Skewed differentiation of bone marrow CD34+ cells of tumor bearers from dendritic toward monocytic cells, and the redirection of differentiation toward dendritic cells by 1alpha,25-dihydroxyvitamin D3

Inflammation and tumor progression: signaling pathways and targeted intervention

Cancer development and its response to therapy are regulated by inflammation, which either promotes or suppresses tumor progression, potentially displaying opposing effects on therapeutic outcomes. Chronic inflammation facilitates tumor progression and treatment resistance, whereas induction of acute inflammatory reactions often stimulates the maturation of dendritic cells (DCs) and antigen presentation, leading to anti-tumor immune responses. In addition, multiple signaling pathways, such as nuclear factor kappa B (NF-kB), Janus kinase/signal transducers and activators of transcription (JAK-STAT), toll-like receptor (TLR) pathways, cGAS/STING, and mitogen-activated protein kinase (MAPK); inflammatory factors, including cytokines (e.g., interleukin (IL), interferon (IFN), and tumor necrosis factor (TNF)-α), chemokines (e.g., C-C motif chemokine ligands (CCLs) and C-X-C motif chemokine ligands (CXCLs)), growth factors (e.g., vascular endothelial growth factor (VEGF), transforming growth factor (TGF)-β), and inflammasome; as well as inflammatory metabolites including prostaglandins, leukotrienes, thromboxane, and specialized proresolving mediators (SPM), have been identified as pivotal regulators of the initiation and resolution of inflammation. Nowadays, local irradiation, recombinant cytokines, neutralizing antibodies, small-molecule inhibitors, DC vaccines, oncolytic viruses, TLR agonists, and SPM have been developed to specifically modulate inflammation in cancer therapy, with some of these factors already undergoing clinical trials. Herein, we discuss the initiation and resolution of inflammation, the crosstalk between tumor development and inflammatory processes. We also highlight potential targets for harnessing inflammation in the treatment of cancer.

1α, 25 Dihydroxyvitamin D (1,25(OH)2D) inhibits the T cell suppressive function of myeloid derived suppressor cells (MDSC)

Myeloid derived suppressor cells (MDSC) suppress the ability of cytotoxic T cells to attack and clear tumor cells from the body. The active form of vitamin D, 1,25 dihydroxyvitamin D (1,25(OH)₂D), regulates myeloid cell biology and previous research showed that in mouse models 1,25(OH)₂D reduced the tumor level of CD34+ cells, an MDSC precursor, and reduced metastasis. We tested whether MDSC are vitamin D target cells by examining granulocytic- (G-MDSC) and monocytic (M-MDSC) MDSC from tumors, spleen, and bone marrow. Vitamin D receptor (VDR) mRNA levels are low in MDSC from bone marrow and spleen but are 20-fold higher in tumor MDSC. At all sites, M-MDSC have 4-fold higher VDR mRNA expression than G-MDSC. Bone marrow MDSC were induced to differentiate in vitro into tumor MDSC-like cells by treating with IFN-γ, IL-13, and GM-CSF for 48 h. This treatment significantly elevated Arg1 and Nos2 levels, activated the T cell-suppressive function of MDSC, increased VDR expression 50-fold, and made the MDSC responsive to 1,25(OH)₂D treatment. Importantly, 1,25(OH)₂D treatment reduced the T cell suppressive capacity of cytokine-induced total MDSC and M-MDSC by ≥70 % and tumor-derived M-MDSC by 30-50 %. Consistent with this finding, VDR deletion (KO) increased T cell suppressive function of in vitro M-MDSC by 30 % and of tumor-derived M-MDSC by 50 % and G-MDSC by 400 %. VDR KO did not alter Nos2 mRNA levels but significantly increased Arg1 mRNA levels in tumor M-MDSC by 100 %. In contrast, 1,25(OH)₂D treatment reduced nitric oxide production in both in vitro derived M- and G- MDSC. The major finding of this study is that 1,25(OH)₂D signaling through the VDR decreases the immunosuppressive capability of MDSC. Collectively, our data suggest that activation of vitamin D signaling could be used to suppress MDSC function and release a constraint on T-cell mediated clearance of tumor cells.

