Experimentally induced liver metastases from colorectal cancer can be prevented by mononuclear phagocyte-mediated monoclonal antibody therapy

Review Article: Drug-Induced Liver Injury Associated With Antibody-Based Therapies in Haematologic Malignancies

BACKGROUND

Drug-induced liver injury (DILI) is a leading cause of liver damage. It is especially prevalent in haematologic malignancies, complicating treatment regimens and posing a risk for severe outcomes such as acute liver failure. Antibody-based therapies have significantly improved treatment outcomes. However, these therapies are increasingly associated with liver injury, posing challenges in clinical management.

AIMS

This review aims to examine the DILI associated with antibody-based therapies in haematologic malignancies, highlighting key mechanisms, risk factors, clinical management strategies, and identifying areas that require further research.

METHODS

We conducted a comprehensive review of the literature on DILI induced by antibody-based therapies, including monoclonal antibodies, antibody-drug conjugates, and T-cell redirecting antibodies, specifically in the context of haematologic malignancies.

RESULTS

DILI associated with antibody-based therapies varies from mild transaminase elevations to severe liver injury. Risk factors include pre-existing liver disease, genetic predisposition, and therapy-specific mechanisms such as immune-mediated liver damage or direct hepatotoxic effects. Current management strategies involve routine liver function monitoring, dose modifications, and therapy discontinuation in severe cases. However, standardised guidelines remain lacking.

CONCLUSIONS

DILI remains a major challenge in the use of antibody-based therapies for haematologic malignancies. While progress has been made in understanding risk factors and management strategies, further research is essential to optimise patient care and balance therapeutic efficacy with liver toxicity risks.

Functional Polarization of Liver Macrophages by Glyco Gold Nanoparticles

Macrophages are crucial drivers of innate immunity. Reprogramming macrophages to a restorative phenotype in cancer or autoimmune diseases can stop their cancer-promoting activity or trigger anti-inflammatory immunity. Glycans have emerged as key components for immunity as they are involved in many pathophysiological disorders. Previous studies have demonstrated that supraphysiological amounts of mannose (Man) or sialic acid (Sia) can inhibit tumor growth and stimulate differentiation of regulatory T cells. Man is known to affect glucose metabolism in glycolysis by competing for the same intracellular transporters and affecting macrophage polarization, whereas Sia alters macrophage differentiation via signaling through Siglec-1. Herein, this work describes a macrophage targeting platform using gold nanoparticles (GNPs) functionalized with Man and Sia monosaccharides which exhibit high liver tropism. A single dose of glyco-GNPs can convert macrophages to a restorative phenotype in two completely different immune environments. Man promotes tumor-associated macrophages toward an antitumorigenic activity in a MC38 liver colorectal cancer model by secretion of TNF-α, IL -1β, and IL -6 in the tumor microenvironment. However, in a proinflammatory environment, as observed in a mouse model of autoimmune disease, primary biliary cholangitis, Man impairs the production of TNF-α, IL-1β, Arg1, and IL-6 cytokines. The results probe the dual role of Man in macrophage repolarization in response to the immune system. This study is a proof-of-concept that demonstrates that nanomedicine using specific glycans designed to target other immune cells such as myeloid cells, are a promising strategy not only against cancer but also against other pathologies such as autoimmune diseases.

Breakthroughs in Cancer Immunotherapy: An Overview of T Cell, NK Cell, Mφ, and DC-Based Treatments

Efforts to treat cancer using chimeric antigen receptor (CAR)-T therapy have made astonishing progress and clinical trials against hematopoietic malignancies have demonstrated their use. However, there are still disadvantages which need to be addressed: high costs, and side effects such as Graft-versus-Host Disease (GvHD) and Cytokine Release Syndrome (CRS). Therefore, recent efforts have been made to harness the properties of certain immune cells to treat cancer-not just T cells, but also natural killer (NK) cells, macrophages (Mφ), dendritic cells (DC), etc. In this paper, we will introduce immune cell-based cellular therapies that use various immune cells and describe their characteristics and their clinical situation. The development of immune cell-based cancer therapy fully utilizing the unique advantages of each and every immune cell is expected to enhance the survival of tumor patients owing to their high efficiency and fewer side effects.

Advancing CAR-based immunotherapies in solid tumors: CAR- macrophages and neutrophils

Macrophages and neutrophils are the main components of the innate immune system and play important roles in promoting angiogenesis, extracellular matrix remodeling, cancer cell proliferation, and metastasis in the tumor microenvironment (TME). They can also be harnessed to mediate cytotoxic tumor killing effects and orchestrate effective anti-tumor immune responses with proper stimulation and modification. Therefore, macrophages and neutrophils have strong potential in cancer immunotherapy. In this review, we briefly outlined the applications of macrophages or neutrophils in adoptive cell therapies, and focused on chimeric antigen receptor (CAR)-engineered macrophages (CAR-Ms) and neutrophils (CAR-Ns). We summarized the construction strategies, the preclinical and clinical studies of CAR-Ms and CAR-Ns. In the end, we briefly discussed the limitations and challenges of CAR-Ms and CAR-Ns, as well as future research directions to extend their applications in treating solid tumors.

Antibody-mediated phagocytosis in cancer immunotherapy

Unconjugated monoclonal antibodies (mAb) have revolutionized the treatment of many types of cancer. Some of these mAbs promote the clearance of malignant cells via direct cytotoxic effects. More recently, antibody-dependent cellular phagocytosis (ADCP) has been appreciated as a major mechanism of action for a number of widely-used mAbs, including anti-CD20 (rituximab, obinutuzumab), anti-HER2 (trazituzumab), and anti-CD38 (daratumumab). However, as a monotherapy these ADCP-inducing mAbs produce insufficient levels of cytotoxicity in vivo and are not curative. As a result, these mAbs are most effectively used in combination therapies. The efficacy of these mAbs is further hampered by the apparent development of drug resistance by many patients. Here we will explore the role of ADCP in cancer immunotherapy and discuss the key factors that could limit the efficacy of ADCP-inducing mAbs in vivo. Finally, we will discuss current insights and approaches being applied to overcome these limitations.

