AV-1451

Amyloid burden was imaged with PET using (11 C)-Pittsburgh Compound B (PIB; Klunk et al., 2004 (link)) or (18 F)-Florbetapir (AV45; Wong et al., 2010 (link)). Regional standard uptake ratios (SUVRs) were modeled from 30 to 60 min after injection for PIB and from 50 to 70 min for AV45, using cerebellar gray as the reference region (Su et al., 2013 (link)). Regions of interest were segmented automatically using FreeSurfer 5.3 (Fischl, 2012 (link)). Global amyloid burden was defined as the mean of partial-volume-corrected (PVC) SUVRs from bilateral precuneus, superior and rostral middle frontal, lateral and medial orbitofrontal, and superior and middle temporal regions (Su et al., 2013 (link)). Amyloid summary SUVRs were harmonized across tracers using a centiloid conversion (Su et al., 2018 (link)).
Tau deposition was imaged with PET using (18 F)-Flortaucipir (AV-1451; Chien et al., 2013 (link)). Regional SUVRs were modeled from 80 to 100 min after injection, using cerebellar gray as the reference region. A tau summary measure was defined in the mean PVC SUVRs from bilateral amygdala, entorhinal, inferior temporal, and lateral occipital regions (Mishra et al., 2017 (link)).
CSF was collected via lumbar puncture using methods described previously (Fagan et al., 2006 (link)). After overnight fasting, 20–30 mL samples of CSF were collected, centrifuged, then aliquoted (500 µL) in polypropylene tubes, and stored at –80°C. CSF amyloid β peptide 42 (Aβ42), Aβ40, and phosphorylated tau-181 (pTau) were measured with automated Lumipulse immunoassays (Fujirebio, Malvern, PA, USA) using a single lot of assays for each analyte. Aβ42 and pTau estimates were each normalized for individual differences in CSF production rates by forming a ratio with Aβ40 as the denominator (Hansson et al., 2019 (link); Guo et al., 2020 (link)). As pTau/Aβ40 was highly skewed, we applied a log transformation to these estimates before statistical analysis.
Amyloid positivity was defined using previously published cutoffs for PIB (SUVR > 1.42; Vlassenko et al., 2016 (link)) or AV45 (SUVR > 1.19; Su et al., 2019 (link)). Additionally, the CSF Aβ42/Aβ40 ratio has been shown to be highly concordant with amyloid PET (positivity cutoff < 0.0673; Schindler et al., 2018 (link); Volluz et al., 2021 (link)). Thus, participants were defined as amyloid-positive (for CN/A+ and CI groups) if they had either a PIB, AV45, or CSF Aβ42/Aβ40 ratio measure in the positive range. Participants with discordant positivity between PET and CSF estimates were defined as amyloid-positive.

Sixty-seven subjects with a terminal illness, a projected life expectancy of less than 6 months, and older than 50 years underwent ante-mortem flortaucipir PET imaging [13 ]. These subjects were then followed with brain autopsy (18-F-AV1451-A16, NCT02516046). Two pathologists blinded to the clinical and imaging results recorded neuropathological findings according to the NIA-AA guidelines [4 (link), 14 (link)]. Braak pathological staging of NFTs was performed by AT8 monoclonal antibody, and Aβ plaques were detected using 6E10 Aβ_1–42 monoclonal antibody using immunohistochemical staining methods [13 ]. The demographics of these subjects are shown in Table 2.Table 2

Demographics of the autopsy-confirmed subjects, where N is the number of subjects, age is represented as mean ± SD, and gender is shown as female/male. CD college degree or higher, HS high school or lower, C Caucasian, NC Not Caucasian (Asian, Black or African American, Other)

	B1		B2		B3
	Braak I	Braak II	Braak III	Braak IV	Braak V	Braak VI
N	2	5	4	11	14	24
Age	67 ± 1.7	76.8 ± 6.8	85.8 ± 10.4	86.8 ± 6.3	85.6 ± 8.5	81.7 ± 9.4
Sex	1F/ 1M	3F/ 2M	3F/ 1M	6F/ 5M	5F/ 9M	15F/ 9M
Education	1CD/1HS	2CD/3HS	3CD/1HS	4CD/7HS	11CD/3HS	14CD/10HS
Race	2C/0NC	4C/1NC	4C/0NC	11C/0NC	14C/0NC	24C/0NC

We quantified two dimensions of tau-PET patterns in our cohort, measured on a continuous scale: typicality, proxied by the ratio of entorhinal tau-PET SUVR to neocortical tau-PET SUVR (hereon referred to as E:N) to capture the atypical patterns, similar to the index in the original neuropathological study [12 (link)]; and severity, proxied by the global tau-PET SUVR to capture the overall disease burden or stage. Our choice of using E:N to represent typicality was motivated by the following: the ratio of neurofibrillary tangles observed at autopsy in the medial temporal lobe relative to those in the neocortex captures atypical patterns [12 (link)]; subsequent in vivo studies using tau-PET (AV-1451) have shown the promise of this measure in quantifying heterogeneity [14 , 18 (link)]; the recently proposed conceptual framework for AD subtypes based on a meta-analysis of various tau pathology- and atrophy-based studies support such a measure to investigate disease heterogeneity [17 (link)]; and the distribution of entorhinal and neocortical tau-PET SUVR in the AD continuum which reflects both individuals with relatively greater tau-PET SUVR in the entorhinal than in the neocortex and vice versa (Supplementary Figure 3). Global tau-PET SUVR was used to represent severity as it is well-known to correlate with the different disease stages and cognitive decline in AD [29 (link)].