Among the identified cell types in our single-cell transcriptome analysis, the proportion of CD8+ T cells was significantly increased in the blood of PD patients compared to healthy controls (t-test, P-value = 0.018), whereas the proportion of CD4+ T cells significantly decreased (t-test, P-value = 0.014) (Fig. 1e, f). The gene discussed is CD8A; the disease is Parkinson disease.