Dysfunction of CD8⁺ T cells around tumor cells leads to occult lymph node metastasis in NSCLC patients

Occult lymph node metastasis (OLNM) is one of the main causes of regional recurrence in inoperable N₀ non-small cell lung cancer (NSCLC) patients following stereotactic ablation body radiotherapy (SABR) treatment. The integration of immunotherapy and SABR (I-SABR) has shown preliminary efficiency in mitigating this recurrence. Therefore, it is necessary to explore the functional dynamics of critical immune effectors, particularly CD8⁺ T cells in the development of OLNM. In this study, tissue microarrays (TMAs) and multiplex immunofluorescence (mIF) were used to identify CD8⁺ T cells and functional subsets (cytotoxic CD8⁺ T cells/predysfunctional CD8⁺ T cells (CD8⁺ T_predys)/dysfunctional CD8⁺ T cells (CD8⁺ T_dys)/other CD8⁺ T cells) among the no lymph node metastasis, OLNM, and clinically evident lymph node metastasis (CLNM) groups. As the degree of lymph node metastasis escalated, the density of total CD8⁺ T cells and CD8⁺ T_dys cells, as well as their proximity to tumor cells, increased progressively and remarkably in the invasive margin (IM). In the tumor center (TC), both the density and proximity of CD8⁺ T_predys cells to tumor cells notably decreased in the OLNM group compared with the group without metastasis. Furthermore, positive correlations were found between the dysfunction of CD8⁺ T cells and HIF-1α⁺CD8 and cancer microvessels (CMVs). In conclusion, the deterioration in CD8⁺ T cell function and interactive dynamics between CD8⁺ T cells and tumor cells play a vital role in the development of OLNM in NSCLC. Strategies aimed at improving hypoxia or targeting CMVs could potentially enhance the efficacy of I-SABR.