Low-dose cyclophosphamide depletes circulating naïve and activated regulatory T cells in malignant pleural mesothelioma patients synergistically treated with dendritic cell-based immunotherapy

Regulatory T Cells in Tumor Microenvironment: Therapeutic Approaches and Clinical Implications

Regulatory T cells (Tregs), previously referred to as suppressor T cells, represent a distinct subset of CD4+ T cells that are uniquely specialized for immune suppression. They are characterized by the constitutive expression of the transcription factor FoxP3 in their nuclei, along with CD25 (the IL-2 receptor α-chain) and CTLA-4 on their cell surface. Tregs not only restrict natural killer cell-mediated cytotoxicity but also inhibit the proliferation of CD4+ and CD8+ T-cells and suppress interferon-γ secretion by immune cells, ultimately impairing an effective antitumor immune response. Treg cells are widely recognized as a significant barrier to the effectiveness of tumor immunotherapy in clinical settings. Extensive research has consistently shown that Treg cells play a pivotal role in facilitating tumor initiation and progression. Conversely, the depletion of Treg cells has been linked to a marked delay in tumor growth and development.

Precision treatment for human epidermal growth factor receptor 2-amplified advanced rectal cancer: A case report

BACKGROUND

Although targeted therapy provides survival benefits for patients with metastatic colorectal cancer, some patients develop resistance to these treatments. Human epidermal growth factor receptor 2 (HER2) is overexpressed in a subset of patients with colorectal cancer and has been established as a therapeutic target.

CASE SUMMARY

This case report describes a Chinese patient with HER2-amplified advanced rectal cancer who showed no response to chemotherapy and targeted therapies against epidermal growth factor receptor and vascular endothelial growth factor but achieved a remarkable response following treatment with immune checkpoint inhibitors (ICIs) in combination with pyrotinib. The combination of oxaliplatin and ICIs with pyrotinib demonstrates synergistic effects after late-stage disease progression.

CONCLUSION

ICIs and pyrotinib may be effective in treating HER2-amplified advanced rectal cancer. Chemotherapy following disease progression could enhance efficacy synergistically.

Metronomic chemotherapy and breast cancer: a critical evaluation of its role in the new landscape of therapeutics

INTRODUCTION

Breast cancer (BC) remains a prevalent and challenging malignancy among women, with significant advancements in treatment strategies over the past decades. Traditional chemotherapy has been progressively supplemented by newer modalities, including Antibody-Drug Conjugates (ADCs), Immunotherapy (IO), and Targeted Therapies (TT). Despite these advancements, there remains a critical need for strategies that maintain efficacy while minimizing toxicity.

AREAS COVERED

This review delves into metronomic chemotherapy (MC), a novel approach involving the frequent administration of low-dose chemotherapy without prolonged breaks. We explore MC's impact across various breast cancer subtypes, such as Estrogen Receptor-Positive (ER+), HER2-Positive, and Triple-Negative Breast Cancer (TNBC). The literature reviewed highlights MC's mechanisms, including its anti-angiogenic, immunomodulatory, and antiproliferative effects, and its potential to improve treatment tolerability and address drug resistance.

EXPERT OPINION

MC represents a promising adjunct to existing therapies, particularly in advanced or resistant cases. Its unique dosing schedule could offer sustained antitumor activity with reduced toxicity, making it a viable option for long-term management. However, further research is warranted to establish optimal dosing regimens, identify predictive biomarkers, and delineate its role within combination treatment strategies. Clarifying these aspects could refine MC's application, potentially reshaping treatment paradigms and enhancing patient outcomes in breast cancer management.

Breaking the shield of solid tumors: a combined approach for enhanced efficacy of CAR-T cells

The use of chimeric antigen receptor (CAR)-T cells has enhanced the range of available therapeutic modalities in the context of cancer treatment. CAR-T cells have demonstrated considerable efficacy in the targeted eradication of blood cancer cells, thereby stimulating substantial interest in the advancement of such therapeutic approaches. However, the efficacy of CAR-T cells against solid tumor cells has been limited due to the presence of various obstacles. Solid tumors exhibit antigenic diversity and an immunosuppressive microenvironment, which presents a challenge for immune cells attempting to penetrate the tumor. CAR-T cells also demonstrate decreased proliferative activity and cytotoxicity. Furthermore, concerns exist regarding tumor antigen loss and therapy-associated toxicity. Currently, scientists are working to enhance the structure of the CAR and improve the survival and efficiency of CAR-T cells in recognizing tumor antigens in solid tumors. Chemotherapy drugs are frequently employed in the treatment of malignant neoplasms and can also be used prior to cell therapy to enhance CAR-T cell engraftment. Recent studies have demonstrated that chemotherapy drugs can mitigate the suppressive impact of TME, eliminate the physical barrier by destroying the tumor stroma, and facilitate greater penetration of immune cells and CAR-T cells into the tumor. This, in turn, increases their survival, persistence, and cytotoxicity, as well as affects the metabolism of immune cells inside the tumor. However, the effectiveness of the combined approach against solid tumors depends on several factors, including the type of tumor, dosage, population of CAR-T cells, and individual characteristics of the body. This review examines the principal obstacles to the utilization of CAR-T cells against solid tumors, proposes solutions to these issues, and assesses the potential advantages of a combined approach to radiation exposure, which has the potential to enhance the sensitivity of the tumor to other agents.

