Transferrin receptor-mediated transport at the blood-brain barrier is elevated during early development and maintained across aging and in an Alzheimer's mouse model.

Transferrin receptor (TfR)-targeting of biologics has emerged as a promising strategy to improve drug delivery across the blood-brain barrier (BBB). However, most preclinical studies evaluating TfR-enabled drugs have been conducted in young adult animals. It remains unclear whether age and aging-related diseases impact TfR protein levels and/or BBB transport capacity. Here, we utilized a previously described TfR-targeting antibody transport vehicle (ATVTfR) to investigate how healthy aging and disease progression in the 5xFAD mouse model of Alzheimer's disease (AD) impact TfR protein and TfR-mediated brain delivery. ATVTfR transport capacity remained stable across 3- to 24-month-old healthy mice and 5xFAD progression did not impair ATVTfR brain transport up to 10.5 months, despite significant amyloid burden. Interestingly, neonates exhibited significantly elevated levels of vascular TfR protein and ATVTfR brain exposure compared to adult mice. Furthermore, vascular TfR in AD patient brains was similar to age-matched controls, suggesting conserved TfR transport is also likely in human AD. Overall, our data demonstrates broad functional utility for TfR-based brain delivery in both healthy aging and in an AD mouse model. Additionally, elevated TfR-mediated brain delivery during early mouse development highlights the potential of added efficacy in utilizing such platforms in disease treatment of infants and children.