Therapeutic regulation of myeloid-derived suppressor cells and immune response to cancer vaccine in patients with extensive stage small cell lung cancer

Myeloid-Derived Suppressor Cells

Myeloid cells developed evolutionarily as a major mechanism to protect the host. They evolved as a critical barrier against infections and are important contributors to tissue remodeling. However, in cancer, myeloid cells are largely converted to serve a new master-tumor cells. This process is epitomized by myeloid-derived suppressor cells (MDSC). These cells are closely related to neutrophils and monocytes. MDSCs are not present in the steady state of healthy individuals and appear in cancer and in pathologic conditions associated with chronic inflammation or stress. These cells have emerged as an important contributor to tumor progression. Ample evidence supports a key role for MDSCs in immune suppression in cancer, as well as their prominent role in tumor angiogenesis, drug resistance, and promotion of tumor metastases. MDSCs have a fascinating biology and are implicated in limiting the effects of cancer immunotherapy. Therefore, targeting these cells may represent an attractive therapeutic opportunity. Cancer Immunol Res; 5(1); 3-8. ©2016 AACR.

Myeloid-Derived Suppressor Cells in the Tumor Microenvironment: Current Knowledge and Future Perspectives

The current knowledge on tumor-infiltrating myeloid-derived suppressor cells (MDSCs) is based mainly on the extensive work performed in murine models. Data obtained for human counterparts are generated on the basis of tumor analysis from patient samples. Both sources of information led to determination of the main suppressive mechanisms used by these cell subsets in tumor-bearing hosts. As a result of the identification of protein targets responsible for MDSCs suppressive activity, different therapeutics agents have been used to eliminate/reduce their adverse effect. In the present work, we review the current knowledge on suppressive mechanisms of MDSCs and therapeutic treatments that interfere with their differentiation, expansion or activity. Based on the accumulation of new evidences supporting their importance for tumor progression and metastasis, the interest in these cell types is increasing. We revise the methods of MDSC generation/differentiation ex vivo that may help in overcoming problems associated with limited numbers of cells available from animals and patients for their study.

Immunomodulatory Monoclonal Antibodies in Combined Immunotherapy Trials for Cutaneous Melanoma

In the last few years, there has been a twist in cancer treatment toward immunotherapy thanks to the impressive results seen in advanced patients from several tumor pathologies. Cutaneous melanoma is a highly mutated and immunogenic tumor that has been a test field for the development of immunotherapy. However, there is still a way on the road to achieving complete and long-lasting responses in most patients. It is desirable that immunotherapeutic strategies induce diverse immune reactivity specific to tumor antigens, including the so-called neoantigens, as well as the blockade of immunosuppressive mechanisms. In this review, we will go through the role of promising monoclonal antibodies in cancer immunotherapy with immunomodulatory function, especially blocking of the inhibitory immune checkpoints CTLA-4 and PD-1, in combination with different immunotherapeutic strategies such as vaccines. We will discuss the rational basis for these combinatorial approaches as well as different schemes currently under study for cutaneous melanoma in the clinical trials arena. In this way, the combination of "push and release" immunomodulatory therapies can contribute to achieving a more robust and durable antitumor immune response in patients.

CD3xPDL1 bi-specific T cell engager (BiTE) simultaneously activates T cells and NKT cells, kills PDL1+ tumor cells, and extends the survival of tumor-bearing humanized mice

Bi-specific T cell engagers (BiTEs) activate T cells through CD3 and target activated T cells to tumor-expressed antigens. BiTEs have shown therapeutic efficacy in patients with liquid tumors; however, they do not benefit all patients. Anti-tumor immunity is limited by Programmed Death 1 (PD1) pathway-mediated immune suppression, and patients who do not benefit from existing BiTES may be non-responders because their T cells are anergized via the PD1 pathway. We have designed a BiTE that activates and targets both T cells and NKT cells to PDL1⁺ cells. In vitro studies demonstrate that the CD3xPDL1 BiTE simultaneously binds to both CD3 and PDL1, and activates healthy donor CD4⁺ and CD8⁺ T cells and NKT cells that are specifically cytotoxic for PDL1⁺ tumor cells. Cancer patients’ PBMC are also activated and cytotoxic, despite the presence of myeloid-derived suppressor cells. The CD3xPDL1 BiTE significantly extends the survival time and maintains activated immune cell levels in humanized NSG mice reconstituted with human PBMC and carrying established human melanoma tumors. These studies suggest that the CD3xPDL1 BiTE may be efficacious for patients with PDL1⁺ solid tumors, in combination with other immunotherapies that do not specifically neutralize PD1 pathway-mediated immune suppression.

Immune biomarkers for chronic inflammation related complications in non-cancerous and cancerous diseases

Chronic inflammation arising in a diverse range of non-cancerous and cancerous diseases, dysregulates immunity and exposes patients to a variety of complications. These include immunosuppression, tissue damage, cardiovascular diseases and more. In cancer, chronic inflammation and related immunosuppression can directly support tumor growth and dramatically reduce the efficacies of traditional treatments, as well as novel immune-based therapies, which require a functional immune system. Nowadays, none of the immune biomarkers, regularly used by clinicians can sense a developing chronic inflammation, thus complications can only be detected upon their appearance. This review focuses on the necessity for such immune status biomarkers, which could predict complications prior to their appearance. Herein we bring examples for the use of cellular and molecular biomarkers in diagnosis, prognosis and follow-up of patients suffering from various cancers, for prediction of response to immune-based anti-cancer therapy and for prediction of cardiovascular disease in type 2 diabetes patients. Monitoring such biomarkers is expected to have a major clinical impact in addition to unraveling of the entangled complexity underlying dysregulated immunity in chronic inflammation. Thus, newly discovered biomarkers and those that are under investigation are projected to open a new era towards combating the silent damage induced by chronic inflammation.

Non-Small Cell Lung Cancer Radiogenomics Map Identifies Relationships between Molecular and Imaging Phenotypes with Prognostic Implications

Purpose To create a radiogenomic map linking computed tomographic (CT) image features and gene expression profiles generated by RNA sequencing for patients with non-small cell lung cancer (NSCLC). Materials and Methods A cohort of 113 patients with NSCLC diagnosed between April 2008 and September 2014 who had preoperative CT data and tumor tissue available was studied. For each tumor, a thoracic radiologist recorded 87 semantic image features, selected to reflect radiologic characteristics of nodule shape, margin, texture, tumor environment, and overall lung characteristics. Next, total RNA was extracted from the tissue and analyzed with RNA sequencing technology. Ten highly coexpressed gene clusters, termed metagenes, were identified, validated in publicly available gene-expression cohorts, and correlated with prognosis. Next, a radiogenomics map was built that linked semantic image features to metagenes by using the t statistic and the Spearman correlation metric with multiple testing correction. Results RNA sequencing analysis resulted in 10 metagenes that capture a variety of molecular pathways, including the epidermal growth factor (EGF) pathway. A radiogenomic map was created with 32 statistically significant correlations between semantic image features and metagenes. For example, nodule attenuation and margins are associated with the late cell-cycle genes, and a metagene that represents the EGF pathway was significantly correlated with the presence of ground-glass opacity and irregular nodules or nodules with poorly defined margins. Conclusion Radiogenomic analysis of NSCLC showed multiple associations between semantic image features and metagenes that represented canonical molecular pathways, and it can result in noninvasive identification of molecular properties of NSCLC. Online supplemental material is available for this article.

