Characterisation and Identification of Cell Engulfment Receptors on cDC1s.

The engulfment of dead cells by type 1 conventional dendritic cells (cDC1s) is essential to maintain tolerance to self-antigens and to induce immunity to infected or malignant cells. cDC1s have the unique ability to engulf dead cells, in contrast to the closely related cDC2s. Moreover, uptake of apoptotic cells induces cDC1 maturation and serves as their key source of antigens. However, we still do not understand which receptors on cDC1s are involved in the recognition and internalisation of dead cell corpses and whether these receptors differ depending on the type of cell death (e.g. apoptosis vs necrosis) that led to corpse formation. Remarkably, our preliminary data indicates that cDC1s, unlike macrophages, 1) do not express many of the classical or canonical engulfment receptors, 2) they tend to nibble pieces from dead cells and 3) are able to ingest parts of live cells. Hence, in the proposed work, I aim to characterise live, apoptotic and necrotic cell engulfment by cDC1s and its phosphatidylserine-dependency using novel reagents and state-of-the-art instrumentation such as high-resolution live cell microscopy. Furthermore, I will use a validated CRISPR-editing protocol and establish a CRISPR screen with both primary and immortalized cDC1 cell lines to discover which receptors on cDC1s are necessary for the engulfment of live, apoptotic and/or necrotic cells. Lastly, I will interrogate in vivo the role of key cDC1-dependent phagocytic receptors in a tumour and tolerance model using novel markers for DC maturation that I identified during my PhD. Altogether, the work in this proposal will elucidate a long-standing question in the DC and phagocytosis field, contribute to our knowledge on how cDC1s mediate anti-tumour immunity and tolerance, and may open new strategies to improve anti-tumour immunity and tolerance to self.