Cancer-Associated Myeloid Regulatory Cells

TREM1 activation of myeloid cells promotes antitumor immunity

Myeloid cells in the tumor microenvironment (TME) can exist in immunosuppressive and immunostimulatory states that impede or promote antitumor immunity, respectively. Blocking suppressive myeloid cells or increasing stimulatory cells to enhance antitumor immune responses is an area of interest for therapeutic intervention. Triggering receptor expressed on myeloid cells-1 (TREM1) is a proinflammatory receptor that amplifies immune responses. TREM1 is expressed on neutrophils, subsets of monocytes and tissue macrophages, and suppressive myeloid populations in the TME, including tumor-associated neutrophils, monocytes, and tumor-associated macrophages. Depletion or inhibition of immunosuppressive myeloid cells, or stimulation by TREM1-mediated inflammatory signaling, could be used to promote an immunostimulatory TME. We developed PY159, an afucosylated humanized anti-TREM1 monoclonal antibody with enhanced FcγR binding. PY159 is a TREM1 agonist that induces signaling, leading to up-regulation of costimulatory molecules on monocytes and macrophages, production of proinflammatory cytokines and chemokines, and enhancement of T cell activation in vitro. An antibody against mouse TREM1, PY159m, promoted antitumor efficacy in syngeneic mouse tumor models. These results suggest that PY159-mediated agonism of TREM1 on tumoral myeloid cells can promote a proinflammatory TME and offer a promising strategy for immunotherapy.

Targeting STING Activation by Antigen-Inspired MnO2 Nanovaccines Optimizes Tumor Radiotherapy

Immune checkpoint blockers therapy can improve the radiotherapy-induced immunosuppression by enhancing interferon secretion, but still suffer from low clinical response rate and potential adverse effects. Mn²⁺ -mediated activation of interferon gene stimulator (STING) pathway provides an alternative for combination radioimmunotherapy of tumor. However, it is still a challenge for specific delivery of Mn²⁺ to innate immune cells and targeting activation of STING pathway. Herein, a novel antigen-inspired MnO₂ nanovaccine is fabricated as Mn²⁺ source and functionalized with mannose, enabling it to target innate immune cells to activate the STING pathway. Meanwhile, the release of Mn²⁺ in the intracellular lysosomes can also be for magnetic resonance imaging to monitor the dynamic distribution of nanovaccines in vivo. The targeting activation of STING pathway can enhance radiotherapy-induced immune responses for inhibiting local and distant tumors, and resisting tumor metastasis. The study proposes an optimized radiotherapy strategy through targeting STING activation of antigen-inspired nanovaccines.

Targeting tumor microenvironment for non-small cell lung cancer immunotherapy

The tumor microenvironment (TME) is composed of different cellular and non-cellular elements. Constant interactions between tumor cells and the TME are responsible for tumor initiation, tumor progression, and responses to therapies. Immune cells in the TME can be classified into two broad categories, namely adaptive and innate immunity. Targeting these immune cells has attracted substantial research and clinical interest. Current research focuses on identifying key molecular players and developing targeted therapies. These approaches may offer more efficient ways of treating different cancers. In this review, we explore the heterogeneity of the TME in non-small cell lung cancer, summarize progress made in targeting the TME in preclinical and clinical studies, discuss the potential predictive value of the TME in immunotherapy, and highlight the promising effects of bispecific antibodies in the era of immunotherapy.

Managing the immune microenvironment of osteosarcoma: the outlook for osteosarcoma treatment

Osteosarcoma, with poor survival after metastasis, is considered the most common primary bone cancer in adolescents. Notwithstanding the efforts of researchers, its five-year survival rate has only shown limited improvement, suggesting that existing therapeutic strategies are insufficient to meet clinical needs. Notably, immunotherapy has shown certain advantages over traditional tumor treatments in inhibiting metastasis. Therefore, managing the immune microenvironment in osteosarcoma can provide novel and valuable insight into the multifaceted mechanisms underlying the heterogeneity and progression of the disease. Additionally, given the advances in nanomedicine, there exist many advanced nanoplatforms for enhanced osteosarcoma immunotherapy with satisfactory physiochemical characteristics. Here, we review the classification, characteristics, and functions of the key components of the immune microenvironment in osteosarcoma. This review also emphasizes the application, progress, and prospects of osteosarcoma immunotherapy and discusses several nanomedicine-based options to enhance the efficiency of osteosarcoma treatment. Furthermore, we examine the disadvantages of standard treatments and present future perspectives for osteosarcoma immunotherapy.

Cancer Stem Cell Relationship with Pro-Tumoral Inflammatory Microenvironment

Inflammatory processes and cancer stem cells (CSCs) are increasingly recognized as factors in the development of tumors. Emerging evidence indicates that CSCs are associated with cancer properties such as metastasis, treatment resistance, and disease recurrence. However, the precise interaction between CSCs and the immune microenvironment remains unexplored. Although evasion of the immune system by CSCs has been extensively studied, new research demonstrates that CSCs can also control and even profit from the immune response. This review provides an overview of the reciprocal interplay between CSCs and tumor-infiltrating immune cells, collecting pertinent data about how CSCs stimulate leukocyte reprogramming, resulting in pro-tumor immune cells that promote metastasis, chemoresistance, tumorigenicity, and even a rise in the number of CSCs. Tumor-associated macrophages, neutrophils, Th17 and regulatory T cells, mesenchymal stem cells, and cancer-associated fibroblasts, as well as the signaling pathways involved in these pro-tumor activities, are among the immune cells studied. Although cytotoxic leukocytes have the potential to eliminate CSCs, immune evasion mechanisms in CSCs and their clinical implications are also known. We intended to compile experimental findings that provide direct evidence of interactions between CSCs and the immune system and CSCs and the inflammatory milieu. In addition, we aimed to summarize key concepts in order to comprehend the cross-talk between CSCs and the tumor microenvironment as a crucial process for the effective design of anti-CSC therapies.

CLEC-1 is a death sensor that limits antigen cross-presentation by dendritic cells and represents a target for cancer immunotherapy

Tumors exploit numerous immune checkpoints, including those deployed by myeloid cells to curtail antitumor immunity. Here, we show that the C-type lectin receptor CLEC-1 expressed by myeloid cells senses dead cells killed by programmed necrosis. Moreover, we identified Tripartite Motif Containing 21 (TRIM21) as an endogenous ligand overexpressed in various cancers. We observed that the combination of CLEC-1 blockade with chemotherapy prolonged mouse survival in tumor models. Loss of CLEC-1 reduced the accumulation of immunosuppressive myeloid cells in tumors and invigorated the activation state of dendritic cells (DCs), thereby increasing T cell responses. Mechanistically, we found that the absence of CLEC-1 increased the cross-presentation of dead cell-associated antigens by conventional type-1 DCs. We identified antihuman CLEC-1 antagonist antibodies able to enhance antitumor immunity in CLEC-1 humanized mice. Together, our results demonstrate that CLEC-1 acts as an immune checkpoint in myeloid cells and support CLEC-1 as a novel target for cancer immunotherapy.