A Bayesian pick-the-winner design in a randomized phase II clinical trial

Purpose

Many phase II clinical trials evaluate unique experimental drugs/combinations through multi-arm design to expedite the screening process (early termination of ineffective drugs) and to identify the most effective drug (pick the winner) to warrant a phase III trial. Various statistical approaches have been developed for the pick-the-winner design but have been criticized for lack of objective comparison among the drug agents.

Methods

We developed a Bayesian pick-the-winner design by integrating a Bayesian posterior probability with Simon two-stage design in a randomized two-arm clinical trial. The Bayesian posterior probability, as the rule to pick the winner, is defined as probability of the response rate in one arm higher than in the other arm. The posterior probability aims to determine the winner when both arms pass the second stage of the Simon two-stage design.

Results

When both arms are competitive (i.e., both passing the second stage), the Bayesian posterior probability performs better to correctly identify the winner compared with the Fisher exact test in the simulation study. In comparison to a standard two-arm randomized design, the Bayesian pick-the-winner design has a higher power to determine a clear winner. In application to two studies, the approach is able to perform statistical comparison of two treatment arms and provides a winner probability (Bayesian posterior probability) to statistically justify the winning arm.

Conclusion

We developed an integrated design that utilizes Bayesian posterior probability, Simon two-stage design, and randomization into a unique setting. It gives objective comparisons between the arms to determine the winner.

Targeting myeloid derived suppressor cells with all-trans retinoic acid is highly time-dependent in therapeutic tumor vaccination

Tumor immune escape is a critical problem which frequently accounts for the failure of therapeutic tumor vaccines. Among the most potent suppressors of tumor immunity are myeloid derived suppressor cells (MDSCs). MDSCs can be targeted by all-trans-retinoic-acid (atRA), which reduced their numbers and increased response rates in several vaccination studies. However, not much is known about the optimal administration interval between atRA and the vaccine as well as about its mode of action. Here we demonstrate in 2 different murine tumor models that mice unresponsive to a therapeutic vaccine harbored higher MDSC numbers than did responders. Application of atRA overcame MDSC-mediated immunosuppression and restored tumor control. Importantly, atRA was protective only when administered 3 d after vaccination (delayed treatment), whereas simultaneous administration even decreased the anti-tumor immune response and reduced survival. When analyzing the underlying mechanisms, we found that delayed, but not simultaneous atRA treatment with vaccination abrogated the suppressive capacity in monocytic MDSCs and instead caused them to upregulate MHC-class-II. Consistently, MDSCs from patients with colorectal carcinoma also failed to upregulate HLA-DR after ex vivo treatment with TLR-ligation. Overall, we demonstrate that atRA can convert non-responders to responders to vaccination by suppressing MDSCs function and not only by reducing their number. Moreover, we identify a novel, strictly time-dependent mode of action of atRA to be considered during immunotherapeutic protocols in the future.

Can the co-dependence of the immune system and angiogenesis facilitate pharmacological targeting of tumours?

Tumours elicit a number of mechanisms to induce a reprogramming of innate and adaptive immune cells to their advantage, inducing a pro-angiogenic phenotype. Investigation of these events is now leading to the identification of specific myeloid and lymphoid cell-targeted therapies, as well as of unexplored off-target activities of clinically relevant chemotherapeutic and metabolic drugs. It is also leading to an enhanced understanding of the interplay between angiogenesis and the immune system, and the value of novel co-targeting approaches using both immunotherapy and anti-angiogenic therapy. Here, we review recently identified mechanisms and potential pharmacological approaches targeting the crosstalk between cancer cells and the host immune system, providing an overview on novel therapeutic opportunities linking immuno-oncology and anti-angiogenic therapy.

Glycolysis regulates the expansion of myeloid-derived suppressor cells in tumor-bearing hosts through prevention of ROS-mediated apoptosis

Immunotherapy aiming to rescue or boost antitumor immunity is an emerging strategy for treatment of cancers. The efficacy of immunotherapy is strongly controlled by the immunological milieu of cancer patients. Myeloid-derived suppressor cells (MDSCs) are heterogeneous immature myeloid cell populations with immunosuppressive functions accumulating in individuals during tumor progression. The signaling mechanisms of MDSC activation have been well studied. However, there is little known about the metabolic status of MDSCs and the physiological role of their metabolic reprogramming. In this study, we discovered that myeloid cells upregulated their glycolytic genes when encountered with tumor-derived factors. MDSCs exhibited higher glycolytic rate than their normal cell compartment did, which contributed to the accumulation of the MDSCs in tumor-bearing hosts. Upregulation of glycolysis prevented excess reactive oxygen species (ROS) production by MDSCs, which protected MDSCs from apoptosis. Most importantly, we identified the glycolytic metabolite, phosphoenolpyruvate (PEP), as a vital antioxidant agent able to prevent excess ROS production and therefore contributed to the survival of MDSCs. These findings suggest that glycolytic metabolites have important roles in the modulation of fitness of MDSCs and could be potential targets for anti-MDSC strategy. Targeting MDSCs with analogs of specific glycolytic metabolites, for example, 2-phosphoglycerate or PEP may diminish the accumulation of MDSCs and reverse the immunosuppressive milieu in tumor-bearing individuals.

Lung cancer and β-glucans: review of potential therapeutic applications

The potential of natural substances with immunotherapeutic properties has long been studied. β-glucans, a cell wall component of certain bacteria and fungi, potentiate the immune system against microbes and toxic substances. Moreover, β-glucans are known to exhibit direct anticancer effects and can suppress cancer proliferation through immunomodulatory pathways. Mortality of lung cancer has been alarmingly increasingly worldwide; therefore, treatment of lung cancer is an urgent necessity. Numerous researchers are now dedicated to using β-glucans as a therapy for lung cancer. In the present attempt, we have reviewed the studies addressing therapeutic effects of β-glucans in primary and metastatic lung cancer published in the time period of 1991-2016.

Mechanisms overseeing myeloid-derived suppressor cell production in neoplastic disease

Perturbations in myeloid cell differentiation are common in neoplasia, culminating in immature populations known as myeloid-derived suppressor cells (MDSCs). MDSCs favor tumor progression due to their ability to suppress host immunity or promote invasion and metastasis. They are thought to originate from the bone marrow as a result of exposure to stromal- or circulating tumor-derived factors (TDFs). Although great interest has been placed on understanding how MDSCs function, less is known regarding how MDSCs develop at a transcriptional level. Our work explores the premise that MDSCs arise because cancer cells, through the production of certain TDFs, inhibit the expression of interferon regulatory factor-8 (IRF8) that is ordinarily essential for controlling fundamental properties of myeloid cell differentiation. Our interest in IRF8 has been based on the following rationale. First, it is well-recognized that IRF8 is a 'master regulator' of normal myelopoiesis, critical not only for producing monocytes, dendritic cells (DCs), and neutrophils, but also for controlling the balance of all three major myeloid cell types. This became quite evident in IRF8^-/- mice, whereby the loss of IRF8 leads to a disproportionate accumulation of neutrophils at the expense of monocytes and DCs. Second, we showed that such myeloid populations from IRF8^-/- mice exhibit similar characteristics to MDSCs from tumor-bearing mice. Third, in a reciprocal fashion, we showed that enforced expression of IRF8 in the myeloid system significantly mitigates tumor-induced MDSC accumulation and improves immunotherapy efficacy. Altogether, these observations support the hypothesis that IRF8 is an integral negative regulator of MDSC biology.

