TIGIT: A Key Inhibitor of the Cancer Immunity Cycle.

Immunotherapies that harness the activity of the immune system against tumors are proving to be an effective therapeutic approach in multiple malignancies. Indeed, through accumulation of genetic mutations, many tumors express antigens that can potentially elicit specific tumor immunity. However, tumors can also suppress these responses by activating negative regulatory pathways and checkpoints such as PD-1/PD-L1 and CTLA-4. Blocking these checkpoints on T cells has provided dramatic clinical benefit, but only a subset of patients exhibit clear and durable responses, suggesting that other mechanisms must be limiting the immune response. We discuss here the role of TIGIT, an inhibitory receptor expressed by lymphocytes, in limiting antitumor responses and we review its mechanisms of action during the cancer immunity cycle.

Mucosally transplanted mesenchymal stem cells stimulate intestinal healing by promoting angiogenesis.

Mesenchymal stem cell (MSC) therapy is an emerging field of regenerative medicine; however, it is often unclear how these cells mediate repair. Here, we investigated the use of MSCs in the treatment of intestinal disease and modeled abnormal repair by creating focal wounds in the colonic mucosa of prostaglandin-deficient mice. These wounds developed into ulcers that infiltrated the outer intestinal wall. We determined that penetrating ulcer formation in this model resulted from increased hypoxia and smooth muscle wall necrosis. Prostaglandin I2 (PGI2) stimulated VEGF-dependent angiogenesis to prevent penetrating ulcers. Treatment of mucosally injured WT mice with a VEGFR inhibitor resulted in the development of penetrating ulcers, further demonstrating that VEGF is critical for mucosal repair. We next used this model to address the role of transplanted colonic MSCs (cMSCs) in intestinal repair. Compared with intravenously injected cMSCs, mucosally injected cMSCs more effectively prevented the development of penetrating ulcers, as they were more efficiently recruited to colonic wounds. Importantly, mucosally injected cMSCs stimulated angiogenesis in a VEGF-dependent manner. Together, our results reveal that penetrating ulcer formation results from a reduction of local angiogenesis and targeted injection of MSCs can optimize transplantation therapy. Moreover, local MSC injection has potential for treating diseases with features of abnormal angiogenesis and repair.

Type I interferons link viral infection to enhanced epithelial turnover and repair.

The host immune system functions constantly to maintain chronic commensal and pathogenic organisms in check. The consequences of these immune responses on host physiology are as yet unexplored, and may have long-term implications in health and disease. We show that chronic viral infection increases epithelial turnover in multiple tissues, and the antiviral cytokines type I interferons (IFNs) mediate this response. Using a murine model with persistently elevated type I IFNs in the absence of exogenous viral infection, the Irgm1(-/-) mouse, we demonstrate that type I IFNs act through nonepithelial cells, including macrophages, to promote increased epithelial turnover and wound repair. Downstream of type I IFN signaling, the highly related IFN-stimulated genes Apolipoprotein L9a and b activate epithelial proliferation through ERK activation. Our findings demonstrate that the host immune response to chronic viral infection has systemic effects on epithelial turnover through a myeloid-epithelial circuit.

IL-6 stimulates intestinal epithelial proliferation and repair after injury.

IL-6 is a pleiotropic cytokine often associated with inflammation. Inhibition of this pathway has led to successful treatment of rheumatoid arthritis, but one unforeseen potential complication of anti-IL-6 therapy is bowel perforation. Within the intestine, IL-6 has been shown to prevent epithelial apoptosis during prolonged inflammation. The role of IL-6 in the intestine during an initial inflammatory insult is unknown. Here, we evaluate the role of IL-6 at the onset of an inflammatory injury. Using two murine models of bowel injury - wound by biopsy and bacterial triggered colitis - we demonstrated that IL-6 is induced soon after injury by multiple cell types including intraepithelial lymphocytes. Inhibition of IL-6 resulted in impaired wound healing due to decreased epithelial proliferation. Using intestinal tissue obtained from patients who underwent surgical resection of the colon due to traumatic perforation, we observed cells with detectable IL-6 within the area of perforation and not at distant sites. Our data demonstrate the important role of IL-6 produced in part by intraepithelial lymphocytes at the onset of an inflammatory injury for epithelial proliferation and wound repair.

