic carcinoma with a strong gender bias expressing in male mice. We found we show that peritoneal invasion in this model is dependent on pleiotropic cytokine IL-6. Mucinous carcinoma arose rapidly and consistently after treatment with IL10-/- T(R) cells, which were found to express Foxp3+ and localize throughout tumor tissue. Carcinogenesis was rapidly reversible with transfer of wild type IL10-competent T(R) cells. Likewise, treatment with IL10-Ig fusion protein was sufficient to revert the lesions histologically, and restore inflammatory cytokine and oncogene expression to base line levels. These studies indicate an essential role for IL 6 in this CRC phenotype. Furthermore, immune-competent T(R) cells were important not only for preventing pathology but also for constructive remodeling of bowel following tumorigenic microbial insults. These data provide insights into etiopathogenesis of inflammation-associated epithelial invasion and maintenance of epithelial homeostasis.

Cancers of breast and bowel are increasingly frequent in humans. Chronic inflammation is known to be a risk factor for these malignancies, yet cellular and molecular mechanisms linking inflammation and carcinogenesis remain poorly understood. Here, we apply a widely used T-cell transfer paradigm, involving adoptive transfer of proinflammatory CD4 + CD45RB hi (T E ) cells to induce inflammatory bowel disease (IBD) in mice, to investigate roles of inflammation on carcinogenesis in the ApcMin/+ mouse model of intestinal polyposis. We find that transfer of T E cells significantly increases adenoma multiplicity and features of malignancy in recipient Apc Min/+ mice. Surprisingly, we find that female Apc Min/+ recipients of T E cells also rapidly develop mammary tumors. Both intestinal polyposis and mammary adenocarcinoma are abolished by cotransfer of anti-inflammatory CD4 + CD45RB lo regulatory lymphocytes or by neutralization of key proinflammatory cytokine tumor necrosis factor-A. Lastly, down-regulation of cyclooxygenase-2 and c-Myc expression is observed coincident with tumor regression. These findings define a novel mouse model of inflammationdriven mammary carcinoma and suggest that epithelial carcinogenesis can be mitigated by anti-inflammatory cells and cytokines known to regulate IBD in humans and mice.