M cells in Peyer's patch epithelium conduct transepithelial transport of luminal antigens to cells of the mucosal immune system. To determine the distribution of specific lectin-binding sites on luminal membranes of living M cells and to follow the transport route of membrane-bound molecules, lectin-ferritin conjugates and cationized ferritin were applied to rabbit Peyer's patch mucosa in vivo and in vitro. The degree to which binding enhances transport was estimated by comparing quantitatively the transport of an adherent probe, wheat germ agglutinin-ferritin, to that of a nonadherent BSA-colloidal gold probe. When applied to fixed tissue, the lectins tested bound equally well to M cells and columnar absorptive cells. On living mucosa, however, ferritin conjugates of wheat germ agglutinin and Ricinus communis agglutinins I and II bound more avidly to M cells. Absorptive cells conducted little uptake and no detectable transepithelial transport. Lectins on M cell membranes were endocytosed from coated pits, rapidly transported in a complex system of tubulocisternae and vesicles, and remained adherent to M cell basolateral membranes. Cationized ferritin adhered to anionic sites and was similarly transported, but was released as free clusters at M cell basolateral surfaces. When applied simultaneously to Peyer's patch mucosa, wheat germ agglutinin-ferritin was transported about 50 times more efficiently than was bovine serum albumin-colloidal gold.

Crypt, but not villus, goblet cells in the ileum accelerate their secretion of mucus within 5 min following cholinergic stimulation. This study was done to determine whether the macromolecular permeability and structure of occluding junctions in the ileum are altered during accelerated secretion. Rats were injected intravenously with horseradish peroxidase followed by carbachol (250 micrograms/kg, subcutaneous) and the intestinal mucosa was fixed 3-12 min later. In control mucosa (saline-injected), peroxidase filled lateral intercellular spaces up to the occluding junctions of both crypt and villus epithelium, but did not enter occluding junctions or pass into the lumen. In 3 of 8 carbachol-stimulated rats, peroxidase was present within occluding junctions in crypt epithelium and in the crypt lumen, although all intermembrane junctional fusion sites appeared intact. Villus epithelial occluding junctions, in contrast, continued to exclude peroxidase. In freeze-fracture replicas of crypt cells prepared after carbachol stimulation, we detected no structural changes in strand networks of occluding junctions that could account for increased paracellular permeability.

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Gastric cancer is a leading cause of cancer-related deaths worldwide. Recently, clinical studies have demonstrated that many of those with advanced gastric cancer are responsive to immune checkpoint antibody therapy, although the median survival even with these new agents is less than 12 months for advanced disease. The gastrointestinal peptide gastrin has been shown to stimulate growth of gastric cancer in a paracrine and autocrine fashion through the cholecystokinin-B receptor (CCK-BR), a receptor that is expressed in at least 56.6% of human gastric cancers. In the current investigation, we studied the role of the gastrin-CCK-BR pathway in vitro and in vivo as well as the expression of the CCK-BR in a human gastric cancer tissue array. CCK-BR and PD-L1 receptor expression and gastrin peptide was found in two murine gastric cancer cells (NCC-S1 and YTN-16) by qRT-PCR and immunocytochemistry. Treatment of NCC-S1 cells with gastrin resulted in increased growth. In vivo, the effects of a cancer vaccine that targets gastrin peptide (polyclonal antibody stimulator—PAS) alone or in combination with a Programed Death-1 antibody (PD-1 Ab) was evaluated in immune competent mice (N = 40) bearing YTN-16 gastric tumors. Mice were treated with PBS, PD-1 Ab (50 µg), PAS (250 µg), or the combination of PD-1 Ab with PAS. Tumor growth was significantly slower than controls in PAS-treated mice, and tumor growth was decreased even more in combination-treated mice. There were no metastases in any of the mice treated with PAS either alone or in combination with PD-1 Ab. Tumor proliferation by the Ki67 staining was significantly decreased in mice treated with PAS monotherapy or the combination therapy. PAS monotherapy or combined with PD-1 Ab increased tumor CD8+ T-lymphocytes and decreased the number of immunosuppressive M2-polarized tumor-associated macrophages. CCK-BR expression was identified in samples from a human tissue array by immunohistochemistry confirming the clinical relevance of this study. These results confirm the significance of the gastrin-CCK-BR signaling pathway in gastric cancer and suggest that the addition of a gastrin vaccine, PAS, to therapy with an immune checkpoint antibody may decrease growth and metastases of gastric cancer by altering the tumor microenvironment.

The incidence of pancreatic cancer is increasing significantly and will soon become the second leading cause of cancer-related deaths in the United States. We have previously shown that the gastrointestinal peptide gastrin, which is only expressed in the fetal pancreas and not in the adult pancreas, is activated during pancreatic carcinogenesis where it stimulates growth in an autocrine fashion. In this investigation, we used transgenic LSL-KrasG12D/+; P48-Cre mice that develop precancerous pancreatic intraepithelial neoplasia (PanIN) lesions and pancreatic cancer over time. Starting at 3 months of age, mice were either left untreated (control) or were treated with a gastrin-targeted vaccine, polyclonal antibody stimulator (PAS 250 μg) followed by a monthly booster until the mice reached 8 months of age when pancreata were excised, and analyzed by histology for PanIN grade in a blinded fashion. High-grade PanIN-3 lesions were significantly less in PAS-treated mice (P = 0.0077), and cancers developed in 33% of the control mice but only in 10% of the PAS-treated mice. Compared with the control mice, fibrosis was reduced by >50%, arginase positive M2 macrophages were reduced by 74%, and CD8+ T cells were increased by 73% in the pancreas extracellular matrix in PAS-treated mice. Prevention Relevance: PAS vaccination significantly decreased high-grade PanIN lesions and altered the pancreas microenvironment, rendering it less carcinogenic.