Hepatic Radiofrequency Ablation Increases T Cell Infiltraion and PD-L1 Expression in Primary Tumor in Patients With Synchronous Colorectal Cancer Liver Metastases

Radiofrequency ablation (RFA) is widely used as a local treatment for tumors such as small hepatocellular carcinomas, renal cancer and solitary colorectal cancer liver metastases (CRCLM). RFA induces localized coagulation necrosis and leads to the release of large amounts of cellular debris in situ, which can serve as a source of tumor antigens to elicit host adaptive immune responses against tumors. Several studies on preclinical animal models have shown that localized tumor ablation by RFA can induce systemic T-cell mediated antitumor immunity. Antigen-specific T cell immune responses were also observed in patients with hepatic tumors after RFA therapy. However, the RFA-induced immune responses are not sufficient to prevent tumor recurrence. The underlying mechanisms remain obscure.

Programmed death-ligand 1 (PD-L1), an important immune checkpoint molecule, is often up-regulated on tumor cells and tumor associated myeloid cells. It impairs T cell-mediated immune responses upon engagement with its cognate co-inhibitory receptor PD-1, which is always highly expressed on tumor-infiltrating lymphocytes. PD-L1 expression can be induced by pro-inflammatory cytokines, especially type I interferon (IFN), as an important self-limiting mechanism to prevent rampant autoimmunity. Recent studies show that PD-L1 expression on tumor cells is associated with T cell infiltration, suggesting PD-L1 is actively involved in suppressing antitumor immune responses in the tumor microenvironment (TME). Whether the PD-L1/PD1 axis is involved in modulating the antitumor T cell immune responses induced by RFA is unclear.

The objective of this investigation was to study the RFA-induced immune responses in tumor tissues from cancer patients.