Lymphodepletion in Chimeric Antigen Receptor T-Cell Therapy for Solid Tumors: A Focus on Brain Tumors

Chimeric antigen receptor (CAR)-T cell therapy, which has demonstrated remarkable efficacy in hematologic malignancies, is being extended to the treatment of refractory solid tumors, including brain tumors. Lymphodepletion (LD) is an essential preconditioning process that enhances CAR-T efficacy by promoting CAR-T cell expansion and persistence in the body, and has become a standard regimen for hematologic cancers. Recent clinical results of CAR-T therapy for solid tumors, including brain tumors, have shown that cyclophosphamide/fludarabine-based preconditioning has potential benefits and is gradually becoming adopted in solid tumor CAR-T trials. Furthermore, some CAR-T trials for solid tumors are attempting to develop LD regimens optimized specifically for solid tumors, distinct from the standard LD regimens used in hematologic cancers. In contrast, CAR-T therapy targeting brain tumors frequently employs locoregionally repeated administration in tumors or cerebrospinal fluid, resulting in less frequent use of LD compared to other solid tumors. Nevertheless, several clinical studies suggest that LD may still provide potential benefits for CAR-T expansion and improvement in clinical responses in systemic CAR-T administration. The studies presented in this review suggest that while LD can be beneficial for enhancing CAR-T efficacy, considerations must be made regarding its compatibility with the CAR-T administration route, potential excessive activation based on CAR-T structural characteristics, and target expression in normal organs. Additionally, given the unique characteristics of brain tumors, optimized selection of LD agents, as well as dosing and regimens, may be required, highlighting the need for further research.

Modulating cancer mechanopathology to restore vascular function and enhance immunotherapy

Solid tumor pathology, characterized by abnormalities in the tumor microenvironment (TME), challenges therapeutic effectiveness. Mechanical factors, including increased tumor stiffness and accumulation of intratumoral forces, can determine the success of cancer treatments, defining the tumor's "mechanopathology" profile. These abnormalities cause extensive vascular compression, leading to hypoperfusion and hypoxia. Hypoperfusion hinders drug delivery, while hypoxia creates an unfavorable TME, promoting tumor progression through immunosuppression, heightened metastatic potential, drug resistance, and chaotic angiogenesis. Strategies targeting TME mechanopathology, such as vascular and stroma normalization, hold promise in enhancing cancer therapies with some already advancing to the clinic. Normalization can be achieved using anti-angiogenic agents, mechanotherapeutics, immune checkpoint inhibitors, engineered bacterial therapeutics, metronomic nanomedicine, and ultrasound sonopermeation. Here, we review the methods developed to rectify tumor mechanopathology, which have even led to cures in preclinical models, and discuss their bench-to-bedside translation, including the derivation of biomarkers from tumor mechanopathology for personalized therapy.

Metronomic chemotherapy in cancer treatment: new wine in an old bottle

Over the past two decades, metronomic chemotherapy has gained considerable attention and has demonstrated remarkable success in the treatment of cancer. Through chronic administration and low-dose regimens, metronomic chemotherapy is associated with fewer adverse events but still effectively induces disease control. The identification of its antiangiogenic properties, direct impact on cancer cells, immunomodulatory effects on the tumour microenvironment, and metabolic reprogramming ability has established the intrinsic multitargeted nature of this therapeutic approach. Recently, the utilization of metronomic chemotherapy has evolved from salvage treatment for metastatic disease to adjuvant maintenance therapy for high-risk cancer patients, which has been prompted by the success of several substantial phase III trials. In this review, we delve into the mechanisms underlying the antitumour effects of metronomic chemotherapy and provide insights into potential combinations with other therapies for the treatment of various malignancies. Additionally, we discuss health-economic advantages and candidates for the utilization of this treatment option.

The use of T-cells with chimeric antigen receptor (CAR-T) in combination with chemotherapy and radiotherapy for the treatment of solid tumors

The introduction of chimeric antigen receptor (CAR) T-cell therapy has revolutionized the treatment of hematological diseases, particularly in combating blood cancer. The success of this cell therapy approach has led to the development of approximately seven commercial CAR-T based drugs. However, the application of CAR-T therapy for solid tumors has proven to be less effective due to challenges such as the varied antigens in solid tumors, an immunosuppressive tumor environment, limited immune cell infiltration, reduced CAR-T cell activity and toxicity issues. To solve these problems, scientists are making efforts to improve and improve the methods of treatment of solid tumors. Chemotherapy is the standard treatment for a large number of malignant neoplasms. It is also used before starting cell therapy for lymphodepletion and better engraftment of injected CAR-T cells. It has been shown that chemotherapy can reduce the immunosuppressive effect of the tumor microenvironment, destroy the stroma, and promote better infiltration of the tumor by CAR-T cells, improving their survival, persistence, cytotoxicity, and influencing the metabolism of immune cells inside the tumor. The effectiveness of combining chemotherapy and CAR-T cell therapy relies on various factors such as tumor type, dosage, treatment schedule, CAR-T cell composition, and individual biological traits. Similarly, radiation therapy can enhance tumor cell vulnerability to specific treatments while also supporting tumor cell survival.

