Immune control in hepatocellular carcinoma development and progression: role of stromal cells

Immune control of hepatocellular carcinoma (HCC) is executed by effector immune cells, which efficiently eliminate malignant transformed cells. However, progression of HCC clearly documents failure of tumor immune control, which led to the concept of immune subversion by the tumor environment.Particularly tumor-associated stromal cells cooperate within an inflammatory network, which is responsible for immune privilege. The stromal cell composition matures during tumor growth and is derived from surrounding noncancerous tissue or from circulating cells recruited to the tumor site. Therefore, immunosuppressive stromal cells represent heterogeneous cell lineages, including myeloid cells, lymphocytes, endothelial cells, and fibroblasts, which interact by direct cell contact, secretion of soluble factors, or production of extracellular matrix. As the stromal cells determine tumor immune control and clinical outcome of HCC, they represent a promising target for cancer immunotherapy.