Depleted polymorphonuclear leukocytes in human metastatic liver reflect an altered immune microenvironment associated with recurrent metastasis

Liver Immunology, Immunotherapy, and Liver Cancers: Time for a Rethink?

The complex immune system of the liver has a major role in tumor surveillance, but also partly explains why current immune therapies are poorly effective against liver cancers. Known primarily for its tolerogenic capacity, the hepatic immune repertoire also comprises diverse populations of armored immune cells with tumor surveillant roles. In healthy people, these work together to successfully identify malignant cells and prevent their proliferation, thus halting tumor formation. When frontline hepatic immune surveillance systems fail, compromised hepatic immunity, driven by obesity, infection, or other pathological factors, allows primary or secondary liver cancers to develop. Tumor growth promotes the normal tolerogenic immunological milieu of the liver, perhaps explaining why current immunotherapies fail to work. This review explores the complex local liver immune system with the hope of identifying potential therapeutic targets needed to best overcome immunological barriers in the liver to create an environment no longer hostile to immunotherapy for the treatment of liver cancer.

Tumor microenvironment conditions that favor vessel co-option in colorectal cancer liver metastases: A theoretical model

Vessel co-option is an alternative strategy by which tumour cells vascularize and gain access to nutrients to support tumour growth, survival and metastasis. In vessel co-option, the cancer cells move towards the pre-existing vasculature and hijack them. Vessel co-option is adopted by a wide range of human tumours including colorectal cancer liver metastases (CRCLM) and is responsible for the effectiveness of treatment in CRCLM. Furthermore, vessel co-option is an intrinsic feature and an acquired mechanism of resistance to anti-angiogenic treatment. In this review, we describe the microenvironment, the molecular players, discovered thus far of co-opting CRCLM lesions and propose a theoretical model. We also highlight key unanswered questions that are critical to improving our understanding of CRCLM vessel co-option and for the development of effective approaches for the treatment of co-opting tumours.

Hepatobiliary surgeons meet immunologists: the case of colorectal liver metastases patients

The burgeoning field of cancer immunology demands a change in the paradigm of cancer patient management. The understanding of the course of a given malignant disease should also include the host immune system as one of the key factors in determining the patient's prognosis. Surgical and medical oncologists need to understand the basic and advanced applications of immunotherapies, which are rapidly evolving, and are nowadays an integral part of the armamentarium for the treatment of cancer patients. In the present work, we review the current knowledge concerning the immune landscape of colorectal cancer (CRC) patients with liver metastases, as recently discovered.

Liver-Derived TGF-β Maintains the EomeshiTbetlo Phenotype of Liver Resident Natural Killer Cells

The adult human liver hosts a complex repertoire of liver resident and transient natural killer (NK) cell populations with diverse phenotypes and functions. Liver resident NK cells are CD56^bright NK cells defined by a unique expression profile of transcription factors and cell surface markers (Eomes^hiTbet^loTIGIT⁺CD69⁺CXCR6⁺CD49e⁻). Despite extensive characterization of the phenotype of liver resident NK cells, it remains unclear how factors within the liver microenvironment induce and maintain this unique phenotype. In this study, we have explored the factors regulating the phenotype of liver resident NK cells. Isolation of healthy liver resident NK cells from donor liver perfusate and in vitro culture results in the gradual loss of the characteristic Tbet^lo phenotype, with the cells increasing Tbet expression significantly at day 7. This phenotypic loss could be halted through the dose-dependent addition of liver conditioned media (LCM), generated from the ex vivo culture of liver biopsies from healthy organ donors. TGF-β, but not IL-10, replicated the Tbet suppressive effects of LCM in both liver resident and peripheral blood NK cells. Furthermore, blocking TGF-β receptor signaling using the inhibitor SB431542, reversed the effect of LCM treatment on liver resident NK cells, causing the loss of tissue resident Eomes^hi Tbet^lo phenotype. Our findings identify liver-derived TGF-β as an important component of the liver microenvironment, which acts to regulate and maintain the phenotype of liver resident NK cells.