In this review, we discuss the use of CAR-T therapy to combat solid tumors, regarding the challenges of treating solid tumors, ways to overcome them, and also touch upon the possibility of using combination treatments to improve the effectiveness of cell therapy.

Chimeric antigen receptor T cells in the treatment of osteosarcoma (Review)

Osteosarcoma (OS) is a frequently occurring primary bone tumor, mostly affecting children, adolescents and young adults. Before 1970, surgical resection was the main treatment method for OS, but the clinical results were not promising. Subsequently, the advent of chemotherapy has improved the prognosis of patients with OS. However, there is still a high incidence of metastasis or recurrence, and chemotherapy has several side effects, thus making the 5‑year survival rate markedly low. Recently, chimeric antigen receptor T (CAR‑T) cell therapy represents an alternative immunotherapy approach with significant potential for hematologic malignancies. Nevertheless, the application of CAR‑T cells in the treatment of OS faces numerous challenges. The present review focused on the advances in the development of CAR‑T cells to improve their clinical efficacy, and discussed ways to overcome the difficulties faced by CAR T‑cell therapy for OS.

Direct immunoactivation by chemotherapeutic drugs in cancer treatment

The immune system plays a crucial role in recognizing and eliminating pathogenic substances and malignant cells in the body. For cancer treatment, immunotherapy is becoming the standard treatment for many types of cancer and is often combined with chemotherapy. Although chemotherapeutic agents are often reported to have adverse effects, including immunosuppression, they can also play a positive role in immunotherapy by directly stimulating the immune system. This has been demonstrated in preclinical and clinical studies in the past decades. Chemotherapeutics can activate immune cells through different immune receptors and signaling pathways depending on their chemical structure and formulation. In this review, we summarize and discuss the direct immunoactivation effects of chemotherapeutics and possible mechanisms behind these effects. Finally, we prospect chemo-immunotherapeutic combinations for the more effective and safer treatment of cancer.

Tumor-Targeted Nonablative Radiation Promotes Solid Tumor CAR T-cell Therapy Efficacy

Infiltration of tumor by T cells is a prerequisite for successful immunotherapy of solid tumors. In this study, we investigate the influence of tumor-targeted radiation on chimeric antigen receptor (CAR) T-cell therapy tumor infiltration, accumulation, and efficacy in clinically relevant models of pleural mesothelioma and non-small cell lung cancers. We use a nonablative dose of tumor-targeted radiation prior to systemic administration of mesothelin-targeted CAR T cells to assess infiltration, proliferation, antitumor efficacy, and functional persistence of CAR T cells at primary and distant sites of tumor. A tumor-targeted, nonablative dose of radiation promotes early and high infiltration, proliferation, and functional persistence of CAR T cells. Tumor-targeted radiation promotes tumor-chemokine expression and chemokine-receptor expression in infiltrating T cells and results in a subpopulation of higher-intensity CAR-expressing T cells with high coexpression of chemokine receptors that further infiltrate distant sites of disease, enhancing CAR T-cell antitumor efficacy. Enhanced CAR T-cell efficacy is evident in models of both high-mesothelin-expressing mesothelioma and mixed-mesothelin-expressing lung cancer-two thoracic cancers for which radiotherapy is part of the standard of care. Our results strongly suggest that the use of tumor-targeted radiation prior to systemic administration of CAR T cells may substantially improve CAR T-cell therapy efficacy for solid tumors. Building on our observations, we describe a translational strategy of "sandwich" cell therapy for solid tumors that combines sequential metastatic site-targeted radiation and CAR T cells-a regional solution to overcome barriers to systemic delivery of CAR T cells.

Metronomic Chemotherapy: Anti-Tumor Pathways and Combination with Immune Checkpoint Inhibitors

Increasing evidence pinpoints metronomic chemotherapy, a frequent and low dose drug administration with no prolonged drug-free intervals, as a potential tool to fight certain types of cancers. The primary identified targets of metronomic chemotherapy were the tumor endothelial cells involved in angiogenesis. After this, metronomic chemotherapy has been shown to efficiently target the heterogeneous population of tumor cells and, more importantly, elicit the innate and adaptive immune system reverting the "cold" to "hot" tumor immunologic phenotype. Although metronomic chemotherapy is primarily used in the context of a palliative setting, with the development of new immunotherapeutic drugs, a synergistic therapeutic role of the combined metronomic chemotherapy and immune checkpoint inhibitors has emerged at both the preclinical and clinical levels. However, some aspects, such as the dose and the most effective scheduling, still remain unknown and need further investigation. Here, we summarize what is currently known of the underlying anti-tumor effects of the metronomic chemotherapy, the importance of the optimal therapeutic dose and time-exposure, and the potential therapeutic effect of the combined administration of metronomic chemotherapy with checkpoint inhibitors in preclinical and clinical settings.