Cancer immunotherapies: A hope for the uncurable?

The use of cancer immunotherapies is not novel but has been used over the decades in the clinic. Only recently have we found the true potential of stimulating an anti-tumor response after the breakthrough of checkpoint inhibitors. Cancer immunotherapies have become the first line treatment for many malignancies at various stages. Nevertheless, the clinical results in terms of overall survival and progression free survival were not as anticipated. Majority of cancer patients do not respond to immunotherapies and the reasons differ. Hence, further improvements for cancer immunotherapies are crucially needed. In the review, we will discuss various forms of cancer immunotherapies that are being tested or already in the clinic. Moreover, we also highlight future directions to improve such therapies.

The role of innate immune cells in the tumor microenvironment and research progress in anti-tumor therapy

Innate immune cells in the tumor microenvironment (TME) mainly include macrophages, neutrophils, natural killer cells, dendritic cells and bone marrow derived suppressor cells. They play an anti-tumor or pro-tumor role by secreting various cytokines, chemokines and other factors, and determine the occurrence and development of tumors. Comprehending the role of innate immune cells in tumorigenesis and progression can help improve therapeutic approaches targeting innate immune cells in the TME, increasing the likelihood of favorable prognosis. In this review, we discussed the cell biology of innate immune cells, their role in tumorigenesis and development, and the current status of innate immune cell-based immunotherapy, in order to provide an overview for future research lines and clinical trials.

Continuous sensing of IFNα by hepatic endothelial cells shapes a vascular antimetastatic barrier

Hepatic metastases are a poor prognostic factor of colorectal carcinoma (CRC) and new strategies to reduce the risk of liver CRC colonization are highly needed. Herein, we used mouse models of hepatic metastatization to demonstrate that the continuous infusion of therapeutic doses of interferon-alpha (IFNα) controls CRC invasion by acting on hepatic endothelial cells (HECs). Mechanistically, IFNα promoted the development of a vascular antimetastatic niche characterized by liver sinusoidal endothelial cells (LSECs) defenestration extracellular matrix and glycocalyx deposition, thus strengthening the liver vascular barrier impairing CRC trans-sinusoidal migration, without requiring a direct action on tumor cells, hepatic stellate cells, hepatocytes, or liver dendritic cells (DCs), Kupffer cells (KCs) and liver capsular macrophages (LCMs). Moreover, IFNα endowed LSECs with efficient cross-priming potential that, along with the early intravascular tumor burden reduction, supported the generation of antitumor CD8+ T cells and ultimately led to the establishment of a protective long-term memory T cell response. These findings provide a rationale for the use of continuous IFNα therapy in perioperative settings to reduce CRC metastatic spreading to the liver.

Liver Colonization by Colorectal Cancer Metastases Requires YAP-Controlled Plasticity at the Micrometastatic Stage

Micrometastases of colorectal cancer can remain dormant for years prior to the formation of actively growing, clinically detectable lesions (i.e., colonization). A better understanding of this step in the metastatic cascade could help improve metastasis prevention and treatment. Here we analyzed liver specimens of patients with colorectal cancer and monitored real-time metastasis formation in mouse livers using intravital microscopy to reveal that micrometastatic lesions are devoid of cancer stem cells (CSC). However, lesions that grow into overt metastases demonstrated appearance of de novo CSCs through cellular plasticity at a multicellular stage. Clonal outgrowth of patient-derived colorectal cancer organoids phenocopied the cellular and transcriptomic changes observed during in vivo metastasis formation. First, formation of mature CSCs occurred at a multicellular stage and promoted growth. Conversely, failure of immature CSCs to generate more differentiated cells arrested growth, implying that cellular heterogeneity is required for continuous growth. Second, early-stage YAP activity was required for the survival of organoid-forming cells. However, subsequent attenuation of early-stage YAP activity was essential to allow for the formation of cell type heterogeneity, while persistent YAP signaling locked micro-organoids in a cellularly homogenous and growth-stalled state. Analysis of metastasis formation in mouse livers using single-cell RNA sequencing confirmed the transient presence of early-stage YAP activity, followed by emergence of CSC and non-CSC phenotypes, irrespective of the initial phenotype of the metastatic cell of origin. Thus, establishment of cellular heterogeneity after an initial YAP-controlled outgrowth phase marks the transition to continuously growing macrometastases.

SIGNIFICANCE

Characterization of the cell type dynamics, composition, and transcriptome of early colorectal cancer liver metastases reveals that failure to establish cellular heterogeneity through YAP-controlled epithelial self-organization prohibits the outgrowth of micrometastases. See related commentary by LeBleu, p. 1870.

An Immunological Perspective of Circulating Tumor Cells as Diagnostic Biomarkers and Therapeutic Targets

Immune modulation is a hallmark of cancer. Cancer-immune interaction shapes the course of disease progression at every step of tumorigenesis, including metastasis, of which circulating tumor cells (CTCs) are regarded as an indicator. These CTCs are a heterogeneous population of tumor cells that have disseminated from the tumor into circulation. They have been increasingly studied in recent years due to their importance in diagnosis, prognosis, and monitoring of treatment response. Ample evidence demonstrates that CTCs interact with immune cells in circulation, where they must evade immune surveillance or modulate immune response. The interaction between CTCs and the immune system is emerging as a critical point by which CTCs facilitate metastatic progression. Understanding the complex crosstalk between the two may provide a basis for devising new diagnostic and treatment strategies. In this review, we will discuss the current understanding of CTCs and the complex immune-CTC interactions. We also present novel options in clinical interventions, targeting the immune-CTC interfaces, and provide some suggestions on future research directions.

