IL-10 dampens antitumor immunity and promotes liver metastasis via PD-L1 induction

BACKGROUND & AIMS

The liver is one of the organs most commonly affected by metastasis. The presence of liver metastases has been reported to be responsible for an immunosuppressive microenvironment and diminished immunotherapy efficacy. Herein, we aimed to investigate the role of IL-10 in liver metastasis and to determine how its modulation could affect the efficacy of immunotherapy in vivo.

METHODS

To induce spontaneous or forced liver metastasis in mice, murine cancer cells (MC38) or colon tumor organoids were injected into the cecum or the spleen, respectively. Mice with complete and cell type-specific deletion of IL-10 and IL-10 receptor alpha were used to identify the source and the target of IL-10 during metastasis formation. Programmed death ligand 1 (PD-L1)-deficient mice were used to test the role of this checkpoint. Flow cytometry was applied to characterize the regulation of PD-L1 by IL-10.

RESULTS

We found that Il10-deficient mice and mice treated with IL-10 receptor alpha antibodies were protected against liver metastasis formation. Furthermore, by using IL-10 reporter mice, we demonstrated that Foxp3+ regulatory T cells (Tregs) were the major cellular source of IL-10 in liver metastatic sites. Accordingly, deletion of IL-10 in Tregs, but not in myeloid cells, led to reduced liver metastasis. Mechanistically, IL-10 acted on Tregs in an autocrine manner, thereby further amplifying IL-10 production. Furthermore, IL-10 acted on myeloid cells, i.e. monocytes, and induced the upregulation of the immune checkpoint protein PD-L1. Finally, the PD-L1/PD-1 axis attenuated CD8-dependent cytotoxicity against metastatic lesions.

CONCLUSIONS

Treg-derived IL-10 upregulates PD-L1 expression in monocytes, which in turn reduces CD8+ T-cell infiltration and related antitumor immunity in the context of colorectal cancer-derived liver metastases. These findings provide the basis for future monitoring and targeting of IL-10 in colorectal cancer-derived liver metastases.

IMPACT AND IMPLICATIONS

Liver metastasis diminishes the effectiveness of immunotherapy and increases the mortality rate in patients with colorectal cancer. We investigated the role of IL-10 in liver metastasis formation and assessed its impact on the effectiveness of immunotherapy. Our data show that IL-10 is a pro-metastatic factor involved in liver metastasis formation and that it acts as a regulator of PD-L1. This provides the basis for future monitoring and targeting of IL-10 in colorectal cancer-derived liver metastasis.

cDC2 plasticity and acquisition of a DC3-like phenotype mediated by IL-6 and PGE2 in a patient-derived colorectal cancer organoids model

Metastatic colorectal cancer (CRC) is highly resistant to therapy and prone to recur. The tumor-induced local and systemic immunosuppression allows cancer cells to evade immunosurveillance, facilitating their proliferation and dissemination. Dendritic cells (DCs) are required for the detection, processing, and presentation of tumor antigens, and subsequently for the activation of antigen-specific T cells to orchestrate an effective antitumor response. Notably, successful tumors have evolved mechanisms to disrupt and impair DC functions, underlining the key role of tumor-induced DC dysfunction in promoting tumor growth, metastasis initiation, and treatment resistance. Conventional DC type 2 (cDC2) are highly prevalent in tumors and have been shown to present high phenotypic and functional plasticity in response to tumor-released environmental cues. This plasticity reverberates on both the development of antitumor responses and on the efficacy of immunotherapies in cancer patients. Uncovering the processes, mechanisms, and mediators by which CRC shapes and disrupts cDC2 functions is crucial to restoring their full antitumor potential. In this study, we use our recently developed 3D DC-tumor co-culture system to investigate how patient-derived primary and metastatic CRC organoids modulate cDC2 phenotype and function. We first demonstrate that our collagen-based system displays extensive interaction between cDC2 and tumor organoids. Interestingly, we show that tumor-corrupted cDC2 shift toward a CD14+ population with defective expression of maturation markers, an intermediate phenotype positioned between cDC2 and monocytes, and impaired T-cell activating abilities. This phenotype aligns with the newly defined DC3 (CD14+ CD1c+ CD163+) subset. Remarkably, a comparable population was found to be present in tumor lesions and enriched in the peripheral blood of metastatic CRC patients. Moreover, using EP2 and EP4 receptor antagonists and an anti-IL-6 neutralizing antibody, we determined that the observed phenotype shift is partially mediated by PGE2 and IL-6. Importantly, our system holds promise as a platform for testing therapies aimed at preventing or mitigating tumor-induced DC dysfunction. Overall, our study offers novel and relevant insights into cDC2 (dys)function in CRC that hold relevance for the design of therapeutic approaches.

