Here, we show that tumor ADORA1 deletion suppresses cell growth in human melanoma cell lines in vitro and tumor development in vivo in immune-deficient xenografts. However, this deletion induces the upregulation of PD-L1 levels, which inactivates cocultured T cells in vitro, compromises anti-tumor immunity in vivo, and reduces anti-tumor efficacy in an immune-competent mouse model. Functionally, PD-1 mAb treatment enhances the efficacy of ADORA1-deficient or ADORA1 antagonist-treated melanoma and NSCLC immune-competent mouse models. Mechanistically, we identify ATF3 as the factor transcriptionally upregulating PD-L1 expression. Tumor ATF3 deletion improves the effect of ADORA1 antagonist treatment of melanoma and NSCLC xenografts. We observe higher ADORA1, lower ATF3, and lower PD-L1 expression levels in tumor tissues from nonresponders among PD-1 mAb-treated NSCLC patients.
Keywords: PD-L1/PD-1; adenosine A1 receptor; adenosine signaling; cAMP-dependent transcription factor 3; combination therapy; immune checkpoint; immunotherapy; melanoma; non-small cell lung cancer; tumor microenvironment.
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