Epidermal Growth Factor Receptor as Target for Perioperative Elimination of Circulating Colorectal Cancer Cells

Surgical resection of the tumor is the primary treatment of colorectal cancer patients. However, we previously demonstrated that abdominal surgery promotes the adherence of circulating tumor cells (CTC) in the liver and subsequent liver metastasis development. Importantly, preoperative treatment with specific tumor-targeting monoclonal antibodies (mAb) prevented surgery-induced liver metastasis development in rats. This study investigated whether the epidermal growth factor receptor (EGFR) represents a suitable target for preoperative antibody treatment of colorectal cancer patients undergoing surgery. The majority of patients with resectable colorectal liver metastases were shown to have EGFR + CTCs. Three different anti-EGFR mAbs (cetuximab, zalutumumab, and panitumumab) were equally efficient in the opsonization of tumor cell lines. Additionally, all three mAbs induced antibody-dependent cellular phagocytosis (ADCP) of tumor cells by macrophages at low antibody concentrations in vitro, independent of mutations in EGFR signaling pathways. The plasma of cetuximab-treated patients efficiently opsonized tumor cells ex vivo and induced phagocytosis. Furthermore, neither proliferation nor migration of epithelial cells was affected in vitro, supporting that wound healing will not be hampered by treatment with low anti-EGFR mAb concentrations. These data support the use of a low dose of anti-EGFR mAbs prior to resection of the tumor to eliminate CTCs without interfering with the healing of the anastomosis. Ultimately, this may reduce the risk of metastasis development, consequently improving long-term patient outcome significantly.

Engineered CAR-Macrophages as Adoptive Immunotherapies for Solid Tumors

Cellular immunotherapies represent a promising approach for the treatment of cancer. Engineered adoptive cell therapies redirect and augment a leukocyte’s inherent ability to mount an immune response by introducing novel anti-tumor capabilities and targeting moieties. A prominent example of this approach is the use of T cells engineered to express chimeric antigen receptors (CARs), which have demonstrated significant efficacy against some hematologic malignancies. Despite increasingly sophisticated strategies to harness immune cell function, efficacy against solid tumors has remained elusive for adoptive cell therapies. Amongst cell types used in immunotherapies, however, macrophages have recently emerged as prominent candidates for the treatment of solid tumors. In this review, we discuss the use of monocytes and macrophages as adoptive cell therapies. Macrophages are innate immune cells that are intrinsically equipped with broad therapeutic effector functions, including active trafficking to tumor sites, direct tumor phagocytosis, activation of the tumor microenvironment and professional antigen presentation. We focus on engineering strategies for manipulating macrophages, with a specific focus on CAR macrophages (CAR-M). We highlight CAR design for macrophages, the production of CAR-M for adoptive cell transfer, and clinical considerations for their use in treating solid malignancies. We then outline recent progress and results in applying CAR-M as immunotherapies. The recent development of engineered macrophage-based therapies holds promise as a key weapon in the immune cell therapy armamentarium.

An Experimental Liver Metastasis Mouse Model Suitable for Short and Long-Term Intravital Imaging

The liver is a frequent site of cancer metastasis, but current treatment options for cancer patients with liver metastasis are limited, resulting in poor prognosis. Colonization of the liver by cancer cells is a multistep and temporally controlled process. Investigating this process in biological relevant settings in a dynamic manner may lead to new therapeutic avenues. Experimental mouse models of liver metastasis combined with high-resolution microscopy methods can facilitate study of the mechanisms that underlie the outgrowth of cancer cells in the liver. Intravital imaging can provide information on the behavior of tumor cells in their biological setting, in time frames of hours to days. In this unit, we describe the experimental induction of liver metastasis through administration of cancer cells into mice via mesenteric vein injection. The behavior of these injected cells can then be studied using intravital imaging by surgical exposure or through an abdominal imaging window. The approach is described for use with an upright multiphoton microscope, making it widely applicable. © 2021 The Authors. Current Protocols published by Wiley Periodicals LLC. Basic Protocol 1: Inducing liver metastasis through mesenteric vein injection Basic Protocol 2: Short-term imaging of tumor cells in mouse liver Basic Protocol 3: Long-term imaging of tumor cells in mouse liver using an abdominal imaging window.

Macrophage-Based Approaches for Cancer Immunotherapy

Adoptive cell therapy with genetically modified T cells has generated exciting outcomes in hematologic malignancies, but its application to solid tumors has proven challenging. This gap has spurred the investigation of alternative immune cells as therapeutics. Macrophages are potent immune effector cells whose functional plasticity leads to antitumor as well as protumor function in different settings, and this plasticity has led to notable efforts to deplete or repolarize tumor-associated macrophages. Alternatively, macrophages could be adoptively transferred after ex vivo genetic modification. In this review, we highlight the role of macrophages in solid tumors, the progress made with macrophage-focused immunotherapeutic modalities, and the emergence of chimeric antigen receptor macrophage cell therapy.

Tumor-Associated Macrophages in Human Breast, Colorectal, Lung, Ovarian and Prostate Cancers

Tumor-associated macrophages (TAMs) are major innate immune cells that constitute up to 50% of the cell mass of human tumors. TAMs are highly heterogeneous cells that originate from resident tissue-specific macrophages and from newly recruited monocytes. TAMs' variability strongly depends on cancer type, stage, and intratumor heterogeneity. Majority of TAMs are programmed by tumor microenvironment to support primary tumor growth and metastatic spread. However, TAMs can also restrict tumor growth and metastasis. In this review, we summarized the knowledge about the role of TAMs in tumor growth, metastasis and in the response to cancer therapy in patients with five aggressive types of cancer: breast, colorectal, lung, ovarian, and prostate cancers that are frequently metastasize into distant organs resulting in high mortality of the patients. Two major TAM parameters are applied for the evaluation of TAM correlation with the cancer progression: total amount of TAMs and specific phenotype of TAMs identified by functional biomarkers. We summarized the data generated in the wide range of international patient cohorts on the correlation of TAMs with clinical and pathological parameters of tumor progression including lymphatic and hematogenous metastasis, recurrence, survival, therapy efficiency. We described currently available biomarkers for TAMs that can be measured in patients' samples (tumor tissue and blood). CD68 is the major biomarker for the quantification of total TAM amounts, while transmembrane receptors (stabilin-1, CD163, CD206, CD204, MARCO) and secreted chitinase-like proteins (YKL-39, YKL-40) are used as biomarkers for the functional TAM polarization. We also considered that specific role of TAMs in tumor progression can depend on the localization in the intratumoral compartments. We have made the conclusion for the role of TAMs in primary tumor growth, metastasis, and therapy sensitivity for breast, colorectal, lung, ovarian, and prostate cancers. In contrast to other cancer types, majority of clinical studies indicate that TAMs in colorectal cancer have protective role for the patient and interfere with primary tumor growth and metastasis. The accumulated data are essential for using TAMs as biomarkers and therapeutic targets to develop cancer-specific immunotherapy and to design efficient combinations of traditional therapy and new immunomodulatory approaches.

