Toll-like Receptor Control of MHC Class I Endocytosis

点击翻译按钮获取中文摘要

PROPOSAL SUMMARY Cross-presentation is the process whereby major histocompatibility complex class I (MHC-I) molecules are loaded with peptides derived from an extracellular source of proteins including internalized soluble proteins, microorganisms and dying cells. Cross-presentation is a specialty of dendritic cells (DCs), cell types responsible for priming naïve T cells, but even in DCs, this specialty can come naturally or must be acquired upon activation. Conventional DCs known as cDC1 are potent cross-presenters and can do so constitutively, while inflammatory monocyte-derived DCs found in inflamed tissues and another subset of conventional DCs, cDC2, can also cross- present under conditions of infection and inflammation. Parallel to the well-established heterogeneity of DCs in tissues at steady state and inflammation, DC subsets have different functional states during homeostasis or inflammation. This functional difference is primarily orchestrated by the engagement of innate signaling receptors, such as Toll-like receptors (TLRs), that mediate diverse cellular programs including the transcription of inflammatory genes and mediators, as well as the rapid reorganization of subcellular vesicular traffic through post-translational events such as phosphorylation. It is imperative that we investigate the full spectrum of DC functions under inflammation when innate receptors are engaged, and to not be limited to DC classifications as subsets with rigid inflexible functions. Defining the nature of the inflammatory innate receptors and signals that enable DCs to augment their cross-presentation capacity or to acquire it anew, will inform vaccine design for infectious diseases and cancer where cytotoxic CD8 T cells are absolutely essential for organismal survival. A mechanistic dissection of the regulation of cross-presentation is important for the identification of novel therapeutic targets that can be exploited to harness CD8 T cell immunity and confer long term protection against future infection or cancer resurgence. Antigen internalization, processing, and presentation rely heavily on subcellular vesicular traffic. In vitro tools developed for studying murine conventional DCs have served as the workhorse responsible for seminal discoveries of the mechanisms of cross-presentation and its regulation, which have translated to human DC subsets and have impacted vaccine design and cellular therapies. Such tools have enabled our discovery of endosomal recycling compartment stores of MHC-I critical for cross-presentation and depleted upon infection by immunoevasive viruses, findings that have been replicated in human DCs. We have now discovered a new link between cross-presentation of endocytosed antigen and a particular innate receptor reported to be expressed by cultured DCs, inflammatory DCs and a cDC2 subset. We hypothesize this receptor intersects MHC-I traffic with endocytic antigen to license cross-presentation during infection. Using cultured and ex-vivo DCs isolated from the lymphoid organs of mice, we will define the distinct innate immune signaling components that regulate MHC-I endocytosis. We will determine the features of MHC-I that enable its regulated endocytosis. Our studies will inform urgently needed T cell vaccines against infectious diseases and cancer.