Squamous Cell Carcinomas Escape Immune Surveillance via Inducing Chronic Activation and Exhaustion of CD8+ T Cells co-expressing PD-1 and LAG-3 Inhibitory Receptors
Ameet K. Mishra1, Tanya Kadoishi1, Xiaoguang Wang1, Emily Driver2, Zhangguo Chen1, Xiao-Jing Wang2, Jing H. Wang1,*
1Department of Immunology and Microbiology, 2Department of Pathology, University of Colorado, Anschutz Medical Campus, Aurora, CO 80045
Squamous cell carcinoma (SCC) is the second commonest type of skin cancer. Moreover, about 90% of head and neck cancers are SCCs. It remains largely unknown how SCCs evade immune recognition. Here, we established a mouse model by injecting tumor cells derived from primary SCCs harboring KrasG12D mutation and Smad4 deletion into wild-type (wt) or CD8-/- recipients. We found comparable tumor growth between wt and CD8-/- recipients, indicating a complete escape of CD8+ T cell-mediated anti-tumor responses by these SCCs. Mechanistically, CD8+ T cells were not defective in infiltrating tumors given their relatively increased percentage among tumor infiltrating lymphocytes (TILs). CD8+ TILs exhibited phenotypes of chronic activation and exhaustion, including overexpression of activation markers, co-expression of programmed death 1 (PD-1) and lymphocyte activation gene-3 (LAG-3), as well as TCRb downregulation. Among CD4+ TILs, T regulatory cells (Tregs) were preferentially expanded. Contradictory to prior findings in melanoma, Treg expansion was independent of CD8+ T cells in our SCC model. Unexpectedly, CD8+ T cells were required for promoting NK cell infiltration within SCCs. Furthermore, we uncovered AKT-dependent lymphocyte-induced PD-L1 upregulation on SCCs, which was contributed greatly by combinatorial effects of CD8+ T and NK cells. Lastly, dual blockade of PD-1 and LAG-3 inhibited the tumor growth of SCCs. Thus, our findings identify novel immune evasion mechanisms of SCCs and suggest that immunosuppressive mechanisms operate in a cancer-type specific and context-dependent manner.