Adaptive resistance: a tumor strategy to evade immune attack

The Regulatory Effects of MicroRNAs on Tumor Immunity

MicroRNAs are endogenous noncoding small RNAs that posttranscriptionally regulate the expressions of their target genes. Accumulating research shows that miRNAs are crucial regulators of immune cell growth and antitumor immune response. Studies on miRNAs and tumors primarily focus on the tumor itself. At the same time, relatively few studies on the indirect regulatory effects of miRNAs in the development of tumors are achieved by affecting the immune system of tumor hosts and altering their immune responses. This review discusses the influence of miRNAs on the antitumor immune system.

CD155 and CD112 as possible therapeutic targets of FLT3 inhibitors for acute myeloid leukemia

Acute myeloid leukemia (AML) relapse is considered to be related to escape from antitumor immunity. Changes in the expression of immune checkpoints, including B7 homolog (H)1 and B7-H2, have been reported to contribute to AML progression. Binding of T cell immunoglobulin and immunoreceptor tyrosine-based inhibitory motif domain (TIGIT) among other immune checkpoints on natural killer (NK) and T cells to CD155/CD112 in tumors is supposed to be inhibitory; however, the mechanism by which changes in CD155 and CD112 expression affect tumor immunity remains unclear. When the increased expression of CD155 and CD112 activates Raf-MEK-ERK pathway and Raf-MEK-ERK pathway is one of the targets of FMS-like tyrosine kinase 3 (FLT3) inhibition. The present study investigated the alterations in CD155 and CD112 expression under FLT3 inhibition (quizartinib and gilteritinib) and studied its effect on NK and T cell cytotoxicity. CD155 and CD112 expression was analyzed using flow cytometry and reverse transcription-quantitative PCR in AML cell lines with or without FLT3 mutation using FLT3 inhibitors. CD155 and CD112 expression was specifically downregulated by FLT3 inhibition in FLT3-mutated cell lines. Direct cytotoxicity and antibody-dependent cellular cytotoxicity against these cells by NK cells were enhanced. However, the cytotoxicity of γδ T cells with low TIGIT expression compared with NK cells was not enhanced in direct cytotoxicity assay using luciferase luminescence. The analysis of clinical trials from The Cancer Genome Atlas (TCGA) revealed that high CD155 and CD112 expression is associated with poor overall survival. The enhanced cytotoxicity of NK cells against CD155- and CD112-downregulated cells following FLT3 inhibition indicated CD155 and CD112 as possible targets of immunotherapy for AML using FLT3 inhibitors.

Small cell lung cancer stem cells display mesenchymal properties and exploit immune checkpoint pathways in activated cytotoxic T lymphocytes

Small cell lung cancer (SCLC) is an aggressive tumor type with early dissemination and distant metastasis capacity. Even though optimal chemotherapy responses are observed initially in many patients, therapy resistance is almost inevitable. Accordingly, SCLC has been regarded as an archetype for cancer stem cell (CSC) dynamics. To determine the immune-modulatory influence of CSC in SCLC, this study focused on the characterization of CD44⁺CD90⁺ CSC-like subpopulations in SCLC. These cells displayed mesenchymal properties, differentiated into different lineages and further contributed to CD8⁺ cytotoxic T lymphocytes (CTL) responses. The interaction between CD44⁺CD90⁺ CSC-like cells and T cells led to the upregulation of checkpoint molecules PD-1, CTLA-4, TIM-3, and LAG3. In the patient-derived lymph nodes, CD44⁺ SCLC metastases were also observed with T cells expressing PD-1, TIM-3, or LAG3. Proliferation and IFN-γ expression capacity of TIM-3 and LAG3 co-expressing CTLs are adversely affected over long-time co-culture with CD44⁺CD90⁺ CSC-like cells. Moreover, especially through IFN-γ secreted by the T cells, the CSC-like SCLC cells highly expressed PD-L1 and PD-L2. Upon a second encounter with immune-experienced, IFN-γ-stimulated CSC-like SCLC cells, both cytotoxic and proliferation capacities of T cells were hampered. In conclusion, our data provide evidence for the superior potential of the SCLC cells with stem-like and mesenchymal properties to gain immune regulatory capacities and cope with cytotoxic T cell responses. With their high metastatic and immune-modulatory assets, the CSC subpopulation in SCLC may serve as a preferential target for checkpoint blockade immunotherapy .