Plasticity of Lgr5-Negative Cancer Cells Drives Metastasis in Colorectal Cancer

Colorectal cancer stem cells (CSCs) express Lgr5 and display extensive stem cell-like multipotency and self-renewal and are thought to seed metastatic disease. Here, we used a mouse model of colorectal cancer (CRC) and human tumor xenografts to investigate the cell of origin of metastases. We found that most disseminated CRC cells in circulation were Lgr5⁻ and formed distant metastases in which Lgr5⁺ CSCs appeared. This plasticity occurred independently of stemness-inducing microenvironmental factors and was indispensable for outgrowth, but not establishment, of metastases. Together, these findings show that most colorectal cancer metastases are seeded by Lgr5⁻ cells, which display intrinsic capacity to become CSCs in a niche-independent manner and can restore epithelial hierarchies in metastatic tumors.

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The majority of disseminating cells of colorectal cancer are Lgr5⁻

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Lgr5⁻ cancer cells are the main seeds of colorectal cancer metastatic lesions

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Long-term metastatic growth from Lgr5⁻ cells requires appearance of Lgr5⁺ cells

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Lgr5⁻ metastases have the intrinsic capacity to re-establish the cellular hierarchy

Circulating tumor cells in cancer patients: developments and clinical applications for immunotherapy

Cancer metastasis is the leading cause of cancer-related death. Circulating tumor cells (CTCs) are shed into the bloodstream from either primary or metastatic tumors during an intermediate stage of metastasis. In recent years, immunotherapy has also become an important focus of cancer research. Thus, to study the relationship between CTCs and immunotherapy is extremely necessary and valuable to improve the treatment of cancer. In this review, based on the advancements of CTC isolation technologies, we mainly discuss the clinical applications of CTCs in cancer immunotherapy and the related immune mechanisms of CTC formation. In order to fully understand CTC formation, sufficiently and completely understood molecular mechanism based on the different immune cells is critical. This understanding is a promising avenue for the development of effective immunotherapeutic strategies targeting CTCs.

Rat IgG mediated circulatory cell depletion in mice requires mononuclear phagocyte system and is facilitated by complement

Application of exogenous Abs targeting cell surface Ags has been widely used as an experimental approach to induce cell depletion or to inhibit receptor functionality. Moreover, Ab therapy is emerging as one of the mainstream strategies for cancer treatment. Previous studies on the mechanisms of Ab-mediated cell depletion mainly employed Abs from the same species as the research subject. However, there has been a recent trend toward using xenogeneic (cross-species) Abs to achieve cell depletion or block receptor-ligand interactions; with rat Abs used in mice being the most common approach. Considering the molecular differences in Abs from different species, the mechanism(s) of xenogeneic Ab-mediated cell depletion is likely to be different than species-matched Ab supplementation. The current work describes our efforts to identify the mechanism of rat anti-mouse Ly6G (clone: 1A8) mAb mediated depletion of mouse neutrophils. The results showed that neutrophils circulating in the blood but not those in the bone marrow are depleted, and depletion depends on mononuclear phagocyte system, especially liver Kupffer cells that efficiently capture and phagocytize targeted cells. Interestingly, whereas species-matched Ab depletion does not require complement functionality, we found that complement activation significantly facilitates cross-species neutrophil depletion. Finally, we found that some rat mAbs (anti-C5aR, anti-CD11a, anti-CD11b, and anti-VLA4) used to block cell surface receptors also induce cell depletion. Thus, our work strongly recommends controlling for cell depletion effect when using these Abs for receptor blockade purposes.

IgA: Structure, Function, and Developability

Immunoglobulin A (IgA) plays a key role in defending mucosal surfaces against attack by infectious microorganisms. Such sites present a major site of susceptibility due to their vast surface area and their constant exposure to ingested and inhaled material. The importance of IgA to effective immune defence is signalled by the fact that more IgA is produced than all the other immunoglobulin classes combined. Indeed, IgA is not just the most prevalent antibody class at mucosal sites, but is also present at significant concentrations in serum. The unique structural features of the IgA heavy chain allow IgA to polymerise, resulting in mainly dimeric forms, along with some higher polymers, in secretions. Both serum IgA, which is principally monomeric, and secretory forms of IgA are capable of neutralising and removing pathogens through a range of mechanisms, including triggering the IgA Fc receptor known as FcαRI or CD89 on phagocytes. The effectiveness of these elimination processes is highlighted by the fact that various pathogens have evolved mechanisms to thwart such IgA-mediated clearance. As the structure–function relationships governing the varied capabilities of this immunoglobulin class come into increasingly clear focus, and means to circumvent any inherent limitations are developed, IgA-based monoclonal antibodies are set to emerge as new and potent options in the therapeutic arena.

Opportunities and Challenges for Antibodies against Intracellular Antigens

Therapeutic antibodies are one most significant advances in immunotherapy, the development of antibodies against disease-associated MHC-peptide complexes led to the introduction of TCR-like antibodies. TCR-like antibodies combine the recognition of intracellular proteins with the therapeutic potency and versatility of monoclonal antibodies (mAb), offering an unparalleled opportunity to expand the repertoire of therapeutic antibodies available to treat diseases like cancer. This review details the current state of TCR-like antibodies and describes their production, mechanisms as well as their applications. In addition, it presents an insight on the challenges that they must overcome in order to become commercially and clinically validated.

Signal regulatory protein alpha blockade potentiates tumoricidal effects of macrophages on gastroenterological neoplastic cells in syngeneic immunocompetent mice

AIM

Immunotherapies blocking the CD47-SIRPα pathway by targeting CD47 enhance macrophage phagocytosis of neoplastic cells in mouse models. As SIRPα exhibits relatively restricted tissue expression, SIRPα antagonists may be better tolerated than agents targeting CD47, which is ubiquitously expressed in many tissues. Here, we investigated the therapeutic impact of monoclonal antibodies (mAbs) against CD47 and/or SIRPα on gastroenterological tumors in syngeneic immunocompetent mouse models.