New Perspectives on Myeloid-Derived Suppressor Cells and Their Emerging Role in Haematology

Myeloid-derived suppressor cells (MDSCs) are immature cells of myeloid origin that have gained researchers’ attention, as they constitute promising biomarkers and targets for novel therapeutic strategies (i.e., blockage of development, differentiation, depletion, and deactivation) in several conditions, including neoplastic, autoimmune, infective, and inflammatory diseases, as well as pregnancy, obesity, and graft rejection. They are characterised in humans by the typical immunophenotype of CD11b⁺CD33⁺HLA-DR^–/low and immune-modulating properties leading to decreased T-cell proliferation, induction of T-regulatory cells (T-regs), hindering of natural killer (NK) cell functionality, and macrophage M2-polarisation. The research in the field is challenging, as there are still difficulties in defining cell-surface markers and gating strategies that uniquely identify the different populations of MDSCs, and the currently available functional assays are highly demanding. There is evidence that MDSCs display altered frequency and/or functionality and could be targeted in immune-mediated and malignant haematologic diseases, although there is a large variability of techniques and results between different laboratories. This review presents the current literature concerning MDSCs in a clinical point of view in an attempt to trigger future investigation by serving as a guide to the clinical haematologist in order to apply them in the context of precision medicine as well as the researcher in the field of experimental haematology.

Identification of immunophenotypes in esophageal squamous cell carcinoma based on immune gene sets

PURPOSE

Esophageal squamous cell carcinoma (ESCC) is a malignant tumor with high heterogeneity. Research on molecular mechanisms involved in the process of tumor origination and progression is extremely limited to investigating mechanisms of molecular typing for ESCC.

METHODS

After comprehensively analyzing the gene expression profiles in The Cancer Genome Atlas and Gene Expression Omnibus databases, we identified four immunotypes of ESCC (referred to as C1-C4) based on the gene sets of 28 immune cell subpopulations. The discrepancies in prognostic value, clinical features, drug sensitivity, and tumor components between the immunotypes were individually analyzed.

RESULTS

The ranking of immune infiltration is C1 > C4 > C3 > C2. These subtypes are characterized by high and low expression of immune checkpoint proteins, enrichment and insufficiency of immune-related pathways, and differential distribution of immune cell subgroups. Poorer survival was observed in the C1 subtype, which we hypothesized could be caused by an immunosuppressive cell population. Fortunately, C1's susceptibility to anti-PD-1 therapy offers hope for patients with poor prognosis in advanced stages. On the other hand, C4 is sensitive to docetaxel, which may offer novel treatment strategies for ESCC in the future. It is worth noting that immunophenotyping is tightly bound to the abundance of stromal components and stem cells, which could explain the tumor immune escape to some extent. Ultimately, determination of hub genes based on the C1 subtypes provides a reference for the discovery of immunotarget drugs against ESCC.

CONCLUSION

The identification of immunophenotypes in our study provides new therapeutic strategies for patients with ESCC.

Nanoparticle-enhanced radiotherapy synergizes with PD-L1 blockade to limit post-surgical cancer recurrence and metastasis

Cancer recurrence after surgical resection (SR) is a considerable challenge, and the biological effect of SR on the tumor microenvironment (TME) that is pivotal in determining postsurgical treatment efficacy remains poorly understood. Here, with an experimental model, we demonstrate that the genomic landscape shaped by SR creates an immunosuppressive milieu characterized by hypoxia and high-influx of myeloid cells, fostering cancer progression and hindering PD-L1 blockade therapy. To address this issue, we engineer a radio-immunostimulant nanomedicine (IPI549@HMP) capable of targeting myeloid cells, and catalyzing endogenous H₂O₂ into O₂ to achieve hypoxia-relieved radiotherapy (RT). The enhanced RT-mediated immunogenic effect results in postsurgical TME reprogramming and increased susceptibility to anti-PD-L1 therapy, which can suppress/eradicate locally residual and distant tumors, and elicits strong immune memory effects to resist tumor rechallenge. Our radioimmunotherapy points to a simple and effective therapeutic intervention against postsurgical cancer recurrence and metastasis.

Tumor recurrence after surgical resection is associated with a poor clinical outcome. Here the authors design a manganese dioxide-based nanosystem to increase response to radio-immunotherapy by relieving tumor hypoxia and targeting myeloid cells, showing reduced post-surgical cancer recurrence and metastasis.

Engineering ROS-Responsive Bioscaffolds for Disrupting Myeloid Cell-Driven Immunosuppressive Niche to Enhance PD-L1 Blockade-Based Postablative Immunotherapy

The existence of inadequate ablation remains an important cause of treatment failure for loco-regional ablation therapies. Here, using a preclinical model, it is reported that inadequate microwave ablation (iMWA) induces immunosuppressive niche predominated by myeloid cells. The gene signature of ablated tumor presented by transcriptome analyses is highly correlated with immune checkpoint blocking (ICB) resistance. Thus, an in situ scaffold with synergistic delivery of IPI549 and anti-programmed death-ligand 1 blocking antibody (aPDL1) for postablative cancer immunotherapy is designed and engineered, in which IPI549 capable of targeting myeloid cells could disrupt the immunosuppressive niche and subsequently improve ICB-mediated antitumor immune response. Based on five mouse cancer models, it is demonstrated that this biomaterial system (aPDL1&IPI549@Gel) could mimic a "hot" tumor-immunity niche to inhibit tumor progression and metastasis, and protect cured mice against tumor rechallenge. This work enables a new standard-of-care paradigm for the immunotherapy of myeloid cells-mediated "cold" tumors after loco-regional inadequate practices.

Cancer Stem Cells in Ovarian Cancer-A Source of Tumor Success and a Challenging Target for Novel Therapies

Ovarian cancer is the most lethal neoplasm of the female genital organs. Despite indisputable progress in the treatment of ovarian cancer, the problems of chemo-resistance and recurrent disease are the main obstacles for successful therapy. One of the main reasons for this is the presence of a specific cell population of cancer stem cells. The aim of this review is to show the most contemporary knowledge concerning the biology of ovarian cancer stem cells (OCSCs) and their impact on chemo-resistance and prognosis in ovarian cancer patients, as well as to present the treatment options targeted exclusively on the OCSCs. The review presents data concerning the role of cancer stem cells in general and then concentrates on OCSCs. The surface and intracellular OCSCs markers and their meaning both for cancer biology and clinical prognosis, signaling pathways specifically activated in OCSCs, the genetic and epigenetic regulation of OCSCs function including the recent studies on the non-coding RNA regulation, cooperation between OCSCs and the tumor microenvironment (ovarian cancer niche) including very specific environment such as ascites fluid, the role of shear stress, autophagy and metabolic changes for the function of OCSCs, and finally mechanisms of OCSCs escape from immune surveillance, are described and discussed extensively. The possibilities of anti-OCSCs therapy both in experimental settings and in clinical trials are presented, including the recent II phase clinical trials and immunotherapy. OCSCs are a unique population of cancer cells showing a great plasticity, self-renewal potential and resistance against anti-cancer treatment. They are responsible for the progression and recurrence of the tumor. Several completed and ongoing clinical trials have tested different anti-OCSCs drugs which, however, have shown unsatisfactory efficacy in most cases. We propose a novel approach to ovarian cancer diagnosis and therapy.

