Immunobiology of hepatocarcinogenesis: Ways to go or almost there?

Abstract

Hepatocellular carcinoma is on the rise and occurs in the setting of chronic liver disease and cirrhosis. Though treatment modalities are available, mortality from this cancer remains high. Medical therapy with the utilization of biologic compounds such as the Food and Drug Administration approved sorafenib might be the only option that can increase survival. Immunotherapy, with modern pharmacologic developments, is a new frontier in cancer therapy and therefore the immunobiology of hepatocarcinogenesis is under investigation. This review will discuss current concepts of immunobiology in hepatocarcinogenesis along with current treatment modalities employing immunotherapy. The tumor microenvironment along with a variety of immune cells coexists and interplays to lead to tumorigenesis. Tumor infiltrating lymphocytes including CD8(+) T cells, CD4(+) T cells along with regulatory T cells, tumor associated macrophages, tumor associated neutrophils, myeloid derived suppressor cells, and natural killer cells interact to actively provide anti-tumor or pro-tumor effects. Furthermore, oncogenic pathways such as Raf/mitogen-activated protein kinase/extracellular-signal-regulated kinase pathway, phosphatidyl-3-kinase/AKT/mammalian target or rapamycin, Wnt/β-catenin, nuclear factor-κB and signal transducers and activators of transcription 3 may lead to activation and proliferation of tumor cells and are also considered cornerstones in tumorigenesis. Immunotherapy directed at this complex milieu of cells has been showned to be successful in cancer treatment. The use of vaccines, adoptive cell therapy and immune checkpoint inhibitor modulation are current options for therapy. Further translational research will shed light to concepts such as anti-tumor immunity which can add another alternative in the therapeutic armamentarium.

Keywords: Adoptive cell therapy; Hepatocarcinogenesis; Hepatocellular carcinoma; Immune checkpoint inhibitors; Immunobiology; Immunology; Immunotherapy; Tumorigenesis.

Figure 1

Mechanisms leading to CD8⁺ T cell suppression. Failure of CD8⁺ T cells to kill tumor cells involves signals from multiple cells including MDSC, T_reg, and TAMs. The interaction of PD-L1 with PD-1 on the CD8⁺ T cell causes suppression and decrease in its effector function leading to decreased tumor cell death. Furthermore, the Galectin-9 and TIM-3 interaction on MDSC’s and IL-10 secretion by T_reg cause a similar effect. PD-1: Programmed death 1; IL: Interleukine; TAM: Tumor associated macrophages; MDSC: Myeloid derived suppressor cells; TIM-3: T-cell immunoglobulin and mucin-domain containing-3; T_reg: Regulatory T cells.

Figure 2

Differentiation of naïve T cells. The Th0 T cell can differentiate into a variety of CD4⁺ cells based on stimulatory signals as seen above. TGF-β: Transforming growth factor beta; IFN-γ: Interferon gamma; IL: Interleukine; T_reg: Regulatory T cells.