SELL and head and neck squamous cell carcinoma: Based on the high-resolution T/NK cell map in HNSCC, we identified four distinct CD4+ T cell clusters including naïve CD4+ T (CD4+ Tn) cells (SELL+), Tfh cells (CXCR5+), Th17 cells (CCL20+), and regulatory T (Treg) cells (FOXP3+).