Targeting CAFs to Improve Anti-PD-1 Checkpoint Immunotherapy

The tumor microenvironment is a complex ecosystem that drives cancer progression and restrains immunity. Although immune checkpoint inhibitors have shown strong potential in a subset of patients, a better understanding of suppressive mechanisms may inspire ways to improve immunotherapeutic efficacy. A new study in this issue of Cancer Research focuses on targeting cancer-associated fibroblasts in preclinical models of gastric tumors. Aiming to rebalance anticancer immunity and enhance treatment responses to checkpoint-blocking antibodies, this work also addresses the potential for multitarget tyrosine kinase inhibitors in treating gastrointestinal cancer. See related article by Akiyama et al., p. 753.

Dendritic cell phenotype and function in a 3D co-culture model of patient-derived metastatic colorectal cancer organoids

Colorectal cancer (CRC) remains one of the most aggressive and lethal cancers, with metastasis accounting for most deaths. As such, there is an unmet need for improved therapies for metastatic CRC (mCRC). Currently, the research focus is shifting towards the reciprocal interactions within the tumor microenvironment (TME), which prevent tumor clearance by the immune system. Dendritic cells (DCs) play a key role in the initiation and amplification of anti-tumor immune responses and in driving the clinical success of immunotherapies. Dissecting the interactions between DCs and CRC cells may open doors to identifying key mediators in tumor progression, and possible therapeutic targets. This requires representative, robust and versatile models and tools. Currently, there is a shortage of such in vitro systems to model the CRC TME and its tumor-immune cell interactions. Here we develop and establish a dynamic organotypic 3D co-culture system to recapitulate and untangle the interactions between DCs and patient-derived mCRC tumor organoids. To our knowledge, this is the first study investigating human DCs in co-culture with tumor organoids in a 3D, organotypic setting. This system reveals how mCRC organoids modulate and shape monocyte-derived DCs (MoDCs) behavior, phenotype, and function, within a collagen matrix, using techniques such as brightfield and fluorescence microscopy, flow cytometry, and fluorescence-activated cell sorting. Our 3D co-culture model shows high viability and extensive interaction between DCs and tumor organoids, and its structure resembles patient tissue sections. Furthermore, it is possible to retrieve DCs from the co-cultures and characterize their phenotypic and functional profile. In our study, the expression of activation markers in both mature and immature DCs and their ability to activate T cells were impacted by co-culture with tumor organoids. In the future, this direct co-culture platform can be adapted and exploited to study the CRC-DC interplay in more detail, enabling novel and broader insights into CRC-driven DC (dys)function.

Multiomics of Colorectal Cancer Organoids Reveals Putative Mediators of Cancer Progression Resulting from SMAD4 Inactivation

The development of metastasis severely reduces the life expectancy of patients with colorectal cancer (CRC). Although loss of SMAD4 is a key event in CRC progression, the resulting changes in biological processes in advanced disease and metastasis are not fully understood. Here, we applied a multiomics approach to a CRC organoid model that faithfully reflects the metastasis-supporting effects of SMAD4 inactivation. We show that loss of SMAD4 results in decreased differentiation and activation of pro-migratory and cell proliferation processes, which is accompanied by the disruption of several key oncogenic pathways, including the TGFβ, WNT, and VEGF pathways. In addition, SMAD4 inactivation leads to increased secretion of proteins that are known to be involved in a variety of pro-metastatic processes. Finally, we show that one of the factors that is specifically secreted by SMAD4-mutant organoids─DKK3─reduces the antitumor effects of natural killer cells (NK cells). Altogether, our data provide new insights into the role of SMAD4 perturbation in advanced CRC.

