Pancreatic Cancer Fostered Immunosuppression Privileges Tumor Gro
Journal of Clinical and Cellular Immunology

Journal of Clinical and Cellular Immunology
Open Access

ISSN: 2155-9899

+44 1223 790975

Review Article - (2014) Volume 5, Issue 6

Pancreatic Cancer Fostered Immunosuppression Privileges Tumor Growth and Progression

Daniela Basso1*, Elisa Gnatta1 and Mario Plebani1,2
1Department of Laboratory Medicine, University Hospital of Padova, Italy
2Department of Medicine - DIMED, University of Padova, Italy
*Corresponding Author: Daniela Basso, Department of Laboratory Medicine, University Hospital of Padova, Via Giustiniani 2, 35128 Padova, Italy, Tel: +390498212801, Fax: 390498211981 Email:


The high progression rate of Pancreatic Ductal Adenocarcinoma (PDAC) depends on intrinsic genetic and epigenetic cancer cell aberrations and a profound imbalance in immune system cells infiltrating the PDAC stroma. Direct or exosome mediated shedding in the tumor microenviroment of different molecules (e.g. cytokines, chemokines, lectins) causes tumor, pancreatic stellate and inflammatory cells to recruit numerous immunosuppressive cells in the PDAC microenvironment and inhibit immune effector cells. CD8+ T and dendritic immune effector cells (DCs) are reduced, while immunosuppressive T regulatory cells (Treg), Myeloid Derived Suppressor Cells (MDSCs) and M2 Tumor Associated Macrophages (TAMs) accumulate in the PDAC stroma, mainly at the invasive front area. The imbalance in CD4+ T cell subsets, with Th2 and Th17 prevailing over the Th1 effector arm, is associated with a worse PDAC prognosis that depends on the failure of immune system cells to destroy cancer cells, and the accumulation of immune cells in the PDAC stroma can have pro-neoplastic and pro-metastatic effects. CD4+ T cells are indispensable for PDAC development; Treg and M2 polarized TAMs favor neoangiogenesis and the epithelial to mesenchymal transition of PDAC cells, a pre-requisite for metastases; MDSCs favor metastases by releasing pro-metastatic inflammatory mediators such as S100A8/A9 proteins, and by creating pre-metastatic niches (in metastatic sites). Of the several treatment strategies aiming to abolish the immune cell imbalance in PDAC, and targeting the immune system, DCs manipulation, vaccination with tumor derived antigens and Treg depletion appear to be of benefit, but still require validation before being recommended in the clinical setting.

Keywords: Pancreatic cancer; Lymphocytes; Myeloid derived suppressor cells; Dendritic cells; Tumor associated macrophages; Vaccines


Pancreatic ductal adenocarcinoma (PDAC), one of the most aggressive malignancies, is refractory to treatment, and the fourth leading cause of cancer related death in the developed world, with 46,420 new estimated cases and 39,590 estimated deaths in the US for the year 2014 [1]. The overall five-year survival rate of PDAC patients is lower than 20%, the dismal prognosis depending on late detection compounded by ineffective treatment options; only 15 to 20% of patients are eligible for radical surgery, the only known curative approach [2]. The first phase of the natural history of PDAC is longstanding, preneoplastic pancreatic intraepithelial neoplasias (PanINs) evolving into invasive cancer, often over several years; the second phase usually lasts a few months, with the rapid growth of established PDAC that invades the surrounding tissues and organs and metastasizes. Progression from PanINs to metastatic PDAC is characterized by the accumulation of cancer cells with several genetic and epigenetic alterations leading to a marked genetic heterogeneity, although mutations of four genes (KRAS, TP53, SMAD4, CDKN2A) are identified in the vast majority of PDAC, KRAS mutations occurring in more than 90% of cases [3,4].

PDAC development and progression depend on genetic and epigenetic tumor cell aberrations, and on the complex interplay between tumor cells and the surrounding stroma, with a pronounced desmoplastic reaction and the presence of several non-neoplastic infiltrating cell types, including mesenchymal-derived cells and cellular components of the vascular and immune systems [5]. These cells interact with each other and with cancer cells through direct contact or the release of cytokines and chemokines acting in an autocrine and/or paracrine manner to control and shape tumor growth. Recent research has focused on the role of the immune system in the development and progression of cancer, a defective immunological monitoring of tumors being considered an emerging hallmark [6]. According to the theory of immune surveillance, cells and tissues are continuously monitored by the immune system, which detects and eliminates incipient cancer cells, nascent tumors and nascent metastases. A highly immunosuppressive microenvironment is present in established PDAC, but the immune response is compromised in the early phase of development of this tumor type; this supports the belief that PDAC-associated immunosuppression originates in tumor inception. Immunosuppression is triggered when tumor cells and/or infiltrating inflammatory cells directly release inhibitory cytokines, followed by the recruitment of immunosuppressive cells in the tumor microenvironment and by the inhibition of immune effector cells [7].

The present review describes changes in the microenvironment in both PanINs and invasive PDAC, focuses on immune cell involvement and immune suppression, examines in vitro and in vivo experimental evidence of cell based treatments reported in the literature, and discusses immune modulating treatment strategies.

The Tumor Microenvironment Maintains Immunosuppression

Rather than merely reacting to cancer growth, the cancer microenvironment takes an active part in cancer development, often having cancer-promoting effects. PDAC is characterized by a dense desmoplastic reaction in which proliferating neoplastic cells co-exist with Pancreatic Stellate Cells (PSCs), Cancer Associated Fibroblasts (CAFs), hematopoietic and mesenchymal cells, and immune cells that permanently interact and influence each other. In the PDAC microenvironment, the prevalent immune cells tending to promote tumor progression via immunosuppression include T regulatory cells (Treg), Myeloid Derived Suppressor Cells (MDSCs) and Type 2 (M2) Tumor Associated Macrophages (TAMs), while dampening immune effector cells [mainly CD8+ and CD4+ T cells, Dendritic Cells (DCs) and Natural Killer Cells (NK)].

Immunosuppressive Cells

T regulatory cells (Treg): CD4+ T cells generally defined as CD4+CD25+FoxP3+ cells exerting an immunosuppressive function, Treg, maintain immune tolerance against self-antigens, thus preventing autoimmunity. Treg block Th1 differentiation by inhibiting the production of interferon (IFN)-γ and IL-2 and reduce antigen presenting cells (APCs)-induced Th1 cell activation; they also inhibit Th17 effector cells [8]. In cancer, Treg produce a local immunosuppressive environment that enhances tumor growth. Malignant tumors can actively recruit, expand and induce a de novo generation of tumor antigen-specific Treg able to suppress immune responses during disease progression. The expansion and accumulation of these immunosuppressive cells correlate with advanced tumor growth and indicate a poor prognosis [9].

In PDAC animal models and humans, Treg accumulate in the tumor microenvironment mainly in close proximity (within 100 μm of the juxatumoral stroma) of tumor cells [10]. Prevalent in pre-neoplastic lesions, Treg accumulate early at the tumor site, progressively increasing proportionate to disease progression as illustrated in Figure 1 [11,12]. Treg accumulation in PDAC might involve tumor antigen specific clones, as described by Amedei et al. [13], who found increased enolase specific Treg in patients with advanced PDAC. The relevance of Treg-associated immunosuppression in PDAC progression is further supported by the observation that increased numbers of infiltrating and/or circulating Treg correlate with more advanced disease, a lower chance of surgical resection and reduced survival after resection, while low circulating Treg levels one year post-resection correlate with prolonged overall survival [11,14-16]. The role of Treg in PDAC progression and resistance to immune mediated therapies has been recently supported by findings made in a series of studies using PDAC animal models, in which prolonged survival was achieved by using different treatments (immune stimulatory complexes, Listeria vaccine, IFN-α, aspirin) only when Treg were depleted [17-20]. However, the inhibitory function of these cells was recently suggested to play a minor role with respect to other dominant immune suppressive mechanisms, such as those correlated with the release of CXCL12 by CAFs [21].


Figure 1: Schematic representation of Treg accumulation in the PDAC microenvironment.

Treg accumulation in the PDAC microenvironment correlates with CD4+ and CD8+ T cells alterations and depends on several mechanisms, most of which appear to be orchestrated by PDAC derived molecules, including chemokines, indoleamine 2,3-dioxygenase (IDO) and Transforming Growth Factor (TGF)-β1 (Table 1) [22-25]. Tumor-associated cytokines and chemokines effects on immune cells have been recently reviewed by Wörmann et al. [26]. IDO, upregulated in pancreatic cancer cells and implicated in suppressing T-cell immunity, is an IFN-γ induced immune regulatory enzyme that catabolizes tryptophan into kynurenin. Since tryptophan is a crucial metabolite for T cells undergoing antigen-dependent activation, its IDO-induced depletion can create an immunosuppressive environment due to T cell arrest, anergy or death and the induction of Treg differentiation [22]. TGF- β1, significantly implicated in PDAC biology, has tumor promoting and tumor inhibitory effects. The signaling pathway of TGF- β1 is altered in PDAC [27]; TGF- β1 and TGF- β2, produced by both tumor cells and the surrounding inflammatory cells induce Treg expansion in the PDAC microenvironment [23,28,29], although recently Shevchenko et al. [30] failed to confirm that TGF- β1 accumulated in the PDAC stroma expands Treg.

PDAC and stromal-derived molecules Effects on T cells References
Adressins (e.g. VCAM-1, CD62E, Mad CAM-1, CD166) Promote Treg transmigration to the PDAC microenvironment [33]
αLβ2 integrin A reduced expression impairs CD8+ T cell infiltration [112]
Galectin-1 Increases Th2 and decreases Th1 cytokines Induces CD4+and CD8+  T cell apoptosis [113,143]
Induces IL-10 production in Treg
L1CAM Reduces CD4+T cell proliferation [105]
CCL2 Induces immunoregulatory DCs which in turn expand Treg [32]
CCL5 More efficient Treg migration to PDAC site [31]
CXCL12 Impedes T cells migration to the tumor site [21]
TGFβ1 Induces Treg expansion [23,28-30,110,115]
Inhibits CD4+ T cell proliferation and migration
Induces Th17
IL-1β and IL-6 Induce Th17 [115]
Fibroblast activation protein (FAP-α) Suppresses effector T cells [135]
Indoleamine 2,3-dioxygenase (IDO) Induces Treg differentiation [22]
Induces T cell arrest, anergy and death.

Table 1: Tumor and stromal cells derived molecules acting on T cells and involved in PDAC immunosuppression.

Treg might first migrate into the PDAC stroma following chemotaxis. Tan et al. [31] demonstrated that PDAC cells direct Treg homing to the tumor by releasing a CCR5 ligand, CCL5, which allows Treg to migrate more efficiently to disease sites. The role of chemokines in inducing Treg expansion in the PDAC stroma, has been emphasized by Kudu-Saito et al. [32], who demonstrated that CCL2 overexpression, in co-operation with Lipocalin 2, induces immunoregulatory DCs that expand Treg. The transmigration of Treg to the tumor microenvironment also appears to be driven by tumor endothelium addressins, such as VCAM-1, CD62-E, MAdCAM-1 and CD166 [33]. Using an orthotopic PDAC model, Shevchenko et al. [30] demonstrated that PDAC infiltrating Treg undergo intense cell division and suggested that this elevated proliferation rate is a major mechanism underlying Treg accumulation in PDAC stroma.

Since Treg play a relevant immunosuppressive role and underlie the high progression rate of PDAC, the efficacy of cancer therapy might be enhanced by their modulation or depletion. In a murine PDAC model, Aida et al. used a monoclonal antibody anti glucocorticoid induced tumor necrosis factor receptor, constitutively expressed by Treg at high levels, and found that tumor infiltrating Treg and tumor growth were reduced [19]. Moreover, low-dose chemotherapy regimens emerged as a promising approach for selective Treg depletion. For instance, low-dose gemcitabine administered in tumor bearing mice, reduced Treg accumulation and improved survival [30], these effects being potentiated by aspirin [18]. Figure 1 summarizes the three main steps (homing, expansion and proliferation) underlying Treg accumulation in PDAC. PDAC cells favor Treg chemotaxis and expansion in the tumor microenvironment through the release of chemokines, IDO and TGF-β1. Accumulated Treg might further proliferate in a TGF-β1 independent manner, thus contributing to making the PDAC microenvironment an extremely immunosuppressive milieau.

Myeloid Derived Suppressor Cells (MDSCs): Comprising a heterogeneous population of immature cells of myeloid origin, these cells can suppress T cell activation. Normally myeloid cells migrate from the bone marrow to peripheral organs, where they differentiate into mature myeloid cells, such as macrophages, DCs, or granulocytes; this process is usually blocked in the tumor microenvironment, immature cells frequently differentiating into MDSCs. CD11b/Gr1 surface markers clearly define MDSCs in mice; since Gr1 has no human homologous marker, any such definition in humans is more complex. Human MDSCs, which lack HLA-DR expression, are characterized by the membranal expression of the immature markers CD33 and CD11b, and by CD14 (monocytic MDSC or mMDSC) or CD15 (granulocytic or gMDSC). In several cancer types both MDSCs populations accumulate in the tumor microenvironment, in peripheral blood and in secondary lymphoid organs, and the prevalence of one subtype over the other appears to be cancer type-related. gMDSC accumulation has been described in patients with renal cell carcinoma, colon cancer and non-small cell lung cancer [34-36], whereas mMDSC has been detected in patients with melanoma, prostate cancer, hepatocellular carcinoma and head and neck cancer [37-39].

