The role of regulatory T cells (Tregs) in human colon cancer (CC) remains controversial: high densities of tumor-infiltrating Tregs can correlate with better or worse clinical outcomes depending on the study. In mouse models of cancer, Tregs have been reported to suppress inflammation and protect the host, suppress T cells and protect the tumor, or even have direct cancer-promoting attributes. These different effects may result from the presence of different Treg subsets. We report the preferential expansion of a Treg subset in human CC with potent T cell–suppressive, but compromised anti-inflammatory, properties; these cells are distinguished from Tregs present in healthy donors by their coexpression of Foxp3 and RORγt. Tregs with similar attributes were found to be expanded in mouse models of hereditary polyposis. Indeed, ablation of the RORγt gene in Foxp3+ cells in polyp-prone mice stabilized Treg anti-inflammatory functions, suppressed inflammation, improved polyp-specific immune surveillance, and severely attenuated polyposis. Ablation of interleukin-6 (IL-6), IL-23, IL-17, or tumor necrosis factor–α in polyp-prone mice reduced polyp number but not to the same extent as loss of RORγt. Surprisingly, loss of IL-17A had a dual effect: IL-17A–deficient mice had fewer polyps but continued to have RORγt+ Tregs and developed invasive cancer. Thus, we conclude that RORγt has a central role in determining the balance between protective and pathogenic Tregs in CC and that Treg subtype regulates inflammation, potency of immune surveillance, and severity of disease outcome.

Imbalance in the regulatory immune mechanisms that control intestinal cellular and bacterial homeostasis may lead to induction of the detrimental inflammatory signals characterized in humans as inflammatory bowel disease. Induction of proinflammatory cytokines (i.e., IL-12) induced by dendritic cells (DCs) expressing pattern recognition receptors may skew naive T cells to T helper 1 polarization, which is strongly implicated in mucosal autoimmunity. Recent studies show the ability of probiotic microbes to treat and prevent numerous intestinal disorders, including Clostridium difficile-induced colitis. To study the molecular mechanisms involved in the induction and repression of intestinal inflammation, the phosphoglycerol transferase gene that plays a key role in lipoteichoic acid (LTA) biosynthesis in Lactobacillus acidophilus NCFM (NCK56) was deleted. The data show that the L. acidophilus LTAnegative in LTA (NCK2025) not only down-regulated IL-12 and TNFα but also significantly enhanced IL-10 in DCs and controlled the regulation of costimulatory DC functions, resulting in their inability to induce CD4 + T-cell activation. Moreover, treatment of mice with NCK2025 compared with NCK56 significantly mitigated dextran sulfate sodium and CD4 + CD45RB high T cell-induced colitis and effectively ameliorated dextran sulfate sodium-established colitis through a mechanism that involves IL-10 and CD4 + FoxP3 + T regulatory cells to dampen exaggerated mucosal inflammation. Directed alteration of cell surface components of L. acidophilus NCFM establishes a potential strategy for the treatment of inflammatory intestinal disorders.antiinflammatory | lactobacilli | Toll-like receptor 2 | innate immunity

Mast cells (MC) are a bone marrow-derived, long-lived, heterogeneous cellular population that function both as positive and negative regulators of immune responses. They are arguably the most productive chemical factory in the body and influence other cells through both soluble mediators and cell-to-cell interaction. MC are commonly seen in various tumors and have been attributed alternatively with tumor rejection or tumor promotion. Tumor-infiltrating MC are derived both from sentinel and recruited progenitor cells. MC can directly influence tumor cell proliferation and invasion but also help tumors indirectly by organizing its microenvironment and modulating immune responses to tumor cells. Best known for orchestrating inflammation and angiogenesis, the role of MC in shaping adaptive immune responses has become a focus of recent investigations. MC mobilize T cells and antigen-presenting dendritic cells. They function as intermediaries in regulatory T cells (Treg)-induced tolerance but can also modify or reverse Treg-suppressive properties. The central role of MC in the control of innate and adaptive immunity endows them with the ability to tune the nature of host responses to cancer and ultimately influence the outcome of disease and fate of the cancer patient.