Mex3a marks drug-tolerant persister colorectal cancer cells that mediate relapse after chemotherapy

Colorectal cancer (CRC) patient-derived organoids predict responses to chemotherapy. Here we used them to investigate relapse after treatment. Patient-derived organoids expand from highly proliferative LGR5⁺ tumor cells; however, we discovered that lack of optimal growth conditions specifies a latent LGR5⁺ cell state. This cell population expressed the gene MEX3A, is chemoresistant and regenerated the organoid culture after treatment. In CRC mouse models, Mex3a⁺ cells contributed marginally to metastatic outgrowth; however, after chemotherapy, Mex3a⁺ cells produced large cell clones that regenerated the disease. Lineage-tracing analysis showed that persister Mex3a⁺ cells downregulate the WNT/stem cell gene program immediately after chemotherapy and adopt a transient state reminiscent to that of YAP⁺ fetal intestinal progenitors. In contrast, Mex3a-deficient cells differentiated toward a goblet cell-like phenotype and were unable to resist chemotherapy. Our findings reveal that adaptation of cancer stem cells to suboptimal niche environments protects them from chemotherapy and identify a candidate cell of origin of relapse after treatment in CRC.

Overcoming TGFβ-mediated immune evasion in cancer

Transforming growth factor-β (TGFβ) signalling controls multiple cell fate decisions during development and tissue homeostasis; hence, dysregulation of this pathway can drive several diseases, including cancer. Here we discuss the influence that TGFβ exerts on the composition and behaviour of different cell populations present in the tumour immune microenvironment, and the context-dependent functions of this cytokine in suppressing or promoting cancer. During homeostasis, TGFβ controls inflammatory responses triggered by exposure to the outside milieu in barrier tissues. Lack of TGFβ exacerbates inflammation, leading to tissue damage and cellular transformation. In contrast, as tumours progress, they leverage TGFβ to drive an unrestrained wound-healing programme in cancer-associated fibroblasts, as well as to suppress the adaptive immune system and the innate immune system. In consonance with this key role in reprogramming the tumour microenvironment, emerging data demonstrate that TGFβ-inhibitory therapies can restore cancer immunity. Indeed, this approach can synergize with other immunotherapies - including immune checkpoint blockade - to unleash robust antitumour immune responses in preclinical cancer models. Despite initial challenges in clinical translation, these findings have sparked the development of multiple therapeutic strategies that inhibit the TGFβ pathway, many of which are currently in clinical evaluation.

The Therapeutic Potential of Tackling Tumor-Induced Dendritic Cell Dysfunction in Colorectal Cancer

Colorectal cancer (CRC) is the third most diagnosed malignancy and the second leading cause of cancer-related deaths worldwide. Locally advanced and metastatic disease exhibit resistance to therapy and are prone to recurrence. Despite significant advances in standard of care and targeted (immuno)therapies, the treatment effects in metastatic CRC patients have been modest. Untreatable cancer metastasis accounts for poor prognosis and most CRC deaths. The generation of a strong immunosuppressive tumor microenvironment (TME) by CRC constitutes a major hurdle for tumor clearance by the immune system. Dendritic cells (DCs), often impaired in the TME, play a critical role in the initiation and amplification of anti-tumor immune responses. Evidence suggests that tumor-mediated DC dysfunction is decisive for tumor growth and metastasis initiation, as well as for the success of immunotherapies. Unravelling and understanding the complex crosstalk between CRC and DCs holds promise for identifying key mechanisms involved in tumor progression and spread that can be exploited for therapy. The main goal of this review is to provide an overview of the current knowledge on the impact of CRC-driven immunosuppression on DCs phenotype and functionality, and its significance for disease progression, patient prognosis, and treatment response. Moreover, present knowledge gaps will be highlighted as promising opportunities to further understand and therapeutically target DC dysfunction in CRC. Given the complexity and heterogeneity of CRC, future research will benefit from the use of patient-derived material and the development of in vitro organoid-based co-culture systems to model and study DCs within the CRC TME.

