According to recent studies, a high abundance of TI Tregs and the high level of PD-1 expression in TI Tregs are associated with poor prognosis in various cancer patients (Park et al., 2012; Tanaka and Sakaguchi, 2017; Kim K. H. et al., 2019; Kumagai et al., 2020; Lucca and Dominguez-Villar, 2020). The gene discussed is PDCD1; the disease is cancer.