Immune checkpoint inhibitors of PD-L1 as cancer therapeutics

Since the discovery of immune checkpoint proteins, there has been a special interest in developing antibodies that block programmed cell death 1 receptor (PD-1) and programmed cell death receptor ligand 1 (PD-L1) for a subset of cancer patients. PD-1 signaling negatively regulates T cell-mediated immune responses and serves as a mechanism for tumors to evade an antigen-specific T cell immunologic response. It plays a role in promoting cancer development and progression by enhancing tumor cell survival. With this background, PD-1 signaling represents a valuable therapeutic target for novel and effective cancer immunotherapy. Clinical data shows that blockade of this PD-1 signaling significantly enhance antitumor immunity, produce durable clinical responses, and prolong survival. Currently, there are three FDA-approved PD-L1 inhibitors for various malignancies ranging from non-small cell lung cancer to Merkel cell carcinoma. This review is to summarize many ongoing phase II/III trials of atezolizumab, durvalumab, avelumab, and new PD-L1 inhibitors in clinical developments. In particular, we focus on key trials that paved the pathway to FDA-approved indications for atezolizumab, durvalumab, and avelumab. Despite the popularity and accelerated FDA approval of PD-L1 inhibitors, further considerations into predictive biomarkers, mechanisms of resistance, treatment duration, immune-related toxicities, and PD-L1 expression threshold are needed to optimize anticancer potential in this class of immunotherapy.

Cancer acidity: An ultimate frontier of tumor immune escape and a novel target of immunomodulation

The link between cancer metabolism and immunosuppression, inflammation and immune escape has generated major interest in investigating the effects of low pH on tumor immunity. Indeed, microenvironmental acidity may differentially impact on diverse components of tumor immune surveillance, eventually contributing to immune escape and cancer progression. Although the molecular pathways underlying acidity-related immune dysfunctions are just emerging, initial evidence indicates that antitumor effectors such as T and NK cells tend to lose their function and undergo a state of mostly reversible anergy followed by apoptosis, when exposed to low pH environment. At opposite, immunosuppressive components such as myeloid cells and regulatory T cells are engaged by tumor acidity to sustain tumor growth while blocking antitumor immune responses. Local acidity could also profoundly influence bioactivity and distribution of antibodies, thus potentially interfering with the clinical efficacy of therapeutic antibodies including immune checkpoint inhibitors. Hence tumor acidity is a central regulator of cancer immunity that orchestrates both local and systemic immunosuppression and that may offer a broad panel of therapeutic targets. This review outlines the fundamental pathways of acidity-driven immune dysfunctions and sheds light on the potential strategies that could be envisaged to potentiate immune-mediated tumor control in cancer patients.

The yin and yang of evasion and immune activation in HCC

Current systemic treatment options for patients with hepatocellular carcinoma (HCC) are limited to sorafenib. With the recent FDA approval of the second PD1-PD-L1 pathway inhibitor, immunotherapy has gained even more interest as a potential novel treatment option for patients with HCC. This is due not only because of the failure of other treatment approaches in the past, but also because immunological mechanisms have been shown to play an important role during tumor development, growth, and treatment. Here we present a review of immunological mechanisms in the liver relevant for tumor progression and treatment. We summarize our current knowledge on immune activating and immune suppressing mechanisms during tumor initiation, development, and treatment. We try to explain the paradox of how inflammatory responses in a setting of chronic infection promote tumor development, while the primary aim of immunotherapy is to activate immunity. Finally we summarize recent advances in addition to providing an outlook for the immunotherapy of HCC.

Soluble immune checkpoints in cancer: production, function and biological significance

Immune checkpoints play important roles in immune regulation, and blocking immune checkpoints on the cell membrane is a promising strategy in the treatment of cancer. Based on this, monoclonal antibodies are having much rapid development, such as those against CTLA-4 (cytotoxic T lymphocyte antigen 4) and PD-1 (programmed cell death protein 1).But the cost of preparation of monoclonal antibodies is too high and the therapeutic effect is still under restrictions. Recently, a series of soluble immune checkpoints have been found such as sCTLA-4 (soluble CTLA-4) and sPD-1 (soluble PD-1). They are functional parts of membrane immune checkpoints produced in different ways and can be secreted by immune cells. Moreover, these soluble checkpoints can diffuse in the serum. Much evidence has demonstrated that these soluble checkpoints are involved in positive or negative immune regulation and that changes in their plasma levels affect the development, prognosis and treatment of cancer. Since they are endogenous molecules, they will not induce immunological rejection in human beings, which might make up for the deficiencies of monoclonal antibodies and enhance the utility value of these molecules. Therefore, there is an increasing need for investigating novel soluble checkpoints and their functions, and it is promising to develop relevant therapies in the future. In this review, we describe the production mechanisms and functions of various soluble immune checkpoint receptors and ligands and discuss their biological significance in regard to biomarkers, potential candidate drugs, therapeutic targets, and other topics.

