MAPT and Alzheimer disease: Finally, the incubation of AD‐tau and CTL‐tau on P301S tau‐venus expressing cells33 revealed substantially higher in vitro seeding activity of the AD‐tau mix compared to the CTL‐tau mix, with a dose‐response effect (Figure 1E,F; two‐way ANOVA, disease (AD‐tau vs. CTL‐tau): F = 32.7, p < 0.0001; volume: F = 11.0, p < 0.0001), confirming an enrichment of seeding competent species in the AD‐tau mix.