Targeting Metabolic Pathways of Myeloid Cells Improves Cancer Immunotherapy

Tumor-infiltrating myeloid cells are a prominent pro-tumorigenic immune cell population that limit host anti-tumor immunity and present a significant obstacle for many cancer immunotherapies. Targeting the mechanisms regulating myeloid cell function within the tumor microenvironment may overcome immunotherapy resistance in some cancers. Recent discoveries in the emerging field of immunometabolism reveal that the metabolic profiles of intratumoral myeloid cells are rewired to adapt to the nutrition-limited tumor microenvironment, and this shapes their pro-tumor phenotypes. Interestingly, metabolic modulation can shift these myeloid cells toward the immune-stimulating anti-tumor phenotype. In this review, we will highlight the roles of specific metabolic pathways in the activation and function of myeloid cells, and discuss the therapeutic value of metabolically reprogramming myeloid cells to augment and improve outcomes with cancer immunotherapy.

The antigen-binding moiety in the driver's seat of CARs

Immuno-oncology has been at the forefront of cancer treatment in recent decades. In particular immune checkpoint and chimeric antigen receptor (CAR)-T cell therapy have achieved spectacular results. Over the years, CAR-T cell development has followed a steady evolutionary path, focusing on increasing T cell potency and sustainability, which has given rise to different CAR generations. However, there was less focus on the mode of interaction between the CAR-T cell and the cancer cell; more specifically on the targeting moiety used in the CAR and its specific properties. Recently, the importance of optimizing this domain has been recognized and the possibilities have been exploited. Over the last 10 years-in addition to the classical scFv-based CARs-single domain CARs, natural receptor-ligand CARs, universal CARs and CARs targeting more than one antigen have emerged. In addition, the specific parameters of the targeting domain and their influence on T cell activation are being examined. In this review, we concisely present the history of CAR-T cell therapy, and then expand on various developments in the CAR ectodomain. We discuss different formats, each with their own advantages and disadvantages, as well as the developments in affinity tuning, avidity effects, epitope location, and influence of the extracellular spacer.

Immunotherapy in older patients with hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is one of the most common types of cancer globally and is currently the third leading cause of cancer-related deaths. Recently, immunotherapy using immune checkpoint inhibitors (ICIs) has been shown with encouraging anticancer activity and safety in clinical trials. To reverse the phenomenon of tumours evading immune response, ICIs can be used to stimulate the natural antitumour potential of cancer cells by blocking the relevant checkpoints to activate T cells. However, the components and functions of the immune system may undergo a series of changes with ageing, known as 'immunosenescence,' potentially affecting the antitumour effect and safety of immunotherapy. In the current phase III clinical trials of ICIs including nivolumab, pembrolizumab and atezolizumab, the proportion of patients with HCC older than 65 years in CheckMate 459, KEYNOTE-240 and IMbrave150 is 51%, 58% and 50%, respectively, which is less than 70%-73% of epidemiological investigation. Therefore, the elderly population recruited in clinical trials may not accurately represent the real-world elderly patients with HCC, which affects the extrapolation of the efficacy and safety profile obtained in clinical trials to the elderly population in the real world. This review provides the latest advances in ICIs immuno-treatment available for HCC and relevant information about their therapeutic effects and safety on elderly patients. We discuss the benefits of ICIs for older HCC patients, and relevant recommendations about conducting further clinical trials are proposed for more complete answers to this clinical issue.

Multifaceted Roles of Chemokines and Chemokine Receptors in Tumor Immunity

Simple Summary

Various immune cells are involved in host immune responses to cancer. T-helper (Th) 1 cells, cytotoxic CD8⁺ T cells, and natural killer cells are the major effector cells in anti-tumor immunity, whereas cells such as regulatory T cells and myeloid-derived suppressor cells are negatively involved in anti-tumor immunity. Th2 cells and Th17 cells have been shown to have both pro-tumor and anti-tumor activities. The migratory properties of various immune cells are essential for their function and critically regulated by the chemokine superfamily. In this review, we summarize the roles of various immune cells in tumor immunity and their migratory regulation by the chemokine superfamily. We also assess the therapeutic possibilities of targeting chemokines and chemokine receptors in cancer immunotherapy.

Abstract

Various immune cells are involved in host tumor immune responses. In particular, there are many T cell subsets with different roles in tumor immunity. T-helper (Th) 1 cells are involved in cellular immunity and thus play the major role in host anti-tumor immunity by inducing and activating cytotoxic T lymphocytes (CTLs). On the other hand, Th2 cells are involved in humoral immunity and suppressive to Th1 responses. Regulatory T (Treg) cells negatively regulate immune responses and contribute to immune evasion of tumor cells. Th17 cells are involved in inflammatory responses and may play a role in tumor progression. However, recent studies have also shown that Th17 cells are capable of directly inducting CTLs and thus may promote anti-tumor immunity. Besides these T cell subsets, there are many other innate immune cells such as dendritic cells (DCs), natural killer (NK) cells, and myeloid-derived suppressor cells (MDSCs) that are involved in host immune responses to cancer. The migratory properties of various immune cells are critical for their functions and largely regulated by the chemokine superfamily. Thus, chemokines and chemokine receptors play vital roles in the orchestration of host immune responses to cancer. In this review, we overview the various immune cells involved in host responses to cancer and their migratory properties regulated by the chemokine superfamily. Understanding the roles of chemokines and chemokine receptors in host immune responses to cancer may provide new therapeutic opportunities for cancer immunotherapy.

Poliovirus receptor (PVR)-like protein cosignaling network: new opportunities for cancer immunotherapy

Immune checkpoint molecules, also known as cosignaling molecules, are pivotal cell-surface molecules that control immune cell responses by either promoting (costimulatory molecules) or inhibiting (coinhibitory molecules) a signal. These molecules have been studied for many years. The application of immune checkpoint drugs in the clinic provides hope for cancer patients. Recently, the poliovirus receptor (PVR)-like protein cosignaling network, which involves several immune checkpoint receptors, i.e., DNAM-1 (DNAX accessory molecule-1, CD226), TIGIT (T-cell immunoglobulin (Ig) and immunoreceptor tyrosine-based inhibitory motif (ITIM)), CD96 (T cell activation, increased late expression (TACLILE)), and CD112R (PVRIG), which interact with their ligands CD155 (PVR/Necl-5), CD112 (PVRL2/nectin-2), CD111 (PVRL1/nectin-1), CD113 (PVRL3/nectin-3), and Nectin4, was discovered. As important components of the immune system, natural killer (NK) and T cells play a vital role in eliminating and killing foreign pathogens and abnormal cells in the body. Recently, increasing evidence has suggested that this novel cosignaling network axis costimulates and coinhibits NK and T cell activation to eliminate cancer cells after engaging with ligands, and this activity may be effectively targeted for cancer immunotherapy. In this article, we review recent advances in research on this novel cosignaling network. We also briefly outline the structure of this cosignaling network, the signaling cascades and mechanisms involved after receptors engage with ligands, and how this novel cosignaling network costimulates and coinhibits NK cell and T cell activation for cancer immunotherapy. Additionally, this review comprehensively summarizes the application of this new network in preclinical trials and clinical trials. This review provides a new immunotherapeutic strategy for cancer treatment.

