HER2-specific synthetic antigen receptor T cell therapy synergizes with radiotherapy to provide improved antitumor efficacy in non-small cell lung cancer

In non-small cell lung cancer (NSCLC), radiotherapy not only mediates cytotoxicity but also activates radioresistance drivers like HER2. We investigated radiotherapy combined with HER2-targeted T cell therapy in an NSCLC model. The antitumor efficacy of radiotherapy and engineered T cells expressing a DAP12-associated synthetic antigen receptor (SAR) targeting HER2 was evaluated in HER2-expressing A549 xenografts. HER2 modulation, transcriptional regulation, and tumor T cell infiltration were assessed using immunoblotting, real-time quantitative polymerase chain reaction, flow cytometry, RNA-seq, and immunohistochemistry. High-dose HER2-SAR T cell infusion abolished A549 tumor growth but induced graft-vs-host disease. Low-dose T cell infusion was well-tolerated and provided partial tumor inhibition. Induction radiotherapy (7 d before T cell infusion) synergistically improved tumor control and survival. Radiotherapy transiently upregulated HER2 expression (4 to 24 h), though administering HER2-SAR T cells within this window did not enhance antitumor efficacy. Radiation did not enhance T cell-mediated cytotoxicity in vitro. However, in tumors, radiotherapy increased intratumoral proliferation and accumulation of HER2-SAR T cells and enhanced the extrinsic apoptotic pathway, including induction of Fas transcript and protein levels and cleaved caspase-3 (CC3). RNA-seq of irradiated tumors revealed lasting transcriptional reprogramming with increased immune activation and decreased proliferation and oncogenic signaling. Induction radiotherapy enhances HER2-SAR T cell infiltration and provides synergistic tumor suppression, likely through additional activation of immune-mediated apoptosis. These findings support further assessment of HER2-SAR T cell therapy in HER2-expressing NSCLC.