Higher CtsL expression is observed in head and neck squamous cell carcinoma (HNSCC) tissues and is associated with immune dysregulation, increased infiltration of multiple immune cells (including CD8+ T cells, CD4+ T cells, B cells, neutrophils, macrophages, and DCs), and greater susceptibility to SARS-CoV-2 infection [148]. Here, CTSL is linked to head and neck squamous cell carcinoma.