Treg-mediated acquired resistance to immune checkpoint inhibitors

T Regulatory cells (Tregs) act as a double-edged sword by regulating immune homeostasis (protective role) and inhibiting immune responses in different disease settings (pathological role). They contribute to cancer development and progression by suppressing T effector cell (Teff) functions. Decreased ratios of intratumoral CD8⁺ T cells to Tregs have been associated with poor prognosis in most cancer types. Targeting immune checkpoints (ICs), such as cytotoxic T lymphocyte-associated antigen-4 (CTLA-4) and programmed cell death-1 (PD-1), by immune checkpoint inhibitors (ICIs) in cancer patients has been beneficial in inducing anti-tumor immune responses and improving clinical outcomes. However, response rates remain relatively low, ranging from 15 to 40% depending on cancer type. Additionally, a significant proportion of patients who initially demonstrates a clinical response can acquire resistance overtime. This acquired resistance could occur due to the emergence of compensatory mechanisms within the tumor microenvironment (TME) to evade the anti-tumor effects of ICIs. In this review, we describe the immunosuppressive role of Tregs in the TME, the effects of currently approved ICIs on Treg phenotype and function, and the mechanisms of acquired resistance to ICIs mediated by Tregs within the TME, such as the over-expression of ICs, the up-regulation of immunosuppressive molecules, and apoptotic Treg-induced immunosuppression. We also describe potential therapeutic strategies to target Tregs in combination with ICIs aiming to overcome such resistance and improve clinical outcomes. Elucidating the Treg-mediated acquired resistance mechanisms should benefit the designing of well-targeted therapeutic strategies to overcome resistance and maximize the therapeutic efficacy in cancer patients.

Immune checkpoints in the tumor microenvironment

Interactions between immune checkpoints (ICs) and their ligands negatively regulate T cell activation pathways involved in physiological immune responses against specific antigens. ICs and their ligands are frequently upregulated in the tumor microenvironment (TME) of various malignancies, and they represent significant barriers for induction of effective anti-tumor immune responses. Several IC inhibitors (ICIs) have been developed, with some currently in clinical trials and others have been approved for the treatment of different cancers. However, tumor cells are able to counteract the activity of ICIs and can commission additional inhibitory pathways via expression of other ICs/ligands within the TME. This review discusses the expression of various ICs/ligands in the TME and their impact on tumor immune evasion. Additionally, we discuss various regulatory mechanisms, including genetic and epigenetic, and other modulatory factors including hypoxia and the presence of immunosuppressive populations in the TME, which result in upregulation of ICs in various cancers. Moreover, we discuss the prognostic significance of ICs and their ligands, and the potential strategies to enhance treatment responses to ICIs. This review aims to advance our current knowledge on the role of ICs in the TME and the clinical benefits of targeting them.

TMB or not TMB as a biomarker: That is the question

Immune checkpoint inhibitors (ICIs) have revolutionized the landscape of therapeutic options for many cancers. These treatments have demonstrated improved efficacy and often a more favourable toxicity profile compared to standard cytotoxic chemotherapy. There are considerable differences among responders, with some patients experiencing durable long-term disease control and even remission. Given this variability, determining a proper biomarker to select patients for ICI therapy has become increasingly important. The only biomarker proven to be predictive of overall survival benefit with ICI therapy is PD-L1 expression level measured by immunohistochemistry. Several attempts have been made to identify different predictive biomarkers. One of the most intriguing and divisive is tumor mutational burden (TMB). TMB represents the number of mutations per megabase (Mut/Mb) of DNA that were sequenced in a specific cancer. With a higher number of mutations detected, and consequentially an increase in the number neo-epitopes, then it is more likely that one or more of those neo-antigens could be immunogenic and trigger a T cell response. Initially, TMB was identified as a biomarker for ICIs in melanoma and subsequent studies suggested a possible clinical role for TMB in non-small cell lung cancer. The initial data were not confirmed in a prospective study assessing OS as the primary endpoint. Recently, the FDA has approved pembrolizumab in all cancers with a TMB > 10Mut/Mb[12] based on findings from the phase 2 KEYNOTE-158. Much criticism has emerged about this pan-cancer approval, in particular about the use of TMB as biomarker to select patients. Here we review the data about the importance and role of TMB as possible pan-cancer one-size-fits-all biomarker. We highlight the strengths and intrinsic limitations of such a complex biomarker and its adoption in the daily practice.

