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Tumour-infiltrating leucocytes (TILs) were isolated from the resected HCC tissue of 14 patients (see online supplementary table S1) by enzymatic digestion, as previously described. Tumour tissues and blood samples were obtained from a total of 41 patients with HCC from the National Cancer Center Singapore and Singapore General Hospital, who underwent surgical resection for HCC with or without prior Y90-RE therapy. In addition, a prediction model was built using the immune profile of pretherapy PBMCs to identify potential sustained responders (SRs) to Y90-RE. We also examined the immune profiles of the peripheral blood mononuclear cells (PBMCs) from patients before and at various time points after Y90-RE and identified key immune subsets, including CD8 + T cells and CD4 + T cells expressing the checkpoint receptors progressive disease-1 (PD-1) and Tim-3 and homing receptors CCR5 and CXCR6 in those who responded to Y90-RE. Next-generation sequencing (NGS) of tumour tissues from patients after Y90-RE identified activation of multiple immune subsets and a potential pathway that induces the recruitment of activated CD8 + T cells.
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12 13 We identified key antitumour immune responses induced by the Y90-RE that we propose underlie the clinical response. We used time-of-flight mass-cytometry (CyTOF) for high-dimensional, in-depth immunophenotyping. Here, we analysed the immune profile of surgically resected HCC, which has been downstaged by Y90-RE. 10 11 In-depth understanding of the impact of radiotherapy on local and systemic immune system in patients with cancer, however, remains to be elucidated. For instance, ionising radiation can induce modest inflammation in the tumour microenvironment, as evidenced by the upregulation of chemokines and cytokines in murine models and cell lines. Previous studies have suggested that an active immune response 8 and interactions with the tumour microenvironment 9 mediate the clinical manifestations of radiotherapy. 7 The mechanisms that underlie this delayed, yet long-lasting antitumour effect remain elusive. 4 6 The half-life of the Y90-isotope is ~64.2 hours, but maximal clinical response, including, tumour regression and decrease in serum α-fetoprotein (AFP), is only seen 3–6 months after treatment. 5 Y90-RE has been shown to elicit a disease-control by tumour-downstaging and delayed disease progression. This precise mode of delivery spares the non-malignant liver parenchyma making Y90-RE an ideal brachytherapy for HCC. 4 Y90-coated microspheres are delivered directly into HCC via transarterial catheter under radiologic guidance. HCC receives its blood supply predominantly through branches of the hepatic artery. 2 The majority of the patients who have locally advanced disease are treated with locoregional therapies such as transarterial chemoembolisation or Yttrium-90 (Y90)-radioembolisation (RE), also known as selective internal radiation therapy (SIRT). 1 The most effective therapeutic options for HCC are tumour resection or liver transplantation, but these are limited to early stage disease. Hepatocellular carcinoma (HCC) is a highly malignant disease, and the third most common cause of cancer-associated deaths worldwide.
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2 Department of Pathology, Singapore General Hospital, Singapore.1 Translational Immunology Institute (TII), SingHealth-DukeNUS Academic Medical Centre, Singapore.