Recent studies have also linked a segment of highly charged, alkaline amino acid transactivator of transcription (TAT) encoded by human immunodeficiency virus type 1 (HIV-1) to the BDNF to improve its transmission through the blood–brain barrier, and the results show that TAT-BDNF can effectively target the brain and improve cognitive function in animals with Alzheimer’s disease [75]. Here, BDNF is linked to Alzheimer disease.