Immune-Checkpoint Blockade Opposes CD8+ T-cell Suppression in Human and Murine Cancer.

Immune-checkpoint blockade enhances antitumor responses against cancers. One cancer type that is sensitive to checkpoint blockade is squamous cell carcinoma of the head and neck (SCCHN), which we use here to study limitations of this treatment modality. We observed that CD8+ tumor-infiltrating lymphocytes (TILs) in SCCHN and melanoma express excess immune checkpoints components PD-1 and Tim-3 and are also CD27-/CD28-, a phenotype we previously associated with immune dysfunction and suppression. In ex vivo experiments, patients' CD8+ TILs with this phenotype suppressed proliferation of autologous peripheral blood T cells. Similar phenotype and function of TILs was observed in the TC-1 mouse tumor model. Treatment of TC-1 tumors with anti-PD-1 or anti-Tim-3 slowed tumor growth in vivo and reversed the suppressive function of multi-checkpoint+ CD8+ TIL. Similarly, treatment of both human and mouse PD-1+ Tim-3+ CD8+ TILs with anticheckpoint antibodies ex vivo reversed their suppressive function. These suppressive CD8+ TILs from mice and humans expressed ligands for PD-1 and Tim-3 and exerted their suppressive function via IL10 and close contact. To model therapeutic strategies, we combined anti-PD-1 blockade with IL7 cytokine therapy or with transfer of antigen-specific T cells. Both strategies resulted in synergistic antitumor effects and reduced suppressor cell function. These findings enhance our understanding of checkpoint blockade in cancer treatment and identify strategies to promote synergistic activities in the context of other immunotherapies.