Background
Checkpoint blockade therapy (CBT) can effectively treat lung tumors; however, only 30% of lung cancer patients respond to CBT [1]. Clinical data showed that patients with low T cell infiltration in the tumor microenvironment (TME) respond poorly to CBT [2]. Gaining insight into the molecular and immunological mechanism that impact the entry of CD8 T cells into the TME will enable the development of innovative therapeutic approaches that can be used in combination to effectively treat individuals with cancer. Using a T cell gene signature, we segregated NSCLC patients into T cell-infiltrated and non-T cell-infiltrated and found that Sox2 upregulation correlates with a lack of T cell infiltration. Here we aimed to investigate how high expression of Sox2 in tumors mediates immune evasion in NSCLC.
Methods
We overexpressed Sox2 in a mouse lung adenocarcinoma cell line driven by KrasG12D/+ and Tp53-/-. SOX2-positive (KPS2) and control (KPCt) tumor cells were inoculated subcutaneously or via tail vein injection to induce lung metastasis. We treated tumors with anti-PD-L1 and anti-CTLA-4 blocking antibodies and analyzed for tumor burden. T cell infiltration was evaluated by fluorescence microscopy. KPCt and KPS2 cell lines were engineered to express the model antigen SIY to characterize tumor-specific T-cell responses. Regulatory T cells were targeted by systemic depletion using the Foxp3.DTR mouse model or via neutralization of DKK1 using the mDKN-01 antibody. Finally, we assessed the therapeutic benefit of combining anti-DKK1 treatment with CBT to treat SOX2 tumors.
Results
We found that Sox2 overexpression induces resistance to CBT mediated by CD8 T cell exclusion from the tumor core. Analysis of tumor-reactive T cells indicated that T cell priming and differentiation into cytotoxic effector T cells were unaffected. However, cytotoxic CD8 T cells failed to infiltrate KPS2 tumors while enriched in the peritumoral regions. Interestingly, we found a high density of regulatory T cells in the peritumoral area. Depletion of regulatory T cells significantly improved the activation of the tumor vasculature and the infiltration of cytotoxic CD8 T cells into the tumor core. Furthermore, we showed that combining a neutralizing antibody against DKK1 with CBT significantly reduced the density of regulatory T cells in the TME, increased CD8 T cell infiltration, and improved tumor control.
Conclusions
Our results show that tumor cell-intrinsic activation of Sox2 in NSCLC promotes immune evasion and contributes to immunotherapy resistance by retaining effector CD8 T cells outside of the tumor mass.
Acknowledgements
This work was supported by NCI K99/R00 award, the Ludwig Center at MIT, the SITC-Nektar Therapeutics Equity and Inclusion in Cancer Immunotherapy Fellowship, and Leap Therapeutics Inc.
References
Hellmann, M. D., Paz-Ares, L., Bernabe Caro, R., Zurawski, B., Kim, S. W., Carcereny Costa, E., Park, K., Alexandru, A., Lupinacci, L., de la Mora Jimenez, E., Sakai, H., Albert, I., Vergnenegre, A., Peters, S., Syrigos, K., Barlesi, F., Reck, M., Borghaei, H., Brahmer, J. R., O’Byrne, K. J., Geese, W. J., Bhagavatheeswaran, P., Rabindran, S. K., Kasinathan, R. S., Nathan, F. E. & Ramalingam, S. S. Nivolumab plus Ipilimumab in Advanced Non-Small-Cell Lung Cancer. N Engl J Med 2019;381, 2020–2031, doi:10.1056/NEJMoa1910231.
Chen, D. S. & Mellman, I. Elements of cancer immunity and the cancer-immune set point. Nature 2017;541, 321–330, doi:10.1038/nature21349.
Ethics Approval
All mouse experiments were approved by MIT’s Committee on Animal Care (CAC) – PHS Animal Welfare Assurance # D16–00078 (A3125–01).