Antibody screening using a human iPSC‐based blood‐brain barrier model identifies antibodies that accumulate in the CNS

Abstract

Drug delivery across the blood‐brain barrier (BBB) remains a significant obstacle for the development of neurological disease therapies. The low penetration of blood‐borne therapeutics into the brain can oftentimes be attributed to the restrictive nature of the brain microvascular endothelial cells (BMECs) that comprise the BBB. One strategy beginning to be successfully leveraged is the use of endogenous receptor‐mediated transcytosis (RMT) systems as a means to shuttle a targeted therapeutic into the brain. Limitations of known RMT targets and their cognate targeting reagents include brain specificity, brain uptake levels, and off‐target effects, driving the search for new and potentially improved brain targeting reagent‐RMT pairs. To this end, we deployed human‐induced pluripotent stem cell (iPSC)‐derived BMEC‐like cells as a model BBB substrate on which to mine for new RMT‐targeting antibody pairs. A nonimmune, human single‐chain variable fragment (scFv) phage display library was screened for binding, internalization, and transcytosis across iPSC‐derived BMECs. Lead candidates exhibited binding and internalization into BMECs as well as binding to both human and mouse BBB in brain tissue sections. Antibodies targeted the murine BBB after intravenous administration with one particular clone, 46.1‐scFv, exhibiting a 26‐fold increase in brain accumulation (8.1 nM). Moreover, clone 46.1‐scFv was found to associate with postvascular, parenchymal cells, indicating its successful receptor‐mediated transport across the BBB. Such a new BBB targeting ligand could enhance the transport of therapeutic molecules into the brain.

Relationship Between Amyloid-β Deposition and Blood–Brain Barrier Dysfunction in Alzheimer’s Disease

“…The BBB is composed of astrocytes, pericytes, and brain microvascular endothelial cells (BMECs) ( Huang Z. et al, 2020 ). Among these, BMECs express a wide range of transporters and receptors involved in the selective uptake of substances from the blood to the brain ( Georgieva et al, 2020 ). Tight junctions (TJs), which are highly specialized intercellular-adhesion complexes, exist in epithelial and endothelial cells ( Zhao et al, 2021 ).…”

Identification of lamprey variable lymphocyte receptors that target the brain vasculature

“…However, the presence of a secondary cell target can serve as a site where a transported antibody is reconcentrated and can be readily detected after penetration into the parenchyma (e.g. anti-TfR binding to postvascular cells 11 , 21 , 48 ). VLR-Fc-30 also binds to parenchymal resident cells, including neurons, in addition to trafficking across the MBEC (Fig.…”

“…Furthermore, promising clones identified from in vitro screening platforms, such as phage and yeast display biopanning on cultured cells, often do not cross-react with in vivo antigens 18 as a result of altered expression profiles of BECs in the petri dish 19 , 20 . To date, the antibody repertoires employed have been limited to nonimmune mammalian antibody fragments, while application of immunization-based approaches in the BBB field have been confined to targets arising from genomic proteomic profiling efforts 14 , 21 – 25 . Therefore, the search for new BBB targets would benefit from the development and application of innovative screening platforms with the ability to more broadly and efficiently sample the in vivo-relevant BBB antigen landscape.…”

Brain Barriers and brain fluids research in 2020 and the fluids and barriers of the CNS thematic series on advances in in vitro modeling of the blood–brain barrier and neurovascular unit

“…Georgieva et al [142] used a human iPSC-based BBB model combined with a human single-chain variable fragment phage display to screen for potential targets for transcytosis. They identified a number of candidates, one of which showed markedly increased uptake into mouse brain.…”