NK Cells Stimulate Recruitment of cDC1 into the Tumor Microenvironment Promoting Cancer Immune Control

NKT Cell-Driven Enhancement of Antitumor Immunity Induced by Clec9a-Targeted Tailorable Nanoemulsion

Invariant natural killer T (iNKT) cells are a subset of lymphocytes with immune regulatory activity. Their ability to bridge the innate and adaptive immune systems has been studied using the glycolipid ligand α-galactosylceramide (αGC). To better harness the immune adjuvant properties of iNKT cells to enhance priming of antigen-specific CD8⁺ T cells, we encapsulated both αGC and antigen in a Clec9a-targeted nanoemulsion (TNE) to deliver these molecules to cross-presenting CD8⁺ dendritic cells (DC). We demonstrate that, even in the absence of exogenous glycolipid, iNKT cells supported the maturation of CD8α⁺ DCs to drive efficient cross-priming of antigen-specific CD8⁺ T cells upon delivery of Clec9a/OVA-TNE. The addition of αGC to the TNE (Clec9a/OVA/αGC) further enhanced activation of iNKT cells, NK cells, CD8α⁺ DCs, and polyfunctional CD8⁺ T cells. When tested therapeutically against HPVE7-expressing TC-1 tumors, long-term tumor suppression was achieved with a single administration of Clec9a/E7 peptide/αGC TNE. Antitumor activity was correlated with the recruitment of mature DCs, NK cells, and tumor-specific effector CD8⁺ T cells to the tumor-draining lymph node and tumor tissue. Thus, Clec9a-TNE codelivery of CD8⁺ T-cell epitopes with αGC induces alternative helper signals from activated iNKT cells, elicits innate (iNKT, NK) immunity, and enhances antitumor CD8⁺ T-cell responses for control of solid tumors.

Modulation of NK cells with checkpoint inhibitors in the context of cancer immunotherapy

The incidence of some types of tumours has increased progressively in recent years and is expected to continue growing in the coming years due in part to the aging of the population. The design of new therapies based on natural killer (NK) cells opens new possibilities especially for the treatment of elderly patients who are particularly susceptible to the toxicity of conventional chemotherapy treatments. In recent years, the potential use of NK cells in cancer immunotherapy has been of great interest thanks to advances in the study of NK cell biology. The identification of key points (checkpoints) in the activation of NK cells that can be regulated by monoclonal antibodies has allowed the design of new therapeutic strategies based on NK cells. However, there are still limitations for its use and the first clinical trials blocking KIR inhibitory receptors have shown little efficacy by inhibiting the maturation of NK cells. Blockade of other inhibitory receptors such as TIGIT, TIM3, LAG3 and PD1 may represent novel strategies to increase NK function in cancer patients. Altogether, the identification of NK cell and tumour cell markers of resistance or susceptibility to the action of NK cells will contribute to identifying those patients that will most likely benefit from NK cell-based immunotherapy.

OMIC signatures to understand cancer immunosurveillance and immunoediting: Melanoma and immune cells interplay in immunotherapy

Melanoma is the deadliest form of skin cancer. Cutaneous melanomas usually originate from exposure to the mutagenic effects of ultraviolet radiation, and as such they exhibit the highest rate of somatic mutations than any other human cancer, and an extensive expression of neoantigens concurrently with a dense infiltrate of immune cells. The coexistence of high immunogenicity and high immune cell infiltration may sound contradictory for cancers carrying a gloomy outcome. However, recent studies have unveiled a variety of immunosuppressive mechanisms that often permeate the tumor microenvironment and that are responsible for tumor escaping from immunosurveillance mechanisms. Nonetheless, this particular immune profile has opened a new window of treatments based on immunotherapy that have significantly improved the clinical outcome of melanoma patients. Still, positive and complete therapy responses have been limited, and this particular cancer continues to be a major clinical challenge. The transcriptomic signatures of those patients with clinical benefit and those with progressive disease have provided a more complete picture of the universe of interactions between the tumor and the immune system. In this review, we integrate the results of the immunotherapy clinical trials to discuss a novel understanding of the mechanisms guiding cancer immunosurveillance and immunoediting. A clear notion of the cellular and molecular processes shaping how the immune system and the tumor are continuously coevolving would result in the rational design of combinatory therapies aiming to counteract the signaling pathways and cellular processes responsible for immunoescape mechanisms and provide clinical benefit to immunotherapy nonresponsive patients.

Beyond a chemopreventive reagent, aspirin is a master regulator of the hallmarks of cancer

PURPOSE

Aspirin, one of the most commonly used nonsteroidal anti-inflammatory drugs (NAIDS), not only shows cancer chemoprevention effects but also improves cancer therapeutic effects when combined with other therapies. Studies that focus on aspirin regulation of the hallmarks of cancer and the associated molecular mechanisms facilitate a more thorough understanding of aspirin in mediating chemoprevention and may supply additional information for the development of novel cancer therapeutic agents.

METHODS

The relevant literatures from PubMed have been reviewed in this article.

RESULTS

Current studies have revealed that aspirin regulates almost all the hallmarks of cancer. Within tumor tissue, aspirin suppresses the bioactivities of cancer cells themselves and deteriorates the tumor microenvironment that supports cancer progression. In addition to tumor tissues, blocking of platelet activation also contributes to the ability of aspirin to inhibit cancer progression. In terms of the molecular mechanism, aspirin targets oncogenes and cancer-related signaling pathways and activates certain tumor suppressors.

CONCLUSION

Beyond a chemopreventive agent, aspirin is a master regulator of the hallmarks of cancer.

The Dendritic Cell Strikes Back

The field of cancer immunotherapy and checkpoint blockade has focused largely on direct effects on T cells. In this issue of Immunity, Garris et al. (2018) show that the efficacy of anti-PD-1 therapy depends on a T-cell-dendritic-cell (DC) licensing loop fueled by IFN-γ and IL-12, thereby establishing a central role for DCs in promoting anti-cancer T cell immunity during checkpoint blockade.