The clinical evidence for targeting human myeloid-derived suppressor cells in cancer patients

Myeloid-derived suppressor cells (MDSCs) are a heterogeneous population of immature myeloid cells that represent a formidable obstacle to the successful treatment of cancer. Patients with high frequencies of MDSCs have significantly decreased progression-free survival (PFS) and overall survival (OS). Whereas there is experimental evidence that the reduction of the number and/or suppressive function of MDSCs in mice improves the efficacy of anti-cancer therapies, there is notably less evidence for this therapeutic strategy in human clinical trials. Here, we discuss currently available data concerning MDSCs from human clinical trials and explore the evidence that targeting MDSCs may improve the efficacy of cancer therapies.

Neutrophils dominate the immune cell composition in non-small cell lung cancer

The response rate to immune checkpoint inhibitor therapy for non-small-cell lung cancer (NSCLC) is just 20%. To improve this figure, several early phase clinical trials combining novel immunotherapeutics with immune checkpoint blockade have been initiated. Unfortunately, these trials have been designed without a strong foundational knowledge of the immune landscape present in NSCLC. Here, we use a flow cytometry panel capable of measuring 51 immune cell populations to comprehensively identify the immune cell composition and function in NSCLC. The results show that the immune cell composition is fundamentally different in lung adenocarcinoma as compared with lung squamous cell carcinoma, and that neutrophils are the most prevalent immune cell type. Using T-cell receptor-β sequencing and tumour reactivity assays, we predict that tumour reactive T cells are frequently present in NSCLC. These results should help to guide the design of clinical trials and the direction of future research in this area.

Myeloid-Derived Suppressor Cells

Myeloid cells developed evolutionarily as a major mechanism to protect the host. They evolved as a critical barrier against infections and are important contributors to tissue remodeling. However, in cancer, myeloid cells are largely converted to serve a new master-tumor cells. This process is epitomized by myeloid-derived suppressor cells (MDSC). These cells are closely related to neutrophils and monocytes. MDSCs are not present in the steady state of healthy individuals and appear in cancer and in pathologic conditions associated with chronic inflammation or stress. These cells have emerged as an important contributor to tumor progression. Ample evidence supports a key role for MDSCs in immune suppression in cancer, as well as their prominent role in tumor angiogenesis, drug resistance, and promotion of tumor metastases. MDSCs have a fascinating biology and are implicated in limiting the effects of cancer immunotherapy. Therefore, targeting these cells may represent an attractive therapeutic opportunity. Cancer Immunol Res; 5(1); 3-8. ©2016 AACR.

The Role of Myeloid-Derived Suppressor Cells in Viral Infection

Myeloid-derived suppressor cells (MDSCs) are heterogeneous immature myeloid cells that are well described as potent immune regulatory cells during human cancer and murine tumor models. Reports of MDSCs during viral infections remain limited, and their association with immunomodulation of viral diseases is still being defined. Here, we provide an overview of MDSCs or MDSC-like cells identified during viral infections, including murine viral models and human viral diseases. Understanding the similarities and/or differences of virally induced versus tumor-derived MDSCs will be important for designing future immunotherapeutic approaches.

Myeloid-Derived Suppressor Cells

Myeloid cells developed evolutionarily as a major mechanism to protect the host. They evolved as a critical barrier against infections and are important contributors to tissue remodeling. However, in cancer, myeloid cells are largely converted to serve a new master-tumor cells. This process is epitomized by myeloid-derived suppressor cells (MDSC). These cells are closely related to neutrophils and monocytes. MDSCs are not present in the steady state of healthy individuals and appear in cancer and in pathologic conditions associated with chronic inflammation or stress. These cells have emerged as an important contributor to tumor progression. Ample evidence supports a key role for MDSCs in immune suppression in cancer, as well as their prominent role in tumor angiogenesis, drug resistance, and promotion of tumor metastases. MDSCs have a fascinating biology and are implicated in limiting the effects of cancer immunotherapy. Therefore, targeting these cells may represent an attractive therapeutic opportunity. Cancer Immunol Res; 5(1); 3-8. ©2016 AACR.

GM-CSF signalling blockade and chemotherapeutic agents act in concert to inhibit the function of myeloid-derived suppressor cells in vitro

Immune evasion is a recently defined hallmark of cancer, and immunotherapeutic approaches that stimulate an immune response to tumours are gaining recognition. However tumours may evade the immune response and resist immune-targeted treatment by promoting an immune-suppressive environment and stimulating the differentiation or recruitment of immunosuppressive cells. Myeloid-derived suppressor cells (MDSC) have been identified in a range of cancers and are often associated with tumour progression and poor patient outcomes. Pancreatic cancer in particular supports MDSC differentiation via the secretion of granulocyte-macrophage colony-stimulating factor (GM-CSF), and MDSC are believed to contribute to the profoundly immune-suppressive microenvironment present in pancreatic tumours. MDSC-targeted therapies that deplete or inhibit this cell population have been proposed as a way to shift the balance in favour of a tumour-clearing immune response. In this study, we have modelled MDSC differentiation and function in vitro and this has provided us with the opportunity to test a range of potential MDSC-targeted therapies to identify candidates for further investigation. Using in vitro modelling we show here that the combination of GM-CSF-signalling blockade and gemcitabine suppresses both the MDSC phenotype and the inhibition of T-cell function by MDSC.

Identification of inhibitors of myeloid-derived suppressor cells activity through phenotypic chemical screening

Tumors are infiltrated by cells of the immune system that interact through complex regulatory networks. Although tumor-specific CD8⁺ T cells can be found in peripheral blood and tumor samples from cancer patients, their function is inhibited by immunosuppressive cells such as regulatory T cells, tumor-associated macrophages, and myeloid-derived suppressor cells (MDSC). Recent clinical successes have demonstrated that alleviating immunosuppression and T cell exhaustion translates into long-term clinical benefits. Although tremendous progress has been achieved, tools that afford unbiased approaches and screenings to uncover new potential inhibitors or gene targets are lacking. In this study, we describe a system based on immortalized progenitors that allows straightforward investigation of myeloid cells. We show that bone marrow progenitors immortalized through the transduction of NUP98-HOXB4 transgene can be differentiated into CD11b⁺Gr-1⁺ MDSC that express Arginase-1 and PD-L1, produce reactive oxygen and nitrogen species, and suppress T cell function in vitro. To uncover chemical probes that interfere with MDSC biology, we performed a chemical phenotypic screening and identified 3-deazaneplanocin A as a novel modulator of MDSC functions. We characterized and compared the effect of 3-deazaneplanocin-A and all-trans retinoic acid, a well-known modulator of MDSC activity, on the expression of effector molecules and immunosuppressive functions of MDSC. Altogether, this proof-of-principle opens new possibilities for the identification of drugs targeting myeloid cells with immunosuppressive activities.

Myeloid derived suppressor cells in breast cancer: A novel therapeutic target?