In human PDAC, MDSCs accumulate in tumor tissue, blood, bone marrow and secondary lymphoid organs [40-42], as occurs in animal models [12,41,43-46], gMDSCs appearing prevalent in tissue and blood [47]. Although MDSCs appear to accumulate at the cancer site at an early stage, they become a prominent component in established PDAC, increasing further during tumor progression, as demonstrated in animal models and illustrated in Figure 2 [12,43]. Unlike Treg and TAMs, which infiltrate the tumor microenvironment at the pre-invasive stage, MDSCs increase most markedly during the transition from pre-invasive to invasive disease to become a dominant immune cell population infiltrating PDAC [48]. Of the several authors who investigated whether MDSCs accumulation parallels tumor stage in humans, some authors demonstrated that this was the case [40,42,49], but others did not [47]. This discrepancy probably reflects the complexity of MDSCs populations and functions, which might complicate their characterization in different settings. The contribution of MDSCs to cancer progression appears to be partly due to their accumulation within the tumor stroma and in metastatic sites, such as the liver, where they suppress T cell proliferation and cytotoxicity and trigger Treg development, thus creating a favourable pre-metastatic niche [44]. In line with their important role in favouring PDAC progression and metastases, the circulating levels of MDSCs were shown to be an independent prognostic index, a unit increase in MDSCs percentage being associated with a 22% increased risk of death [40].


Figure 2: Schematic representation of MDSCs accumulation in the PDAC microenvironment.

Experimental and animal studies have provided insight on MDSCs recruitment at the tumor site and its effects on tumor progression. Both PSCs and PDAC cells produce MDSCs-promoting cytokines, such as IL-6, VEGF, macrophage colony-stimulating factor (M-CSF) and chemokines (SDF-1, MCP-1), which promote MDSCs expansion by stimulating myelopoiesis and inhibiting mature myeloid cell differentiation in a Stat3- dependent manner [26,41,50]. PDAC probably promotes MDSCs expansion also by giving rise to high lactate levels in the surrounding medium [51,52]. The most relevant PDAC-derived molecules involved in MDSCs expansion are GM-CSF, IL-1β, IL-6, TGF- β1, and prostaglandin E2 [45,53-58]. The mechanism underlying MDSCs expansion following exposure to PDAC derived molecules involves the activation of several transduction pathways, mainly JAK/STAT kinase, TGFβ and RAGE [59], and the down-regulation of β-catenin, recently shown to lead to MDSCs-mediated tumor expansion in mice and humans [60]. In the expansion of MDSCs in PDAC-bearing mice, IL-6 and IL-1β activated Stat3 interacts with transcriptional factors such as C/EBPβ, which plays a key role in myeloid development and can also affect downstream targets, including the proinflammatory proteins S100A8 and S100A9 [45,61-63].

The more relevant mechanisms used by MDSCs to control antitumor immunity are high levels of inducible nitric oxide synthase (iNOS) and arginase 1, both enzymes acting on L-arginine, catalyzing the release of nitric oxides (NO) and converting l-arginine to urea and l-ornithine. MDSCs are also a source of the free radical peroxynitrite, which inhibits the binding of processed peptides to tumor cell-associated MHC, rendering tumor cells resistant to antigen-specific cytotoxic T cells [64]. The increased Stat3 and NADPH activity in the gMDSCs subset results in increased levels of ROS, while upregulation of Stat1 and iNOS expression in the mMDSC subset results in increased levels of NO. ROS and peroxynitrite induce the post-translational modification of T cell receptors and may cause antigen-specific T cell unresponsiveness, while NO suppresses T cell function via different mechanisms including the inhibition of Janus kinase 3, Stat5, MHC class II expression and the induction of T cell apoptosis. MDSCs-mediated immune suppression also includes the sequestration of cysteine, which is essential for T cells.

MDSCs create favorable conditions for tumorigenesis, tumor growth and metastasis, and neoangiogenesis. These closely related processes are governed by MDSCs-derived mediators, such as matrix metalloproteinases (MMPs), apoptotic factors (TNF-α, Api6), interleukins (IL-1, IL-6), growth factors (TGF-β1, VEGF, bFGF), and the hypoxia-induced factor (HIF)-1α, which was recently reviewed by Kumar et al. [65].

S100 proteins and MDSCs: S100A9 overexpression inhibits the differentiation of DCs and macrophages, and promotes MDSCs formation whereas S100A9 inhibition results in the reduction of MDSCs in the spleen of tumor bearing mice. Although the mechanism governing this phenomenon has not been identified, it has been suggested that the S100A8 and S100A9 heterodimers assist in the formation of the NADPH oxidase complex generating reactive oxygen species (ROS) in myeloid cells, which can interfere with their differentiation [66]. S100A8 and S100A9 inflammatory proteins have high expression not only in human MDSCs [67], but are also produced by PDAC cells and can induce MDSCs expansion [42]. The accumulation of S100A8/S100A9 producing MDSCs in the PDAC microenvironment probably contributes to the enhancement of PDAC progression, since these molecules, like TGF-β1, favor epithelial to mesenchymal transition (EMT) [68]. The main receptors of S100A8/S100A9 proteins are advanced glycation end products (RAGE) and TLR4 [69]. As demonstrated by Vernon et al. [70], RAGE plays a critical role in MDSCs accumulation in the context of pancreatic carcinogenesis: the targeted ablation of RAGE in mice expressing an oncogenic variant of Kras limits the development of PanIN lesions and the associated accumulation of MDSCs. Interestingly, during pancreatic cancer progression in the absence of RAGE, the majority of immature myeloid cells (CD11b+) exhibit a more mature phenotype with the expression of the mature macrophage marker F4/80 and a loss of Gr1 expression. It has been suggested that RAGE overexpression within the PDAC tumor and stromal compartments undergo ligation by S100A8/S100A9 synthesized by MDSCs thus inducing a regulatory chemokine tumor gene profile and serving as a positive feed-back loop for the further recruitment of MDSCs [63]. The release of S100A8/S100A9 proteins by MDSCs accumulated in organs distant from the primary site might also play a role in establishing the pre-metastatic niche [67,71-75].

Exososomes and MDSCs: Researchers are paying increasing attention to the role of exosomes in the cross-talk between tumor and microenvironment cells, including MDSCs [76]. Exosomes are small vesicles (30-100 nm diameter) that can traffic from one cell to another and transfer their large cargo (proteins, RNA, microRNA, DNA and lipids), thus affecting cell function. Tumor-derived exosomes can alter myelopoiesis by modulating myeloid cells in the tumor microenvironment, in hematopoietic organs and in pre-metastatic sites; this leads to abnormal myeloid cell differentiation in favor of MDSCs [77]. On the other hand, MDSCs might also release exosomes, which are enriched with S100A8/S100A9 molecules [78]. Figure 2 summarizes the main mechanisms involved in PDAC-induced expansion of MDSCs.

Tumor-associated macrophages (TAMs): The mononuclear phagocytic system includes monocytes, macrophages and DCs. On migrating to tissues, circulating monocytes differentiate into resident macrophages that, in tumors, are named TAMs. M1 macrophages, or classically activated macrophages are pro-inflammatory, conferring an anti-tumor immune response through the release of Tumor Necrosis Factor α (TNF-α), IL-12, reactive nitrogen and oxygen intermediates; M2 macrophages are immunosuppressive and promote angiogenesis, matrix remodeling and metastasis, and induce a Th2 differentiation of T lymphocytes through the release of IL-10 [79]. M1 or M2 polarization depends on stimuli from PDAC cells and the tumor microenvironment, including cytokines and Reg3β lectin [80]. TNF-β and IL-1β are M1 polarizing cytokines, while IL-4 switches the differentiation from M1 to M2; this phenomenon, occuring in the PDAC setting, is associated with a worse prognosis [81]. While in PanINs macrophage abundance is reportedly fairly uniform at all stages, within the broader tumor microenvironment macrophage distribution is non-uniform, with a greater accumulation in regions of disrupted collagen where tumor invasion is mainly due to single cells [82]. M2 macrophages and one of their subsets expressing folate receptor beta accumulate mainly at the invasive front of PDAC and correlate with tumor stage and survival, probably because they favor angiogenesis by releasing VEGF [16,83-85]. By releasing VEGF, M2 macrophages infiltrating regional lymph nodes are also implicated in nodal lymphangiogenesis and occult nodal involvement in pN0 PDAC [86]. M2 and M1 macrophages may concur in favoring PDAC progression and metastases, also because they induce EMT as well as metalloproteinase (MMP)2 and MMP9 proteolytic activity in PDAC cells [87,88]. As recently demonstrated, the adverse effects of M2 TAMs on PDAC prognosis also depend on their ability to induce in cancer cells the expression of cytidine deaminase involved in the metabolism of gemcitabine thus preventing apoptosis during gemcitabine treatment [89]. Informations on the molecular pathways underlying M2 polarization in PDAC are scarse. Pancreatic cancer cell lines conditioned media were demonstrated to induce macrophage polarization through c-MYC expression, involved in controlling the transcription of key genes for tumor progression and metastases (MMP9, VEGF, HIF-1α, and TGF-β) [90]. Moreover, the embryonic homeobox transcription factor CUX1, highly expressed in PDAC upon TGF-β exposure, represses the M1 phenotype of macrophages by interacting with NF-κB [91]. Hyperglycemia, frequently found in PDAC, both the cause and consequence of diabetes mellitus, was shown to enhance in vitro tumor-driven macrophage enrichment and polarization [92].

In view of their relevance in PDAC and in the biology of other solid tumors, Adams et al. [93] evaluated whether TAMs identification in blood might be useful in diagnosing cancer. The authors found that, unlike controls but like patients with breast cancer, 93% of patients with PDAC have circulating cancer-associated macrophage-like cells (CAMLs). In the same study CAMLs were attached to circulating tumor cells in 10% of late-stage patients, this finding supporting the observation that interactions between tumor cells and immune cells are highly complex.

Immune effector cells

T cell lymphocytes: In cancer types including invasive colon cancer, melanoma, multiple myeloma, and PDAC, an increase in T cells (specifically activated CTLs and Th) is correlated with a better survival [94-96], although there is evidence that many T cell subsets present in solid tumors are involved in tumor promotion, progression and/or metastasis. Immune-mediated tumor rejection calls for a fully functional T-cell anti-tumor response, for which CD8+ and CD4+ T cells are considered the main effectors. The selective binding of CD4+ T cells to class II MHC molecules ensures the response of CD4+ cells to class II-associated peptide antigens, and that of CD8+ T cells to class I-associated peptides. Because most solid tumors express MHC class I, but not MHC class II, it has been assumed that class-I restricted CD8+ T cells are the main vectors of T cell tumor destruction. However CD4+ T cells play a critical role in orchestrating the antitumor response. Accordingly, it has been found in animal models that T cell deficiency or disruption of specific cytotoxic mechanisms increase susceptibility to spontaneous or chemically induced carcinogenesis [95,97]. In PDAC animal model, tumor-specific CD4+ T cells are required for the full expression of the CD8+ T cell antitumor effect [98]. Recent studies on animals have highlighted the dark side of CD4+ T cells in PDAC, and have further evidenced the close relations between these cells and CD8+ T cells: in CD4+ T cell genetically depleted mice, Kras-driven pancreatic carcinogenesis is inhibited, unlike in CD4+ non-depleted mice which rapidly develop PanINs and progress to higher grade lesions over time [99]. In the absence of CD4+ T cells, CD8+ T cells accumulate proximal to PanIN lesions, but also present an enhanced effector function by releasing IFN-γ and granzyme B; in the presence of CD4+ T cells, few CD8+ T cells infiltrate the neoplastic pancreas [99].

