The Immune Landscape of Cancer

We performed an extensive immunogenomic analysis of more than 10,000 tumors comprising 33 diverse cancer types by utilizing data compiled by TCGA. Across cancer types, we identified six immune subtypes-wound healing, IFN-γ dominant, inflammatory, lymphocyte depleted, immunologically quiet, and TGF-β dominant-characterized by differences in macrophage or lymphocyte signatures, Th1:Th2 cell ratio, extent of intratumoral heterogeneity, aneuploidy, extent of neoantigen load, overall cell proliferation, expression of immunomodulatory genes, and prognosis. Specific driver mutations correlated with lower (CTNNB1, NRAS, or IDH1) or higher (BRAF, TP53, or CASP8) leukocyte levels across all cancers. Multiple control modalities of the intracellular and extracellular networks (transcription, microRNAs, copy number, and epigenetic processes) were involved in tumor-immune cell interactions, both across and within immune subtypes. Our immunogenomics pipeline to characterize these heterogeneous tumors and the resulting data are intended to serve as a resource for future targeted studies to further advance the field.

Inflammation and Cancer: Triggers, Mechanisms, and Consequences

Inflammation predisposes to the development of cancer and promotes all stages of tumorigenesis. Cancer cells, as well as surrounding stromal and inflammatory cells, engage in well-orchestrated reciprocal interactions to form an inflammatory tumor microenvironment (TME). Cells within the TME are highly plastic, continuously changing their phenotypic and functional characteristics. Here, we review the origins of inflammation in tumors, and the mechanisms whereby inflammation drives tumor initiation, growth, progression, and metastasis. We discuss how tumor-promoting inflammation closely resembles inflammatory processes typically found during development, immunity, maintenance of tissue homeostasis, or tissue repair and illuminate the distinctions between tissue-protective and pro-tumorigenic inflammation, including spatiotemporal considerations. Defining the cornerstone rules of engagement governing molecular and cellular mechanisms of tumor-promoting inflammation will be essential for further development of anti-cancer therapies.

PD-L1 (B7-H1) and PD-1 pathway blockade for cancer therapy: Mechanisms, response biomarkers, and combinations

PD-L1 and PD-1 (PD) pathway blockade is a highly promising therapy and has elicited durable antitumor responses and long-term remissions in a subset of patients with a broad spectrum of cancers. How to improve, widen, and predict the clinical response to anti-PD therapy is a central theme in the field of cancer immunology and immunotherapy. Oncologic, immunologic, genetic, and biological studies focused on the human cancer microenvironment have yielded substantial insight into this issue. Here, we focus on tumor microenvironment and evaluate several potential therapeutic response markers including the PD-L1 and PD-1 expression pattern, genetic mutations within cancer cells and neoantigens, cancer epigenetics and effector T cell landscape, and microbiota. We further clarify the mechanisms of action of these markers and their roles in shaping, being shaped, and/or predicting therapeutic responses. We also discuss a variety of combinations with PD pathway blockade and their scientific rationales for cancer treatment.

Single-Cell Transcriptomic Analysis of Primary and Metastatic Tumor Ecosystems in Head and Neck Cancer

The diverse malignant, stromal, and immune cells in tumors affect growth, metastasis, and response to therapy. We profiled transcriptomes of ∼6,000 single cells from 18 head and neck squamous cell carcinoma (HNSCC) patients, including five matched pairs of primary tumors and lymph node metastases. Stromal and immune cells had consistent expression programs across patients. Conversely, malignant cells varied within and between tumors in their expression of signatures related to cell cycle, stress, hypoxia, epithelial differentiation, and partial epithelial-to-mesenchymal transition (p-EMT). Cells expressing the p-EMT program spatially localized to the leading edge of primary tumors. By integrating single-cell transcriptomes with bulk expression profiles for hundreds of tumors, we refined HNSCC subtypes by their malignant and stromal composition and established p-EMT as an independent predictor of nodal metastasis, grade, and adverse pathologic features. Our results provide insight into the HNSCC ecosystem and define stromal interactions and a p-EMT program associated with metastasis.

Macrophages as regulators of tumour immunity and immunotherapy

Macrophages are critical mediators of tissue homeostasis, with tumours distorting this proclivity to stimulate proliferation, angiogenesis and metastasis. This had led to an interest in targeting macrophages in cancer, and preclinical studies have demonstrated efficacy across therapeutic modalities and tumour types. Much of the observed efficacy can be traced to the suppressive capacity of macrophages, driven by microenvironmental cues such as hypoxia and fibrosis. As a result, tumour macrophages display an ability to suppress T cell recruitment and function as well as to regulate other aspects of tumour immunity. With the increasing impact of cancer immunotherapy, macrophage targeting is now being evaluated in this context. Here, we discuss the results of clinical trials and the future of combinatorial immunotherapy.