The relationship of the immune system and tumour cells is complex; although recognised that the immune system can protect the host against tumour development, the immune system also facilitates tumour progression through immune suppression. Pro-inflammatory mediators associated with chronic inflammation are responsible for the expansion and activation of myeloid derived suppressor cells (MDSCs); a heterogeneous group of cells that originates from myeloid progenitor cells but does not complete the final stages of differentiation. A causal relationship between chronic inflammation and tumour progression relies on the accumulation and maintenance of MDSCs as its linchpin; responsible for immunosuppression through the down-regulation of anti-tumour responses. MDSCs cause immunosuppression through a number of mechanisms; inhibiting the proliferation of CD4⁺ and CD8⁺ T cells, blocking natural killer cell activation and limiting dendritic cell maturation and function. As well as using various mechanisms to inhibit adaptive and immune responses, MDSCs also have non-immunological functions that aid tumour spread; including directly promoting tumour proliferation and metastasis by having an important role in tumour angiogenesis, secretion of matrix metalloproteinases and induction of epithelial-mesenchymal transition. Breast cancer is the most common cancer among women in the United Kingdom with 44540 new cases of invasive carcinoma in 2013 and results in the second highest cancer mortality rate in women, with 11600 deaths in 2012. Considering this, the need for novel therapeutic interventions is higher than ever. This review summarises the rationale for the targeting of MDSCs in breast cancer as a realistic avenue to increase survival from breast cancer.

The Role of Myeloid-Derived Suppressor Cells (MDSC) in Cancer Progression

The immunosuppressive tumor microenvironment represents not only one of the key factors stimulating tumor progression but also a strong obstacle for efficient tumor immunotherapy. Immunosuppression was found to be associated with chronic inflammatory mediators including cytokines, chemokines and growth factors produced by cancer and stroma cells. Long-term intensive production of these factors induces the formation of myeloid-derived suppressor cells (MDSCs) representing one of the most important players mediating immunosuppression. Moreover, MDSCs could not only inhibit anti-tumor immune reactions but also directly stimulate tumor growth and metastasis. Therefore, understanding the mechanisms of their generation, expansion, recruitment and activation is required for the development of novel strategies for tumor immunotherapy.

A clinical and biological perspective of human myeloid-derived suppressor cells in cancer

Considering the large number of studies focused on myeloid-derived suppressor cells (MDSCs) to date, only a handful of well-defined relationships in human cancer have been established. The difficulty of assessing the impact of MDSCs in human cancer is partly due to the relatively small number of studies performed in humans. This is compounded in the literature by a common lack of clear indication of which species is being referred to for each characteristic described. These aspects may result in inappropriate extrapolation of animal studies to those in the human setting. This is especially the case for studies focused on investigating therapies which can be used to target MDSCs or those aimed at understanding their mechanism. Here, we attempt to rectify this by reviewing only studies on MDSC performed in humans. We survey studies which explore (1) whether MDSC levels are altered in cancer patients and if this is correlated with patient survival, (2) the so far identified mechanisms employed by MDSC to exert immune suppression, and (3) whether therapeutic agents can be used to target MDSCs by either altering their level, influencing their differentiation or inhibiting their suppressive function. Despite the fact that these studies clearly show that MDSCs are important in human cancer, the clinical employment of agents intended to target them has not yet been accomplished. We identify factors which have contributed to this and propose steps which may facilitate the translation of these therapies to the clinic in future.

Immature myeloid cells in the tumor microenvironment: Implications for immunotherapy

Various preclinical studies have demonstrated that the success of immunotherapeutic strategies in inhibiting tumor progression in animal models of Glioblastoma multiforme (GBM). It is also evident that tumor-induced immune suppression drastically impacts the efficacy of immune based therapies. Among the mechanisms employed by GBM to induce immunosuppression is the accumulation of regulatory T cells (Tregs) and Myeloid derived suppressor cells (MDSCs). Advancing our understanding about the pathways regulating the expansion, accumulation and activity of MDSCs will allow for the development of therapies aimed at abolishing the inhibitory effect of these cells on immunotherapeutic approaches. In this review, we have focused on the origin, expansion and immunosuppressive mechanisms of MDSCs in animal models and human cancer, in particular GBM.

Immune response and long-term clinical outcome in advanced melanoma patients vaccinated with tumor-mRNA-transfected dendritic cells

The most effective anticancer immune responses are probably directed against patient-specific neoantigens. We have developed a melanoma vaccine targeting this individual mutanome based on dendritic cells (DCs) loaded with autologous tumor-mRNA. Here, we report a phase I/II trial evaluating toxicity, immune response and clinical outcome in 31 metastatic melanoma patients. The first cohort (n = 22) received the vaccine without any adjuvant; the next cohort (n = 9) received adjuvant IL2. Each subject received four weekly intranodal or intradermal injections, followed by optional monthly vaccines. Immune response was evaluated by delayed-type hypersensitivity (DTH), T cell proliferation and cytokine assays. Data were collected for 10 y after inclusion of the last patient. No serious adverse events were detected. In the intention-to-treat-cohort, we demonstrated significantly superior survival compared to matched controls from a benchmark meta-analysis (1 y survival 43% vs. 24%, 2 y 23% vs. 6.6%). A tumor-specific immune response was demonstrated in 16/31 patients. The response rate was higher after intradermal than intranodal vaccination (80% vs. 38%). Immune responders had improved survival compared to non-responders (median 14 mo vs. 6 mo; p = 0.030), and all eight patients surviving >20 mo were immune responders. In addition to the tumor-specific response, most patients developed a response against autologous DC antigens. The cytokine profile was polyfunctional and did not follow a Th1/Th2 dichotomy. We conclude that the favorable safety profile and evidence of a possible survival benefit warrant further studies of the RNA/DC vaccine. The vaccine appears insufficient as monotherapy, but there is a strong rationale for combination with checkpoint modulators.

Helminth Regulation of Immunity: A Three-pronged Approach to Treat Colitis

By reputation, the parasite is a pariah, an unwelcome guest. Infection with helminth parasites evokes stereotypic immune responses in humans and mice that are dominated by T helper (Th)-2 responses; thus, a hypothesis arises that infection with helminths would limit immunopathology in concomitant inflammatory disease. Although infection with some species of helminths can cause devastating disease and affect the course of microbial infections, analyses of rodent models of inflammatory disease reveal that infection with helminth parasites, or treatment with helminth extracts, can limit the severity of autoinflammatory disease, including colitis. Intriguing, but fewer, studies show that adoptive transfer of myeloid immune cells treated with helminth products/extracts in vitro can suppress inflammation. Herein, 3 facets of helminth therapy are reviewed and critiqued: treatment with viable ova or larvae, treatment with crude extracts of the worm or purified molecules, and cellular immunotherapy. The beneficial effect of helminth therapy often converges on the mobilization of IL-10 and regulatory/alternatively activated macrophages, while there are reports on transforming growth factor (TGF)-β, regulatory T cells and dendritic cells, and recent data suggest that helminth-evoked changes in the microbiota should be considered when defining anticolitic mechanisms. We speculate that if the data from animal models translate to humans, noting the heterogeneity therein, then the choice between use of viable helminth ova, helminth extracts/molecules or antigen-pulsed immune cells could be matched to disease management in defined cohorts of patients with inflammatory bowel disease.