Combining chemotherapy with CAR-T cell therapy in treating solid tumors

Chemotherapy has long been a standard treatment for a wide range of malignancies, where patients typically undergo multiple rounds of chemotherapy regimens to control tumor growth. In the clinic, the chemotherapy drugs cyclophosphamide and fludarabine are commonly used prior to Chimeric Antigen Receptor T (CAR-T) cell therapy to lymphodeplete and improve CAR-T cell engraftment. In this review, we discuss the use of chemotherapy in combination with CAR-T cell therapy. We also show that chemotherapy can deplete immunosuppressive cells, promote a pro-inflammatory tumor microenvironment, disrupt tumor stroma, and improve CAR-T cell recruitment to the tumor. Although the combination of chemotherapy plus CAR-T cell therapy is promising, certain aspects of chemotherapy also pose a challenge. In addition, the combined therapeutic effect may be heavily dependent on the dose and the treatment schedule. Thus, we also discussed the obstacles to effective clinical outcomes of the combination therapy.

Case report: A case of duodenal adenocarcinoma achieving significantly long survival treating with immune checkpoint inhibitors and chemotherapy without positive biomarkers

Small bowel adenocarcinoma (SBA), particularly duodenal adenocarcinoma (DA), is a rare gastrointestinal cancer with a dismal prognosis. Data on SBA treatments are limited, and the therapeutic strategy remains uncertain. Currently, chemotherapy is the most used treatment; however, it has a poor median progression-free survival (mPFS) of no more than five months in the second-line setting. We report a case with DA that responded well to the immune checkpoint inhibitor (ICI) tislelizumab plus irinotecan in the second-line treatment. To our knowledge, this is the first report of administering ICIs plus chemotherapy to SBA. Despite the absence of microsatellite instability-high (MSI-H) and high tumor mutational burden (TMB), the patient with TP53/KRAS mutation achieved a significantly long PFS of 17 months, and the benefit is still ongoing. The mechanism of this remarkable efficacy might be associated with an increase in tumor immunogenicity after chemotherapy. The current study presents a promising effect of ICIs plus chemotherapy on SBA, affirming the need to investigate the clinical value of this combination in SBA and the underlying mechanism behind it.

Therapeutic targeting of regulatory T cells in cancer

The success of immunotherapy in oncology underscores the vital role of the immune system in cancer development. Regulatory T cells (Tregs) maintain a fine balance between autoimmunity and immune suppression. They have multiple roles in the tumor microenvironment (TME) but act particularly in suppressing T cell activation. This review focuses on the detrimental and sometimes beneficial roles of Tregs in tumors, our current understanding of recruitment and stabilization of Tregs within the TME, and current Treg-targeted therapeutics. Research identifying subpopulations of Tregs and their respective functions and interactions within the complex networks of the TME will be crucial to develop the next generation of immunotherapies. Through these advances, Treg-targeted immunotherapy could have important implications for the future of oncology.

Challenges and opportunities in achieving effective regulatory T cell therapy in autoimmune liver disease

Autoimmune liver diseases (AILD) include autoimmune hepatitis (AIH), primary biliary cholangitis (PBC) and primary sclerosing cholangitis (PSC). These immune-mediated liver diseases involve a break down in peripheral self-tolerance with largely unknown aetiology. Regulatory T cells (Treg) are crucial in maintaining immunological tolerance. Hence, Treg immunotherapy is an attractive therapeutic option in AILD. Currently, AILD do not have a curative treatment option and patients take life-long immunosuppression or bile acids to control hepatic or biliary inflammation. Clinical investigations using good manufacturing practice (GMP) Treg in autoimmune liver disease have thus far demonstrated that Treg therapy is safe and that Treg migrate to inflamed liver tissue. For Treg immunotherapy to achieve efficacy in AILD, Treg must be retained within the liver and maintain their suppressive phenotype to dampen ongoing immune responses to hepatocytes and biliary epithelium. Therefore, therapeutic Treg subsets should be selected for tissue residency markers and maximal functionality. Optimisation of dosing regime and understanding longevity of Treg in vivo are critical to successful Treg therapy. It is also essential to consider combination therapy options to complement infused Treg, for instance low-dose interleukin-2 (IL-2) to support pre-existing and infused Treg survival and suppressive function. Understanding the hepatic microenvironment in both early- and late-stage AILD presents significant opportunity to better tailor Treg therapy in different patient groups. Modification of a hostile microenvironment to a more favourable one either prior to or during Treg therapy could enhance the efficacy and longevity of infused GMP-Treg. Applying recent technology to discovery of autoantigen responses in AILD, T cell receptor (TCR) sequencing and use of chimeric antigen receptor (CAR) technology represents the next frontier for disease-specific CAR-Treg therapies. Consideration of all these aspects in future trials and discovery research would position GMP Treg immunotherapy as a viable personalised-medicine treatment option for effective control of autoimmune liver diseases.

Two-year intermittent exposure of a multiwalled carbon nanotube by intratracheal instillation induces lung tumors and pleural mesotheliomas in F344 rats

BACKGROUND

A mounting number of studies have been documenting the carcinogenic potential of multiwalled carbon nanotubes (MWCNTs); however, only a few studies have evaluated the pulmonary carcinogenicity of MWCNTs in vivo. A 2-year inhalation study demonstrated that MWNT-7, a widely used MWCNT, was a pulmonary carcinogen in rats. In another 2-year study, rats administered MWNT-7 by intratracheal instillation at the beginning of the experimental period developed pleural mesotheliomas but not lung tumors. To obtain data more comparable with rats exposed to MWNT-7 by inhalation, we administered MWNT-7 to F344 rats by intratracheal instillation once every 4-weeks over the course of 2 years at 0, 0.125, and 0.5 mg/kg body weight, allowing lung burdens of MWNT-7 to increase over the entire experimental period, similar to the inhalation study.

