PD1/PDL1 checkpoint blockade exerts a potent protective effect against cognitive impairment and tau hyperphosphorylation in various mouse models of AD (Baruch et al., 2016; Rosenzweig et al., 2019) and stroke (Ren et al., 2011; Bodhankar et al., 2015); but there are also some contradictory conclusions (Latta-Mahieu et al., 2018; Lin et al., 2019). This evidence concerns the gene PDCD1 and Alzheimer disease.