Antitumor Activity of Pembrolizumab in Biomarker-Unselected Patients With Recurrent and/or Metastatic Head and Neck Squamous Cell Carcinoma: Results From the Phase Ib KEYNOTE-012 Expansion Cohort

Among the most promising approaches to activating therapeutic antitumour immunity is the blockade of immune checkpoints. Immune checkpoints refer to a plethora of inhibitory pathways hardwired into the immune system that are crucial for maintaining self-tolerance and modulating the duration and amplitude of physiological immune responses in peripheral tissues in order to minimize collateral tissue damage. It is now clear that tumours co-opt certain immune-checkpoint pathways as a major mechanism of immune resistance, particularly against T cells that are specific for tumour antigens. Because many of the immune checkpoints are initiated by ligand-receptor interactions, they can be readily blocked by antibodies or modulated by recombinant forms of ligands or receptors. Cytotoxic T-lymphocyte-associated antigen 4 (CTLA4) antibodies were the first of this class of immunotherapeutics to achieve US Food and Drug Administration (FDA) approval. Preliminary clinical findings with blockers of additional immune-checkpoint proteins, such as programmed cell death protein 1 (PD1), indicate broad and diverse opportunities to enhance antitumour immunity with the potential to produce durable clinical responses.

PD-1 is a receptor of the Ig superfamily that negatively regulates T cell antigen receptor signaling by interacting with the specific ligands (PD-L) and is suggested to play a role in the maintenance of self-tolerance. In the present study, we examined possible roles of the PD-1/PD-L system in tumor immunity. Transgenic expression of PD-L1, one of the PD-L, in P815 tumor cells rendered them less susceptible to the specific T cell antigen receptor-mediated lysis by cytotoxic T cells in vitro, and markedly enhanced their tumorigenesis and invasiveness in vivo in the syngeneic hosts as compared with the parental tumor cells that lacked endogenous PD-L. Both effects could be reversed by anti-PD-L1 Ab. Survey of murine tumor lines revealed that all of the myeloma cell lines examined naturally expressed PD-L1. Growth of the myeloma cells in normal syngeneic mice was inhibited significantly albeit transiently by the administration of anti-PD-L1 Ab in vivo and was suppressed completely in the syngeneic PD-1-deficient mice. These results suggest that the expression of PD-L1 can serve as a potent mechanism for potentially immunogenic tumors to escape from host immune responses and that blockade of interaction between PD-1 and PD-L may provide a promising strategy for specific tumor immunotherapy.

To evaluate the efficacy and safety of the epidermal growth factor receptor-directed monoclonal antibody cetuximab administered as a single agent in patients with recurrent and/or metastatic squamous cell carcinoma of the head and neck (SCCHN) who experience disease progression on platinum therapy. An open-label multicenter study in which patients with disease progression on two to six cycles of platinum therapy received single-agent cetuximab (initial dose 400 mg/m2 followed by subsequent weekly doses of 250 mg/m2) for > or = 6 weeks (single-agent phase). Patients who experienced disease progression could receive salvage therapy with cetuximab plus platinum (combination-therapy phase). From June 2001 to December 2002, 103 patients were enrolled and treated with cetuximab, 53 of whom subsequently received combination therapy. In the single-agent phase, response rate was 13%, disease control rate (complete response/partial response/stable disease) was 46%, and median time to progression (TTP) was 70 days. During the combination-therapy phase, the objective response rate was zero, disease control rate was 26%, and TTP was 50 days. Median overall survival was 178 days. Treatment was well tolerated. The most common cetuximab-related adverse events in the single-agent phase were skin reactions, particularly rash (49% of patients, mainly grade 1 or 2). There was one treatment-related death due to an infusion-related reaction. Single-agent cetuximab was active and generally well tolerated in the treatment of recurrent and/or metastatic SCCHN that progressed on platinum therapy. Response was comparable to that seen with cetuximab plus platinum combination regimens in the same setting.