Stimulator of interferon genes agonist augmented antitumor immunity of osimertinib in <i>Egfr</i> ‐mutated lung cancer

Epidermal growth factor receptor (EGFR)-mutant non-small-cell lung cancers (NSCLCs) lack effective immunotherapy due to a noninflamed tumor microenvironment (TME). We previously reported that EGFR tyrosine-kinase-inhibitor (TKI) induced CD8+ T-cell immunity, which was insufficient for tumor eradication. We evaluated the potential of combining EGFR-TKI with stimulator of interferon genes (STING) agonists in activating a systemic antitumor response. Using a syngeneic mouse model of genetically engineered Egfr-mutant NSCLC, we evaluated the antitumor effects of STING agonist ADU-S100, alone and combined with osimertinib. Immunohistochemistry and flow cytometry were used to assess the TME. Osimertinib alone enhanced CD8+ T-cell infiltration but not Natural Killer (NK) cell infiltration. ADU-S100 injection alone modestly suppressed tumor growth with increasing CD8+/NK cell infiltration in the TME, but lacked an abscopal effect. Combining ADU-S100 with osimertinib significantly enhanced the antitumor effects and CD8+/NK cell infiltration. Depletion of either CD8+ or NK cells reduced the combination effect. Crucially, the combination induced an abscopal effect accompanied by PD-1+/CD8+ cell infiltration. Combining osimertinib with a STING agonist augmented innate and adaptive immunity, inducing systemic antitumor responses in EGFR-mutant NSCLC.