RESULTS

Absolute and relative lung weights were significantly elevated in both MWNT-7-treated groups. Dose- and time-dependent toxic effects in the lung and pleura, such as inflammatory, fibrotic, and hyperplastic lesions, were found in both treated groups. The incidences of lung carcinomas, lung adenomas, and pleural mesotheliomas were significantly increased in the high-dose group compared with the control group. The pleural mesotheliomas developed mainly at the mediastinum. No MWNT-7-related neoplastic lesions were noted in the other organs. Cytological and biochemical parameters of the bronchoalveolar lavage fluid (BALF) were elevated in both treated groups. The lung burden of MWNT-7 was dose- and time-dependent, and at the terminal necropsy, the average value was 0.9 and 3.6 mg/lung in the low-dose and high-dose groups, respectively. The number of fibers in the pleural cavity was also dose- and time-dependent.

CONCLUSIONS

Repeated administration of MWNT-7 by intratracheal instillation over the 2 years indicates that MWNT-7 is carcinogenic to both the lung and pleura of rats, which differs from the results of the 2 carcinogenicity tests by inhalation or intratracheal instillation.

Combination strategies with PD-1/PD-L1 blockade: current advances and future directions

Antibodies targeting programmed cell death protein-1 (PD-1) or its ligand PD-L1 rescue T cells from exhausted status and revive immune response against cancer cells. Based on the immense success in clinical trials, ten α-PD-1 (nivolumab, pembrolizumab, cemiplimab, sintilimab, camrelizumab, toripalimab, tislelizumab, zimberelimab, prolgolimab, and dostarlimab) and three α-PD-L1 antibodies (atezolizumab, durvalumab, and avelumab) have been approved for various types of cancers. Nevertheless, the low response rate of α-PD-1/PD-L1 therapy remains to be resolved. For most cancer patients, PD-1/PD-L1 pathway is not the sole speed-limiting factor of antitumor immunity, and it is insufficient to motivate effective antitumor immune response by blocking PD-1/PD-L1 axis. It has been validated that some combination therapies, including α-PD-1/PD-L1 plus chemotherapy, radiotherapy, angiogenesis inhibitors, targeted therapy, other immune checkpoint inhibitors, agonists of the co-stimulatory molecule, stimulator of interferon genes agonists, fecal microbiota transplantation, epigenetic modulators, or metabolic modulators, have superior antitumor efficacies and higher response rates. Moreover, bifunctional or bispecific antibodies containing α-PD-1/PD-L1 moiety also elicited more potent antitumor activity. These combination strategies simultaneously boost multiple processes in cancer-immunity cycle, remove immunosuppressive brakes, and orchestrate an immunosupportive tumor microenvironment. In this review, we summarized the synergistic antitumor efficacies and mechanisms of α-PD-1/PD-L1 in combination with other therapies. Moreover, we focused on the advances of α-PD-1/PD-L1-based immunomodulatory strategies in clinical studies. Given the heterogeneity across patients and cancer types, individualized combination selection could improve the effects of α-PD-1/PD-L1-based immunomodulatory strategies and relieve treatment resistance.

G6PD functions as a metabolic checkpoint to regulate granzyme B expression in tumor-specific cytotoxic T lymphocytes

Background

Granzyme B is a key effector of cytotoxic T lymphocytes (CTLs), and its expression level positively correlates with the response of patients with mesothelioma to immune checkpoint inhibitor immunotherapy. Whether metabolic pathways regulate Gzmb expression in CTLs is incompletely understood.

Methods

A tumor-specific CTL and tumor coculture model and a tumor-bearing mouse model were used to determine the role of glucose-6-phosphate dehydrogenase (G6PD) in CTL function and tumor immune evasion. A link between granzyme B expression and patient survival was analyzed in human patients with epithelioid mesothelioma.

Results

Mesothelioma cells alone are sufficient to activate tumor-specific CTLs and to enhance aerobic glycolysis to induce a PD-1^hi Gzmb^lo CTL phenotype. However, inhibition of lactate dehydrogenase A, the key enzyme of the aerobic glycolysis pathway, has no significant effect on tumor-induced CTL activation. Tumor cells induce H3K9me3 deposition at the promoter of G6pd, the gene that encodes the rate-limiting enzyme G6PD in the pentose phosphate pathway, to downregulate G6pd expression in tumor-specific CTLs. G6PD activation increases acetyl-coenzyme A (CoA) production to increase H3K9ac deposition at the Gzmb promoter and to increase Gzmb expression in tumor-specific CTLs converting them from a Gzmb^lo to a Gzmb^hi phenotype, thus increasing CTL tumor lytic activity. Activation of G6PD increases Gzmb⁺ tumor-specific CTLs and suppresses tumor growth in tumor-bearing mice. Consistent with these findings, GZMB expression level was found to correlate with increased survival in patients with epithelioid mesothelioma.