Immunotherapy for triple-negative breast cancer: Existing challenges and exciting prospects

Patients with breast tumors that do not express the estrogen receptor, the progesterone receptor, nor Her-2/neu are hence termed "triple negatives", and generally have a poor prognosis, with high rates of systemic recurrence and refractoriness to conventional therapy regardless of the choice of adjuvant treatment. Thus, more effective therapeutic options are sorely needed for triple-negative breast cancer (TNBC), which occurs in approximately 20% of diagnosed breast cancers. In recent years, exploiting intrinsic mechanisms of the host immune system to eradicate cancer cells has achieved impressive success, and the advances in immunotherapy have yielded potential new therapeutic strategies for the treatment of this devastating subtype of breast cancer. It is anticipated that the responses initiated by immunotherapeutic interventions will explicitly target and annihilate tumor cells, while at the same time spare normal cells. Various immunotherapeutic approaches have been already developed and tested, which include the blockade of immune checkpoints using neutralizing or blocking antibodies, induction of cytotoxic T lymphocytes (CTLs), adoptive cell transfer-based therapy, and modulation of the tumor microenvironment to enhance the activity of CTLs. One of the most important areas of breast cancer research today is understanding the immune features and profiles of TNBC and devising novel immune-modulatory strategies to tackling TNBC, a subtype of breast cancer notorious for its poor prognosis and its imperviousness to conventional treatments. On the optimal side, one can anticipate that novel, effective, and personalized immunotherapy for TNBC will soon achieve more success and impact clinical treatment of this disease which afflicts approximately 20% of patients with breast cancer. In the present review, we highlight the current progress and encouraging developments in cancer immunotherapy, with a goal to discuss the challenges and to provide future perspectives on how to exploit a variety of new immunotherapeutic approaches including checkpoint inhibitors and neoadjuvant immunotherapy for the treatment of patients with TNBC.

Immune checkpoint blockade and CAR-T cell therapy in hematologic malignancies

Harnessing the power of the immune system to recognize and eliminate cancer cells is a longtime exploration. In the past decade, monoclonal antibody (mAb)-based immune checkpoint blockade (ICB) and chimeric antigen receptor T (CAR-T) cell therapy have proven to be safe and effective in hematologic malignancies. Despite the unprecedented success of ICB and CAR-T therapy, only a subset of patients can benefit partially due to immune dysfunction and lack of appropriate targets. Here, we review the preclinical and clinical advances of CTLA-4 and PD-L1/PD-1-based ICB and CD19-specific CAR-T cell therapy in hematologic malignancies. We also discuss the basic research and ongoing clinical trials on emerging immune checkpoints (Galectin-9/Tim-3, CD70/CD27, LAG-3, and LILRBs) and on new targets for CAR-T cell therapy (CD22, CD33, CD123, BCMA, CD38, and CD138) for the treatment of hematologic malignancies.

STING Pathway Expression Identifies NSCLC With an Immune-Responsive Phenotype

INTRODUCTION

Although the combination of anti-programmed cell death-1 or anti-programmed cell death ligand-1 (PD-L1) with platinum chemotherapy is a standard of care for NSCLC, clinical responses vary. Even though predictive biomarkers (which include PD-L1 expression, tumor mutational burden, and inflamed immune microenvironment) are validated for immunotherapy, their relevance to chemoimmunotherapy combinations is less clear. We have recently reported that activation of the stimulator of interferon genes (STING) innate immune pathway enhances immunotherapy response in SCLC. Here, we hypothesize that STING pathway activation may predict and underlie predictive correlates of antitumor immunity in NSCLC.

METHODS

We analyzed transcriptomic and proteomic profiles in two NSCLC cohorts from our institution (treatment-naive patients in the Profiling of Resistance Patterns and Oncogenic Signaling Pathways in Evaluation of Cancers of the Thorax study and relapsed patients in the Biomarker-Integrated Approaches of Targeted Therapy for Lung Cancer Elimination study) and The Cancer Genome Atlas (N = 1320). Tumors were stratified by STING activation on the basis of protein or mRNA expression of cyclic GMP-AMP synthase, phospho-STING, and STING-mediated chemokines (chemokine ligand 5 [CCL5] and C-X-C motif chemokine 10 [CXCL10]). STING activation in patient tumors and in platinum-treated preclinical NSCLC models was correlated with biomarkers of immunotherapy response.

RESULTS

STING activation is associated with higher levels of intrinsic DNA damage, targetable immune checkpoints, and chemokines in treatment-naive and relapsed lung adenocarcinoma. We observed that tumors with lower STING and immune gene expression show higher frequency of serine-threonine kinase 11 (STK11) mutations; however, we identified a subset of these tumors that are TP53 comutated and display high immune- and STING-related gene expression. Treatment with cisplatin increases STING pathway activation and PD-L1 expression in multiple NSCLC preclinical models, including adeno- and squamous cell carcinoma.

CONCLUSIONS

STING pathway activation in NSCLC predicts features of immunotherapy response and is enhanced by cisplatin treatment. This suggests a possible predictive biomarker and mechanism for improved response to chemoimmunotherapy combinations.

