Defining anti-tumour immunity of mucosal-associated invariant T (MAIT) cells in hepatocellular carcinoma (HCC)

Student thesis: Doctoral ThesisDoctor of Philosophy

Abstract

Hepatocellular carcinoma (HCC) is one of the most common malignant tumours of the digestive system, accounting for more than 90% of primary liver cancers. Various liver resident immune cells were involved in the development of HCC, among which mucosal-associated invariant T (MAIT) cell has been considered as one of the immune cells with significant anti-tumour potential, however, little is known about its antitumour and immunomodulatory roles in HCC. In this thesis, I investigated the immune profile changes of MAIT cells using multiple assays. The frequency, phenotypes and function of MAIT cells in both peripheral blood and liver tissue from patients with HCC and healthy controls were characterised using multiple-parameter flow cytometer (BD Fortessa). The gene expression of cytokine and activation markers of MAIT cells were analysed through real-time quantitative polymerase chain reaction (PCR). Both Immunohistochemistry (IHC) and Immunofluorescence (IF) assays were performed to localise MAIT cells in liver tissue. Enzyme-linked immunosorbent assay was conducted to explore the association between MAIT cells and immune markers. Meanwhile, co-culture experiments were performed to explore the interactions between activated MAIT cells and tumour cells.

There was a significant decrease of peripheral CD8pos T cells in HCC compared to healthy controls. The expression of CCR4 increased on CD4pos T cells whereas the expression of CXCR3 decreased on CD8pos T cells. Moreover, the percentage of Tregs also increased in HCC suggesting the impairment of T effector immunity. Plasma soluble PD-1, PD-L1 and OPN levels significantly increased in patients with HCC suggesting that an immunosuppressive microenvironment existed in these patients. The percentages of MAIT cells decreased in both peripheral blood and liver tissues in patients with HCC compared to healthy controls., The expression of CD69 on tumour infiltrating MAIT cells decreased whereas the expression of CD39 increased. A higher percentage of PD-1pos MAIT cells was observed in HCC. In addition, the chemotaxis of MAIT cells was affected in HCC. The percentage of CXCR3posMAIT cells reduced in peripheral blood whereas CCR4posMAIT cells increased in both peripheral blood and liver tissue. The production of IFN-γ and cytotoxicity of MAIT cells were impaired in patients with HCC. The phenotype and genetic profile of MAIT cells changed with tumour status. The percentage of peripheral MAIT cells is associated with HCC patients’ clinical parameters including tumour diameter and status.

Moreover, it was found that osteopotin (OPN) was a critical driver of immune escape in HCC setting. OPN was overexpressed in both plasma and liver tissue of HCC patients. Multiple assays including ELISA, IHC, IF, FACS and PCR revealed its close association with immune evasion, overexpression of OPN could facilitate the upregulation of PD-L1. Patients with high plasma levels of OPN had a significantly higher percentage of Tregs and CCR4posCD4posT cells in peripheral blood while CXCR3posCD8posT cells. OPN silencing could downregulate the activity of CCL17/CCR4 axis. In addition, it could directly suppress T effectors including MAIT cells and promote the proliferation of both tumour cells and Tregs.

In conclusion, the anti-tumour ability of MAIT cells was impaired in the setting of HCC. OPN could be one an important factor contributing to the immune escape of HCC and immune suppression of MAIT cells.
Date of Award1 Mar 2024
Original languageEnglish
Awarding Institution
  • King's College London
SupervisorYun Ma (Supervisor) & Nigel Heaton (Supervisor)

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