Sparks Fly in PGE2-Modulated Macrophage Polarization

How macrophages convey extracellular signals by bridging metabolism and functions remains unclear. In this issue of Immunity, Sanin et al. (2018) report that prostaglandin E2 (PGE2) treatment in interleukin-4-activated macrophages suppresses mitochondrial membrane potential to control voltage-regulated genes involved in proliferation and immune responses.

The clinical application of cancer immunotherapy based on naturally circulating dendritic cells

Dendritic cells (DCs) can initiate and direct adaptive immune responses. This ability is exploitable in DC vaccination strategies, in which DCs are educated ex vivo to present tumor antigens and are administered into the patient with the aim to induce a tumor-specific immune response. DC vaccination remains a promising approach with the potential to further improve cancer immunotherapy with little or no evidence of treatment-limiting toxicity. However, evidence for objective clinical antitumor activity of DC vaccination is currently limited, hampering the clinical implementation. One possible explanation for this is that the most commonly used monocyte-derived DCs may not be the best source for DC-based immunotherapy. The novel approach to use naturally circulating DCs may be an attractive alternative. In contrast to monocyte-derived DCs, naturally circulating DCs are relatively scarce but do not require extensive culture periods. Thereby, their functional capabilities are preserved, the reproducibility of clinical applications is increased, and the cells are not dysfunctional before injection. In human blood, at least three DC subsets can be distinguished, plasmacytoid DCs, CD141⁺ and CD1c⁺ myeloid/conventional DCs, each with distinct functional characteristics. In completed clinical trials, either CD1c⁺ myeloid DCs or plasmacytoid DCs were administered and showed encouraging immunological and clinical outcomes. Currently, also the combination of CD1c⁺ myeloid and plasmacytoid DCs as well as the intratumoral use of CD1c⁺ myeloid DCs is under investigation in the clinic. Isolation and culture strategies for CD141⁺ myeloid DCs are being developed. Here, we summarize and discuss recent clinical developments and future prospects of natural DC-based immunotherapy.

Oncogenic kinase inhibition limits Batf3-dependent dendritic cell development and antitumor immunity

Medina et al. demonstrate that Kit oncogene activity in gastrointestinal stromal tumor modulates the CD103⁺CD11b⁻ dendritic cell (DC) lineage. The antitumor efficacy of oncogene inhibition initially depends on preexisting immunity orchestrated by CD103⁺CD11b⁻ DCs, but subsequently is limited by a decrease in DC lineage maturation.

Gastrointestinal stromal tumor (GIST) is driven by an activating mutation in the KIT proto-oncogene. Using a mouse model of GIST and human specimens, we show that intratumoral murine CD103⁺CD11b⁻ dendritic cells (DCs) and human CD141⁺ DCs are associated with CD8⁺ T cell infiltration and differentiation. In mice, the antitumor effect of the Kit inhibitor imatinib is partially mediated by CD103⁺CD11b⁻ DCs, and effector CD8⁺ T cells initially proliferate. However, in both mice and humans, chronic imatinib therapy decreases intratumoral DCs and effector CD8⁺ T cells. The mechanism in our mouse model depends on Kit inhibition, which reduces intratumoral GM-CSF, leading to the accumulation of Batf3-lineage DC progenitors. GM-CSF is produced by γδ T cells via macrophage IL-1β. Stimulants that expand and mature DCs during imatinib treatment improve antitumor immunity. Our findings identify the importance of tumor cell oncogene activity in modulating the Batf3-dependent DC lineage and reveal therapeutic limitations for combined checkpoint blockade and tyrosine kinase inhibition.

The clinical application of cancer immunotherapy based on naturally circulating dendritic cells

Dendritic cells (DCs) can initiate and direct adaptive immune responses. This ability is exploitable in DC vaccination strategies, in which DCs are educated ex vivo to present tumor antigens and are administered into the patient with the aim to induce a tumor-specific immune response. DC vaccination remains a promising approach with the potential to further improve cancer immunotherapy with little or no evidence of treatment-limiting toxicity. However, evidence for objective clinical antitumor activity of DC vaccination is currently limited, hampering the clinical implementation. One possible explanation for this is that the most commonly used monocyte-derived DCs may not be the best source for DC-based immunotherapy. The novel approach to use naturally circulating DCs may be an attractive alternative. In contrast to monocyte-derived DCs, naturally circulating DCs are relatively scarce but do not require extensive culture periods. Thereby, their functional capabilities are preserved, the reproducibility of clinical applications is increased, and the cells are not dysfunctional before injection. In human blood, at least three DC subsets can be distinguished, plasmacytoid DCs, CD141+ and CD1c+ myeloid/conventional DCs, each with distinct functional characteristics. In completed clinical trials, either CD1c+ myeloid DCs or plasmacytoid DCs were administered and showed encouraging immunological and clinical outcomes. Currently, also the combination of CD1c+ myeloid and plasmacytoid DCs as well as the intratumoral use of CD1c+ myeloid DCs is under investigation in the clinic. Isolation and culture strategies for CD141+ myeloid DCs are being developed. Here, we summarize and discuss recent clinical developments and future prospects of natural DC-based immunotherapy.

Cancer Immunoediting by Innate Lymphoid Cells

The immune system plays a dual role in cancer. It conveys protective immunity but also facilitates malignant progression, either by sculpting tumor immunogenicity or by creating a microenvironment that can stimulate tumor outgrowth or aid in a subsequent metastatic cascade. Innate lymphoid cells (ILCs) embody this functional heterogeneity, although the nature of their responses in cancer has only recently begun to be unveiled. We provide an overview of recent insights into the role of ILCs in cancer. We also discuss how ILCs fit into the conceptual framework of cancer immunoediting, which integrates the dual role of the immune system in carcinogenesis. A broader understanding of their relevance in cancer is essential towards the design of successful therapeutic strategies.

