Abstract 1741 APOL7C control of protein antigen escape and cross-presentation in classical dendritic cells

Cross-presentation is the essential process that links the detection of "danger" by dendritic cells to the generation of potent cytotoxic T cell responses against pathogens and cancer. Despite the obvious importance of cross-presentation, the molecular pathways driving cross-presentation remain unclear. It is believed that an essential step in cross-presentation is the transfer of phagocytosed protein antigens from within the phagosomes of dendritic cells to the cytosol. We have obtained exciting new evidence using bulk RNA sequencing and qPCR that upon exposure to "danger" signals, such as viral RNA, dendritic cells increase the expression of a poorly characterized pore-forming protein called apolipoprotein 7C (APOL7C). Utilizing live cell microscopy and immunofluorescence assays, we have found that APOL7C is recruited to phagosomal membranes and, strikingly, these phagosomes begin to show signs of breached membranes shortly after the arrival of APOL7C. APOL7C arrival on phagosomes and is accompanied by the arrival endolysosomal damage markers such as galectin 3 and correlates with the escape of luminal, membrane-impermeant fluorescent dyes and fluid-phase proteins to the cytosol. We have found that APOL7C-mediated phagosomal damage leads to protein antigen export from the phagosome to the cytosol where they can be processed for cross-presentation. This work will investigate the molecular mechanisms of APOL7C recruitment to phagosomes, elucidating pathways of protein antigen escape and processing for cross-presentation, and provide insight into new avenues of vaccine and cancer therapy development. Canadian Institutes of Health Research, Natural Sciences and Engineering Research Council of Canada, Canadian Cancer Society, University of Calgary Veterinary Medicine.