Development and Exploration of Immunohistochemistry as An in vitro Assay for Predicting Antibody Transcytosis in vivo

Abstract

The blood-brain barrier (BBB) poses a major challenge for developing effective antibody (Ab) therapies for neurological diseases. The delivery of Ab therapeutics into the brain to treat central nervous system (CNS) disease has been a major challenge in drug development. With the support of astrocytes and pericytes, a monolayer of endothelial cells (ECs) creates the blood-brain barrier (BBB), which serves to restrict the movement of substances from the circulating blood to the CNS. Many endogenous molecules can cross the BBB via specific transporters expressed on the luminal side of brain ECs. These membrane protein pathways provide a promising route for delivering Abs across the BBB by utilizing receptor mediate transcytosis (RMT). Previous studies have shown that systemic administration of Abs against the transferrin receptor (TfR), which is highly expressed in brain microvascular endothelial cells (BMECs), enhances CNS delivery of therapeutic Abs across the BBB in both rodents and non-human primates. Abs that bind to TfR, which is enriched in BMECs, have been shown to cross the BBB and are being developed as fusion proteins to deliver therapeutic cargos to brain targets. Dr. Gorman’s team recently developed a panel of novel anti-TfR Ab shuttles by immunizing llamas to generate single domain antibodies (SdAbs). One or two copies of each TfR SdAb were then fused with a therapeutic Ab directed to beta-site APP cleaving enzyme-1 (BACE) to form monovalent or bivalent format test Abs. In this study, an immunohistochemistry assay was developed and explored as an in vitro screening for predicting Ab transcytosis in vivo in a humanized knock-in mouse model.