Cellular immune responses to hepatocellular carcinoma: lessons for immunotherapy

Hepatocellular carcinoma (HCC) is the fifth most common cancer worldwide, with a continuously high mortality. Thus, the development of new therapeutic strategies is crucial to decrease recurrence rates and to improve the overall survival rates of HCC patients. The rationale for immunotherapy is based on the findings of several studies showing specific CD8(+) T-cell responses against various tumor-associated antigens (TAAs) in HCC patients and a clinical benefit of T-cell infiltration in the tumor tissue. However, the impact of TAA-specific CD8(+) T-cell responses on tumor control seems to be rather weak. Several different mechanisms contribute to the failure of the cellular immune response and will be summarized in this review. The aim of immune-based therapies is to overcome these mechanisms of T-cell failure and to induce or boost TAA-specific CD8(+) and CD4(+) T-cell responses. Several preclinical and clinical studies of immune-based therapeutic approaches show encouraging results and will be discussed in this review.