Targeting Myeloid-Derived Suppressor Cells in Cancer

Myeloid derived suppressor cells (MDSC) represent only a minor fraction of circulating blood cells but play an important role in tumor formation and progression. They are a heterogeneous group of cells that influence the tumor microenvironment by depletion of amino acids, oxidative stress, decreased trafficking of antitumor effector cells, and increased regulatory T and regulatory dendritic cell responses. Investigational treatment strategies targeting MDSCs have attempted to inhibit MDSC development and expansion (stem cell factor blockade, modulate of cell signaling, and target MDSC migration and recruitment), inhibit MDSC function (nitric oxide inhibition and reactive oxygen and nitrogen species inhibition), differentiate MDSCs into more mature cells (Vitamins A and D, all-trans retinoic acid, interleukin-2, toll-like receptor 9 inhibitors, taxanes, beta-glucan particles, tumor-derived exosome inhibition, and very small size proteoliposomes), and destroy MDSCs (cytotoxic agents, ephrin A2 degradation, anti-interleukin 13, and histamine blockers). To date, there are no Food and Drug Administration approved therapies selectively targeting MDSCs, but such therapies are likely to be implemented in the future, due to the key role of MDSCs in antitumor immunity.

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.

Myeloid-derived suppressor cells: their role in the pathophysiology of hematologic malignancies and potential as therapeutic targets

Myeloid-derived suppressor cells (MDSCs) are a heterogeneous population of immature myeloid cells at various stages of differentiation/maturation that have a role in cancer induction and progression. They function as vasculogenic and immunosuppressive cells, utilizing multiple mechanisms to block both innate and adaptive anti-tumor immunity. Recently, their mechanism of action and clinical importance have been defined, and the cross-talk between myeloid cells and cancer cells has been shown to contribute to tumor induction, progression, metastasis and tolerance. In this review, we focus on the role of MDSCs in hematologic malignancies and the therapeutic approaches targeting MDSCs that are currently in clinical studies.

The tumour-induced systemic environment as a critical regulator of cancer progression and metastasis

Recent pre-clinical and clinical research has provided evidence that cancer progression is driven not only by a tumour's underlying genetic alterations and paracrine interactions within the tumour microenvironment, but also by complex systemic processes. We review these emerging paradigms of cancer pathophysiology and discuss how a clearer understanding of systemic regulation of cancer progression could guide development of new therapeutic modalities and efforts to prevent disease relapse following initial diagnosis and treatment.

Hampering immune suppressors: therapeutic targeting of myeloid-derived suppressor cells in cancer

Myeloid-derived suppressor cells (MDSCs) are a heterogeneous population of immature myeloid cells with suppressive properties that preferentially expand in cancer. Myeloid-derived suppressor cells mainly suppress T-cell proliferation and cytotoxicity, inhibit natural killer cell activation, and induce the differentiation and expansion of regulatory T cells. The wide spectrum of MDSC suppressive activity in cancer and its role in tumor progression have rendered these cells a promising target for effective cancer immunotherapy. In this review we briefly discuss the origin of MDSCs and their main mechanisms of suppression and focus more on the approaches developed up to date targeting of MDSCs in tumor-bearing animals and cancer patients.

The immune system and head and neck squamous cell carcinoma: from carcinogenesis to new therapeutic opportunities

Head and neck squamous cell carcinomas (HNSCCs) exhibit complex interactions with the host immune system that may simultaneously explain resistance to various therapeutic modalities and that may also provide opportunities for therapeutic intervention. Discoveries in immunologic research over the last decade have led to an increased understanding of these interactions as well as the development of a multitude of investigational immunotherapies. Here, we describe the interaction between HNSCC and the immune system, including a discussion of immune cells involved with tumor carcinogenesis and the role of immune-modulating factors derived from tumors. We also describe the current immunotherapeutic approaches being investigated for HNSCC, including a discussion of the successes and limitations. With this review, we hope to present HNSCC as a model to guide future research in cancer immunology.

Tumors induce the formation of suppressor endothelial cells in vivo

Patients with solid tumors have defects in immune effector cells, which have been associated with a poorer prognosis. Previous studies by our laboratory have shown that exposure to Lewis lung carcinoma (LLC)- secreted products induces the formation of suppressor endothelial cells in vitro. The current studies examined if tumors could induce the formation of suppressor endothelial cells in vivo. Endothelial cells were immunomagnetically isolated from the lungs of tumor-bearing mice or normal controls and examined for their ability to modulate NK cell, T-cell and macrophage functions. Compared to normal controls, supernatants from endothelial cells isolated from tumor-bearing lungs had elevated secretion of PGE2, IL-6, IL-10 and VEGF. Conditioned media from endothelial cells isolated from normal lungs increased CD8+ T-cell IFN-γ and CD4+ T-cell IL-2 production in response to anti-CD3 stimulation, while media conditioned by endothelial cells from tumor-bearing lungs had a diminished stimulatory capacity. Examination of NK cell functions showed that supernatants from endothelial cells isolated from normal lungs were potent activators of NK cells, as indicated by their secretion of TNF- and IFN-γ. Endothelial cells isolated from tumor-bearing lungs had a significantly diminished capacity to activate NK cells. Finally, supernatants from endothelial cells of tumor-bearing lungs diminished macrophage phagocytosis compared to either treatment with supernatants of normal endothelial cells or treatment with media alone. The results of these studies demonstrate that tumors induce the formation of suppressor endothelial cells in vivo and provide support for the role of endothelial cells in tumor-induced immune suppression.