Evaluation of PD-L1 and other immune markers in bladder urothelial carcinoma stratified by histologic variants and molecular subtypes

Although advanced bladder cancer overall has a poor prognosis, a subset of patients demonstrate durable response to immune checkpoint inhibitors. Evidence shows that the response to checkpoint inhibitors may be associated with type and degree of immune infiltration in the tumor microenvironment. Here, we evaluated immune markers stratified by molecular subtypes and histologic variants. The study utilized a series of urothelial carcinomas (UCs) by tissue microarray, on which histologic variants and molecular subtypes had previously been established. PD1, CD3, CD8 and CD68 expression was evaluated by immunohistochemistry in tumor infiltrating immune cells, while PD-L1 expression in the tumor microenvironment was assessed. Each marker was scored semi-quantitatively (score 0–3). Tumors were clustered by marker scores using agglomerative methods, and associations among markers, histologies, and molecular subtypes were analyzed. PD-L1 expression in the tumor microenvironment significantly correlated with presence of CD3, CD8 and chronic inflammation. Urothelial carcinoma may be classified as either immune high or low based on marker expression. The immune high group is enriched in higher CD3, PD-L1, and genomically-unstable molecular subtype, suggesting it may respond to checkpoint inhibitors. We also identified a degree of intratumoral heterogeneity in immune markers in bladder cancer.

Myeloid maturation potentiates STAT3-mediated atypical IFN-γ signaling and upregulation of PD-1 ligands in AML and MDS

Interferon (IFN)-γ is the major mediator of anti-tumor immune responses; nevertheless, cancer cells use intrigue strategies to alter IFN-γ signaling and avoid elimination. Understanding the immune regulatory mechanisms employed by acute myeloid leukemia (AML) and myelodysplastic syndrome (MDS) cells upon exposure to IFN-γ is critical for development of immunotherapy and checkpoint blockade therapy approaches. This study aims to explore the influence of myeloid maturation on IFN-γ-induced PD-L1 and PD-L2 expression and on pro-leukemogenic transcription factor STAT3 signaling in AML and MDS. Stimulation of myeloid blasts’ maturation by all-trans retinoic acid (ATRA) or 1α,25-dihydroxyvitamin D3 (vitamin D) increased the CD11b⁺ fraction that expressed PD-1 ligands in response to IFN-γ. Intriguingly, STAT3 pathway was potently induced by IFN-γ and strengthened upon prolonged exposure. Nonetheless, STAT3-mediated atypical IFN-γ signaling appeared as a negligible factor for PD-L1 and PD-L2 expression. These negative influences of IFN-γ could be alleviated by a small-molecule inhibitor of STAT3, stattic, which also inhibited the upregulation of PD-L1. In conclusion, induction of myeloid maturation enhances the responsiveness of AML and MDS cells to IFN-γ. However, these malignant myeloid cells can exploit both STAT3 pathway and PD-1 ligands to survive IFN-γ-mediated immunity and maintain secondary immune resistance.

Immunotherapy for non-small cell lung cancers: biomarkers for predicting responses and strategies to overcome resistance

Recent breakthroughs in targeted therapy and immunotherapy have revolutionized the treatment of lung cancer, the leading cause of cancer-related deaths in the United States and worldwide. Here we provide an overview of recent progress in immune checkpoint blockade therapy for treatment of non-small cell lung cancer (NSCLC), and discuss biomarkers associated with the treatment responses, mechanisms underlying resistance and strategies to overcome resistance. The success of immune checkpoint blockade therapies is driven by immunogenicity of tumor cells, which is associated with mutation burden and neoantigen burden in cancers. Lymphocyte infiltration in cancer tissues and interferon-γ-induced PD-L1 expression in tumor microenvironments may serve as surrogate biomarkers for adaptive immune resistance and likelihood of responses to immune checkpoint blockade therapy. In contrast, weak immunogenicity of, and/or impaired antigen presentation in, tumor cells are primary causes of resistance to these therapies. Thus, approaches that increase immunogenicity of cancer cells and/or enhance immune cell recruitment to cancer sites will likely overcome resistance to immunotherapy.

D-2-Hydroxyglutarate Is an Intercellular Mediator in IDH-Mutant Gliomas Inhibiting Complement and T Cells