Conclusion

G6PD is a metabolic checkpoint in tumor-activated CTLs. The H3K9me3/G6PD/acetyl-CoA/H3K9ac/Gzmb pathway is particularly important in CTL activation and immune evasion in epithelioid mesothelioma.

Mesothelioma Malignancy and the Microenvironment: Molecular Mechanisms

Several studies have reported that cellular and soluble components of the tumor microenvironment (TME) play a key role in cancer-initiation and progression. Considering the relevance and the complexity of TME in cancer biology, recent research has focused on the investigation of the TME content, in terms of players and informational exchange. Understanding the crosstalk between tumor and non-tumor cells is crucial to design more beneficial anti-cancer therapeutic strategies. Malignant pleural mesothelioma (MPM) is a complex and heterogenous tumor mainly caused by asbestos exposure with few treatment options and low life expectancy after standard therapy. MPM leukocyte infiltration is rich in macrophages. Given the failure of macrophages to eliminate asbestos fibers, these immune cells accumulate in pleural cavity leading to the establishment of a unique inflammatory environment and to the malignant transformation of mesothelial cells. In this inflammatory landscape, stromal and immune cells play a driven role to support tumor development and progression via a bidirectional communication with tumor cells. Characterization of the MPM microenvironment (MPM-ME) may be useful to understand the complexity of mesothelioma biology, such as to identify new molecular druggable targets, with the aim to improve the outcome of the disease. In this review, we summarize the known evidence about the MPM-ME network, including its prognostic and therapeutic relevance.

Immunological configuration of ovarian carcinoma: features and impact on disease outcome

Epithelial ovarian carcinoma (EOC) is a relatively rare malignancy but is the fifth-leading cause of cancer-related death in women, largely reflecting early, prediagnosis dissemination of malignant disease to the peritoneum. At odds with other neoplasms, EOC is virtually insensitive to immune checkpoint inhibitors, correlating with a tumor microenvironment that exhibits poor infiltration by immune cells and active immunosuppression. Here, we comparatively summarize the humoral and cellular features of primary and metastatic EOC, comparatively analyze their impact on disease outcome, and propose measures to alter them in support of treatment sensitivity and superior patient survival.

Matter of TIME: the tumor-immune microenvironment of mesothelioma and implications for checkpoint blockade efficacy

Malignant pleural mesothelioma (MPM) is an incurable cancer with a dismal prognosis and few effective treatment options. Nonetheless, recent positive phase III trial results for immune checkpoint blockade (ICB) in MPM herald a new dawn in the fight to advance effective treatments for this cancer. Tumor mutation burden (TMB) has been widely reported to predict ICB in other cancers, but MPM is considered a low-TMB tumor. Similarly, tumor programmed death-ligand 1 (PD-L1) expression has not been proven predictive in phase III clinical trials in MPM. Consequently, the precise mechanisms that determine response to immunotherapy in this cancer remain unknown. The present review therefore aimed to synthesize our current understanding of the tumor immune microenvironment in MPM and reflects on how specific cellular features might impact immunotherapy responses or lead to resistance. This approach will inform stratified approaches to therapy and advance immunotherapy combinations in MPM to improve clinical outcomes further.

Randomized phase II trial of a first-in-human cancer cell lysate vaccine in patients with thoracic malignancies

BACKGROUND

Although most malignancies express cancer-testis antigens (CTA), immune responses to these proteins are limited in thoracic oncology patients. This trial was undertaken to examine if a cancer cell lysate vaccine could induce immunity to CTA, and to ascertain if metronomic cyclophosphamide and celecoxib enhances vaccine-induced immune responses.

METHODS

Eleven patients with primary thoracic malignancies and 10 patients with extrathoracic neoplasms metastatic to the chest rendered NED by conventional therapies were randomized to receive H1299 lung cancer cell lysates (10 mg protein/vaccine) with Iscomatrix™ adjuvant via deep intradermal injection q 4 weeks ×6 with or without daily oral metronomic cyclophosphamide/celecoxib. The primary endpoint was serologic response to purified CTA assessed 1 month after the 6th vaccination. Secondary endpoints included assessment of the effects of cyclophosphamide and celecoxib on frequency and magnitude of vaccine-induced immune responses to CTA. Exploratory endpoints included evaluation of the effects of the vaccine regimens on peripheral immune subsets. Standard of care imaging studies were obtained at baseline and 1 month after the 3rd and 6th vaccinations.

RESULTS

All patients exhibited local and systemic inflammatory responses lasting 72-96 hours following vaccinations. There were no dose limiting treatment related toxicities. Fourteen patients (67%) completed all six vaccinations. Eight of 14 patients (57%) exhibited serologic responses to NY-ESO-1. One patient developed antibodies to GAGE7; several patients exhibited reactivity to XAGE and MAGE-C2. Vaccine therapy decreased the percent of Tregs (P=0.0068), PD-1 expression on Tregs (P=0.0027), PD-L1 expression on CD14+ monocytes (P=0.0089), PD-L1 expression on classical monocytes (P=0.016), and PD-L1 expression on intermediate monocytes (P=0.0031). Cyclophosphamide/celecoxib did not appear to increase immune responses or enhance vaccine-induced alterations in peripheral immune subsets.

