Varada P. Rao

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 gamma 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 beta-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.

Roles for host immune response in carcinogenesis are not well defined. Recent studies have shown that microbially driven inflammation can lead to colon cancer and that prior transfer of regulatory lymphocytes expressing CD4 and CD25 prevents the innate inflammatory events that lead to colon cancer in mice. To further examine the ability of regulatory lymphocytes to inhibit carcinogenesis, 129/SvEv Rag-2-deficient mice were inoculated by gastric gavage with Helicobacter hepaticus, an enteric bacterial pathogen of mice. Mice were then treated at 1, 3, or 12 months after infection with adoptive transfer of CD4(+)CD45RB(lo)CD25(+)-regulatory cells. Mice dosed with regulatory cells at 4 or 12 weeks after H. hepaticus infection had reduced severity of inflammatory bowel disease and significantly lower risk of colon cancer during the 8 month observation period, compared with infected mice that had not received cells. This suggested that regulatory cells were able to interrupt the ongoing innate immune events in the stepwise progression to cancer. Transfer of regulatory cells into chronically infected mice with established cancer reduced severity of colitis, epithelial dysplasia, and cancer, but did not eliminate all tumors. Regulatory cells lacking anti-inflammatory cytokine interleukin (IL)-10 were unable to inhibit inflammatory bowel disease, dysplasia, or cancer, showing that IL-10 was required for the protective effects of lymphocytes in this setting. Taken together, the data suggest that IL-10-mediated suppression of host innate inflammatory response was pivotal in interrupting carcinogenesis. Regulatory lymphocytes and cytokines may have implications for novel therapies for colon cancer in humans.

Colorectal cancer in humans results from sequential genetic changes in intestinal epithelia commencing with inactivation of the APC tumor suppressor gene. Roles for host immunity in epithelial tumorigenesis are poorly understood. It has been previously shown that CD4+CD25+ lymphocytes inhibit colitis-associated epithelial tumors in Rag-deficient mice. Here we show that addition of CD4+CD25+ lymphocytes in ApcMin/+ mice reduces multiplicity of epithelial adenomas. Interleukin-10 was required in regulatory cells for therapeutic effect. Recipients of regulatory cells showed increased apoptosis and down-regulation of cyclooxygenase-2 within tumors coincident with tumor regression. These data suggest a role for regulatory lymphocytes in epithelial homeostasis in the ApcMin/+ mouse model of intestinal polyposis. Similarities with cancer of the breast, prostate, lung, and other sites raise the possibility of broader roles for regulatory lymphocytes in prevention and treatment of epithelial cancers in humans.

Abstract 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 ApcMin/+ mice with an intestinal bacterial pathogen, Helicobacter hepaticus, significantly promotes mammary carcinoma in females and enhances intestinal adenoma multiplicity by a tumor necrosis factor α (TNFα)–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+CD45RBloCD25+ regulatory (TR) cells. Furthermore, prior exposure of donor mice to H. hepaticus significantly enhances antitumor potency of their TR cells. Interestingly, these microbially experienced TR cells suppress tumorigenesis more effectively in recipient mice irrespective of their tumor etiology. These data suggest that infections with enteric pathogens enhance TR-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)