METHODS

We used in vitro and in vivo phagocytosis assays in C57BL/6J (B6) mice to investigate anti-CD47/SIRPα mAb effects on Hepa1-6 and CMT93 originating from B6 mice. The influence of these mAbs on macrophage transmigration was also assessed. To investigate anti-SIRPα mAb therapy-induced inhibitory effects on sporadic colon cancer growth, we used a CDX2P9.5-NLS Cre;APC + /FLOX (CPC-APC) mouse model.

RESULTS

Systemic anti-SIRPα mAb administration significantly increased Hepa1-6 and CMT93 cell susceptibility to macrophage phagocytosis, both in vitro and in vivo. Conversely, similarly administered anti-CD47 mAb did not promote macrophage phagocytosis of target cells, whereas cells incubated with anti-CD47 mAb prior to inoculation were more susceptible to macrophage phagocytosis. In vitro cell migration assays revealed that binding with anti-CD47 mAb inhibited macrophage transmigration. Anti-SIRPα mAb treatment inhibited tumor progression in CPC-APC mice and significantly improved overall survival. Anti-CD47 mAb administration in vivo eliminated the phagocytosis-promoting CD47 blockade effect, probably by inhibiting macrophage transmigration/chemotaxis. In contrast, anti-SIRPα mAb exhibited enhanced macrophage phagocytic activity and marked anti-tumor effects against gastroenterological malignancies.

CONCLUSION

SIRPα mAb augmentation of macrophage phagocytic activity may represent an effective treatment strategy for human gastrointestinal tumors.

Monoclonal antibody-mediated killing of tumour cells by neutrophils

Neutrophils represent the most abundant population of circulating cytotoxic effector cells. Moreover, their number can be easily increased by treatment with granulocyte-colony stimulating factor or granulocyte macrophage-colony stimulating factor, without the need for ex vivo expansion. Because neutrophils express Fc receptors, they have the potential to act as effector cells during monoclonal antibody therapy of cancer. Additionally, as neutrophils play a role in the regulation of adaptive immune responses, exploiting neutrophils in mAb therapy may result in long-term antitumour immunity. There is limited evidence that neutrophils play a prominent role in current immunoglobulin G-based immunotherapy. However, as IgA induces neutrophil recruitment, novel therapeutic strategies that aim to target the IgA Fc receptor FcαRI may fully unleash the potential of enlisting neutrophils as cytotoxic effector cells in antibody therapy of cancer.

The role of hepatic macrophages in liver metastasis

The liver is a major target organ for metastasis of both gastrointestinal and extra-gastrointestinal cancers. Due to its frequently inoperable nature, liver metastasis represents a leading cause of cancer-associated death worldwide. In the past years, the pivotal role of the immune system in this process is being increasingly recognised. In particular, the role of the hepatic macrophages, both recruited monocyte-derived macrophages (Mo-Mfs) and tissue-resident Kupffer cells (KCs), has been shown to be more versatile than initially imagined. However, the lack of tools to easily distinguish between these two macrophage populations has hampered the assignment of particular functionalities to specific hepatic macrophage subsets. In this Review, we highlight the most remarkable findings regarding the origin and functions of hepatic macrophage populations, and we provide a detailed description of their distinct roles in the different phases of the liver metastatic process.

Redox control of cancer cell destruction

Redox regulation has been proposed to control various aspects of carcinogenesis, cancer cell growth, metabolism, migration, invasion, metastasis and cancer vascularization. As cancer has many faces, the role of redox control in different cancers and in the numerous cancer-related processes often point in different directions. In this review, we focus on the redox control mechanisms of tumor cell destruction. The review covers the tumor-intrinsic role of oxidants derived from the reduction of oxygen and nitrogen in the control of tumor cell proliferation as well as the roles of oxidants and antioxidant systems in cancer cell death caused by traditional anticancer weapons (chemotherapeutic agents, radiotherapy, photodynamic therapy). Emphasis is also put on the role of oxidants and redox status in the outcome following interactions between cancer cells, cytotoxic lymphocytes and tumor infiltrating macrophages.

Immunological considerations underlying heat shock protein-mediated cancer vaccine strategies

The success of active immunotherapies in the prevention of many infectious diseases over the course of over 200 years has lead scientists to wonder if the same principles could be applied to cancer. Antigen-specific active immunotherapies for the treatment of cancer have been researched for over two decades, however, the overwhelming majority of these studies have failed to stimulate robust clinical responses. It is clear that current active immunotherapy research should incorporate methods to increase the immunostimulatory capacity of these therapies. To directly address this need, we propose the addition of the immunostimulatory heat shock proteins (HSPs) to active immunotherapeutic strategies to augment their efficacy. Heat shock proteins are a family of highly conserved intracellular chaperone proteins, and are the most abundant family proteins inside cells. This ubiquity, and their robust immunostimulatory capacity, points to their importance in regulation of intracellular processes and, therefore, indicators of loss of cellular integrity if found extracellularly. Thus, we emphasize the importance of taking into consideration the location of vaccine-derived HSP/tumor-antigen complexes when designing active immunotheraputic strategies.

Impact of Depleting Therapeutic Monoclonal Antibodies on the Host Adaptive Immunity: A Bonus or a Malus?

Clinical responses to anti-tumor monoclonal antibody (mAb) treatment have been regarded for many years only as a consequence of the ability of mAbs to destroy tumor cells by innate immune effector mechanisms. More recently, it has also been shown that anti-tumor antibodies can induce a long-lasting anti-tumor adaptive immunity, likely responsible for durable clinical responses, a phenomenon that has been termed the vaccinal effect of antibodies. However, some of these anti-tumor antibodies are directed against molecules expressed both by tumor cells and normal immune cells, in particular lymphocytes, and, hence, can also strongly affect the host adaptive immunity. In addition to a delayed recovery of target cells, lymphocyte depleting-mAb treatments can have dramatic consequences on the adaptive immune cell network, its rebound, and its functional capacities. Thus, in this review, we will not only discuss the mAb-induced vaccinal effect that has emerged from experimental preclinical studies and clinical trials but also the multifaceted impact of lymphocytes-depleting therapeutic antibodies on the host adaptive immunity. We will also discuss some of the molecular and cellular mechanisms of action whereby therapeutic mAbs induce a long-term protective anti-tumor effect and the relationship between the mAb-induced vaccinal effect and the immune response against self-antigens.

