GDF15 and head and neck squamous cell carcinoma: A comprehensive workflow illustrating the coculture, conditioned medium transfer, and neutrophil functional assays is provided in Fig. S10F. Flow cytometric analysis showed that the expression of neutrophil activation markers CD154 and CD95 was increased in HNSCC cells after exposure to GDF15 or CAF culture medium, which was reversed by TNF-α neutralization (Fig. S10G).