Background Targeting immunosuppressive checkpoints has proven to be an efficacious treatment strategy for non-small cell lung cancer (NSCLC), in which response rates are as high as 35% in patients harboring Kras/p53 (KP) mutations.1 However, most patients demonstrate no or only partial response to immune checkpoint blockade (ICB), underscoring the need to better understand the suppressive mechanisms in the tumor-immune microenvironment. Murine models of KP mutant lung cancer demonstrate upfront sensitivity to PD-1 checkpoint blockade but rapidly acquire resistance2, providing useful tools to discover tumor-intrinsic mechanisms of resistance.
Methods We generated new KP syngeneic and autochthonous lung tumor models with intrinsic resistance to anti-PD-1 treatment via in vivo passaging in the face of ICB treatment. Additionally, we analyzed transcriptome data from anti-PD-L1 treated KP tumors, identified differentially expressed genes between response and resistance timepoints, and queried these in the newly generated anti-PD-1 resistant tumor models. We utilized flow cytometry to characterize the tumor-infiltrating immune microenvironment with manipulation of candidate gene expression.
Results Our data identified a stable upregulation of the phosphodiesterase enzyme, autotaxin (ATX), and the metabolite that it generates, lysophosphatidic acid (LPA), in ICB resistant tumors. Analyses of lung adenocarcinoma patient datasets revealed a significant positive correlation between ATX and immune signatures, including a previously published dataset encompassing immune checkpoints and suppressive molecules3, suggesting that ATX is upregulated in the face of normal anti-tumor immunity. Mechanistic studies utilizing isogenic pairs of tumors demonstrated that ATX expression inversely correlated with CD8+ T cell proliferation and cytotoxic functionality, with ATX-overexpression in anti-PD-1 sensitive tumors promoting intrinsic resistance. We next sought to define LPA receptor (LPAR) expression on T cells. Flow cytometry on tumor-infiltrating CD8+ T cells demonstrated significantly altered expression of LPARs within anti-PD-1 resistant versus sensitive tumors, with upregulation of LPAR5 and downregulation of LPAR2. Additionally, analysis of previously published RNA-sequencing of CD8+ T cells from NSCLC patients4 revealed that lower LPAR2 versus LPAR5 correlated with worse response to ICB. Importantly, targeting ATX or LPAR5 with PD-1 blockade caused significant tumor regressions in clinically relevant models of KP mutant lung cancer via invigoration of anti-tumor CD8+ T cells.
Conclusions Our data indicate that increased ATX/LPA activity occurs downstream of immune activation, which in turn stimulates LPAR5 signaling on CD8+ T cells to diminish cytolytic functions. These results provide evidence that this axis acts as an immunosuppressive checkpoint, providing rationale that co-targeting it with ICB should improve anti-tumor immune response.
Skoulidis F, Goldberg ME, Greenawalt DM, et al. STK11/LKB1 Mutations and PD-1 Inhibitor Resistance in KRAS-Mutant Lung Adenocarcinoma. Cancer Discovery 2018:CD-18-0099.
Chen L, Diao L, Yang Y, et al. CD38-mediated immunosuppression as a mechanism of tumor cell escape from PD-1/PD-L1 blockade. Cancer Discovery 2018.
Lou Y, Diao L, Cuentas ER, et al. Epithelial-mesenchymal transition is associated with a distinct tumor microenvironment including elevation of inflammatory signals and multiple immune checkpoints in lung adenocarcinoma. Clinical Cancer Research : an Official Journal of the American Association For Cancer Research 2016;22:3630-42.
Trefny MP, Rothschild SI, Uhlenbrock F, et al. A Variant of a Killer Cell Immunoglobulin-like Receptor Is Associated with Resistance to PD-1 Blockade in Lung Cancer. Clinical Cancer Research 2019;25:3026–34.
Ethics Approval All animal studies were completed under the approval of the University of Texas MD Anderson Cancer Center Institutional Animal Care and Use Committee (protocol# 1271).
Statistics from Altmetric.com
If you wish to reuse any or all of this article please use the link below which will take you to the Copyright Clearance Center’s RightsLink service. You will be able to get a quick price and instant permission to reuse the content in many different ways.