Purpose: Somatic mutations in the isocitrate dehydrogenase (IDH)-1 and -2 genes are remarkably penetrant in diffuse gliomas. These highly effective gain-of-function mutations enable mutant IDH to efficiently metabolize isocitrate to D-2-hydroxyglutarate (D 2-HG) that accumulates to high concentrations within the tumor microenvironment. D 2-HG is an intracellular effector that promotes tumor growth through widespread epigenetic changes in IDH-mutant tumor cells, but its potential role as an intercellular immune regulator remains understudied.Experimental Design: Complement activation and CD4⁺, CD8⁺, or FOXP3⁺ T-cell infiltration into primary tumor tissue were determined by immunohistochemistry using sections from 72 gliomas of World Health Organization (WHO) grade III and IV with or without IDH mutations. Ex vivo experiments with D 2-HG identified immune inhibitory mechanisms.Results: IDH mutation associated with significantly reduced complement activation and decreased numbers of tumor-infiltrating CD4⁺ and CD8⁺ T cells with comparable FOXP3⁺/CD4⁺ ratios. D 2-HG potently inhibited activation of complement by the classical and alternative pathways, attenuated complement-mediated glioma cell damage, decreased cellular C3b(iC3b) opsonization, and impaired complement-mediated phagocytosis. Although D 2-HG did not affect dendritic cell differentiation or function, it significantly inhibited activated T-cell migration, proliferation, and cytokine secretion.Conclusions: D 2-HG suppresses the host immune system, potentially promoting immune escape of IDH-mutant tumors. Clin Cancer Res; 24(21); 5381-91. ©2018 AACR.

Regulation of cancer immune escape: The roles of miRNAs in immune checkpoint proteins

Immune checkpoint proteins (ICPs) are regulators of immune system. The ICP dysregulation silences the host immune response to cancer-specific antigens, contributing to the occurrence and progress of various cancers. MiRNAs are regulatory molecules and function in mRNA silencing and post-transcriptional regulation of gene expression. MiRNAs that modulate the immunity via ICPs have received increasing attention. Many studies have shown that the expressions of ICPs are directly or indirectly repressed by miRNAs in multiple types of cancers. MiRNAs are also subject to regulation by ICPs. In this review, recent studies of the relationship between miRNAs and ICPs (including the PD-1, PD-L1, CTLA-4, ICOS, B7-1, B7-2, B7-H2, B7-H3, CD27, CD70, CD40, and CD40L) in cancer immune escape are comprehensively discussed, which provide critical detailed mechanistic insights into the functions of the miRNA-ICP axes and their effects on immune escape, and will be beneficial for the potential applications of immune checkpoint therapy and miRNA-based guidance for personalized medicine as well as for predicting the prognosis.

Type Iγ phosphatidylinositol phosphate kinase regulates PD-L1 expression by activating NF-κB

The programmed death-ligand 1 (PD-L1), by binding to PD-1 on the surface of immune cells, activates a major immune checkpoint pathway. Elevated expression of PD-L1 in tumor cells mediates tumor-induced T-cell exhaustion and immune suppression; therefore protect the survival of tumor cells. Although blockade of the PD-1/PD-L1 axis exhibits great potential in cancer treatment, mechanisms driving the up-regulation of PD-L1 in tumor cells remain not fully understood. Here we found that type Iγ phosphatidylinositol 4-phosphate (PtdIns(4)P) 5-kinase (PIPKIγ) is required for PD-L1 expression in triple negative breast cancer cells. Depletion of PIPKIγ inhibits both intrinsic and induced PD-L1 expression. Results from further analyses suggest that PIPKIγ promotes the transcription of the PD-L1 gene by activating the NF-κB pathway in these cells. These results demonstrate that PIPKIγ-dependent expression of PD-L1 is likely important for the progression of triple negative breast cancer.

Role of the Immune Response in Disease Progression and Therapy in Multiple Myeloma

Multiple myeloma (MM) is a hematologic cancer derived from malignant plasma cells within the bone marrow. Unlike most solid tumors, which originate from epithelial cells, the myeloma tumor is a plasma cell derived from the lymphoid cell lineage originating from a post-germinal B-cell. As such, the MM plasma cell represents an integral component of the immune system in terms of both antibody production and antigen presentation, albeit not efficiently. This fundamental difference has significant implications when one considers the implications of immunotherapy. In the case of lymphoid malignancies such as myeloma, immune-based strategies must take into consideration this important difference, potentially necessitating immunotherapy targeted toward MM to be altered from that targeted at solid tumors. Typically, the immune system "surveys" cells within our body and is able to recognize and attack cancerous cells that may arise. However, some cancer cells are able to evade immune surveillance and continue to flourish, causing disease. The major mechanism leading to an effective tumor-specific response is one that enables effective antigen processing and presentation with subsequent T-cell activation, expansion, and effective trafficking to the tumor site. Plasma cells employ several mechanisms to escape immune surveillance which include altered interactions with T-cells, DCs, bone marrow stromal cells (BMSC's), and natural killer cells (NK Cells) that can be mediated by immunosuppressive cells such as and myeloid-derived suppressor cells (MDSC's) and cytokines such as IL-10, TGFβ, and IL-6 as well as down-regulation of the antigen processing machinery. Many therapies have been developed to reestablish a functional immune system in MM patients. These include adoptive T-cell therapies to deliver more tumor-specific T-cells, vaccines to increase the tumor-specific precursor frequency of the endogenous T-cell population, immunomodulatory agents (IMiDs) such as thalidomide and lenalidomide to enhance global endogenous immunity, immunostimulatory cytokines, and antibodies to specifically target tumor-specific cell-surface proteins or cytokines. This review will dissect these various approaches currently being explored in MM as well as highlight some future directions for myeloma-specific immune-based strategies.