Tumor and Microenvironment Evolution during Immunotherapy with Nivolumab

The mechanisms by which immune checkpoint blockade modulates tumor evolution during therapy are unclear. We assessed genomic changes in tumors from 68 patients with advanced melanoma, who progressed on ipilimumab or were ipilimumab-naive, before and after nivolumab initiation (CA209-038 study). Tumors were analyzed by whole-exome, transcriptome, and/or T cell receptor (TCR) sequencing. In responding patients, mutation and neoantigen load were reduced from baseline, and analysis of intratumoral heterogeneity during therapy demonstrated differential clonal evolution within tumors and putative selection against neoantigenic mutations on-therapy. Transcriptome analyses before and during nivolumab therapy revealed increases in distinct immune cell subsets, activation of specific transcriptional networks, and upregulation of immune checkpoint genes that were more pronounced in patients with response. Temporal changes in intratumoral TCR repertoire revealed expansion of T cell clones in the setting of neoantigen loss. Comprehensive genomic profiling data in this study provide insight into nivolumab's mechanism of action.

Single-Cell Map of Diverse Immune Phenotypes in the Breast Tumor Microenvironment

Knowledge of immune cell phenotypes in the tumor microenvironment is essential for understanding mechanisms of cancer progression and immunotherapy response. We profiled 45,000 immune cells from eight breast carcinomas, as well as matched normal breast tissue, blood, and lymph nodes, using single-cell RNA-seq. We developed a preprocessing pipeline, SEQC, and a Bayesian clustering and normalization method, Biscuit, to address computational challenges inherent to single-cell data. Despite significant similarity between normal and tumor tissue-resident immune cells, we observed continuous phenotypic expansions specific to the tumor microenvironment. Analysis of paired single-cell RNA and T cell receptor (TCR) sequencing data from 27,000 additional T cells revealed the combinatorial impact of TCR utilization on phenotypic diversity. Our results support a model of continuous activation in T cells and do not comport with the macrophage polarization model in cancer. Our results have important implications for characterizing tumor-infiltrating immune cells.

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

Conventional type 1 dendritic cells (cDC1) are critical for antitumor immunity, and their abundance within tumors is associated with immune-mediated rejection and the success of immunotherapy. Here, we show that cDC1 accumulation in mouse tumors often depends on natural killer (NK) cells that produce the cDC1 chemoattractants CCL5 and XCL1. Similarly, in human cancers, intratumoral CCL5, XCL1, and XCL2 transcripts closely correlate with gene signatures of both NK cells and cDC1 and are associated with increased overall patient survival. Notably, tumor production of prostaglandin E2 (PGE2) leads to evasion of the NK cell-cDC1 axis in part by impairing NK cell viability and chemokine production, as well as by causing downregulation of chemokine receptor expression in cDC1. Our findings reveal a cellular and molecular checkpoint for intratumoral cDC1 recruitment that is targeted by tumor-derived PGE2 for immune evasion and that could be exploited for cancer therapy.

Tumor Evolution of Glioma-Intrinsic Gene Expression Subtypes Associates with Immunological Changes in the Microenvironment

We leveraged IDH wild-type glioblastomas, derivative neurospheres, and single-cell gene expression profiles to define three tumor-intrinsic transcriptional subtypes designated as proneural, mesenchymal, and classical. Transcriptomic subtype multiplicity correlated with increased intratumoral heterogeneity and presence of tumor microenvironment. In silico cell sorting identified macrophages/microglia, CD4⁺ T lymphocytes, and neutrophils in the glioma microenvironment. NF1 deficiency resulted in increased tumor-associated macrophages/microglia infiltration. Longitudinal transcriptome analysis showed that expression subtype is retained in 55% of cases. Gene signature-based tumor microenvironment inference revealed a decrease in invading monocytes and a subtype-dependent increase in macrophages/microglia cells upon disease recurrence. Hypermutation at diagnosis or at recurrence associated with CD8⁺ T cell enrichment. Frequency of M2 macrophages detection associated with short-term relapse after radiation therapy.