Hot or cold: Bioengineering immune contextures into in vitro patient-derived tumor models

In the past decade, immune checkpoint inhibitors (ICI) have proven to be tremendously effective for a subset of cancer patients. However, it is difficult to predict the response of individual patients and efforts are now directed at understanding the mechanisms of ICI resistance. Current models of patient tumors poorly recapitulate the immune contexture, which describe immune parameters that are associated with patient survival. In this Review, we discuss parameters that influence the induction of different immune contextures found within tumors and how engineering strategies may be leveraged to recapitulate these contextures to develop the next generation of immune-competent patient-derived in vitro models.

Beyond Promoter: The Role of Macrophage in Invasion and Progression of Renal Cell Carcinoma

Renal cell carcinoma (RCC) is one of the common urologic neoplasms, and its incidence has been increasing over the past several decades; however, its pathogenesis is still unknown up to now. Recent studies have found that in addition to tumor cells, other cells in the tumor microenvironment also affect the biological behavior of the tumor. Among them, macrophages exist in a large amount in tumor microenvironment, and they are generally considered to play a key role in promoting tumorigenesis. Therefore, we summarized the recent researches on macrophage in the invasiveness and progression of RCC in latest years, and we also introduced and discussed many studies about macrophage in RCC to promote angiogenesis by changing tumor microenvironment and inhibit immune response in order to activate tumor progression. Moreover, macrophage interactes with various cytokines to promote tumor proliferation, invasion and metastasis, and it also promotes tumor stem cell formation and induces drug resistance in the progression of RCC. The highlight of this review is to make a summary of the roles of macrophage in the invasion and progression of RCC; at the same time to raise some potential and possible targets for future RCC therapy.

Distinct Patterns of Myeloid Cell Infiltration in Patients With hrHPV-Positive and hrHPV-Negative Penile Squamous Cell Carcinoma: The Importance of Assessing Myeloid Cell Densities Within the Spatial Context of the Tumor

Comprehensive analysis of tumor infiltrating myeloid cells in the tumor microenvironment of penile squamous cell carcinoma (PSCC) is lacking. In this retrospective study, for the first time, PSCC resection specimens (N = 103) were annotated into the following compartments: intratumoral tumor (IT Tumor), intratumoral stroma (IT Stroma), peritumoral tumor (PT Tumor) and peritumoral stroma (PT Stroma) compartments. We then quantified CD14+, CD68+ and CD163+ myeloid cells within these compartments using an image analysis software and assessed their association with various clinical parameters, including high-risk human papillomavirus (hrHPV) status. In the total cohort, hrHPV status, grade of differentiation, age and tumor size were associated with myeloid cell densities. hrHPV⁺ tumors had higher infiltration rates of CD14+, CD68+ and CD163+ myeloid cells in the IT tumor compartment (p < 0.001, for all) compared to hrHPV^- tumors. Furthermore, when examining the association between compartment-specific infiltration and differentiation grade, increased myeloid cell densities in the IT tumor compartment were associated with a more advanced histological grade (p < 0.001, for all). This association remained significant when the hrHPV^- cohort (N = 60) was analyzed (CD14+ p = 0.001; CD68+ p < 0.001; CD163+ p = 0.004). Subgroup analysis in the hrHPV⁺ group (N = 43) showed that high infiltration rates of CD68+ and CD163+ cells in the PT tumor compartment were associated with lymph node (LN) metastasis (p = 0.031 and p = 0.026, respectively). Regarding the association between myeloid cell densities and disease-specific survival, the risk of death was found to decrease slightly as the number of myeloid cells in the IT tumor compartment increased (CD14+ p = 0.04; CD68+ p = 0.05; CD163+ p = 0.02). However, after adjusting for hrHPV, no independent association between myeloid densities and disease-specific survival were found. Altogether, these findings demonstrate the importance of assessing myeloid cell densities within the spatial context of the tumor. Further studies are needed to unravel the specific phenotype of myeloid cells residing in the different compartments, their effect on clinical parameters and the impact of hrHPV on the recruitment of myeloid cell populations in PSCC.

Epigenetic Modifiers: Anti-Neoplastic Drugs With Immunomodulating Potential

Cancer cells are under the surveillance of the host immune system. Nevertheless, a number of immunosuppressive mechanisms allow tumors to escape protective responses and impose immune tolerance. Epigenetic alterations are central to cancer cell biology and cancer immune evasion. Accordingly, epigenetic modulating agents (EMAs) are being exploited as anti-neoplastic and immunomodulatory agents to restore immunological fitness. By simultaneously acting on cancer cells, e.g. by changing expression of tumor antigens, immune checkpoints, chemokines or innate defense pathways, and on immune cells, e.g. by remodeling the tumor stroma or enhancing effector cell functionality, EMAs can indeed overcome peripheral tolerance to transformed cells. Therefore, combinations of EMAs with chemo- or immunotherapy have become interesting strategies to fight cancer. Here we review several examples of epigenetic changes critical for immune cell functions and tumor-immune evasion and of the use of EMAs in promoting anti-tumor immunity. Finally, we provide our perspective on how EMAs could represent a game changer for combinatorial therapies and the clinical management of cancer.

mRNA in cancer immunotherapy: beyond a source of antigen

mRNA therapeutics have become the focus of molecular medicine research. Various mRNA applications have reached major milestones at high speed in the immuno-oncology field. This can be attributed to the knowledge that mRNA is one of nature's core building blocks carrying important information and can be considered as a powerful vector for delivery of therapeutic proteins to the patient.For a long time, the major focus in the use of in vitro transcribed mRNA was on development of cancer vaccines, using mRNA encoding tumor antigens to modify dendritic cells ex vivo. However, the versatility of mRNA and its many advantages have paved the path beyond this application. In addition, due to smart design of both the structural properties of the mRNA molecule as well as pharmaceutical formulations that improve its in vivo stability and selective targeting, the therapeutic potential of mRNA can be considered as endless.As a consequence, many novel immunotherapeutic strategies focus on the use of mRNA beyond its use as the source of tumor antigens. This review aims to summarize the state-of-the-art on these applications and to provide a rationale for their clinical application.

Tumor Microenvironment Composition and Severe Cytokine Release Syndrome (CRS) Influence Toxicity in Patients with Large B-Cell Lymphoma Treated with Axicabtagene Ciloleucel

PURPOSE

One of the challenges of adoptive T-cell therapy is the development of immune-mediated toxicities including cytokine release syndrome (CRS) and neurotoxicity (NT). We aimed to identify factors that place patients at high risk of severe toxicity or treatment-related death in a cohort of 75 patients with large B-cell lymphoma treated with a standard of care CD19 targeted CAR T-cell product (axicabtagene ciloleucel).

EXPERIMENTAL DESIGN

Serum cytokine and catecholamine levels were measured prior to lymphodepleting chemotherapy, on the day of CAR T infusion and daily thereafter while patients remained hospitalized. Tumor biopsies were taken within 1 month prior to CAR T infusion for evaluation of gene expression.