The CD4+ T cell population comprises Th1, Th2, Th17 and Treg cells. The permissive effect of CD4+ T cells on pancreatic carcinogenesis has mainly been attributed to CD4+ Treg and Th17 cells, which infiltrate the neoplastic pancreas and suppress CD8+ T cell activity [99,100]. PDAC animal models and human tumors without CD4+ T cell depletion, commonly contain a scarce and irregular CD8+ T cell infiltration that is denser near the invasive front and scarcer at the tumor center [12,16,101]. As recently highlighted, the reduced migration of CD8+ T cells to the PDAC stromal compartment depends not only on CD4+ T cells, but also on activated PSCs [10]. These stromal cells and CAFs are primarily involved in creating the dense desmoplasia surrounding cancer cells, which might impede cell migration as it impedes drug delivery by causing increased interstitial fluid pressure and vascular collapse [102]. The reduced CD8+ T cell infiltration in PDAC tumors implies a reduced trafficking of tumor specific CD8+ T cells, this phenomenon being reflected, at least in part, by a reduction in the number of circulating CD8+ T cells observed in PDAC, as well as in other solid tumors [42]. Moreover, the reduction in tissue and blood CD8+ T cells associated with the concomitant accumulation of Treg, indicates an adverse outcome [11,16], while an enhanced juxtatumoral CD8+ T cell infiltrate correlates with a better survival in PDAC patients [10]. In line with the suggestion that CD4+ T cells have potential tumor promoting effects, an increased tumor infiltration has been described in animals [12] and humans [16], although this finding has not been consistently made across studies [103-105]. This discrepancy may depend on the heterogeneity of CD4+ T cells, the increase being mainly due to immunosuppressive rather than immune-effector subtypes, namely CD4+CD25+ Treg but also to CD4+CD69+ T cells, a newly identified immunosuppressive CD4+ T cell subset [105]. CD69 expression might affect the immune response by inhibiting CD4+CD69- cell cytokine synthesis; this process seems to partly depend on TGF-β [106,107]. CD4+CD69+ T cells might also regulate the Th1/Th2 balance which, in several cancer types including PDAC, is reported to be driven toward Th2, which, unlike Th1 cells, favor a predominantly humoral response and do not secrete IFN-γ and TNF-α, responsible for activating and regulating the development and persistence of cytotoxic T cells [108,109]. Reduced levels of IL-2 and increased levels of IL-10 have also been implicated in the imbalance between Th1/Th2 [104]. The complex mechanism underlying the profound imbalance of T cells subsets, characterized by the expansion of immunosuppressive T cells with the dampening of immune effector T cells during the progression of pancreatic lesions from premalignant to malignant, is due to both soluble mediators and adhesion molecules (Table 1). By releasing soluble cytokines and chemokines, including TGF-β1, IL-8, GM-CSF, PDAC cells directly target CD4+ T cells thus inhibiting their proliferation and migration and, interestingly, induce CD69 rather than CD25, expression [110]. The adhesion molecule L1CAM (CD171), which increases during PDAC progression in the ductal epithelium [111], also appears to be involved in reducing CD4+ T cell proliferation and in inducing CD69 expression, probably because it mediates the release of soluble factors promoting the generation of CD4+ T cells with a CD69+phenotype [105]. Another PDAC-associated adhesion molecule, an ICAM-1 receptor αLβ2 integrin (also known as LFA-1 or CD11a/CD18), regulates CD8+ T cell recruitment: only its knockout results in a marked impairment of CD8+ T cell infiltration in experimental pancreatic tumors in mice, probably because its lack of expression impairs T cells activation and differentiation [112]. Overexpression and secretion by activated PSCs of β-galactoside-binding protein Galectin-1 (Gal-1), another molecule that mediates immunosuppression in PDAC by targeting T cell, increases Th2 and decreases Th1 cytokines, inducing CD4+ and CD8+ T cell apoptosis [113].

The Th17 T cell subset plays a potent pro-inflammatory role in certain infections, tumors and autoimmune disorders [114]. Th17 cells, able to release the interleukins IL-17A, IL-21 and IL-22, develop from naïve CD4+ T cells in the presence of TGF-β, IL-6, and IL-1β and are maintained long-term in the presence of IL-21 and IL-23 [115]. An increased infiltration of Th17 cells has been detected in PDAC murine tumors [99,100], while increased Th17 associated serum cytokines have been reported in humans, high IL-17A and TGF-β1 levels being correlated with a worse prognosis [116]. The role of this CD4+ T cell subset in the onset and progression of PDAC has not yet been completely clarified [115]. However, in an animal model it has been demonstrated that an enforced Kras driven IL-17 expression is required for the initiation and progression of PDAC [100] and experimental embelin treatment in tumor bearing mice reduces tumorigenicity and Th17 accumulation [62,117].

Natural killer cells (NKs): Large granular lymphocytes, NKs cooperate with adaptive immunity and rapidly detect and eliminate atypical cells. In PDAC there is a significant down-regulation of NKG2D, NKp30, NKp46 receptors, which participate in killing of tumor cells by recognizing specific ligands and perforin positive circulating NKs [118]. Lactate, which is overproduced in PDAC tumors, reduces both NKs cytotoxicity and NKp46 receptor expression [52]. The involvement of these cells in controlling tumor growth is borne out by the observation that, in a patient with regression of several pancreatic cancer metastases following the administration of the immune modulator Ipilimumab (anti-CTLA-4 antibody), NKs were increased and caused lysis of an autologous tumor as well as pancreatic cancer lines [119]. Moreover, the degree of NKs impairment appears to be directly related to the invasiveness of malignancy, the risk of recurrence after surgery and an unfavourable prognosis [120]. The concept that NKs act only in one-way by destroying tumor cells, thus exerting an anti-tumor effect, has been recently re-evaluated since these cells may acquire a pro-angiogenic phenotype and be potentially (pro-) tumorigenic [121]. Distinct NKs populations, anergized/regulatory NK cells (NKreg) and activated NK may be found in the tumor inflammatory microenvironment. NKreg can induce differentiation of the pancreatic cancer cell line MiaPaCa2, thus conferring a resistance to NKs-mediated cytotoxicity [122], while IL-15 activated NKs inhibit tumor growth and prolong the survival of tumor-bearing mice, being associated with tumor cell apoptosis, NKs and T-cell accumulation [123]. Interestingly, NKs may be able to eliminate cancer stem or cancer initiating cells, which have slow replication, are resistant to most chemotherapeutic agents and radiotherapy, and can give rise to rapidly proliferating cells.

Dendritic cells (DCs): like macrophages, DCs are APCs and, unlike other antigen-presenting cells, such as B cells and macrophages, can trigger secondary and primary immune responses (such as naive T cell activation) directed against specific antigens, thus linking the innate and the adaptive immune response. There are two functionally heterogeneous and distinct subsets: myeloid-DCs (CD11c+ DCs) and lymphoid-DCs (CD11c- DCs) both of which express high levels of HLA-DR and lack the lineage markers CD3, CD14, CD15, CD16 and CD19. In PDAC, circulating myeloid DCs progressively decrease as tumor stage increases, while lymphoid DCs behave differently. DCs from PDAC patients demonstrate a significantly reduced ability to stimulate allogenic T cells, but both their number and their allogenic stimulatory capacity are restored following chemoradiotherapy and surgical resection [26, 42,124-128].

In agreement with the hypothesis that an impaired immune response to cancer cells contributes to favoring tumor progression, and in view of the role played by DCs in activating the immune response, it has been demonstrated that high levels of circulating DCs are an independent favorable prognostic factor in patients with resectable and unresectable PDAC [129,130]; similar findings were made on considering patients with tumor infiltrating DCs [131]. Of the numerous cytokines and chemokines released by pancreatic cancer cells and the surrounding stromal cells, IL-6 and G-CSF are believed to play an important role in inhibiting the maturation and activation of DCs [132].

The desmoplastic stroma

The immune infiltrate of cancer is but a part of the tumor microenvironment. CAFs, cells of mesenchymal origin, combined with extra cellular matrix (ECM) proteins and tumor associated vasculature, are also important components. By providing a physical framework and acting as a reservoir for soluble mitogens, the ECM influences the growth, differentiation, survival and motility of cancer cells in various malignancies. In addition, the various effects that malignant and non-malignant components of the cancer mass can have on each other alter angiogenesis, ECM components, epithelial-mesenchymal interactions, substratum adhesiveness, and cancer-directed immune responses, all of which influence cancer behavior [133]. A dense desmoplastic stroma reaction, long recognized as a hallmark of PDAC, promotes tumorigenesis and resistance to therapy. This concept is corroborated by the observations made by Provenzano et al. [102], who identified hyaluronic acid as the principal ECM component involved in causing high interstitial fluid pressure, vascular collapse and resistance to chemotherapy. By interacting with the immune system CAFs promote tumor progression, attracting TAMs to the tumor microenvironment (NF-κB related mechanism) and causing increased fibrosis and tumor growth [134]. Moreover, CAFs by secreting the fibroblast activation protein (FAP-α) and the chemokine ligand 12 (CXCL12) further suppress effector T cells and impede T cells migration to the tumor site [21,135].

The histological assessment of the pancreata of patients with PDAC or mice engineered to express oncogenic Kras in the epithelial compartment of the pancreas reveals that even the early stages of PanIN development are associated with a stromal reaction characterized by a robust desmoplastic response and the recruitment of immune cells. Based on the composition of the immune infiltrates surrounding PanINs, it has been shown that the stromal constituents surrounding PanINs form an inflammatory and immune suppressive environment thereby allowing the precursor lesions to escape immune surveillance [136]. The main pancreatic cancer-associated stromal fibroblasts, PSCs, are key players in the development of desmoplasia [137], and predominantly secrete gelatinases (MMP2, MMP9), which degrade the basement membrane collagen (type IV) and are associated with inflammation, fibrosis, angiogenesis, and cancer invasion. In various cancers including PDAC, basement membrane breaching, a critical step in cancer progression, brings malignant cells into direct contact with ECM proteins such as collagen type-1, thus supporting their growth, contributing to their chemo-resistance, and paving the way for invasion and metastasis.

Changes in Tumor-Associated Antigens (TAAs)

An effective anti-tumor immune response involves recognition of TAAs by the immune system and the generation of T or B cell responses that kills the tumor cells but leave life-sustaining normal tissue intact. This mechanism, however, might induce a selective pressure, killing tumor cells with TAAs expression and favouring the proliferation of tumor cells with fewer immunogenic surface antigens. TAAs include mucins, oncogenes and tumor suppressor gene products. Muc1, an epithelial cell membrane-bound glycoprotein that is approximately 80% carbohydrate, is expressed in normal pancreas but it is overexpressed and aberrantly glycosylated in >90% of metastatic PDAC; its aberrant expression has been associated with increased metastasis and the poor prognosis of PDAC and other cancers [138].

In agreement with the concept that mucins play a functional role in PDAC progression, Rachagani et al. have shown that there is a progressive increase correlated with the increased expression of the mucin inducer inflammatory cytokines IFN-γ, CXCL1 and CXCL2, in the expression of mucins particularly Muc1, Muc4 and Muc5AC in the pancreas of mice with advanced PanIN lesions and PDAC both at mRNA and protein levels [139]. Accordingly, knock-down in Muc1, Muc4 or Muc5AC was shown to decrease the growth and metastatic potential of pancreatic cancer cells [140-142]. This suggests that mucins expression may play an important role in the development of PDAC and may be a potential tumor specific target for treatment.

Known to contribute to the immunosuppressive tumor microenvironment and evasion of immune responses, galectins are soluble immunomodulating glycoproteins involved in T- cell homeostasis, the suppression of autoimmunity, survival and inflammation. Gal-1 promotes a Th2 cytokine profile in PDAC, induces IL-10 production in Treg, activates DCs and regulates immune cell trafficking [143]; this glycoprotein, overexpressed by pancreatic tumor cells, has been identified as a proteomic biomarker closely correlated with disease stage [144]. Gal-1, also expressed on PSCs, contributes to stellate cell activation and maintenance of the immunosuppressive microenvironment. Genetic ablation of Gal-1 in a murine PDAC model dampened tumor progression by inhibiting proliferation, angiogenesis and the desmoplasic reaction, and also by triggering a tumor-associated immune response, thus leading toa 20% increase in relative lifespan [145]. However, Gal-1 overexpression is found on the stromal tissues of long term pancreatic cancer survivors [113], indicating that the prognostic significance of Gal-1 expression is not entirely clear. Blocking molecules for Gal-1 is a potential strategy for cancer treatment.

The analysis of antibodies in patients’ cancer sera that recognize TAAs has been suggested as a useful tool in identifying new diagnostic indicators and/or new potential targets for therapy [146]; antibodies identified include those elicited against mutated tumor suppressor genes (p53, p16) or other key pro-survival molecules (e.g. survivin), the epithelial cell adhesion molecule (EpCAM) and mucins such as the well-known CA19-9 and CD44 [147]. However, since these antibodies are detectable at a low frequency, they are not recommended for diagnosis, although they do indicate a down-regulated immune response to these antigens.

Tumor antigens are processed and presented to T cells by HLA class I and class II molecules on the surface of APCs. The resulting T cells kill tumor cells expressing specific tumor antigens in class I molecules. In PDAC, tumor cells down-regulate or lose expression of HLA class I and its associated β2-microglobulin [148]. Reportedly HLA class I expression can be re-induced in PDAC cell lines in vitro by IFN-γ treatment [149], thus making it possible to alter the balance between cellular and humoral immunity by promoting Th1/cell-mediated immunity.

Treatment Strategies: Focus On the Immune System

The front-line approaches in PDAC treatment are surgery and chemotherapy. Recently, immunotherapy has proven promising although more effective when used in anadjuvant setting for patients with operable disease at a high risk of post-operative recurrence than in patients with advanced disease [150]. The aim of immunotherapeutic strategies against PDAC is to amplify the immune reaction to cancer. The present paper focuses on vaccination, DCs based therapies, interference with co-stimulatory and inhibitory receptors, approaches designed to increase the number of tumor specific cytotoxic T cells (adoptive T cell immunotherapy), chimeric antigen receptors (CARs) and Treg depletion.