Molecularly annotation of mouse avatar models derived from patients with colorectal cancer liver metastasis

Background: Liver is the most common metastatic site in advanced colorectal cancer. Most patients with colorectal cancer liver metastasis (CRLM) do not benefit from current treatment. Patient-derived xenografts (PDXs) with defined molecular signatures are attractive models for preclinical studies. Methods: Successfully established PDXs were evaluated to elucidate their fidelity of patients' biologic characteristics (pathologic, genetic and protein properties, together with chemosensitivity). The genomic variations of PDXs were analyzed by next-generation sequencing to explore the underlying molecular mechanism of metastasis and potential therapeutic targets. Results: CRLM (N=73) showed a significantly higher successful PDX establishment rate than primary specimens (N=26; 76.7% vs. 57.7%). CRLM PDXs recapitulated the pathologic, genetic and protein properties of parental tumors, as well as chemosensitivity. Frequent altered genes in PDXs showed high consistency compared to patients' genomic alterations and were enriched in MAPK, ErbB, cell cycle, focal adhesion pathways for CRLM PDXs, whereas primary tumor-derived PDXs only exhibited genomic variations involving ErbB and cell cycle. The genetic alterations showed high concordance between paired PDXs from primary and metastatic tissues, except for recurrent gene mutations (ARID1A, CDK8, ETV1, STAT5B and WNK3) and common copy number gains in chromosomes 20q (e.g., SRC/AURKA). Several potential drug targets such as KRAS, HER2, and FGFR2 were validated using corresponding inhibitors. Additionally, PDX models could also be used in screening efficient regimens for patients with no druggable alterations. Conclusion: This study has successfully established and validated a large panel of molecularly annotated platforms from patients with CRLM for preclinical studies.

Lactate-Mediated Acidification of Tumor Microenvironment Induces Apoptosis of Liver-Resident NK Cells in Colorectal Liver Metastasis

Colorectal cancer is the third most common malignancy worldwide, with 1.3 million new cases annually. Metastasis to the liver is a leading cause of mortality in these patients. In human liver, metastatic cancer cells must evade populations of liver-resident natural killer (NK) cells with potent cytotoxic capabilities. Here, we investigated how these tumors evade liver NK-cell surveillance. Tissue biopsies were obtained from patients undergoing resection of colorectal liver metastasis (CRLM, n = 18), from the tumor, adjacent tissue, and distal resection margin. The number and phenotype of liver-resident NK cells, at each site, were analyzed by flow cytometry. Tumor-conditioned media (TCM) was generated for cytokine and metabolite quantification and used to treat healthy liver-resident NK cells, isolated from donor liver perfusate during transplantation. Liver-resident NK cells were significantly depleted from CRLM tumors. Healthy liver-resident NK cells exposed to TCM underwent apoptosis in vitro, associated with elevated lactate. Tumor-infiltrating liver-resident NK cells showed signs of mitochondrial stress, which was recapitulated in vitro by treating liver-resident NK cells with lactic acid. Lactic acid induced apoptosis by decreasing the intracellular pH of NK cells, resulting in mitochondrial dysfunction that could be prevented by blocking mitochondrial ROS accumulation. CRLM tumors produced lactate, thus decreasing the pH of the tumor microenvironment. Liver-resident NK cells migrating toward the tumor were unable to regulate intracellular pH resulting in mitochondrial stress and apoptosis. Targeting CRLM metabolism provides a promising therapeutic approach to restoring local NK-cell activity and preventing tumor growth.

Getting TANned: How the tumor microenvironment drives neutrophil recruitment

The directed migration of neutrophils to sites of injury or infection is mediated by complex networks of chemoattractant-receptor signaling cascades. The recent appreciation of neutrophils as active participants in tumor progression and metastasis has drawn attention to a number of chemokine-receptor systems that may drive their recruitment to tumors. However, the dynamic nature of the tumor microenvironment (TME) along with the phenotypic diversity among tumor-associated neutrophils (TANs) call for a more comprehensive approach to understand neutrophil trafficking to tumors. Here, we review recent advances in understanding how guidance cues underlie neutrophil migration to primary and secondary tumor sites. We also discuss how the presence of other myeloid cells, such as functionally diverse subsets of tumor-associated macrophages (TAMs), can further influence neutrophil accumulation in tumors. Finally, we highlight the importance of hypoxia sensing in localizing TAMs and TANs in the tumor niche and provide a cohesive view on how both myeloid cell types shape TME-associated extracellular matrix organization, which in turn contribute to tumor progression.

The Shifting Paradigm of Prognostic Factors of Colorectal Liver Metastases: From Tumor-Centered to Host Immune-Centered Factors

The determinants of prognosis in patients with colorectal liver metastases (CLM) have been traditionally searched among the tumoral factors, either of the primary colorectal tumor or of the CLM. While many different scoring systems have been developed based on those clinic-pathological factors with disparate results, there has been the introduction of genetic biological markers that added a theranostic perspective. More recently, other important elements, such as those factors related to the host immune system, have been proposed as determinants of prognosis of CLM patients. In the present work, we review the current prognostic factors of CLM patients as well as the burgeoning shifting paradigm of prognostication that relies on the host immune system.