Abstract
Dendritic cells (DCs) are the only antigen-presenting cells able to prime naïve T cells and cross-prime antigen-specific CD8+ T cells. Their functionality is a requirement for the induction and maintenance of long-lasting cancer immunity. Albeit intensively investigated, the in vivo mechanisms underlying efficient antigen cross-processing and presentation are not fully understood. Several pieces of evidence indicate that antigen transfer to DCs mediated by microvesicles (MVs) enhances antigen immunogenicity. This mechanism is also relevant for cross-presentation of those tumor-associated glycoproteins such as MUC1 that are blocked in HLA class II compartment when internalized by DCs as soluble molecules. Here, we present pieces of evidence that the internalization of tumor-derived MVs modulates antigen-processing machinery of DCs. Employing MVs derived from ovarian cancer ascites fluid and established tumor cell lines, we show that MV uptake modifies DC phagosomal microenvironment, triggering reactive oxygen species (ROS) accumulation and early alkalinization. Indeed, tumor MVs carry radical species and the MV uptake by DCs counteracts the chemically mediated acidification of the phagosomal compartment. Further pieces of evidence suggest that efficacious antigen cross-priming of the MUC1 antigen carried by the tumor MVs results from the early signaling induced by MV internalization and the function of the antigen-processing machinery of DCs. These results strongly support the hypothesis that tumor-derived MVs impact antigen immunogenicity by tuning the antigen-processing machinery of DCs, besides being carrier of tumor antigens. Furthermore, these findings have important implications for the exploitation of MVs as antigenic cell-free immunogen for DC-based therapeutic strategies.
Highlights
Dendritic cells (DCs) are key regulators of the immune response and are required to induce long-lasting T-cell-mediated cancer immunity [1]
Using MVs derived from ovarian cancer ascites fluid as well as from a MUC1 engineered tumor cell line, we show that MV internalization modifies DC phagosomal microenvironment, inducing accumulation of reactive oxygen species (ROS) and alkalinization
MV Uptake Induces Alkalinization in DC Phagosomal Compartment In DCs, alkalinization of the phagosomal compartment seems to be crucial for efficient antigen cross-processing and presentation [4]
Summary
Dendritic cells (DCs) are key regulators of the immune response and are required to induce long-lasting T-cell-mediated cancer immunity [1]. Among antigen-presenting cells (APCs), DCs own a unique antigen-presenting machinery that endows them to cross-process and present exogenous antigens, resulting in the activation of both CD4+ and CD8+ T cell response [2]. Upon internalization by DCs, exogenous antigens are delivered into a complex network of intracellular organelles dynamically interacting among each other. The phagosome of DCs appears to play a fundamental role in exogenous antigen cross-processing by dampening proteases activity, reducing protein degradation. It regulates the export/import of degraded antigens to/from cytoplasm redirecting them to other intracellular pathways for final association to HLA class I and II molecules [4]
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