Dendritic Cells and Cancer: From Biology to Therapeutic Intervention

Inducing effective anti-tumor immunity has become a major therapeutic strategy against cancer. Dendritic cells (DC) are a heterogenous population of antigen presenting cells that infiltrate tumors. While DC play a critical role in the priming and maintenance of local immunity, their functions are often diminished, or suppressed, by factors encountered in the tumor microenvironment. Furthermore, DC populations with immunosuppressive activities are also recruited to tumors, limiting T cell infiltration and promoting tumor growth. Anti-cancer therapies can impact the function of tumor-associated DC and/or alter their phenotype. Therefore, the design of effective anti-cancer therapies for clinical translation should consider how best to boost tumor-associated DC function to drive anti-tumor immunity. In this review, we discuss the different subsets of tumor-infiltrating DC and their role in anti-tumor immunity. Moreover, we describe strategies to enhance DC function within tumors and harness these cells for effective tumor immunotherapy.

Seq-ing out the Killers of Mice and Men

The diversity of natural killer cells between mouse and human is poorly understood. In this issue of Immunity, Crinier et al. (2018) utilize single-cell RNA-seq to profile splenic and blood NK cells from both organisms, uncovering both tissue- and species-specific transcriptomic signatures.

Plant Virus-Like Particle In Situ Vaccine for Intracranial Glioma Immunotherapy

Despite aggressive multi-modality treatment with surgery, radiation and chemotherapies, malignant glioma inevitably recurs and has dismal survival rates. Recent progress in immunotherapy has led to a resurgence of interest, and immunotherapies are being investigated for treatment of glioma. However, the unique brain anatomy and a highly immunosuppressive glioma microenvironment pose significant challenges to achieving efficacy. Thus, there is a critical need for assessment of next-generation immunotherapies for glioma. In this study, we have investigated the efficacy of the nanoparticle platform technology based on plant-derived Cowpea mosaic virus like particles (empty CPMV or eCPMV) to instigate a potent immune response against intracranial glioma. CPMV immunotherapy has been shown to efficiently reverse the immunosuppressive tumor microenvironments in pre-clinical murine models of dermal melanoma and metastatic melanoma, metastatic breast cancer, intraperitoneal ovarian cancer and in canine patients with oral melanoma. In the present study, we demonstrate that in situ administration of CPMV immunotherapy in the setting of glioma can effectively recruit unique subset of effector innate and adaptive immune cells to the brain parenchyma while reducing immune suppressive cellular population, leading to regression of intracranial glioma. The in situ CPMV nanoparticle vaccine offers a potent yet safe and localized immunotherapy for intracranial glioma.

Hide and seek: Plasticity of innate lymphoid cells in cancer

The advance of immunotherapies has revolutionized the treatment of cancer patients. Mostly agents modulating the adaptive immune system are currently used. More recently, attempts to stimulate the innate immune system are being promoted for clinical evaluation. Innate lymphoid cells (ILCs) are a highly plastic population of immune cells crucial for tissue homeostasis and the regulation of immune responses and maybe a promising target to improve current cancer immunotherapies. Although we have made significant progress in understanding ILC biology, their impact on tumor development, progression and therapy is controversial. In this review, we discuss the recent advances of ILC function and plasticity in the context of cancer.

Effective cancer immunotherapy by natural mouse conventional type-1 dendritic cells bearing dead tumor antigen

Background

The manipulation of dendritic cells (DCs) for cancer vaccination has not reached its full potential, despite the revolution in cancer immunotherapy. DCs are fundamental for CD8+ T cell activation, which relies on cross-presentation of exogenous antigen on MHC-I and can be fostered by immunogenic cancer cell death. Translational and clinical research has focused on in vitro-generated monocyte-derived DCs, while the vaccination efficacy of natural conventional type 1 DCs (cDC1s), which are associated with improved anti-tumor immunity and specialize on antigen cross-presentation, remains unknown.

Methods

We isolated primary spleen mouse cDC1s and established a protocol for fast ex vivo activation and antigen-loading with lysates of tumor cells that underwent immunogenic cell death by UV irradiation. Natural tumor antigen-loaded cDC1s were transferred and their potential for induction of endogenous CD8+ and CD4+ T cell responses in vivo, cancer prevention and therapy were assessed in three grafted cancer models. Further, we tested the efficacy of natural cDC1 vaccination in combination and comparison with anti-PD-1 treatment in two “wildtype” tumor models not expressing exogenous antigens.

Results

Herein, we reveal that primary mouse cDC1s ex vivo loaded with dead tumor cell-derived antigen are activated and induce strong CD8+ T cell responses from the endogenous repertoire upon adoptive transfer in vivo through tumor antigen cross-presentation. Notably, cDC1-based vaccines enhance tumor infiltration by cancer-reactive CD8+ and CD4+ T cells and halt progression of engrafted cancer models, including tumors that are refractory to anti-PD-1 treatment. Moreover, combined tumor antigen-loaded primary cDC1 and anti-PD-1 therapy had strong synergistic effects in a PD-1 checkpoint inhibition susceptible cancer model.

Conclusions

This preclinical proof-of-principle study is first to support the therapeutic efficacy of cancer immunotherapy with syngeneic dead tumor cell antigen-loaded mouse cDC1s, the equivalents of the human dendritic cell subset that correlates with beneficial prognosis of cancer patients. Our data pave the way for translation of cDC1-based cancer treatments into the clinic when isolation of natural human cDC1s becomes feasible.

Electronic supplementary material

The online version of this article (10.1186/s40425-019-0565-5) contains supplementary material, which is available to authorized users.

Host tissue determinants of tumour immunity

Although common evolutionary principles drive the growth of cancer cells regardless of the tissue of origin, the microenvironment in which tumours arise substantially differs across various organ sites. Recent studies have established that, in addition to cell-intrinsic effects, tumour growth regulation also depends on local cues driven by tissue environmental factors. In this Review, we discuss how tissue-specific determinants might influence tumour development and argue that unravelling the tissue-specific contribution to tumour immunity should help the development of precise immunotherapeutic strategies for patients with cancer.

