Intratumoral CD103⁺CD8⁺ T cells predict response to neoadjuvant chemoimmunotherapy in advanced head and neck squamous cell carcinoma

Immune cell heterogenicity is known to determine the therapeutic response to cancer progression. Neoadjuvant chemoimmunotherapy (NACI) has shown clinical benefits in some patients with advanced head and neck squamous cell carcinoma (HNSCC), but the underlying mechanism behind this clinical response is unknown. The efficacy of NACI needs to be potentiated by identifying accurate biomarkers to predict clinical responses. Here, we attempted to identify molecules predicting NACI response in advanced HNSCC.We performed combined single-cell RNA sequencing (scRNA-seq) and multiplex immunofluorescence (mIHC) staining with tumor samples derived from NACI-treated HNSCC patients to identify a new tumor-infiltrating cell (TIL) subtype, CD103+ CD8+ TILs, associated with clinical response, while both in vitro and in vivo assays were carried out to determine its antitumor efficiency. The regulatory mechanism of the CD103+ CD8+ TILs population was examined by performing cell-cell interaction analysis of the scRNA-seq data and spatial analysis of the mIHC images.We established intratumoral CD103+ CD8+ TILs density as a determinant of NACI efficacy in cancers. Our scRNA-seq results indicated that the population of CD103+ CD8+ TILs was dramatically increased in the responders of NACI-treated HNSCC patients, while mIHC analysis confirmed the correlation between intratumoral CD103+ CD8+ TILs density and NACI efficacy in HNSCC patients. Further receiver operating characteristic curve analysis defined this TIL subset as a potent marker to predict patient response to NACI. Functional assays showed that CD103+ CD8+ TILs were tumor-reactive T cells, while programmed cell death protein-1 (PD-1) blockade enhanced CD103+ CD8+ TILs cytotoxicity against tumor growth in vivo. Mechanistically, targeting the triggering receptor expressed on myeloid cells 2-positive (TREM2+ ) macrophages might enhance the population of CD103+ CD8+ TILs and facilitate antitumor immunity during NACI treatment.Our study highlights the impact of intratumoral CD103+ CD8+ TILs density on NACI efficacy in different cancers, while the efforts to elevate its population warrant further clinical investigation.