Olfactory cleft biopsy analysis of Alzheimer's disease pathobiology across disease stages

Alzheimer's Disease (AD) is a neurodegenerative condition affecting millions worldwide. Defining early pathobiological events remains challenging, in part due to inaccessibility of neural tissue. Because olfactory neurons are accessible, and olfactory loss is prevalent in AD, we evaluated olfactory brush biopsies from controls, individuals with cerebrospinal fluid (CSF) biomarker-confirmed AD, and cognitively typical individuals whose positive CSF biomarkers signal a pre-clinical AD stage. Here we show via single cell RNA-sequencing (n = 22 subjects) conserved neuroinflammatory T cell, myeloid cell, and olfactory neuron changes detectable even in pre-clinical AD subjects, and corroborate heightened CD8 T-cell activation by flow cytometry. Activated memory T cell states in the olfactory epithelium were a hallmark of pre-clinical AD, paralleling CSF T cell phenotypes seen in advanced disease, accompanied by both microglia-like inflammatory programs and evidence of olfactory neuron inflammatory injury. Together, our findings establish a platform permitting analysis of neural tissue in AD at its earliest stages.