Postdoctoral Fellow Earle A. Chiles Res. Inst., Providence Cancer Inst., Oregon, United States
Disclosure(s):
David Friedman, PhD: No financial relationships to disclose
Introduction/Rationale: Radiation therapy is a potent local cancer treatment but depletes intratumoral CD8 T cells. Despite this, tumors rapidly refill with T cells post-treatment. The source and activation mechanisms of these repopulating T cells remain unclear. Understanding early recruitment and differentiation is critical to optimizing radiation-immunotherapy combinations.
Methods: We used Kaede photoconvertible mice to track CD8 T cells migrating from tumor-draining lymph nodes (TdLN) to irradiated tumors. Tumors were implanted subcutaneously and treated with CT-guided radiation (2–12Gy) using the SARRP. Photoconversion was performed by targeted 405nm light exposure to TdLN prior to radiation. CD8 T cell activation and phenotype were assessed by flow cytometry and scRNA-seq. Mechanistic studies used IFNAR1-/-, Sting-/-, and cGAS-/- mice, and adoptive transfer of antigen-specific 2C T cells. Fractionation effects and IFN signaling were evaluated using knockout models and RNA-seq datasets.
Results: TdLN-derived CD8 T cells preferentially migrated to irradiated tumors and rapidly upregulated CD69 independent of antigen specificity. Activation was mediated by type I IFN signaling triggered by cGAS in irradiated cancer cells. CD69 expression was dose-dependent and enriched in progenitor exhausted T cells. scRNA-seq revealed a shift toward stem-like and proliferating subsets post-radiation. Antigen-specific CD8 T cells also migrated and acquired exhaustion markers upon tumor entry, but their recruitment was not increased by radiation. Fractionated radiation (e.g., 2Gy ×3) induced similar CD69 upregulation at higher single doses.
Conclusion: Radiation induces early, non-specific activation of newly recruited CD8 T cells via type I IFN, shaping the tumor immune environment before antigen-specific expansion. These findings highlight the role of TdLN-derived T cells and suggest that radiation timing and dose critically influence immune synergy.
