GDNF and neoplasm: Interestingly, GDNF also upregulates the immune inhibitory factor Programmed Death Ligand (PDL-1) in some tumors (Lin et al., 2017; Figure 2), which when bound to its PD-1 receptor can mediate suppression of local immune responses, leading to immune evasion by tumor cells (Alsaab et al., 2017).