Investigating the spatiotemporal dynamics of mononuclear phagocytes in solid tumours.

Mononuclear phagocytes (MNP), consisting of monocytes, macrophages and dendritic cells (DC), are major cell types of the innate immune system and their activation is required for an effective immune response, including the anti-cancer response. Tumour-associated macrophages (TAM) are a universal feature of solid tumours, regardless of the cancer’s immunogenicity, but variably influence outcomes and treatment responses. DCs capture tumour antigens and upregulate CCR7, which directs their migration to secondary lymphoid organs, where they prime anti-tumour T cell activity. In this work, we aimed to resolve the spatiotemporal dynamics of MNPs following tumour infiltration and investigate how immune checkpoint blockade (ICB) treatment influences this. We utilised a photo-convertible mouse model, combined with single-cell RNA sequencing, confocal imaging and spatial transcriptomics to precisely track tumour MNP entry and egress. This enabled the distinction of rapidly replenished, monocyte-derived (md)TAMs that are enriched at the tumour core from resident-like (r)TAMs that interact with fibroblasts at the tumour-normal interface. Upon tumour infiltration, mdTAMs differentiate along two divergent fate trajectories, distinguished by the expression of class II MHC, with different capacities for endocytosis, Fcγ-receptor- mediated phagocytosis and cytokine production. Both mdTAM subsets quickly undergo anti- inflammatory gene expression changes, but this is attenuated by ICB, which also promotes IFNγ-driven chemokine signalling from TAMs to enhance T cell infiltration. Surprisingly, we found that a subset of CCR7+ DCs acquire prolonged tumour-residence despite their activation and upregulation of the migratory programme. Tumour-retained CCR7+ DCs are phenotypically and transcriptionally distinct from CCR7+ DC emigrants in the draining lymph nodes, progressively downregulate expression of antigen presentation and pro-inflammatory transcripts with increasing tumour dwell-time, and co-localise with PD-1+CD8+ T cells in multiple tumour types. Following ICB, intratumoural CCR7+ DCs upregulate stimulatory molecules, thereby augmenting anti-tumour cytolytic activity. In the final element of this thesis, we generated single-cell and spatial transcriptomics data from clinical cohorts of patients with triple-negative breast cancer, including longitudinal tumour samples, to investigate the intratumoural MNP landscape and its temporal changes with treatment. These analyses demonstrated how MNPs co-evolve with the treatment response-associated tissue state and influence treatment outcomes in a context-dependent manner. Altogether, this work resolves distinct temporal, spatial and functional properties of tumour MNPs from the pre-clinical to clinical settings, to provide fundamental insights into their role in tumour immunity.

Name dc:type.qualificationname

Doctor of Philosophy (PhD)

Level dc:type.qualificationlevel

Doctoral

Grantor dc:publisher.institution

University of Cambridge

Year dc:date.issued

2024

Author dc:creator

• Lee, Colin

Advisor dc:contributor.advisor

• Clatworthy, Menna

• Mononuclear phagocytes
• Spatiotemporal dynamics
• Tumour immunology

Licence

• https://apollo8-f-pro.lib.cam.ac.uk/bitstreams/f8181f15-2daa-4d79-8b58-f87e61bc37f3/download
• http://purl.org/NET/rdflicense/allrightsreserved

Language dc:language

eng

Author Identifier

0000-0001-8380-4917

OAI identifier oai:identifier

oai:www.repository.cam.ac.uk:1810/379768