Cognitive impairment in chronic well-controlled HIV infection continues to affect from 30%-60% of individuals. Mechanisms are still unknown but probably associated with continued neuroinflammation. Biomarkers for cognitive impairment have been inconsistent although neuroimaging has emerged as a possibility. Unfortunately, imaging is expensive with limited access. Exosomes are small microvesicles shed from most all cells under normal and pathologic conditions. The cellular cargo packaged into exosomes can represent the state of the parent cell. We have isolated neuron-derived exosomes (NDE) in plasma using a 2-step isolation procedure and a cell surface neuron specific antibody. We have shown in a recently completed R21 using mass spectroscopy that NDE are rich in over 50 neuronal proteins. In addition, using proximity extension analysis (PEA) for neurology biomarkers, we identified an additional 28 proteins that were present. At least 7 proteins were statistically significantly differentially expressed in HIV infection alone, neurocognitive impairment in HIV+ women versus men and 1 protein that was significantly correlated with age and impairment. Several NDE proteins correlate with cognitive domains and several differentiate HIV cognitive impairment from Alzheimer’s disease. Our overall hypothesis is that NDE can be used to diagnose cognitive impairment in HIV infection and that men and women have different proteins in NDE that will influence diagnosis and treatment. We further plan to differentiate mild cognitive impairment with that associated with a pre-Alzheimer’s mild cognitive impairment (MCI) diagnosis. To test this hypothesis, we propose the following Specific Aims: (1) Select and verify a set of neuronal exosome proteins that predict and diagnose HIV cognitive impairment with aging in women and men, (2) Determine whether neuronal exosome cargo can differentiate HIV-associated cognitive impairment from mild MCI/Alzheimer’s disease (3) Correlate HIV NDE protein targets and cognitive domains associated with neuroimaging markers of injury and (4) Establish a rapid ultrasensitive assay using verified neuronal exosome target proteins for diagnosis of HIV cognitive impairment in a longitudinal cohort. We will utilize a multidisciplinary approach that includes basic research of protein targets correlated with cognitive domains and clinical diagnosis using neuroimaging correlation with selected biomarker proteins. These results will have major impact on treatment and cure of HIV in the brain as fluid biomarkers are discovered and the health of the neuron can be assessed in “real time.”