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ItemReprogramming tumour immune microenvironment of colorectal liver metastases with renin-angiotensin inhibitorsVallejo Ardila, Dora Lucia ( 2021)Background Renin-angiotensin system inhibitors (RASi) have shown anti-tumour effects that may significantly impact the response to current cancer immunotherapies and the prognosis in patients with colorectal liver metastases (CLM). RAS components are expressed by various immune cells and adult hematopoietic cells. The mechanisms by which RASi reprogram the tumour immune microenvironment toward an immunostimulatory milieu involves modulating the function of immune T lymphocytes, myeloid cells and cancer-associated fibroblasts. Experimental Design Liver metastases were established in a mouse model using an autologous colorectal cancer cell line. RASi captopril 750mg/kg or saline was administered to the mice daily via intraperitoneal injection, from day one post-tumour induction to the endpoint, day 15 or 21 post tumour induction. At the endpoint, tumour growth was determined, and lymphocyte and myeloid-derived infiltration and composition in the tumour and liver tissues were analyzed by flow cytometry and immunohistochemistry. At endpoint day 15, livers and tumour tissues were collected, and tissue lysates were prepared and analyzed using liquid chromatography-tandem mass spectrometry proteomic techniques to determine relative changes in protein abundance. The proteomics results were analyzed using open-source software such as MaxQuant and Perseus. A 7-plex OPAL protocol was used to assess the composition and spatial distribution of T cell markers CD3, CD8, FoxP3 and CD103 and the epithelial to mesenchymal transition markers alpha- Smooth muscle actin and E-cadherin. The protocol was manually optimized and validated in two independent cohorts of formalin-fixed, paraffin-embedded CLM patient tissues using well-established antibodies, a single spectral library, negative controls, and biological controls corroborating the staining pattern of immune infiltrates. Results Captopril significantly decreased tumour viability and impaired metastatic growth, increased the infiltration of CD3 T cells into both tissues, and the primary contributing phenotype to this influx is a CD4 and CD8 double-negative T cell subtype, while CD4 T cells decreased and CD8 T cells remained unchanged. Furthermore, clustering and functional enrichment showed that captopril modulates the expression of some of the immunoproteasome subunits, including PSMB8, PSMB10, PSMB5 and PSME1. Also, T lymphocyte phenotypes’ spatial distribution was seen in significantly higher levels in the invasive tumour margin compared to their density within the liver parenchyma or the tumour centre in human CLM. Thus, high CD3 density in the tumour core or high CD8 density in the invasive tumour margin predicts a significantly better overall survival. Moreover, high CD3 T cell density at the adjacent liver parenchyma and a high CD8 density at the tumour core segment influenced patient survival after CLM resection in patients who received RASi antihypertensive medication. In the case of myeloid cells, a significant decline in myeloid cells expressing CD31pos was induced by captopril, while the relative proportion of CD31neg cells was preserved when comparing between the liver and the tumour. RASi significantly reduces a CD31pos monocyte-derived subset F480neg Ly6C intermediate and High, which may have a pro-angiogenic and immunosuppressive function. Conclusion The work of this thesis highlights the mechanism by which RAS inhibitors decreased tumour viability and impaired metastatic growth by effectively restoring the immunogenicity of CLM toward an immunostimulatory milieu.