RESULTS

We identified an association between pretreatment levels of IL6 and life-threatening CRS and NT. Because the risk of toxicity was related to pretreatment factors, we hypothesized that the tumor microenvironment (TME) may influence CAR T-cell toxicity. In pretreatment patient tumor biopsies, gene expression of myeloid markers was associated with higher toxicity.

CONCLUSIONS

These results suggest that a proinflammatory state and an unfavorable TME preemptively put patients at risk for toxicity after CAR T-cell therapy. Tailoring toxicity management strategies to patient risk may reduce morbidity and mortality.

The Role of Tumor-Associated Myeloid Cells in Modulating Cancer Therapy

Myeloid cells include various cellular subtypes that are distinguished into mononuclear and polymorphonuclear cells, derived from either common myeloid progenitor cells (CMPs) or myeloid stem cells. They play pivotal roles in innate immunity since, following invasion by pathogens, myeloid cells are recruited and initiate phagocytosis and secretion of inflammatory cytokines into local tissues. Moreover, mounting evidence suggests that myeloid cells may also regulate cancer development by infiltrating the tumor to directly interact with cancer cells or by affecting the tumor microenvironment. Importantly, mononuclear phagocytes, including macrophages and dendritic cells (DCs), can have either a positive or negative impact on the efficacy of chemotherapy, radiotherapy as well as targeted anti-cancer therapies. Tumor-associated macrophages (TAMs), profusely found in the tumor stroma, can promote resistance to chemotherapeutic drugs, such as Taxol and Paclitaxel, whereas the suppression of TAMs can lead to an improved radiotherapy outcome. On the contrary, the presence of TAMs may be beneficial for targeted therapies as they can facilitate the accumulation of large quantities of nanoparticles carrying therapeutic compounds. Tumor infiltrating DCs, however, are generally thought to enhance cytotoxic therapies, including those using anthracyclines. This review focuses on the role of tumor-infiltrating and stroma myeloid cells in modulating tumor responses to various treatments. We herein report the impact of myeloid cells in a number of therapeutic approaches across a wide range of malignancies, as well as the efforts toward the elimination of myeloid cells or the exploitation of their presence for the enhancement of therapeutic efficacy against cancer.

Friend or Foe? Recent Strategies to Target Myeloid Cells in Cancer

The tumor microenvironment (TME) is a complex network of epithelial and stromal cells, wherein stromal components provide support to tumor cells during all stages of tumorigenesis. Among these stromal cell populations are myeloid cells, which are comprised mainly of tumor-associated macrophages (TAM), dendritic cells (DC), myeloid-derived suppressor cells (MDSC), and tumor-associated neutrophils (TAN). Myeloid cells play a major role in tumor growth through nurturing cancer stem cells by providing growth factors and metabolites, increasing angiogenesis, as well as promoting immune evasion through the creation of an immune-suppressive microenvironment. Immunosuppression in the TME is achieved by preventing critical anti-tumor immune responses by natural killer and T cells within the primary tumor and in metastatic niches. Therapeutic success in targeting myeloid cells in malignancies may prove to be an effective strategy to overcome chemotherapy and immunotherapy limitations. Current therapeutic approaches to target myeloid cells in various cancers include inhibition of their recruitment, alteration of function, or functional re-education to an antitumor phenotype to overcome immunosuppression. In this review, we describe strategies to target TAMs and MDSCs, consisting of single agent therapies, nanoparticle-targeted approaches and combination therapies including chemotherapy and immunotherapy. We also summarize recent molecular targets that are specific to myeloid cell populations in the TME, while providing a critical review of the limitations of current strategies aimed at targeting a single subtype of the myeloid cell compartment. The goal of this review is to provide the reader with an understanding of the critical role of myeloid cells in the TME and current therapeutic approaches including ongoing or recently completed clinical trials.

Influence of Innate Immunity on Cancer Cell Stemness

Even if cancer stem cells (CSCs) represent only a small proportion of the tumor mass, they significantly account for tumor maintenance, resistance to therapies, relapse and metastatic spread, due to their increased capacity of self-renewal, multipotency, tumorigenicity and quiescence. Emerging evidence suggests that the immune contexture within the tumor microenvironment (TME) determines both the response to therapy and the clinical outcome. In this context, CSCs acquire immune evasion skills by editing immune cell functions and sculpting the immunosuppressive landscape of TME. Reciprocally, infiltrating immune cells influence CSCs self-renewal, tumorigenicity and metastasis. In this review, we summarize the immunomodulatory properties of CSCs, as well as the impact of innate immune cells on cancer cells stemness in the different phases of cancer immunoediting process and neoplastic progression.

Breast cancer induces systemic immune changes on cytokine signaling in peripheral blood monocytes and lymphocytes

Background

It is increasingly recognized that cancer progression induces systemic immune changes in the host. Alterations in number and function of immune cells have been identified in cancer patients’ peripheral blood and lymphoid organs. Recently, we found dysregulated cytokine signaling in peripheral blood T cells from breast cancer (BC) patients, even those with localized disease.

Methods

We used phosphoflow cytometry to determine the clinical significance of cytokine signaling responsiveness in peripheral blood monocytes from non-metastatic BC patients at diagnosis. We also examined the correlation between cytokine signaling in peripheral monocytes and the number of tumor-infiltrating macrophages in paired breast tumors.

Findings

Our results show that cytokine (IFNγ) signaling may also be dysregulated in peripheral blood monocytes at diagnosis, specifically in BC patients who later relapsed. Some patients exhibited concurrent cytokine signaling defects in monocytes and lymphocytes at diagnosis, which predict the risk of future relapse in two independent cohorts of BC patients. Moreover, IFNγ signaling negatively correlates with expression of CSF1R on monocytes, thus modulating their ability to infiltrate into tumors.

Interpretation

Our results demonstrate that tumor-induced systemic immune changes are evident in peripheral blood immune cells for both myeloid and lymphoid lineages, and point to cytokine signaling responsiveness as important biomarkers to evaluate the overall immune status of BC patients.

Funding

This study was supported by the Department of Defense Breast Cancer Research Program (BCRP), The V Foundation, Stand Up to Cancer (SU2C), and Breast Cancer Research Foundation (BCRF).

Immune Effects of M51R Vesicular Stomatitis Virus Treatment of Carcinomatosis From Colon Cancer

BACKGROUND

The purpose of this study was to analyze the oncolytic and immunomodulatory functions of an M protein mutant of vesicular stomatitis virus (M51R VSV) in a murine model of peritoneal surface dissemination from colon cancer (PSD from CRC).

METHODS

Luciferase-expressing CT26 peritoneal tumors were established in Balb/c mice to evaluate the impact of M51R VSV treatment on intraperitoneal tumor growth and overall survival. The mice were treated with either intraperitoneal phosphate buffered saline (n = 10) or 5 × 10⁶ PFU M51R VSV (n = 10) at 5 d after tumor implantation. Tumor bioluminescence was measured every 3 d during the 60-day study period. The immunomodulatory effect of M51R VSV treatment was evaluated in mice treated with either intraperitoneal phosphate buffered saline (n = 21) or M51R VSV (n = 21). Peritoneal lavages were collected at days 1, 3, and 7 after M51R VSV treatment for flow cytometry and multiplex cytokine bead analysis.

