Transcriptional profiling of tumor-specific CD8 T cells shows contribution of TIGIT to T cell exhaustion in liver cancer

Hepatocellular carcinoma (HCC) is the second leading cause of cancer-related death and the fifth most common kind of cancer worldwide. This cancer has a 5-year survival rate of 10% and its increasing incidence requires the development of efficacious treatments against HCC. Recent advances in immunotherapy demonstrated its capability in treatment of cancer, but there is still potential for further development of immunotherapies against liver cancer. Immune responses against cancer are often hampered by upregulation of co-inhibitory receptors on the surface of CD8 T cells. This inhibition leads to emergence of T cell exhaustion, where tumor-infiltrating lymphocytes (TILs) show a reduced proliferative capacity and low production of effector cytokines IFNγ and TNFα, a mechanism that impedes tumor rejection by CD8 T cells. We have utilized the Sleeping beauty" (SB) and transposon system for the development of an autochtonous HCC mouse model. Using adoptive T cell transfer allowed us in-depth phenotyping of tumor-specific CD8 T cells and we could demonstrate pronounced upregulation of co-inhibitory receptors PD-1, TIM-3, CD160, LAG-3, 2B4 on T cell surface. The tumor-specific CD8 T cells also showed a reduced cytokine production and degranulation capacity, indicating the emergence of T cell exhaustion. In order to elucidate the molecular cause of tumor-induced T cell exhaustion we have performed the first whole transcriptome microarray analysis of tumor-specific CD8 T cells in a murine autochthonous liver cancer model, that allowed us to compare the mRNA profiles of naive, functional effector and exhausted tumor-specific CD8 T cells. The comprehensive transcriptomic data represents a means for the identification of candidate genes and pathways that play a role in T cell exhaustion. Particularly, the substantial upregulation of TIGIT suggested the involvement of this inhibitory T cell receptor in T cell exhaustion in liver cancer. Utilization of immune checkpoint-blockade against TIGIT in combination with PD-1 inhibition prolonged survival of tumor-bearing mice, compared to single inhibition of PD-1. We could further verify the expression of TIGIT on tumor-infiltrating CD8 T cells in patients with liver cancer. Our results suggest that TIGIT is involved in the appearance of T cell exhaustion in human liver cancer and presents a potential target for combination treatment by immune checkpoint blockade.