Increased PD-1⁺ and TIM-3⁺ TILs during cetuximab therapy inversely correlate with response in head and neck cancer patients

Despite emerging appreciation for the important role of immune checkpoint receptors in regulating the effector functions of T cells, it is unknown whether their expression is involved in determining the clinical outcome in response to cetuximab therapy. We examined the expression patterns of immune checkpoint receptors (including PD-1, CTLA-4, and TIM-3) and cytolytic molecules (including granzyme B and perforin) of CD8⁺ tumor-infiltrating lymphocytes (TIL) and compared them with those of peripheral blood T lymphocytes (PBL) in patients with head and neck cancer (HNSCC) during cetuximab therapy. The frequency of PD-1 and TIM-3 expression was significantly increased in CD8⁺ TILs compared with CD8⁺ PBLs (P = 0.008 and P = 0.02, respectively). This increased CD8⁺ TIL population coexpressed granzyme B/perforin and PD-1/TIM-3, which suggests a regulatory role for these immune checkpoint receptors in cetuximab-promoting cytolytic activities of CD8⁺ TILs. Indeed, the increased frequency of PD-1⁺ and TIM-3⁺ CD8⁺ TILs was inversely correlated with clinical outcome of cetuximab therapy. These findings support the use of PD-1 and TIM-3 as biomarkers to reflect immune status of CD8⁺ T cells in the tumor microenvironment during cetuximab therapy. Blockade of these immune checkpoint receptors might enhance cetuximabbased cancer immunotherapy to reverse CD8⁺ TIL dysfunction, thus potentially improving clinical outcomes of HNSCC patients.