Tu, Hsin-FangHsin-FangTuChun-Jung KoLee, Ching-TaiChing-TaiLeeLee, Cheng-FanCheng-FanLeeLan, Shao-WeiShao-WeiLanLin, Hsin-HsienHsin-HsienLinLin, Hsin-YingHsin-YingLinCHIA-CHI KULee, Der-YenDer-YenLeeI-CHUN CHENYA-HUI CHUANGDel Caño-Ochoa, FranciscoFranciscoDel Caño-OchoaRamón-Maiques, SantiagoSantiagoRamón-MaiquesCHAO-CHI HOMING-SHYUE LEEGEEN-DONG CHANG2021-11-172021-11-172021-06-1500085472https://scholars.lib.ntu.edu.tw/handle/123456789/586920Current clinical trials of combined EGFR-tyrosine kinase inhibitors (TKI) and immune checkpoint blockade (ICB) therapies show no additional effect. This raises questions regarding whether EGFR-TKIs attenuate ICB-enhanced CD8+ T lymphocyte function. Here we show that the EGFR-TKI afatinib suppresses CD8+ T lymphocyte proliferation, and we identify CAD, a key enzyme of de novo pyrimidine biosynthesis, to be a novel afatinib target. Afatinib reduced tumor-infiltrating lymphocyte numbers in Lewis lung carcinoma (LLC)-bearing mice. Early afatinib treatment inhibited CD8+ T lymphocyte proliferation in patients with non-small cell lung cancer, but their proliferation unexpectedly rebounded following long-term treatment. This suggests a transient immunomodulatory effect of afatinib on CD8+ T lymphocytes. Sequential treatment of afatinib with anti-PD1 immunotherapy substantially enhanced therapeutic efficacy in MC38 and LLC-bearing mice, while simultaneous combination therapy showed only marginal improvement over each single treatment. These results suggest that afatinib can suppress CD8+ T lymphocyte proliferation by targeting CAD, proposing a timing window for combined therapy that may prevent the dampening of ICB efficacy by EGFR-TKIs. SIGNIFICANCE: This study elucidates a mechanism of afatinib-mediated immunosuppression and provides new insights into treatment timing for combined targeted therapy and immunotherapy. GRAPHICAL ABSTRACT: http://cancerres.aacrjournals.org/content/canres/81/12/3270/F1.large.jpg.en[SDGs]SDG3afatinib; aspartate carbamoyltransferase; carbamoyl phosphate synthase; dihydroorotase; programmed death 1 ligand 1; protein carbamoyl phosphate synthetase 2; unclassified drug; afatinib; antineoplastic agent; caspase activated deoxyribonuclease; deoxyribjournal article10.1158/0008-5472.CAN-20-3436337718972-s2.0-85107904111https://scholars.lib.ntu.edu.tw/handle/123456789/567463