Immune privilege in corneal transplantation

Corneal transplantation is the most successful solid organ transplantation performed in humans. The extraordinary success of orthotopic corneal allografts, in both humans and experimental animals, is related to the phenomenon of "immune privilege". Inflammation is self-regulated to preserve ocular functions because the eye has immune privilege. At present, three major mechanisms are considered to provide immune privilege in corneal transplantation: 1) anatomical, cellular, and molecular barriers in the cornea; 2) tolerance related to anterior chamber-associated immune deviation and regulatory T cells; and 3) an immunosuppressive intraocular microenvironment. This review describes the mechanisms of immune privilege that have been elucidated from animal models of ocular inflammation, especially those involving corneal transplantation, and its relevance for the clinic. An update on molecular, cellular, and neural interactions in local and systemic immune regulation is provided. Therapeutic strategies for restoring immune privilege are also discussed.

Altered cancer metabolism in mechanisms of immunotherapy resistance

Many metabolic alterations, including the Warburg effect, occur in cancer cells that influence the tumor microenvironment, including switching to glycolysis from oxidative phosphorylation, using opportunistic modes of nutrient acquisition, and increasing lipid biosynthesis. The altered metabolic landscape of the tumor microenvironment can suppress the infiltration of immune cells and other functions of antitumor immunity through the production of immune-suppressive metabolites. Metabolic dysregulation in cancer cells further affects the expression of cell surface markers, which interferes with immune surveillance. Immune checkpoint therapies have revolutionized the standard of care for some patients with cancer, but disease in many others is resistant to immunotherapy. Specific metabolic pathways involved in immunotherapy resistance include PI3K-Akt-mTOR, hypoxia-inducible factor (HIF), adenosine, JAK/STAT, and Wnt/Beta-catenin. Depletion of essential amino acids such as glutamine and tryptophan and production of metabolites like kynurenine in the tumor microenvironment also blunt immune cell function. Targeted therapies against metabolic checkpoints could work in synergy with immune checkpoint therapy. This combined strategy could be refined by profiling patients' mutation status before treatment and identifying the optimal sequencing of therapies. This personalized combinatorial approach, which has yet to be explored, may well pave the way for overcoming resistance to immunotherapy.

Immunotherapy in NSCLC: A Promising and Revolutionary Weapon

Lung cancer is the leader malignancy worldwide accounting 1.5 millions of deaths every year. In the United States the 5 year-overall survival is less than 20% for all the newly diagnosed patients. Cisplatin-based cytotoxic chemotherapy for unresectable or metastatic NSCLC patients in the first line of treatment, and docetaxel in the second line, have achieved positive results but with limited benefit in overall survival. Targeted therapies for EGFR and ALK mutant patients have showed better results when compared with chemotherapy, nevertheless most of patients will fail and need to be treated with chemotherapy if they still have a good performance status.Immunotherapy recently has become the most revolutionary treatment in solid tumors patients. First results in unresectable and metastatic melanoma patients treated with an anti CTLA-4 monoclonal antibody showed an unexpected 3-year overall survival of at least 25%.Lung cancer cells have multiple immunosuppressive mechanisms that allow to escape of the immune system and survive, however blocking CTLA-4 pathway with antibodies as monotherapy treatment have not achieved same results than in melanoma patients. PD-1 expression has been demonstrated in different tumor types, suggesting than PD-1 / PD-L1 pathway is a common mechanism used by tumors to avoid immune surveillance and favoring tumor growth. Anti PD-1 and anti PD-L1 antibodies have showed activity in non-small cell lung cancer patients with significant benefit in overall survival, long lasting responses and good safety profile, including naïve and pretreated patients regardless of the histological subtype. Even more, PD-1 negative expression patients achieve similar results in overall survival when compared with patients treated with chemotherapy. In the other side high PD-1 expression patients that undergo immunotherapy treatment achieve better results in terms of survival with lesser toxicity. Combining different immunotherapy treatments, combination of immunotherapy with chemotherapy or with targeted treatment are under research with some promising PRELIMINARY results in non-small cell lung cancer patients.This chapter attempts to summarize the development of immunotherapy treatment in non-small cell lung cancer patients and explain the results that have leaded immunotherapy as a new standard of treatment in selected NSCLC patients.

DNA methylation and repressive H3K9 and H3K27 trimethylation in the promoter regions of PD-1, CTLA-4, TIM-3, LAG-3, TIGIT, and PD-L1 genes in human primary breast cancer

BACKGROUND

High expression of immune checkpoints in tumor microenvironment plays significant roles in inhibiting anti-tumor immunity, which is associated with poor prognosis and cancer progression. Major epigenetic modifications in both DNA and histone could be involved in upregulation of immune checkpoints in cancer.