Notch2-dependent classical dendritic cells orchestrate intestinal immunity to attaching-and-effacing bacterial pathogens.

Defense against attaching-and-effacing bacteria requires the sequential generation of interleukin 23 (IL-23) and IL-22 to induce protective mucosal responses. Although CD4(+) and NKp46(+) innate lymphoid cells (ILCs) are the critical source of IL-22 during infection, the precise source of IL-23 is unclear. We used genetic techniques to deplete mice of specific subsets of classical dendritic cells (cDCs) and analyzed immunity to the attaching-and-effacing pathogen Citrobacter rodentium. We found that the signaling receptor Notch2 controlled the terminal stage of cDC differentiation. Notch2-dependent intestinal CD11b(+) cDCs were an obligate source of IL-23 required for survival after infection with C. rodentium, but CD103(+) cDCs dependent on the transcription factor Batf3 were not. Our results demonstrate a nonredundant function for CD11b(+) cDCs in the response to pathogens in vivo.

Igf2bp1 is required for full induction of Ptgs2 mRNA in colonic mesenchymal stem cells in mice.

BACKGROUND & AIMS: Prostaglandin-endoperoxide synthase (Ptgs)2 is an enzyme involved in prostaglandin production during the response to mucosal damage. Its expression is regulated, in part, by messenger RNA (mRNA)-binding proteins that control the stability of Ptgs2 mRNA. We used a precise system of colonic injury and repair to identify Ptgs2 mRNA-binding proteins. METHODS: We used endoscopy-guided mucosal excision to create focal injury sites in colons of mice. Wound beds from wild-type, Ptgs2(-/-), Ptgs2(+/-), and Myd88(-/-) mice were analyzed at 2-day intervals after injury for aspects of repair and Ptgs2 expression. We used cultured colonic mesenchymal stem cells (cMSCs) that express Ptgs2 to identify and analyze molecules that regulate Ptgs2 expression. RESULTS: Ptgs2(-/-) mice had defects in wound repair, validating the biopsy technique as a system to study the regulation of Ptgs2. Ptgs2(+/-) mice had similar defects in wound healing, so full induction of Ptgs2 is required for wound repair. In wild-type mice, levels of Ptgs2 mRNA increased significantly in the wound bed 2 and 4 days after injury; the highest levels of Ptgs2 were observed in cMSCs. In a functional short hairpin RNA knockdown screen, we identified Igf2bp1, a VICKZ (Vg1 RNA binding protein, Insulin-like growth factor II mRNA binding protein 1, Coding region determinant-binding protein, KH domain containing protein overexpressed in cancer, and Zipcode-binding protein-1) mRNA-binding protein, as a regulator of Ptgs2 expression in cMSCs. Igf2bp1 also interacted physically with Ptgs2 mRNA. Igf2bp1 expression was induced exclusively in wound-bed cMSCs, and full induction of Ptgs2 and Igf2bp1 during repair required Myd88. CONCLUSIONS: We identified Igf2bp1 as a regulator of Ptgs2 mRNA in mice. Igf2bp1 is required for full induction of Ptgs2 mRNA in cMSCs.

Mesenchymal stem cell therapy of intestinal disease: are their effects systemic or localized?

PURPOSE OF REVIEW: Stem cell therapy for intestinal diseases is an emerging area in clinical gastroenterology. We will review recent literature regarding mesenchymal stem cells, which have been utilized in preclinical models and are now headed for clinical trials in several gastrointestinal diseases including inflammatory bowel disease. RECENT FINDINGS: Important studies over the last 2 years have made significant inroads into understanding the mechanisms of action of these cell types. The two major competing hypotheses are that mesenchymal stem cells home to areas of injury where they repair based on their stem cell activity or that mesenchymal stem cells act as a source of secreted factors that stimulate repair and inhibit inflammation. SUMMARY: Mesenchymal stem cells show promise for therapy in a number of intestinal diseases. Further understanding of their mechanism of action should improve our ability to use them therapeutically.