NKG2D/NKG2-Ligand Pathway Offers New Opportunities in Cancer Treatment

The antitumor functions of NK cells are regulated by the integration of positive and negative signals triggered by numerous membrane receptors present on the NK cells themselves. Among the main activating receptors, NKG2D binds several stress-induced molecules on tumor targets. Engagement of NKG2D by its ligands (NKG2D-Ls) induces NK cell activation leading to production of cytokines and target cell lysis. These effects have therapeutic potential as NKG2D-Ls are widely expressed by solid tumors, whereas their expression in healthy cells is limited. Here, we describe the genetic and environmental factors regulating the NKG2D/NKG2D-L pathway in tumors. NKG2D-L expression is linked to cellular stress and cell proliferation, and has been associated with oncogenic mutations. Tumors have been found to alter their to NKG2D-L expression as they progress, which interferes with the antitumor function of the pathway. Nevertheless, this pathway could be advantageously exploited for cancer therapy. Various cancer treatments, including chemotherapy and targeted therapies, indirectly interfere with the cellular and soluble forms of NKG2D-Ls. In addition, NKG2D introduced into chimeric antigen receptors in T- and NK cells is a promising tumor immunotherapy approach.

Enhancing Dendritic Cell Therapy in Solid Tumors with Immunomodulating Conventional Treatment

Dendritic cells (DCs) are the most potent antigen-presenting cells and are the key initiator of tumor-specific immune responses. These characteristics are exploited by DC therapy, where DCs are ex vivo loaded with tumor-associated antigens (TAAs) and used to induce tumor-specific immune responses. Unfortunately, clinical responses remain limited to a proportion of the patients. Tumor characteristics and the immunosuppressive tumor microenvironment (TME) of the tumor are likely hampering efficacy of DC therapy. Therefore, reducing the immunosuppressive TME by combining DC therapy with other treatments could be a promising strategy. Initially, conventional cancer therapies, such as chemotherapy and radiotherapy, were thought to specifically target cancerous cells. Recent insights indicate that these therapies additionally augment tumor immunity by targeting immunosuppressive cell subsets in the TME, inducing immunogenic cell death (ICD), or blocking inhibitory molecules. Therefore, combining DC therapy with registered therapies such as chemotherapy, radiotherapy, or checkpoint inhibitors could be a promising treatment strategy to improve the efficacy of DC therapy. In this review, we evaluate various clinical applicable combination strategies to improve the efficacy of DC therapy.

TLR3 Activation of Intratumoral CD103+ Dendritic Cells Modifies the Tumor Infiltrate Conferring Anti-tumor Immunity

An important challenge in cancer immunotherapy is to expand the number of patients that benefit from immune checkpoint inhibitors (CI), a fact that has been related to the pre-existence of an efficient anti-tumor immune response. Different strategies are being proposed to promote tumor immunity and to be used in combined therapies with CI. Recently, we reported that intratumoral administration of naked poly A:U, a dsRNA mimetic empirically used in early clinical trials with some success, delays tumor growth and prolongs mice survival in several murine cancer models. Here, we show that CD103⁺ cDC1 and, to a much lesser extent CD11b⁺ cDC2, are the only populations expressing TLR3 at the tumor site, and consequently could be potential targets of poly A:U. Upon poly A:U administration these cells become activated and elicit profound changes in the composition of the tumor immune infiltrate, switching the immune suppressive tumor environment to anti-tumor immunity. The sole administration of naked poly A:U promotes striking changes within the lymphoid compartment, with all the anti-tumoral parameters being enhanced: a higher frequency of CD8⁺ Granzyme B⁺ T cells, (lower Treg/CD8⁺ ratio) and an important expansion of tumor-antigen specific CD8⁺ T cells. Also, PD1/PDL1 showed an increased expression indicating that neutralization of this axis could be exploited in combination with poly A:U. Our results shed new light to promote further assays in this dsRNA mimetic to the clinical field.

Innate lymphoid cells: A potential link between microbiota and immune responses against cancer

The adaptive immune system plays a crucial role in anti-tumor surveillance. Enhancement of T cell responses through checkpoint blockade has become a major therapeutic avenue of intervention for several tumors. Because it shapes immune responses and regulates their amplitude and duration, the microbiota has a substantial impact on anti-tumor immunity. Innate lymphoid cells (ILCs) comprise a heterogeneous population of lymphocytes devoid of antigen-specific receptors that mirror T helper cells in their ability to secrete cytokines that activate immune responses. Ongoing studies suggest that ILCs contribute to anti-tumor responses. Moreover, since ILCs are present at barrier surfaces, they are stimulated by the microbiota and, reciprocally, influence the composition of the microbiota by regulating the surface barrier microenvironment. Thus, ILC-microbiota cross-talk may in part underpin the effects of the microbiota on anti-tumor responses. In this article, we review current evidence linking ILCs to cancer and discuss the potential impact of ILC-microbiota cross-talk in anti-tumor immune responses.

Size Matters: The Functional Role of the CEACAM1 Isoform Signature and Its Impact for NK Cell-Mediated Killing in Melanoma

Malignant melanoma is the most aggressive and treatment resistant type of skin cancer. It is characterized by continuously rising incidence and high mortality rate due to its high metastatic potential. Various types of cell adhesion molecules have been implicated in tumor progression in melanoma. One of these, the carcinoembryonic antigen-related cell adhesion molecule 1 (CEACAM1), is a multi-functional receptor protein potentially expressed in epithelia, endothelia, and leukocytes. CEACAM1 often appears in four isoforms differing in the length of their extracellular and intracellular domains. Both the CEACAM1 expression in general, and the ratio of the expressed CEACAM1 splice variants appear very dynamic. They depend on both the cell activation stage and the cell growth phase. Interestingly, normal melanocytes are negative for CEACAM1, while melanomas often show high expression. As a cell–cell communication molecule, CEACAM1 mediates the direct interaction between tumor and immune cells. In the tumor cell this interaction leads to functional inhibitions, and indirectly to decreased cancer cell immunogenicity by down-regulation of ligands of the NKG2D receptor. On natural killer (NK) cells it inhibits NKG2D-mediated cytolysis and signaling. This review focuses on novel mechanistic insights into CEACAM1 isoforms for NK cell-mediated immune escape mechanisms in melanoma, and their clinical relevance in patients suffering from malignant melanoma.