Human IgG3 with extended half-life does not improve Fc-gamma receptor-mediated cancer antibody therapies in mice

Background

Current anti-cancer therapeutic antibodies that are used in the clinic are predominantly humanized or fully human immunoglobulin G1 (IgG1). These antibodies bind with high affinity to the target antigen and are efficient in activating the immune system via IgG Fc receptors and/or complement. In addition to IgG1, three more isotypes are present in humans, of which IgG3 has been found to be superior compared to human IgG1 in inducing antibody dependent cell cytotoxicity (ADCC), phagocytosis or activation of complement in some models. Nonetheless, no therapeutic human IgG3 mAbs have been developed due to the short in vivo half-life of most known IgG3 allotypes. In this manuscript, we compared the efficacy of V-gene matched IgG1 and IgG3 anti-tumour mAb (TA99) in mice, using natural variants of human IgG3 with short- or long half-life, differing only at position 435 with an arginine or histidine, respectively.

Results

In vitro human IgG1 and IgG3 did not show any differences in opsonisation ability of B16F10-gp75 mouse melanoma cells. IgG1, however, was superior in inducing phagocytosis of tumour cells by mouse macrophages. Similarly, in a mouse peritoneal metastasis model we did not detect an improved effect of IgG3 in preventing tumour outgrowth. Moreover, replacing the arginine at position 435 for a histidine in IgG3 to enhance half-life did not result in better suppression of tumour outgrowth compared to wild type IgG3 when injected prior to tumour cell injection.

Conclusion

In conclusion, human IgG3 does not have improved therapeutic efficacy compared to human IgG1 in a mouse tumour model.

Genetic dissection of colorectal cancer progression by orthotopic transplantation of engineered cancer organoids

In the adenoma-carcinoma sequence, it is proposed that intestinal polyps evolve through a set of defined mutations toward metastatic colorectal cancer (CRC). Here, we dissect this adenoma-carcinoma sequence in vivo by using an orthotopic organoid transplantation model of human colon organoids engineered to harbor different CRC mutation combinations. We demonstrate that sequential accumulation of oncogenic mutations in Wnt, EGFR, P53, and TGF-β signaling pathways facilitates efficient tumor growth, migration, and metastatic colonization. We show that reconstitution of specific niche signals can restore metastatic growth potential of tumor cells lacking one of the oncogenic mutations. Our findings imply that the ability to metastasize-i.e., to colonize distant sites-is the direct consequence of the loss of dependency on specific niche signals.

The many faces of FcγRI: implications for therapeutic antibody function

Fcγ receptor I (FcγRI or CD64) is the sole human Fc receptor with high affinity for monovalent IgG. While it contains an immunoreceptor tyrosine-based activation motif in its cytoplasmic domain, binding of FcγRI can result in a complex array of activating and inhibitory outcomes. For instance, binding of monomeric IgG provides a low-intensity tonic signal through FcγRI that is necessary for full interferon γ receptor signaling in the same cell. Interaction of FcγRI with larger high-avidity complexes can result in phagocytosis, the generation of reactive oxygen species, as well as the synthesis and release of inflammatory cytokines. However, numerous reports also document potent anti-inflammatory effects brought about by FcγRI engagement with immune complexes such as the inhibition of IFNγ and TLR4 signaling, and secretion of interleukin-10. This has led to conflicting hypotheses regarding the function of FcγRI, especially with regard to its role in the efficacy of several therapeutic monoclonal antibodies. While many of these issues are still unclear, continued characterization of the regulation and context dependence of FcγRI function, as well as the molecular mechanisms responsible for these various outcomes, will improve our understanding of FcγRI biology as well as the therapeutic strategies designed to harness or constrain its actions.

Antibody-Dependent Phagocytosis of Tumor Cells by Macrophages: A Potent Effector Mechanism of Monoclonal Antibody Therapy of Cancer

Nowadays, it is impossible to imagine modern cancer treatment without targeted therapies, such as mAbs, that bind to tumor-associated antigens. Subsequently, mAbs can use a wide range of effector functions that mostly engage the immune system. mAbs can bridge immune effector cells with tumor cells, which can result in antibody-dependent cytotoxicity. Increasing evidence, however, identified macrophages as prominent effector cells and induction of antibody-dependent cell phagocytosis as one of the primary mechanisms of action mediated by mAbs. Macrophages are extremely effective in eliminating tumor cells from the circulation. Several immunosuppressive mechanisms may, however, hamper their function, particularly in solid malignancies. In this review, we discuss the evolving insight of macrophages as effector cells in mAb therapy and address novel (co)therapeutic strategies that may be used to fully unleash their cytotoxic capacity for the treatment of cancer.

Macrophages are critical effectors of antibody therapies for cancer

Macrophages are innate immune cells that derive from circulating monocytes, reside in all tissues, and participate in many states of pathology. Macrophages play a dichotomous role in cancer, where they promote tumor growth but also serve as critical immune effectors of therapeutic antibodies. Macrophages express all classes of Fcγ receptors, and they have immense potential to destroy tumors via the process of antibody-dependent phagocytosis. A number of studies have demonstrated that macrophage phagocytosis is a major mechanism of action of many antibodies approved to treat cancer. Consequently, a number of approaches to augment macrophage responses to therapeutic antibodies are under investigation, including the exploration of new targets and development of antibodies with enhanced functions. For example, the interaction of CD47 with signal-regulatory protein α (SIRPα) serves as a myeloid-specific immune checkpoint that limits the response of macrophages to antibody therapies, and CD47-blocking agents overcome this barrier to augment phagocytosis. The response of macrophages to antibody therapies can also be enhanced with engineered Fc variants, bispecific antibodies, or antibody-drug conjugates. Macrophages have demonstrated success as effectors of cancer immunotherapy, and further investigation will unlock their full potential for the benefit of patients.

