NHE8 Deficiency Promotes Colitis-Associated Cancer in Mice via Expansion of Lgr5-Expressing Cells

BACKGROUND & AIMS

Lgr5 overexpression has been detected in colorectal cancers (CRCs), including some cases of colitis-associated CRCs. In colitis-associated CRCs, chronic inflammation is a contributing factor in carcinogenesis. We recently reported that intestinal Na⁺/H⁺ exchanger isoform 8 (NHE8) plays an important role in intestinal mucosal protection and that loss of NHE8 expression results in an ulcerative colitis-like condition. Therefore, we hypothesized that NHE8 may be involved in the development of intestinal tumors.

METHODS

We assessed NHE8 expression in human CRCs by immunohistochemistry and studied tumor burden in NHE8 knockout (KO) mice using an azoxymethane/dextran sodium sulfate colon cancer model. We also evaluated cell proliferation in HT29^NHE8KO cells and assessed tumor growth in NOD scid gamma (NSG) mice xenografted with HT29^NHE8KO cells. To verify if a relationship exists between Lgr5 and NHE8 expression, we analyzed Lgr5 expression in NHE8KO mice by polymerase chain reaction and in situ hybridization. Lgr5 expression and cell proliferation in the absence of NHE8 were confirmed in colonic organoid cultures. The expression of β-catenin and c-Myc also were analyzed to evaluate Wnt/β-catenin activation.

RESULTS

NHE8 was undetectable in human CRC tissues. Although only 9% of NHE8 wild-type mice showed tumorigenesis in the azoxymethane/dextran sodium sulfate colon cancer model, almost 10 times more NHE8KO mice (89%) developed tumors. In the absence of NHE8, a higher colony formation unit was discovered in HT29^NHE8KO cells. In NSG mice, larger tumors developed at the site where HT29^NHE8KO cells were injected compared with HT29^{NHE8 wild type} cells. Furthermore, NHE8 deficiency resulted in increased Lgr5 expression in the colon, in HT29-derived tumors, and in colonoids. The absence of NHE8 also increased Wnt/β-catenin activation.

CONCLUSIONS

NHE8 might be an intrinsic factor that regulates Wnt/β-catenin in the intestine.

IL22 Inhibits Epithelial Stem Cell Expansion in an Ileal Organoid Model

Background & Aims

Crohn's disease is an inflammatory bowel disease that affects the ileum and is associated with increased cytokines. Although interleukin (IL)6, IL17, IL21, and IL22 are increased in Crohn's disease and are associated with disrupted epithelial regeneration, little is known about their effects on the intestinal stem cells (ISCs) that mediate tissue repair. We hypothesized that ILs may target ISCs and reduce ISC-driven epithelial renewal.

Methods

A screen of IL6, IL17, IL21, or IL22 was performed on ileal mouse organoids. Computational modeling was used to predict microenvironment cytokine concentrations. Organoid size, survival, proliferation, and differentiation were characterized by morphometrics, quantitative reverse-transcription polymerase chain reaction, and immunostaining on whole organoids or isolated ISCs. ISC function was assayed using serial passaging to single cells followed by organoid quantification. Single-cell RNA sequencing was used to assess Il22ra1 expression patterns in ISCs and transit-amplifying (TA) progenitors. An IL22-transgenic mouse was used to confirm the impact of increased IL22 on proliferative cells in vivo.

Results

High IL22 levels caused decreased ileal organoid survival, however, resistant organoids grew larger and showed increased proliferation over controls. Il22ra1 was expressed on only a subset of ISCs and TA progenitors. IL22-treated ISCs did not show appreciable differentiation defects, but ISC biomarker expression and self-renewal-associated pathway activity was reduced and accompanied by an inhibition of ISC expansion. In vivo, chronically increased IL22 levels, similar to predicted microenvironment levels, showed increases in proliferative cells in the TA zone with no increase in ISCs.

Conclusions

Increased IL22 limits ISC expansion in favor of increased TA progenitor cell expansion.