CONCLUSIONS

H1299 lysate vaccines with Iscomatrix™ induce immune responses to CTA and modulate peripheral immune subsets in a manner that may enhance antitumor immunity in patients with thoracic malignancies.

Long-Term Follow-Up of Mesothelioma Patients Treated with Dendritic Cell Therapy in Three Phase I/II Trials

Background: Malignant pleural mesothelioma (MPM) is a fatal neoplasm with, if untreated, poor survival of approximately nine months from diagnosis. Until recently, phase II–III immunotherapy trials did not show any significant benefit. The lack of immunotherapy efficacy can be explained by the fact that mesothelioma is a tumor with an “immune desert” phenotype, meaning a non-inflamed tumor characterized by low T-cell infiltration. By administration of DCs, which were ex-vivo cultured, exposed to (tumor-associated) antigens, and subsequently activated, this “immune desert” phenotype might be turned into an “inflamed” phenotype. Three phase I/II studies have been performed and published using activated DCs, which support this concept. We here report on the long-term survival of patients treated with DCs in three phase I/II studies. Methods: Survival data of the phase I/II trials using DC therapy in MPM patients were obtained and subsequently analyzed. In the first two trials, DCs were loaded with autologous tumor lysate. In the third trial, DCs were loaded with allogeneic mesothelioma tumor cell line lysate. Results: In the three studies combined, 29 patients with MPM were treated with DC vaccination between 2006 and 2015. At data cut-off, the median OS was 27 months (95% CI: 21–47 months). OS at 2 years was 55.2% (95% CI: 39.7–76.6%), and OS at 5 years was 20.7% (95% CI: 10.1–42.2%). Conclusions: The long-term survival of DC therapy in MPM in these three trials is promising, which is the basis for the randomized phase II/III DENIM study. This DENIM study is currently enrolling, and the results of which have to be awaited for definite conclusions.

A phase 1b clinical trial optimizing regulatory T cell depletion in combination with platinum-based chemotherapy in thoracic cancers

Background: Single-agent cyclophosphamide can deplete regulatory T-cells (Treg). We aimed to determine optimal dosing and scheduling of oral cyclophosphamide, alongside pemetrexed-based chemotherapy, to deplete Treg in mesothelioma or non-small-cell lung cancer patients.Methods: 31 Patients received pemetrexed ± cisplatin or carboplatin on day 1 of a 21-day cycle (maximum 6 cycles). From cycle two, patients received cyclophosphamide, 50 mg/day, with intrapatient escalation to maximum 100/150 mg/day alternately. Immunological changes were examined by flow cytometry. Primary endpoint was Treg proportion of CD4⁺ T-cells, with doses tailored to target Treg nadir <4%.Results: Reduction in Treg proportion was observed on day 8 of all cycles, and was not augmented by cyclophosphamide. Few patients achieved the <4% Treg target. Treg proliferation reached nadir one week after chemotherapy, and peaked on day 1 of the subsequent cycle. Efficacy parameters were similar to chemotherapy alone. Seventeen percent of patients ceased cyclophosphamide due to toxicity.Conclusions: Specific Treg depletion to the degree seen with single-agent cyclophosphamide was not observed during pemetrexed-based chemotherapy. This study highlights the poor evidence basis for use of cyclophosphamide as an immunotherapeutic in combination with chemotherapy, and the importance of detailed flow cytometry studies.Trial registration: Clinical trial registration: www.anzctr.org.au identifier is ACTRN12609000260224.

Chemotherapeutic and targeted agents can modulate the tumor microenvironment and increase the efficacy of immune checkpoint blockades

The development of immune checkpoint blockade (ICB)-based immunotherapy has dramatically changed methods of cancer treatment. This approach triggers a durable treatment response and prolongs patients' survival; however, not all patients can benefit. Accumulating evidence demonstrated that the efficacy of ICB is dependent on a robust antitumor immune response that is usually damaged in most tumors. Conventional chemotherapy and targeted therapy promote the antitumor immune response by increasing the immunogenicity of tumor cells, improving CD8+ T cell infiltration, or inhibiting immunosuppressive cells in the tumor microenvironment. Such immunomodulation provides a convincing rationale for the combination therapy of chemotherapeutics and ICBs, and both preclinical and clinical investigations have shown encouraging results. However, the optimal drug combinations, doses, timing, and sequence of administration, all of which affect the immunomodulatory effect of chemotherapeutics, as well as the benefit of combination therapy, are not yet determined. Future studies should focus on these issues and help to develop the optimal combination regimen for each cancer.

