Brain-derived tau for monitoring brain injury in acute ischemic stroke.

A specific and accurate blood test for acute brain injury could help monitor infarct growth in ischemic stroke and serve as a surrogate end point in clinical trials. Using a single-molecule detection assay, we assessed plasma brain-derived tau (BD-tau), a marker selectively quantifying tau protein from the central nervous system, in a prospective cohort of 502 patients with acute ischemic stroke with serial blood sampling from admission to day 7. Higher BD-tau concentrations at admission were associated with more extensive early brain injury on computed tomography and predicted larger final infarct volumes. BD-tau increases from admission to day 2 were related to infarct growth. BD-tau concentrations rose until day 7 and were higher in patients with secondary events, including recurrent stroke. After thrombectomy, the rise of BD-tau was smaller in patients with complete versus incomplete recanalization. BD-tau outperformed other blood markers and imaging metrics in predicting 90-day functional outcome across infarct size strata and time points. In an independent multicenter prospective cohort (N = 519), BD-tau showed higher performance than magnetic resonance imaging-derived final infarct volume in predicting functional outcomes at 3, 12, and 36 months. In the biomarker substudy of a phase 3 trial assessing nerinetide in patients with ischemic stroke (N = 193), BD-tau showed predictive performance comparable to the other cohorts, mediated the relationship between recanalization and functional outcome, and showed a 49% smaller increase in the nerinetide group versus placebo. Overall, plasma BD-tau tracked ischemic brain injury over time, outperformed other biomarkers in predicting functional outcomes, and identified possible treatment responses.