Stromal SOX2 Upregulation Promotes Tumorigenesis through the Generation of a SFRP1/2-Expressing Cancer-Associated Fibroblast Population

Cancer-associated fibroblasts (CAFs) promote tumor malignancy, but the precise transcriptional mechanisms regulating the acquisition of the CAF phenotype are not well understood. We show that the upregulation of SOX2 is central to this process, which is repressed by protein kinase Cζ (PKCζ). PKCζ deficiency activates the reprogramming of colonic fibroblasts to generate a predominant SOX2-dependent CAF population expressing the WNT regulator Sfrp2 as its top biomarker. SOX2 directly binds the Sfrp1/2 promoters, and the inactivation of Sox2 or Sfrp1/2 in CAFs impaired the induction of migration and invasion of colon cancer cells, as well as their tumorigenicity in vivo. Importantly, recurrence-free and overall survival of colorectal cancer (CRC) patients negatively correlates with stromal PKCζ levels. Also, SOX2 expression in the stroma is associated with CRC T invasion and worse prognosis of recurrence-free survival. Therefore, the PKCζ-SOX2 axis emerges as a critical step in the control of CAF pro-tumorigenic potential.

Combinatorial Immunotherapies for Metastatic Colorectal Cancer

Colorectal cancer (CRC) is one of the most frequent and deadly forms of cancer. About half of patients are affected by metastasis, with the cancer spreading to e.g., liver, lungs or the peritoneum. The majority of these patients cannot be cured despite steady advances in treatment options. Immunotherapies are currently not widely applicable for this disease, yet show potential in preclinical models and clinical translation. The tumour microenvironment (TME) has emerged as a key factor in CRC metastasis, including by means of immune evasion-forming a major barrier to effective immuno-oncology. Several approaches are in development that aim to overcome the immunosuppressive environment and boost anti-tumour immunity. Among them are vaccination strategies, cellular transplantation therapies, and targeted treatments. Given the complexity of the system, we argue for rational design of combinatorial therapies and consider the implications of precision medicine in this context.

Simultaneous Loss of Both Atypical Protein Kinase C Genes in the Intestinal Epithelium Drives Serrated Intestinal Cancer by Impairing Immunosurveillance

Serrated adenocarcinoma, an alternative pathway for colorectal cancer (CRC) development, accounts for 15%-30% of all CRCs and is aggressive and treatment resistant. We show that the expression of atypical protein kinase C ζ (PKCζ) and PKCλ/ι was reduced in human serrated tumors. Simultaneous inactivation of the encoding genes in the mouse intestinal epithelium resulted in spontaneous serrated tumorigenesis that progressed to advanced cancer with a strongly reactive and immunosuppressive stroma. Whereas epithelial PKCλ/ι deficiency led to immunogenic cell death and the infiltration of CD8⁺ T cells, which repressed tumor initiation, PKCζ loss impaired interferon and CD8⁺ T cell responses, which resulted in tumorigenesis. Combined treatment with a TGF-β receptor inhibitor plus anti-PD-L1 checkpoint blockade showed synergistic curative activity. Analysis of human samples supported the relevance of these kinases in the immunosurveillance defects of human serrated CRC. These findings provide insight into avenues for the detection and treatment of this poor-prognosis subtype of CRC.

Determinants of metastatic competency in colorectal cancer

Colorectal cancer (CRC) is one of the most common cancer types and represents a major therapeutic challenge. Although initial events in colorectal carcinogenesis are relatively well characterized and treatment for early‐stage disease has significantly improved over the last decades, the mechanisms underlying metastasis – the main cause of death – remain poorly understood. Correspondingly, no effective therapy is currently available for advanced or metastatic disease. There is increasing evidence that colorectal cancer is hierarchically organized and sustained by cancer stem cells, in concert with various stromal cell types. Here, we review the interplay between cancer stem cells and their microenvironment in promoting metastasis and discuss recent insights relating to both patient prognosis and novel targeted treatment strategies. A better understanding of these topics may aid the prevention or reduction of metastatic burden.

