Distinct T-cell subsets as drivers of response to different neoadjuvant treatments in esophageal squamous cell carcinoma.

2638 Background: The optimal integration of immunotherapy with chemoradiotherapy (CRT) in the neoadjuvant treatment of esophageal squamous cell carcinoma (ESCC) remains unclear, largely due to limited mechanistic insight into immune determinants of response. Methods: we performed paired single-cell RNA and TCR sequencing of ESCC tumor samples collected before and after treatment across three neoadjuvant modalities—immunochemotherapy (NICT), chemoradiotherapy (NCRT), and immuno-chemoradiotherapy (NICRT)—to dissect intratumoral CD8 + T cell dynamics. Results: We identified two distinct immune response programs. In NICT responders, pre-existing immunoresponsive CXCL13 + PD-1 + CD8 + T cells underwent clonal expansion and transcriptional reprogramming into a less exhausted yet CXCL13+ progenitor-like state (CD8Tex_CXCR4), accompanied by the formation of tertiary lymphoid structures. Conversely, CRT responders exhibited depletion of the subset of CXCL13 + CD8 + T cells and enrichment of PD-1 - cytotoxic CD8Teff_NIBAN1 cells, which originated from the peripheral blood and were characterized by robust clonal expansion, high effector gene expression, and association with tumor regression. We validated the association of these two T cell subsets with distinct neoadjuvant modalities and treatment responses using public datasets and independent prospective cohorts encompassing NICT, NICRT, and NCRT. Mechanistically, conventional radiotherapy suppressed PD-1 + T cell expansion—even in the presence of ICB—while a sequential strategy of induction ICB followed by delayed radiotherapy preserved the process of clonal expansion in exhausted T cell populations and achieved superior tumor control in vivo. Conclusions: These findings reveal divergent CD8 + T cell–mediated immune programs driving response to neoadjuvant therapies in ESCC and identify CD8Teff_NIBAN1 as a key effector population following CRT. Our study provides mechanistic insight into ICB–radiotherapy interactions and supports the rational design of temporally optimized combination strategies in solid tumors.