Vaccination strategies

The development of vaccination strategies was prompted by the finding that TAAs administration induces a specific T-cell response in both animals and humans. Tumor antigens might be normal proteins expressed at much higher concentrations by PDAC cells than normal cells (e.g. Muc1, VEGF-R) or mutated proteins expressed exclusively by PDAC cells (e.g. mutated K-ras). The antigens can be administered as whole proteins or peptide fragments. Human clinical phase I/II trials have been conducted to verify safety, immune activation and clinical response to different vaccines including cancer cells transduced to express GM-CSF, mutant K-ras peptide, telomerase peptide GV1001, Muc1 peptide, and synthetic peptides derived from the cancer-testis antigens KIF20A and CDCA1 [151-164]. Although vaccines are safe, and trigger the specific immune response, clinical responses have been weak.

DCs based vaccines

Based on the observation that DCs maturation and function is impaired in PDAC and in view of the fact that these cells are readily available in vitro following stimulation of monocytes with GM-CSF and IL4, several studies have aimed to obtain DCs-precursor cells from the blood or the bone marrow of cancer bearing mice or patients, differentiate and activate them in culture, load them with tumor antigens, and re-inject the cells in the tumor bearing mice or the patient. Different tumor antigens and protocols have been used in this DCs vaccination strategy, which has achieved activation of anti-tumor immune response, delayed tumor growth and improvement in survival, as shown in Table 2 [165-184].

Type of study DCs source Pulse antigen Verification model Results References
          No. Year
In vitro PB of patients with PDAC CA 19-9 Cytotoxicity in co-culture with pancreatic cancer cells Higher cytotoxic activity against pancreatic cancer cells using CA 19-9 pulsed DCs [165] 2000
In vitro PB of blood donors Pancreatic cancer cell lines lysates Cytotoxicity in co-culture with pancreatic cancer cells Higher cytotoxic activity against pancreatic cancer cells using pulsed DCs [166] 2001
In vitro PB or buffy coats of blood donors Lysates of apoptotic and non apoptotic pancreatic cancer cell lines Cytotoxicity in co-culture with pancreatic cancer cells Higher cytotoxic activity against pancreatic cancer cells using DCs pulsed with apoptotic pancreatic cancer cell lysates [167] 2002
In vivo animal model Syrian hamster BM Pancreatic cancer cell lines lysates Hamsters inoculated s.c. with a piece of tumor and treated with s.c. injection of unpulsed or pulsed DCs Inhibition of tumor growth in hamsters treated with pulsed DCs [168] 2002
Human study Autologous PB monocytes mRNA encoding CEA Three patients with resected PDAC following neoadjuvant chemoradiotherapy received DCs monthly for 6 months All three alive without evidence of disease more than 2.5 yr from the original diagnosis [169] 2002
Human study Autologous PB monocytes Autologous tumor cell lysate for 10 vaccinations and lysate of the tumor cell lines AsPc-1 and BxPc-3 for a further five vaccinations. One patient with stage IV PDAC given pulsed DCs in three-week intervals injected into a growing lymph node for a total of fifteen vaccinations Stable disease for six months [170] 2003
In vivo animal model Syngenic BM RNA derived from a pancreatic cancer cell line Intratumor injections of DCs in orthotopic PDAC DCs administration induced significant antitumor immunity and significantly reduced tumor volume [171] 2003
In vivo animal model Syngenic BM Heat-treated tumor lysate (HTL-DC) and tumor lysate (TL-DC) from a pancreatic cancer cell line Immunocompetent C57BL/6 mice inoculated s.c. with PANC02 cells at −18 day. At day 0, 7, and 15, s.c. immunization The group treated with HTL-DC had significantly smaller tumors at 30 days [172] 2006
In vivo animal model Syngenic BM Alpha-galactosylceramide Immunocompetent C57BL/6 mice inoculated s.c. with PANC02 cells. At day 0, 14, and 28, s.c. immunization Pulsed DCs strongly decreased tumor growth and increased the percentage of tumor-free mice [173] 2006
In vivo animal model Syngenic BM Panc02 cells Immunocompetent C57BL/6 mice inoculated s.c. with PANC02 cells. Mice received either no treatment, Panc02-pulsed DCs, gemcitabine (Gem) or Panc02-pulsed DCs plus Gem DC-based vaccination alone was almost as equally effective as Gem treatment in preventing death. Survival could be significantly increased in the combined treatment arm [174] 2007
Human study Autologous PB mononuclear cells Unpulsed Seven patients unsuccessfully treated (Gem) for unresectable PDAC received intratumoral injection of 10 billion or more immature DCs Safety: unpulsed DCs delivered into the pancreatic cancer using endoscopic ultrasound-guided fine needle injection is safe [175] 2007
Human study Autologous PB mononuclear cells MUC1 peptide 20 pts with stage III – IV PDAC received 2 to 15 times intradermal injection of pulsed DCs One patient with multiple lung metastases had a complete response. Five patients had stable disease. The long survival group (more than 6 months) showed significantly higher expression of mature DC (CD83+) [176] 2008
Human study Autologous PB mononuclear cells OK432 (a penicillin-killed and lyophilized preparation of a low-virulence strain of Streptococcus pyogenes) 5 non metastatic inoperable PDAC treated with Gem and with endoscopic ultrasound-guided fine needle injection of OK432-pulsed DC 1 patient had partial response and 2 were long-standing survivors (more than 6 months). Induction of tumor antigen-specific CTLs [177] 2009
Human study Autologous PB mononuclear cells Autologous tumor cell lysate 12 patients with advanced disease treated with Gem and DCs injected intradermally next to an inguinal lymph node. Patients were treated in bi-weekly intervals for the first 6 weeks, then once every 4 weeks 1 patient had a partial remission, 2 had stable disease, and 5 survived 1year or more after diagnosis of advanced disease [178] 2011
Human study Autologous PB mononuclear cells MUC1 7 patients with recurrent lesions or metastasis after surgery underwent intradermal vaccinations at 2 week intervals Safety: DCs is non-toxic and capable of inducing immunological response to tumor antigen MUC1 in advanced. pancreatic cancer patients. The vaccination did not prolong patients’ survival time or stabilize their disease [179] 2012
Human study Autologous PB mononuclear cells None 9 PDAC received (DC group) while 15 PDAC did not received  (non-DC group), preoperative endoscopic ultrasound-guided tumor inoculation of  iDCs and OK432 Two DC group patients, one of whom was stage IV with distant lymph node metastasis, survived more than 5 years without requiring adjuvant therapy [180] 2012
In vivo animal model Syngenic BM None Mice received Panc02 cells s.c. and were treated with PBS, Gem alone, DCs alone, or combination therapy with DCs and Gem Gem therapy alone delayed tumor growth. Combined therapy with Gem and DC vaccination delayed tumor growth, this combination leading to significantly prolonged survival in Panc02-bearing mice [181] 2013
Human study Autologous PB mononuclear cells CA 19-9 Retrospective analysis of 134 patients subjected to long antigen exposition DCs therapy Median survival was significantly higher in group of patients who started immunotherapy within 2 months of diagnosis  or repeated immunotherapy [182] 2013
In vivo animal model Syngenic BM OVA protein Mice were implanted with orthotopic PancOVA tumors and treated with combinations of DC-OVA i.p. and/or Gem Mice treated with OVA-DC showed highly efficient tumor control, 9/13 mice having complete remission leading to long-term survival of more than 150 days [183] 2014
Human study Autologous PB mononuclear cells WT1 and/or MUC1 peptide antigens according to patient’s HLA-A type 255 patients were injected 5 or more times intradermally with DCs in close proximity to axial and/or inguinal lymph nodes, biweekly. 12 patients received DC vaccines simultaneouswith first-line chemotherapy; the other 243 patients began receiving DC vaccines after first- or second-line chemotherapy Erythema after vaccination > 3 cm was an independent and treatment-related prognostic factor for better survival [184] 2014

Table 2: Dendritic cells (DCs) vaccination strategy. Precursor DCs obtained from peripheral blood (PB) or bone marrow (BM) were pulsed with different tumor derived antigens before testing their ability to activate anti tumor T cell based cytotoxicity or their effects on tumor growth and disease prognosis. In vitro, in vivo animal models and human studies are reported.

Immune checkpoint blockade

A complex balance of multiple stimulatory and inhibitory receptors on the surface of T cells ensures proper functioning of the immune system. Receptors such as cytotoxic T lymphocyte-associate protein-4 (CTLA-4) and programmed death 1 (PD-1) expressed on the surface of activated T cells inhibit T cell activation upon binding to ligands CD80/CD86 and PD-L1/PD-L2, respectively. CTLA-4 and/or PD-1 overexpression by immune and/or tumor cells might dampen local anti-tumor immunity that, in turn, might favour tumor progression. PD-1 expression by cancer cells in PDAC is associated with reduced cytotoxic T-cell infiltration, advanced stage disease and a poor prognosis [185]; these co-inhibitory molecules might also be expressed by immature myeloid cells, probably contributing to limiting their immunosuppressive effects. Following this hypothesis, we demonstrated a reduced CTLA4 expression in immature myeloid cells in PDAC patients, and found that this reduced expression is associated with an immunosuppressive phenotype [42].

Various monoclonal antibodies targeting CTLA-4, PD-1 and their ligands, considered critical immune check-points, have been developed for cancer therapy. Monoclonal antibodies that bind and inhibit CTLA-4, ipilimumab and tremelimumab, are currently being tested in multiple clinical trials ( The clinical response to ipilimumab in patients with advanced PDAC is poor: in one phase 2 trial, only 2/15 had disease stabilization after an initial period of progression [186], and only 1/ 27 patients had a delayed response [187].

Monoclonal antibodies targeting PD-1 or its ligand (PD-L1) trigger significant antitumor responses and inhibit tumor growth in mice with PDAC by inducing CD8+ T cells tumor infiltration [188]. Antibodies against PD-1 and PD-L1 have entered clinical trials with great success in patients with advanced melanoma and advanced non-small cell lung cancer [189,190]. In their multicenter phase 1 trial, Brahmer et al. [191] administered intravenous anti-PD-L1 antibody to patients with different types of cancer. The antibody-mediated blockade of PD-L1 induced durable tumor regression and prolonged stabilization of disease in some patients with non-small-cell lung cancer, melanoma, and renal-cell cancer but not in patients with PDAC. Therefore, while immune check-point blockade evokes clinical responses in several tumor types, no well-defined benefit was observed in PDAC. This failure probably depends on the complexity of the immune alterations occurring in PDAC and on the dual face nature of CTLA-4 and PD-1, the inhibition of which might enhance anti-tumor immunity in immune effector cells, while the same inhibition might reduce anti-tumor immunity in immature myeloid cells. The findings made by Zhu et al. [192] in their study on a PDAC animal model, support this hypothesis: CTLA-4 and PD-1 blockade significantly benefitted PDAC bearing mice only when the treatment was associated with the inhibition of CSF1/CSF1R signaling, relevant for MDSCs. This suggests that combined therapeutic regimens may be necessary for the successful treatment of PDAC.

Adoptive T cell immunotherapy

Adoptive T-cell immunotherapy, which involves the transfer of tumor infiltrating lymphocytes (TILs) derived from ex vivo expanded tumor biopsies, aims to enhance the immune system response. After being removed from the tumor tissue expanded and manipulated, a massive number of TILs are returned to the patient to allow the cells to prime to tumor antigens, or transfection with recombinant DNA encoding for T cell receptors specifically directed towards tumor-antigens. The expanded TILs are then re-infused in combination with immune-adjuvant therapy, such as IL-2. Results with this approach have been very encouraging in selected melanoma patients. Since abundant patient tumor material is not always available, genetic modification of autologous isolated peripheral lymphocytes is another option. Rather than being isolated from the tumor, lymphocytes are obtained from the peripheral blood, after which they are exposed to retroviral vectors encoding for specific genetically modified TCR designed to target specific tumor antigens. In the PDAC setting, Muc1-specific autologous T cells isolated from patients’PBMCs were expanded by incubation with a Muc1-presenting cell line prior to administration to eight patients with unresectable and 20 patients with resectable PDAC postsurgically [193]. This treatment reduced post-surgical hepatic recurrence and improve survival with respect to surgery alone, although the overall benefit was minimal (median survival: 17.8 vs. 14.0 months).

Chimeric antigen receptor (CARs)

Another approach uses lymphocytes genetically engineered to carry chimeric antigen receptors (CARs) that are transmembrane proteins typically comprising the extracellular domain of CARs (an Fab fragment of an antibody specific for a tumor antigen), a spacer, a membrane spanning element and the intracellular domain of CARs (signaling portion containing intracellulardomains of the T-cell receptor–CD3); T-cells thus target specific tumor antigens and are activated upon binding. This approach was successful in the treatment of relapsed or refractory acute lymphoblastic leukemia [194]: treatment with autologous T cells transduced with a CD19-directed chimeric antigen receptor (CTL019) was followed by complete disease remission in 27/30 cases. PDAC treatment with this specific CAR is likely to be ineffective, since the CD19 antigen is not PDAC associated, but this emerging therapy was effective in a PDAC murine model when using T cells engineered to express a CAR for CEA [195]. Prostate stem cell antigen (PSCA), a small extracellular glycoprotein of unknown function that is overexpressed in PDAC cells, was recently used in adoptive immunotherapy using CAR-transduced T cells [196]; in this study, in vivo antitumor efficacy was improved, but several hurdles must be overcome before this treatment can be employed in patients.