An imbalance of commensal bacteria and their gene products underlies mucosal and, in particular, gastrointestinal inflammation and a predisposition to cancer. Lactobacillus species have received considerable attention as examples of beneficial microbiota. We have reported previously that deletion of the phosphoglycerol transferase gene that is responsible for lipoteichoic acid (LTA) biosynthesis in Lactobacillus acidophilus (NCK2025) rendered this bacterium able to significantly protect mice against induced colitis when delivered orally. Here we report that oral treatment with LTA-deficient NCK2025 normalizes innate and adaptive pathogenic immune responses and causes regression of established colonic polyps. This study reveals the proinflammatory role of LTA and the ability of LTA-deficient L. acidophilus to regulate inflammation and protect against colonic polyposis in a unique mouse model. dendritic cells | regulatory T cells | anti-inflammatory I dentifying bacterial gene products that enhance protective versus pathogenic inflammation in the gut is critical to rebalance homeostasis in gastrointestinal (GI) chronic inflammatory diseases and malignancies. Commensal Lactobacillus species (i.e., Lactobacillus acidophilus) are normal inhabitants of the natural microbiota in the human GI tract (1, 2). L. acidophilus stimulates innate cells to produce inflammatory and regulatory cytokines through interaction of their surface layer proteins and other cell surface components (3-7). To investigate the potential role of lipoteichoic acid (LTA) of L. acidophilus in the induction of inflammatory signals, we deleted the phosphoglycerol transferase gene (LBA0447) that synthesizes LTA. LTA is a zwitterionic glycolipid found in the cell wall of several Gram-positive bacterial strains, including L. acidophilus, which stimulates dendritic cells (DCs) through Toll-like receptor 2, resulting in cytokine release (8, 9). Disruption of LTA synthesis generated a L. acidophilus derivative (NCK2025) that mitigates colitis in mice (10). Based on these observations and those of others (11,12), it was proposed that LTA induces inflammation and that its absence significantly attenuates overt intestinal inflammation.Inflammation has a tumor-promoting role in mice with polyposis and in human colon cancer (13)(14)(15)(16)(17). T regulatory cells (Tregs) critically regulate inflammation and play a protective role in polyposis (15, 18) and colon cancer (19-21). However, chronic interaction of Tregs with proinflammatory cells and their cytokines can reverse the anti-inflammatory properties of these cells and render them proinflammatory (15,16,22,23). Consensus suggests that interactions between lymphocytes and myeloid cells regulate pro-vs. antitumor immunity (17, 24), and we hypothesized that the gut microbiota plays an essential role in control of this balance. We used L. acidophilus NCK2025, deficient in LTA, to investigate the moderation of pathogenic inflammation within the tumor microenvironment in a unique mouse model of colonic polyposis...

The density and type of lymphocytes that infiltrate colon tumors are predictive of the clinical outcome of colon cancer. High densities of TH17 cells and inflammation predict poor outcome, while infiltration by Tregs that naturally suppress inflammation is associated with longer patient survival. However, the role of Tregs in cancer remains controversial. We recently reported that Tregs in colon cancer patients can become pro-inflammatory and tumor promoting. These properties were directly linked with their expression of RORγt, the signature transcription factor of TH17 cells. Here, we report that Wnt/β-catenin signaling in T-cells promotes expression of RORγt. Expression of β-catenin was elevated in T-cells and Tregs of patients with colitis and colon cancer. Genetically engineered activation of β-catenin in mouse T-cells resulted in enhanced chromatin accessibility in the proximity of Tcf-1 binding sites genome-wide, induced expression of TH17 signature genes including RORγt, and promoted TH17-mediated inflammation. Strikingly, the mice had inflammation of intestine and colon and developed lesions indistinguishable from colitis-induced cancer. Activation of β-catenin only in Tregs was sufficient to produce inflammation and initiate cancer. Based on these findings we conclude that activation of Wnt/β-catenin signaling in T-cells and/or Tregs is causatively linked with the imprinting of pro-inflammatory properties and the promotion of colon cancer.