The delicate balance of macrophages in colorectal cancer; their role in tumour development and therapeutic potential

Most tumours are heavily infiltrated by immune cells. This has been correlated with either a good or a bad patient prognosis, depending on the (sub) type of immune cells. Macrophages represent one of the most prominent leukocyte populations in the majority of tumours. Functions of macrophages range from cytotoxicity, to stimulation of tumour growth by secretion of cytokines, growth and angiogenic factors, or suppressing immune responses. In most tumours macrophages are described as cells with immune suppressing, and wound healing properties, which aids tumour development. Yet, increasing evidence shows that macrophages are potent inhibitors of tumour growth in colorectal cancer. Macrophages in this respect show high plasticity. The presence of high macrophage numbers in the tumour may therefore become advantageous, if cells can be reprogrammed from tumour promoting macrophages into potent effector cells. Enhancing cytotoxic properties of macrophages by microbial products, pro-inflammatory cytokines or monoclonal antibody therapy are promising possibilities, and are currently tested in clinical trials.

T cell receptor mimic antibodies for cancer therapy

The major hurdle to the creation of cancer-specific monoclonal antibodies (mAb) exhibiting limited cross-reactivity with healthy human cells is the paucity of known tumor-specific or mutated protein epitopes expressed on the cancer cell surface. Mutated and overexpressed oncoproteins are typically cytoplasmic or nuclear. Cells can present peptides from these distinguishing proteins on their cell surface in the context of human leukocyte antigen (HLA). T cell receptor mimic (TCRm) mAb can be discovered that react specifically to these complexes, allowing for selective targeting of cancer cells. The state-of-the-art for TCRm and the challenges and opportunities are discussed. Several such TCRm are moving toward clinical trials now.

Kupffer cells decrease metastasis of colon cancer cells to the liver in the early stage

Although Kupffer cells (KCs) play an important role in the liver's immune response, their role in colon cancer metastasis to the liver is unclear. We here analyzed the relationship between KCs and tumor cells (TCs) in colon cancer metastasis to the liver. Fischer 344 (F344) rats were divided into control group (KC+ group) and KC elimination group (KC‑ group), in which KC elimination was induced by Cl2MDP liposome injection. RCN‑H4 colon cancer cells were injected into the rats of both groups, and the relationship between the two types of cells was observed by intravital microscopy (IVM) for 6 h. Moreover, to investigate the effect of KCs on liver metastasis formation, KCs were eliminated at different time points before and after the TC injection. The number of metastatic nodules 2 weeks after the injection was evaluated. In the KC‑ group, IVM revealed that the number of adherent TCs had increased 1.5‑fold at 6 h after the TC injection as compared with in the KC+ group. Moreover, in the KC+ group, 74% of the TCs adhered to the KCs, and KC activation and KC phagocytosis of the TCs were observed. Two weeks after the injection, the number of metastatic nodules was significantly increased in rats in which the KCs had been eliminated before the injection, but not in rats in which the KCs had been eliminated after the injection. KC activation and KC phagocytosis of TCs decreased colon cancer cell metastasis to the liver.

Macrophages eliminate circulating tumor cells after monoclonal antibody therapy

The use of monoclonal antibodies (mAbs) as therapeutic tools has increased dramatically in the last decade and is now one of the mainstream strategies to treat cancer. Nonetheless, it is still not completely understood how mAbs mediate tumor cell elimination or the effector cells that are involved. Using intravital microscopy, we found that antibody-dependent phagocytosis (ADPh) by macrophages is a prominent mechanism for removal of tumor cells from the circulation in a murine tumor cell opsonization model. Tumor cells were rapidly recognized and arrested by liver macrophages (Kupffer cells). In the absence of mAbs, Kupffer cells sampled tumor cells; however, this sampling was not sufficient for elimination. By contrast, antitumor mAb treatment resulted in rapid phagocytosis of tumor cells by Kupffer cells that was dependent on the high-affinity IgG-binding Fc receptor (FcγRI) and the low-affinity IgG-binding Fc receptor (FcγRIV). Uptake and intracellular degradation were independent of reactive oxygen or nitrogen species production. Importantly, ADPh prevented the development of liver metastases. Tumor cell capture and therapeutic efficacy were lost after Kupffer cell depletion. Our data indicate that macrophages play a prominent role in mAb-mediated eradication of tumor cells. These findings may help to optimize mAb therapeutic strategies for patients with cancer by helping us to aim to enhance macrophage recruitment and activity.

Fc receptor-dependent mechanisms of monoclonal antibody therapy of cancer

Targeted therapies like treatment with monoclonal antibodies (mAbs) have entered the arsenal of modern anticancer drugs. mAbs combine specificity with multiple effector functions that can lead to reduction of tumour burden. Direct mechanisms of action, including induction of apoptosis or growth inhibition, depend on the biology of the target antigen. Fc tails of mAbs have furthermore the potential to initiate complement-dependent lysis as well as immune effector cell-mediated tumour cell killing via binding to Fc receptors. Natural killer cells can induce apoptosis via antibody-dependent cellular cytotoxicity (ADCC), whereas macrophages are able to phagocytose mAb-opsonized tumour cells (antibody-dependent cellular phagocytosis; ADCP). Finally, neutrophils can induce non-apoptotic tumour cell death, especially in the presence of immunoglobulin A (IgA) antitumour mAbs. In spite of promising clinical successes in some malignancies, improvement of mAb immunotherapy is required to achieve overall complete remission in cancer patients. New strategies to enhance Fc receptor-mediated mechanisms of action or to overcome the immunosuppressive microenvironment of the tumour in mAb therapy of cancer are therefore currently being explored and will be addressed in this chapter.

