In this review, we described the properties of CD8+ T-cell differentiation and function, summarized the roles of CD8+ T cells in brain injury, including ischemic stroke and traumatic brain injury (TBI), and neurodegenerative diseases, including Alzheimer’s disease (AD) and Parkinson’s disease (PD), and discussed future study goals. The gene discussed is CD8A; the disease is neurodegenerative disease.