METHODS

Expressions of different immune checkpoint genes and PD-L1 were assessed using qRT-PCR, and the underlying epigenetic modifications including CpG methylation and repressive histone abundance were determined using bisulfite sequencing, and histone 3 lysine 9 trimethylation (H3K9me3) and histone 3 lysine 27 trimethylation (H3K27me3) chromatin immunoprecipitation assays (ChIP), respectively.

RESULTS

We first assessed the expression level of six immune checkpoints/ligands and found that PD-1, CTLA-4, TIM-3, and LAG-3 were significantly upregulated in breast tumor tissues (TT), compared with breast normal tissues (NT). We investigated the epigenetic modifications beyond this upregulation in immune checkpoint genes. Interestingly, we found that CpG islands in the promoter regions of PD-1, CTLA-4, and TIM-3 were significantly hypomethylated in tumor compared with normal tissues. Additionally, CpG islands of PD-L1 promoter were completely demethylated (100%), LAG-3 were highly hypomethylated (80-90%), and TIGIT were poorly hypomethylated (20-30%), in both NT and TT. These demethylation findings are in accordance with the relative expression data that, out of all these genes, PD-L1 was highly expressed and completely demethylated and TIGIT was poorly expressed and hypermethylated in both NT and TT. Moreover, bindings of H3K9me3 and H3K27me3 were found to be reduced in the promoter loci of PD-1, CTLA-4, TIM-3, and LAG-3 in tumor tissues.

CONCLUSION

Our data demonstrate that both DNA and histone modifications are involved in upregulation of PD-1, CTLA-4, TIM-3, and LAG-3 in breast tumor tissue and these epigenetic modifications could be useful as diagnostic/prognostic biomarkers and/or therapeutic targets in breast cancer.

An immune stratification reveals a subset of PD-1/LAG-3 double-positive triple-negative breast cancers

Background

Stromal tumor-infiltrating lymphocytes (TILs) are a robust prognostic factor in triple-negative breast cancer (TNBC). However, the clinical significance of TILs may be influenced by the complex landscape of the tumor immune microenvironment. In this study, we aimed to evaluate the composition and the functionality of lymphocytic infiltration and checkpoint receptors in TNBC.

Methods

Formalin-fixed, paraffin-embedded tissues were retrospectively collected from a cohort of patients with early-stage TNBC treated with adjuvant anthracycline-based chemotherapy (n = 259). Results were validated in an independent cohort of patients with TNBC (n = 104). Stromal TILs were evaluated on hematoxylin-and-eosin-stained sections. The density of CD4+, CD8+, and FOXP3+ lymphocytes, and the expression of the immune checkpoints PD-1 and LAG-3, were assessed by immunohistochemical analysis.

Results

The presence of elevated TILs positively correlated with the density of all T cell subtypes, especially cytotoxic CD8+ lymphocytes. We showed that increasing stromal TILs assessed as a continuous variable is an independent prognostic marker of prolonged relapse-free survival and overall survival in TNBC. Among immune subpopulations, CD8+ lymphocytes are the main effectors of anti-tumor immune responses. In two independent cohorts, we found that PD-1 and LAG-3 were concurrently expressed in approximately 15% of patients with TNBC. The expression of both checkpoint receptors positively correlated with the presence of TILs, but was not significantly associated with patient outcome.

Conclusions

Overall, our data indicate that the evaluation of stromal TILs remains the most reliable immune prognostic marker in TNBC, and support the clinical evaluation of anti-PD-1/PD-L1 and anti-LAG-3 in a subset of patients with TNBC who have concurrent expression of both checkpoint receptors.

Electronic supplementary material

The online version of this article (doi:10.1186/s13058-016-0783-4) contains supplementary material, which is available to authorized users.

Expression of immune checkpoints and T cell exhaustion markers in early and advanced stages of colorectal cancer

Despite recent advances in colorectal cancer (CRC) treatment, a large proportion of patients show limited responses to therapies, especially in advanced stages. There is an urgent need to identify prognostic biomarkers and/or therapeutic targets in advanced stages, aiming to improve the efficacy of current treatments. We aimed to determine prognostic biomarkers in tumor tissue and circulation of CRC patients, with a special focus on T cell exhaustion markers. We found that mRNA levels of PD-1, TIM-3, CTLA-4, TIGIT, CD160, CD244, KLRG1, TOX2, TOX3, Ki-67, and PRDM1 were elevated in CRC tumor tissues. We also investigated differences in gene expression between early and advanced disease stages. We found that TOX and potentially TIM-3, CTLA-4, VISTA, TIGIT, KLRG1, TOX2, SIRT1, Ki-67, and Helios mRNA levels in tumor tissue were elevated in advanced disease stages, suggesting their potential roles in CRC progression. In contrast, PD-1 and CD160 levels in tumor tissue were downregulated in advanced stages. In the circulation of CRC patients, mRNA levels of PD-1, VISTA and LAG-3 were higher than those of healthy individuals. Moreover, in circulation, PD-1, CTLA-4 and TIGIT mRNA levels were reduced in advanced stages. Interestingly, levels of PD-1 in both tumor tissue and circulation were reduced in advanced stages, suggesting that targeting PD-1 in patients with advanced stages could be less effective. Altogether, these findings suggest some potential T cell exhaustion markers that could be utilized as prognostic biomarkers and/or therapeutic targets for CRC. However, further investigations and validations in larger cohorts are required to confirm these findings.

