Role of tumour associated neutrophils in metabolic dysfunction-associated hepatocellular carcinoma development

Abstract

Neutrophils accumulate in solid tumours and their abundance are often associated with poor prognosis. Emerging evidence reveals that tumour-associated neutrophils (TANs) are highly heterogeneous, comprising of both pro- and anti-tumour subsets. Hence, TANs can differentially influence tumour progression and therapy efficacy depending on their diversity within the tumour microenvironment (TME). However, the factors driving TAN diversity, the functions of specific TAN subsets, and the spread of their heterogeneity in different cancer contexts remain largely unknown. Metabolic dysfunction-associated steatohepatitis (MASH) is the fastest growing cause of hepatocellular carcinoma (HCC). Crucially, despite abundant T cell infiltration, this fatty liver etiology is notoriously resistant towards immune checkpoint blockade (ICB) therapy. This treatment deficit likely arises from immunosuppressive factors in the TME. As neutrophils are one of the most prominent immune populations in the HCC TME, their diversity likely play key roles in MASH-HCC pathogenesis and ICB resistance. This thesis investigates how these TANs affect MASH-HCC progression, and how the MASH TME in turn shapes TAN development and diversification. Through reanalysis of the transcriptomic data of over 1000 HCC patients; interrogation of 5 different murine HCC models; and validation with HCC patient tissues, this thesis uncovered a MASH-specific subversion of TANs into a pro-tumour state. Specifically, TANs expressing high levels of SiglecF were enriched in MASH-related HCC tumours, and were found to be competent secretors of TGFβ. Through this pleiotropic cytokine, SiglecFhiTANs perpetuated tumour stemness, promoted tumour proliferation, and aided tumour migration. Critically, SiglecFhiTAN-derived TGFβ supported immune evasion by directly suppressing the antigen presentation machinery of tumour cells. SiglecFhiTAN removal, or ablation of their TGFβ production capability, increased the immunogenicity of a MASH-related HCC model and sensitized it to ICB therapy. Likewise, a high SiglecFhiTAN signature was associated with poor prognosis and ICB resistance in MASH-HCC patients. Thus, SiglecFhiTANs play significant detrimental roles in MASH-related HCC, and are therefore important therapeutic targets. Given the lipid-rich nature of MASH-HCC, fatty acids were likely a key factor underlying the preferential enrichment of detrimental TANs. Indeed, linoleic acid (LA), which was enriched in the MASH-HCC TME, synergised with GM-CSF to reactivate the c-Myc regulon in TANs. This LA/GM-CSF/c-Myc axis subsequently fostered the development of SiglecFhiTANs. This finding emphasized the ability of a cancer’s etiology to shape the TAN landscape within, suggesting that immunotherapy treatments should be tailored whilst taking etiology into account. Overall, this thesis has outlined a novel mechanism by which TANs promoted immune evasion and tumour aggressiveness. It also highlighted the importance of understanding how cancer etiology impacts the immune response within the TME.