RESULTS

A single, intraperitoneal treatment with M51R VSV inhibited the growth of PSD from CRC as evidenced by decreased bioluminescence and improved survival. This treatment approach also resulted in significantly higher frequencies of peritoneal CD4+ T (10.95 ± 1.17 versus 6.19 ± 0.44, P = 0.004) and B1b cells (5.01 ± 0.97 versus 2.20 ± 0.2, P = 0.024). On the other hand, treatment with M51R VSV resulted in fewer myeloid-derived suppressor cells relative to controls (10.66 ± 1.48 versus 14.47 ± 1.06, P = 0.035). M51R-treated peritoneal cavities also contained lower concentrations of immunosuppressive monocyte chemoattractant protein-1 and interleukin 6 cytokines relative to controls.

CONCLUSIONS

Our findings suggest that M51R VSV alters the innate and adaptive immune responses in PSD from CRC. Future studies will delineate specific components of antitumor immunity that result in its therapeutic effect.

Acute Lymphoblastic Leukaemia Cells Impair Dendritic Cell and Macrophage Differentiation: Role of BMP4

Dendritic cells and macrophages are common components of the tumour immune microenvironment and can contribute to immune suppression in both solid and haematological cancers. The Bone Morphogenetic Protein (BMP) pathway has been reported to be involved in cancer, and more recently in leukaemia development and progression. In the present study, we analyse whether acute lymphoblastic leukaemia (ALL) cells can affect the differentiation of dendritic cells and macrophages and the involvement of BMP pathway in the process. We show that ALL cells produce BMP4 and that conditioned media from ALL cells promote the generation of dendritic cells with immunosuppressive features and skew M1-like macrophage polarization towards a less pro-inflammatory phenotype. Likewise, BMP4 overexpression in ALL cells potentiates their ability to induce immunosuppressive dendritic cells and favours the generation of M2-like macrophages with pro-tumoral features. These results suggest that BMP4 is in part responsible for the alterations in dendritic cell and macrophage differentiation produced by ALL cells.

Evaluating a Single Domain Antibody Targeting Human PD-L1 as a Nuclear Imaging and Therapeutic Agent

The PD-1:PD-L1 immune checkpoint axis is central in the escape of cancer cells from anticancer immune responses. Monoclonal antibodies (mAbs) specific for PD-L1 have been approved for treatment of various cancer types. Although PD-L1 blockade has proven its merit, there are still several aspects that require further attention to fully capitalize on its potential. One of these is the development of antigen-binding moieties that enable PD-L1 diagnosis and therapy. We generated human PD-L1 binding single domain antibodies (sdAbs) and selected sdAb K2, a sdAb with a high affinity for PD-L1, as a lead compound. SPECT/CT imaging in mice following intravenous injection of Technetium-99m (^99mTc)-labeled sdAb K2 revealed high signal-to-noise ratios, strong ability to specifically detect PD-L1 in melanoma and breast tumors, and relatively low kidney retention, which is a unique property for radiolabeled sdAbs. We further showed using surface plasmon resonance that sdAb K2 binds to the same epitope on PD-L1 as the mAb avelumab, and antagonizes PD-1:PD-L1 interactions. Different human cell-based assays corroborated the PD-1:PD-L1 blocking activity, showing enhanced T-cell receptor signaling and tumor cell killing when PD-1^POS T cells interacted with PD-L1^POS tumor cells. Taken together, we present sdAb K2, which specifically binds to human PD-L1, as a new diagnostic and therapeutic agent in cancer management.

The prognosis of head and neck squamous cell carcinoma related to immunosuppressive tumor microenvironment regulated by IL-6 signaling

Evasion of immune surveillance is a significant factor in head and neck squamous cell carcinoma (HNSCC) carcinogenesis. IL-6 signaling is a critical mechanism for the induction of dysfunctional immune responses. In the present study, we examined the role of IL-6 in the prognosis of HNSCC regarding the immunosuppressive tumor microenvironment. We retrospectively analyzed the clinical outcomes of HNSCC patients and examined its correlation with the levels of IL-6 in tumors and circulating myeloid-derived suppressor cells (MDSCs) in peripheral blood. Furthermore, the relationships between IL and 6, programmed death ligand (PD-L1) expression, and immune response were examined in vitro and in vivo. Our data revealed that IL-6 overexpression was associated with the increased risk of developing disease failure and poor prognosis for HNSCC. The immunoreactivity of IL-6 in HNSCC specimens was positively linked to the staining of PD-L1 and the level of circulating MDSCs. By cellular and animal experiments, there were augmented radiation-induced increases in the expression of PD-L1 and the activation of MDSCs noted in IL-6-positive tumors. When IL-6 signaling was inhibited, the levels of PD-L1 and MDSC recruitment were significantly down-regulated. Furthermore, the neutrophil-to-lymphocyte ratio (NLR) was positively correlated with the levels of IL-6 and PD-L1 in tumor, and circulating MDSCs. In conclusion, IL-6 is a significant predictor of treatment outcome in HNSCC patients, and plays an important role in the induction of immunosuppressive tumor microenvironment mediated by increased MDSCs and PD-L1 expression. Furthermore, IL-6 combined with NLR can assist the clinician to make an informed decision regarding treatment options.

Spatial Mapping of Myeloid Cells and Macrophages by Multiplexed Tissue Staining

An array of phenotypically diverse myeloid cells and macrophages (MC&M) resides in the tumor microenvironment, requiring multiplexed detection systems for visualization. Here we report an automated, multiplexed staining approach, named PLEXODY, that consists of five MC&M-related fluorescently-tagged antibodies (anti - CD68, - CD163, - CD206, - CD11b, and - CD11c), and three chromogenic antibodies, reactive with high- and low-molecular weight cytokeratins and CD3, highlighting tumor regions, benign glands and T cells. The staining prototype and image analysis methods which include a pixel/area-based quantification were developed using tissues from inflamed colon and tonsil and revealed a unique tissue-specific composition of 14 MC&M-associated pixel classes. As a proof-of-principle, PLEXODY was applied to three cases of pancreatic, prostate and renal cancers. Across digital images from these cancer types we observed 10 MC&M-associated pixel classes at frequencies greater than 3%. Cases revealed higher frequencies of single positive compared to multi-color pixels and a high abundance of CD68+/CD163+ and CD68+/CD163+/CD206+ pixels. Significantly more CD68+ and CD163+ vs. CD11b+ and CD11c+ pixels were in direct contact with tumor cells and T cells. While the greatest percentage (~70%) of CD68+ and CD163+ pixels was 0–20 microns away from tumor and T cell borders, CD11b+ and CD11c+ pixels were detected up to 240 microns away from tumor/T cell masks. Together, these data demonstrate significant differences in densities and spatial organization of MC&M-associated pixel classes, but surprising similarities between the three cancer types.