Mutually assured destruction: the cold war between viruses and natural killer cells

Natural killer (NK) cells play a multitude of antiviral roles that are significant enough to provoke viral counterefforts to subvert their activity. As innate lymphocytes, NK cells provide a rapid source of pro-inflammatory antiviral cytokines and bring to bear cytolytic activities that are collectively meant to constrain viral replication and dissemination. Additionally, NK cells participate in adaptive immunity both by shaping virus-specific T-cell responses and by developing adaptive features themselves, including enhanced antibody-dependent effector functions. The relative importance of different functional activities of NK cells are poorly understood, thereby obfuscating clinical use of these cells. Here we focus on opposing efforts of NK cells and viruses to gain tactical superiority during infection.

Innate lymphoid cells as regulators of the tumor microenvironment

As crucial players in innate immunity, Innate Lymphoid Cells (ILCs) have been distinctly associated with either tumor-promoting or tumor-inhibiting activities. This dichotomy arises from the high degree of heterogeneity and plasticity between the ILC family subsets. Also, the tissue microenvironment is crucial for the function of ILCs. Especially within the tumor niche, each of the ILC subsets participates in a complex network of interactions with other cells and molecules. Although extensive research has unraveled several aspects of the crosstalk ILCs establish with the tumor microenvironment (TME), numerous questions remain to be answered. Here, we will discuss a role for the different ILC subsets that goes beyond their direct effects on the tumor cells. Instead, we will highlight the ability of ILCs to communicate with the surrounding milieu and the impact this has on tumor progression.

The Ins and Outs of Chemokine-Mediated Immune Cell Trafficking in Skin Cancer

Recent studies of the patterns of chemokine-mediated immune cell recruitment into solid tumors have enhanced our understanding of the role played by various immune cell subsets both in amplifying and inhibiting tumor cell growth and spread. Here we discuss how the chemokine/chemokine receptor networks bring together immune cells within the microenvironment of skin tumors, particularly melanomas, including their effect on disease progression, prognosis and therapeutic options.

Chemokines Modulate Immune Surveillance in Tumorigenesis, Metastasis, and Response to Immunotherapy

Chemokines are small secreted proteins that orchestrate migration and positioning of immune cells within the tissues. Chemokines are essential for the function of the immune system. Accumulating evidence suggest that chemokines play important roles in tumor microenvironment. In this review we discuss an association of chemokine expression and activity within the tumor microenvironment with cancer outcome. We summarize regulation of immune cell recruitment into the tumor by chemokine-chemokine receptor interactions and describe evidence implicating chemokines in promotion of the "inflamed" immune-cell enriched tumor microenvironment. We review both tumor-promoting function of chemokines, such as regulation of tumor metastasis, and beneficial chemokine roles, including stimulation of anti-tumor immunity and response to immunotherapy. Finally, we discuss the therapeutic strategies target tumor-promoting chemokines or induce/deliver beneficial chemokines within the tumor focusing on pre-clinical studies and clinical trials going forward. The goal of this review is to provide insight into comprehensive role of chemokines and their receptors in tumor pathobiology and treatment.

A Variant of a Killer Cell Immunoglobulin-like Receptor Is Associated with Resistance to PD-1 Blockade in Lung Cancer

PURPOSE

PD-(L)1-blocking antibodies have clinical activity in metastatic non-small cell lung cancer (NSCLC) and mediate durable tumor remissions. However, the majority of patients are resistant to PD-(L)1 blockade. Understanding mechanisms of primary resistance may allow prediction of clinical response and identification of new targetable pathways.

EXPERIMENTAL DESIGN

Peripheral blood mononuclear cells were collected from 35 patients with NSCLC receiving nivolumab monotherapy. Cellular changes, cytokine levels, gene expression, and polymorphisms were compared between responders and nonresponders to treatment. Findings were confirmed in additional cohorts of patients with NSCLC receiving immune checkpoint blockade.

RESULTS

We identified a genetic variant of a killer cell immunoglobulin-like receptor (KIR) KIR3DS1 that is associated with primary resistance to PD-1 blockade in patients with NSCLC. This association could be confirmed in independent cohorts of patients with NSCLC. In a multivariate analysis of the pooled cohort of 135 patients, the progression-free survival was significantly associated with presence of the KIR3DS1 allele (HR, 1.72; 95% confidence interval, 1.10-2.68; P = 0.017). No relationship was seen in cohorts of patients with NSCLC who did not receive immunotherapy. Cellular assays from patients before and during PD-1 blockade showed that resistance may be due to NK-cell dysfunction.

CONCLUSIONS

We identified an association of the KIR3DS1 allelic variant with response to PD-1-targeted immunotherapy in patients with NSCLC. This finding links NK cells with response to PD-1 therapy. Although the findings are interesting, a larger analysis in a randomized trial will be needed to confirm KIRs as predictive markers for response to PD-1-targeted immunotherapy.

Are Conventional Type 1 Dendritic Cells Critical for Protective Antitumor Immunity and How?

Dendritic cells (DCs) are endowed with a unique potency to prime T cells, as well as to orchestrate their expansion, functional polarization and effector activity in non-lymphoid tissues or in their draining lymph nodes. The concept of harnessing DC immunogenicity to induce protective responses in cancer patients was put forward about 25 years ago and has led to a multitude of DC-based vaccine trials. However, until very recently, objective clinical responses were below expectations. Conventional type 1 DCs (cDC1) excel in the activation of cytotoxic lymphocytes including CD8⁺ T cells (CTLs), natural killer (NK) cells, and NKT cells, which are all critical effector cell types in antitumor immunity. Efforts to investigate whether cDC1 might orchestrate immune defenses against cancer are ongoing, thanks to the recent blossoming of tools allowing their manipulation in vivo. Here we are reporting on these studies. We discuss the mouse models used to genetically deplete or manipulate cDC1, and their main caveats. We present current knowledge on the role of cDC1 in the spontaneous immune rejection of tumors engrafted in syngeneic mouse recipients, as a surrogate model to cancer immunosurveillance, and how this process is promoted by type I interferon (IFN-I) effects on cDC1. We also discuss cDC1 implication in promoting the protective effects of immunotherapies in mouse preclinical models, especially for adoptive cell transfer (ACT) and immune checkpoint blockers (ICB). We elaborate on how to improve this process by in vivo reprogramming of certain cDC1 functions with off-the-shelf compounds. We also summarize and discuss basic research and clinical data supporting the hypothesis that the protective antitumor functions of cDC1 inferred from mouse preclinical models are conserved in humans. This analysis supports potential applicability to cancer patients of the cDC1-targeting adjuvant immunotherapies showing promising results in mouse models. Nonetheless, further investigations on cDC1 and their implications in anti-cancer mechanisms are needed to determine whether they are the missing key that will ultimately help switching cold tumors into therapeutically responsive hot tumors, and how precisely they mediate their protective effects.