Expression of Viral Antigen by the Liver Leads to Chronic Infection Through the Generation of Regulatory T Cells

BACKGROUND & AIMS

The constant exposure of the liver to food and bacterial antigens through the mesenteric circulation requires it to maintain tolerance while preserving the ability to mount an effective immune response against pathogens. We investigated the contribution of the liver's tolerogenic nature on the establishment of chronic viral infections.

METHODS

TTR-NP mice, which express the nucleoprotein (NP) of lymphocytic choriomeningitis virus (LCMV) specifically in hepatocytes under control of a modified transthyretin (TTR) promoter, were infected with the Armstrong (Arm) or WE acute strains of LCMV.

RESULTS

The infection persisted for at least 147 days in TTR-NP mice. Expression of NP by the liver induced a strong peripheral tolerance against NP that was mediated by interleukin-10-secreting CD4⁺ regulatory T cells, leading to high PD-1 (programmed death-1) expression and reduced effector function of virus-specific T cells. Despite an active immune response against LCMV, peripheral tolerance against a single viral protein was sufficient to induce T-cell exhaustion and chronic LCMV Armstrong (Arm) or WE infection by limiting the antiviral T-cell response in an otherwise immunocompetent host. Regulatory T-cell depletion of chronically infected TTR-NP mice led to functional restoration of LCMV-specific CD4⁺ and CD8⁺ T cell responses and viral clearance.

CONCLUSIONS

Expression of a viral antigen by hepatocytes can induce a state of peripheral tolerance mediated by regulatory T cells that can lead to the establishment of a chronic viral infection. Strategies targeting regulatory T cells in patients chronically infected with hepatotropic viruses could represent a promising approach to restore functional antiviral immunity and clear infection.

A monoclonal antibody against hinge-cleaved IgG restores effector function to proteolytically-inactivated IgGs in vitro and in vivo

We report a chimeric monoclonal antibody (mAb) directed to a neo-epitope that is exposed in the IgG lower hinge following proteolytic cleavage. The mAb, designated 2095-2, displays specificity for IdeS-generated F(ab')₂ fragments, but not for full-length IgG or for closely-related F(ab')₂ fragments generated with other proteases. A critical component of the specificity is provided by the C-terminal amino acid of the epitope corresponding to gly-236 in the IgG1 (also IgG4) hinge. By its ability to bind to IdeS-cleaved anti-CD20 mAb, mAb 2095-2 fully restored antibody-dependent cell-mediated cytotoxicity (ADCC) and complement-dependent cytotoxicity (CDC) against WIL2-S cells to the otherwise inactive anti-CD20 IgG1 F(ab')₂ fragment. Similarly, 2095-2 reinstated ADCC against MDA-MB-231 cells to an anti-CD142 IgG1 F(ab')₂ fragment. mAb 2095-2 was also capable of eliciting both CDC and ADCC to IgG4 F(ab')₂ fragments, an IgG subclass that has weaker ADCC and CDC when intact relative to intact IgG1. The in vitro cell-based efficacy of 2095-2 was extended to the in vivo setting using platelets as a cell clearance surrogate. In a canine model, the co-administration of 2095-2 together with IdeS-generated, platelet-targeting anti-CD41/61 F(ab')₂ fragment not only restored platelet clearance, but did so at a rate and extent of clearance that exceeded that of intact anti-CD41/61 IgG at comparable concentrations. To further explore this unexpected amplification effect, we conducted a rat study in which 2095-2 was administered at a series of doses in combination with a fixed dose of anti-CD41/61 F(ab')₂ fragments. Again, the combination, at ratios as low as 1:10 (w/w) 2095-2 to F(ab')₂, proved more effective than the anti-CD41/61 IgG1 alone. These findings suggest a novel mechanism for enhancing antibody-mediated cell-killing effector functions with potential applications in pathologic settings such as tumors and acute infections where protease activity is abundant.