Inhibition of mouse breast adenocarcinoma growth by ablation with intratumoral alpha-irradiation combined with inhibitors of immunosuppression and CpG

It has been demonstrated that aggressive in situ tumor destruction (ablation) could lead to the release of tumor antigens, which can stimulate anti-tumor immune responses. We developed an innovative method of tumor ablation based on intratumoral alpha-irradiation, diffusing alpha-emitters radiation therapy (DaRT), which efficiently ablates local tumors and enhances anti-tumor immunity. In this study, we investigated the anti-tumor potency of a treatment strategy, which combines DaRT tumor ablation with two approaches for the enhancement of anti-tumor reactivity: (1) neutralization of immunosuppressive cells such as regulatory T cells (Tregs) and myeloid-derived suppressor cells (MDSCs) and (2) boost the immune response by the immunoadjuvant CpG. Mice bearing DA3 mammary adenocarcinoma with metastases were treated with DaRT wires in combination with a MDSC inhibitor (sildenafil), Treg inhibitor (cyclophosphamide at low dose), and the immunostimulant, CpG. Combination of all four therapies led to a complete rejection of primary tumors (in 3 out of 20 tumor-bearing mice) and to the elimination of lung metastases. The treatment with DaRT and Treg or MDSC inhibitors (without CpG) also resulted in a significant reduction in tumor size, reduced the lung metastatic burden, and extended survival compared to the corresponding controls. We suggest that the therapy with DaRT combined with the inhibition of immunosuppressive cells and CpG reinforced both local and systemic anti-tumor immune responses and displayed a significant anti-tumor effect in tumor-bearing mice.

Peripheral blood myeloid-derived suppressor cells reflect disease status in idiopathic pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is a fibroproliferative disease with irreversible lung function loss and poor survival. Myeloid-derived suppressor cells (MDSC) are associated with poor prognosis in cancer, facilitating immune evasion. The abundance and function of MDSC in IPF is currently unknown.

Fluorescence-activated cell sorting was performed in 170 patients (IPF: n=69; non-IPF interstitial lung disease (ILD): n=56; chronic obstructive pulmonary disease (COPD): n=23; healthy controls: n=22) to quantify blood MDSC and lymphocyte subtypes. MDSC abundance was correlated with lung function, MDSC localisation was performed by immunofluorescence. Peripheral blood mononuclear cell (PBMC) mRNA levels were analysed by qRT-PCR.

We detected increased MDSC in IPF and non-IPF ILD compared with controls (30.99±15.61% versus 18.96±8.17%, p≤0.01). Circulating MDSC inversely correlated with maximum vital capacity (r= −0.48, p≤0.0001) in IPF, but not in COPD or non-IPF ILD. MDSC suppressed autologous T-cells. The mRNA levels of co-stimulatory T-cell signals were significantly downregulated in IPF PBMC. Importantly, CD33+CD11b+ cells, suggestive of MDSC, were detected in fibrotic niches of IPF lungs.

We identified increased MDSC in IPF and non-IPF ILD, suggesting that elevated MDSC may cause a blunted immune response. MDSC inversely correlate with lung function only in IPF, identifying them as potent biomarkers for disease progression. Controlling expansion and accumulation of MDSC, or blocking their T-cell suppression, represents a promising therapy in IPF.

Reduction of MDSCs with All-trans Retinoic Acid Improves CAR Therapy Efficacy for Sarcomas

Genetically engineered T cells expressing CD19-specific chimeric antigen receptors (CAR) have shown impressive activity against B-cell malignancies, and preliminary results suggest that T cells expressing a first-generation disialoganglioside (GD2)-specific CAR can also provide clinical benefit in patients with neuroblastoma. We sought to assess the potential of GD2-CAR therapies to treat pediatric sarcomas. We observed that 18 of 18 (100%) of osteosarcomas, 2 of 15 (13%) of rhabdomyosarcomas, and 7 of 35 (20%) of Ewing sarcomas expressed GD2. T cells engineered to express a third-generation GD2-CAR incorporating the 14g2a-scFv with the CD28, OX40, and CD3ζ signaling domains (14g2a.CD28.OX40.ζ) mediated efficient and comparable lysis of both GD2⁺ sarcoma and neuroblastoma cell lines in vitro However, in xenograft models, GD2-CAR T cells had no antitumor effect against GD2⁺ sarcoma, despite effectively controlling GD2⁺ neuroblastoma. We observed that pediatric sarcoma xenografts, but not neuroblastoma xenografts, induced large populations of monocytic and granulocytic murine myeloid-derived suppressor cells (MDSC) that inhibited human CAR T-cell responses in vitro Treatment of sarcoma-bearing mice with all-trans retinoic acid (ATRA) largely eradicated monocytic MDSCs and diminished the suppressive capacity of granulocytic MDSCs. Combined therapy using GD2-CAR T cells plus ATRA significantly improved antitumor efficacy against sarcoma xenografts. We conclude that retinoids provide a clinically accessible class of agents capable of diminishing the suppressive effects of MDSCs, and that co-administration of retinoids may enhance the efficacy of CAR therapies targeting solid tumors. Cancer Immunol Res; 4(10); 869-80. ©2016 AACR.

Myeloid-derived suppressor cells as effectors of immune suppression in cancer

The tumor microenvironment consists of an immunosuppressive niche created by the complex interactions between cancer cells and surrounding stromal cells. A critical component of this environment are myeloid-derived suppressor cells (MDSCs), a heterogeneous group of immature myeloid cells arrested at different stages of differentiation and expanded in response to a variety of tumor factors. MDSCs exert diverse effects in modulating the interactions between immune effector cells and the malignant cells. An increased presence of MDSCs is associated with tumor progression, poorer outcomes, and decreased effectiveness of immunotherapeutic strategies. In this article, we will review our current understanding of the mechanisms that underlie MDSC expansion and their immune-suppressive function. Finally, we review the preclinical studies and clinical trials that have attempted to target MDSCs, in order to improve responses to cancer therapies.

Signal transducer and activator of transcription 3 in myeloid-derived suppressor cells: an opportunity for cancer therapy

Cancer progression is in part determined by interactions between cancer cells and stromal cells in the tumor microenvironment (TME). The identification of cytotoxic tumor-infiltrating lymphocytes has instigated research into immune stimulating cancer therapies. Although a promising direction, immunosuppressive mechanisms exerted at the TME hamper its success. Myeloid-derived suppressor cells (MDSCs) have come to the forefront as stromal cells that orchestrate the immunosuppressive TME. Consequently, this heterogeneous cell population has been the object of investigation. Studies revealed that the transcription factor signal transducer and activator of transcription 3 (STAT3) largely dictates the recruitment, activation and function of MDSCs in the TME. Therefore, this review will focus on the role of this key transcription factor during the MDSC's life cycle and on the therapeutic opportunities it offers.

Myeloid-derived suppressor cells as intruders and targets: clinical implications in cancer therapy

Chronic inflammation, typical of various diseases including cancer, is a "silent bomb within the body," leading to complications that are only evident in most cases upon their appearance, when disease is already deteriorated. Chronic inflammation is associated with accumulation of myeloid-derived suppressor cells (MDSCs), which lead to immunosuppression. MDSCs have numerous harmful effects as they support tumor initiation, tumor growth and spreading, which in turn, perpetuate the inflammatory and suppressive conditions, thus preventing anticancer responses. As the concept of the immune system combating many types of tumors was revived in recent years, immunotherapy has dramatically changed the view of cancer treatment, and numerous novel therapies have been developed and approved by the FDA. However, cumulative clinical data point at very limited success rates. It is most likely that the developing chronic inflammation and MDSC-induced immunosuppression interfere with responses to such treatments and hence are major obstacles in achieving higher response rates to immune-based therapies. Moreover, chemotherapies were shown to have adverse immunoregulatory effects, enhancing or decreasing MDSC levels and activity, thus affecting treatment success. Therefore, therapeutic manipulations of chronic inflammation and MDSCs during cancer development are likely to enhance efficacy of immune- and chemo-based treatments, switching chronic pro-cancer inflammatory environments to an anticancerous milieu. Based on the functional relevance of immune networking in tumors, it is critical to merge monitoring immune system biomarkers into the traditional patient's categorization and treatment regimens. This will provide new tools for clinical practice, allowing appropriate management of cancer patients toward a better-personalized medicine.