Treg depletion

Given the importance of Treg in attenuating anti-tumor immune response, one strategy is to target Treg directly. Two different types of Treg depletion strategies have been developed and tested in clinical trials, particularly in melanoma [197]; both target the IL-2 receptor alpha chain (CD25), highly expressed by Treg, by an IL-2-diptheria toxin fusion protein (denileukin diftitox) or by a monoclonal antibody directed against CD25. Treg depletion obtained with the latter strategy reduced progression of early stage, but not late-stage, PanINs in a murine model after immunization with Listeria monocytogenes (which induces CD4+ and CD8+ T-cell immunity) [20]. This approach enhances lesion infiltration with inflammatory cells, and it may prove possible to design immunotherapies against PanIN lesions to slow or prevent progression to PDAC.


PDAC induces a profound imbalance between immune effector and immune suppressor cells. The resultant immunosuppressive microenvironment favours tumor growth and metastases not only because it underlies tumor immune tolerance, but also because it shapes a more aggressive tumor cell phenotype through soluble factors, cell to cell contact and exosomes shuttle.

Although the overall efficacy of immune based therapies evaluated in the PDAC setting appears to be limited, the altered immune response occurring in cancer growth and progression is relevant, with evolving alterations paralleling tumor plasticity from the pre-invasive to the invasive phase. For this reason it is likely that different immune therapies approaches should be applied in different clinical setting: early PDAC will probably benefit from Treg targeted therapies, while advanced PDAC will probably benefit from combined treatments aimed to induce tumor-specific DCs while dampening MDSCs.


