Work in the lab is funded by Cancer Research UK and the European Research Council

We work on the crosstalk between immune cells and non-immune cells in lymph nodes to understand how lymph node remodelling is controlled during adaptive immune responses. We focus  on the role of dendritic cells and their interactions with the fibroblastic reticular cell network. Through this work on fundamental immune mechanisms, we discover pathways directly relevant to tumour microenvironments, such as dendritic cell migration and tumour infiltration, contractility mechanisms in cancer-associated fibroblasts and extracellular matrix remodelling.

Lymph Node Remodelling

Lymph node swelling (LN) is a classical hallmark of immunity. This expansion is observed by doctors, researchers and patients, yet as obvious as this process is, our understanding of the remodelling mechanisms involved are in their infancy. Lymph node remodelling is rapid and yet completely reversible, occurring countless times throughout our lifetimes.

The architecture of lymphoid organs is key to the effective operation of our immune system and is dictated by structures formed by non-haematopoetic stromal cells, including endothelial cells, and fibroblasts. Beyond their structural roles, stromal cells play an active role in immune responses, and the field of stromal immunology has become one of the most dynamic and exciting areas of immunology research.

In the lab we focus on the changing behaviour of fibroblastic reticular cells (FRCs) throughout cycles of lymph node remodelling. The purpose of this project is to understand how lymph node remodelling occurs and is resolved, repeatedly; to understand immunity in a whole organ context. We use a range of models from FRC cell lines to in vivo studies studying the whole organ. We are especially interested in how the function of FRCs is directed by their interactions with neighbouring immune cells such as the arriving antigen-bearing dendritic cells.

Project 1 – The role of actin cytoskeleton regulation pathways in lymph node stromal remodelling

During acute inflammation, rapid T-lymphocyte proliferation occurs within spaces in the FRC network, but initially FRC numbers remain stable. This proliferation lag suggests that FRCs elongate to accommodate T-cells. Whilst gap analysis has confirmed enlarged spaces in the network, the morphology of individual FRCs, within the lymph node network has not previously been studied.

Following stimulation with CLEC-2+dendritic cells in vitro, FRCs reduce actomyosin contractility and undergo Rac1-dependent elongated spreading through the CLEC-2/Podoplanin signalling axis. CLEC-2 is required for full lymph node expansion, however we do not understand the contribution of the actin-dependent processes to changes to FRC phenotypes during acute lymph node expansion.

Lindsey Millward (PhD student) has been working to elucidate the mechanism whereby CLEC-2/podoplanin signalling initiates elongated spreading. She has used been using mouse models to interrogate the elongating behaviour of FRCs within their network during acute lymph node expansion. Finally, she has been translating my mechanistic findings to the lymph node, to understand the contribution of CLEC-2/podoplanin- controlled spreading pathways to acute lymph node expansion. Preprint coming Summer 2021

Project 2 – Lymph node mechanics

FRCs are considered immunologically specialised myofibroblasts that generate forces to control lymph node size and architecture. Yet there has been a dearth of direct evidence for mechanical forces generated inside the tissue. Furthermore, whether FRCs can mechanically adapt to extrinsic mechanical forces during inflammation to maintain connectivity and maximise the immune response is not known.

Harry Horsnell (PhD student) utilises in vivo, ex vivo and in vitro biophysical assays, combined with live imaging, to determine the mechanical nature of the FRC network. By understanding how mechanical forces are integrated into the FRCs response to inflammation we may better understand how the FRC network might use mechanical cues to coordinate a unified expansion of the lymph node. Preprint coming Spring 2021

Media (left): Vibrotome cut section of lymph node showing vessels. (right): Serial z-sections through a vessel within the lymph node. Cell membranes are shown in red, centre/nucleus of FRCs is shown in green.

 (Right): Schematic showing Lymph node expansion time course, and below, the changing organisation of the fibroblastic reticular cell network

Podoplanin (PDPN) Expression

PDPN expression is normally restricted to specific cell types such as FRCs and lymphatic endothelium. However, many tumour types over-express PDPN. PDPN+ tumours correlate with poor prognosis and increased invasion and metastasis. Our previous work on PDPN function shows that PDPN controls contractility of fibroblasts and that crosstalk between PDPN+ cells and DCs inhibits the contractile function of PDPN.

This project investigates additional functions of PDPN in FRCs and other cell types including cancer cells and how these functions are modulated by interactions with DCs.

Tumour Immunology

The interplay between DCs and stroma is relevant to cancer in several ways.  There is significant overlap in both phenotype and function of fibroblastic reticular cells (FRCs) and carcinoma-associated fibroblasts (CAFs). Both are highly contractile specialised fibroblasts, and have significant roles in extracellular matrix organisation and controlling the behaviour of neighbouring cells in the microenvironment.

Many cancer cells escape primary tumours and spread via lymphatic vessels to draining LNs. LN metastases will be in close proximity to FRCs and leukocytes. The interplay between cancer cells and lymphoid stroma is an unaddressed question in both stromal immunology and cancer biology, but of significant impact to both fields.

The purpose of this project is to translate our understanding of the function of FRCs in lymphoid organs to give us parallel insights into the function and origins of CAFs in the tumour microenvironment

We collaborate with the talented Tape lab also at UCL –  to investigate the reciprocal signalling between fibroblasts and dendritic cells using phosphoproteomics.