Improving cancer immunotherapy by targeting the STATe of MDSCs

Cancer immunotherapy is a promising therapeutic avenue; however, in practice its efficacy is hampered by an immunosuppressive tumor microenvironment that consists of suppressive cell types like myeloid-derived suppressor cells (MDSCs). Eradication or reprogramming of MDSCs could therefore enhance clinical responses to immunotherapy. Here, we review clinically available drugs that target MDSCs, often through inhibition of STAT signaling, which is essential for MDSC accumulation and suppressive functions. Interestingly, several drugs used for non-cancerous indications and natural compounds similarly inhibit MDSCs by STAT inhibition, but have fewer side effects than anticancer drugs. Therefore, they show great potential for combination strategies with immunotherapy.

Cancer-Associated Myeloid Regulatory Cells

Myeloid cells are critically involved in the pathophysiology of cancers. In the tumor microenvironment (TME), they comprise tumor-associated macrophages (TAMs), neutrophils (TANs), dendritic cells, and myeloid-derived suppressor cells, which are further subdivided into a monocytic subset and a granulocytic subset. Some of these myeloid cells, in particular TAMs and TANs, are divided into type 1 or type 2 cells, according to the paradigm of T helper type 1 or type 2 cells. Type 1-activated cells are generally characterized as cells that aid tumor rejection, while all other myeloid cells are shown to favor tumor progression. Moreover, these cells are often at the basis of resistance to various therapies. Much research has been devoted to study the biology of myeloid cells. This endeavor has proven to be challenging, as the markers used to categorize myeloid cells in the TME are not restricted to particular subsets. Also from a functional and metabolic point of view, myeloid cells share many features. Finally, myeloid cells are endowed with a certain level of plasticity, which further complicates studying them outside their environment. In this article, we challenge the exclusive use of cell markers to unambiguously identify myeloid cell subsets in the TME. We further propose to divide myeloid cells into myeloid regulatory or stimulatory cells according to their pro- or antitumor function, because we contend that for therapeutic purposes it is not targeting the cell subsets but rather targeting their protumor traits; hence, myeloid regulatory cells will push antitumor immunotherapy to the next level.

Myeloid-Derived Suppressor Cell Survival and Function Are Regulated by the Transcription Factor Nrf2

Tumor-induced myeloid-derived suppressor cells (MDSC) contribute to immune suppression in tumor-bearing individuals and are a major obstacle to effective immunotherapy. Reactive oxygen species (ROS) are one of the mechanisms used by MDSC to suppress T cell activation. Although ROS are toxic to most cells, MDSC survive despite their elevated content and release of ROS. NF erythroid 2-related factor 2 (Nrf2) is a transcription factor that regulates a battery of genes that attenuate oxidative stress. Therefore, we hypothesized that MDSC resistance to ROS may be regulated by Nrf2. To test this hypothesis, we used Nrf2(+/+)and Nrf2(-/-)BALB/c and C57BL/6 mice bearing 4T1 mammary carcinoma and MC38 colon carcinoma, respectively. Nrf2 enhanced MDSC suppressive activity by increasing MDSC production of H2O2, and it increased the quantity of tumor-infiltrating MDSC by reducing their oxidative stress and rate of apoptosis. Nrf2 did not affect circulating levels of MDSC in tumor-bearing mice because the decreased apoptotic rate of tumor-infiltrating MDSC was balanced by a decreased rate of differentiation from bone marrow progenitor cells. These results demonstrate that Nrf2 regulates the generation, survival, and suppressive potency of MDSC, and that a feedback homeostatic mechanism maintains a steady-state level of circulating MDSC in tumor-bearing individuals.

The induction of human myeloid derived suppressor cells through hepatic stellate cells is dose-dependently inhibited by the tyrosine kinase inhibitors nilotinib, dasatinib and sorafenib, but not sunitinib

Increased numbers of immunosuppressive myeloid derived suppressor cells (MDSCs) correlate with a poor prognosis in cancer patients. Tyrosine kinase inhibitors (TKIs) are used as standard therapy for the treatment of several neoplastic diseases. However, TKIs not only exert effects on the malignant cell clone itself but also affect immune cells. Here, we investigate the effect of TKIs on the induction of MDSCs that differentiate from mature human monocytes using a new in vitro model of MDSC induction through activated hepatic stellate cells (HSCs). We show that frequencies of monocytic CD14(+)HLA-DR(-/low) MDSCs derived from mature monocytes were significantly and dose-dependently reduced in the presence of dasatinib, nilotinib and sorafenib, whereas sunitinib had no effect. These regulatory effects were only observed when TKIs were present during the early induction phase of MDSCs through activated HSCs, whereas already differentiated MDSCs were not further influenced by TKIs. Neither the MAPK nor the NFκB pathway was modulated in MDSCs when any of the TKIs was applied. When functional analyses were performed, we found that myeloid cells treated with sorafenib, nilotinib or dasatinib, but not sunitinib, displayed decreased suppressive capacity with regard to CD8+ T cell proliferation. Our results indicate that sorafenib, nilotinib and dasatinib, but not sunitinib, decrease the HSC-mediated differentiation of monocytes into functional MDSCs. Therefore, treatment of cancer patients with these TKIs may in addition to having a direct effect on cancer cells also prevent the differentiation of monocytes into MDSCs and thereby differentially modulate the success of immunotherapeutic or other anti-cancer approaches.

Clinically feasible approaches to potentiating cancer cell-based immunotherapies

The immune system exerts both tumor-destructive and tumor-protective functions. Mature dendritic cells (DCs), classically activated macrophages (M1), granulocytes, B lymphocytes, aβ and ɣδ T lymphocytes, natural killer T (NKT) cells, and natural killer (NK) cells may be implicated in antitumor immunoprotection. Conversely, tolerogenic DCs, alternatively activated macrophages (M2), myeloid-derived suppressor cells (MDSCs), and regulatory T (Tregs) and B cells (Bregs) are capable of suppressing antitumor immune responses. Anti-cancer vaccination is a useful strategy to elicit antitumor immune responses, while overcoming immunosuppressive mechanisms. Whole tumor cells or lysates derived thereof hold more promise as cancer vaccines than individual tumor-associated antigens (TAAs), because vaccinal cells can elicit immune responses to multiple TAAs. Cancer cell-based vaccines can be autologous, allogeneic or xenogeneic. Clinical use of xenogeneic vaccines is advantageous in that they can be most effective in breaking the preexisting immune tolerance to TAAs. To potentiate immunotherapy, vaccinations can be combined with other modalities that target different immune pathways. These modalities include 1) genetic or chemical modification of cell-based vaccines; 2) cross-priming TAAs to T cells by engaging dendritic cells; 3) T-cell adoptive therapy; 4) stimulation of cytotoxic inflammation by non-specific immunomodulators, toll-like receptor (TLR) agonists, cytokines, chemokines or hormones; 5) reduction of immunosuppression and/or stimulation of antitumor effector cells using antibodies, small molecules; and 6) various cytoreductive modalities. The authors envisage that combined immunotherapeutic strategies will allow for substantial improvements in clinical outcomes in the near future.