Chloroquine (CQ) exerts anti-breast cancer through modulating microenvironment and inducing apoptosis

CQ is an anti-malaria drug, which has been used for years. However, there are published articles about its activity in anti-cancers. The aim of this approach was to look at possibility and related mechanisms of anti-breast cancer (mouse breast cancer cell line 4T1) by CQ alone. The studies of anti 4T1 in vitro and in vivo by CQ were performed. The growth of 4T1 in vitro and in vivo, survival of mice post treatment with CQ, changes of immune parameters and microenvironment in mice were evaluated. Our results demonstrate that CQ could markedly inhibit growth of 4T1 in vitro through inducing apoptosis of cells, inhibiting secretion of TGF-β and prolong the mice survival in vivo through boosting immune system by upregulating CD8+ T cell, and through down-regulating tumor associated macrophages (TAM), myeloid derived suppressing cells (MDSC) and Tregs, in microenvironment of mice bearing tumor. This provides a new mode of action for CQ and it is therefore concluded that CQ could be with potential in breast cancer therapy.

Functional exhaustion of CD4+ T cells induced by co-stimulatory signals from myeloid leukaemia cells

To cope with immune responses, tumour cells implement elaborate strategies such as adaptive resistance and induction of T-cell exhaustion. T-cell exhaustion has been identified as a state of hyporesponsiveness that arises under continuous antigenic stimulus. Nevertheless, contribution of co-stimulatory molecules to T-cell exhaustion in cancer remains to be better defined. This study explores the role of myeloid leukaemia-derived co-stimulatory signals on CD4⁺ T helper (Th) cell exhaustion, which may limit anti-tumour immunity. Here, CD86 and inducible T-cell co-stimulator ligand (ICOS-LG) co-stimulatory molecules that are found on myeloid leukaemia cells supported Th cell activation and proliferation. However, under continuous stimulation, T cells co-cultured with leukaemia cells, but not with peripheral blood monocytes, became functionally exhausted. These in vitro-generated exhausted Th cells were defined by up-regulation of programmed cell death 1 (PD-1), cytotoxic T-lymphocyte antigen 4 (CTLA-4), lymphocyte activation gene 3 (LAG3) and T-cell immunoglobulin and mucin domain-containing protein 3 (TIM-3) inhibitory receptors. They were reluctant to proliferate upon re-stimulation and produced reduced amounts of interleukin-2 (IL-2), tumour necrosis factor-α (TNF-α) and interferon-γ (IFN-γ). Nonetheless, IL-2 supplementation restored the proliferation capacity of the exhausted Th cells. When the co-stimulation supplied by the myeloid leukaemia cells were blocked, the amount of exhausted Th cells was significantly decreased. Moreover, in the bone marrow aspirates from patients with acute myeloid leukaemia (AML) or myelodysplastic syndrome (MDS), a subpopulation of Th cells expressing PD-1, TIM-3 and/or LAG3 was identified together with CD86⁺ and/or ICOS-LG⁺ myeloid blasts. Collectively, co-stimulatory signals derived from myeloid leukaemia cells possess the capacity to facilitate functional exhaustion in Th cells.

Critical issues in cancer vaccine trial design

As the clinical experience with cancer vaccines and cancer immunotherapy increases, there are important lessons that can be learned from the successes and failures of past trials. Many lessons affect the design and conduct of clinical trials themselves. Appropriate patient selection, clinical trial design, immunologic monitoring, and appropriate endpoints are all essential to the efficiency and success of bringing cancer vaccines from conception to clinical use.

A co-stimulatory trap set by myeloid leukemia cells

The straightforward notion that tumor cells always exert immunosuppressive functions has been contradicted by the finding that myeloid leukemia cells can express potent co-stimulatory molecules. Indeed, the co-stimulatory support offered by leukemia cells can provoke helper T-cell responses. Unfavorably, this interaction allows leukemia cells to acquire immunosuppressive capacities.