CD4 and Alzheimer disease: Then, we summarize three groups of AD-associated compounds according to their effect on CD4+ T cell subpopulation interactions with the BBB: (i) classical AD drugs; (ii) current known compounds that can selectively inhibit CD4+ Th17 infiltration of the brain, and known to have a positive impact on AD prognosis; and (iii) compounds that are known to inhibit CD4+ Th17 and can be repurposed to treat AD.