BH3-mimetic drugs prevent tumour onset in an orthotopic mouse model of hepatoblastoma

Drug resistance and metastasis remain major challenges in the treatment of high-risk hepatoblastoma (HB) and require the development of alternative therapeutic strategies. Modulation of apoptosis in HB cells enhances the sensitivity of these cells towards various drugs and has been discussed to enforce treatment. We investigated the impact of apoptosis sensitisers, BH3-mimetics, on the interaction between the host and HB to reduce tumour growth and dissemination while enhancing immunity. BH3-mimetics, such as obatoclax and ABT-737, enhanced the apoptosis-inducing effect of TRAIL and TNF-α resistant HB cells (HepT1 and HUH6). Tumour cell migration was inhibited by ABT-737 and more markedly by obatoclax. In an orthotopic model of HB, tumour uptake was reduced when the cells were pretreated with low concentrations of obatoclax. Only 1 of 7 mice developed HB in the liver, compared with an incidence of 0.8 in the control group. In summary, our study showed that apoptosis sensitisers had broader effects on HB cells than expected including migration and susceptibility to cytokines in addition to the known effects on drug sensitization. Sensitising HB to apoptosis may also allow resistant HB to be targeted by immune cells and prevent tumour cell dissemination.

The mechanism of anti-CD20-mediated B cell depletion revealed by intravital imaging

Anti-CD20 Ab therapy has proven successful for treating B cell malignancies and a number of autoimmune diseases. However, how anti-CD20 Abs operate in vivo to mediate B cell depletion is not fully understood. In particular, the anatomical location, the type of effector cells, and the mechanism underlying anti-CD20 therapy remain uncertain. Here, we found that the liver is a major site for B cell depletion and that recirculation accounts for the decrease in B cell numbers observed in secondary lymphoid organs. Using intravital imaging, we established that, upon anti-CD20 treatment, Kupffer cells (KCs) mediate the abrupt arrest and subsequent engulfment of B cells circulating in the liver sinusoids. KCs were also effective in depleting malignant B cells in a model of spontaneous lymphoma. Our results identify Ab-dependent cellular phagocytosis by KCs as a primary mechanism of anti-CD20 therapy and provide an experimental framework for optimizing the efficacy of therapeutic Abs.

Local antitumor effects of intratumoral delivery of rlL-2 loaded sustained-release dextran/PLGA-PLA core/shell microspheres

In this study, we formulated a rIL-2 loaded sustained-release dextran/PLGA-PLA core/shell microsphere, mimicking the paracrine mechanisms of cytokine action, to investigate its local antitumor efficacy. The presented microspheres were formed in two steps: rIL-2 was firstly loaded into dextran particles to keep its bioactivity by a unique method of stabilizing aqueous-aqueous "emulsion"; subsequently, the particles were encapsulated into poly(dl-lactide-co-glycolide)/polylactic acid (PLGA/PLA). A stable sustained release behavior in vitro was achieved for a period of about 25 days. In the subcutaneous colon carcinoma BALB/c mice models, a single dose of microspheres was introtumorally administrated and compared with multiple doses of rIL-2 solution to investigate the long acting effect of microspheres on tumor. The animal experiments showed the local efficacy at tumor site mediated by rIL-2 from a single dose of microspheres was better than that of multiple rIL-2 solution injections. Based on the experimental results, we conclude that rlL-2 loaded sustained-release dextran/PLGA-PLA core/shell microspheres represent a promising approach for local cancer treatment in animals.

Effective cooperation of monoclonal antibody and peptide vaccine for the treatment of mouse melanoma

mAbs binding to tumor-associated surface Ags are therapeutically applied in a range of malignancies. Therapeutic vaccination only recently met with clinical success, and the first cancer vaccine received U.S. Food and Drug Administration approval last year. To improve current protocols, we combined peptide vaccines with mAb to the tyrosinase-related protein (TRP)-1 surface Ag for the treatment of B16F10 skin melanoma. Vaccine formulations with synthetic long peptides failed to elicit strong CD8 T cell responses to self-differentiation Ags gp100 and TRP-2, whereas altered peptide sequences recruited gp100-specific CD8 T cells from the endogenous repertoire with frequencies of 40%. However, these high frequencies were reached too late; large, progressively growing melanomas had already emerged. Addition of the TRP-1-directed mAb TA99 to the treatment protocol mediated eradication of s.c. lesions. The mode of action of the Ab did not depend on complement factor C3 and did not lead to improved Ag presentation and CD8 T cell immunity; rather, it recruited FcγR-bearing innate immune cells during early tumor control, thereby creating a window of time for the generation of protective cellular immunity. These data support the concept of combination therapy, in which passive transfer of mAbs is supplemented with cancer peptide vaccines. Moreover, we advocate that tumor Ag-specific T cell immunity directed against self-proteins can be exploited from the endogenous repertoire.

Prevention of colorectal cancer liver metastasis by exploiting liver immunity via chitosan-TPP/nanoparticles formulated with IL-12

The development of effective therapies for the prevention of colorectal cancer (CRC) liver metastasis is of great importance. Recently, chitosan (CS) nanoparticles have been utilized as carriers of interluekin-12 (IL-12) administered locally to deliver therapeutic proteins and genes. In this study, we encapsulated IL-12 by incorporation using tripolyphosphate (TPP) as the coacervated crosslinking agent to form CS-TPP/IL-12 nanoparticles. We further characterized the association efficiency, rate of release, liver-targeting, and toxicity, which were predominantly dependent on the factors of particle size, zeta potential, pH of solution, and whether or not modified with TPP. Systemic delivery of CS-TPP/IL-12 nanoparticles significantly reduced the number and volume of CRC liver metastasis foci compared to the CS-TPP treated mouse group. Although delivery of IL-12 alone also inhibited the number of CRC liver metastasis observed, further study of the change in hepatic metastasis volume demonstrated no significant differences between the groups treated with CS-TPP or IL-12 alone. Mechanistically, CS-TPP nanoparticles blocked the toxicity of IL-12 and induced infiltration of NK cells and some T cells, which are most likely the effector cells that mediate tumor metastasis inhibition during CS-TPP/IL-12 immunotherapy. The results obtained from this study demonstrate the potential benefit of using chitosan modification technology as a cytokine delivery system for the successful prevention of CRC liver metastasis by exploiting liver immunity.