Bidirectional activation of stem-like programs between metastatic cancer and alveolar type 2 cells within the niche.

A key step for metastatic outgrowth involves the generation of a deeply altered microenvironment (niche) that supports the malignant behavior of cancer cells. The complexity of the metastatic niche has posed a significant challenge in elucidating the underlying programs driving its origin. Here, by focusing on early stages of breast cancer metastasis to the lung in mice, we describe a cancer-dependent chromatin remodeling and activation of developmental programs in alveolar type 2 (AT2) cells within the niche. We show that metastatic cells can prime AT2 cells into a reprogrammed multilineage state. In turn, this cancer-induced reprogramming of AT2 cells promoted stem-like features in cancer cells and enhanced their initiation capacity. In conclusion, we propose the concept of "reflected stemness" as an early phenomenon during metastatic niche initiation, wherein metastatic cells reprogram the local tissue into a stem-like state that enhances intrinsic cancer-initiating potential, creating a positive feedback loop where tumorigenic programs are amplified.

STAT Family Protein Expression and Phosphorylation State during moDC Development Is Altered by Platinum-Based Chemotherapeutics.

The STAT signaling pathway is important in dendritic cell (DC) development and function. Tumor cells can induce STAT signaling, thereby inhibiting DC maturation and immunostimulatory functions, leading to hampered efficacy of DC-based immunotherapies. Platinum-based chemotherapeutics can inhibit STAT signaling, thereby making them an interesting tool to improve DC development and function. In this study, we provide a comprehensive overview of STAT expression and phosphorylation during DC differentiation and maturation and investigate the effects of platinum drugs on STAT signaling during these processes. Monocytes were differentiated into monocyte-derived DCs (moDCs) with IL-4 and GM-CSF and matured with cytokines or TLR ligands. STAT expression and phosphorylation were analyzed by western blotting, and moDC viability and phenotype were analyzed by flow cytometry. Platinum drugs were added at day 3 of differentiation or at the start of maturation to investigate regulation of the STAT signaling pathway. All STAT proteins were expressed during moDC differentiation and STAT1, STAT5, and STAT6 were phosphorylated. No significant changes occurred in the expression and phosphorylation state of the STAT proteins during differentiation. After maturation with TLR ligands, the expression of STAT1 increased, but other STAT proteins were not affected. Phosphorylation of STAT1 and STAT3 increased during maturation, where TLR ligands induced significantly higher levels of phosphorylation than cytokines. Platinum drugs cisplatin and oxaliplatin significantly inhibited phosphorylation of STAT6 during differentiation and maturation. Treatment did not affect the phenotype or viability of the cells. As STAT6 is an important regulator of DC function, these findings suggest a role for platinum-based chemotherapeutics to enhance DC function via inhibition of STAT signaling, thereby potentially enhancing efficacy of DC-based immunotherapies.

Multispectral imaging for highly accurate analysis of tumour-infiltrating lymphocytes in primary melanoma.

AIMS: The quality and quantity of the infiltration of immune cells into tumour tissues have substantial impacts on patients' clinical outcomes, and are associated with response to immunotherapy. Therefore, the precise analysis of tumour-infiltrating lymphocytes (TILs) is becoming an important additional pathological biomarker. Analysis of TILs is usually performed semiquantitatively by pathologists on haematoxylin and eosin-stained or immunostained tissue sections. However, automated quantification outperforms semiquantitative approaches, and is becoming the standard. Owing to the presence of melanin pigment, this approach is seriously hampered in melanoma, because the spectrum of melanin lies close to that of commonly used immunohistochemical stains. Aim of this study is to overcome the technical issues due to the presence of melanin for an automated and accurate quantification of TILs in melanoma. METHODS AND RESULTS: Here, we successfully applied a novel multispectral imaging (MSI) technique to enumerate T cells in human primary melanomas. This microscopy technique combines imaging with spectroscopy to obtain both quantitative expression data and the tissue distributions of different cellular markers. We demonstrate that MSI allows complete and accurate analysis of TILs, successfully avoiding the blurring of images by melanin pigments, in whole tissue slide primary melanoma lesions, which could otherwise not be accurately detected by conventional digital image methodologies. CONCLUSIONS: Our study highlights the potential of MSI for accurate assessment of immune cell infiltrates, including those in notoriously difficult tissues, such as pigmented melanomas. Quantification of tumour infiltration by different immune cell types is crucial in the search for new biomarkers to predict patient responses to immunotherapies. Our findings show that this innovative microscopy technique is an important extension of the armamentarium of pathologists.

Human CD1c(+) DCs are critical cellular mediators of immune responses induced by immunogenic cell death.

