High-Sensitivity PD-L1 Staining Using Clone 73-10 Antibody and Spatial Transcriptomics for Precise Expression Analysis in Non-Tumorous, Intraepithelial Neoplasia, and Squamous Cell Carcinoma of Head and Neck.

Purpose: While immune checkpoint inhibitors (ICIs) targeting the PD-1/PD-L1 axis have improved outcomes in head and neck squamous cell carcinoma (HNSCC), eligibility criteria based on immunohistochemistry (IHC) target PD-1 solely. We aimed to evaluate the PD-L1 (CD274) expression using highly sensitive clone 73 - 10 and spatial transcriptomics (ST) analysis to elucidate the role of PD-L1 in HNSCC and thus potentially expand the pool of eligible patients.

Methods: Immunohistochemical staining of 73 - 10, CD3, CD4, and CD8 were performed in 94 HNSCC clinical samples along with paired adjacent squamous intraepithelial neoplasm (SIN) and normal oral mucosa (NOM) samples. The 73 - 10 positivity was evaluated using a tumor cell score ≥ 1%, and the results were analyzed against clinicopathological features including CD4⁺ and CD8⁺ tumor-infiltrating lymphocytes (TILs), and clinical outcomes. Furthermore, ST and PD-L1 related pathway analysis was performed in 6 paired HNSCC, SIN and NOM samples.

Results: The 73 - 10 detected-PD-L1 positivity was high in HNSCC (79%) compared to SIN (10%) and NOM (3%). 73 - 10⁺ correlated with high CD4⁺ TILs, as well as the independent prognostic factor of OS, DSS, and PFS of HNSCC (all p < 0.05). ST analysis revealed that the upregulated distribution of CD274 correlated with 73 - 10 positivity. Pathway analysis revealed a significant upregulation of CD274 and CD4 in HNSCC compared to SIN and NOM, and HIF-1α and IFN-γ as key regulators of PD-L1 expression in HNSCC.

Conclusion: Clone 73 - 10 is a relatively suitable candidate for identifying patients with PD-L1 expression eligible for ICI therapy. It demonstrates high sensitivity in detecting PD-L1 (CD274) in HNSCC, offering immunological and prognostic insights.