Uptake of Apoptotic K562 Leukaemia Cells by Immature Dendritic Cells is Greatly Facilitated by Serum

Extracellular matrix educates an immunoregulatory tumor macrophage phenotype found in ovarian cancer metastasis

Recent studies have shown that the tumor extracellular matrix (ECM) associates with immunosuppression, and that targeting the ECM can improve immune infiltration and responsiveness to immunotherapy. A question that remains unresolved is whether the ECM directly educates the immune phenotypes seen in tumors. Here, we identify a tumor-associated macrophage (TAM) population associated with poor prognosis, interruption of the cancer immunity cycle, and tumor ECM composition. To investigate whether the ECM was capable of generating this TAM phenotype, we developed a decellularized tissue model that retains the native ECM architecture and composition. Macrophages cultured on decellularized ovarian metastasis shared transcriptional profiles with the TAMs found in human tissue. ECM-educated macrophages have a tissue-remodeling and immunoregulatory phenotype, inducing altered T cell marker expression and proliferation. We conclude that the tumor ECM directly educates this macrophage population found in cancer tissues. Therefore, current and emerging cancer therapies that target the tumor ECM may be tailored to improve macrophage phenotype and their downstream regulation of immunity.

The impact of radiation therapy on the antitumor immunity: local effects and systemic consequences

The main antitumor efficacy of irradiation relies in its direct cytotoxic effect. Increasing evidence indicates a systemic effect of radiation though, mediated mainly by the immune system. In this review we wish to focus on the radiotherapy induced modifications of the soluble and cellular mediators of the antitumor immune response and summarize some of the mechanisms by which radiation driven local and systemic bystander effects can influence tumor immunogenicity. In different tumor types due to the intrinsic immunogenicity of the tumor cells and the immunological characteristics of the tumor microenvironment, different radiation induced immune modulatory mechanisms are predominant. Radiation most probably can only amplify or augment a pro-immunogenic phenotype and can hardly change by itself a net immune suppressing environment into an immune stimulating one. This immune modulatory potential of radiotherapy could be exploited in tumor treatment by developing combined radiotherapeutic and immunotherapeutic approaches. The last few years showed a dramatic increase in the knowledge of radiation induced out-of field and systemic effects, which foresees a rapid progress in the development and clinical application of these new, combined therapies for cancer cure.

Dendritic cell vaccines in acute leukaemia

There is a need for novel treatment for acute leukaemia as relapse rates remain unacceptably high. Immunotherapy aims to stimulate the patient's immune responses to recognize and destroy leukaemia cells whilst activating immune memory. The qualities of the most potent professional antigen-presenting cell, the dendritic cell (DC), can be used to stimulate leukaemia-specific cytotoxic T cells. DCs can be loaded with leukaemia antigens, or leukaemia blasts can be modified to express DC-like properties for use in vaccine therapy. This chapter will review the rationale for DC vaccine therapy, the preclinical and clinical trials to date, the barriers to successful DC vaccine therapies and the role of immune adjuncts to improve outcomes.

Differentiation of CD1a- and CD1a+ monocyte-derived dendritic cells is biased by lipid environment and PPARgamma

Accumulating data have shown that the microenvironment of dendritic cells modulates subtype differentiation and CD1 expression, but the mechanisms by which exogenous factors confer these effects are poorly understood. Here we describe the dependence of CD1a- monocyte-derived dendritic cell (moDC) development on lipids associated with the expression of peroxisome proliferator-activated receptor-gamma (PPARgamma). We also show the consecutive differentiation of immature CD1a-PPARgamma+ moDCs to CD1a+PPARgamma- cells limited by serum lipoproteins and terminated by proinflammatory cytokines. Immature CD1a- moDCs possess higher internalizing capacity than CD1a+ cells, whereas both activated subtypes have similar migratory potential but differ in their cytokine and chemokine profiles, which translates to distinct T-lymphocyte-polarizing capacities. CD1a+ moDCs stand out by their capability to secrete high amounts of IL-12p70 and CCL1. As lipoproteins skew moDC differentiation toward the generation of CD1a-PPARgamma+ cells and inhibit the development of CD1a+PPARgamma- cells, we suggest that the uptake of lipids results in endogenous PPARgamma agonists that induce a cascade of gene transcription coordinating lipid metabolism, the expression of lipid-presenting CD1 molecules, subtype dichotomy, and function. The presence of CD1a-PPARgamma+ and CD1a+PPARgamma- DCs in lymph nodes and in pulmonary Langerhans cell histiocytosis confirms the functional relevance of these DC subsets in vivo.

Differential capability for phagocytosis of apoptotic and necrotic leukemia cells by human peripheral blood dendritic cell subsets

CD11c+ dendritic cells (DC) and plasmacytoid DC (PDC) are the two major DC subsets in human peripheral blood. For the purpose of immunotherapy with DC, it is important to investigate the phagocytosis of killed tumor cells by different DC subsets. Using immature monocyte-derived DC (iMoDC) as reference, we have compared the ability of CD11c+ DC and PDC to phagocytose apoptotic and necrotic K562 leukemia cells. Freshly isolated CD11c+ DC phagocytosed apoptotic and necrotic K562 cells, whereas PDC did not show any evidence of uptake of dead cells. Blocking studies showed that CD36 is importantly involved in uptake of apoptotic and necrotic material. CD91 and CD11c were also involved. In addition, we found that beta5 integrin was expressed on CD11c+ DC but not in its classical association with alphaV. Uptake of apoptotic K562 cells by CD11c+ DC was increased following incubation with granulocyte macrophage-colony stimulating factor (GM-CSF) and interleukin (IL)-4, alone or in combination with transforming growth factor-beta1, to levels comparable with those observed for iMoDC. Phagocytosis of dead cellular material by the GM-CSF/IL-4-treated CD11c+ DC was largely restricted to a subset expressing low levels of human leukocyte antigen-DR and CD83. Thus, the relationship between phagocytosis of antigenic material and expression of maturation-related cell-surface molecules is similar for CD11c+ DC and MoDC. We conclude that CD11c+ DC in peripheral blood are precursor cells, which under the influence of cytokines, differentiate to cells with DC phenotype and function.