CD8+ T cells infiltrate the substantia nigra pars compacta (SNpc) in patients during the early stage of PD before α-synuclein aggregation, which leads to neuronal death and synucleinopathy (Brochard et al., 2009; Galiano-Landeira et al., 2020; Halliday, 2020). The gene discussed is CD8A; the disease is Parkinson disease.