Tumor microenvironment and therapeutic response

The tumor microenvironment significantly influences therapeutic response and clinical outcome. Microenvironment-mediated drug resistance can be induced by soluble factors secreted by tumor or stromal cells. The adhesion of tumor cells to stromal fibroblasts or to components of the extracellular matrix can also blunt therapeutic response. Microenvironment-targeted therapy strategies include inhibition of the extracellular ligand-receptor interactions and downstream pathways. Immune cells can both improve and obstruct therapeutic efficacy and may vary in their activation status within the tumor microenvironment; thus, re-programme of the immune response would be substantially more beneficial. The development of rational drug combinations that can simultaneously target tumor cells and the microenvironment may represent a solution to overcome therapeutic resistance.

Yeast-Derived Particulate β-Glucan Treatment Subverts the Suppression of Myeloid-Derived Suppressor Cells (MDSC) by Inducing Polymorphonuclear MDSC Apoptosis and Monocytic MDSC Differentiation to APC in Cancer

Myeloid-derived suppressor cells (MDSC) are a heterogeneous population of immature myeloid cells that promote tumor progression. In this study, we demonstrated that activation of a C-type lectin receptor, dectin-1, in MDSC differentially modulates the function of different MDSC subsets. Yeast-derived whole β-glucan particles (WGP; a ligand to engage and activate dectin-1, oral treatment in vivo) significantly decreased tumor weight and splenomegaly in tumor-bearing mice with reduced accumulation of polymorphonuclear MDSC but not monocytic MDSC (M-MDSC), and decreased polymorphonuclear MDSC suppression in vitro through the induction of respiratory burst and apoptosis. On a different axis, WGP-treated M-MDSC differentiated into F4/80(+)CD11c(+) cells in vitro that served as potent APC to induce Ag-specific CD4(+) and CD8(+) T cell responses in a dectin-1-dependent manner. Additionally, Erk1/2 phosphorylation was required for the acquisition of APC properties in M-MDSC. Moreover, WGP-treated M-MDSC differentiated into CD11c(+) cells in vivo with high MHC class II expression and induced decreased tumor burden when inoculated s.c. with Lewis lung carcinoma cells. This effect was dependent on the dectin-1 receptor. Strikingly, patients with non-small cell lung carcinoma that had received WGP treatment for 10-14 d prior to any other treatment had a decreased frequency of CD14(-)HLA-DR(-)CD11b(+)CD33(+) MDSC in the peripheral blood. Overall, these data indicate that WGP may be a potent immune modulator of MDSC suppressive function and differentiation in cancer.

The diverse roles of the TNF axis in cancer progression and metastasis

Metastasis is a multi-step process that ultimately depends on the ability of disseminating cancer cells to establish favorable communications with their microenvironment. The tumor microenvironment consists of multiple and continuously changing cellular and molecular components. One of the factors regulating the tumor microenvironment is TNF-α, a pleiotropic cytokine that plays key roles in apoptosis, angiogenesis, inflammation and immunity. TNF-α can have both pro- and anti-tumoral effects and these are transmitted via two major receptors, the 55 kDa TNFR1 and the 75 kDa TNFR2 that have distinct, as well as overlapping functions. TNFR1 is ubiquitously expressed while the expression of TNFR2 is more restricted, mainly to immune cells. While TNFR1 can transmit pro-apoptotic or pro-survival signals through a complex network of downstream mediators, the role of TNFR2 is less well understood. One of its main functions is to act as a survival factor and moderate the pro-apoptotic effects of TNFR1, particularly in immune cells. In this review, we summarize the evidence for the involvement of the TNF system in the progression of the metastatic process from its contribution to the early steps of tumor cell invasion to its role in the colonization of distant sites, particularly the liver. We show how the TNF receptors each contribute to these processes by regulating and shaping the tumor microenvironment. Current evidence and concepts on the potential use of TNF targeting agents for cancer prevention and therapy are discussed.

The Microenvironment of Lung Cancer and Therapeutic Implications

The tumor microenvironment (TME) represents a milieu that enables tumor cells to acquire the hallmarks of cancer. The TME is heterogeneous in composition and consists of cellular components, growth factors, proteases, and extracellular matrix. Concerted interactions between genetically altered tumor cells and genetically stable intratumoral stromal cells result in an "activated/reprogramed" stroma that promotes carcinogenesis by contributing to inflammation, immune suppression, therapeutic resistance, and generating premetastatic niches that support the initiation and establishment of distant metastasis. The lungs present a unique milieu in which tumors progress in collusion with the TME, as evidenced by regions of aberrant angiogenesis, acidosis and hypoxia. Inflammation plays an important role in the pathogenesis of lung cancer, and pulmonary disorders in lung cancer patients such as chronic obstructive pulmonary disease (COPD) and emphysema, constitute comorbid conditions and are independent risk factors for lung cancer. The TME also contributes to immune suppression, induces epithelial-to-mesenchymal transition (EMT) and diminishes efficacy of chemotherapies. Thus, the TME has begun to emerge as the "Achilles heel" of the disease, and constitutes an attractive target for anti-cancer therapy. Drugs targeting the components of the TME are making their way into clinical trials. Here, we will focus on recent advances and emerging concepts regarding the intriguing role of the TME in lung cancer progression, and discuss future directions in the context of novel diagnostic and therapeutic opportunities.

Immune Therapy

Lung cancer has long been considered an unsuitable target for immunotherapy due to its proposed immunoresistant properties. However, recent evidence has shown that anti-tumor immune responses can occur in lung cancer patients, paving the way for lung cancer as a novel target for immunotherapy. In order to take full advantage of the potential of immunotherapy, research is focusing on the presence and function of various immunological cell types in the tumor microenvironment. Immune cells which facilitate or inhibit antitumor responses have been identified and their prognostic value in lung cancer has been established. Knowledge regarding these pro- and anti-tumor immune cells and their mechanisms of action has facilitated the identification of numerous potential immunotherapeutic strategies and opportunities for intervention. A plethora of immunotherapeutic approaches is currently being developed and studied in lung cancer patients and phase 3 clinical trials are ongoing. Many different immunotherapies have shown promising clinical effects in patients with limited and advanced stage lung cancer, however, future years will have to tell whether immunotherapy will earn its place in the standard treatment of lung cancer.

Haptoglobin promoter polymorphism rs5472 as a prognostic biomarker for peptide vaccine efficacy in castration-resistant prostate cancer patients

Personalized peptide vaccination (PPV) is an attractive approach to cancer immunotherapy with strong immune-boosting effects conferring significant clinical benefit. However, as with most therapeutic agents, there is a difference in clinical efficacy among patients receiving PPV. Therefore, a useful biomarker is urgently needed for prognosticating clinical outcomes to preselect patients who would benefit the most from PPV. In this retrospective study, to detect a molecular prognosticator of clinical outcomes for PPV, we analyzed whole-genome gene expression profiles of peripheral blood mononuclear cells (PBMCs) in castration-resistant prostate cancer (CRPC) patients before administration of PPV. Cox regression analysis revealed that mRNA expression of myeloperoxidase, haptoglobin, and neutrophil elastase was significantly associated with overall survival (OS) among vaccinated CRPC patients (adjusted P < 0.01). By promoter sequence analysis of these three genes, we found that rs5472 of haptoglobin (HP), an acute-phase plasma glycoprotein, was strongly correlated to OS of vaccinated CRPC patients (P = 0.0047, hazard ratio 0.47; 95 % confidence interval 0.28-0.80). Furthermore, both HP mRNA expression in PBMCs and protein level in plasma of CRPC patients before administration of PPV exhibited rs5472 dependence (P < 0.001 for mRNA expression and P < 0.05 for protein level). Our findings suggest that rs5472 may play an important role in the immune response to PPV via regulation of HP. Thus, we concluded that rs5472 is a potential prognostic biomarker for PPV.