Cold Tumors: A Therapeutic Challenge for Immunotherapy

Therapeutic monoclonal antibodies targeting immune checkpoints (ICPs) have changed the treatment landscape of many tumors. However, response rate remains relatively low in most cases. A major factor involved in initial resistance to ICP inhibitors is the lack or paucity of tumor T cell infiltration, characterizing the so-called “cold tumors.” In this review, we describe the main mechanisms involved in the absence of T cell infiltration, including lack of tumor antigens, defect in antigen presentation, absence of T cell activation and deficit of homing into the tumor bed. We discuss then the different therapeutic approaches that could turn cold into hot tumors. In this way, specific therapies are proposed according to their mechanism of action. In addition, ‘‘supra-physiological’’ therapies, such as T cell recruiting bispecific antibodies and Chimeric Antigen Receptor (CAR) T cells, may be active regardless of the mechanism involved, especially in MHC class I negative tumors. The determination of the main factors implicated in the lack of preexisting tumor T cell infiltration is crucial for the development of adapted algorithms of treatments for cold tumors.

Inhibition of EZH2 induces NK cell-mediated differentiation and death in muscle-invasive bladder cancer

Lysine-specific demethylase 6A (KDM6A) and members of the Switch/Sucrose Non-Fermentable (SWI/SNF) family are known to counteract the activity of Enhancer of Zeste Homolog 2 (EZH2), which is often overexpressed and is associated with poor prognosis in muscle-invasive bladder cancer. Here we provide evidence that alterations in chromatin modifying enzymes, including KDM6A and members of the SWI/SNF complex, are frequent in muscle-invasive bladder cancer. We exploit the loss of function mutations in KDM6A and SWI/SNF complex to make bladder cancer cells susceptible to EZH2-based epigenetic therapy that activates an immune response to drive tumor cell differentiation and death. We reveal a novel mechanism of action of EZH2 inhibition, alone and in combination with cisplatin, which induces immune signaling with the largest changes observed in interferon gamma (IFN-γ). This upregulation is a result of activated natural killer (NK) signaling as demonstrated by the increase in NK cell-associated genes MIP-1α, ICAM1, ICAM2, and CD86 in xenografts treated with EZH2 inhibitors. Conversely, EZH2 inhibition results in decreased expression of pluripotency markers, ALDH2 and CK5, and increased cell death. Our results reveal a novel sensitivity of muscle-invasive bladder cancer cells with KMD6A and SWI/SNF mutations to EZH2 inhibition alone and in combination with cisplatin. This sensitivity is mediated through increased NK cell-related signaling resulting in tumor cell differentiation and cell death.

Nanobody Engineering: Toward Next Generation Immunotherapies and Immunoimaging of Cancer

In the last decade, cancer immunotherapies have produced impressive therapeutic results. However, the potency of immunotherapy is tightly linked to immune cell infiltration within the tumor and varies from patient to patient. Thus, it is becoming increasingly important to monitor and modulate the tumor immune infiltrate for an efficient diagnosis and therapy. Various bispecific approaches are being developed to favor immune cell infiltration through specific tumor targeting. The discovery of antibodies devoid of light chains in camelids has spurred the development of single domain antibodies (also called VHH or nanobody), allowing for an increased diversity of multispecific and/or multivalent formats of relatively small sizes endowed with high tissue penetration. The small size of nanobodies is also an asset leading to high contrasts for non-invasive imaging. The approval of the first therapeutic nanobody directed against the von Willebrand factor for the treatment of acquired thrombotic thrombocypenic purpura (Caplacizumab, Ablynx), is expected to bolster the rise of these innovative molecules. In this review, we discuss the latest advances in the development of nanobodies and nanobody-derived molecules for use in cancer immunotherapy and immunoimaging.

Born to Kill: NK Cells Go to War against Cancer

Preclinical and clinical data emerging over the past year demonstrate that cancer cells suppress the cytotoxic functions of natural killer cells by a variety of mechanisms. These findings reveal a new arsenal of actionable therapeutic targets to drive clinically relevant immune responses against cancer.

The Emergence of Natural Killer Cells as a Major Target in Cancer Immunotherapy

Immune 'checkpoint' inhibitors can increase the activity of tumor-resident cytotoxic lymphocytes and have revolutionized cancer treatment. Current therapies block inhibitory pathways in tumor-infiltrating CD8⁺ T cells and recent studies have shown similar programs in other effector populations such as natural killer (NK) cells. NK cells are critical for immunosurveillance, particularly the control of metastatic cells or hematological cancers. However, how NK cells specifically recognize transformed cells and dominant negative feedback pathways, as well as how tumors escape NK cell control, remains undefined. This review summarizes recent advances that have illuminated inhibitory checkpoints in NK cells, some of which are shared with conventional cytotoxic T lymphocytes. It also outlines emerging approaches aimed at unleashing the potential of NK cells in immunotherapy.

