CXCL13 and head and neck squamous cell carcinoma: On the other hand, the single cell RNA sequence (scRNA-seq) analysis of the HNSCC patients (primary tumor) by Puram et al. (2017) revealed the presence of CD8 + cytotoxic killer T cells, CD4 + helper T cells, CD4 + CD25 + regulator T cells, and CxCL13 + exhausted T cells [34].