Such hypothesis is further supported by evidence in PD patients regarding increased CD4+ T cell production of IFN-γ and TNF-α, two Th1 cytokines critical for antitumor immunity, and their insensitivity to Treg, as well as by the preferential differentiation of naive CD4+ T cells from PD patients toward the Th1 lineage (30). This evidence concerns the gene IFNG and Parkinson disease.