Batf3-Dependent Genes Control Tumor Rejection Induced by Dendritic Cells Independently of Cross-Presentation

The BATF3-dependent cDC1 lineage of conventional dendritic cells (cDC) is required for rejection of immunogenic sarcomas and for rejection of progressive sarcomas during checkpoint blockade therapy. One unique function of the cDC1 lineage is the efficient cross-presentation of tumor-derived neoantigens to CD8+ T cells, but it is not clear that this is the only unique function of cDC1 required for tumor rejection. We previously showed that BATF3 functions during cDC1 lineage commitment to maintain IRF8 expression in the specified cDC1 progenitor. However, since cDC1 progenitors do not develop into mature cDC1s in Batf3 -/- mice, it is still unclear whether BATF3 has additional functions in mature cDC1 cells. A transgenic Irf8-Venus reporter allele increases IRF8 protein concentration sufficiently to allow autonomous cDC1 development in spleens of Batf3 -/- mice. These restored Batf3 -/- cDC1s are transcriptionally similar to control wild-type cDC1s but have reduced expression of a restricted set of cDC1-specific genes. Restored Batf3 -/- cDC1s are able to cross-present cell-associated antigens both in vitro and in vivo However, Batf3 -/- cDC1 exhibit altered characteristics in vivo and are unable to mediate tumor rejection. These results show that BATF3, in addition to regulating Irf8 expression to stabilize cDC1 lineage commitment, also controls expression of a small set of genes required for cDC1-mediated tumor rejection. These BATF3-regulated genes may be useful targets in immunotherapies aimed at promoting tumor rejection.

The Uncovered Role of Immune Cells and NK Cells in the Regulation of Bone Metastasis

Bone is one of the main metastatic sites of solid tumors like breast, lung, and prostate cancer. Disseminated tumor cells (DTCs) and cancer stem cells (CSCs) represent the main target to counteract bone metastatization. These cells often localize in bone marrow (BM) at level of pre-metastatic niche: they can remain dormant for years or directly grow and create bone lesion, according to the different stimulations received in BM. The immune system in bone marrow is dampened and represents an appealing site for DTCs/CSCs. NK cells have an important role in controlling tumor progression, but their involvement in bone metastasis formation is an interesting and not fully investigated issue. Indeed, whether NK cells can interfere with CSC formation, kill them at the site of primary tumor, during circulation or in the pre-metastic niche needs to be elucidated. This review focuses on different aspects that regulate DTC/CSC life in bone and how NK cells potentially control bone metastasis formation.

NK Cell-Based Immunotherapy in Cancer Metastasis

Metastasis represents the leading cause of cancer-related death mainly owing to the limited efficacy of current anticancer therapies on advanced malignancies. Although immunotherapy is rendering promising results in the treatment of cancer, many adverse events and factors hampering therapeutic efficacy, especially in solid tumors and metastases, still need to be solved. Moreover, immunotherapeutic strategies have mainly focused on modulating the activity of T cells, while Natural Killer (NK) cells have only recently been taken into consideration. NK cells represent an attractive target for cancer immunotherapy owing to their innate capacity to eliminate malignant tumors in a non-Major Histocompatibility Complex (MHC) and non-tumor antigen-restricted manner. In this review, we analyze the mechanisms and efficacy of NK cells in the control of metastasis and we detail the immunosubversive strategies developed by metastatic cells to evade NK cell-mediated immunosurveillance. We also share current and cutting-edge clinical approaches aimed at unleashing the full anti-metastatic potential of NK cells, including the adoptive transfer of NK cells, boosting of NK cell activity, redirecting NK cell activity against metastatic cells and the release of evasion mechanisms dampening NK cell immunosurveillance.

Competitive Immunoassays for the Detection of Small Molecules Using Single Molecule Arrays

Small-molecule detection is important for many applications including clinical diagnostics, drug discovery, and measurements of environmental samples and agricultural products. Current techniques for small-molecule detection suffer from various limitations including low analytical sensitivity and complex sample processing. Furthermore, as a result of their small size, small molecules are difficult to detect using an antibody pair in a traditional sandwich assay format. To overcome these limitations, we developed an ultrasensitive competitive immunoassay for small-molecule detection using Single Molecule Arrays (Simoa). We show that the competitive Simoa assay is approximately 50-fold more sensitive than the conventional ELISA. We performed theoretical calculations to determine the factors that influence the sensitivity of competitive Simoa assays and used them to achieve maximal sensitivity. We also demonstrate detection of small molecules in complex biological samples. We show that the competitive Simoa assay is a simple, fast, and highly sensitive approach for ultrasensitive detection of small molecules.

NK Cell Infiltrates and HLA Class I Expression in Primary HER2+ Breast Cancer Predict and Uncouple Pathological Response and Disease-free Survival

PURPOSE

We investigated the value of tumor-infiltrating NK (TI-NK) cells and HLA class I tumor expression as biomarkers of response to neoadjuvant anti-HER2 antibody-based treatment in breast cancer.

EXPERIMENTAL DESIGN

TI-NK cells and HLA-I were determined by IHC in pretreatment tumor biopsies from two cohorts of patients with HER2-positive breast cancer [discovery cohort (n = 42) and validation cohort (n = 71)]. Tumor-infiltrating lymphocytes (TIL) were scored according to international guidelines. Biomarker association with pathologic complete response (pCR) and disease-free survival (DFS) was adjusted for prognostic factors. Gene set variation analysis was used for determining immune cell populations concomitant to NK-cell enrichment in HER2-positive tumors from the Cancer Genome Atlas (n = 190).

RESULTS

TI-NK cells were significantly associated with pCR in the discovery cohort as well as in the validation cohort (P < 0.0001), independently of clinicopathologic factors. A ≥3 TI-NK cells/50x high-power field (HPF) cutoff predicted pCR in the discovery and validation cohort [OR, 188 (11-3154); OR, 19.5 (5.3-71.8)]. Presence of TI-NK cells associated with prolonged DFS in both patient cohorts [HR, 0.07 (0.01-0.6); P = 0.01; HR, 0.3 (0.08-1.3); P = 0.1]. NK-, activated dendritic- and CD8 T-cell gene expression signatures positively correlated in HER2-positive tumors, supporting the value of NK cells as surrogates of effective antitumor immunity. Stratification of patients by tumor HLA-I expression identified patients with low and high relapse risk independently of pCR.

