The receptor DNGR-1 signals for phagosomal rupture to promote cross-presentation of dead-cell-associated antigens.

Type 1 conventional dendritic (cDC1) cells are necessary for cross-presentation of many viral and tumor antigens to CD8+ T cells. cDC1 cells can be identified in mice and humans by high expression of DNGR-1 (also known as CLEC9A), a receptor that binds dead-cell debris and facilitates XP of corpse-associated antigens. Here, we show that DNGR-1 is a dedicated XP receptor that signals upon ligand engagement to promote phagosomal rupture. This allows escape of phagosomal contents into the cytosol, where they access the endogenous major histocompatibility complex class I antigen processing pathway. The activity of DNGR-1 maps to its signaling domain, which activates SYK and NADPH oxidase to cause phagosomal damage even when spliced into a heterologous receptor and expressed in heterologous cells. Our data reveal the existence of innate immune receptors that couple ligand binding to endocytic vesicle damage to permit MHC class I antigen presentation of exogenous antigens and to regulate adaptive immunity.

Vitamin D regulates microbiome-dependent cancer immunity.

A role for vitamin D in immune modulation and in cancer has been suggested. In this work, we report that mice with increased availability of vitamin D display greater immune-dependent resistance to transplantable cancers and augmented responses to checkpoint blockade immunotherapies. Similarly, in humans, vitamin D-induced genes correlate with improved responses to immune checkpoint inhibitor treatment as well as with immunity to cancer and increased overall survival. In mice, resistance is attributable to the activity of vitamin D on intestinal epithelial cells, which alters microbiome composition in favor of Bacteroides fragilis, which positively regulates cancer immunity. Our findings indicate a previously unappreciated connection between vitamin D, microbial commensal communities, and immune responses to cancer. Collectively, they highlight vitamin D levels as a potential determinant of cancer immunity and immunotherapy success.

ZBTB18 restricts chromatin accessibility and prevents transcriptional adaptations that drive metastasis.

Metastases arise from rare cancer cells that successfully adapt to the diverse microenvironments encountered during dissemination through the bloodstream and colonization of distant tissues. How cancer cells acquire the ability to appropriately respond to microenvironmental stimuli remains largely unexplored. Here, we report an epigenetic pliancy mechanism that allows cancer cells to successfully metastasize. We find that a decline in the activity of the transcriptional repressor ZBTB18 defines metastasis-competent cancer cells in mouse models. Restoration of ZBTB18 activity reduces chromatin accessibility at the promoters of genes that drive metastasis, such as Tgfbr2, and this prevents TGFß1 pathway activation and consequently reduces cell migration and invasion. Besides repressing the expression of metastatic genes, ZBTB18 also induces widespread chromatin closing, a global epigenetic adaptation previously linked to reduced phenotypic flexibility. Thus, ZBTB18 is a potent chromatin regulator, and the loss of its activity enhances chromatin accessibility and transcriptional adaptations that promote the phenotypic changes required for metastasis.

Maintenance and loss of endocytic organelle integrity: mechanisms and implications for antigen cross-presentation.

The membranes of endosomes, phagosomes and macropinosomes can become damaged by the physical properties of internalized cargo, by active pathogenic invasion or by cellular processes, including endocytic maturation. Loss of membrane integrity is often deleterious and is, therefore, prevented by mitigation and repair mechanisms. However, it can occasionally be beneficial and actively induced by cells. Here, we summarize the mechanisms by which cells, in particular phagocytes, try to prevent membrane damage and how, when this fails, they repair or destroy damaged endocytic organelles. We also detail how one type of phagocyte, the dendritic cell, can deliberately trigger localized damage to endocytic organelles to allow for major histocompatibility complex class I presentation of exogenous antigens and initiation of CD8+ T-cell responses to viruses and tumours. Our review highlights mechanisms for the regulation of endocytic organelle membrane integrity at the intersection of cell biology and immunology that could be co-opted for improving vaccination and intracellular drug delivery.