Chemotherapeutics, including the platinum compounds oxaliplatin (OXP) and cisplatin (CDDP), are standard care of treatment for cancer. Although chemotherapy has long been considered immunosuppressive, evidence now suggests that certain cytotoxic agents can efficiently stimulate antitumor responses, through the induction of a form of apoptosis, called immunogenic cell death (ICD). ICD is characterized by exposure of calreticulin and heat shock proteins (HSPs), secretion of ATP and release of high-mobility group box 1 (HMGB1). Proper activation of the immune system relies on the integration of these signals by dendritic cells (DCs). Studies on the crucial role of DCs, in the context of ICD, have been performed using mouse models or human in vitro-generated monocyte-derived DCs (moDCs), which do not fully recapitulate the in vivo situation. Here, we explore the effect of platinum-induced ICD on phenotype and function of human blood circulating DCs. Tumor cells were treated with OXP or CDDP and induction of ICD was investigated. We show that both platinum drugs triggered translocation of calreticulin and HSP70, as well as the release of ATP and HMGB1. Platinum treatment increased phagocytosis of tumor fragments by human blood DCs and enhanced phenotypic maturation of blood myeloid and plasmacytoid DCs. Moreover, upon interaction with platinum-treated tumor cells, CD1c(+) DCs efficiently stimulated allogeneic proliferation of T lymphocytes. Together, our observations indicate that platinum-treated tumor cells may exert an active stimulatory effect on human blood DCs. In particular, these data suggest that CD1c(+) DCs are critical mediators of immune responses induced by ICD.

Preclinical exploration of combining plasmacytoid and myeloid dendritic cell vaccination with BRAF inhibition.

BACKGROUND: Melanoma is the most lethal type of skin cancer and its incidence is progressively increasing. The introductions of immunotherapy and targeted therapies have tremendously improved the treatment of melanoma. Selective inhibition of BRAF by vemurafenib results in objective clinical responses in around 50 % of patients suffering from BRAFV600 mutated melanoma. However, drug resistance often results in hampering long-term tumor control. Alternatively, immunotherapy by vaccination with natural dendritic cells (nDCs) demonstrated long-term tumor control in a proportion of patients. We postulate that the rapid tumor debulking by vemurafenib can synergize the long-term tumor control of nDC vaccination to result in an effective treatment modality in a large proportion of patients. Here, we investigated the feasibility of this combination by analyzing the effect of vemurafenib on the functionality of nDCs. METHODS: Plasmacytoid DCs (pDCs) and myeloid DCs (mDCs) were isolated from PBMCs obtained from buffy coats from healthy volunteers or vemurafenib-treated melanoma patients. Maturation of pDCs, mDCs and immature monocyte-derived DCs was induced by R848 in the presence or absence of vemurafenib and analyzed by FACS. Cytokine production and T cell proliferation induced by mature DCs were analyzed. RESULTS: Vemurafenib inhibited maturation and cytokine production of highly purified nDCs of healthy volunteers resulting in diminished allogeneic T cell proliferation. This deleterious effect of vemurafenib on nDC functionality was absent when total PBMCs were exposed to vemurafenib. In patients receiving vemurafenib, nDC functionality and T cell allostimulatory capacity were unaffected. CONCLUSION: Although vemurafenib inhibited the functionality of purified nDC of healthy volunteers, this effect was not observed when nDCs were matured in the complete PBMC fraction. This might have been caused by increased vemurafenib uptake in absence of other cell types. In accordance, nDCs isolated from patients on active vemurafenib treatment showed no negative effects. In conclusion, our results pave the way for a combinatorial treatment strategy and, we propose that combining vemurafenib with nDC vaccination represent a powerful opportunity that deserves more investigation in the clinic.

Clinical Implications of Co-Inhibitory Molecule Expression in the Tumor Microenvironment for DC Vaccination: A Game of Stop and Go.

The aim of therapeutic dendritic cell (DC) vaccines in cancer immunotherapy is to activate cytotoxic T cells to recognize and attack the tumor. T cell activation requires the interaction of the T cell receptor with a cognate major-histocompatibility complex-peptide complex. Although initiated by antigen engagement, it is the complex balance between co-stimulatory and co-inhibitory signals on DCs that results in T cell activation or tolerance. Even when already activated, tumor-specific T cells can be neutralized by the expression of co-inhibitory molecules on tumor cells. These and other immunosuppressive cues in the tumor microenvironment are major factors currently hampering the application of DC vaccination. In this review, we discuss recent data regarding the essential and complex role of co-inhibitory molecules in regulating the immune response within the tumor microenvironment. In particular, possible therapeutic intervention strategies aimed at reversing or neutralizing suppressive networks within the tumor microenvironment will be emphasized. Importantly, blocking co-inhibitory molecule signaling, often referred to as immune checkpoint blockade, does not necessarily lead to an effective activation of tumor-specific T cells. Therefore, combination of checkpoint blockade with other immune potentiating therapeutic strategies, such as DC vaccination, might serve as a synergistic combination, capable of reversing effector T cells immunosuppression while at the same time increasing the efficacy of T cell-mediated immunotherapies. This will ultimately result in long-term anti-tumor immunity.