TGF-β Inhibitor Potentiates Osimertinib-Induced Anti-Tumor Immunity in Egfr-Mutant Lung Cancer

Immunotherapy for epidermal growth factor receptor (EGFR)-mutated non-small cell lung cancer (NSCLC) remains challenging. We previously found that EGFR-tyrosine kinase inhibitors induced antitumor immunity but also triggered immunosuppressive cytokines, including transforming growth factor-β (TGF-β), in Egfr-mutant lung cancer. Here, we investigate whether TGF-β inhibition potentiates osimertinib-induced antitumor immunity using a syngeneic mouse model of Egfr-mutated lung cancer, with cancer cells subcutaneously transplanted into wild-type C57BL/6J mice. We evaluated the antitumor effect of the combination therapy with osimertinib and either nintedanib (an indirect TGF-β inhibitor) or vactosertib (a specific TGF-β type I receptor kinase inhibitor). Changes in the tumor microenvironment during treatment were assessed using immunohistochemical staining, western blot analysis, and flow cytometry. We found that TGF-β expression was upregulated in the tumor treated with osimertinib. Nintedanib monotherapy showed no significant antitumor effect, whereas osimertinib combined with nintedanib significantly potentiates the antitumor effect compared with osimertinib monotherapy in vivo. Crucially, no additive effect of nintedanib on osimertinib monotherapy was observed in vitro. Combination therapy with osimertinib and nintedanib significantly increased effector T cells (CD8+CD44+CD62L−) and Granzyme B+ areas and decreased CD206+ cells, while significantly decreasing TGF-β and SMAD2/3 expression. Similar effects were observed with vactosertib but not with a vascular endothelial growth factor receptor 2 inhibitor. In conclusion, combination therapy with osimertinib and TGF-β inhibitors potentiates osimertinib-induced antitumor immunity. These findings highlight a novel therapeutic strategy for EGFR-mutated NSCLC and warrant further clinical investigation.