title: Investigating the crosstalk between hepatic stellate cells and antigen presenting cells in pancreatic cancer liver metastases
Creators: name: Simms, Nicole
Publisher: name: University of Liverpool Repository
Year: 2024

description: Metastatic pancreatic cancer is a fatal disease with a lack of effective therapies. Patients do not respond to standard chemotherapy and show in clinical trials resistance to immune checkpoint therapies. The tumour microenvironment (TME) consists of a diverse network of cellular components whose dynamic and complex interactions drive a conducive milieu for immune evasion and metastatic progression. The cancer associated fibroblast (CAF) is a major component of the TME that can suppress anti-tumour immunity by inducing a dense fibrotic reaction which can physically impede immune cell infiltration and function, and through engaging in a reciprocal interaction with antigen presenting cells (APC). CAFs, however, are a heterogenous population that can be tumour promoting or restraining. A better understanding of CAF heterogeneity, their interactions with immune cells, and how this affects anti-tumour immunity, is therefore crucial to design better treatment strategies for metastatic pancreatic cancer patients. This thesis describes the use of a platelet derived growth factor receptor β-enhanced green fluorescent reporter (PDGFRβ-eGFP) mouse model to investigate the heterogeneity of the tissue resident fibroblasts in pancreatic cancer liver metastases, termed tumour associated hepatic stellates (taHSCs). In addition, the thesis addresses how tumour associated macrophages (TAMs) affect taHSC activation state and how TAMs can modulate taHSC subtypes. It was observed that in liver metastatic bearing PDGFRβ-eGFP mice the administration of an anti-CSF1 neutralising antibody to deplete TAMs, reduced taHSC activation and changed taHSCs subtypes in metastatic tumours. Moreover, TAM depletion increased CD8 T cell infiltration and reduced tumour burden in liver metastases. Interestingly, dendritic cells (DC) the professional APC numbers also decreased in tumour bearing livers of anti-CSF-1 treated animals compared to control IgG treated mice. Immune tolerance in pancreatic cancer liver metastases is mediated through suppression of CD8 T cell cytotoxic response against cancer cells. Studies utilising a genetically engineered mouse model of pancreatic ductal adenocarcinoma (KPC; LSL-KrasG12D/+, Trp53R172H, Pdx1-Cre), demonstrated that the lack of tumour cell killing by CD8 T cells is due DC impairment in the TME. The research described in this thesis also explores whether and how taHSCs affect DC activation by (i) using the PDGFRβ-eGFP reporter mouse model to uncover the spatial proximity of taHSCs and DCs in liver metastases, and (ii) performing in vitro assays to determine how culture activated hepatic stellate cells (aHSCs) affect DC migration and activation. Immunofluorescent analyses of taHSCs and DC populations in liver metastases, demonstrated DCs accumulated in areas where taHSCs were abundant, in contrast few DCs were observed in regions that were lacking taHSC infiltration. In vitro, flow cytometry analyses of DC maturation markers MHCII, CD80 and CD86, demonstrated that aHSCs promote an immature DC phenotype. Furthermore in vitro analysis showed that aHSCs reduce the expression the DC migration marker CCR7 and that aHSCs can inhibit DC migration capacity towards chemoattractant factors. Therefore, this thesis uncovers that during pancreatic cancer liver metastasis, DCs accumulate in taHSC rich areas in vivo and that ex vivo, aHSC inhibit DC migration towards chemoattractant factors and reduce DC maturation. Thus, during pancreatic cancer liver metastasis, taHSC might function as traps for DCs by retaining DCs within fibrotic areas and reducing their activation state. Altogether, these data uncover diverse taHSC subtypes in metastatic tumour lesions and show that the depletion of TAMs reshapes taHSC subtypes. Moreover, taHSCs might contribute to the generation of an immune suppressive TME in pancreatic cancer liver metastases by trapping DCs in fibrotic areas.