PDCD1 and neoplasm: The effects of PDT on immune responses may in fact synergize with the effects of immunotherapeutic applications, such as the approaches aimed at attenuating the immune suppression in the tumor milieu via utilizing immune checkpoint inhibitors (e.g., anti-PD-L1, anti-PD-1 and anti-CTLA-4) (Kleinovink et al., 2017; Cramer et al., 2020; Xu et al., 2020).