Immunological factors influencing clinical outcome in lung cancer patients after telomerase peptide vaccination

We have previously reported two trials in non-small cell lung cancer (NSCLC) evaluating vaccine therapy with the telomerase peptide GV1001. The studies demonstrated considerable differences in survival among immune responders, highlighting that an immune response is not necessarily beneficial. In the present study, we conducted long-term clinical follow-up and investigated immunological factors hypothesized to influence clinical efficacy. Peripheral blood mononuclear cells from 33 NSCLC trial patients and 15 healthy donors were analyzed by flow cytometry for T regulatory cells (Tregs, CD4(+)CD25(+)CD127(low/-)FOXP3(+)) and two types of myeloid-derived suppressor cells (MDSCs, HLA-DR (low) CD14 (+) or Lin (-/lo) HLA-DR (-) CD33 (+) CD11b (+)). T cell cultures were analyzed for 17 cytokines. The results demonstrated that immune responders had increased overall survival (OS, p < 0.001) and progression-free survival (p = 0.003), compared to subjects without immunological response. The mean OS advantage was 54 versus 13 months. Six patients were still alive at the last clinical update, all belonging to the immune responders. No serious toxicity had developed (maximum observation 13 years). Most patients developed a polyfunctional cytokine profile, with high IFNγ/IL-4 and IFNγ/IL-10 ratios. Low Treg levels were associated with improved OS (p = 0.037) and a favorable cytokine profile, including higher IFNγ/IL-10 ratios. High CD33(+) MDSC levels were associated with poorer immune response rate (p = 0.005). The levels of CD14(+) MDSC were significantly higher in patients than in healthy controls (p = 0.012). We conclude that a randomized GV1001 trial in NSCLC is warranted. The findings suggest that Tregs and MDSCs are associated with a tolerogenic cytokine milieu and impaired clinical efficacy of vaccine responses.

Manipulation of Innate Immunity for Cancer Therapy in Dogs

Over the last one to two decades, the field of cancer immunotherapy has rapidly progressed from early preclinical studies to a successful clinical reality and fourth major pillar of human cancer therapy. While current excitement in the field of immunotherapy is being driven by several major breakthroughs including immune checkpoint inhibitors and adoptive cell therapies, these advances stem from a foundation of pivotal studies demonstrating the immune systems role in tumor control and eradication. The following will be a succinct review on veterinary cancer immunotherapy as it pertains to manipulation of the innate immune system to control tumor growth and metastasis. In addition, we will provide an update on recent progress in our understanding of the innate immune system in veterinary tumor immunology, and how these gains may lead to novel therapies for the treatment of cancer in companion animals.

Bone marrow PMN-MDSCs and neutrophils are functionally similar in protection of multiple myeloma from chemotherapy

Multiple myeloma (MM) is an incurable cancer of plasma cells localized preferentially in the bone marrow (BM). Resistance to chemotherapy represents one of the main challenges in MM management. BM microenvironment is known to play a critical role in protection of MM cells from chemotherapeutics; however, mechanisms responsible for this effect are largely unknown. Development of MM is associated with accumulation of myeloid-derived suppressor cells (MDSCs) mostly represented by pathologically activated relatively immature polymorphonuclear neutrophils (PMN-MDSCs). Here, we investigated whether PMN-MDSCs are responsible for BM microenvironment-mediated MM chemoresistance. Using in vivo mouse models allowing manipulation of myeloid cell number, we demonstrated a critical role for myeloid cells in MM growth and chemoresistance. PMN-MDSCs isolated from MM-bearing host are immunosuppressive and thus, functionally distinct from their counterpart in tumor-free host neutrophils. We found, however, that both PMN-MDSCs and neutrophils equally promote MM survival from doxorubicin and melphalan and that this effect is mediated by soluble factors rather than direct cell-cell contact. Our data indicate that targeting PMN-MDSCs would enhance chemotherapy efficacy in MM.

Myeloid-derived suppressor cells enhance the expression of melanoma-associated antigen A4 in a Lewis lung cancer murine model

The cancer-testis (CT) family of antigens are expressed in multiple types of malignant neoplasm and are silent in normal tissues, apart from the testis. Immunotherapy targeting CT antigens is a promising therapeutic strategy for treatment of solid tumors. One member of this family, melanoma-associated antigen A4 (MAGE-A4), has been demonstrated to be expressed in melanomas and lung cancer. Patients with tumors expressing the MAGE-A4 antigen exhibit specific cellular and humoral immune responses to the antigen, resulting in a favorable prognosis. Conversely, the expression of MAGE-A4 is associated with poor survival in lung cancer. Myeloid-derived suppressor cells (MDSCs) are a heterogeneous population of immunosuppressive cells, which are upregulated in the cancer microenvironment. Little is known regarding any potential correlation between the expression of MAGE-A4 antigens and the accumulation of MDSCs. The present study aimed to examine the association between circulating MDSC levels and MAGE-A4 expression in a mouse model of Lewis lung cancer. The expression of MAGE-A4 in tumor cells or tissues was evaluated using western blotting, while the percentage of MDSCs (CD11b⁺Gr-1⁺) in the blood was detected by flow cytometry. In addition, the suppressive capacity of MDSCs and the effectiveness of MDSC depletion were assessed in C57BL/6 tumor-bearing mice. MDSCs were demonstrated to upregulate MAGE-A4 expression via the phosphosphorylated-signal transducer and activator of transcription 3⁷⁰⁵ pathway, while depletion of MDSCs decreased the tumor growth rate, prolonged median survival and enhanced the recognition of MAGE-A4 by CD8⁺ T cells. These findings indicated that immunotherapeutic strategies involving induction of cytotoxic T lymphocytes that target MAGE-A4, in combination with MDSC depletion, may be an effective approach to immunotherapy for cancer types with high expression of MAGE-A4.

Immunoregulatory Cell Depletion Improves the Efficacy of Photodynamic Therapy-Generated Cancer Vaccines

Photodynamic therapy (PDT)-generated cancer vaccine represents an attractive potential application of PDT, therapeutic modality destroying targeted lesions by localized photooxidative stress. Since immunoregulatory cell activity has become recognized as a major obstacle to effective cancer immunotherapy, the present study examined their participation in the therapeutic effect of PDT cancer vaccine. Following protocols from previous studies, mouse with squamous cell carcinoma SCCVII tumors were vaccinated by SCCVII cells treated by PDT and response monitored by tumor size measurement. The effects of low-dose cyclophosphamide (50 mg/kg) and all-trans retinoic acid (ATRA) on the numbers of Tregs and myeloid-derived suppressor cells (MDSCs) were determined by antibody staining followed by flow cytometry, while their impact on PDT vaccine therapy was evaluated by monitoring changes in tumor responses. Cyclophosphamide effectively reduced the numbers of Tregs, which became elevated following PDT vaccine treatment, and this resulted in an increase in the vaccine’s effectiveness. A similar benefit for the therapy outcome with PDT vaccine was attained by ATRA treatment. The activities of Tregs and MDSCs thus have a critical impact on therapy outcome with PDT vaccine and reducing their numbers substantially improves the vaccine’s effectiveness.