Use of alpha,25-dihydroxyvitamin D3 treatment to stimulate immune infiltration into head and neck squamous cell carcinoma

Prior studies have shown that treatment of head and neck squamous cell carcinoma (HNSCC) patients with 1alpha,25-dihydroxyvitamin D(3) [1,25(OH)(2)D(3)] reduced intratumoral levels of immune inhibitory CD34(+) progenitor cells while increasing levels of mature progeny dendritic cells. This finding was extended to a pilot study to determine whether 1,25(OH)(2)D(3) treatment concurrently increases levels of intratumoral CD4(+) and CD8(+) T cells, increases intratumoral levels of immune cells expressing the early activation marker CD69, and prolongs time to HNSCC recurrence. The clinical trial comprised 16 patients with newly diagnosed HNSCC being untreated and 16 patients being treated with 1,25(OH)(2)D(3) during the 3-week interval between cancer diagnosis and surgical treatment. Immunologic effects of treatment were monitored by immunohistochemical analyses of surgically removed HNSCC. Clinical effectiveness of 1,25(OH)(2)D(3) treatment in this study was measured by the time to HNSCC recurrence. HNSCC tissues of patients who received treatment with 1,25(OH)(2)D(3) contained increased levels of CD4(+) cells and, more significantly, CD8(+) T cells. Also prominent was an increase in cells expressing the lymphoid activation marker CD69. Results of this pilot study suggest that patients treated with 1,25(OH)(2)D(3) had a lengthier time to tumor recurrence compared with patients who were not treated before surgery.

In vivoHeparan Sulfate Treatment Alters the Immune Response of Normal and LLC-Bearing Mice

Despite the large amount of research dedicated to the understanding and treatment of tumor growth, the majority of cancers continue to lack effective therapeutic options. As in the case of most solid tumors, growth requires evasion of the host immune system. Our previous work using the Lewis Lung Carcinoma (LLC) model of tumor bearing (TB)-mice has shown several tumor-induced immune suppressing effects to be present. These effects include a decreased T-cell proliferative response to Con A and altered cytokine secretion patterns that favor neither a Th1 nor a Th2 response. To address these immune alterations, immune modulating approaches have been a central area of study. Of the many potential immune modulating compounds, we believe promising therapeutic potential lies in the heparin family. Heparan sulfate (HS), in particular, has been shown to increase T-cell proliferative response in non TB-mouse splenocytes as well as promotion of a beneficial Th1 response. In this paper, we studied the potential of HS to decrease tumor burden via in vivo treatment of TB-mice. Results showed both normal and TB-mice splenocytes had a dose response change in proliferation as a result of HS treatment. Furthermore, splenocytes from HS treated TB-mice showed a potentially beneficial decrease in basal level proliferation. On gross examination, HS treatment produced a decrease in tumor surface necrosis with a visible (2 +/- 1.8%) surface necrotic area in treated mice as opposed to a (43 +/- 16%) surface necrotic area in untreated mice. HS treatment decreased TB-mice splenomegaly when comparing mice spleen weights in treated (0.3 +/- 0.05 g) vs. untreated (0.14 +/- 0.02 g) groups. These results show a potential role of HS as an immune modulating agent with antitumor properties.

A novel function of dcf1 during the differentiation of neural stem cells in vitro

The study of neural dendrite formation is of great significance both in theory and applications. However, the molecular mechanisms of regulation remain unclear. We previously described a novel EST, which has high homology with dentritic cell factors (DCF1), expressed differentially between undifferentiated and differentiated neural stem cells (NSCs). In this study, we cloned, expressed, and silenced the dcf1 gene and offered insight into its function in regulating dendrite formation during the differentiation of NSCs. The results indicated that dcf1 encoded a 42 kD protein and could be successfully expressed both in Escherichia coli and NSCs. In order to silence dcf1 gene, three different kinds of siRNA vectors were constructed and transformed into the NSC line C17.2 and primary NSCs, resulting in down regulation of the dcf1 mRNA. Analysis of immunofluorescence or GFP illuminated that with overexpression of the dcf1 gene, the NSCs were maintained in undifferentiated status. After the dcf1 gene was silenced, cells tended to differentiate into neurons and astrocytes.

