Interestingly, single-cell trajectory analysis shows that the terminal effector CD8+ T cells (TEMRA cells) in the CSF from PD patients display two differentiation directions, with one expressing high levels of killer-like receptors (KLRs) and killer cell immunoglobulin-like receptors (KIRs) [5], raising the possibility of that some of the clonally expanded CD8+ T cells in neurologic diseases are immune suppressive KIR+CD8+ T cells (Fig. 1). The gene discussed is CD8A; the disease is Parkinson disease.