Immune checkpoint blockade therapies for HCC: current status and future implications

Abstract

Hepatocellular carcinoma (HCC) is the most lethal and common type of liver cancer with limited treatment options at the advanced stage. The use of immune checkpoint inhibitor (ICI) based immunotherapy is exponentially increasing in the treatment of patients with advanced solid tumors. The expression of immune checkpoints on tumor cells leading to lower activity of T-cells is one of the major mechanisms of immune escape. Checkpoint blockade immunotherapies with antibodies against PD-1, PD-L1 or CTLA-4 are being investigated in clinical trials in HCC patients. ICIs have improved survival in patients with inoperable advanced stage HCC where other curative treatments are not applicable. However, the response rates remain low with only a small subset of patients responding to this therapy. There is an unmet need to identify predictive markers to select those HCC patients who would benefit from ICI therapies. Importantly, epithelial-to-mesenchymal transition (EMT), a major process driving HCC invasion and metastasis by regulating the phenotypic cellular switching from epithelial to mesenchymal state, has been implicated as a resistance mechanism associated with ICI therapies. The role of EMT as a regulator of immune checkpoint molecule in HCC is just emerging. However, the consequence of EMT as a resistance mechanism in HCC patients undergoing ICI treatments remains unexplored. In this review, we summarize the recent clinical studies with ICIs in HCC and highlight the trials underway featuring novel monotherapies and combinatorial approaches based on immune and non-immune therapies. We will discuss the ongoing efforts to discover new immune checkpoint molecules in HCC as potential drug targets. We also highlight the role of EMT in facilitating therapy resistance in HCC treated with ICIs and discuss potential strategies to circumvent resistance in ICI treated HCC patients.