Stromal gene expression defines poor-prognosis subtypes in colorectal cancer

Recent molecular classifications of colorectal cancer (CRC) based on global gene expression profiles have defined subtypes displaying resistance to therapy and poor prognosis. Upon evaluation of these classification systems, we discovered that their predictive power arises from genes expressed by stromal cells rather than epithelial tumor cells. Bioinformatic and immunohistochemical analyses identify stromal markers that associate robustly with disease relapse across the various classifications. Functional studies indicate that cancer-associated fibroblasts (CAFs) increase the frequency of tumor-initiating cells, an effect that is dramatically enhanced by transforming growth factor (TGF)-β signaling. Likewise, we find that all poor-prognosis CRC subtypes share a gene program induced by TGF-β in tumor stromal cells. Using patient-derived tumor organoids and xenografts, we show that the use of TGF-β signaling inhibitors to block the cross-talk between cancer cells and the microenvironment halts disease progression.

Immunostaining Protocol: P-Stat3 (Xenograft and Mice)

We sought to understand the mechanisms behind the potent effect of stromal TGF-beta program on the capacity of colorectal cancer (CRC) cells to initiate metastasis. We discovered that mice subcutaneous tumors and metastases generated in the context of a TGF-beta activated microenvironment displayed prominent accumulation of p-STAT3 in CRC cells compared with those derived from control cells. STAT3 signaling depended on GP130 as shown by strong reduction of epithelial p STAT3 levels upon GP130 shRNA-mediated knockdown in CRC cells.

TGF-beta in CAF-mediated tumor growth and metastasis

TGF-beta signaling is one of the major pathways controlling cell and tissue behavior not only in homeostasis but also in disease. During tumorigenesis TGF-beta orchestrated processes are key due to its dual role as tumor suppressor and tumor promoter. Important functions of this pathway have been described in a context-dependent manner both in epithelial cancer cells and in the tumor microenvironment during tumor progression. Carcinoma-associated fibroblasts (CAFs) are one of the most abundant stromal cell types in virtually all solid tumors. CAFs favor malignant progression by providing cancer cells with proliferative, migratory, survival and invasive capacities. A complex network of signaling pathways underlying their tumor-promoting properties is beginning to take shape. In this review, we examine current evidence on the emerging mechanisms involving TGF-beta in CAF-mediated cancer progression, and discuss their potential as therapeutic targets.

Long range epigenetic silencing is a trans-species mechanism that results in cancer specific deregulation by overriding the chromatin domains of normal cells

DNA methylation and chromatin remodeling are frequently implicated in the silencing of genes involved in carcinogenesis. Long Range Epigenetic Silencing (LRES) is a mechanism of gene inactivation that affects multiple contiguous CpG islands and has been described in different human cancer types. However, it is unknown whether there is a coordinated regulation of the genes embedded in these regions in normal cells and in early stages of tumor progression. To better characterize the molecular events associated with the regulation and remodeling of these regions we analyzed two regions undergoing LRES in human colon cancer in the mouse model. We demonstrate that LRES also occurs in murine cancer in vivo and mimics the molecular features of the human phenomenon, namely, downregulation of gene expression, acquisition of inactive histone marks, and DNA hypermethylation of specific CpG islands. The genes embedded in these regions showed a dynamic and autonomous regulation during mouse intestinal cell differentiation, indicating that, in the framework considered here, the coordinated regulation in LRES is restricted to cancer. Unexpectedly, benign adenomas in Apc(Min/+) mice showed overexpression of most of the genes affected by LRES in cancer, which suggests that the repressive remodeling of the region is a late event. Chromatin immunoprecipitation analysis of the transcriptional insulator CTCF in mouse colon cancer cells revealed disrupted chromatin domain boundaries as compared with normal cells. Malignant regression of cancer cells by in vitro differentiation resulted in partial reversion of LRES and gain of CTCF binding. We conclude that genes in LRES regions are plastically regulated in cell differentiation and hyperproliferation, but are constrained to a coordinated repression by abolishing boundaries and the autonomous regulation of chromatin domains in cancer cells.