Tumor-Associated Macrophages in Tumor Immunity

Tumor-associated macrophages (TAMs) represent one of the main tumor-infiltrating immune cell types and are generally categorized into either of two functionally contrasting subtypes, namely classical activated M1 macrophages and alternatively activated M2 macrophages. The former typically exerts anti-tumor functions, including directly mediate cytotoxicity and antibody-dependent cell-mediated cytotoxicity (ADCC) to kill tumor cells; the latter can promote the occurrence and metastasis of tumor cells, inhibit T cell-mediated anti-tumor immune response, promote tumor angiogenesis, and lead to tumor progression. Both M1 and M2 macrophages have high degree of plasticity and thus can be converted into each other upon tumor microenvironment changes or therapeutic interventions. As the relationship between TAMs and malignant tumors becoming clearer, TAMs have become a promising target for developing new cancer treatment. In this review, we summarize the origin and types of TAMs, TAMs interaction with tumors and tumor microenvironment, and up-to-date treatment strategies targeting TAMs.

Oncolytic Virotherapy Promotes Intratumoral T Cell Infiltration and Improves Anti-PD-1 Immunotherapy

Here we report a phase 1b clinical trial testing the impact of oncolytic virotherapy with talimogene laherparepvec on cytotoxic T cell infiltration and therapeutic efficacy of the anti-PD-1 antibody pembrolizumab. Twenty-one patients with advanced melanoma were treated with talimogene laherparepvec followed by combination therapy with pembrolizumab. Therapy was generally well tolerated, with fatigue, fevers, and chills as the most common adverse events. No dose-limiting toxicities occurred. Confirmed objective response rate was 62%, with a complete response rate of 33% per immune-related response criteria. Patients who responded to combination therapy had increased CD8⁺ T cells, elevated PD-L1 protein expression, as well as IFN-γ gene expression on several cell subsets in tumors after talimogene laherparepvec treatment. Response to combination therapy did not appear to be associated with baseline CD8⁺ T cell infiltration or baseline IFN-γ signature. These findings suggest that oncolytic virotherapy may improve the efficacy of anti-PD-1 therapy by changing the tumor microenvironment. VIDEO ABSTRACT.

FAK in cancer: mechanistic findings and clinical applications

Focal adhesion kinase (FAK) is a cytoplasmic protein tyrosine kinase that is overexpressed and activated in several advanced-stage solid cancers. FAK promotes tumour progression and metastasis through effects on cancer cells, as well as stromal cells of the tumour microenvironment. The kinase-dependent and kinase-independent functions of FAK control cell movement, invasion, survival, gene expression and cancer stem cell self-renewal. Small molecule FAK inhibitors decrease tumour growth and metastasis in several preclinical models and have initial clinical activity in patients with limited adverse events. In this Review, we discuss FAK signalling effects on both tumour and stromal cell biology that provide rationale and support for future therapeutic opportunities.

Recent Progress in Ferroptosis Inducers for Cancer Therapy

Ferroptosis is a newly discovered form of regulated cell death that is the nexus between metabolism, redox biology, and human health. Emerging evidence shows the potential of triggering ferroptosis for cancer therapy, particularly for eradicating aggressive malignancies that are resistant to traditional therapies. Recently, there has been a great deal of effort to design and develop anticancer drugs based on ferroptosis induction. Recent advances of ferroptosis-inducing agents at the intersection of chemistry, materials science, and cancer biology are presented. The basis of ferroptosis is summarized first to highlight the feasibility and characteristics of triggering ferroptosis for cancer therapy. A literature review of ferroptosis inducers (including small molecules and nanomaterials) is then presented to delineate their design, action mechanisms, and anticancer applications. Finally, some considerations for research on ferroptosis inducers are spotlighted, followed by a discussion on the challenges and future development directions of this burgeoning field.

Single-Cell Transcriptomics of Human and Mouse Lung Cancers Reveals Conserved Myeloid Populations across Individuals and Species

Tumor-infiltrating myeloid cells (TIMs) comprise monocytes, macrophages, dendritic cells, and neutrophils, and have emerged as key regulators of cancer growth. These cells can diversify into a spectrum of states, which might promote or limit tumor outgrowth but remain poorly understood. Here, we used single-cell RNA sequencing (scRNA-seq) to map TIMs in non-small-cell lung cancer patients. We uncovered 25 TIM states, most of which were reproducibly found across patients. To facilitate translational research of these populations, we also profiled TIMs in mice. In comparing TIMs across species, we identified a near-complete congruence of population structures among dendritic cells and monocytes; conserved neutrophil subsets; and species differences among macrophages. By contrast, myeloid cell population structures in patients' blood showed limited overlap with those of TIMs. This study determines the lung TIM landscape and sets the stage for future investigations into the potential of TIMs as immunotherapy targets.