MicroRNA-342 inhibits tumor growth via targeting chemokine CXCL12 involved in macrophages recruitment/activation

MicroRNAs (miRNAs) play important roles in initiation, development, progression and metastasis of tumors. MiR-342 has been reported as a tumor suppressor or an onco-miRNA based on functions or expression changes in various types of cancers. However, the biological roles and underlying molecular mechanisms of miR-342 in tumorigenesis remain largely unknown. Here, we found that miR-342 was expressed significantly less in a murine MS-K tumor cell line that showed riched blood vessels. Over-expression of miR-342 in MS-K cells inhibited cell proliferation, colony formation, reduced frequency of S phase population in vitro and suppressed tumor growth in vivo. Moreover, increasing miR-342 impeded blood vessels formation and accumulation of macrophages (CD11b⁺ ) in tumors. By bioinformatic analysis and dual-luciferase reporter assays, chemokine CXCL12 was identified as a direct target of miR-342. Restored Cxcl12 expression in MS-K-miR-342 cells could rescue cell proliferation in vitro. In MS-K-miR-342 tumor-infiltrated macrophages, expression of proangiogenic genes (Vegf-A and Thbs1) and M2-subtype macrophage markers (Cd163, Dectin1 and Ym1) was significantly down-regulated compared with controls. Moreover, lower level of Cxcl12 and its receptor Cxcr4 was observed in the macrophages of MS-K-miR-342 tumors, and MS-K-miR-342 derived miR-342, but not endogenous miR-342, might contribute to Cxcl12 suppression in TAM. These results suggest that miR-342 is involved in MS-K tumor growth as a tumor suppressor by targeting chemokine CXCL12.

Aging, immune senescence, and immunotherapy: A comprehensive review

The advent of immune checkpoint inhibitors (ICIs) has changed the landscape of cancer treatment. Older adults represent the majority of cancer patients; however, direct data evaluating ICIs in this patient population is lacking. Aging is associated with changes in the immune system known as "immunosenescence" that could impact the efficacy and safety profile of ICIs. In this paper, we review aging-associated changes in the immune system as they may relate to cancer and immunotherapy, with mention of the effect of chronic viral infections and frailty. Furthermore, we summarize the current clinical evidence of ICI effectiveness and toxicity among older adults with cancer.

CD177+ neutrophils suppress epithelial cell tumourigenesis in colitis-associated cancer and predict good prognosis in colorectal cancer

Neutrophils are found to be infiltrated in tumour tissues of patients with colitis-associated cancer (CAC) and colorectal cancer (CRC), and CD177 is mainly expressed in neutrophils. In our study, expression of CD177 in tumour tissues from patients with CAC or CRC was analysed byquantitative real-time polymerase chain reaction, flow cytometry and immunohistochemistry. We recruited 378 patients with CRC, determined CD177 expression in tumours and examined its correlation with clinicopathological features. Moreover, CAC model was induced in wild-type and CD177-/- mice by azoxymethane/dextran sodium sulphate. CD177+ neutrophils were significantly increased in colon tumour tissues from patients with CRC or CAC compared with controls. Expression of CD177 mRNA and percentages of CD177+ neutrophils were also markedly increased in tumour tissues from CRC patients compared with controls. Patients with high density of CD177+ neutrophils had better overall survival and disease-free survival compared with controls. Multivariate analyses revealed that the density of CD177+ neutrophils was an independent factor in predicting overall survival and disease-free survival. Consistently, CD177 depletion aggravated azoxymethane/dextran sodium sulphate-induced CAC in mice. Expression of Ki67 and proliferating cell nuclear antigen was increased in tumour tissues from CD177-/- mice compared with wild-type counterparts. Moreover, CD177-/- neutrophils failed to migrate in response to fMLP[AU: Please expand fMLP, DN, TNM and HIF-1α.] stimulation compared with wild-type controls. Our data indicate that CD177+ neutrophils suppress epithelial cell tumourigenesis and act as an independent factor in predicting the prognosis in patients with CRC. CD177+ neutrophils may serve as a novel therapeutic target in the treatment and predict the prognosis of CAC and CRC.

Diamonds in the Rough: Harnessing Tumor-Associated Myeloid Cells for Cancer Therapy

Therapeutic approaches that engage immune cells to treat cancer are becoming increasingly utilized in the clinics and demonstrated durable clinical benefit in several solid tumor types. Most of the current immunotherapies focus on manipulating T cells, however, the tumor microenvironment (TME) is abundantly infiltrated by a heterogeneous population of tumor-associated myeloid cells, including tumor-associated macrophages (TAMs), tumor-associated dendritic cells (TADCs), tumor-associated neutrophils (TANs), and myeloid-derived suppressor cells (MDSCs). Educated by signals perceived in the TME, these cells often acquire tumor-promoting properties ultimately favoring disease progression. Upon appropriate stimuli, myeloid cells can exhibit cytoxic, phagocytic, and antigen-presenting activities thereby bolstering antitumor immune responses. Thus, depletion, reprogramming or reactivation of myeloid cells to either directly eradicate malignant cells or promote antitumor T-cell responses is an emerging field of interest. In this review, we briefly discuss the tumor-promoting and tumor-suppressive roles of myeloid cells in the TME, and describe potential therapeutic strategies in preclinical and clinical development that aim to target them to further expand the range of current treatment options.

Predictive Value of the Pretreatment Neutrophil-to-Lymphocyte Ratio in Head and Neck Squamous Cell Carcinoma

This study assessed the significance of the neutrophil-to-lymphocyte ratio (NLR) in head and neck squamous cell carcinoma (HNSCC), and the relationships of the NLR with the aldehyde dehydrogenase 1 (ALDH1) level in tumors and the proportion of myeloid-derived suppressor cells (MDSCs) in the peripheral circulation. In total, 227 HNSCC patients who had received curative treatment at our hospital were enrolled into the present study. The NLR of each HNSCC patient before treatment was calculated. The associations of NLR with various clinicopathological parameters and prognoses were then examined. In addition, correlations between the proportion of MDSCs and level of ALDH1 with the NLR were assessed. Our data revealed that an elevated NLR was significantly correlated with the risk of developing locoregional recurrence and with a reduced overall survival in HNSCC patients. Multivariate analyses revealed that the NLR pretreatment and surgical resection were significantly correlated with the rate of treatment failure and the overall survival rate in HNSCC patients. Furthermore, the levels of ALDH1 in tumors and MDSCs in the peripheral circulation were significantly correlated with the prognosis of HNSCC, and the NLR was positively correlated with MDSC levels in the circulation and ALDH1 staining intensity in tumor specimens. In conclusion, the NLR has power in predicting the expression of ALDH1 in tumors, the circulating level of MDSCs, and the prognosis in HNSCC. We suggest that the NLR is an important biomarker that can assist the clinician and patient in making informed decisions regarding treatment options for HNSCC patients.

Turn Back the TIMe: Targeting Tumor Infiltrating Myeloid Cells to Revert Cancer Progression

Tumor cells frequently produce soluble factors that favor myelopoiesis and recruitment of myeloid cells to the tumor microenvironment (TME). Consequently, the TME of many cancer types is characterized by high infiltration of monocytes, macrophages, dendritic cells and granulocytes. Experimental and clinical studies show that most myeloid cells are kept in an immature state in the TME. These studies further show that tumor-derived factors mold these myeloid cells into cells that support cancer initiation and progression, amongst others by enabling immune evasion, tumor cell survival, proliferation, migration and metastasis. The key role of myeloid cells in cancer is further evidenced by the fact that they negatively impact on virtually all types of cancer therapy. Therefore, tumor-associated myeloid cells have been designated as the culprits in cancer. We review myeloid cells in the TME with a focus on the mechanisms they exploit to support cancer cells. In addition, we provide an overview of approaches that are under investigation to deplete myeloid cells or redirect their function, as these hold promise to overcome resistance to current cancer therapies.

