Local Single-Dose Radiation Improves Adoptive Cell Therapy With Tumor-Infiltrating Lymphocytes

The potential for radiation therapy (RT) to enhance adoptive cell therapy (ACT) with tumor-reactive T cells has not been fully explored. This study evaluated combining RT with ACT, applying RT at two critical time points: (1) before tumor resection to improve ex vivo expansion of tumor-infiltrating lymphocytes (TIL) and (2) on the day of ACT using antigen-specific T cells to enhance T cell infiltration after transfer.

Using a murine human papillomavirus (HPV)-positive head and neck squamous cell carcinoma (HNSCC) model, we administered single-dose RT (8 Gy × 1) 5 days before tumor resection. RNA sequencing was performed to measure chemokine expression post-RT. Tumor fragments were cultured in interleukin-2 (IL-2) for TIL expansion, and TIL reactivity was assessed through cytokine production assays. Tumor-bearing mice were treated with ACT with TIL expanded from untreated or RT-treated tumors. In additional experiments, we assessed whether RT given in combination with ACT could improve infiltration of T cells and antitumor activity.

RT preconditioning significantly enhanced ex vivo TIL expansion (96% vs 74%; P < .05) and increased tumor necrosis factor α (TNF-α) production (P = .03), indicating improved reactivity. RT also significantly increased the expansion of TNF-α + GzmB + CD8 + TILs (P = .02), suggesting enhanced polyfunctionality within a cytotoxic subset. RNA sequencing revealed upregulation of chemokines (eg, CCL21 and CXCL10) and their receptors (CCR7 and CXCR4), supporting enhanced TIL recruitment. ACT with TIL from RT-preconditioned tumors demonstrated superior tumor control, with 50% of mice achieving complete tumor regression (CR) compared with 12.5% in controls. RT on the day of ACT increased T cell infiltration into tumor and improved tumor rejection compared with mice receiving either ACT or RT alone.

RT at two distinct time points-before tumor resection to enhance TIL expansion and on the day of ACT to boost T cell infiltration-significantly improves the efficacy of ACT. These findings highlight the potential for combining RT with ACT to enhance therapeutic outcomes in metastatic disease.