Since 4-nitroquinoline 1-oxide (4NQO)-induced premalignant oral lesions and oral cancer share expression of a number of tumor antigens [31], studies were conducted to determine if treating premalignant lesion-bearing mice with PD-1 antibody would stimulate reactivity of their lymph node cells to an in vitro challenge of premalignant lesions or HNSCC. Here, PDCD1 is linked to head and neck squamous cell carcinoma.