CONCLUSIONS

This study identifies baseline TI-NK cells as an independent biomarker with great predictive value for pCR to anti-HER2 antibody-based treatment and points to the complementary value of tumor HLA-I status for defining patient prognosis independently of pCR.

Novel Cre-Expressing Mouse Strains Permitting to Selectively Track and Edit Type 1 Conventional Dendritic Cells Facilitate Disentangling Their Complexity in vivo

Type 1 conventional DCs (cDC1) excel in the cross-priming of CD8⁺ T cells, which is crucial for orchestrating efficient immune responses against viruses or tumors. However, our understanding of their physiological functions and molecular regulation has been limited by the lack of proper mutant mouse models allowing their conditional genetic targeting. Because the Xcr1 and A530099j19rik (Karma/Gpr141b) genes belong to the core transcriptomic fingerprint of mouse cDC1, we used them to engineer two novel Cre-driver lines, the Xcr1^Cre and Karma^Cre mice, by knocking in an IRES-Cre expression cassette into their 3′-UTR. We used genetic tracing to characterize the specificity and efficiency of these new models in several lymphoid and non-lymphoid tissues, and compared them to the Clec9a^Cre mouse model, which targets the immediate precursors of cDCs. Amongst the three Cre-driver mouse models examined, the Xcr1^Cre model was the most efficient and specific for the fate mapping of all cDC1, regardless of the tissues examined. The Karma^Cre model was rather specific for cDC1 when compared with the Clec9a^Cre mouse, but less efficient than the Xcr1^Cre model. Unexpectedly, the Xcr1^Cre model targeted a small fraction of CD4⁺ T cells, and the Karma^Cre model a significant proportion of mast cells in the skin. Importantly, the targeting specificity of these two mouse models was not changed upon inflammation. A high frequency of germline recombination was observed solely in the Xcr1^Cre mouse model when both the Cre and the floxed alleles were brought by the same gamete irrespective of its gender. Xcr1, Karma, and Clec9a being differentially expressed within the cDC1 population, the three CRE-driver lines examined showed distinct recombination patterns in cDC1 phenotypic subsets. This advances our understanding of cDC1 subset heterogeneity and the differentiation trajectory of these cells. Therefore, to the best of our knowledge, upon informed use, the Xcr1^Cre and Karma^Cre mouse models represent the best tools currently reported to specifically and faithfully target cDC1 in vivo, both at steady state and upon inflammation. Future use of these mutant mouse models will undoubtedly boost our understanding of the biology of cDC1.

CIMT 2018: Pushing frontiers in cancer immunotherapy — Report on the 16th Annual Meeting of the Association for Cancer Immunotherapy

The 16th Annual Meeting of the Association for Cancer Immunotherapy (CIMT), Europe’s largest meeting series of its kind, took place in Mainz, Germany from 15–17 May, 2018. Cutting-edge advancements in cancer immunotherapy were discussed among more than 700 scientists under the motto “Pushing Frontiers in Cancer Immunotherapy”. This meeting report is a summary of some of the CIMT 2018 highlights.

Intratumoral Immunotherapy with XCL1 and sFlt3L Encoded in Recombinant Semliki Forest Virus-Derived Vectors Fosters Dendritic Cell-Mediated T-cell Cross-Priming

: Multiple lines of evidence indicate a critical role of antigen cross-presentation by conventional BATF3-dependent type 1 classical dendritic cells (cDC1) in CD8-mediated antitumor immunity. Flt3L and XCL1, respectively, constitute a key growth/differentiation factor and a potent and specific chemoattractant for cDC1. To exploit their antitumor functions in local immunotherapy, we prepared Semliki Forest Virus (SFV)-based vectors encoding XCL1 and soluble Flt3L (sFlt3L). These vectors readily conferred transgene expression to the tumor cells in culture and when engrafted as subcutaneous mouse tumor models. In syngeneic mice, intratumoral injection of SFV-XCL1-sFlt3L (SFV-XF) delayed progression of MC38- and B16-derived tumors. Therapeutic activity was observed and exerted additive effects in combination with anti-PD-1, anti-CD137, or CTLA-4 immunostimulatory mAbs. Therapeutic effects were abolished by CD8β T-cell depletion and were enhanced by CD4 T-cell depletion, but not by T regulatory cell predepletion with anti-CD25 mAb. Antitumor effects were also abolished in BATF3- and IFNAR-deficient mice. In B16-OVA tumors, SFV-XF increased the number of infiltrating CD8 T cells, including those recognizing OVA. Consistently, following the intratumoral SFV-XF treatment courses, we observed increased BATF3-dependent cDC1 among B16-OVA tumor-infiltrating leukocytes. Such an intratumoral increase was not seen in MC38-derived tumors, but both resident and migratory cDC1 were boosted in SFV-XF-treated MC38 tumor-draining lymph nodes. In conclusion, viral gene transfer of sFlt3L and XCL1 is feasible, safe, and biologically active in mice, exerting antitumor effects that can be potentiated by CD4 T-cell depletion. SIGNIFICANCE: These findings demonstrate that transgenic expression of sFLT3L and XCL1 in tumor cells mediates cross-priming of, and elicits potent antitumor activity from, CD8 T lymphocytes, particularly in combination with CD4 T-cell depletion.

Resident-Memory T Cells in Tissue-Restricted Immune Responses: For Better or Worse?

Tissue-resident-memory CD8+ T cells (T_RM) have been described as a non-circulating memory T cell subset that persists at sites of previous infection. While T_RM in all non-lymphoid organs probably share a core signature differentiation pathway, certain aspects of their maintenance and effector functions may vary. It is well-established that T_RM provide long-lived protective immunity through immediate effector function and accelerated recruitment of circulating immune cells. Besides immune defense against pathogens, other immunological roles of T_RM are less well-studied. Likewise, evidence of a putative detrimental role of T_RM for inflammatory diseases is only beginning to emerge. In this review, we discuss the protective and harmful role of T_RM in organ-specific immunity and immunopathology as well as prospective implications for immunomodulatory therapy.