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. Mishra 1 , Tanya Kadoishi 1 , Xiaoguang Wang 1 , Emily Driver 3 , Zhangguo Chen 1, 2 , Xiao-Jing Wang 3 , Jing H. Wang 1, 2 1 Department of Immunology and Microbiology, University of Colorado, Anschutz Medical Campus, Aurora, CO 80045, USA 2 Department of Biomedical Research, National Jewish Health, Denver, CO 80206, USA 3 Department of Pathology, University of Colorado, Anschutz Medical Campus, Aurora, CO 80045, USA Correspondence to: Jing H. Wang, email: jing.wang@ucdenver.edu Keywords: squamous cell carcinoma, immune evasion, PD-1, LAG-3, Smad4 loss Received: July 14, 2016 Accepted: October 28, 2016 Published: November 09, 2016 ABSTRACT Squamous cell carcinoma (SCC) is the second commonest type of skin cancer. Moreover, about 90% of head and neck cancers are SCCs. SCCs develop at a significantly higher rate under chronic immunosuppressive conditions, implicating a role of immune surveillance in controlling 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 Kras G12D 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 apparently 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 cell death 1 (PD-1) and lymphocyte activation gene-3 (LAG-3), as well as TCRβ 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.