PDCD1 and head and neck squamous cell carcinoma: A combination of SRC family kinases inhibition with CTLA-4 blockade may increase the immunotherapy efficacy in head and neck squamous cell carcinoma (HNSCC).23 Interleukin 2 (IL-2) combined with anti-CTLA-4 and anti-PD-1 can induce tumour specific CD8+ T cell expansion and overcome immunological resistance.24 In summary, CTLA-4, as the target of the earliest generation of immune checkpoint inhibitors, still has a large space for exploration in the tumour immune regulatory network.