Protective mechanisms of head and neck squamous cell carcinomas from immune assault

Head and neck squamous cell carcinoma (HNSCC) is an aggressive malignancy that is the sixth most common neoplasm in the world. Despite advances in treatments involving surgery, radiation, and chemotherapy, the 5-year survival has remained at less than 50% for the past 30 years, primarily because of local recurrences. Thus, the possibility of immunotherapeutic approaches for patients with HNSCC has gained interest. Unfortunately, patients with HNSCC have profound immune defects that are associated with increased recurrence. This review aims to provide an overview of both the defensive and immune subversive mechanisms by which patients with HNSCC can protect themselves from immune antitumor assault.

Dendritic cells derived from metastatic cancer patients vaccinated with allogeneic dendritic cell-autologous tumor cell hybrids express more CD86 and induce higher levels of interferon-gamma in mixed lymphocyte reactions

Dendritic cells (DCs) are highly effective antigen-presenting cells that, when derived from cancer patients, seem to be functionally deficient. Herein, we show that vaccination with allogeneic DC-autologous tumor cell hybrids affects the phenotype and improves the function of monocyte-derived DCs (Mo-DCs) from cancer patients. Mononuclear cells were isolated from patients' peripheral blood by density gradient centrifugation, and adherent cells were cultured in medium containing GM-CSF plus IL-4 and, after 5 days, TNF-alpha. After 2 more days, Mo-DCs were harvested and their CD80, CD86, and CD83 expression was assessed by flow cytometry. They were also used as stimulators in mixed lymphocyte reactions (MLR), where IFN-gamma production was measured by ELISA. Mo-DCs from unvaccinated patients expressed significantly lower levels of CD86, and tended to express lower levels of CD83 than Mo-DCs from healthy donors. However, Mo-DCs generated after hybrid cell vaccination presented increased expression of the same markers and induced significantly higher levels of IFN-gamma in MLR. These results indicate that the use of allogeneic DC-based cancer vaccines induces recovery of DC function in metastatic cancer patients and, therefore, could precede the use of autologous DCs for vaccine preparation. Such an approach could be relevant and should be investigated in clinical trials.

Phase IB study of 25-hydroxyvitamin D(3) treatment to diminish suppressor cells in head and neck cancer patients

Patients with head and neck squamous cell carcinoma (HNSCC) have profound immune defects. These defects are associated with a poor prognosis and are mediated, in part, by an increased number of immune inhibitory CD34(+) progenitor cells in their peripheral blood and tumor. The CD34(+) cells suppress autologous T-cell functions. Our prior work had shown that the differentiation inducer 1alpha,25-dihydroxyvitamin D(3) could drive the differentiation of CD34(+) cells isolated from HNSCC patients into dendritic cells. A phase IB clinical trial was initiated with HNSCC patients to determine if 25-hydroxyvitamin D(3) treatment could diminish CD34(+) cell levels and improve immune function. Six patients per treatment group were orally administered 20 or 40 microg/day 25-hydroxyvitamin D(3) for six weeks. Peripheral blood was collected at 0, 1, 2, 4, 6, and 8 weeks, and assessed for markers of immune activity. Although no clinical responses were observed, results of these pilot studies showed that 25-hydroxyvitamin D(3) reduced the presence of immune suppressive CD34(+) cells and improved immune competence of HNSCC patients.

Chemoattraction of femoral CD34+ progenitor cells by tumor-derived vascular endothelial cell growth factor

Patients and animals with GM-CSF-producing tumors have an increased number of mobilized CD34+ progenitor cells within their peripheral blood and tumor tissue. These CD34+ cells are inhibitory to the activity of intratumoral T-cells. The present study used the murine Lewis lung carcinoma (LLC) model to assess mechanisms that could lead to the accumulation of CD34+ cells within the tumor tissue. In vitro analyses showed that LLC tumor explants released chemoattractants for normal femoral CD34+ cells. The LLC tumor cells contributed to the production of this activity since CD34+ cell chemoattractants were also released by cultured LLC cells. Antibody neutralization studies showed that most, although not all, of the chemotactic activity that was produced by LLC cells could be attributed to VEGF. In vivo studies with fluorescent-tagged CD34+ cells showed their accumulation within the tumor tissue, but not within the lungs, spleen or bone marrow, suggesting a selective accumulation within the tumor. Whether or not VEGF could chemoattract CD34+ cells in vivo was measured with a VEGF-containing Matrigel plug assay. Infusion of fluorescent-tagged CD34+ cells into mice after the plugs became vascularized revealed the accumulation of fluorescent-tagged cells within the plugs. However, these CD34+ cells failed to accumulate within the VEGF-containing Matrigel plugs when they were infused together with neutralizing anti-VEGF antibody. Through a combination of in vitro and in vivo analyses, the LLC cells were shown to be capable of chemoattracting CD34+ cells, with most of the tumor-derived chemotactic activity being due to tumor release of VEGF.