PDCD1 and metastatic melanoma: For example, in mouse models of head and neck cancers, Herpes simplex virus-1 has shown increased efficacy when combined with cisplatin [2], and coxsackievirus A21 has greater anti-tumour activity when combined with anti-programmed cell death protein 1 (PD-1) antibodies against metastatic melanoma, bladder cancer, and non-small-cell lung cancer [3].