Cancer immunotherapy: Challenges and limitations

Although cancer immunotherapy has taken center stage in mainstream oncology inducing complete and long-lasting tumor regression, only a subset of patients receiving treatment respond and others relapse after an initial response. Different tumor types respond differently, and even in cancer types that respond (hot tumors), we still observe tumors that are unresponsive (cold tumors), suggesting the presence of resistance. Hence, the development of intrinsic or acquired resistance is a big challenge for the cancer immunotherapy field. Resistance to immunotherapy, including checkpoint inhibitors, CAR-T cell therapy, oncolytic viruses, and recombinant cytokines arises due to cancer cells employing several mechanisms to evade immunosurveillance.

Interaction of host immunity with HER2-targeted treatment and tumor heterogeneity in HER2-positive breast cancer

Growing evidence suggests a clear role of the host immune system in HER2+ breast cancer. In addition, HER2+ breast cancer is generally considered more immunogenic than hormone receptor-positive (HR+)/HER2-, and specific molecular HER2+ subgroups (e.g. HER2-enriched disease) are more immunogenic than others (e.g. Luminal A or B). From a clinical perspective, the immune system plays a relevant prognostic role in HER2+ breast cancer and contributes to the therapeutic effects of trastuzumab. However, as more HER2-targeted agents become available, a better understanding of the role played by the immune system in modulating therapy response to different agents will be needed. Furthermore, the recent introduction in oncology of immune checkpoint inhibitors capable of unleashing anti-tumor immune response opens new possibilities for therapeutic combinations in HER2+ breast cancer. Here, we review the current pre-clinical and clinical data on the interplay between the immune system and HER2+ breast cancer, focusing on different HER2-targeted treatments and the biological heterogeneity that exists within HER2+ disease. Finally, we discuss new therapeutic approaches exploiting the immune system to increase activity or revert resistance to HER2-targeted agents.

A deep insight into CRISPR/Cas9 application in CAR-T cell-based tumor immunotherapies

To date, two chimeric antigen receptors (CAR)-T cell products from autologous T cells have been approved by The United States Food and Drug Administration (FDA). The case-by-case autologous T cell generation setting is largely considered as a pivotal restraining cause for its large-scale clinical use because of the costly and prolonged manufacturing procedure. Further, activated CAR-T cells mainly express immune checkpoint molecules, including CTLA4, PD1, LAG3, abrogating CAR-T anti-tumor activity. In addition, CAR-T cell therapy potently results in some toxicity, such as cytokine releases syndrome (CRS). Therefore, the development of the universal allogeneic T cells with higher anti-tumor effects is of paramount importance. Thus, genome-editing technologies, in particular, clustered regularly interspaced short palindromic repeat (CRISPR)-Cas9 are currently being used to establish "off-the-shelf" CAR-T cells with robust resistance to immune cell-suppressive molecules. In fact, that simultaneous ablation of PD-1, T cell receptor alpha constant (TRAC or TCR), and also β-2 microglobulin (B2M) by CRISPR-Cas9 technique can support the manufacture of universal CAR-T cells with robust resistance to PD-L1. . Indeed, the ablation of β2M or TARC can severely hinder swift elimination of allogeneic T cells those express foreign HLA-I molecules, and thereby enables the generation of CAR-T cells from allogeneic healthy donors T cells with higher persistence in vivo. Herein, we will deliver a brief overview of the CAR-T cell application in the context of tumor immunotherapy. More importantly, we will discuss recent finding concerning the application of genome editing technologies for preparing universal CAR-T cells or cells that can effectively counter tumor escape, with a special focus on CRISPR-Cas9 technology.

Immune evasion by cancer stem cells

Tumor immunity represents a new avenue for cancer therapy. Immune checkpoint inhibitors have successfully improved outcomes in several tumor types. In addition, currently, immune cell-based therapy is also attracting significant attention. However, the clinical efficacy of these treatments requires further improvement. The mechanisms through which cancer cells escape the immune response must be identified and clarified. Cancer stem cells (CSCs) play a central role in multiple aspects of malignant tumors. CSCs can initiate tumors in partially immunocompromised mice, whereas non-CSCs fail to form tumors, suggesting that tumor initiation is a definitive function of CSCs. However, the fact that non-CSCs also initiate tumors in more highly immunocompromised mice suggests that the immune evasion property may be a more fundamental feature of CSCs rather than a tumor-initiating property. In this review, we summarize studies that have elucidated how CSCs evade tumor immunity and create an immunosuppressive milieu with a focus on CSC-specific characteristics and functions. These profound mechanisms provide important clues for the development of novel tumor immunotherapies.