  1. Siegel R, Ma J, Zou Z, Jemal A (2014) Cancer statistics, 2014. CA Cancer J Clin 64: 9-29.
  2. Hartwig W, Vollmer CM, Fingerhut A, Yeo CJ, Neoptolemos JP, et al. (2014) International Study Group on Pancreatic Surgery. Extended pancreatectomy in pancreatic ductal adenocarcinoma: definition and consensus of the International Study Group for Pancreatic Surgery (ISGPS). Surgery 56: 1-14.
  3. Jamieson NB, Chang DK, Grimmond SM, Biankin AV (2014) Can we move towards personalised pancreatic cancer therapy? Expert Rev Gastroenterol Hepatol 8: 335-338.
  4. Nones K, Waddell N, Song S, Patch AM, Miller D, et al. (2014) Genome-wide DNA methylation patterns in pancreatic ductal adenocarcinoma reveal epigenetic deregulation of SLIT-ROBO, ITGA2 and MET signaling. Int J Cancer 135: 1110-1118.
  5. Kerkar SP, Restifo NP (2012) Cellular constituents of immune escape within the tumor microenvironment. Cancer Res 72: 3125-3130.
  6. Hanahan D, Weinberg RA (2011) Hallmarks of cancer: the next generation. Cell 144: 646-674.
  7. Goedegebuure P, Mitchem JB, Porembka MR, Tan MC, Belt BA, et al. (2011) Myeloid-derived suppressor cells: general characteristics and relevance to clinical management of pancreatic cancer. Curr Cancer Drug Targets 11: 734-751.
  8. Bettelli E, Carrier Y, Gao W, Korn T, Strom TB, et al. (2006) Reciprocal developmental pathways for the generation of pathogenic effector TH17 and regulatory T cells. Nature 441: 235-238.
  9. Qin FX (2009) Dynamic behavior and function of Foxp3+ regulatory T cells in tumor bearing host. Cell Mol Immunol 6: 3-13.
  10. Ene-Obong A, Clear AJ, Watt J, Wang J, Fatah R, et al. (2013) Activated pancreatic stellate cells sequester CD8+ T cells to reduce their infiltration of the juxtatumoral compartment of pancreatic ductal adenocarcinoma. Gastroenterology 145: 1121-1132.
  11. Hiraoka N, Onozato K, Kosuge T, Hirohashi S (2006) Prevalence of FOXP3+ regulatory T cells increases during the progression of pancreatic ductal adenocarcinoma and its premalignant lesions. Clin Cancer Res 12: 5423-5434.
  12. Clark CE, Hingorani SR, Mick R, Combs C, Tuveson DA, et al. (2007) Dynamics of the immune reaction to pancreatic cancer from inception to invasion. Cancer Res 67: 9518-9527.
  13. Amedei A, Niccolai E, Benagiano M, Della Bella C, Cianchi F, et al. (2013) Ex vivo analysis of pancreatic cancer-infiltrating T lymphocytes reveals that ENO-specific Tregs accumulate in tumor tissue and inhibit Th1/Th17 effector cell functions. Cancer Immunol Immunother 62: 1249-1260.
  14. Ikemoto T, Yamaguchi T, Morine Y, Imura S, Soejima Y, et al. (2006) Clinical roles of increased populations of Foxp3+CD4+ T cells in peripheral blood from advanced pancreatic cancer patients. Pancreas 33: 386-390.
  15. Yamamoto T, Yanagimoto H, Satoi S, Toyokawa H, Hirooka S, et al. (2012) Circulating CD4+CD25+ regulatory T cells in patients with pancreatic cancer. Pancreas 41: 409-415.
  16. Ino Y, Yamazaki-Itoh R, Shimada K, Iwasaki M, Kosuge T, et al. (2013) Immune cell infiltration as an indicator of the immune microenvironment of pancreatic cancer. Br J Cancer 108: 914-923.
  17. Jacobs C, Duewell P, Heckelsmiller K, Wei J, Bauernfeind F, et al. (2011) An ISCOM vaccine combined with a TLR9 agonist breaks immune evasion mediated by regulatory T cells in an orthotopic model of pancreatic carcinoma. Int J Cancer 128: 897-907.
  18. Plassmeier L, Knoop R, Waldmann J, Kesselring R, Buchholz M, et al. (2013) Aspirin prolongs survival and reduces the number of Foxp3+ regulatory T cells in a genetically engineered mouse model of pancreatic cancer. Langenbecks Arch Surg 398: 989-996.
  19. Aida K, Miyakawa R, Suzuki K, Narumi K, Udagawa T, et al. (2014) Suppression of Tregs by anti-glucocorticoid induced TNF receptor antibody enhances the antitumor immunity of interferon-α gene therapy for pancreatic cancer. Cancer Sci 105: 159-167.
  20. Keenan BP, Saenger Y, Kafrouni MI, Leubner A, Lauer P, et al. (2014) A Listeria vaccine and depletion of T-regulatory cells activate immunity against early stage pancreatic intraepithelial neoplasms and prolong survival of mice. Gastroenterology 146: 1784-1794.
  21. Feig C, Jones JO, Kraman M, Wells RJ, Deonarine A, et al. (2013) Targeting CXCL12 from FAP-expressing carcinoma-associated fibroblasts synergizes with anti-PD-L1 immunotherapy in pancreatic cancer. Proc Natl Acad Sci U S A 110: 20212-20217.
  22. Witkiewicz A, Williams TK, Cozzitorto J, Durkan B, Showalter SL, et al. (2008) Expression of indoleamine 2,3-dioxygenase in metastatic pancreatic ductal adenocarcinoma recruits regulatory T cells to avoid immune detection. J Am Coll Surg 206: 849-854.
  23. Moo-Young TA, Larson JW, Belt BA, Tan MC, Hawkins WG, et al. (2009) Tumor-derived TGF-beta mediates conversion of CD4+Foxp3+ regulatory T cells in a murine model of pancreas cancer. J Immunother 32: 12-21.
  24. Kobayashi N, Kubota K, Kato S, Watanabe S, Shimamura T, et al. (2010) FOXP3+ regulatory T cells and tumoral indoleamine 2,3-dioxygenase expression predicts the carcinogenesis of intraductal papillary mucinous neoplasms of the pancreas. Pancreatology 10: 631-640.
  25. Ikemoto T, Shimada M, Komatsu M, Yamada S, Saito Y, et al. (2013) Indoleamine 2,3-dioxygenase affects the aggressiveness of intraductal papillary mucinous neoplasms through Foxp3+CD4+CD25+ T cells in peripheral blood. Pancreas 42: 130-134.
  26. Wörmann SM, Diakopoulos KN, Lesina M, Algül H (2014) The immune network in pancreatic cancer development and progression. Oncogene 33: 2956-2967.
  27. Jones S, Zhang X, Parsons DW, Lin JC, Leary RJ, et al. (2008) Core signaling pathways in human pancreatic cancers revealed by global genomic analyses. Science 321: 1801-1806.
  28. Liyanage UK, Goedegebuure PS, Moore TT, Viehl CT, Moo-Young TA, et al. (2006) Increased prevalence of regulatory T cells (Treg) is induced by pancreas adenocarcinoma. J Immunother 29: 416-424.
  29. Hinz S, Pagerols-Raluy L, Oberg HH, Ammerpohl O, Grüssel S, et al. (2007) Foxp3 expression in pancreatic carcinoma cells as a novel mechanism of immune evasion in cancer. Cancer Res 67: 8344-8350.
  30. Shevchenko I, Karakhanova S, Soltek S, Link J, Bayry J, et al. (2013) Low-dose gemcitabine depletes regulatory T cells and improves survival in the orthotopic Panc02 model of pancreatic cancer. Int J Cancer 133: 98-107.
  31. Tan MC, Goedegebuure PS, Belt BA, Flaherty B, Sankpal N, et al. (2009) Disruption of CCR5-dependent homing of regulatory T cells inhibits tumor growth in a murine model of pancreatic cancer. J Immunol 182: 1746-1755.
  32. Kudo-Saito C, Shirako H, Ohike M, Tsukamoto N, Kawakami Y (2013) CCL2 is critical for immunosuppression to promote cancer metastasis. Clin Exp Metastasis 30: 393-405.
  33. Nummer D, Suri-Payer E, Schmitz-Winnenthal H, Bonertz A, Galindo L, et al. (2007) Role of tumor endothelium in CD4+ CD25+ regulatory T cell infiltration of human pancreatic carcinoma. J Natl Cancer Inst 99: 1188-1199.
  34. Mandruzzato S, Solito S, Falisi E, Francescato S, Chiarion-Sileni V, et al. (2009) IL4Ralpha+ myeloid-derived suppressor cell expansion in cancer patients. J Immunol 182: 6562-6568.
  35. Rodriguez PC, Ernstoff MS, Hernandez C, Atkins M, Zabaleta J, et al. (2009) Arginase I-producing myeloid-derived suppressor cells in renal cell carcinoma are a subpopulation of activated granulocytes. Cancer Res 69: 1553-1560.
  36. Liu CY, Wang YM, Wang CL, Feng PH, Ko HW, et al. (2010) Population alterations of L-arginase- and inducible nitric oxide synthase-expressed CD11b+/CD14?/CD15+/CD33+ myeloid-derived suppressor cells and CD8+ T lymphocytes in patients with advanced-stage non-small cell lung cancer. J Cancer Res Clin Oncol 136: 35-45.
  37. Serafini P, Meckel K, Kelso M, Noonan K, Califano J, et al. (2006) Phosphodiesterase-5 inhibition augments endogenous antitumor immunity by reducing myeloid-derived suppressor cell function. J Exp Med 203: 2691-2702.
  38. Hoechst B, Ormandy LA, Ballmaier M, Lehner F, Krüger C, et al. (2008) A new population of myeloid-derived suppressor cells in hepatocellular carcinoma patients induces CD4(+)CD25(+)Foxp3(+) T cells. Gastroenterology 135: 234-243.
  39. Vuk-Pavlović S, Bulur PA, Lin Y, Qin R, Szumlanski CL, et al. (2010) Immunosuppressive CD14+HLA-DRlow/- monocytes in prostate cancer. Prostate 70: 443-455.
  40. Gabitass RF, Annels NE, Stocken DD, Pandha HA, Middleton GW (2011) Elevated myeloid-derived suppressor cells in pancreatic, esophageal and gastric cancer are an independent prognostic factor and are associated with significant elevation of the Th2 cytokine interleukin-13. Cancer Immunol Immunother 60: 1419-1430.
  41. Porembka MR, Mitchem JB, Belt BA, Hsieh CS, Lee HM, et al. (2012) Pancreatic adenocarcinoma induces bone marrow mobilization of myeloid-derived suppressor cells which promote primary tumor growth. Cancer Immunol Immunother 61: 1373-1385.
  42. Basso D, Fogar P, Falconi M, Fadi E, Sperti C, et al. (2013) Pancreatic tumors and immature immunosuppressive myeloid cells in blood and spleen: role of inhibitory co-stimulatory molecules PDL1 and CTLA4. An in vivo and in vitro study. PLoS One 8: e54824.
  43. Zhao F, Obermann S, von Wasielewski R, Haile L, Manns MP, et al. (2009) Increase in frequency of myeloid-derived suppressor cells in mice with spontaneous pancreatic carcinoma. Immunology 128: 141-149.
  44. Connolly MK, Mallen-St Clair J, Bedrosian AS, Malhotra A, Vera V, et al. (2010) Distinct populations of metastases-enabling myeloid cells expand in the liver of mice harboring invasive and preinvasive intra-abdominal tumor. J Leukoc Biol 87: 713-725.
  45. Marigo I, Bosio E, Solito S, Mesa C, Fernandez A, et al. (2010) Tumor-induced tolerance and immune suppression depend on the C/EBPbeta transcription factor. Immunity 32: 790-802.
  46. Nagaraj S, Youn JI, Weber H, Iclozan C, Lu L, et al. (2010) Anti-inflammatory triterpenoid blocks immune suppressive function of MDSCs and improves immune response in cancer. Clin Cancer Res 16: 1812-1823.
  47. Khaled YS, Ammori BJ, Elkord E3 (2014) Increased levels of granulocytic myeloid-derived suppressor cells in peripheral blood and tumour tissue of pancreatic cancer patients. J Immunol Res 2014: 879897.
  48. Stromnes IM, Brockenbrough JS, Izeradjene K, Carlson MA, Cuevas C, et al. (2014) Targeted depletion of an MDSC subset unmasks pancreatic ductal adenocarcinoma to adaptive immunity. Gut 63: 1769-1781.
  49. Diaz-Montero CM, Salem ML, Nishimura MI, Garrett-Mayer E, Cole DJ, et al. (2009) Increased circulating myeloid-derived suppressor cells correlate with clinicalcancer stage, metastatic tumor burden, and doxorubicin-cyclophosphamidechemotherapy. Cancer Immunol Immunother 58: 49-59.
  50. Mace TA, Ameen Z, Collins A, Wojcik S, Mair M, et al. (2013) Pancreatic cancer-associated stellate cells promote differentiation of myeloid-derived suppressor cells in a STAT3-dependent manner. Cancer Res 73: 3007-3018.
  51. Basso D, Millino C, Greco E, Romualdi C, Fogar P, et al. (2004) Altered glucose metabolism and proteolysis in pancreatic cancer cell conditioned myoblasts: searching for a gene expression pattern with a microarray analysis of 5000 skeletal muscle genes. Gut 53: 1159-1166.
  52. Husain Z, Huang Y, Seth P, Sukhatme VP (2013) Tumor-derived lactate modifies antitumor immune response: effect on myeloid-derived suppressor cells and NK cells. J Immunol 191: 1486-1495.
  53. Eruslanov E, Kaliberov S, Daurkin I, Kaliberova L, Buchsbaum D, et al. (2009) Altered expression of 15-hydroxyprostaglandin dehydrogenase in tumor-infiltrated CD11b myeloid cells: a mechanism for immune evasion in cancer. J Immunol 182: 7548-7557.
  54. Lechner MG, Liebertz DJ, Epstein AL (2010) Characterization of cytokine-induced myeloid-derived suppressor cells from normal human peripheral blood mononuclear cells. J Immunol 185: 2273-2284.
  55. Condamine T, Gabrilovich DI (2011) Molecular mechanisms regulating myeloid-derived suppressor cell differentiation and function. Trends Immunol 32: 19-25.
  56. Lechner MG, Megiel C, Russell SM, Bingham B, Arger N, et al. (2011) Functional characterization of human Cd33+ and Cd11b+ myeloid-derived suppressor cell subsets induced from peripheral blood mononuclear cells co-cultured with a diverse set of human tumor cell lines. J Transl Med 9: 90.
  57. Bayne LJ, Beatty GL, Jhala N, Clark CE, Rhim AD, et al. (2012) Tumor-derived granulocyte-macrophage colony-stimulating factor regulates myeloid inflammation and T cell immunity in pancreatic cancer. Cancer Cell 21: 822-835.
  58. Kidiyoor A, Schettini J, Besmer DM, Rego SL, Nath S, et al. (2014) Pancreatic Cancer Cells Isolated from Muc1-Null Tumors Favor the Generation of a Mature Less Suppressive MDSC Population. Front Immunol 5: 67.
  59. Trikha P, Carson WE 3rd2 (2014) Signaling pathways involved in MDSC regulation. Biochim Biophys Acta 1846: 55-65.
  60. Capietto AH, Kim S, Sanford DE, Linehan DC, Hikida M, et al. (2013) Down-regulation of PLCγ2-β-catenin pathway promotes activation and expansion of myeloid-derived suppressor cells in cancer. J Exp Med 210: 2257-2271.
  61. Panni RZ, Sanford DE, Belt BA, Mitchem JB, Worley LA, et al. (2014) Tumor-induced STAT3 activation in monocytic myeloid-derived suppressor cells enhances stemness and mesenchymal properties in human pancreatic cancer. Cancer Immunol Immunother 63: 513-528.
  62. Peng M, Huang B, Zhang Q, Fu S, Wang D, et al. (2014) Embelin inhibits pancreatic cancer progression by directly inducing cancer cell apoptosis and indirectly restricting IL-6 associated inflammatory and immune suppressive cells. Cancer Lett Aug 354: 407-416.
  63. Sinha P, Okoro C, Foell D, Freeze HH, Ostrand-Rosenberg S, et al. (2008) Proinflammatory S100 proteins regulate the accumulation of myeloid-derived suppressor cells. J Immunol 181: 4666-4675.
  64. Lu T, Ramakrishnan R, Altiok S, Youn JI, Cheng P, et al. (2011) Tumor-infiltrating myeloid cells induce tumor cell resistance to cytotoxic T cells in mice. J Clin Invest 121: 4015-4029.
  65. Kumar V, Gabrilovich DI (2014) Hypoxia-inducible factors in regulation of immune responses in tumour microenvironment. Immunology 143: 512-519.
