PDCD1 and neoplasm: It was also suggested that expressing other inhibitory immune checkpoint molecules, such as T cell immunoglobulin domain and mucin domain-3 (TIM-3) and T cell immunoreceptor with Ig and ITIM domains (TIGIT) on tumor-infiltrated cytotoxic lymphocytes, or recruiting immunosuppressive cells such as regulatory T cells promoted PD-1 blockade resistance (Koyama et al., 2016; Sharma et al., 2017; Hung et al., 2018); however, the mechanisms of resistance to anti–PD-L1 (aPD-L1) therapies are mostly unknown.