Tumor-infiltrating lymphocytes and hepatocellular carcinoma: Pathology and clinical management

The presence of tumor-infiltrating lymphocytes (TILs) in hepatocellular carcinoma (HCC) is relatively rare. The prognosis of patients with HCC and marked TILs is better than that of patients with HCC without TILs. TILs in HCC tissues are mainly T cells, and previous reports suggested that TILs might be important antitumor effector cells. TILs have been extensively analyzed, and subpopulations of CD3⁺, CD4⁺, and CD8⁺ T cells are often present in HCC. Some studies have reported that the percentage of CD8⁺ T cells, which might have cytotoxic activity, is decreased in tumors with TILs, as compared with noncancerous tissues. Although the antitumor effects of TILs seem to be impaired in HCCs, the underlying mechanism has remained unclear until quite recently. Pathological and in vitro studies have now shown that regulatory T cells play important roles in the deterioration of the antitumor effects of TILs. The aim of this review is to introduce recent pathological findings for TILs in HCC and to evaluate new therapeutic strategies in this field.