Dependency of colorectal cancer on a TGF-β-driven program in stromal cells for metastasis initiation

A large proportion of colorectal cancers (CRCs) display mutational inactivation of the TGF-β pathway, yet, paradoxically, they are characterized by elevated TGF-β production. Here, we unveil a prometastatic program induced by TGF-β in the microenvironment that associates with a high risk of CRC relapse upon treatment. The activity of TGF-β on stromal cells increases the efficiency of organ colonization by CRC cells, whereas mice treated with a pharmacological inhibitor of TGFBR1 are resilient to metastasis formation. Secretion of IL11 by TGF-β-stimulated cancer-associated fibroblasts (CAFs) triggers GP130/STAT3 signaling in tumor cells. This crosstalk confers a survival advantage to metastatic cells. The dependency on the TGF-β stromal program for metastasis initiation could be exploited to improve the diagnosis and treatment of CRC.

Rac1 acts in conjunction with Nedd4 and dishevelled-1 to promote maturation of cell-cell contacts

The Rho-GTPase Rac1 promotes actin polymerization and membrane protrusion that mediate initial contact and subsequent maturation of cell-cell junctions. Here we report that Rac1 associates with the ubiquitin-protein ligase neural precursor cell expressed developmentally down-regulated 4 (Nedd4). This interaction requires the hypervariable C-terminal domain of Rac1 and the WW domains of Nedd4. Activated Rac1 colocalises with endogenous Nedd4 at epithelial cell-cell contacts. Reduction of Nedd4 expression by shRNA results in reduced transepithelial electrical resistance (TER) and concomitant changes in the distribution of adherens and tight junction markers. Conversely, expression of Nedd4 promotes TER, suggesting that Nedd4 cooperates with Rac1 in the induction of junctional maturation. We found that Nedd4, but not Nedd4-2, mediates the ubiquitylation and degradation of the adapter protein dishevelled-1 (Dvl1), the expression of which negatively regulates cell-cell contact. Nedd4-mediated ubiquitylation requires its binding to the C-terminal domain of Dvl1, comprising the DEP domain, and targets an N-terminal lysine-rich region upstream of the Dvl1 DIX domain. We found that endogenous Rac1 colocalises with endogenous Dvl1 in intracellular puncta as well as on cell-cell junctions. Finally, activated Rac1 was found to stimulate Nedd4 activity, resulting in increased ubiquitylation of Dvl1. Together, these data reveal a novel Rac1-dependent signalling pathway that, through Nedd4-mediated ubiquitylation of Dvl1, stimulates the maturation of epithelial cell-cell contacts.

The various roles of ubiquitin in Wnt pathway regulation

Wnt signaling mediates key developmental and homeostatic processes including stem cell maintenance, growth and cell fate specification, cell polarity and migration. Inappropriate activation of Wnt signaling is linked to a range of human disorders, most notably cancer and neurodegenerative diseases. In the Wnt/β-catenin cascade, signaling events converge on the regulation of ubiquitin-mediated degradation of the crucial transcriptional regulator β-catenin. The emerging mechanisms by which ubiquitin modification of proteins controls cellular pathways comprise both proteolytic and nonproteolytic functions. In nonproteolytic functions, ubiquitin acts as a signaling device in the control of protein activity, subcellular localization and complex formation. Here, we review and discuss recent developments that implicate ubiquitin-mediated mechanisms at multiple steps of Wnt pathway activation.

Loss of the tumor suppressor CYLD enhances Wnt/beta-catenin signaling through K63-linked ubiquitination of Dvl

The mechanism by which Wnt receptors transduce signals to activate downstream beta-catenin-mediated target gene transcription remains incompletely understood but involves Frizzled (Fz) receptor-mediated plasma membrane recruitment and activation of the cytoplasmic effector Dishevelled (Dvl). Here, we identify the deubiquitinating enzyme CYLD, the familial cylindromatosis tumor suppressor gene, as a negative regulator of proximal events in Wnt/beta-catenin signaling. Depletion of CYLD from cultured cells markedly enhances Wnt-induced accumulation of beta-catenin and target gene activation. Moreover, we demonstrate hyperactive Wnt signaling in human cylindroma skin tumors that arise from mutations in CYLD. At the molecular level, CYLD interacts with and regulates K63-linked ubiquitination of Dvl. Enhanced ubiquitination of the polymerization-prone DIX domain in CYLD-deficient cells positively links to the signaling activity of Dvl. Together, our results argue that loss of CYLD instigates tumor growth in human cylindromatosis through a mechanism in which hyperubiquitination of polymerized Dvl drives enhancement of Wnt responses.