  66. Cheng P, Corzo CA, Luetteke N, Yu B, Nagaraj S, et al. (2008) Inhibition of dendritic cell differentiation and accumulation of myeloid-derived suppressor cells in cancer is regulated by S100A9 protein. J Exp Med 205: 2235-2249.
  67. Zhao F, Hoechst B, Duffy A, Gamrekelashvili J, Fioravanti S, et al. (2012) S100A9 a new marker for monocytic human myeloid-derived suppressor cells. Immunology 136: 176-183.
  68. Basso D, Bozzato D, Padoan A, Moz S, Zambon CF, et al. (2014) Inflammation and pancreatic cancer: molecular and functional interactions between S100A8, S100A9, NT-S100A8 and TGFβ1. Cell Commun Signal 12: 20.
  69. Ibrahim ZA, Armour CL, Phipps S, Sukkar MB (2013) RAGE and TLRs: relatives, friends or neighbours? Mol Immunol 56: 739-744.
  70. Vernon PJ, Loux TJ, Schapiro NE, Kang R, Muthuswamy R, et al. (2013) The receptor for advanced glycation end products promotes pancreatic carcinogenesis and accumulation of myeloid-derived suppressor cells. J Immunol 190: 1372-1379.
  71. Hiratsuka S, Watanabe A, Sakurai Y, Akashi-Takamura S, Ishibashi S, et al. (2008) The S100A8-serum amyloid A3-TLR4 paracrine cascade establishes a pre-metastatic phase. Nat Cell Biol 10: 1349-1355.
  72. Feng PH, Lee KY, Chang YL, Chan YF, Kuo LW, et al. (2012) CD14(+)S100A9(+) monocytic myeloid-derived suppressor cells and their clinical relevance in non-small cell lung cancer. Am J Respir Crit Care Med 186: 1025-1036.
  73. Kim JH, Oh SH, Kim EJ, Park SJ, Hong SP, et al. (2012) The role of myofibroblasts in upregulation of S100A8 and S100A9 and the differentiation of myeloid cells in the colorectal cancer microenvironment. Biochem Biophys Res Commun 423: 60-66.
  74. Sharma S, Dubinett S, Salgia R (2012) CD14(+)S100A9(+) myeloid-derived suppressor cells portend decreased survival in patients with advanced lung cancer. Am J Respir Crit Care Med 186: 940-941.
  75. Liu Y, Kosaka A, Ikeura M, Kohanbash G, Fellows-Mayle W, et al. (2013) Premetastatic soil and prevention of breast cancer brain metastasis. Neuro Oncol 15: 891-903.
  76. Filipazzi P, Bürdek M, Villa A, Rivoltini L, Huber V (2012) Recent advances on the role of tumor exosomes in immunosuppression and disease progression. Semin Cancer Biol 22: 342-349.
  77. Sevko A, Umansky V (2013) Myeloid-derived suppressor cells interact with tumors in terms of myelopoiesis, tumorigenesis and immunosuppression: thick as thieves. J Cancer 4: 3-11.
  78. Burke M, Choksawangkarn W, Edwards N, Ostrand-Rosenberg S, Fenselau C (2014) Exosomes from myeloid-derived suppressor cells carry biologically active proteins. J Proteome Res 13: 836-843.
  79. Mielgo A, Schmid MC (2013) Impact of tumour associated macrophages in pancreatic cancer. BMB Rep 46: 131-138.
  80. Gironella M, Calvo C, Fernández A, Closa D, Iovanna JL, et al. (2013) Reg3β deficiency impairs pancreatic tumor growth by skewing macrophage polarization. Cancer Res 73: 5682-5694.
  81. Kurahara H, Shinchi H, Mataki Y, Maemura K, Noma H, et al. (2011) Significance of M2-polarized tumor-associated macrophage in pancreatic cancer. J Surg Res 167: e211-219.
  82. Shi C, Washington MK, Chaturvedi R, Drosos Y, Revetta FL, et al. (2014) Fibrogenesis in pancreatic cancer is a dynamic process regulated by macrophage-stellate cell interaction. Lab Invest 94: 409-421.
  83. Kurahara H, Takao S, Kuwahata T, Nagai T, Ding Q, et al. (2012) Clinical significance of folate receptor β-expressing tumor-associated macrophages in pancreatic cancer. Ann Surg Oncol 19: 2264-2271.
  84. Yoshikawa K, Mitsunaga S, Kinoshita T, Konishi M, Takahashi S, et al. (2012) Impact of tumor-associated macrophages on invasive ductal carcinoma of the pancreas head. Cancer Sci 103: 2012-2020.
  85. Hou YC, Chao YJ, Tung HL, Wang HC, Shan YS (2014) Coexpression of CD44-positive/CD133-positive cancer stem cells and CD204-positive tumor-associated macrophages is a predictor of survival in pancreatic ductal adenocarcinoma. Cancer 120: 2766-2777.
  86. Kurahara H, Takao S, Maemura K, Mataki Y, Kuwahata T, et al. (2013) M2-polarized tumor-associated macrophage infiltration of regional lymph nodes is associated with nodal lymphangiogenesis and occult nodal involvement in pN0 pancreatic cancer. Pancreas 42: 155-159.
  87. Liu CY, Xu JY, Shi XY, Huang W, Ruan TY, et al. (2013) M2-polarized tumor-associated macrophages promoted epithelial-mesenchymal transition in pancreatic cancer cells, partially through TLR4/IL-10 signaling pathway. Lab Invest 93: 844-854.
  88. Helm O, Held-Feindt J, Grage-Griebenow E, Reiling N, Ungefroren H, et al. (2014) Tumor-associated macrophages exhibit pro- and anti-inflammatory properties by which they impact on pancreatic tumorigenesis. Int J Cancer 135: 843-861.
  89. Weizman N, Krelin Y, Shabtay-Orbach A, Amit M, Binenbaum Y, et al. (2014) Macrophages mediate gemcitabine resistance of pancreatic adenocarcinoma by upregulating cytidine deaminase. Oncogene 33: 3812-3819.
  90. Pello OM, De Pizzol M, Mirolo M, Soucek L, Zammataro L, et al. (2012) Role of c-MYC in alternative activation of human macrophages and tumor-associated macrophage biology. Blood 119: 411-421.
  91. Kühnemuth B, Mühlberg L, Schipper M, Griesmann H, Neesse A, et al. (2013) CUX1 modulates polarization of tumor-associated macrophages by antagonizing NF-κB signaling. Oncogene .
  92. Karnevi E, Andersson R, Rosendahl AH2 (2014) Tumour-educated macrophages display a mixed polarisation and enhance pancreatic cancer cell invasion. Immunol Cell Biol 92: 543-552.
  93. Adams DL, Martin SS, Alpaugh RK, Charpentier M, Tsai S, et al. (2014) Circulating giant macrophages as a potential biomarker of solid tumors. Proc Natl Acad Sci U S A 111: 3514-3519.
  94. Galon J, Costes A, Sanchez-Cabo F, Kirilovsky A, Mlecnik B, et al. (2006) Type, density, and location of immune cells within human colorectal tumors predict clinical outcome. Science 313: 1960-1964.
  95. Swann JB, Smyth MJ (2007) Immune surveillance of tumors. J Clin Invest 117: 1137-1146.
  96. Laghi L, Bianchi P, Miranda E, Balladore E, Pacetti V, et al. (2009) CD3+ cells at the invasive margin of deeply invading (pT3-T4) colorectal cancer and risk of post-surgical metastasis: a longitudinal study. Lancet Oncol 10: 877-884.
  97. Shankaran V, Ikeda H, Bruce AT, White JM, Swanson PE, et al. (2001) IFNgamma and lymphocytes prevent primary tumour development and shape tumour immunogenicity. Nature 410: 1107-1111.
  98. Wong SB, Bos R, Sherman LA (2008) Tumor-specific CD4+ T cells render the tumor environment permissive for infiltration by low-avidity CD8+ T cells. J Immunol 180: 3122-3131.
  99. Zhang Y, Yan W, Mathew E, Bednar F, Wan S, et al. (2014) CD4+ T lymphocyte ablation prevents pancreatic carcinogenesis in mice. Cancer Immunol Res 2: 423-435.
  100. McAllister F, Bailey JM, Alsina J, Nirschl CJ, Sharma R, et al. (2014) Oncogenic Kras activates a hematopoietic-to-epithelial IL-17 signaling axis in preinvasive pancreatic neoplasia. Cancer Cell 25: 621-637.
  101. Helm O, Mennrich R, Petrick D, Goebel L, Freitag-Wolf S, et al. (2014) Comparative characterization of stroma cells and ductal epithelium in chronic pancreatitis and pancreatic ductal adenocarcinoma. PLoS One 9: e94357.
  102. Provenzano PP, Cuevas C, Chang AE, Goel VK, Von Hoff DD, et al. (2012) Enzymatic targeting of the stroma ablates physical barriers to treatment of pancreatic ductal adenocarcinoma. Cancer Cell 21: 418-429.
  103. Fogar P, Sperti C, Basso D, Sanzari MC, Greco E, et al. (2006) Decreased total lymphocyte counts in pancreatic cancer: an index of adverse outcome. Pancreas 32: 22-28.
  104. Poch B, Lotspeich E, Ramadani M, Gansauge S, Beger HG, et al. (2007) Systemic immune dysfunction in pancreatic cancer patients. Langenbecks Arch Surg 392: 353-358.
  105. Grage-Griebenow E, Jerg E, Gorys A, Wicklein D, Wesch D, et al. (2014) L1CAM promotes enrichment of immunosuppressive T cells in human pancreatic cancer correlating with malignant progression. Mol Oncol 8: 982-997.
  106. Sancho D, Gómez M, Sánchez-Madrid F (2005) CD69 is an immunoregulatory molecule induced following activation. Trends Immunol 26: 136-140.
  107. Han Y, Guo Q, Zhang M, Chen Z, Cao X (2009) CD69+ CD4+ CD25- T cells, a new subset of regulatory T cells, suppress T cell proliferation through membrane-bound TGF-beta 1. J Immunol 182: 111-120.
  108. Knutson KL, Disis ML (2005) Tumor antigen-specific T helper cells in cancer immunity and immunotherapy. Cancer Immunol Immunother 54: 721-728.
  109. De Monte L, Reni M, Tassi E, Clavenna D, Papa I, et al. (2011) Intratumor T helper type 2 cell infiltrate correlates with cancer-associated fibroblast thymic stromal lymphopoietin production and reduced survival in pancreatic cancer. J Exp Med 208: 469-478.
  110. Fogar P, Basso D, Fadi E, Greco E, Pantano G, et al. (2011) Pancreatic cancer alters human CD4+ T lymphocyte function: a piece in the immune evasion puzzle. Pancreas 40: 1131-1137.
  111. Ben QW, Wang JC, Liu J, Zhu Y, Yuan F, et al. (2010) Positive expression of L1-CAM is associated with perineural invasion and poor outcome in pancreatic ductal adenocarcinoma. Ann Surg Oncol 17: 2213-2221.
  112. Takeichi T, Mocevicius P, Deduchovas O, Salnikova O, Castro-Santa E, et al. (2012) αL β2 integrin is indispensable for CD8+ T-cell recruitment in experimental pancreatic and hepatocellular cancer. Int J Cancer 130: 2067-2076.
  113. Tang D, Yuan Z, Xue X, Lu Z, Zhang Y, et al. (2012) High expression of Galectin-1 in pancreatic stellate cells plays a role in the development and maintenance of an immunosuppressive microenvironment in pancreatic cancer. Int J Cancer 130: 2337-2348.
  114. Qi W, Huang X, Wang J (2013) Correlation between Th17 cells and tumor microenvironment. Cell Immunol 285: 18-22.
  115. Bailey SR, Nelson MH, Himes RA, Li Z, Mehrotra S, et al. (2014) Th17 cells in cancer: the ultimate identity crisis. Front Immunol 5: 276.
  116. Vizio B, Novarino A, Giacobino A, Cristiano C, Prati A, et al. (2012) Potential plasticity of T regulatory cells in pancreatic carcinoma in relation to disease progression and outcome. Exp Ther Med 4: 70-78.
  117. Marsh JL, Jackman CP, Tang SN, Shankar S, Srivastava RK2 (2014) Embelin suppresses pancreatic cancer growth by modulating tumor immune microenvironment. Front Biosci (Landmark Ed) 19: 113-125.
  118. Peng YP, Zhu Y, Zhang JJ, Xu ZK, Qian ZY, et al. (2013) Comprehensive analysis of the percentage of surface receptors and cytotoxic granules positive natural killer cells in patients with pancreatic cancer, gastric cancer, and colorectal cancer. J Transl Med 11: 262.
  119. Frankel TL, Burns W, Riley J, Morgan RA, Davis JL, et al. (2010) Identification and characterization of a tumor infiltrating CD56(+)/CD16 (-) NK cell subset with specificity for pancreatic and prostate cancer cell lines. Cancer Immunol Immunother 59: 1757-1769.
  120. Duan X, Deng L, Chen X, Lu Y, Zhang Q, et al. (2011) Clinical significance of the immunostimulatory MHC class I chain-related molecule A and NKG2D receptor on NK cells in pancreatic cancer. Med Oncol 28: 466-474.
  121. Bruno A, Ferlazzo G, Albini A, Noonan DM (2014) A think tank of TINK/TANKs: tumor-infiltrating/tumor-associated natural killer cells in tumor progression and angiogenesis. J Natl Cancer Inst 106: dju200.
  122. Tseng HC, Bui V, Man YG, Cacalano N, Jewett A4 (2014) Induction of Split Anergy Conditions Natural Killer Cells to Promote Differentiation of Stem Cells through Cell-Cell Contact and Secreted Factors. Front Immunol 5: 269.
  123. Jing W, Chen Y, Lu L, Hu X, Shao C, et al. (2014) Human umbilical cord blood-derived mesenchymal stem cells producing IL15 eradicate established pancreatic tumor in syngeneic mice. Mol Cancer Ther 13: 2127-2137.
  124. Yanagimoto H, Takai S, Satoi S, Toyokawa H, Takahashi K, et al. (2005) Impaired function of circulating dendritic cells in patients with pancreatic cancer. Clin Immunol 114: 52-60.
  125. Bang S, Kim HS, Choo YS, Park SW, Chung JB, et al. (2006) Differences in immune cells engaged in cell-mediated immunity after chemotherapy for far advanced pancreatic cancer. Pancreas 32: 29-36.
  126. Bellone G, Novarino A, Vizio B, Brondino G, Addeo A, et al. (2009) Impact of surgery and chemotherapy on cellular immunity in pancreatic carcinoma patients in view of an integration of standard cancer treatment with immunotherapy. Int J Oncol 34: 1701-1715.
  127. Soeda A, Morita-Hoshi Y, Makiyama H, Morizane C, Ueno H, et al. (2009) Regular dose of gemcitabine induces an increase in CD14+ monocytes and CD11c+ dendritic cells in patients with advanced pancreatic cancer. Jpn J Clin Oncol 39: 797-806.
  128. Tjomsland V, Spångeus A, Sandström P, Borch K, Messmer D, et al. (2010) Semi mature blood dendritic cells exist in patients with ductal pancreatic adenocarcinoma owing to inflammatory factors released from the tumor. PLoS One 5: e13441.
  129. Yamamoto T, Yanagimoto H, Satoi S, Toyokawa H, Yamao J, et al. (2012) Circulating myeloid dendritic cells as prognostic factors in patients with pancreatic cancer who have undergone surgical resection. J Surg Res 173: 299-308.
  130. Hirooka S, Yanagimoto H, Satoi S, Yamamoto T, Toyokawa H, et al. (2011) The role of circulating dendritic cells in patients with unresectable pancreatic cancer. Anticancer Res 31: 3827-3834.
  131. Tjomsland V, Niklasson L, Sandström P, Borch K, Druid H, et al. (2011) The desmoplastic stroma plays an essential role in the accumulation and modulation of infiltrated immune cells in pancreatic adenocarcinoma. Clin Dev Immunol 2011: 212810.
  132. Bharadwaj U, Li M, Zhang R, Chen C, Yao Q (2007) Elevated interleukin-6 and G-CSF in human pancreatic cancer cell conditioned medium suppress dendritic cell differentiation and activation. Cancer Res 67: 5479-5488.
  133. Kleeff J, Beckhove P, Esposito I, Herzig S, Huber PE, et al. (2007) Pancreatic cancer microenvironment. Int J Cancer 121: 699-705.
  134. Erez N, Truitt M, Olson P, Arron ST, Hanahan D (2010) Cancer-Associated Fibroblasts Are Activated in Incipient Neoplasia to Orchestrate Tumor-Promoting Inflammation in an NF-kappaB-Dependent Manner. Cancer Cell 17: 135-147.
  135. Kraman M, Bambrough PJ, Arnold JN, Roberts EW, Magiera L, et al. (2010) Suppression of antitumor immunity by stromal cells expressing fibroblast activation protein-alpha. Science 330: 827-830.
