Correlation analyses showed an association between the frequency of CD28 + CD8 + T cells and p-tau (p = 0.004), total tau (p = 0.0292), Amyloid-β 1–40 (p < 0.0001), and the Amyloid-β ratio (Amyloid-β 1–42/1–40; p = 0.0338) and a positive correlation between ICOS + CD8 + T cells and total tau (p = 0.0489) in AD patients (Table 2a). Here, ICOS is linked to Alzheimer disease.