CD8A and Parkinson disease: During the early stages of PD, the population of terminally differentiated effector CD8+ TEMRA T cells, the hallmarks of immunosenescence, in peripheral blood is reduced and PD patients exhibits downregulated expression of senescence-related markers such as p16INK4a compared with age and sex-matched healthy controls (Williams-Gray et al., 2018; Kouli et al., 2021).