  136. Pylayeva-Gupta Y, Lee KE, Hajdu CH, Miller G, Bar-Sagi D (2012) Oncogenic Kras-induced GM-CSF production promotes the development of pancreatic neoplasia. Cancer Cell 21: 836-847.
  137. Dunér S, Lopatko Lindman J, Ansari D, Gundewar C, Andersson R (2010) Pancreatic cancer: the role of pancreatic stellate cells in tumor progression. Pancreatology 10: 673-681.
  138. Yonezawa S, Higashi M, Yamada N, Yokoyama S, Goto M (2010) Significance of mucin expression in pancreatobiliary neoplasms. J Hepatobiliary Pancreat Sci 17: 108-124.
  139. Rachagani S, Torres MP, Kumar S, Haridas D, Baine M, et al. (2012) Mucin (Muc) expression during pancreatic cancer progression in spontaneous mouse model: potential implications for diagnosis and therapy. J Hematol Oncol 5: 68.
  140. Tsutsumida H, Swanson BJ, Singh PK, Caffrey TC, Kitajima S, et al. (2006) RNA interference suppression of MUC1 reduces the growth rate and metastatic phenotype of human pancreatic cancer cells. Clin Cancer Res 12: 2976-2987.
  141. Chaturvedi P, Singh AP, Moniaux N, Senapati S, Chakraborty S, et al. (2007) MUC4 mucin potentiates pancreatic tumor cell proliferation, survival, and invasive properties and interferes with its interaction to extracellular matrix proteins. Mol Cancer Res 5: 309-320.
  142. Hoshi H, Sawada T, Uchida M, Saito H, Iijima H, et al. (2011) Tumor-associated MUC5AC stimulates in vivo tumorigenicity of human pancreatic cancer. Int J Oncol 38: 619-627.
  143. Xue X, Lu Z, Tang D, Yao J, An Y, et al. (2011) Galectin-1 secreted by activated stellate cells in pancreatic ductal adenocarcinoma stroma promotes proliferation and invasion of pancreatic cancer cells: an in vitro study on the microenvironment of pancreatic ductal adenocarcinoma. Pancreas 40: 832-839.
  144. Chung JC, Oh MJ, Choi SH, Bae CD (2008) Proteomic analysis to identify biomarker proteins in pancreatic ductal adenocarcinoma. ANZ J Surg 78: 245-251.
  145. Martínez-Bosch N, Fernández-Barrena MG, Moreno M, Ortiz-Zapater E, Munné-Collado J, et al. (2014) Galectin-1 drives pancreatic carcinogenesis through stroma remodeling and Hedgehog signaling activation. Cancer Res 74: 3512-3524.
  146. Li J, Wang LJ, Ying X, Han SX, Bai E, et al. (2012) Immunodiagnostic value of combined detection of autoantibodies to tumor-associated antigens as biomarkers in pancreatic cancer. Scand J Immunol 75: 342-349.
  147. Li L, Hao X, Qin J, Tang W, He F, et al. (2014) Antibody against CD44s inhibits pancreatic tumor initiation and postradiation recurrence in mice. Gastroenterology 146: 1108-1118.
  148. Imanishi T, Kamigaki T, Nakamura T, Hayashi S, Yasuda T, et al. (2006) Correlation betweenexpressionof major histocompatibility complex class I and that of antigen presenting machineries in carcinoma cell lines of the pancreas, biliary tract and colon. Kobe J Med Sci 52: 85-95.
  149. Pandha H, Rigg A, John J, Lemoine N (2007) Loss of expression of antigen-presenting molecules in human pancreatic cancer and pancreatic cancer cell lines. Clin Exp Immunol 148: 127-135.
  150. Kirkwood JM, Butterfield LH, Tarhini AA, Zarour H, Kalinski P, et al. (2012) Immunotherapy of cancer in 2012. CA Cancer J Clin 62: 309-335.
  151. Lutz E, Yeo CJ, Lillemoe KD, Biedrzycki B, Kobrin B, et al. (2011) A lethally irradiated allogeneic granulocyte-macrophage colony stimulating factor-secreting tumor vaccine for pancreatic adenocarcinoma. A Phase II trial of safety, efficacy, and immune activation. Ann Surg 253: 328-335.
  152. Laheru D, Lutz E, Burke J, Biedrzycki B, Solt S, et al. (2008) Allogeneic granulocyte macrophage colony-stimulating factor-secreting tumor immunotherapy alone or in sequence with cyclophosphamide for metastatic pancreatic cancer: a pilot study of safety, feasibility, and immune activation. Clin Cancer Res 14: 1455-1463.
  153. Gjertsen MK, Buanes T, Rosseland AR, Bakka A, Gladhaug I, et al. (2001) Intradermal ras peptide vaccination with granulocyte-macrophage colony-stimulating factor as adjuvant: Clinical and immunological responses in patients with pancreatic adenocarcinoma. Int J Cancer 92: 441-450.
  154. Abou-Alfa GK, Chapman PB, Feilchenfeldt J, Brennan MF, Capanu M, et al. (2011) Targeting mutated K-ras in pancreatic adenocarcinoma using an adjuvant vaccine. Am J Clin Oncol 34: 321-325.
  155. Wedén S, Klemp M, Gladhaug IP, Møller M, Eriksen JA, et al. (2011) Long-term follow-up of patients with resected pancreatic cancer following vaccination against mutant K-ras. Int J Cancer 128: 1120-1128.
  156. Middleton G, Silcocks P, Cox T, Valle J, Wadsley J, et al. (2014) Gemcitabine and capecitabine with or without telomerase peptide vaccine GV1001 in patients with locally advanced or metastatic pancreatic cancer (TeloVac): an open-label, randomised, phase 3 trial. Lancet Oncol 15: 829-840.
  157. Suso EM, Dueland S, Rasmussen AM, Vetrhus T, Aamdal S, et al. (2011) hTERT mRNA dendritic cell vaccination: complete response in a pancreatic cancer patient associated with response against several hTERT epitopes. Cancer Immunol Immunother 60: 809-818.
  158. Bernhardt SL, Gjertsen MK, Trachsel S, Møller M, Eriksen JA, et al. (2006) Telomerase peptide vaccination of patients with non-resectable pancreatic cancer: A dose escalating phase I/II study. Br J Cancer 95: 1474-1482.
  159. Staff C, Mozaffari F, Frödin JE, Mellstedt H, Liljefors M1 (2014) Telomerase (GV1001) vaccination together with gemcitabine in advanced pancreatic cancer patients. Int J Oncol 45: 1293-1303.
  160. Ramanathan RK, Lee KM, McKolanis J, Hitbold E, Schraut W, et al. (2005) Phase I study of a MUC1 vaccine composed of different doses of MUC1 peptide with SB-AS2 adjuvant in resected and locally advanced pancreatic cancer. Cancer Immunol Immunother 54: 254-264.
  161. Okuyama R, Aruga A, Hatori T, Takeda K, Yamamoto M1 (2013) Immunological responses to a multi-peptide vaccine targeting cancer-testis antigens and VEGFRs in advanced pancreatic cancer patients. Oncoimmunology 2: e27010.
  162. Suzuki N, Hazama S, Ueno T, Matsui H, Shindo Y, et al. (2014) A phase I clinical trial of vaccination with KIF20A-derived peptide in combination with gemcitabine for patients with advanced pancreatic cancer. J Immunother 37: 36-42.
  163. Asahara S, Takeda K, Yamao K, Maguchi H, Yamaue H (2013) Phase I/II clinical trial using HLA-A24-restricted peptide vaccine derived from KIF20A for patients with advanced pancreatic cancer. J Transl Med 11: 291.
  164. Yutani S, Komatsu N, Yoshitomi M, Matsueda S, Yonemoto K, et al. (2013) A phase II study of a personalized peptide vaccination for chemotherapy-resistant advanced pancreatic cancer patients. Oncol Rep 30: 1094-1100.
  165. Marten A, Schöttker B, Ziske C, Weineck S, Buttgereit P, et al. (2000) Increase of the immunostimulatory effect of dendritic cells by pulsing with CA 19-9 protein. J Immunother 23: 464-472.
  166. Schnurr M, Galambos P, Scholz C, Then F, Dauer M, et al. (2001) Tumor cell lysate-pulsed human dendritic cells induce a T-cell response against pancreatic carcinoma cells: an in vitro model for the assessment of tumor vaccines. Cancer Res 61: 6445-6450.
  167. Schnurr M, Scholz C, Rothenfusser S, Galambos P, Dauer M, et al. (2002) Apoptotic pancreatic tumor cells are superior to cell lysates in promoting cross-priming of cytotoxic T cells and activate NK and gammadelta T cells. Cancer Res 62: 2347-2352.
  168. Akiyama Y, Maruyama K, Nara N, Hojo T, Cheng JY, et al. (2002) Antitumor effects induced by dendritic cell-based immunotherapy against established pancreatic cancer in hamsters. Cancer Lett 184: 37-47.
  169. Morse MA, Nair SK, Boczkowski D, Tyler D, Hurwitz HI, et al. (2002) The feasibility and safety of immunotherapy with dendritic cells loaded with CEA mRNA following neoadjuvant chemoradiotherapy and resection of pancreatic cancer. Int J Gastrointest Cancer 32: 1-6.
  170. Stift A, Friedl J, Dubsky P, Bachleitner-Hofmann T, Benkoe T, et al. (2003) In vivo induction of dendritic cell-mediated cytotoxicity against allogeneic pancreatic carcinoma cells. Int J Oncol 22: 651-656.
  171. Schmidt T, Ziske C, Märten A, Endres S, Tiemann K, et al. (2003) Intratumoral immunization with tumor RNA-pulsed dendritic cells confers antitumor immunity in a C57BL/6 pancreatic murine tumor model. Cancer Res 63: 8962-8967.
  172. Kim HS, Choo YS, Koo T, Bang S, Oh TY, et al. (2006) Enhancement of antitumor immunity of dendritic cells pulsed with heat-treated tumor lysate in murine pancreatic cancer. Immunol Lett 103: 142-148.
  173. Nagaraj S, Ziske C, Strehl J, Messmer D, Sauerbruch T, et al. (2006) Dendritic cells pulsed with alpha-galactosylceramide induce anti-tumor immunity against pancreatic cancer in vivo. Int Immunol 18: 1279-1283.
  174. Bauer C, Bauernfeind F, Sterzik A, Orban M, Schnurr M, et al. (2007) Dendritic cell-based vaccination combined with gemcitabine increases survival in a murine pancreatic carcinoma model. Gut 56: 1275-1282.
  175. Irisawa A, Takagi T, Kanazawa M, Ogata T, Sato Y, et al. (2007) Endoscopic ultrasound-guided fine-needle injection of immature dendritic cells into advanced pancreatic cancer refractory to gemcitabine: a pilot study. Pancreas 35: 189-190.
  176. Kondo H, Hazama S, Kawaoka T, Yoshino S, Yoshida S, et al. (2008) Adoptive immunotherapy for pancreatic cancer using MUC1 peptide-pulsed dendritic cells and activated T lymphocytes. Anticancer Res 28: 379-387.
  177. Hirooka Y, Itoh A, Kawashima H, Hara K, Nonogaki K, et al. (2009) A combination therapy of gemcitabine with immunotherapy for patients with inoperable locally advanced pancreatic cancer. Pancreas 38: e69-74.
  178. Bauer C, Dauer M, Saraj S, Schnurr M, Bauernfeind F, et al. (2011) Dendritic cell-based vaccination of patients with advanced pancreatic carcinoma: results of a pilot study. Cancer Immunol Immunother 60: 1097-1107.
  179. Rong Y, Qin X, Jin D, Lou W, Wu L, et al. (2012) A phase I pilot trial of MUC1-peptide-pulsed dendritic cells in the treatment of advanced pancreatic cancer. Clin Exp Med 12: 173-180.
  180. Endo H, Saito T, Kenjo A, Hoshino M, Terashima M, et al. (2012) Phase I trial of preoperative intratumoral injection of immature dendritic cells and OK-432 for resectable pancreatic cancer patients. J Hepatobiliary Pancreat Sci 19: 465-475.
  181. Ghansah T, Vohra N, Kinney K, Weber A, Kodumudi K, et al. (2013) Dendritic cell immunotherapy combined with gemcitabine chemotherapy enhances survival in a murine model of pancreatic carcinoma. Cancer Immunol Immunother 62: 1083-1091.
  182. Gansauge F, Poch B, Kleef R, Schwarz M (2013) Effectivity of long antigen exposition dendritic cell therapy (LANEXDC®) in the palliative treatment of pancreatic cancer. Curr Med Chem 20: 4827-4835.
  183. Bauer C, Sterzik A, Bauernfeind F, Duewell P, Conrad C, et al. (2014) Concomitant gemcitabine therapy negatively affects DC vaccine-induced CD8(+) T-cell and B-cell responses but improves clinical efficacy in a murine pancreatic carcinoma model. Cancer Immunol Immunother 63: 321-333.
  184. Kobayashi M, Shimodaira S, Nagai K, Ogasawara M, Takahashi H, et al. (2014) Prognostic factors related to add-on dendritic cell vaccines on patients with inoperable pancreatic cancer receiving chemotherapy: a multicenter analysis. Cancer Immunol Immunother 63: 797-806.
  185. Nomi T, Sho M, Akahori T, Hamada K, Kubo A, et al. (2007) Clinical significance and therapeutic potential of the programmed death-1 ligand/programmed death-1 pathway in human pancreatic cancer. Clin Cancer Res 13: 2151-2157.
  186. Le DT, Lutz E, Uram JN, Sugar EA, Onners B, et al. (2013) Evaluation of ipilimumab in combination with allogeneic pancreatic tumor cells transfected with a GM-CSF gene in previously treated pancreatic cancer. J Immunother 36: 382-389.
  187. Royal RE, Levy C, Turner K, Mathur A, Hughes M, et al. (2010) Phase 2 trial of single agent Ipilimumab (anti-CTLA-4) for locally advanced or metastatic pancreatic adenocarcinoma. J Immunother 33: 828-833.
  188. Okudaira K, Hokari R, Tsuzuki Y, Okada Y, Komoto S, et al. (2009) Blockade of B7-H1 or B7-DC induces an anti-tumor effect in a mouse pancreatic cancer model. Int J Oncol 35: 741-749.
  189. Topalian SL, Hodi FS, Brahmer JR, Gettinger SN, Smith DC, et al. (2012) Safety, activity, and immune correlates of anti-PD-1 antibody in cancer. N Engl J Med 366: 2443-2454.
  190. Hamid O, Robert C, Daud A, Hodi FS, Hwu WJ, et al. (2013) Safety and tumor responses with lambrolizumab (anti-PD-1) in melanoma. N Engl J Med 369: 134-144.
  191. Brahmer JR, Tykodi SS, Chow LQ, Hwu WJ, Topalian SL, et al. (2012) Safety and activity of anti-PD-L1 antibody in patients with advanced cancer. N Engl J Med 366: 2455-2465.
  192. Zhu Y, Knolhoff BL, Meyer MA, Nywening TM, West BL, et al. (2014) CSF1/CSF1R blockade reprograms tumor-infiltrating macrophages and improves response to T-cell checkpoint immunotherapy in pancreatic cancer models. Cancer Res 74: 5057-5069.
  193. Kawaoka T, Oka M, Takashima M, Ueno T, Yamamoto K, et al. (2008) Adoptive immunotherapy for pancreatic cancer: cytotoxic T lymphocytes stimulated by the MUC1-expressing human pancreatic cancer cell line YPK-1. Oncol Rep 20: 155-163.
  194. Maude SL, Frey N, Shaw PA, Aplenc R, Barrett DM, et al. (2014) Chimeric antigen receptor T cells for sustained remissions in leukemia. N Engl J Med 371: 1507-1517.
  195. Chmielewski M, Hahn O, Rappl G, Nowak M, Schmidt-Wolf IH, et al. (2012) T cells that target carcinoembryonic antigen eradicate orthotopic pancreatic carcinomas without inducing autoimmune colitis in mice. Gastroenterology 143: 1095-1107.
  196. Abate-Daga D, Rosenberg SA, Morgan RA (2014) Pancreatic cancer: Hurdles in the engineering of CAR-based immunotherapies. Oncoimmunology 3: e29194.
  197. Rech AJ, Vonderheide RH (2009) Clinical use of anti-CD25 antibody daclizumab to enhance immune responses to tumor antigen vaccination by targeting regulatory T cells. Ann N Y Acad Sci 1174: 99-106.
Citation: Basso D, Gnatta E, Plebani M (2014) Pancreatic Cancer Fostered Immunosuppression Privileges Tumor Growth and Progression. J Clin Cell Immunol 5:278.

Copyright: © 2014 Basso D, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.