Cellular and matrix interactions of F4/80, an adhesion GPCR which defines murine tissue macrophages, in the normal and tumor microenvironment.

PROJECT OVERVIEW

The immune system seeks out and destroys tumors, but tumors develop effective strategies to evade elimination. Re-activating cytotoxic T cells after they have been disarmed by tumors has revolutionized cancer treatment. However, this approach does not work for all patients, nor all types of tumor, and can be associated with severe autoimmune side effects. Macrophages play a key role in dictating whether the immune response will attack, or shield, tumors. Recent data show that F4/80, a protein that spans the surface of macrophages, is essential for Treg generation and tumor survival. However, nothing is known about how this is achieved, nor what F4/80 binds to, either inside or outside of the macrophage, to drive this response. Focusing on these questions, this project will lead to a better understanding of how cancer evades immune destruction, and enable design of new therapeutic strategies to prevent this escape strategy.

Macrophages are widely dispersed throughout all tissues in health and disease. They are terminally differentiated migratory leucocytes which sense physiologic and pathologic changes in their microenvironment through a variety of plasma membrane receptors that regulate their biosynthetic responses to maintain homeostasis [1]. In addition to specialised phagocytic receptors to recognize and clear senescent, apoptotic and necrotic cells and microbes, they are potent secretory cells able to nourish or destroy abnormal host cells and microbial targets, depending on their functional activation state. Tissue resident and recruited macrophages also express adhesion molecules such as F4/80, a widely used biomarker and the founder member of a family of transmembrane G protein coupled receptors (GPCRs). More than 30 adhesion GPCRs exist, utilizing large extracellular epidermal growth factor like domains to form multimeric signalosome-like structures. However, despite identification of ligands in extracellular matrix and cells for other GPCRs [2], F4/80 remains an orphan receptor. A major breakthrough in our understanding of its immunological function derived from studies using F4/80 knockout mice, which revealed this molecule to be dispensible for macrophage development, but responsible for peripheral tolerance. Required for Treg generation in vivo in response to a model antigen introduced into the anterior chamber of the eye [3], F4/80 expression is also essential for organ transplantation [4] and engraftment of Lewis lung cancer cells. This project will explore the role of F4/80 in tumour-host interactions in vivo and identify cellular and extracellular binding partners of this adhesion GPCR.

We will investigate the cellular and molecular basis of F4/80-mediated tolerance using a syngeneic, orthotopic breast cancer grafting model [5] in wild type or F4/80 null mice. Immune profiling and single cell transcriptomic analysis will reveal F4/80 dependent changes in abundance, and activation/polarization status, across myeloid and lymphoid compartments, as well as candidate pathways and effector molecules. Multiplexed immunofluorescent imaging will map cell interaction partners of F4/80+ macrophages, and identify components of the extracellular matrix that interact with these cells. Adhesion of macrophage cell lines from wild type and F4/80 knockout mice to purified matrix molecules, and complex 3D matrices, will be assessed, and binding sites mapped and downstream signalling examined.

KEYWORDS

Macrophages, peripheral tolerance, cell adhesion, extracellular matrix, tumor microenvironment

TRAINING OPPORTUNITIES

KEY PUBLICATIONS

1. Gordon, S. and A. Plüddemann, Tissue macrophages: heterogeneity and functions. BMC Biology, 2017.
2. Boucard, A.A., Self-activated adhesion receptor proteins visualized. Nature, 2022.
3. Lin, H.H., et al., The macrophage F4/80 receptor is required for the induction of antigen-specific efferent regulatory T cells in peripheral tolerance. J Exp Med, 2005.
4. Conde, P., et al., DC-SIGN(+) Macrophages Control the Induction of Transplantation Tolerance. Immunity, 2015.
5. Deligne C et al, Matrix-Targeting Immunotherapy Controls Tumor Growth and Spread by Switching Macrophage Phenotype. Cancer Immunol Res. 2020.

KEY THEMES

Inflammation, Oncology, Tissue Biology, Translational Medicine