Several receptors, including cytotoxic T lymphocyte associated protein-4 (CTLA-4), lymphocyte-activation gene-3 (LAG-3), T cell immunoglobulin mucin protein-3 (TIM-3), and PD-1, have been identified on exhausted and dysfunctional lymphocytes and are upregulated in cell lines of multiple tumor types, including HNSCC8, 11. Here, PDCD1 is linked to neoplasm.