Macrophage Polarization States in the Tumor Microenvironment

The M1/M2 macrophage paradigm plays a key role in tumor progression. M1 macrophages are historically regarded as anti-tumor, while M2-polarized macrophages, commonly deemed tumor-associated macrophages (TAMs), are contributors to many pro-tumorigenic outcomes in cancer through angiogenic and lymphangiogenic regulation, immune suppression, hypoxia induction, tumor cell proliferation, and metastasis. The tumor microenvironment (TME) can influence macrophage recruitment and polarization, giving way to these pro-tumorigenic outcomes. Investigating TME-induced macrophage polarization is critical for further understanding of TAM-related pro-tumor outcomes and potential development of new therapeutic approaches. This review explores the current understanding of TME-induced macrophage polarization and the role of M2-polarized macrophages in promoting tumor progression.

Targeting the tumor microenvironment: removing obstruction to anticancer immune responses and immunotherapy

The tumor microenvironment (TME) is an integral part of cancer. Recognition of the essential nature of the TME in cancer evolution has led to a shift from a tumor cell-centered view of cancer development to the concept of a complex tumor ecosystem that supports tumor growth and metastatic dissemination. Accordingly, novel targets within the TME have been uncovered that can help direct and improve the actions of various cancer therapies, notably immunotherapies that work by potentiating host antitumor immune responses. Here, we review the composition of the TME, how this attenuates immunosurveillance, and discuss existing and potential strategies aimed at targeting cellular and molecular TME components.

Bone marrow-derived myofibroblasts contribute to the mesenchymal stem cell niche and promote tumor growth

Carcinoma-associated fibroblasts (CAFs) that express α-smooth muscle actin (αSMA) contribute to cancer progression, but their precise origin and role are unclear. Using mouse models of inflammation-induced gastric cancer, we show that at least 20% of CAFs originate from bone marrow (BM) and derive from mesenchymal stem cells (MSCs). αSMA+ myofibroblasts (MFs) are niche cells normally present in BM and increase markedly during cancer progression. MSC-derived CAFs that are recruited to the dysplastic stomach express IL-6, Wnt5α and BMP4, show DNA hypomethylation, and promote tumor growth. Moreover, CAFs are generated from MSCs and are recruited to the tumor in a TGF-β- and SDF-1α-dependent manner. Therefore, carcinogenesis involves expansion and relocation of BM-niche cells to the tumor to create a niche to sustain cancer progression.

T Cell Dysfunction in Cancer

Therapeutic reinvigoration of tumor-specific T cells has greatly improved clinical outcome in cancer. Nevertheless, many patients still do not achieve durable benefit. Recent evidence from studies in murine and human cancer suggest that intratumoral T cells display a broad spectrum of (dys-)functional states, shaped by the multifaceted suppressive signals that occur within the tumor microenvironment. Here we discuss the current understanding of T cell dysfunction in cancer, the value of novel technologies to dissect such dysfunction at the single cell level, and how our emerging understanding of T cell dysfunction may be utilized to develop personalized strategies to restore antitumor immunity.

Metabolic Instruction of Immunity

Choices have consequences. Immune cells survey and migrate throughout the body and sometimes take residence in niche environments with distinct communities of cells, extracellular matrix, and nutrients that may differ from those in which they matured. Imbedded in immune cell physiology are metabolic pathways and metabolites that not only provide energy and substrates for growth and survival, but also instruct effector functions, differentiation, and gene expression. This review of immunometabolism will reference the most recent literature to cover the choices that environments impose on the metabolism and function of immune cells and highlight their consequences during homeostasis and disease.

TGF-β-Mediated Epithelial-Mesenchymal Transition and Cancer Metastasis

Transforming growth factor β (TGF-β) is a secreted cytokine that regulates cell proliferation, migration, and the differentiation of a plethora of different cell types. Consistent with these findings, TGF-β plays a key role in controlling embryogenic development, inflammation, and tissue repair, as well as in maintaining adult tissue homeostasis. TGF-β elicits a broad range of context-dependent cellular responses, and consequently, alterations in TGF-β signaling have been implicated in many diseases, including cancer. During the early stages of tumorigenesis, TGF-β acts as a tumor suppressor by inducing cytostasis and the apoptosis of normal and premalignant cells. However, at later stages, when cancer cells have acquired oncogenic mutations and/or have lost tumor suppressor gene function, cells are resistant to TGF-β-induced growth arrest, and TGF-β functions as a tumor promotor by stimulating tumor cells to undergo the so-called epithelial-mesenchymal transition (EMT). The latter leads to metastasis and chemotherapy resistance. TGF-β further supports cancer growth and progression by activating tumor angiogenesis and cancer-associated fibroblasts and enabling the tumor to evade inhibitory immune responses. In this review, we will consider the role of TGF-β signaling in cell cycle arrest, apoptosis, EMT and cancer cell metastasis. In particular, we will highlight recent insights into the multistep and dynamically controlled process of TGF-β-induced EMT and the functions of miRNAs and long noncoding RNAs in this process. Finally, we will discuss how these new mechanistic insights might be exploited to develop novel therapeutic interventions.