The immune system and hormone-receptor positive breast cancer: Is it really a dead end?

Even if breast cancer has not been traditionally considered an immunogenic tumor, recent data suggest that immunity, and its interaction with tumor cells and tumor microenvironment, might play an important role in this malignancy, in particular in triple negative and HER2+ subtypes. As no consistent data on the potential clinical relevance of tumor infiltrating lymphocytes have been produced in hormone receptor positive (HR+) HER2- breast cancer, the interest in studying immune aspects in this subtype has become less appealing. Nevertheless, some scattered evidence indicates that immunity and inflammation may be implicated in the biology of this subtype as well. In HR+ breast cancer, the interaction between tumor cells and the immune milieu might rely on different mechanisms than in other BC subtypes, involving the modulation of the tumor microenvironment by mutual interplays of endocrine factors, pro-inflammatory status and immune cells. These subtle mechanisms may require more refined methods of evaluation, such as the assessment of tumor infiltrating lymphocytes subpopulations or gene signatures. In this paper we aim to perform a comprehensive review of pre-clinical and clinical data on the interplay between the immune system and breast cancer in the HR+ subtype, to guide further research in the field.

NLRP3 inflammasome upregulates PD-L1 expression and contributes to immune suppression in lymphoma

The NLRP3 inflammasome plays a pro-tumorigenic role in various malignancies. However, its potential role in lymphomagenesis remains unclear. In this study, we identified an immunosuppressive state in patients with diffuse large B cell lymphoma (DLBCL), which was characterized by markedly elevated interleukin (IL)-18 levels in lymphoma tissues and positive correlation with programmed death ligand 1 (PD-L1) expression. Furthermore, NLRP3 inflammasome activation in DLBCL cell lines upregulated PD-L1 and reduced the proportion of cytotoxic T cells. NLRP3 inflammasome blockade in vivo suppressed lymphoma growth and ameliorated anti-tumor immunity by downregulating PD-L1 in the tumor microenvironment and decreasing the proportion of PD-1/TIM-3-expressing T cells, myeloid-derived suppressor cells, tumor-associated macrophages, and regulatory T cells. Further in vivo studies revealed IL-18 as the main effector cytokine involved in the negative regulation of anti-lymphoma immunity. Interestingly, NLRP3 blockers combined with anti-PD-L1 treatment exerted antagonistic effects during lymphoma therapy. Altogether, our findings indicate that NLRP3 inflammasome promotes immunosuppression by modulating PD-L1 and immune cells. Accordingly, this study highlights the prognostic and therapeutic values of the NLRP3 inflammasome in lymphoma.

Expression profiles and clinical value of plasma exosomal Tim-3 and Galectin-9 in non-small cell lung cancer

Exosomes are membrane-bound, virus-sized vesicles present in circulating blood. Tumor cells are avid producers of exosomes, which are thought to mimic molecular features of parent tumor cells. T-cell immunoglobulin- and mucin-domain-containing molecule 3 (Tim-3) is a the next-generation immune checkpoint that can be activated by its ligand Galectin-9 to negatively regulate the anti-tumor immune response. However, the characteristics of plasma exosomal Tim-3 and Galectin-9 (Exo-T/G) in cancer remained unknown. This study was conducted to investigate the expression patterns and clinical value of plasma exosomal total protein (Exo-pro) and Exo-T/G in non-small cell lung cancer (NSCLC). Plasma was collected from 103 NSCLC patients including 60 early stages and 43 advanced stages disease samples as well as 56 healthy subjects. Exosomes were isolated from plasma by commercial exosome precipitation solution and identified by western blotting of CD63 and transmission electron microscopy. Exo-pro concentration was measured by the BCA assay. Enzyme-linked immunosorbent assay was used to quantify Exo-T/G. Additionally, 34 NSCLC samples were applied to directly detect plasma TIM-3 (Plas-T) and Galectin-9 (Plas-G). Our results showed that Exo-pro, Exo-T, and Exo-G were significantly increased in NSCLC plasma compared to that in the healthy samples. High levels of Exo-T and Exo-G were all positively correlated with several malignant parameters, including larger tumor size, advanced stages, and more distant metastasis. High levels of Exo-pro and Exo-T were also correlated with more lymph node metastasis. Additionally, plasma from lung squamous cell carcinoma showed higher Exo-T and Exo-G compared with that from lung adenocarcinoma. ALK-positive patients showed to have decreased Exo-T and Exo-G levels. Pearson's correlation analysis revealed a significant correlation between Exo-pro and Exo-T/G, Exo-T and Exo-G, Exo-T and Plas-T, Exo-G and Plas-G, and Plas-T and Plas-G. Together, our data revealed that Exo-pro, especially Exo-T and Exo-G could be potential biomarkers for NSCLC. Further studies focusing on pure tumor-derived exosomes isolated from plasma were needed.