Noninvasive imaging of the PD-1:PD-L1 immune checkpoint: Embracing nuclear medicine for the benefit of personalized immunotherapy

Molecular imaging of the immune checkpoint receptor PD-1 and its ligand PD-L1 is increasingly investigated as a strategy to guide and monitor PD-1:PD-L1-targeted immune checkpoint therapy. We provide an overview of the current state-of-the-art on PD-1- and PD-L1-specific imaging agents for quantitative, real-time assessment of PD-1:PD-L1 expression in the tumor environment and discuss their potential for clinical translation.

The role of tumor microenvironment in therapeutic resistance

Cancer cells undergo unlimited progression and survival owing to activation of oncogenes. However, support of the tumor microenvironment is essential to the formation of clinically relevant tumors. Recent evidence indicates that the tumor microenvironment is a critical regulator of immune escape, progression, and distant metastasis of cancer. Moreover, the tumor microenvironment is known to be involved in acquired resistance of tumors to various therapies. Despite significant advances in chemotherapy and radiotherapy, occurrence of therapeutic resistance leads to reduced efficacy. This review highlights myeloid cells, cancer-associated fibroblasts, and mesenchymal stem cells consisting of the tumor microenvironment, as well as the relevant signaling pathways that eventually render cancer cells to be therapeutically resistant.

Effects of dermal wounding on distal primary tumor immunobiology in mice

BACKGROUND

Before primary oral tumors are treated, various prophylactic procedures that require tissue repair are often necessary (e.g. biopsies, tooth extractions, radiation, and tracheotomies). Wound healing and tumor growth harness similar immune/inflammatory mechanisms. Our previous work indicates that tumors impair wound healing, although the extent to which tissue repair conversely influences tumor growth is poorly understood. Here, we test the hypothesis that dermal wound healing exacerbates primary tumor growth and influences tumor immunobiology.

MATERIALS AND METHODS

Female, immunocompetent mice were inoculated subcutaneously with murine oral cancer cells (AT-84) to induce flank tumors. Half of the mice received dermal excisional wounds (4 × 3.5 mm diameter) on their dorsum 16 days later, whereas the skin of controls remained intact. Tumor and blood tissues were harvested 1 and 5 days post wounding, and tumor myeloid cell populations and inflammatory gene expression were measured. Circulating myeloid cells, cytokines, and corticosterone were also quantified.

RESULTS

Wounding increased tumor mass, early tumor infiltration of macrophages, and tumor inflammatory gene expression. While wounding attenuated tumor growth-induced increases in circulating myeloid cells, no effects of wounding on circulating cytokine/endocrine measures were observed.

CONCLUSIONS

These results indicate that modest skin immune/inflammatory processes can enhance distal tumor growth and alter innate tumor immunity. The implication for this work is that, in the presence of a tumor, the benefits of tissue-damaging procedures that occur clinically must be weighed against the potential consequences for tumor biology.

Myeloid-Derived Suppressor Cells in the Tumor Microenvironment: Current Knowledge and Future Perspectives

The current knowledge on tumor-infiltrating myeloid-derived suppressor cells (MDSCs) is based mainly on the extensive work performed in murine models. Data obtained for human counterparts are generated on the basis of tumor analysis from patient samples. Both sources of information led to determination of the main suppressive mechanisms used by these cell subsets in tumor-bearing hosts. As a result of the identification of protein targets responsible for MDSCs suppressive activity, different therapeutics agents have been used to eliminate/reduce their adverse effect. In the present work, we review the current knowledge on suppressive mechanisms of MDSCs and therapeutic treatments that interfere with their differentiation, expansion or activity. Based on the accumulation of new evidences supporting their importance for tumor progression and metastasis, the interest in these cell types is increasing. We revise the methods of MDSC generation/differentiation ex vivo that may help in overcoming problems associated with limited numbers of cells available from animals and patients for their study.

Genome-Wide Approaches to Defining Macrophage Identity and Function

Macrophages play essential roles in the response to injury and infection and contribute to the development and/or homeostasis of the various tissues they reside in. Conversely, macrophages also influence the pathogenesis of metabolic, neurodegenerative, and neoplastic diseases. Mechanisms that contribute to the phenotypic diversity of macrophages in health and disease remain poorly understood. Here we review the recent application of genome-wide approaches to characterize the transcriptomes and epigenetic landscapes of tissue-resident macrophages. These studies are beginning to provide insights into how distinct tissue environments are interpreted by transcriptional regulatory elements to drive specialized programs of gene expression.

TIGIT and CD96: new checkpoint receptor targets for cancer immunotherapy

While therapies targeting the co-inhibitory or immune checkpoint receptors PD-1 and CTLA-4 have shown remarkable success in many cancers, not all patients benefit from these therapies. This has catalyzed enormous interest in the targeting of other immune checkpoint receptors. In this regard, TIGIT and CD96 have recently entered the limelight as novel immune checkpoint receptor targets. TIGIT and CD96 together with the co-stimulatory receptor CD226 form a pathway that is analogous to the CD28/CTLA-4 pathway, in which shared ligands and differential receptor:ligand affinities fine-tune the immune response. Although the roles of TIGIT and CD96 as immune checkpoint receptors in T cell and natural killer cell biology are just beginning to be uncovered, accumulating data support the targeting of these receptors for improving anti-tumor immune responses. A clear understanding of the immune cell populations regulated by TIGIT and CD96 is key to the design of immunotherapies that target these receptors in combination with other existing immune checkpoint blockade therapies.

Pyruvate controls the checkpoint inhibitor PD-L1 and suppresses T cell immunity

Patients with coronary artery disease (CAD) are at high risk for reactivation of the varicella zoster virus (VZV) and development of herpes zoster (HZ). Here, we found that macrophages from patients with CAD actively suppress T cell activation and expansion, leading to defective VZV-specific T cell immunity. Monocyte-derived and plaque-infiltrating macrophages from patients with CAD spontaneously expressed high surface density of the immunoinhibitory ligand programmed death ligand-1 (PD-L1), thereby providing negative signals to programmed death-1+ (PD-1+) T cells. We determined that aberrant PD-L1 expression in patient-derived macrophages was metabolically controlled. Oversupply of the glycolytic intermediate pyruvate in mitochondria from CAD macrophages promoted expression of PD-L1 via induction of the bone morphogenetic protein 4/phosphorylated SMAD1/5/IFN regulatory factor 1 (BMP4/p-SMAD1/5/IRF1) signaling pathway. Thus, CAD macrophages respond to nutrient excess by activating the immunoinhibitory PD-1/PD-L1 checkpoint, leading to impaired T cell immunity. This finding indicates that metabolite-based immunotherapy may be a potential strategy for restoring adaptive immunity in CAD.