Abrogation of TGF beta signaling in mammary carcinomas recruits Gr-1+CD11b+ myeloid cells that promote metastasis

Aberrant TGFbeta signaling is common in human cancers and contributes to tumor metastasis. Here, we demonstrate that Gr-1+CD11b+ myeloid cells are recruited into mammary carcinomas with type II TGF beta receptor gene (Tgfbr2) deletion and directly promote tumor metastasis. Gr-1+CD11b+ cells infiltrate into the invasive front of tumor tissues and facilitate tumor cell invasion and metastasis through a process involving metalloproteinase activity. This infiltration of Gr-1+CD11b+ cells also results in increased abundance of TGF beta 1 in tumors with Tgfbr2 deletion. The recruitment of Gr-1+CD11b+ cells into tumors with Tgfbr2 deletion involves two chemokine receptor axes, the SDF-1/CXCR4 and CXCL5/CXCR2 axes. Together, these data indicate that Gr-1+CD11b+ cells contribute to TGFbeta-mediated metastasis through enhancing tumor cell invasion and metastasis.

Intelligent Albumin-MnO2 Nanoparticles as pH-/H2 O2 -Responsive Dissociable Nanocarriers to Modulate Tumor Hypoxia for Effective Combination Therapy

A unique type of pH/H2 O2 dual-responsive intelligent nanoscale delivery system based on albumin-coated MnO2 is presented, which is capable of modulating the tumor microenvironment (TME) by relieving hypoxia. Additionally, TME-responsive size changes enable effective intratumor diffusion. A highly effective combined photodynamic and chemotherapy is realized with these nanoparticles in a mouse tumor model.

Dysfunctional CD8 T Cells Form a Proliferative, Dynamically Regulated Compartment within Human Melanoma

Tumor immune cell compositions play a major role in response to immunotherapy, but the heterogeneity and dynamics of immune infiltrates in human cancer lesions remain poorly characterized. Here, we identify conserved intratumoral CD4 and CD8 T cell behaviors in scRNA-seq data from 25 melanoma patients. We discover a large population of CD8 T cells showing continuous progression from an early effector "transitional" into a dysfunctional T cell state. CD8 T cells that express a complete cytotoxic gene set are rare, and TCR sharing data suggest their independence from the transitional and dysfunctional cell states. Notably, we demonstrate that dysfunctional T cells are the major intratumoral proliferating immune cell compartment and that the intensity of the dysfunctional signature is associated with tumor reactivity. Our data demonstrate that CD8 T cells previously defined as exhausted are in fact a highly proliferating, clonal, and dynamically differentiating cell population within the human tumor microenvironment.

Systemic Immunity Is Required for Effective Cancer Immunotherapy

Immune responses involve coordination across cell types and tissues. However, studies in cancer immunotherapy have focused heavily on local immune responses in the tumor microenvironment. To investigate immune activity more broadly, we performed an organism-wide study in genetically engineered cancer models using mass cytometry. We analyzed immune responses in several tissues after immunotherapy by developing intuitive models for visualizing single-cell data with statistical inference. Immune activation was evident in the tumor and systemically shortly after effective therapy was administered. However, during tumor rejection, only peripheral immune cells sustained their proliferation. This systemic response was coordinated across tissues and required for tumor eradication in several immunotherapy models. An emergent population of peripheral CD4 T cells conferred protection against new tumors and was significantly expanded in patients responding to immunotherapy. These studies demonstrate the critical impact of systemic immune responses that drive tumor rejection.

Exosomes in tumor microenvironment influence cancer progression and metastasis

Exosomes are small membrane vesicles of endocytic origin with a size of 50-100 nm. They can contain microRNAs, mRNAs, DNA fragments, and proteins, which are shuttled from a donor cell to recipient cells. Many different cell types including immune cells, mesenchymal cells, and cancer cells release exosomes. There is emerging evidence that cancer-derived exosomes contribute to the recruitment and reprogramming of constituents associated with tumor environment. Here, we discuss different mechanisms associated with biogenesis, payload, and transport of exosomes. We highlight the functional relevance of exosomes in cancer, as related to tumor microenvironment, tumor immunology, angiogenesis, and metastasis. Exosomes may exert an immunosuppressive function as well as trigger an anti-tumor response by presenting tumor antigens to dendritic cells. Exosomes may serve as cancer biomarkers and aid in the treatment of cancer.