Tumor microenvironment dictates regulatory T cell phenotype: Upregulated immune checkpoints reinforce suppressive function

Background

Regulatory T (T_reg) cells have an immunosuppressive function in cancer, but the underlying mechanism of immunosuppression in the tumor microenvironment (TME) is unclear.

Methods

We compared the phenotypes of T cell subsets, including T_reg cells, obtained from peripheral blood, malignant effusion, and tumors of 103 cancer patients. Our primary focus was on the expression of immune checkpoint (IC)-molecules, such as programmed death (PD)-1, T-cell immunoglobulin and mucin-domain containing (TIM)-3, T cell Ig and ITIM domain (TIGIT), and cytotoxic T lymphocyte antigen (CTLA)-4, on T_reg cells in paired lymphocytes from blood, peritumoral tissue, and tumors of 12 patients with lung cancer. To identify the immunosuppressive mechanisms acting on tumor-infiltrating T_reg cells, we conducted immunosuppressive functional assays in a mouse model.

Results

CD8⁺, CD4⁺ T cells, and T_reg cells exhibited a gradual upregulation of IC-molecules the closer they were to the tumor. Interestingly, PD-1 expression was more prominent in T_reg cells than in conventional T (T_conv) cells. In lung cancer patients_, higher levels of IC-molecules were expressed on T_reg cells than on T_conv cells, and T_reg cells were also more enriched in the tumor than in the peri-tumor and blood. In a mouse lung cancer model, IC-molecules were also preferentially upregulated on T_reg cells, compared to T_conv cells. PD-1 showed the greatest increase on most cell types, especially T_reg cells, and this increase occurred gradually over time after the cells entered the TME. PD-1 high-expressing tumor-infiltrating T_reg cells displayed potent suppressive activity, which could be partially inhibited with a blocking anti-PD-1 antibody.

Conclusions

We demonstrate that the TME confers a suppressive function on T_reg cells by upregulating IC-molecule expression. Targeting IC-molecules, including PD-1, on T_reg cells may be effective for cancer treatment.

DNA methylation and repressive histones in the promoters of PD-1, CTLA-4, TIM-3, LAG-3, TIGIT, PD-L1, and galectin-9 genes in human colorectal cancer

Background

Colorectal cancer (CRC) is the third most commonly diagnosed human malignancy worldwide. Upregulation of inhibitory immune checkpoints by tumor-infiltrating immune cells (TIICs) or their ligands by tumor cells leads to tumor evasion from host immunosurveillance. Changes in DNA methylation pattern and enrichment of methylated histone marks in the promoter regions could be major contributors to the upregulation of immune checkpoints (ICs) in the tumor microenvironment (TME).

Methods

Relative expressions of various immune checkpoints and ligands in colon normal tissues (NT) and colorectal tumor tissues (TT) were assessed by qRT-PCR. The epigenetic modifications behind this upregulation were determined by investigating the CpG methylation status of their promoter regions using bisulfite sequencing. Distributions of histone 3 lysine 9 trimethylation (H3K9me3) and histone 3 lysine 27 trimethylation (H3K27me3) in promoter regions of these genes were assessed by chromatin immunoprecipitation (ChIP) assay.

Results

We found that the expression levels of PD-1, CTLA-4, TIM-3, TIGIT, PD-L1, and galectin-9 were significantly higher in colorectal tumor tissues, compared with colon normal tissues. To study the role of DNA methylation, we checked the promoter CpG methylation of ICs and ligands and found that only CTLA-4 and TIGIT, among other genes, were significantly hypomethylated in TT compared with NT. Next, we checked the abundance of repressive histones (H3K9me3 and H3K27me3) in the promoter regions of ICs/ligands. We found that bindings of H3K9me3 in PD-1 and TIGIT promoters and H3K27me3 in CTLA-4 promotor were significantly lower in TT compared with NT. Additionally, bindings of both H3K9me3 and H3K27me3 in the TIM-3 promoter were significantly lower in TT compared with NT.

Conclusion

This study shows that both DNA hypomethylation and H3K9me3 and H3K27me3 repressive histones are involved in upregulation of CTLA-4 and TIGIT genes. However, repressive histones, but not DNA hypomethylation, are involved in upregulation of PD-1 and TIM-3 genes in CRC tumor tissue. These epigenetic modifications could be utilized as diagnostic biomarkers for CRC.

Electronic supplementary material

The online version of this article (10.1186/s13148-018-0539-3) contains supplementary material, which is available to authorized users.