Carbon Nanotubes under Scrutiny: Their Toxicity and Utility in Mesothelioma Research

Research on the toxicity of engineered carbon nanotubes (CNT) was initiated by Belgian academic chemists and toxicologists more than 15 years ago. It is now undisputed that some of these attractive nanomaterials induce serious illness such as fibrosis and cancer. The physico-chemical determinants of CNT-induced adverse effects are now elucidated and include shape, nanoscale diameter, and structural defects. Generated in vitro and in vivo data on their inflammogenic and fibrogenic activities were combined and translated in AOP (adverse outcome pathways) available for risk assessment and regulatory policies. The asbestos-like carcinogenic effect of CNT, notably their capacity to induce malignant mesothelioma (MM), remain, however, a cause of concern for public health and strongly curb the craze for CNT in industries. MM still represents a real challenge for clinicians and a highly refractory cancer to existing therapeutic strategies. By comparing mesotheliomagenic CNT (needle-like CNT-N) to non mesotheliomagenic CNT (tangled-like CNT-T), our group generated a relevant animal model that highlights immune pathways specifically associated to the carcinogenic process. Evidence indicates that only CNT-N possess the intrinsic capacity to induce a preferential, rapid, and sustained accumulation of host immunosuppressive cells that subvert immune surveillance and suppress anti-mesothelioma immunity. This new concept offers novel horizons for the clinical management of mesothelioma and represents an additional tool for predicting the mesotheliomagenic activity of newly elaborated CNT or nanoparticles.

Cellular Immunotherapy and Locoregional Administration of CAR T-Cells in Malignant Pleural Mesothelioma

Malignant pleural mesothelioma (MPM) is a treatment recalcitrant tumor with a poor overall survival (OS). Current approved treatment consists of first line chemotherapy that only modestly increases OS, illustrating the desperate need for other treatment options in MPM. Unfortunately, clinical studies that investigate the effectivity of checkpoint inhibitor (CI) treatment failed to improve clinical outcome over current applied therapies. In general, MPM is characterized as an immunological cold tumor with low T-cell infiltration, which could explain the disappointing results of clinical trials investigating CI treatment in MPM. Currently, many other therapeutic approaches, such as cellular therapies and cancer vaccines are investigated that could induce a tumor-specific immune response and increase of the number of tumor-infiltrating lymphocytes. In this review we will discuss these novel treatment approaches for MPM.

Acidosis-Induced TGF-β2 Production Promotes Lipid Droplet Formation in Dendritic Cells and Alters Their Potential to Support Anti-Mesothelioma T Cell Response

For poorly immunogenic tumors such as mesothelioma there is an imperious need to understand why antigen-presenting cells such as dendritic cells (DCs) are not prone to supporting the anticancer T cell response. The tumor microenvironment (TME) is thought to be a major contributor to this DC dysfunction. We have reported that the acidic TME component promotes lipid droplet (LD) formation together with epithelial-to-mesenchymal transition in cancer cells through autocrine transforming growth factor-β2 (TGF-β2) signaling. Since TGF-β is also a master regulator of immune tolerance, we have here examined whether acidosis can impede immunostimulatory DC activity. We have found that exposure of mesothelioma cells to acidosis promotes TGF-β2 secretion, which in turn leads to LD accumulation and profound metabolic rewiring in DCs. We have further documented how DCs exposed to the mesothelioma acidic milieu make the anticancer vaccine less efficient in vivo, with a reduced extent of both DC migratory potential and T cell activation. Interestingly, inhibition of TGF-β2 signaling and diacylglycerol O-acyltransferase (DGAT), the last enzyme involved in triglyceride synthesis, led to a significant restoration of DC activity and anticancer immune response. In conclusion, our study has identified that acidic mesothelioma milieu drives DC dysfunction and altered T cell response through pharmacologically reversible TGF-β2-dependent mechanisms.

Assessment of Immune Response Following Dendritic Cell-Based Immunotherapy in Pediatric Patients With Relapsing Sarcoma

Monocyte-derived dendritic cell (DC)-based vaccines loaded with tumor self-antigens represent a novel approach in anticancer therapy. We evaluated DC-based anticancer immunotherapy (ITx) in an academic Phase I/II clinical trial for children, adolescent, and young adults with progressive, recurrent, or primarily metastatic high-risk tumors. The primary endpoint was safety of intradermal administration of manufactured DCs. Here, we focused on relapsing high-risk sarcoma subgroup representing a major diagnosis in DC clinical trial. As a part of peripheral blood immunomonitoring, we evaluated quantitative association between basic cell-based immune parameters. Furthermore, we describe the pattern of these parameters and their time-dependent variations during the DC vaccination in the peripheral blood immunograms. The peripheral blood immunograms revealed distinct patterns in particular patients in the study group. As a functional testing, we evaluated immune response of patient T-cells to the tumor antigens presented by DCs in the autoMLR proliferation assay. This analysis was performed with T-cells obtained prior to DC ITx initiation and with T-cells collected after the fifth dose of DCs, demonstrating that the anticancer DC-based vaccine stimulates a preexisting immune response against self-tumor antigens. Finally, we present clinical and immunological findings in a Ewing's sarcoma patient with an interesting clinical course. Prior to DC therapy, we observed prevailing CD8+ T-cell stimulation and low immunosuppressive monocytic myeloid-derived suppressor cells (M-MDSC) and regulatory T-cells (Tregs). This patient was subsequently treated with 19 doses of DCs and experienced substantial regression of metastatic lesions after second disease relapse and was further rechallenged with DCs. In this patient, functional ex vivo testing of autologous T-cell activation by manufactured DC medicinal product during the course of DC ITx revealed that personalized anticancer DC-based vaccine stimulates a preexisting immune response against self-tumor antigens and that the T-cell reactivity persisted for the period without DC treatment and was further boosted by DC rechallenge. Trial Registration Number: EudraCT 2014-003388-39.

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.